DSLR Astrophotography - Get the Best Results from your Camera!
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- เผยแพร่เมื่อ 28 มิ.ย. 2024
- For more information on post-processing, check out my Patreon:
/ peterzelinka
I've also got full-length courses for Milky Way Photography and Deep Space Astrophotography available on my website:
www.peterzelinka.com/tutorials
For proper dark frames.
"The key thing to remember about taking dark frames, is that the images must be the same exposure length, temperature, and ISO as your light frames (the picture files)."
how many dark frames do you need
@@antdx316 40 is ideal, 20 at least. I am not convinced that taking dark is a waste of time, I always take dark and bias frames and I never have banding in my images.
Love the mass effect music
Me too ☺
was just about to mention it, galaxy map tune.
*shivers with nostalgia*
I thought I was losing my mind. This dude is too cool.
@@hbastronomer517 ☺👌
@@hbastronomer517 do you own a telescope!
OH MY GOD.. Mass Effect music fits so perfectly.. Love it!
You can also take one exposure for the stars and one for the foreground, when shooting the foreground reduce the iso as much as possible and shoot a very long exposure to get no grain and more light, expose for the stars normally and take multiple images and run them through a star stacker program then blend foreground and bacground images in photoshop
Wow... The mass effect theme in the background is just perfect.
I'd like to say thank you. You have gained a subscriber and provided useful information. There are numerous videos on each and every subject out there. It can be true that the overwhelming majority does not provide useful information. Many of which are popular channels. However, through digging around or quite possibly appearing on your recommended page lies informative knowledge. You are an excellent representation of just that. You got straight to the point and did not overly represent your channel with a couple of minutes of essentially stating like and subscribe. No, you provided usable knowledge in a relatively quick video that I will actually use. You were understandable, knowledgable in this subject, and the title held to be true throughout the extent of the video. It's uncommon to find channels like this where you truly appreciate the content and their hardworking creators. Your an example of exactly that. Keep working hard, and thank you.
WOW that test of sensor is mind blowing. Thanks for sharing!
This was such good info! I always wondered about the banding in night photography! I need to do my dark frame!
Omg thank you so much for explaining what dark frames do. So many channels talk about how to take dark frames but don’t explain what they actually do.
Peter your a darling. Just checked my 6D, it's not green it's pinkish but with next to no banding on the sensor. Very even throught out. Thanks mate, you just restored my "faith" in the 6D that I bought for £350!
The images specially the last one, you took are blown my mind. Seriously! And Background music took me into that world while watching these images!😱😇😳
You can also take a "dark frame" and substract it from your images to get rid of regular sensor noise which is what the purple glow is.
That's exactly what I was thinking. These dark frames are all repeatable(the important bit) characteristics for any given sensor, so couldn't software 'subtract' that (in a user-controlled way if possible) from the light frame image.
Daft question (I'm new to this very fascinating subject) - what software did you use to subtract the dark frame and, of course, did it actually work!
You can use the free software called Deep Sky Tracker to do this, but you can also use flat frames to remove vignetting
I was thinking the same thing, however, if you do the light sensor test image, you could use that to remove the bands in photoshop as a inverted filtered image over, to neutralize the banding.
Deep sky stacker does all this for you, or any software for that matter. There's no need to do any manual stuff
The purple glow looks to be amp glow
It's the most useful astrophotography video I've ever watched. Every minute is useful. And your channel is HIGH QUALITY :)
This is ground breaking, no one has done anything like this. Thank you!
I am seriously becoming your fan Peter! Nice videos!
This is such a great video! I can’t believe your camera is not modified!
Thank you for this video
that is absolutely amazing. i was just sitting behind the computer the other day thinking, stacking cannot possibly be the only way of getting good results. and sure enough i find this video of you doing this extensive test and thanks for sharing the result. this is pure photography. spend more time in the field and get the right shot rather than wasting so much time in post processing.
It’s not stacking that’s the issue, he is talking about dark and bias frames if you don’t need them, a part of most true astrophotography is always enhanced or at least stacked, even when done with dedicated Astro cams and serious telescope rigs, at its simplest form, it’s essentially just stacking multiple images you took yes? bringing the image into much greater view, this guy (great photographer I must add) created these really “popping” Astro images by stacking and post enhancements, like these ones at 18:10 for example.
stacking is simply stacking images taken, it doesn’t really take away anything to with it being pure... it’s a crucial part of the majority of most exciting Astrophotography you always see.
Great video with very helpful information Peter! Thank you!
I have that exact band on the bottom of my D750 images, I wondered why I was getting it, is such a pain! i just checked a dark frame and can see the correlation. I just got a z6 so will have to test that out! Thanks Peter, very useful info!
My Z6 sensor is silky smooth and clean as!
hello , does the z6 also suffer from same purple issue?
@@nissaarwz4645 yes
Very Detailed explanation about light and dark and why you should take them, THANK YOU FOR THIS VIDEO! i will carry this information into my next astro shoot.
Tested this on my Nikon D5300. Lens cap on and wrapped in a blanket:
- Test 1: ISO 500, F4, 20 sec = Same purple glow at bottom, but as well some horrible yellow/orange round dots splattered around the sensor, most from center towards the right.
- Test 2: Went into menu, did a "Clean Image Sensor", then performed above test again: ISO 500, F4, 20 sec = All the yellow/orange round dots were gone, though the purple band at the bottom remains.
- Test 3: ISO 6400, F4, 20 sec = Without increasing exposure nor whites, one can notice a very faint purple glow at the bottom. When both are increased picture is very uniform, and somewhat clean.
So learned that I must clean the sensor from the menu, much more frequently due to this, thank you! And lovely channel by the way. (.. Subscribed due to this)
I feel like your testing is flawed. Why did you take first two tests at iso 500 and then third one suddenly at 6400? Also, you should try longer exposures. I just don't see how the sensor cleaning function changes anything as what it does is it shakes the sensor or IR filter which is totally unrelated. Also, most cameras do it automatically when they're turned on and off.
@2'35": 'no real grain anymore' ... love your optimism :)
It’s a lot less though :)
I tested the sensor on my D610. It looks gooood, also as flat as the D6's sensor from your video, except a small triangle orange-ish shape top-midle and one in the top-right corner. But barely visible even with the exposure set to max and the whites cranked. I am pleased with the results, thank you. I didn't know these things
Great video. Awesome to see how the different sensors perform.
You may want to do some reading on why each of the different types of frames are taken, and the difference between random noise and average noise. These can both be applied to shot noise, read noise, thermal noise etc. Random noise in these categories will only be benefited from more light frames as you concluded from your pragmatic approach. The sensor read noise you keep stretching out would have to be dithered out. But these are technicalities. Overall if someone is doing wide field, the best bang for their buck (time) is more light frames. There is enough light in a wide angle Astro (landscape or deep sky) that with fairly limited light frames the amount of stretching required to balance the photo won’t bring out the problems, but obviously needs more than one shot. With higher focal lengths and much dimmer objects, the stretching required is going to bring out every little problem hidden. In that case, understanding all the different kinds of noise is ++helpful to make some of the best shots.
Clear Skies!
Thanks for making these videos!
Peter, great video, really useful information.
Brilliant....thank you.....and you didn't push the point too much....it was perfect....a true clear lesson.....and haven't done any astro yet....but wow....thanks for the heads up....well done !
Thanks so much for a very informative Video Peter
i love how you used the Mass Effect 3 Galaxy Map song
That's what I thought, I was like this sounds familiar lol
Some ❤ for the Mass Effect background music! 😁
Thanks for this.
An important lesson to think about.
Interesting video. I discovered something quite interesting regarding banding. I have a Canon 80D and have been using it for DSO imaging for the past couple of years. Out of all of the images I've taken I've only ever seen banding once, in one stack of images. I couldn't understand what was causing it as I'd never seen it before. After doing some tests I realised what it was... I use APT for imaging, and I always choose to save my images to 'Card and PC' in APT (obviously saving it to the camera card, and my laptop hard drive). But for this particular imaging session, on M81 and M82, I accidentally set it to save to Card only. The resulting 7 hour stack had these purple bands across the final stacked image. I then realised the only thing I changed was how I saved the images, so I set it back to save to PC and Card, and since then, and before then, never seen any banding at all. I read somewhere that it can be something to do with saving images to memory cards in the DSLR and that's exactly how it was!
Thanks for the good information Peter. I'll check my cameras and pass on the link to this video.
The dark frames need to be taken with the exact same settings (ISO and exposure) as the light frames, or otherwise you need to scale them to match them. From what I saw in the video lights and darks were taken with different settings, which explains why the noise was not completely eliminated. Differences in temperature also change differences in noise levels, which is why professional observatories (and more serious astrophotographers) have cooled, temperature controlled CCDs.
How do you 'scale' them? That sounds like an important detail.
Your videos are so nice to watch and very informative
Excellent technical explanation using the dark frames. I immediately took some dark frames with my Sony A7RIII and Canon EOS R5. They both have areas of splotches and banding but the Sony is much cleaner. Great stuff Peter, thank you!
Good informative vid, thanks Peter
Thanks a lot Peter. This was very informative. On some cameras, some of the peripheral blotches can be fixed with specific camera settings or minor hardware modifications. My canon 6D was leaking light both from Life View and from the red led indicator, leading to horrible magenta and red blotches when stretching long exposure photos. The purple blotches were removed by disabling silent LV in the menu. The red blotches by opening the camera and putting some black silicon on the led.
Thanks for your content and your clean language
Excellent video Peter. I wrote to you perhaps about a year ago as I saw this image of your SUV parked in a dark sky site with the Milky Way sky in the background. You had displayed it in a popular Facebook adtrophotography site to explain the importance of longer exposures.
I had to concur with your advice, as an astrophotographer since my early teen years in the mid 1960's using crude consumer-grade cameras, actually my parents Kodak Box camera, starting in about 1956 as they handed it to me at around age 2 to take phototograghs of them on my birthdays.
I'm backtracking here to the Dark Ages, so to speak, for most of the younger generations now entering astrophotography with digital cameras today. If only to make the point, that I dropped all the photography about the time I left High School, to instead become an art major in college in 1973 at the age of 18. I actually also purchased a new 35mm Mamiya/Sekor camera and took Photography and darkroom courses to learn how to process the wet-film-base photography that we were are all using long before digital photography came along a generation later.
This may be a rather lengthy comment to leave but I later learned in recent years why I admired the great film directors, say out of Italy, or other foreign film directors such a Stanley Kubrick who left America to live in England the remainder of his life, as many people know he's the director producer of the great film 2001: A Space Odyssey, that is still admired today for it's groundbreaking photographic work.
The early motion film directors too, had a similar childhood process of attrition as their parents gave them advanced photographic film cameras when they were very young. Many great figures in the history books today, that are known for their hand drawn and painted artwork also started out in photography and hand-drawn art work. As I began producing very large pastel sketches, starting with the sun, produced from live observation, with h-alpha filtered solar telescopes in 1999, during the daytime, and then the moon at night, also took me away from the photography for a while as I contributed these to the Cloudy Nights Astronomy Forums for competition in sketching, which I held the records there, for quite a while, after these large hand drawn pastel sketches first appeared in the NASA websites, Spaceweather several times, and Astronomy Picture of the Day. Now Sky & Telescope magazine is asking to display some of my large hand drawn pastels of the Moon, which will appear in the upcoming May 2020 issue.
So finally today discovering your video here, I'm so appreciative of the fact that you explained in fine detail, the failure that many new astrophotographers make by under exposing their images and wondering why they have so much noise and color banding, even after using stacking programs and shooting dark frames, in hopes to cancel out the visual noise and color banding errors. To this day I'm only using a Sony NEX 5r consumer grade Mirrorless Camera with APS-C sensor and an older Sony NEX 5, that I photographed the famous American Solar Total Eclipse with in 2017 in the Oregon desert through my Celestron Nexstar 5i Cassegrain telescope, not far from my home in Portland Oregon. I was asked by the Oregon State Park Administration Directors to give a few lectures to the public in a large State Park about an hour drive from The Painted Hills Oregon for a few nights before the actual Eclipse occurred on that Monday morning August 21st 2017. I also produce very large panorama photo stitches of the Milky Way over beautiful dark landscapes such as at the Oregon Coast Beaches.
As you may know, that these large panorama's, up to a hundred photographs in each finished image, can be reproduced into very large prints without any resolution loss up to perhaps 6, or even or 10 feet wide. Where most photographers today will only display their work as digital online images that are only viewed in cell phone screens of only 2 by 4 inches. I'm also employing my old world camera lenses from the 1970s and 80s adapted onto my newer Sony digital mirrorless camera to allow much more light through, say, an antique 55mm f/1.2 lens, so this goes without saying, in taking your advice on initially capturing more light, with only the most modest equipment available, that of a free camera lens from my college days. Many people are now discovering this by utilizing these huge old and fine quality camera lenses from the 1960s, 70s, and 80s, found and rediscovered in their parents closets, garages, and attics, collecting dust, and adapted onto their new digital cameras to capture the most light from the Milky Way.
So my subjects of astrophotography, starting from the deep dark sky of my teen years at our parents front yard in the far Northeast edges of Portland Oregon under fairly dark skies with my parents crude Kodak box camera strapped to the top of my Tasco 60mm refractor, that I bought at age 13 with my berry picking money, in my first efforts to take a hand guided while through the eyepiece, as a 5-minute exposure of the Orion Nebula, which I still have that negative today somewhere stored away, and now ranging to the bright solar sunlight of the solar total eclipse a couple years ago, with my modestly advanced digital cameras attached to my modern equatorially tracking motor-driven Celestron Cassegrain telescope, that was given to me for free by the Celestron company, as I was invited to teach astronomy overseas in the South Pacific in 2004, which are all still my most modestly advanced equipment that I have today.
I've often thought about taking the leap to the newest astrophotography cameras, like the ZWO that you mentioned in your videos, but living now in retirement at age 65, on a diminished Social Security, and retirement pension income, I've trimmed down my living expenses, to be satisfied with this very modest astrophotography equipment, because my greatest efforts for the past 20 years have been dedicated to the public, in providing thousands of hours of sidewalk astronomy which I later spoke about on National Public Radio many times, and I've been covered in other news articles Across the Nation and overseas in the Fiji islands later, about this service that I provide for the public and schools students for free, still today.
If this isn't enough of a spectrum to tackle over 50 years, I also became a very active sidewalk astronomer for the purpose of Public Service, to the public community, spanning the entire United States and Canadian continent in 2000, when I borrowed from our astronomy club in Portland, a large h-alpha solar telescope, taking it onto a 10,000 mile cross-continental solo road trip over six weeks, to allow thousands of the public on sidewalks, to view the Sun's solar sunspot maximum and huge solar flares, safely, and directly, live through this instrument. I audio recorded thousands of responses from the public and assembled them into a best excerpts 15-minute video in my TH-cam channel, as my top cover page displayed video. Three trips a few years later in 2003~2004 to the Fiji Islands, I did not record audio of the public responses but only relied on their hand written responses, in a large guest registry book, which now includes over 3,000 handwritten comments in many different languages and locations across the United States and Canada, and also in the South Pacific Fiji Islands in 2004. All these ventures are covered in my Facebook albums, with many candid photographic images on location. Also some of the higher resolution photographs of the sky, I have uploaded into the famous Digital Photography Review site gallery.
Today I'm sharing your great video here with others that are getting started in astrophotography because you've covered so many great points that they need to know about basics in a proper Time Exposure. Thanks for posting and providing this.
Great demo Peter. I just finished stacking 6 hours worth of 4 minute subs with an old Canon 450D and noticed some horizontal banding on mine. I'll test my dark frames now but I bet I know what I'll find. Great information.
Extremely interesting: food for thought, thank you.
This has helped me a lot - cheers!
That Mass Effect map music tho. Man, it's just so timeless and fits astrophotography so well
Cool video! I do deep sky AP but love shooting time lapses of my scope as it images the night sky behind (i include those time lapses in my videos). I use an a6400 and want to try milkyway shot in the summer! Clear skies!
Thank you 🙏🏼 for the great tutorial
Much appreciate it!
Hey Peter, interesting video as always. Agreed with Voldy that dark frames must be taken with exact same settings (and temperature/humidity etc). Usually do that when packing up at the end of a session. Also, in your example (1:47 vs 2:31) you are comparing single exposures and for those, you are quite right that the more light (exposure time) you get, the better Signal-to-Noise Ratio (SNR) you have. On single exposure, sensor and images are usually not that good in terms of SNR and if stacking doesn't increase the amount of light received, it dramatically increases the SNR by removing/averaging most of sensor/atmospheric noises. That's what allows in post processing to enhance so much the image compared to a single exposure, this large increase in SNR. IMO, I think your comparison of image quality when increasing exposure/white would have been fairer if you compared 13 stack of 20s vs the 260s image. But FYI, there was a test by another astrophotographer (possibly Alyn Wallace ?) who compared the difference of stacking vs single exposure (but with same total exposure time). Single exposure was showing indeed more details as they do get more light, but the difference was much more gentle (and acceptable) than what you showed. Clear skies !
the dark frames from my fujifilm xt2 is a lovely uniform green like the canon 6d! was actually really worried it would have a terrible sensor. i havent gotten into astrophotography yet but now i am definitely reassured that i have the sensor capability! thanks for the great information!
Hello. I have a X-T2 and I'm going to get a X-T3. Which stacking software do you use? Because DeepSkyStacker doesn't work with the RAF files. Thank you.
Great video with good information! I’ve purchased one of your astro courses and it was great! I’ll test out my D500 and D850 tonight. Sad to think how much time I’ve wasted getting dark and bias frames. I’m also not too thrilled with my star adventurer as it’s not very good at handling my 150-600 lens. I’ve spent this whole last year learning all this stuff and you’ve been very very helpful. I need to spend some learning how to do that blending you talked about in this video. Thanks!
How long are you able to shoot with the 150-600mm? We've been using the Star Adventurer with that lens this week and getting up to 2 minute exposures. Although, we are using an auto-guider too
The Star map theme from Mass Effect
This is brilliant, thank you
That was incredibly informative! ✨
My D810 does that purple-reddish "glow" -- guess it's a Nikon thing haha -- but now thanks to this video, I know it's easily fixable (I'll just composite/blend shots) 🙌🏽
This really helped educate me
Thanks - very useful tips!
Awesome video and content.
Excellent information .
This is so useful!
Thanks! Helpful video! 👍🏻🌌
Also you really do need to match settings with your lights. The noise pattern can change noticably at different iso and temp, especially if your camera is dual native iso or highly iso variant.
Really fantastic video, thank you. Got me thinking, while checking my Darkframe, I also checked the Lens Profile Correction in Camera Raw and could see even more distortions added to the Darkframe noise... Now I know where that circular banding was coming from; I knew it was lens related as it was circular... but good to know!
Yeah! I tend to get a weird banding problem too, usually at the very end of creating a star trails image. I realized that applying the lens distortion corrections causes that problem apparently.
That's why I normally just allow the vignette correction now.
Love your videos dude... I just got an eos r and went out to try and get some milkyway pics. They came out way better than I anticipated however after seeing your video I took some dark frames to see what they looked like on the R and it has some of the same issues with the banding. Its really interesting what the LR profile corrections do to the image as well.
Thank you Peter great insights into sensors any info on the Sony full frame sensors
I had a few Sony sensors that got sent in, but unfortunately the data wasn't reliable enough to draw any conclusions. Most of the dark frames I received had odd bright areas. I can't rule out that is just stray light entering the camera during the dark frame.
Sony usually makes the sensors in the Nikon cameras though, so they should perform similar to the Nikon cameras. Minimal banding, but possibly some odd glow.
Thanks for the video.
The discussion of the dark frames is really very interesting
Not the one with the hot pixels, but the one with the banding and the light and dark areas.
I took my Fuji X-T20, made a dark frame and was pleasantly surprised.
No banding, no differently bright surfaces.
A homogeneous surface.
Purple, but homogeneous. :-)
Hehe... the Mass Effect soundtrack threw me for a few minutes until I realized it was playing in your video... nice touch!
This is a great video as I'm trying to get into astro photography. I have a question though. If we take the reference dark still to find the sensor flaws, can't that be used as some sort of stencil to take the shorter light stills?
I remember my 5dIII also having obscene amounts of magenta blotches + banding; Just did the "dark frame" test on my 90d - It looks like your 6d image (even/ NO BANDING!!!), so could be worse! Will be interesting to redo it at the end of the night when theoretically the senor is warmer after a few hours of timelapse work. THank you!
Beginner. Subscribed. Thank you.!
excellent review
OMG PETER IM A BIG Fan!
I use the Pentax K-1 and is so amazing camera, the sensor have astro tracer, means the sensor ibis follow the stars without use of a star tracker and can make long exposures from more then 2 minutes, i'm so in love of my pentax K-1, really recomended camera for astro photography
Interesting feature! Never heard of it before.
@7:00 coming from a Photoshop approach to fix the sensor noise issue, in theory (I haven't done this my self but will try it soon), you could clean up the noise by importing the 'dark frame' and main exposure into Ps: Place the dark-frame layer over the main exposure shot and set the dark-frame blending mode to one of the 'canceling ' filters : Difference, Exclusion, Subtract or Divide.
EVEN AS A MONUMENTAL UNINFORMED AMATEUR, THIS VID IS AWESOME AND I THANK YOU FOR SHARING
Very interesting, my D7500 was smooth across the image with only a small amount of purple glumped in one corner when I did the Darks test. I was very surprised as this is not a high end camera. I recently (June 2021) took 48, two min, ISO 1600, exposures of Andromeda with a Kit lens and got the most amazing picture. Thanks for this great information !
My canon 60d produces almost the same result as the 6d you have here, so that's pleasing!
Good use of Mass Effect soundtrack!
Nice info 👍👍👍
I really miss the sensor on my 6D. The grain pattern felt like film and color noise was never a problem. I've "upgraded" to a Sony but despite being many years newer, the sensor doesn't always feel as slick.
Very interesting, thank you.
1) Those are not starlink satellites, Those a geostationary satellites (mostly weather)
2) Dither, even if it's one axis, Dithering in RA helps heaps, Any imperfections in PA will take care of DEC dither.
3) Darks and bias frames help with dark current, but not completely remove it, that's where dither lands the final punch.
4) If you want REALLY clean shots, Do all that with a Cooled astro camera adapted to DSLR lenses.
be careful about pixel scale, too!
Couple of corrections: you need to take dark frames at the exact settings of the photos you intend to correct ( and possible even at the same temperature) so that the noise pattern is consistent to the one you get in the light frame, otherwise you end up under correcting or over correcting the noise in the original image and that can cause problems.
Another thing, what you see over Orion are not Starlink but the "usual" geostationary satellites that orbit that area of the sky, there are so many because it's a special orbit. Starlinks in orbit now would probably appear brigther than that.
1 more correction. He was wrong when he said the earth rotates. truth is the stars travel around the flat earth.
@@hughmongus1233 please don't vote !!
@@RPMac please don't think.
@@hughmongus1233 flat brainer huh?
V0LDY, it cannot be geostationary, because those do not move accross the sky as they are - geostationary, meaning they are always above fixed point on the Equator.
Mass effect music from Noveria makes everything special❤
the only thing that rivals your excellent star photo techniques is your narration and presentation. Both super-clear!!
First of all let me say this: AWESOME video, what I like especially much is that you have presented a ton of examples of different shots, flat, light, dark/offset frames, from different cameras. (Offset for me is a very quick dark frame, so sometimes they're mixed up by ppl)
Nevertheless, I wanna make some comments here as well. One of your major points in this video is that the banding/spots of color/lit corners remain no matter if you use a dark frame in the stacking process etc. So this is kinda true, and kinda obvious, but in fact you are committing a slight maths mistake. Let me try to do some short talk to present this.
1) SNR: probably everybody knows best about SNR here, so true: more light -> more signal -> read noise, electric noise, thermal noise contribute to a lesser percentage -> better SNR
2) but what happens to signal/background when stacking images? well 3:1 ratio + 3:1 ratio + 3:1 ratio = 3:1 ratio. It stays more or less constant. that is the main problem with stacking and that is why you need the background. There is a slight difference between signal/bgd and signal/noise. that's why we need to subtract the background for.
3) how to estimate background noise and what is the problem?
3a) if the background had zero average (which is completely not the case in photography) then by doing many many experiments we should come closer and closer to zero (law of large numbers). but wait? how does a dark frame look -> it is a collection of pixels (and 3 channels) from which each has a NON-ZERO average luminosity and some deviation from it, which is random, or so we hope.
3b) thus by taking a humongous amount of frames (try it, number goes to 1000 rather than 25) you establish a map of the AVERAGE VALUES of noise in each pixel and channel. Maths: the estimation of the average is accurate to about sigma/sqrt(number of tries); so for 100 tries you have only 1/10th of the initial variance in noise luminosity, for 1000 tries you have 1/30th, sort of, of the variance, and only for 10000 tries you get down to 1% of the original noise variance.
3c) the same estimation rules apply to flat, dark, light frames etc
4) so now we know that by stacking we don't change the SNR, tho we hope that after stacking 100 pictures we have the average noise (times 100!!) in our background (coz how could it possibly go away) and we can try to bring it's AVERAGE level down, it will NEVER reduce the grain coz this is the randomness that you would need thousands of shots to remove, and even then by exposing the interesting part of the histogram really much you'd amp it up again!
5) you are using the exposure slider "just so", don't really putting care in how much you slide it, so you don't notice the decrease in AVERAGE noise level, but you still notice the band, coz it's there! you cannot reduce background noise this way! it's just smaller on average but has the same shape, and you can always amp it up again and show it on screen.
5a) overblown example: suppose you have taken 1000 offset, dark, flat frames each (what a titan). and then you took just ONE light pic. The light pic has a RANDOM instance of the noise, and when you subtract/divide etc by your calibration frames you bring the AVERAGE level down, but not the actual variance. So the random instance of the noise is just there, it's average has only been brought down to almost zero.
5b) if you took 1000 identical pix (hard to do of course -> triple titan) you'd bring the noise variance down a lot and by subtracting the stacked picture you'd get a comparable noise variance level, but if you exposed it HARD ENOUGH you'd still see the same banding (tho quantitatively it now constitutes less of the signal)
6) to sum up: by even saying that you should expect that band to go away, you are making a statistical mistake, you can never get rid of that banding etc, you can just reduce the standard deviation around the average by averaging it many times, same goes for any other calibration frame.
sort of encapsulation try:
(sig+noise) x100 stacked = (same snr) 100x signal + (random_noise x100 different instances summed up)
= 100x signal + 100x average_noise + 10x noise deviation (sqrt(100) x orig deviation)! (same average snr 100sig/100av_noise)
( noise ) x100 averaged = av_noise (10% of noise variance as compared to 1 frame)
now we subtract 100x average noise from stacked pic -> we still are left with 10x noise deviation! the band are actually more visible and easier to expose!
pre-final result: 100x signal + 10x (one-frame) noise deviation!
so if we are ok with 1x noise deviation level, we can then DIVIDE by 10 and we get final result
FINAL = 10x signal + 1x noise deviation so we converted a godzillion calibration frames and 100 light frames into a ten-tuple signal with the initial noise variance, thus all be the bands etc. will be visible when sufficiently exposed.
MORE SNR, yes but only on average!, grain is EXACTLY THE SAME, but could be 10 times more wild! So what you say is dead true and kinda obvious and I want to add that by stacking (adding) signal you INCREASE the noise variance, and you are only able to get rid of its average!
I hope that wasn't just mathematician's/theoretical physicist's mumbo-jumbo coz I am a big fan of channels such as your and astronomy!
If that seems instructive and has helped you and you want me to clarify more and are interested in actual computations I will be more than happy if any1 contacts me on my channel or later via facebook/gmail. Clear skies!
EDIT: I used variance in the common sense, as something being changeable. in fact variance = deviation^2 for a mathematician, so I edited back to "deviation" as a more accurate wording.
To show how averaging works in pictures I prepared examples with controlled exposure bumping:
drive.google.com/open?id=1xQH6w4xnAI9D-AZOl0hRheu98h4BmKk0
drive.google.com/open?id=1kIAkedV-q9QxZc_kktPxI4YZShKhWHX6
The bands, splashes and noises are now virtually out of the Master files, but if they were present in the stacked light frame, they're just there.
@@przemekmajewski1 Thank you for this, Przemek.
Just examined my Sony A99ii sensor. Clean and smooth like baby skin.
Hi. Great video, and thanks for sharing your findings and knowledge. I followed your advice and took a range of dark frames with my unmodded Canon 600D. I was quite surprised at the results. I'm happy to report that my noise appears to be quite uniform and there don't appear to be any obvious dark or light regions. However, unlike some of the Canon dark frames you showed which were green in colour after you adjusted the exposure and whites sliders in Raw, my frame was abundantly red/magenta. Why is this so? What makes one sensor show an abundance of one colour over another in terms of its noise? Many thanks
Dss works really well in terms of dark, flat and bias frames as compared to sequator. I don't have a tracker. I manually track(it damn difficult)... Taking more lights really works... I took 75 lights on first attempt on m42 and then 150 lights the second time... And i can say the second time the results were really awesome... Those dark frames really help in decreasing the noise and mainly useful for stretching the final stacked images
Do you remember how long the exposure for each photo was? Tell me please🙂
@@michael.1032 It depends on the focal length. Since it was untracked I took 1 sec exposures
Love the Mass Effect music.
Those are Geosynchronous satellites in the photo of the Orion Nebula (M42). M42 is almost right on the celesital equator, and is the primary orbit that the geosynchronous satellites get launched into.
In fact, you can prove this if you measure how many arcseconds long those satellite trails are. The trail length will be close to, if not exactly the same value you get if you were to multiply your exposure duration in seconds by 15 (because the earth rotates at 15 arcseconds per second).
Good stuff....Even on a dark frame w/cap..... the sensor only sees what the lens allows it to see. so taking the lens into consideration is a must. Change the lens to find the best lens to camera combination also.
Possible solution to the banding problem - Take a few photos then rotate the camera on the tripod by a few degrees and recompose the photo with the important feature in the center again. Repeat this several times while taking the whole set for the stack. This will require using an app that can align the stars before doing the stack. This might work because all the banding will not be close to the same positions. Averaged over a larger set, if the bands are in six directions, each band should not contribute as much to the finished result. Disclaimer: I am just getting into night photography (generally too much light pollution, haze, and clouds where I live) and my camera is not a Canon. Thanks for the video. You give us much to consider.
Thank you so much for this tutorial/video i really aprraciate it as I start my journey to amateur astrophoto, and I just see that I need a star tracker at least! (and bright lens!) would you tell me why so many people use Canon DSLR instead of other (Nikon/ Sony?) if Canon has such a banding and color noise issue? is it because of astro-software related thing that Canon astro community had developed thru years? cheers!
My a6500 dark frame is pretty clean. A thin band running down the left side and a little bit on the right top corner. Nothing much throughout the middle of the frame. Thanks for the tip.
Really cool investigative video Peter, Traditionally a Canon shooter I've recently picked up a Fuji after hearing the odd comment about them having a inherently weak IR filters which might be great for nebulae? After seeing your video I'm also keen to fire off a dark and stretch the histogram to see how uniform the sensor is on my XT100! I used to dabble in stacked shots with darks, lights and bias and never noticed the darks weren't doing there job, so no I have just got my hands on a star tracker again I'm ALSO keen to double check your findings here. Thanks for the upload, really interesting stuff and some of the shots you demoed were fab, thumbs up :)
Yeah, most DSLRs have an aggressive IR Cut Filter which blocks about 80% of the H-Alpha (red) light coming from the nebulae. It's possible the Fuji camera's have a better IR Cut filter, which allows more of that H-Alpha light through.
Hey, I have an X-T2 & I did the same test & it's a completely black frame...I have just started to try Capture1 as my Adobe annual subscription ended & thought maybe something is wrong with C1..or maybe I am doing something wrong 😂
the reason Fuji is better is because of it's X-trans Sensor, which is more sensitive to the H-Alpha here's a link to the video
th-cam.com/video/KNloULA7A7w/w-d-xo.html
Hey Peter, big fan of your content. One strange phenomenon I've observed when shooting deepsky on my 7D ii is that the banding can be affected by the ISO setting. The standard ISO stops perform well (100,200,400,800,1600,3200,6400) but irregular ISO's (like ISO 640, 2000, 4000 etc) do not and have more pronounced banding. Hope that helps, it fixed my banding problems for deepsky.
My sony alpha a7R 3 doesn't have those banding issues. I just started taking astrophotography and the guys that said to get the best you need longer photos like you said. I don't have a start tracker so I'm limited to 45 seconds before I get star streak. Thanks for the info man. You definitely have a handle on astrophotography. I love it but it's so expensive haha
Yes, those are definitely starlinks. I saw 16 or more of them back to back in two parallel lines with binoculars at around 4:15 am a couple of months ago and they can ruin a photo.
oh damn just tried that dark frame thing to check my sensor. almost no banding and perfectly flat!! the noise also turns white instead of green or purple. this is a Sony A7RIII
can you upload the RAW file somewhere so I can compare it? I am interesting to this camera as well. Thanks in advance :)
Great video Peter.im just starting astronomy and astrophotography.does your same approach work when the camera is modded and put on a telescope?I've got a Canon eos and I've been told to take the filter or sensor out.dont know why.
My D850 sensor was not too bad. A little green on the right side. D500 has a thin horizontal band. All those times I thought it was just me.
Just did this test on my Sony A7RIII, was from Left to right got green, magenta and green for each third of the sensor. There is a slight darkest on the right third of the sensor. but overall it seems not too bad, being quite even and no noticable banding
I know this video is a year old but after watching it I checked my darks and saw some banding but it doesn't show up in my photos. I checked my master dark and there were only the hot pixels which is what darks are supposed to remove. I think the difference is I also use bias frames which accounts for the noise created when data is read from the sensor. DSS combines darks and bias to create the master dark if I remember correctly which eliminates the unevenness you see in dark frames and the final pictures.