My 4" Telescope beat my 5" - Atmospheric Conditions and or Cooling?
ฝัง
- เผยแพร่เมื่อ 10 ต.ค. 2024
- Join me as I capture the edge-on rings of Saturn using both my 4" and 5" refractors on the same night. Interestingly, I faced more challenges with the 5" scope. It’s possible that a longer cooldown period was needed, or perhaps the larger aperture was more affected by the seeing conditions. The 4" is a premium Takahashi and the more expensive of the two telescopes, but even so! I noticed significantly more atmospheric dispersion with the 5".
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I observed a noticeable increase in atmospheric dispersion with the 5" refractor that night, which made achieving precise focus more challenging compared to the 4", which snapped into focus with ease as usual.
To mitigate this, I captured four sets of AVI files, stacked them, and selected the sharpest of the four for further processing. Additionally, I applied RGB adjustments in SharpCap to correct the prominent blue and red shifts caused by atmospheric dispersion. This was applied specifically to the 5" and was the only difference in the processing. While this did help to some extent, the image still appeared a touch soft at this large image scale.
Investing in an Atmospheric Dispersion Corrector (ADC) seems necessary, especially with planets being so low on the horizon most of the time. I've included links to better results captured with the 5". Just click on one of the videos at the end of this one.
There is an article on atmosperic dispersion and how it scales with aperture here: britastro.org/2017/atmospheric-dispersion-and-its-effect-on-high-resolution-
imaging
I might tweak the title to mention this issue.
It may be seeing related despite capturing all the data in the space of an hour or two. I spent a lot of time making sure everything else was ok - E.g. Four attempts of focus with 4 AVI files for each scope, both were checked for collimation during focusing, and the same process was applied with post processing bar some RGB adjustment to improve the image of the 5". Both scopes were stored in my garage so should be close to ambient in terms of temperature, but I guess the 5" would take longer to cool, so that could be partly to blame.
Whilst capturing the AVI's I felt that I knew the Tak was well focused but never felt sure with the 5" despite spending significantly longer trying to nail focus.
I don't think stacking 50% helped (I usually stack 20-30%), The images looked noisy when stacking only 30% of 2000 total frames for each AVI. I was limited to 2000 frames because of low frame rates (I kept finding slow USB2 cables, but not my faster USB3).
Thanks Chris.
Hello! I am a planetary photographer, the fat tube offers you better results if the seeing conditions are good enough, hence the difference. As seen in the video, the seeing conditions worsened when using the large tube.
Greetings.
Thank you! :)
Same here. Not sure of the interval between the images being taken as scene conditions can change within a matter of minutes but the larger tube likely needed to cool down more IMHO. I love imaging with my 5 inch refractor despite the loss of magnification.
Another great comparison Chris the Tak definitely gives very nice images
Thanks Tony! the Tak always seems to give razor sharp images no matter what, and easily snaps into focus, whilst the larger frac appears to be a bit more seeing and cool down dependant, then focus can then feel a little more vague.
Takahashi gives beautiful images.👍 Did the guy across the road turn off his 'football pitch' floodlights?🤔
Haha! yeah, I still can't get my head around why they need so many lights! Thankfully I think they are away at the moment, pitch black once the street lights went out at 12 :)
Wow ! Nice results for the takahashi , one thing though , when processing the final image, you may want to try manual rgb alignment sometimes to get rid of the chromatic aberration . The software may get it wrong sometimes .
Thanks so much Mohamed! Crazy coincidence, I've just dropped a video about RGB align to tame atmospheric dispersion.
@@Astrolavistanice ! ill make sure to see it !!
Interesting comparison. I wonder why the image of the 5 inch Stellamira is so washed out / less sharp compared to that of the 4 inch Takahashi. The difference is ridiculous. Maybe different seeing conditions or not enough cool down time ?!?
Hi! The 4" was much easier to work with-it snapped into focus effortlessly. Although collimation was spot on, the 5" showed significantly more atmospheric dispersion and may have needed more time to cool down. I've pinned a post that details the steps I took and the challenges I encountered. I might also update the title to highlight the differences. Plus, I've linked to additional comparison videos with both telescopes at the end of the video. Thanks for watching!
I own the AT125EDL version of this scope. My scope is not a CF OTA, but the Hoya FCD100 & La elements made by KUO is the same. Astronomics guarantees these at >.95 Strehl and mine has been tested higher than that.
IMO the focus on these SD doublets isn’t very snappy, especially when comparing next to a Tak, and can be a little annoying to nail down sometimes.
I also own the 4" version of this scope, the AT102EDL. I live in an area (mountains of western NC in USA) that experiences very good seeing throughout the summer & fall but bad to horrible seeing in winter. The 5" blows the 4" out of the water most of the year but the 4" can match it if conditions are right (or bad really 😂).
Hey there Astro Ape :) I'll try not to be jealous of your mountains. I live in a place called Suffolk, UK. A place renowned for being as flat as a pancake :D I totally agree that the 5" doublet usually performs well when the seeing allows but the focus is vague compared to to Tak which seems to be tack sharp and snappy no matter what. The Tak was a big purchase, but I'm yet to regret it! Clear skies : )
Would love a video on how to use a barlow for photographing planets
Hello. Is the seeing comparable? The image with the 5" is so much less sharp, it almost seems the scope is not collimated or something. I am not sure a "regular" 5" apo should be THAT less sharp than even a 4" premium apo. The 5" lacks any detail on the disc which I am sure should be visible on a 5" apo, even a regular non-premium sample.
Hi! The 4" was much easier to work with-it snapped into focus effortlessly. Although collimation was spot on, the 5" showed significantly more atmospheric dispersion and may have needed more time to cool down. I've pinned a post that details the steps I took and the challenges I encountered. I might also update the title to highlight the differences. Plus, I've linked to additional comparison videos with both telescopes at the end of the video. Thanks for watching!
@@Astrolavista Thank you! What was the altitude of Saturn in your location?
@@infinitychannel450 I just checked Stellarium and Saturn was at 22 degrees at the time. If you checkout the following video, I've had better results at low latitudes before now, so it's all very strange. I found the data from the 5" frustrating and time consuming to work with this time around, whereas the 4" Tak data started looking good the moment I touched the wavelet sliders in Registax6: th-cam.com/video/grH0O3RekgU/w-d-xo.html
@Astrolavista 22° is getting pretty low.
Hmm weird results, how can the huge difference be explained since in your other videos those 2 refractors were neck and neck ?
Here's a copy of the pinned comment in case it's not visible on your device "I observed a noticeable increase in atmospheric dispersion with the 5" refractor that night, which made achieving precise focus more challenging compared to the 4", which snapped into focus with ease as usual.
To mitigate this, I captured four sets of AVI files, stacked them, and selected the sharpest of the four for further processing. Additionally, I applied RGB adjustments in SharpCap to correct the prominent blue and red shifts caused by atmospheric dispersion. This was applied specifically to the 5" and was the only difference in the processing. While this did help to some extent, the image still appeared a touch soft at this large image scale.
Investing in an Atmospheric Dispersion Corrector (ADC) seems necessary, especially with planets being so low on the horizon most of the time. I've included links to better results captured with the 5". Just click on one of the videos at the end of this one.
There is an article on atmosperic dispersion and how it scales with aperture here: britastro.org/2017/atmospheric-dispersion-and-its-effect-on-high-resolution-
imaging
I might tweak the title to mention this issue.
It may be seeing related despite capturing all the data in the space of an hour or two. I spent a lot of time making sure everything else was ok - E.g. Four attempts of focus with 4 AVI files for each scope, both were checked for collimation during focusing, and the same process was applied with post processing bar some RGB adjustment to improve the image of the 5". Both scopes were stored in my garage so should be close to ambient in terms of temperature, but I guess the 5" would take longer to cool, so that could be partly to blame.
Whilst capturing the AVI's I felt that I knew the Tak was well focused but never felt sure with the 5" despite spending significantly longer trying to nail focus.
I don't think stacking 50% helped (I usually stack 20-30%), The images looked noisy when stacking only 30% of 2000 total frames for each AVI. I was limited to 2000 frames because of low frame rates (I kept finding slow USB2 cables, but not my faster USB3)."
I've also changed the video title because I agree this isn't typical.
Los telescopios takahashy son muy buenos excelente óptica
Estoy muy de acuerdo
The 4" results make me think it is a triplet (without looking it up). If your 5" is a doublet or APO, there's no way it could achieve as good than what a triplet can. And with atmospheric dispersion there isn't a piece a of software made that can eliminate the false colors. Only a dispersion corrector ahead of your camera can fix that issue. But usually if you can shoot above 30 degrees or so dispersion should be much less, I like to keep it 30 degrees elevation and above before capturing any planets. My 5" Orion EON triplet gives my large SCTs a run for there money. Nice comparison!
Thanks Mike! The Takahashi FC-100dc is a flourite doublet, arguably one of the best though! On previous comparisons between the two, the 5" ED doublet and the 4" Flourite doublet have performed remarkably close, but something didn't seem right with the 5" image this night, I couldn't nail down the focus like I could with the Tak. Collimation was fine so maybe the seeing and atmospheric dispersion with Saturn at 22 degrees in the south. I performed RGB alignment on the 5" ED doublet data to do my best without an ADC. I've actually just dropped a video about that wondering how RGB align in Sharpcap compares to an ADC. Cheers!
@@Astrolavista Okay, I have to agree your Takahashi is spot on. I did purchase a ADC a while back for the very reason your 5" suffered as demonstrated in your test, also when you have dispersions like that focusing will be difficult anyway. I wish you could have reversed your telescope setups with the 5" inch first, just to see how well your Takahashi handles dispersions,...yes at 22 degrees you will definitely be afflicted by dispersion and is bit low. I was not impressed using my ADC, it was very picky as to the exactness and took a lot of fiddling, I lost patience, then decided to keep planetary captures above 25 degrees and preferably 30. If you've ever done 45 deg. or more that is where the best atmosphere for planetary I've ever seen, unless it's unsteady skies anyway. I was amazed how well you pics converted to video for public showing...nice going!
Chris please explain to your best knowledge the differences in the images? Is this due to optical quality or atmospheric differences? From the scatter on the 5 inch I am assuming its the optics.
Hi, please see my pinned comment :)
Here's a copy of the pinned comment in case it's not visible on your device "I observed a noticeable increase in atmospheric dispersion with the 5" refractor that night, which made achieving precise focus more challenging compared to the 4", which snapped into focus with ease as usual.
To mitigate this, I captured four sets of AVI files, stacked them, and selected the sharpest of the four for further processing. Additionally, I applied RGB adjustments in SharpCap to correct the prominent blue and red shifts caused by atmospheric dispersion. This was applied specifically to the 5" and was the only difference in the processing. While this did help to some extent, the image still appeared a touch soft at this large image scale.
Investing in an Atmospheric Dispersion Corrector (ADC) seems necessary, especially with planets being so low on the horizon most of the time. I've included links to better results captured with the 5". Just click on one of the videos at the end of this one.
There is an article on atmosperic dispersion and how it scales with aperture here: britastro.org/2017/atmospheric-dispersion-and-its-effect-on-high-resolution-
imaging
I might tweak the title to mention this issue.
It may be seeing related despite capturing all the data in the space of an hour or two. I spent a lot of time making sure everything else was ok - E.g. Four attempts of focus with 4 AVI files for each scope, both were checked for collimation during focusing, and the same process was applied with post processing bar some RGB adjustment to improve the image of the 5". Both scopes were stored in my garage so should be close to ambient in terms of temperature, but I guess the 5" would take longer to cool, so that could be partly to blame.
Whilst capturing the AVI's I felt that I knew the Tak was well focused but never felt sure with the 5" despite spending significantly longer trying to nail focus.
I don't think stacking 50% helped (I usually stack 20-30%), The images looked noisy when stacking only 30% of 2000 total frames for each AVI. I was limited to 2000 frames because of low frame rates (I kept finding slow USB2 cables, but not my faster USB3)."
@@Astrolavista Thanks!