Back-Focus 101: Celestron EdgeHD: C9.25, C11, and C14 Basic Back-Focus for DSLR and CCD/CMOS Cameras
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- เผยแพร่เมื่อ 25 เม.ย. 2021
- In this episode of Back-Focus 101 I cover the basics for attaching a DSLR camera or CCD/CMOS style camera to either the Celestron C9.25 EdgeHD, C11 EdgeHD, and C14 EdgeHD. These three telescopes all have the same back-focus requirement of 146.05mm whether you use the Celestron 0.7x EdgeHD reducer, or not. They also all have the same 3.25" large Schmidt-Cassegrain threads on the rear-cell.
This episode just covers the basics. In the next episode of Back-Focus 101, I'll be going into an advanced imaging train for these telescopes, by installing the Celestron Off-Axis Guider, an electronic filter wheel, and monochrome camera.
If you'd like to see how filters affect your back-focus distance, please check out the following episode of Back-Focus 101: • Back-Focus 101: How Fi...
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![Telescope Back Focus: The Ultimate Guide [TAIC Short]](http://i.ytimg.com/vi/5J654T0UpBc/mqdefault.jpg)
Since I have decided to get an Edgehd, this video is a lifeline in explaining and showing what is required! Thank you :)
Glad to hear!
Best explanation for the back focus of 925 EDGE HD with .7x reducer.
Hi Cody,
This was another great video.
Perfectly done, to the point and very informative. Thanks Buddy!
Great video, as always!
ZWO EAF Bracket for Celestron C8/C9.25/C11/C14
For Celestron EdgeHD 9.25" and the Celestron .7x Reducer Lens for EdgeHD 925 # 94245 you will have to file down the rounded end of the Bracket that mounts to the Telescope Focus. If not you cannot screw on the Reducer and when you have the Reducer installed you cannot mount the bracket to the Telescope Focus, 1/16 of an inch to big. I found this out today after watching the above video and also a Great Video.
Very well explained! Best explanation on TH-cam!
Glad you think so, thanks!
Thank you so much for this. It's one of thes videos that I waited for a long time and you explained that greatly and clearly... Nice, nice work... Thank you... ( sorry for my english, I'm french)...
Your English seems good to me! I’m glad you found it helpful.
Excellent video. Was very helpful!!
That was EXCELLENT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Very good explanation! Thank you!
Absolutely love your videos! Keep up the great work! You’re helping newbies like myself get into this amazing hobby!
Thanks Zac, it’s why I put these videos together! I’m glad you find them helpful!
Outstanding video
Thanks, Craig.
Great video!
Thanks Chris.
Awesome info. Thx!
Glad it was helpful!
Thanks - that helped a lot.
Very Helpful... Thankyou...
Thanks for video
I've read in multiple posts online, that backfocus doesn't matter one bit with SCTs. "Doesn't matter" as in nobody would notice any difference if the backfocus was longer or shorter. I would love to see some comparison images that showed exact backfocus, 20mm too short, and 20mm too long.
Nice video. Thanks.
You bet!
Yes please!
FYI, the EdgeHD 8" .7 focal reducer uses up 105mm of backspace out of 133.35mm, so when using the T-adapter, you have to remove the extension part of it or it will be too long.
Very helpful, thanks. Can you provide a list of "starter" 2" filter recommendations based on your experience?
FYI, from Amazon & eBay when you buy a M42 or M48 T adapter they sell a 10mm thick T adapter, so if it does not say the thickness (11mm) more than likely it's a 10mm.
Hi Cody, thank you for this great and detailed video. I have noticed that you are using as a guide scope the Celestron one that comes with the 9.25” Edge HD and also ZWO ASI cameras. Can you please let me know how do you attach a guide camera to the very tiny end of that guide scope?
Great Video! Thoroughly enjoyed it. (a) On a slightly different topic, EDGE HD is little too costly for me. If I settle with C9.25, how much will I lose? (b) Do you have any video for setting up EAA? (What to buy, back focus and putting it together etc.)
Hmmm! I have the C11 Edge +0.7 reducer. The Williams Optics adapter for my EOS Canon is bigger than the one you show.
I've got the 9.25" EdgeHD combined with the 0.7x reducer, Esatto 2" focuser, Zwo OAG and filterwheel and 294MM pro camera, i've added 21mm of spacers and racked out the Esatto to get to 146mm backfocus, but i've found this does not give me nice round stars. After some testing (witch i need do do some more of) i've found my stars look better at less then 146mm, i believe i'm at 143mm. I'm curious what your findings are after testing.
Can you explain how this all works without using a reducer? I have an 8 inch on order and I'm trying to find someone that can tell me the correct way to set it up. I have a ZWO cam and filter wheel. Do you need a T-Adapter or can you use the visual back?
The problem with clip in filters is that they're always loose inside the body of your DLSR and move around as the scope tracks the sky. I always have to tape them down. Definitly better to invest in thread-on filters to avoid this issue.
Newb here, I'm planning on getting a CGEM II 9.25 I have look but I can't find the backfocus requirement or measurements for it , how do you obtain it or it's a standard for 9.25 146.5mm, and keep thise videos coming 😁
How does a diagonal fit in these measurements? For example the zwo guides have their planetary cameras (i.e. ASI224MC) mounted in the diagonal replacing a eyepiece.
For visual use, do you need the extender?
Hey thanks for the video. Question though , maybe you can help me with. I have a Meade LX200 gps 6.3 native scope , no 6.3 reducer. I am getting a lot of vignetting and stars on the edges that pull towards the center.. That means I need to go back further but I cant find how far my scope back focuse should be , so I guess I just have to add some but no idea how much unless by some chance you know , I cant find it
Does the backfocus of 146 mm also applies to a old fasion C11 ( the black one with an orange logo & orange dovetail plate ) ?
Even though this video is 2 years old and not sure if you check comments. Is there a pro or con to having the filter drawer closer? Swapping the filter drawer and other spacer bringing the filter closer to the camera sensor?
Hi thanks for your video. Can you advice me pleas how i have to setup well, my 224 and C9.25? Now i'm trying to see the moon but i don't reach the focus. Thanks
Thanks so much for the video. Best explanation ever. Would it be the same for a celestron 8se?
No, the 8SE doesn’t have an integrated field flattener.
I have Celestron C8, and I use the standard T-Adapter for my Canon DSLR. I want to use an OAG which adds 15mm. Where can I get the right T-adapter to bring back the backfocus?
Hi, I have a adapter Optec Lepus for Celestron 9.25 I have edge: the question is: backfocus Optec is 101 while the backfocus Celestron is 146,05. How do we calculate the backfocus? 146-101 - 13,5 ( ccd ) or 101 - 13,5? Thank you.
I have exactly this setup. Is there any way to introduce a Tele Vue Powermate into this train?
Cody…what is the name of the piece on the back of the OTA that you have attached to the main threads. The piece with the orange collar? Did that come standard with the OTA or is it an add-on? Ty
Great video but why would you want to have the filter drawer farther away from sensor than it needs to be? The closer the better. You just had to replace the 21mm extension with the filter drawer in the position you had it at the start. Just do 0.7x reducer --> 16.5mm --> filter drawer ---> 11mm+camera.
Great video. Can i ask if it matters which way you attach the filter drawer (ie have the words on the draw facing the reverse to your set up with the 48mm side next to the camera)? I have connecters that make this easier for me to access the slide and the draw locking nut. Thanks.
I would say it matters because most filters have different coatings. You want the reflective side to face the telescope, and the less shiny side to face the camera.
How does one add an ADC to this image train? The spacers don't have thumbscrews to make it secure, so how do you attach one?
Hi, Cody - I just got the 9.25 and have set it up with a ZWO EFW, EAF and OAG-L (OAG and EFW are screwed onto the camera and so rotating the camera means rotating the EFW). When not using the 0.7 reducer, the back focus is such that the camera cannot be rotated more than a few degrees because: a) the cable coming out of the EAF blocks the EFW from rotating; and b) the guide cam on the OAG does not clear the EAF. So, camera rotation is blocked from both sides. Is there any workaround for this? Thanks!
Great video Cody. I do planetary imaging with a 14” Edge HD. I use the 48mm T adapter, a 2X Barlow plus a ZWO ADC and finally a ZWO planetary camera. My question is back focus. My image train is longer than 146.5mm but the system seems to work. Any hints or suggestions
For planetary you don’t need to worry about it so much. I have a video all planned out about back focus for barlows and power mates but haven’t gotten around to it yet.
Hi Cody. I have learned a lot by watching your videos. I appreciate the time you put into these. I have a few questions. They are not directly related to this video so I apologize for that, but I could really use your advice. I have been doing visual observing for over 10 years, but I plan on getting into EAA. At this point I do not intend to invest the time into image processing, but that may change in the future. For now, I am just excited to try EAA. I have already purchased an ASI294MC Pro, and I plan on buying an ASI224MC and an ASIAir Pro as soon as they are in stock.
For wide field nebula I will use my Stellarvue 80mm APO. It has a 560mm focal length but with a .8x reducer it will be at f/5.6. Planetary and galaxies is a different story however.
I will buy a Celestron 9.25 if necessary, but I want to try my Orion 150mm Mak Cass. I understand this is not widely accepted for imaging in any form, but I already own it so I would like to give it a try. It has an 1800mm focal length and it's at f/12. Yes, that's long. I bought a Celestron f/6.3 focal reducer for it as my Mak has SCT threads once you remove the visual back so connectivity is not an issue. Assuming the multiplier is .63x, I should be at f/7.5 with the Celestron reducer.
Can you please explain why a Maksutov Cassegrain is not considered feasible for imaging/EAA? Does it have to do with field curvature or is it strictly due to the long focal length? Do you think I am wasting my time trying to use it?
Thank you for your help, Cody.
I don’t think it’s a waste of time at all. I love MCTs, such an easy to use scope. The reality is the slow focal ratio makes long exposure imaging take more time, increasing the probability of tracking errors, etc. For EAA you’ll still always get more color/detail even with short exposures then you would your eye, so I think it is just fine, personally. I haven’t done much EAA though, so take my opinion with a grain of salt.
@@AstroBlender Thank you. I'm looking forward to trying it out.
@@jimhackney4727 May I ask, what is EAA? I am a newbie and not familiar with this term. At least I don't remember it. Thank you.
@@Big.Ron1 EAA is Electronically Assisted Astronomy. It allows a person to see much, much more than is possible with the naked eye. The short answer is it is similar to AP but without all of the post-processing. Of course you also lose the end result of a fantastic photo.
EAA uses the same gear as AP, but it allows a person to acquire an image very quickly. Instead of long exposures taken over a longer period of time, you capture images with much shorter exposures anywhere from 1 to 30 seconds in length. These images are improved by using software to do live stacking. Also, the contrast, sharpness, gain, and binning can all be adjusted in near real time. The results are quite good.
If seeing is good, and if it's the right time of year, a person can view 10, 20, 30, or more objects in one evening. And all of the images can be saved to your personal library for sharing. You can also save the individual frames for post processing at a later date if you so desire.
Since exposure times are greatly reduced, it is possible to acquire images using alt-az mounts although a GEM is still preferred and will yield better results. The same thing applies to an auto guide scope. It's not required, but it could help. Search online for EAA images. Cloudy nights has an entire forum dedicated to EAA. Some are stunning. Again, they will never be as good as a post-processed AP image, but they can be very nice. I think the main draw is the ability to see good results that can be shared with family and friends in near real time.
EAA is awesome for outreach. I still prefer an eyepiece for outreach but many people find the view underwhelming. Pop in a camera and all of that changed. Great explanation!
Was seriously thinking of getting a telescope for viewing and some astrophotography, something I've wanted to do since I was a kid. Buried myself in research and videos of telescopes, mounts, cameras, accessories etc, etc......not so interested anymore. Doesn't seem worth it to spend even a couple thousand to end up with a so-so setup that I probably wouldn't be happy with, and would need to win the lottery to get a rewarding setup.
Hey Cody, Great video as always. I have an Edge HD8 with the ZWO filter drawer and ASI294MC. After Reducer and T-adapter (for and 8" Edge) is connected it needs 55mm of backfocus as you describe. The problem that the T-adapter is not wide enough to stop the drawer if you are screwing it in (if that makes any sense). Any ideas on how to make this work? Cheers Kurt
Do you mean the T-Adapter is M42 and the Drawer is M48? If so, I assume you’re using the ZWO M42-M48 adapter, but it threads in too far?
@@AstroBlender Hey Cody, I think I found the solution, if I use two M42-M48 adapters next to each other, it holds/stops the spacer at the edge of the t-adapter.
Sounds good. Just make sure the side that has the spanner wrench cut outs is facing you in case you lock the threads up.
@@AstroBlender Good Point, Thanks for the advice.
Cody: Could you do a video on how to hook up the optical train to include a Barlow lens? I see people with these big SCTs imaging planets with the help of the Barlow. Thanks
Barlow lens back-focus has more to do with magnification than anything. The further the sensor from the Barlow, the greater the magnification factor. If a back-focus is specified for say a 2x Barlow, at that distance you will get 2x magnification. Closer in you’ll get maybe 1.8x, further out maybe 2.2x.
Video on this subject will be coming though.
Cody check out the Primaluce Esatto focuser, it is more expensive than the ZWO EAF but no reportedly no issues with mirror flop. I got one but have not been able to test yet.
I would check it out, but the ASI Air Pro makes me use their Focuser too. It’s almost like Apple fan boy, but forced upon me by ZWO. :D
@@AstroBlender BTW, for planetary, what is the change in backfocus if I use an extender (let's say 2.0x) such as Powermate or Explore Scientific?
I dont get one thing the ZWO camer need 55 back focus when using with williams optics telescope, so why it is 146 here?
The camera doesn’t set the backfocus requirement, the telescope and its lenses do.
Hi Cody
I can't choose between a 10 inch ritchey chretien and a 9.25edge hd
my main goal is good astrophotography and decent planetry
please help
Thanks for a helpful video, as always.
Question - if I got the 48mm T adapter, so that I could use it down the line with an ASI camera, in the meantime could I use it with my crop sensor DSLR fitted with a 48mm T ring (instead of a 42mm) with no ille effects? Would I see vignetting or anything like that? Thanks
Yes, you certainly could do that. The larger aperture of 48mm actually prevents vignetting on larger cameras because it allows more of the light to get to the sensor through the larger diameter.
@@AstroBlender Thanks Cody. So all I would need to get is a 48mm T ring for my DSLR. I'd rather have 2 rings knocking around than 2 T adapters, probably cheaper, too! You have the Williams Optics one, right?
For an Edge SCT I use a Celestron Edge T-Adapter and a WO 48mm T-ring
@@AstroBlender Thanks Cody! Clear skies & thanks for all your great videos
Hi Cody,would you recommend OAG or guidescope?
For SCTs I would always use an OAG.
146.05mm is measured from where exactly? I think this is an important detail to mention.
End of the threads on either the main scope or reducer to the sensor of the camera. Give or take a 1mm usually. CCD inspector works great if you want as much precision as possible. If not the 146mm should be fine in general.
Do you need 48mm t adapter and spacers to make a 2” system?
Yes, 42mm would be too small for that. Starizona makes a T-adapter that allows you to include a filter in the imaging train. It’s a clever design and very recommended.
what if i wanna use a filter drawer with a DSLR would that work to? ore would that not work? will i still be able to focus?
You can use the Starizona EdgeHD T-adapter. It has filter capability built into the T-adapter and would work great!
Is there a spanner wrench available to remove the convertor ring (42mm/48mm)?
Agena Astro sells one, but I just use my calipers. They do the exact same thing.
Hello, how are you fitting the reducer with the eaf bracket? With eaf installed, when I try to attach my reducer, it seems too wide and it runs into the eaf bracket at the bottom. What have you done to fix this issue? Looks like I need to shave a small portion like an 8th of an inch off of the eaf bracket?
Im not sure if you said what size your edgehd is, but I have the 9.25 version. Also, thank you for these great videos!
I have the C11 Edge HD, the .7X reducer for that scope, the Celestron T-adapter, a Canon EOS T-Ring, and a Canon EOS camera. This is exactly what you are showing. However, I cannot achieve focus. I turn my focus knob all the way counter clockwise and I still cannot focus.....almost, but not quite. It will focus without the .7X reducer. My question is Why......and what should I do????? I want to use the .7X reducer. I appreciate your reply.
Do you have a mirrorless camera?
No. It is a Canon DSLR. I have all the correct attachments per Celestron.
@chaprick0106 I assume you have the EdgeHD T-adapter for the larger scopes and not the smaller one for the 8”. In that case, your telescope with and without reducer should be at 146mm of back-focus and you shouldn’t have any issues achieving focus. The only thing I can possibly think of is the t-adapter isn’t the right size. Other than that, if you have the right t-adapter, t-ring and a standard DSLR, focus shouldn’t be an issue, and you might be running into another problem. I also assume you have the proper t-ring.
I have an cpc 800 edge hd on the way and downloaded the manual. I may have missed it, i looked several times but didnt see the back focus. Where will I find it? Thank you and. Be safe.
The 8” Edge has a back-focus of 133mm, or 5.25 inches.
What about a normal XLT (so no HD)
I wouldnt thread anything with your camera on, because of the friction there may come off some metal dust and harm your sensor. But maybe its just me overly careful lol.
Hi I have a Celestron CPC 1100 delux SCT without EdgeHD. Is this compatible with the celestron .7x reducer lens. I installed it but despite 146 mm back focus I cannot get a sharp image . My Camera is ZWO ASI 6200 MC pro . Can you help me . \
Greg Otto
No you would want to use the f6.3 reducer/corrector. The flattener in the EdgeHD sets the backfocus, this is not the case in the non-edge scopes.
"...today I will be FOCUSING on the Celestron EdgeHD..." How on earth did you keep a straight face when you said that?
You know I totally smirked in my head when I said it!
hahaha
New to all this and I feel like an idiot but… I don’t get it?
I have a 2" Optolong light suppression filter. I will be shooting with my Canon EOS once my setup comes (what you show exactly). Is there anywhere to put the filter? I don't want to have to buy another filter if I don't have to. I just want to be ready to image once it gets here. Except I'll also be using the Celestron OAG.
The Celestron OAG eats up 91.05mm of back-focus with the SCT adapters, and your DSLR (unless your camera is mirrorless) and T-ring will use the rest. I’m not aware of any T-rings that incorporate 2” filters and stay 11mm thick. You could ask around, but it’s why I’ve always used clip-ins with my DSLR on an SCT.
@@AstroBlender I'll see what I come up with. I'll probably end up going to a ZWO anyway, to be honest. Also, what's your opinion on monochrome? I guess I'm hesitant on the extra cost for filters and time for taking more exposures for each color.
I started with color and don’t regret it. Monochrome is a lot more work but the images are also amazing. However, the images I’m starting to see folks produce with color cameras are amazing, so the technology (or post processing editing) has become so good that the gap between mono and color has narrowed.
After doing some research I found a solution for you: Starizona makes an EdgeHD T-adapter that includes a 2” filter attachment.
@@AstroBlender sweet! Do you have a link?
I have a question, I recently bought a Celestron SCT 9.25 and a Nikon Z6, I attached the camera directly to the back of the telescope (removed the visual back and installed the mount for the camera) and then move the little wheel to focus ... I got a clear and beauty pic of the moon but I didn't use any spacer.... Do I'm missing something?
Is your C9.25 and EdgeHD? If it’s a standard you’re good.
@@AstroBlender is standard! So I relax a bit being the case, but why is the case… and thanks so much!
The EdgeHD has a built in two-lens field flattener in the baffle tube. The field flattener requires an exact back-focus to flatten the field properly. Too much distance or too little from the specified back-focus results in aberrations.
@@AstroBlender I just see this! thanks so much for the information, Now I feel good to have chosen the standard version to begin astrophotography!
How did you find the reducer in stock and from where?
I got lucky and got it brand spanking new from a classified ad! These back-order days are tough!
@@AstroBlender You were so lucky. Over the past 6 weeks I just went through 3 focal reducers for my C11 EdgeHD from different retailers, all with threading issues. Each had the same issue of bad threads.Celestron took them back but now are having me wait until July-Oct for a new batch. Sounds like a common issue. So bummed to go through galaxy season without it.
Really?? That’s strange, it feels like an extremely quality part. I wonder if manufacturing these days is trying to make things so fast the QA has gone down? 3 of them though, seems unusual.
Are Backfocus requirements really needed with the Flatfield EdgeHD OTA's ? I've never fussed with this with my EdgeHD and I get sharp round stars out to the edges as expected . What am I supposed to be missing here ? /SRK
Absolutely! Check out the Celestron EdgeHD white pages paper or their other published documentation to see the performance decline as you move away from proper backfocus.
@@AstroBlender Thanks ! I'd love to see some actual Images taken with and without proper backfocus to "see" what I'm missing . LOL ./SRK
It’s pretty obvious, the off-axis performance degrades quickly. Zoom in on the stars on the edges of your image and you’ll see the distortion. That being said, a larger sensor will see greater effects since your getting more of the outer edge of the light cone. A smaller sensor you won’t see the effects as much.
Aarghhh ... just discovered that my ASI1600mm Pro has a back focus of 6.5mm, not the same as the 17.5mm for the ASI2600. Now I can do the math all over again ;(
Dude uno where watching this Because No one can aford it 🤔
Just show us the hot chick 1-2 miles away sunbathing at her pool .
this lense can see into the future .