Back-Focus 101: Celestron EdgeHD: C9.25, C11, and C14 Advanced Back-Focus with the Celestron OAG

[@jcj2249]

You are a PRO, AstroBlender ! This is clearly explained and easily understandable for non-English persons. Thank you.

[@AstroBlender]

I’m glad you found it helpful!

[@Caedo12]

Just received my 9.25 EdgeHD so I’ve saved this video to a playlist. Good stuff!

[@franklinriley]

This video was incredibly helpful. I have the exact same setup and was having the hardest time figuring out the spacing and guidescope. Your channel was a Godsend!

[@AstroBlender]

I’m glad to hear that!

[@HeavenlyBackyardAstronomy]

This video is VERY HELPFUL. Thank you. I just received my Celestron OAG and ZWO 174 mini. I am hooking is tall up to my C11 EdgeHD. Now all I need is for the clouds to depart.

[@kenkoskela3357]

Fantastic videos on back-focus for the EdgeHD... exactly what I needed. Thanks!

[@norbertdelorme8892]

Thank you very much Cody, I've a C14 and just begining astrophoto. Celestron OAG is on the way, your video and your channel in general are very helpful !!! thanks a lot from France !!!

[@AstroBlender]

I’m super happy to hear that! Good luck imaging!

[@r.fortner4661]

Celestron should hire you to do instructional videos for them. No one has ever walked through that the way you did online. And even as much as I thought I knew all the details, it escaped me that baffle nut added 12.7 mm and i added an additional 13mm on the camera side of the OAG.

[@ayanhanna7409]

The best video I watched today thank you for the effort

[@AstroBlender]

Oh I’m very glad to hear that. You’re welcome, it took quite awhile to put this one together!

[@ayanhanna7409]

I do have the zwo oag tho the rest is the same

[@paulhathaway6292]

Phenomenal video Cody. Such a clear explanation. You have saved me a lot of time and frustration!

[@deepthought1569]

Nice video bud, I just picked up a c11 so all this info is gold. Thanks

[@tomdaigon8707]

Excellent tutorial. Your instructional videos are the best Ive seen. Nice job!

[@AstroBlender]

Thanks Tom, I try. Haha. Have a great day!

[@jero184]

Where were you all my life. Excellent video

[@geldingmakr]

Definitely the best video out there on this subject. Thanks again for putting this together!!

[@robmatson1575]

Cody: perfect video for me, as I have the same EdgeHD 11", Celestron 0.7x focal reducer, COAG, large V2 adapter, 7-position EFW and even the same ZWO mini guide camera. Thanks to your video, I had perfect back-focus for my imaging camera on the first try! However (like you), I discovered that there wasn't enough back focus for the guide camera -- seems to be maybe a couple cm short. Fortunately I have that same T2 --> 1.25" adapter (perhaps it came with one of the two cameras), though strangely it did not come with any thumb screws. Had a devil of a time figuring out which knurled thumb screw replacement fits it. The ones on the COAG match, which I'm guessing are type M4. Finally, one of the cameras came with a 4mm wide female-to-female ring, but that's too skinny for a reliable connection, so I'm going to have to track down your 11mm F-F ring. Thanks again for sharing your very detailed imaging train connection sequence!

[@phfen]

Discovering your channel with this video ! Amazingly clear, informative and well done ! Many thanks !

[@AstroBlender]

You’re welcome, I’m glad it was helpful!

[@paulhathaway6292]

Such a great video. I would love to see a version of this that covers an imaging train with an ADC and 2x or 3x Focal Extender for planetary imaging with a ZWO color camera. Just can't seem to figure out the back-focus on my C14 with the 3x focal extender.

[@jean-clauderoussil6830]

You are a very good teacher, hope a day I will be able to do the same thank you, clear sky

[@wbick8154]

Exactly what I needed. Now a video on cable/wiring? I see some folks plug the guide camera into the back of the ZWO ASI2600, while others plug in the electronic auto focuser. Any guidance and suggestions? Any thoughts on adding a powered USB Hub to reduce load on the PC and camera?

[@nikivan]

Where do you measure the backfocus from? I have a Moonlite focuser and it is unclear how to calculate the backfocus with it.

[@michaelmangieri5989]

Very nice and informative video. You are an excellent speaker. I had used the COAG for a few years, but when I decided to go with the Moonlite Crayford autofocuser I ran into some serious trouble. The Moonlite adds (by my calculations) 73mm to the backfocus, and because the ASI2600 has such a large backfocus to the sensor (17.5) the COAG is just too wide and therefore I had to go with the thin ZWO OAG to get the proper backfocus.

[@w8bya]

Like part 1 a wonderful video, thank you. I have a C11 Edge HD and am wondering what the imaging train needs to be for lunar imaging using a ZWO camera? Can you provide some guidance please?

[@miguelmorales9667]

Excellent video, very concise and clearly explained with just the information that is needed and nothing more. I don't have a Celestron scope but I enjoyed the video regardless. Nice job. Now to check out what other videos you have. 😀

[@MrKClauss]

I have this exact setup (9.25hd) and cannot get into focus - oh and a filter drawer. My measurement is right at 146.4mm. Great video, just trying to figure out what I'm doing wrong.

[@JoseLausuch]

Great video, very informative! I have the same setup but with the 2'' filter wheel and a M52 adapter. It would be nice that the OAG is closer to the wheel, it's hard to reach focus with the guidecam... With the ZWO OAG I was simply screwing the OAG to the wheel directly, so it was almost in perfect backfocus.

[@MrGuitar50]

Another great video on guiding! I have the 9.25" Celestron but not HD. Is the back-focus the same vs. the HD? Thanks!!

[@pablotwa1]

H Cody great video can you please post the part number for the large focal reducer OAG attachment and the OAG camera extensio tube? it's exactly what I need!. Thank you!

[@f.k.6151]

Great video, thanks. Question: in minute 3:39 you mention that the backfocus remains the same whether the reducer is used or not. I use an 800 Edge HD, and for that scope Celestron measures backfocus either from the end of the reducer as 105mm, or the end of the adapter plate as 133.0mm. Should I interpret your statement to mean that the physical space taken by the reducer is 133 - 105 = 28mm? The reason is that the actual physical space I have measured for the 0.7 reducer is 53mm. Maybe I don't understand the concept of backfocus but I am assuming it is where the light can come into focus. Thanks for clarifying.

[@AstroBlender]

This video is only for the C9.25 EdgeHD, C11 EdgeHD, and C14 EdgeHD. The C8 EdgeHD has totally different back-focus requirements. Without a focal reducer you need 133mm. If you use the Celestron 0.7x reducer for the C8 EdgeHD, then you need 105mm of total back-focus.

[@f.k.6151]

@@AstroBlender Thank you for clarifying your statement does not include the C8 breed of the Edge HD. So, in case of the scopes the statement does apply to, where is that backfocus measured from in cases of reducer and no reducer? Thanks.

[@AstroBlender]

In both cases the back-focus measurement should begin at the flat surface of the baffle locking nut or focal reducer, basically the very end of the telescope.

[@markmayer9290]

Many videos in the past you enthusiastically reviewed the Baader ClickLock system. It would be very helpful to know how much back focus this consumes when its installed on a f/6.3 focal reducer . The clicklock is so convenient for swapping cameras with eye pieces and diagonals, that I have one screwed onto the f/6.3 focal reducer and I love the convenience. I also have the 1.25" ClickLock for use without the focal reducer, which is super helpful for swapping a Barlow in front of the camera.

[@AstroQuest1]

Well done as always Cody! I am still waiting for the EdgeHD8. Your video has a lot of useful info even with a different size scope. I did order the Celestron OAG but cancelled it mainly because I did want to spend the $500 dollars for the ASI174 which is what you really need. I already have various guidescope options that I will try first. - Cheers

[@AstroBlender]

Yeah, it’s a tough hit to shell out ~$800 for that set-up, but for me it was so worth it. My guiding is so much tighter with an OAG than with the Guidescope. I was surprised at just how much difference it made. Good luck with the new set-up, I hope it all goes well!

[@troubydoo]

Getting better cameras gets addicting. I just got the 2600mc Pro and it cost me $2000....so $500 is cheap ;) Look at the ASI174mm mini too....great guide cam...large sensor...and its $400 approx...just for a guide cam...but heck, its my main guide cam for my several setups so glad I have it...

[@marvinwhisman3333]

Another absolutely amazing video packed with tons of useful information. You present the material in an easy to understand way and show things I probably wouldn't have known how to handle (direction of the mirror in the OAG). Not sure if you have ever done a video on collimating the EdgeHD but I am sure it would be very helpful.

[@AstroBlender]

Thanks, I’m glad you found it enjoyable. I tried to throw in some tips for off-axis guiding as I went along. I actually have a collimation video on my list of future videos as well!

[@troubydoo]

I had my OAG in backwards until I watched this video..I just got my C11 put up since the mount I was using was in the shop....Cody covered it here and I was like, ARG! So thats why!! ;)

[@ArthurDaire]

Thanks for this tutorial. I just got a Edge Hd C9.24 . I amusing the ZWO asi2600 duo, therefore takes away need for OAG. Having issues focusing, am thinking my backfocus is probably off. I got the T adapter to help achieve the 146mm BF. I am using an filter drawer. Mind advising me please if there is another way of achieving the BF. Should I get the celestron Oag adapter (tough am not using the OAG and connect the filter drawer to it? Thanks for the help.

[@johnathanedwards8706]

Thank you for making this video. I was needing this information and now I have it. I should probably buy a vernier caliper.

[@adrigerritsen17]

Great video: this is what I was looking for. One question. At 9.50 it is said that the spacer came with your camera. Because the OAG comes with a lot of adapters/spacers, I think you meant to say that the spacer came with your OAG. Right?

[@andyevans29]

Fantastic video, as with your other will explained and informative. I have a question, I have exactly the same set up as you but have issues with star shapes and collimation to the point I recently purchased a Hotech Advanced CT Laser Collimator. What it showed was my focal point, moved when using the reducer, did you notice that you have to refocus with or with out the reducer by quite a few turns? I have not actually used the scope without the reducer but I will try this (when we get clear skies next) and see if the star shape / collimation is different without the reducer. I'd appreciate any insight? Thanks Andy

[@Ronbo765]

I assume some vignetting could occur if the sensor was rotated (for framing) independently of the prism?

[@ForeverLearning]

Thanks for a great video - I was knee deep into getting my OAG and Guide camera working - and having quite a few difficulties with the back focus. I'm using the ASI 290. very similar to your 174. I managed to get it all working but it seems I may have been chasing my tail the whole time. I couldn't get the image to focus in the Guide Camera, so I kept going back to Back Focus. Turns out a bush was in the way (I too was using a neighbors property about 1/4 mile down the road). Imaging camera was centered on my target, but the OAG was just enough off target to have its view and focusing ability obstructed.... :)

[@AstroBlender]

You’re welcome, I’m glad it helped you out, that’s why I make these!

[@crm114.]

An extremely useful and well thought out presentation, thanks. I was hoping to use the Celestron off-axis guider with my Edge HD800 + 0.7 reducer which reduces the back focus distance to 105mm. I can position the main CMOS camera to get the correct spacing but am concerned that I may not be able to move the ASI174 close enough to the prism to obtain focus. In your case, the main camera sensor is approx 80mm from the outer edge of the OAG. In my case it would be reduced to 51mm. Do you know the minimum distance the guide camera can be placed from the prism in the case of the Celestron OAG? Thanks for any help.

[@malanstecker]

Thanks for the excellent tutorial! What is the name and model number of the "original 25.3 mm adapter" and the one piece "38 mm adapter" that go between the 0.7X reducer and the Celestron OAG? Do you have a link on where to buy them?

[@timothysheridan5602]

Gr8 videos.... I have an 8 sc and just picked a celestron oag . I talked with celestron and they told me i would have to put my 6.3 focal reducer behind the oag to get it to work and i would need to have a custom adapter made or just use the oag without a focal reducer. This is confusing me even more. Not sure what i can do now.

[@daveherron]

Yup thanks for the video - looking into an OAG for my EdgeHD8. Not complaining and Im newb but what Ive learned about astrophotography is take the cost of your scope and you'll need at least 50% more to buy everything else. And then you'll want a better scope and better overall setup. hahaha. Guider, guide scope or OAG, camera(s), heaters, software, etc. Part of the fun I guess. I pulled mine out of the closet after about 6 years and would like to improve my setup. I have an Orion 80 on top with like 400$ worth of ADM rails and side weights just to mount and balance everything. I think this will let me ditch the Orion 80 and shave a lot of weight and setup time. My mount is the CGemII so weight isnt the issue - up to 40lbs - its just a beast to setup.

[@kevinlemoi7837]

I just added a Moonlite CHL to my Edge HD 11 setup ... wondering how this changes the distance and such with the Reducer, Celestron OAG, ZWO Filter Wheel and 2600MM Pro Camera...?

[@larrycable984]

I note that it appears as though your OAG (and thus the prism) is not aligned with the CCD sensor "rectangle"?

[@tomtoka]

interesting, so I have SCT 11". the scenario will be the same? can we replace the OAG with something else? I dont use guiding camera and this piece is pricy

[@Robin87091]

Would you have a part number for the 48mm adapter attached to the reducer? Want one but don't see it listed at Agena. Thanx

[@deepthought1569]

Such a helpful video thanks! Hey, im using the zwo 533 on a non hd c11. If i have m42 as barrel spacing will it work? Thanks for the video and any response, God bless

[@Tom-n2t]

What Helical Focuser did you use for the Guide camera for the OAG? My OAG has just the basic Camera holder, but i can't quite achieve back focus with the basic OAG for the Guide Camera.

[@nigelgoodman9028]

Hi Cody. Your videos are great and very clear. Thank you ! I see you have a ZWO EAF fitted to your Edge 9.25. Would it be possible for you to do a video on how you calibrated the EAF to this telescope ? I use NINA as my acquisition software.

[@joekritz8227]

I have one more question. I have a ASI482MC with a pixel size of 5.8um. Would you know what the gain and exposure settings would be for shooting Jupiter and Saturn? Also what would be the best planetary camera for 9.25?

[@svenop]

I am having trouble with the helical focuser portion binding and my 174mm mini is not traveling up and down. I see you added a 1.25" extension to the top of yours, im assuming possibly for the same reason or to give more outward travel. What part is that? I probably need to add it

[@uschi414]

Thanks for another great video! I expect I’ll be referring back to it when my EdgeHD 925 order arrives. One question/suggestion - you talked about aligning the pick-off prism on the OAG with the long side of the sensor, and that sounds like good general advice. But maybe you could do a video where you show how to use Stellarium or other planetarium program to find the best orientation for you guide camera relative to he imaging camera to get good guide stars. You might end up with the pick-off prism on the short side of the sensor which means you’ll have to back out the prism a little to prevent the shadow.

[@AstroBlender]

You’re welcome! I suppose that could be true, but with the large pick-off prism in the Celestron OAG and the large sensor in the ASI 174MM Mini, I usually have 4-5 guide stars to pick from. I haven’t had to rotate my initial prism-sensor alignment a single time. It’s really such a great combo!

[@uschi414]

@@AstroBlender thanks for the reply! That’s great to hear. Sounds like the Celestron OAG and ASI 174 mini mono are a winning combination!

[@bbllaakkeeee]

Where did you get the extension tube from? I’m in the same boat as you are with my rig.

[@skyboy98046]

Thanks for the video. Wish it had been out when I was setting up my system. lol. Nonetheless, it would be nice if you added an example of the spacers on the guide camera end. I use a ASI120MM and had to use one spacer to reach my 146mm bf.

[@joekritz8227]

I’m trying to use an Askar OAG with my Edge HD. I first have the .7x Reducer with 3.25” threads, then the Large SCT HD Adapter V2 for Off Axis Guider. I can’t fit the Askar OAG. Are there any other adapters I can use to fit to the Large SCT Adapter? Maybe I can bypass the Large adapter and use a SCT 3.25 Thread to M48 Reducer straight to the the .7x Reducer?

[@MikeCasmey-d3g]

Do you know what the total weight of the C11 reducer and the total gear including the camera weighs? I’m looking at the exact setup but need to keep the total weight on my mount below 44 lbs.

[@eduardoflores-nl8gl]

Is back focus 133 or 147 like you said thank you

[@Dudleydogg]

If I read correctly the Edge 800 wont work with Reducer and OAG makes the Train too long, Thoughts?

[@kevinlemoi7837]

Exceptional Video that helped me a great deal! Many Thanks!!

[@bored9260]

Ok so as far as I can tell do not run an auto focuser on a cpc deluxe HD 925… 🤷‍♂️ because of the locking clutch of the back mirrors or is there a settling of this in a solution

[@sanddollarastro8017]

Hi.. what if i don't have the reducer but i have the OAG, EFW, and cam? I also have the 91mm extension... thanks - UPDATE: What is i have a moonlite focuser? Thanks

[@antoniodepieri7386]

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.

[@anthonysacco2276]

Thank you. Excellent explanation.

[@neilneil1385]

Hi Cody, great videos. Well done and thank you for those! I have almost the same setup with a C14 scope, but what length tube, and where did you obtain it for the ASI 174 MM mini guide scope and celestron OAG? Thanks in advance,

[@AstroBlender]

Hi there, to get the additional length I used this: bit.ly/3D3tiX0 To get the adapter to connect to the OAG I ordered this: bit.ly/3N5GT4L This should allow you to have an easier time getting the ZWO 174MM Mini focused with the Celestron OAG.

[@leonglei8445]

This video was very helpful. Many thanks.

[@AstroBlender]

Glad to hear it!

[@LookintomyBarrel]

Best Video on subject i have seen, Can you tell us where all the wires go? maybe a vid would be helpful.. thanks

[@yvonneanthony7295]

Want to inquire what the weight is for the image train that you have in this video. Thanks.

[@nightsky8585]

Where do you find these measurements or do you measure them yourself?

[@Arcteek]

Extremely helpful video!

[@royalwulff0918]

Cody - an excellent overview - where did you get the extension tubing for your OAG? I have the same cameras and OTA - i have been using a setup that increases the distance between the reducer and OAG to shorten the distance between OAG and imaging camera so that I can achieve the same back focus to my 174mm mini...

[@AstroBlender]

The female/female adapter is just a ZWO one that came attached to my camera (11mm adapter). The other piece is a 1.25” compression ring to t-thread. It just screws into the 11mm ring. Works great!

[@nersimaz5074]

Having a hard time finding the medium (11.5mm) and camera spacer (16.5mm). Would you be able to tell me the part# or where you purchased these. Thank you

[@jtbrower]

The 11.55 comes with the Celestron OAG and I’m not positive about the 16.5 but it likely comes with a camera or the guider.

[@Bonspieler]

Thanks for this. I've owned the Celestron OAG for several years now and could never get the guide cam to focus when on my 8SE. So it went back in it's box and stored away. I just got a new 11 HD and was going to use a guide scope if I could ever get a mounting base to fit the 11. Just ran across your video and I'm ready to give it another try. Now you mentioned using adapters on the 174 to attain focus. I saw in your reply to someone that you used some spare parts. 11 mm spacer and a T2 to 1.25 EP adapter? What is the total amount of spacing needed? You made me feel like I didn't waste 300 bucks on something that didn't work. Thanks for that!

[@AstroBlender]

Good to hear! The back-focus on the OAG should be the same as the imaging train (minus the filter). Basically, if you can get the guide camera to focus then you’re in the right spot. Most people can get the ASI 174MM to focus without additional spacers because their main imaging sensor is smaller and they can push the prism in further. Since I’m using a large sensor I had to back the prism out. To get focus with my 174MM mini, I used a ZWO 11mm female/female spacer, and a ZWO T2 to 1.25” eyepiece adapter. Works like a charm!

[@Bonspieler]

@@AstroBlender Just wanted to say thanks. My 174 came in today. Followed your instructions and I actually got it to focus. 3 years I've been farting around with it!! 3 years!! Thank you very much!!

[@troubydoo]

@@Bonspieler It makes you wonder why Celestron just cant put out simple how to videos for their products over their marketing junk.....I mean, good products need to have good setup and use instructions..

[@1966monkeyman]

Hey Cody. I wanted to pick you brain with regards to the guiding on this setup. As i mentioned before i just bought the 9.25 Edge. I have a CEM60 for a mount and the same filter wheel and camera and I'm also using the ASIAIR Pro. I was using a 60mm guide scope with a ASI290mm camera for my autoguiding. Even with a polar alignment down to .14rms and great balance I'm still having star trailing issues at F7. What kind of exposure times are you running with your setup and does the OAG eliminate the star trailing issues? Thanks again for all your help and the great videos.

[@AstroBlender]

Anywhere from 5-10 minutes. At these focal lengths off-axis guiding is a must! The differential flex tire between long-focal length scopes and mounted guide scopes is the cause for star-trailing problems. That said, off-axis guiding solves these problems as changes in your scope affect main camera and guide camera the same. I would highly, highly recommend the ZWO 174MM mini for off-axis guiding. The huge sensor makes finding a bunch of stars for multi-star guiding very easy!

[@1966monkeyman]

@@AstroBlender Thanks Cody. I really appreciate the info. I was really struggling to understand why I couldn’t get rid of the trailing stars. Keep up the great videos bud. Blue Skies.

[@robertmyers4964]

Great video, but I'm still confused about using a Canon DSLR with the Celestron OAG on the Edge HD 8" along with the reducer. I read in a lot of forums that the combination of the reducer and the Celestron OAG on the Edge 8" is impossible with a DSLR and that the correct back focus cannot be achieved. I purchased the OAG and a reducer for my Edge 8", but was that a mistake? Does the combo only work on the C 9.25, C11, and C14 Edge HD telescopes? I was depending on compatibility between the Celestron products. The Celestron OAG Manual says "Your camera sensor should be 133mm away from the Rear Adapter Plate of the EdgeHD 800 telescope. This configuration assumes a camera with 55mm of backfocus to the sensor". You always explain things really well and maybe I'm missing something. Is that the same back focus with the reducer? or is it 105 mm with the reducer? Or, is it something else.

[@AstroBlender]

On the C8 EdgeHD the back-focus is 133mm at f/10 and 105mm at f/7 with the Celestron .7x reducer. The Celestron OAG eats up about 78.5mm of back-focus (without extra spacers). A standard DSLR eats up 55mm, so that’s 128.5mm, well beyond the 105mm. You could use the OAG and DSLR without a reducer, but with the Celestron reducer you’d blow past that 105mm.

[@robertmyers4964]

@@AstroBlender Thanks for the info although I am disappointed with the response. The reducer is a useful tool, but not being able to use it with the Celestron OAG on my EDGE 8" using a DSLR makes me wish I hadn't purchased it in the first place. Celestron should put a disclaimer on it's OAG that it will not work with the reducer on the EDGE HD 800 and a DSLR. The idea of two different OAG's for one telescopes makes no sense. I'm hoping I can sell my Celestron OAG as I search for an alternative that will work for me. I enjoy your videos and their information and look forward to future posts.

[@AstroBlender]

Yeah, you could also use a different OAG like a ZWO, but the prism is much smaller. The great utility in the Celestron OAG is the huge prism which always gives me guide stars. 105mm seems like a ton of back-focus but a standard DSLR has such a large distance from sensor to flange it makes goes quick.

[@AstroBlender]

ZWO just announced a new OAG with a 12x12 prism. This could solved all your problems. Just thought I’d mention it.

[@troubydoo]

@@AstroBlender Hi Cody, on that note, would this new ZWO prism work on refractors by chance? Or am I better off just using a guide scope there? I use the Celestron OAG on my C11HD and thanks to your video, I fixed my dumb mistakes and got it working. And on my C8 non EdgeHD (just the standard C8), would this ZWO 12x12 also be recommended over the Celestron OAG? I use cooled cameras, like the 294mc Pro, etc and not DSLR.... Thank you!

[@ericbkim]

Can COAG back focus requirements for the primary camera and the guide camera with filter wheel be met incorporating the PrimaLuceLab ESATTO 3" Robotic Microfocuser which is 77" thick?

[@Otter2k2]

Where did you find the 2mm M48 to M42 adapter? I have the same filter wheel and camera as you, but I only have M48 to M54 2mm adapter.

[@AstroBlender]

The adapter came with my ZWO 36mm EFW-II filter wheel. :)

[@centenojoel]

Great video Cody. I want to achieve the same imaging train (I have the exact parts in the video) but would need to install the ZWO EAF. Currently I have the Moonlite focuser which limits me to only using cameras with 6.5mm back focus. Do you leave the mirror unlocked throughout the night when using the ZWO EAF? Any issues with mirror shift? Thanks

[@AstroBlender]

Mirror flop is typically an issue with Celestron SCTs, but I have the ZWO EAF re-perform autofocus after meridian flips and every 1C temperature change, so mirror flop hasn’t ever been an issue. Definitely leave the mirrors unlocked, yes.

[@stephenmcarthur2250]

Have been trying to set up the same system (filter draw rather than wheel) on my edge 8 hd and wondered what parts would you recommend to achieve 105 mm back focus?

[@timothysheridan5602]

Hi cody I am new to astrophotography and watched this video but i am not sure about my back focus spcs. I am using a sct 8 with 6.3 focal reducer, celestron oag, filter wheel and zwo 533. Is my back focus 105mm, 133mm, or 147mm?? Would you be able to help me sort this out

[@scadet17]

Just for clarification, are you saying if you're not going to use a reducer you would thread your OAG directly onto the back of the scope - losing the 38mm? Or would you need to attach spacers to make up for that difference? Great video btw, it was a huge help!

[@AstroBlender]

No, the imaging train stays the same. With or without the reducer you need 146mm. So, the 38mm adapter stays. The 8” EdgeHD back-focus is 133mm at the native f/10. With the 0.7x reducer, it is 105mm. That is why it is not included in this video. The C9.25, C11 and C14 EdgeHD always have 146.05mm of back-focus required with or without the reducer. It makes things very convenient!

[@lalankekarunaratne9318]

@AstroBlender Thank you. Is there anyway to put 2" filter infront of filter wheel. Since i live in heavy light polluted area, i need to use L-Pro filter in front of my filter wheel.

[@jtbrower]

If you really wanted to do that you could use a filter drawer.

[@darksky7810]

Ive watched this video about 50 times....I think Ive got it within less than1 mm ty...

[@joekritz8227]

I have an 9.25 edge hd. What is the back focus for planetary imaging with a 2.25x Barlow? I heard it’s unnecessary to worry about back focus with planetary, but I don’t understand why.

[@AstroBlender]

For planetary imaging you’re using such a tiny portion of your telescope’s field of view that just getting the planet in focus is good enough. You don’t have to worry about any back-focus defects when using such a tiny portion of the FOV.

[@1966monkeyman]

Hey Cody. Great videos bud. I recently purchased a Celestron 9.25 Edge. I also picked up a Televue 2.5x powermate. I would like to use it with my ASI178MM camera and filters on Jupiter and Saturn. Do you have any ideas on how to figure out the back-focus math when you introduce a barlow?

[@AstroBlender]

Back-focus isn’t too big an issue when imaging planets. It mainly effects the edges when it’s off, so it is more of a concern for deep-sky imaging. When you incorporate a Barlow lens, Barlow back-focus isn’t a property of image flatness, but of magnification. The closer your sensor to the Barlow elements, the less magnification. The further away the more magnification.

[@1966monkeyman]

@@AstroBlender Thanks fir your help Cody. Very much appreciated. Have an awesome rest of the week. Hopefully you’re getting good skies. 🥂🥂

[@1966monkeyman]

@@AstroBlender Hey Cody. I wanted to pick you brain with regards to the guiding on this setup. As i mentioned before i just bought the 9.25 Edge. I have a CEM60 for a mount and the same filter wheel and camera and I'm also using the ASIAIR Pro. I was using a 60mm guide scope with a ASI290mm camera for my autoguiding. Even with a polar alignment down to .14rms and great balance I'm still having star trailing issues at F7. What kind of exposure times are you running with your setup and does the OAG eliminate the star trailing issues? Thanks again for all your help and the great videos.

[@petef.4361]

Does it matter which way the asi174mm mini is oriented when installed into the OAG? Or can it be rotated any direction?

[@jiltardiff5543]

Great video, Cody - my COAG is one of my favorite imaging accessories for my Edge. Quick question, which size ZWO filter wheel is that and what size filters are you using? I also have the asi2600 but thought I was stuck using the ZWO OAG with it (not a fan of the ZWO) . Any appreciable vignetting? Thanks!

[@AstroBlender]

Hi Jil, it’s the ZWO 36mm EFW II designed for the 2600MM Pro. I get no vignetting with 36mm filters. I still have to take flats of course with each filter, especially when using a reducer, but that’s just typical.

[@jiltardiff5543]

@@AstroBlender What great news- I thought it looked like the new one, I have the same setup, for some reason I thought it wouldn’t work with the COAG - thanks a million!

[@AstroBlender]

Yep, no problem!

[@ericbkim]

Great video! Does the 11.55mm medium spacer ring come with the COAG package or do I have to purchase additionally? For 2" filter wheel, do I need to use a 48mm to 48mm spacer ring rather than the 48mm to 42mm one you used?

[@AstroBlender]

The Celestron OAG comes with both an M42 11.55mm spacer and an M48 11.55mm spacer. :) It really has everything you need to get to the 91.05mm mark. The 2” ZWO filter wheels should come with a M54-M48 adapter and M54-M42 adapter I believe.

[@ericbkim]

@@AstroBlender Thank you!

[@AstroBlender]

Anytime!

[@marshawilcox]

First, thank you Cody for such a clear video - and all your other videos - much appreciated. I discovered the hard way that the procedure is very different for the 2” EFW. That EFW does not come with a 2mm male to male adaptor and does not come with caps. It was a mystery to me - as was the last step in the ZWO instructions which appeared to show female EFW to female camera. After a little further investigation it made sense. In order to connect the 2” EFW, you have to take the EFW apart, including taking the wheel out, and physically screw the EFW to the camera - then reassemble the EFW. The procedure does not use a m/m adaptor and leaves you with 1 place that needs a cap and the camera cap will do. The back-focus is 56mm. At least that’s the best I could discover reading documentation and looking for other videos. So, very different from the smaller EFW. Grateful for your thoughts. If this is correct, you might consider adding something to your video re: the 2” EFW connection differences.

[@malanstecker]

What is the URL for Part 1?

[@adrigerritsen17]

There was some confusion considering the word 'camera' (see comment below). I thought you were referring to de DSLR. In the meantime I found the answer to my question as I discovered the same 16.5 mm spacer in the accessory tray of my ASI1600MM Pro. Problem solved ;)

[@billbecher2338]

With the ZWO 2" filter wheel you need to attach it to the ZWO cameras directly with machine screws not a threaded ring or you will jam the filter wheel.

[@offraed6156]

How do figure out the exact focal length of each instruments when you change the back focus position?

[@AstroBlender]

The simplest way is to plate solve.

[@offraed6156]

@@AstroBlender You will have to explain what Plate Solve means. Thanks.

[@davidfayolle4432]

Thank you very much Cody, great video and lot lot of precious informations for me...Very nice .... ;-)

[@AstroBlender]

You’re welcome!

[@davidfayolle4432]

@@AstroBlender Hi Cody, I saw your videos about the Celestron Focuser and a little bit after about the Zwo EAF ...I'm asking to me : What is the better choice for my C9.25 Edge ? What do you think about it ? Thank you for reading ;-)

[@olivierleger1]

how do you setup your extension tube for the guidecam and where can i get them? I just figured out this is why i couldnt get a guide star in the OAG... now i gotta get my backfocus right for the guidecam but it did not come with the extension tubes.

[@AstroBlender]

I use a ZWO 11mm female/female t-adapter. I then use a T2 to 1.25” eyepiece adapter that came with my ZWO filter wheel. I get my guide camera in the middle of the focus, then I can make fine adjustments as needed.

[@TheJoshuaCarter]

Which brand and size extension tube are you using here to extend the focus of the OAG for the ASI174MM Mini?

[@AstroBlender]

It’s the ZWO 11mm female/female ring from one of my cameras and a t2-> 1.25” eyepiece adapter. Both spare parts I had in my collection.

[@hiramabiff1418]

Great video thx much, Cody you are the best, super helpful as always. Keep up the great work!

[@AstroBlender]

Glad to hear, thanks!

[@lewislawson5461]

what backfocus to you use according to my sct non edge 9.25 i need 139mm but zwo says 55mm ?

[@AstroBlender]

ZWO includes spacers to get their cameras to 55mm. The proper back focus for an a typical SCT is much longer than 55mm. Go with what Celestron recommends in this case.

[@anata5127]

What size of filters do you use for asi2600? Thanks

[@AstroBlender]

36mm

[@astrocarpets3896]

What about using a guide scope, zwo 294mm and 1.25 8 position filter wheel?

[@AstroBlender]

If you’re using a Guidescope and 294MM, I’d watch part 1. Your 8 position filter wheel should replace a spacer. Also with the 294MM you may want to use 31mm filters if you’re not already.

[@astrocarpets3896]

AstroBlender Are you sure? Because I don’t get vignetting at all even at all

[@AstroBlender]

It depends on how close your filters are to your sensor. If 1.25” they should work alright, but the general consensus is 31mm with a 4/3. Again, it really depends on your imaging train though and how far the filters are from your sensor.

[@10microncustomer89]

Can you actually get round stars with this on 5 or 10 minute subs. I have a CGX-L and I cannot get round stars on a 30 second sub. It would be a dream come true to get round stars on a 5 minute subs with my SCT.

[@AstroBlender]

Is it just in the corners or is it trailing?

[@10microncustomer89]

@@AstroBlender It is trailing sir.

[@grkuntzmd]

Nice video. Thanks.

[@chrispoupart7231]

Thanks Chris Evans!

[@AstroBlender]

Lol, you’re like the 5th person that’s said that over the last year!

[@skylinevspec000]

But why does it matter that much. I can stil get focus with a baader click lock and 2" DSLR adapter.