Backfocus on the EdgeHD 8 using an OAG

This video provides a few possible solutions to the back focus puzzle that you encounter should you want to implement the Celestron OAG on an Celestron EdgeHD 8" telescope and a ZWO cooled astronomy camera.
I will not cover how to setup your guide camera in the OAG. I'll leave that for another video.
How I solved my puzzle can also be seen in this sheet: docs.google.com/spreadsheets/...
F7:
OAG SCT adapter 25.3
OAG body 29
OAG male M48 12.5
ZWO filter drawer 21
ZWO spacer 11
Sensor depth. 6.5
Total 105.3mm (required 105mm)
F10:
Celestron T-adapter 50
OAG female M42 4.5
OAG body 29
OAG male M48 12.5
ZWO filter drawer 21
ZWO spacer 11
Sensor depth 6.5
Total 134.5mm (required 133.35mm)
If I got away with the small discrepancies will have to be seen. No clear nights yet over here...
In case you want to go with the nosepiece solution (the one I feared) than you'll need a 2" nosepiece which adds 1.7mm back focus distance and the Telescope Service SCT visual back which can be bought here (not affiliate): www.teleskop-express.de/shop/...
The safer bet is to use the Celestron #93644 T-adapter: www.ganymedes.nl/product/cele...
#asiairpro #asiairplus #zwo #optolong #ioptron #cem40 #celestron #edgehd #williamoptics #gt81
My links
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TWITTER: / mjschoenmaker
INSTAGRAM: / astrokoplamp
TELESCOPIUS: telescopius.com/profile/schoe...
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Music/Sound effects:
Space - Saturn Dust - / @saturndust
"Subscribe Button" by MrNumber112 • Free Download: Subscri...
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Edited in #Shotcut www.shotcut.org/

[@KopLamp]

In case you have an OAG, but you struggle finding focus with the guide camera; my most recent video might be of assistance: The Easiest Way Achieving OAG Focus With an ASIAIR and EAF kzbin.info/www/bejne/Y2qkZ39qaNBmjNU

[@leoruiz3614]

I recently bought my c8 Edge+Oag+filter Drawer and the first time I tried to install it, I even got nervous. I searched on KZbin and your video came up. Thank you so much for taking the time to make our lives easier. It's a huge help.

[@KopLamp]

You’re welcome! I would like to thank you too for taking the time to leave your comment. Making these videos takes lots of time (which I enjoy). Getting these kinds of comments enhances that enjoyment even further!

[@johnmheaton]

Thank you Martin, you always make clear and concise videos which I enjoy watching. I hope your next imaging session goes well with this latest setup!

[@KopLamp]

Thanks John! And yes, I do hope I get some clear skies soon. ClearOutside.com keeps promising green though... Fingers crossed the prediction turns out to be accurate once :P

[@geralddubesa9324]

Thank you. The video was just what I needed. Very concise and I enjoyed your humor.

[@KopLamp]

Glad you liked it.

[@mrkutube]

Hi Martin, recently I bought a Celestron OAG for my Evolution 9.25" OTA with ZWO filter drawer. Your video is a gem for me, explains everything very clearly. Thanks for making the video, keep them coming.

[@KopLamp]

You’re very welcome. Thank you for your kind comment.

[@tkone9594]

Hi Martin, greetings from Germany! This is the best video on this topic i have ever seen. Superb and answered all my questions. Thanks!

[@KopLamp]

Thank you. Glad it has helped!

[@Naztronomy]

Very clever opening! Nice video, Martin!

[@KopLamp]

Thanks. Yes I like some puns 😅

[@nathantw]

Thank you! I’ve had the t-adapter for over a year and I never thought of taking it apart and using it for my image train with the Astro camera.

[@KopLamp]

Glad my video helped you discover that handy feature!

[@jwastroimaging2711]

That is an excellent instructional video. I've finally managed to buy a reducer after two years due to them being unavailable because of the rare glass shortage. You've saved me hours of messing about with spacers! A big thank you!!

[@KopLamp]

You’re welcome!

[@jds1776]

Thank you for this video which is perfect as usual !👍🏻 Can't wait to see the next video: how to properly set the OAG in this configuration. (keep the right back focus at the OAG...)

[@KopLamp]

That video is on my todo list. I am a bit busy though as is evident on my channel

[@LogansAstro]

Nice video. I'm sure it will greatly help out those with this telescope setup. Figuring out the correct backspacing/backfocus just does my head in sometimes.

[@KopLamp]

Thanks! It was a puzzle for me indeed. Which was exactly why I thought to make a video about it.

[@EastSideAussieQuest]

Excellent video. 🙂 Just the video I was looking for.... Thank you very much.

[@KopLamp]

Glad it was helpful! If you are looking for something which I did not yet cover, feel free to reach out!

[@EastSideAussieQuest]

Just need to go to my local astronomy store and buy a spacer ring kit , so that i can get the proper focus length for my 224mc camera

[@edouardleclercq3814]

Very well explained, thx for sharing your time and expérience.

[@KopLamp]

You’re welcome

[@bobbeanbags]

Awesome video as usual!

[@KopLamp]

Thanks Robert. Much appreciated.

[@AstroCrescent]

Thanks for the video. I am expecting my Edge HD 8 sometime next week. Right now, I do not have the money to buy Celestron OAG, but will use my existing William Optics 50mm slide base guide scope from my existing W/O GT71 imaging setup. I don't know how much it will affect the image quality. I'll ultimately get an OAG soon. As always, your videos are very helpful 👍. Keep up the good work, my friend.

[@KopLamp]

A guide scope will work. Even in native focal length. If you search my Telescopius profile there is an Pelican Nebula shot that way.

[@Arcteek]

Extremely helpful, thank you so much

[@KopLamp]

You're welcome.

[@jonb595]

I appreciate your video. and clear explanation Exastly what I am trying to do now with focal reducer and OAG for my edge 8

[@KopLamp]

Glad it helped you. Clear Skies!

[@luisrivera-lopez3648]

Thank you for sharing, Martin.

[@KopLamp]

You’re welcome. Let me know if I missed something in my video.

[@KopLamp]

Hey there, and thanks for finding my video. The video description contains the solution I think will work for me in both native f/10 and reduced f/7 setups. "I think", because I'll still need to test the f/10 setup, but weather is not cooperating. You can expect some follow videos ;)

[@ez60rlr]

Thanks a lot for the video. Great info and easy to follow. Can you tell me you exposure amount and times. I'm just starting with astrophotography. Thanks

[@KopLamp]

Hey there@@ez60rlr! Thanks for watching! Exposure time is depending on a lot of things. If I use a narrow band filter I usually go for 5 minute exposures and I try to shoot as many as I can fit in a night. In case of broad band or unfiltered shots I lower the exposure time to around 3 minutes (sometimes less). Try to find the exposure time that works best for your location and mount. Sometimes light pollution just makes longer exposures less worthwhile. And if you don't have the luxury of guiding you are dependent on how well your mount tracks the night sky. So, sorry for the long answer, but there is not really a simple answer. Experiment and try what works best for you. Clear Skies!

[@ez60rlr]

Thanks for the information 👍 it helps me a lot

[@pksacoma]

I love your videos

[@rockhauling.d.4816]

Excellent video

[@KopLamp]

You’re welcome!

[@poruatokin]

Loved seeing "Allen" at 6:24

[@KopLamp]

Haha... it is a bit of a running gag on my channel. There are videos with multiple Allans in it ;-) For instance, this one: kzbin.info/www/bejne/n2q2qqCho9qfhs0

[@alexisfarfaro5378]

Thank you! very helpful

[@chrislee8886]

Always enjoy these videos especially the humour! Curiously i decided to try an experiment and image M1 with my Classic 8” using a 2x barlow. This was simply because i had the image train set up for planets. My system will not plate solve at this focal length (3000mm) but the mount was aligned to the planet Mars so a short hop across to M1 in Taurus was OK. No chance for my ZWO basic OAG to find any stars! Hence relied on old fashioned “no guiding” at 30s exposures. Seemed to work - good capture. Do you find the Edge HD without the focal reducer still plate solves with no worries? Or is the FoV too small?

[@KopLamp]

It platesolves just fine on my ASIAIR. I’ve just posted a first result on Twitter.

[@Q_Bits]

Thank you this was very helpful! What are you using to mount your ASIAIR to your OTA?

[@KopLamp]

I have a baader finder shoe in which I clamp the dovetail of the ASIAIR. www.astroshop.eu/mounting-brackets-and-accessories/baader-skyscout-finder-scope-shoe/p,8903

[@georgehatfield9473]

Martin... another question. One thing you did not cover is getting the backfocus correct for the guide camera. I am using the ASI174mm camera, and if I remove the bottom "filter ring" that is supplied on the camera (4mm thick) and move the camera into the OAG until the top of the OAG is even with the top side of the "M" of Mini, the backfocus appears to be 104.8mm. I had the helical focuser all the way in when I took measurements. Also I measured from the center of the prism and assumed the reflecting surface was in the middle of the 29mm thickness of the OAG. From the video it looks like you have your guide camera in a similar position. Did you measure the backfocus for the guide camera?

[@KopLamp]

I did leave that part out. My apologies. I’ll cover it in an update video where I show the results I am getting with the setup. It comes down to this; Once a proper backfocus for the main camera is dialed in, it is a matter of focusing the guidescope in the classical way. Using a bahtinov on a bright star for instance.

[@siegfriednoet]

Very well explained, will have to do this for "galaxy season". How were you images at native f10 ?

[@KopLamp]

So far, things have been looking very nice. I post some of my results on Telescopius.com, but by writing this I realize that I have so far only posted an image of M42 which was more or less just the result of some goofing around. telescopius.com/profile/schoenmaker

[@siegfriednoet]

@@KopLamp Thank you Martin it looks like it gathers a lot of light even at it's native f10

[@KopLamp]

@@siegfriednoet It does. I just uploaded a new f/10 image to my telescopius profile and I accidentally imaged it at gain 0 instead of the usual gain 120. Still, it turned out nice.

[@siegfriednoet]

@@KopLamp It looks good, and an interesting target, beautiful !

[@sreeshab4093]

many thanks for this. at 9:32 u show entire unit rotating. that is if u want a different orientation of frame, to suit the subject - which i perfectly understand. but if i want to get more guide stars how do i rotate the prism?

[@KopLamp]

When using an OAG there usually is no other way of rotating the prism other than I show. If you would rotate it separately from the camera you risk seeing the shadow of the prism in your images.

[@mikedols2759]

Hi Martin! Super duidelijke video! Ik heb sinds kort ook een EdgeHD8 (dus ja, busted.... sorry voor de wolken🙈) en heb lang gezocht naar duidelijke info over de optical train. Geweldig dat je de native FL én met reducer behandeld! Ik heb mijn bestellijstje klaar, hopelijk alles nog op tijd binnen voordat Jupiter verdwijnt🙄

[@KopLamp]

Veel succes! Ik ben benieuwd naar je resultaten. Laat maar weten waar je ze post.

[@mikedols2759]

@@KopLamp Thanks, ga ik zeker doen tzt! Zojuist al even tijdens daglicht correcte focus kunnen krijgen, superblij! Uiteraard is het bewolkt nu ik vanavond tijd heb 🤣

[@KopLamp]

@@mikedols2759 De bekende vloek. Astrospullen kopen betekent bewolking. Ik denk dat de laatste weken Ganymedes en Robtics goede zaken gedaan hebben in Nederland - als ik op het weer af ga.

[@teslar1]

Hi Martin. I’ve been told that the backfocus measure should come from the internal corrector lens face. You show the backfocus measure coming from the 3.5” to SCT adapter fitted to the internal corrector. Did you confirm the front measuring point with anyone? Which is correct ?

[@KopLamp]

The measure starts at the SCT thread. So in native focal length directly at the scope. If reduced at the reducer. See the whitepaper on Celestrons website: www.celestron.com/pages/white-papers

[@teslar1]

@@KopLamp thank you for clearing that up. That helps a lot

[@georgehatfield9473]

Martin... Well done. Have you tested the f/7 setup with your 8" Edge HD? The reason I ask is that the image circle is only 26.7mm in diameter with the 0.7x reducer. There is very little room for a camera sensor, let alone the 12x12mm prism of the OAG to be fully illuminated. There is not even enough room for the little ASI533 and the Celestron prism. What camera are you using? There is a long tread on Cloudy Nights concerning problems with the f/7 setup and using an OAG. When the OAG is not fully illuminated, many are getting such distorted stars that it is impossible to get good guiding. I would give the link, but I've been told that KZbin does not allow them in comments. See Cloudy Nights message for link. I would be interested in your experience. George Hatfield

[@KopLamp]

I have switched to f/10 mode because of the ASI174MM mini camera. Before that I was using it in f/7 but had issues finding proper guidestars with the ASI290MM mini. Your question makes me wonder if I wasn't just getting into trouble because your mentioned issue. Thanks for your comment. When galaxy season is over I'll give that some proper investigation.

[@georgehatfield9473]

@@KopLamp Thank you for the response. What imaging camera are you using with the C8EdgeHD? I think I am going with the ASI533i. I was thinking of the ASI294, but the smaller field of the 533 is OK for me needs and I like not having amp glow and a low read noise.

[@KopLamp]

I use the 294MC Pro. It has the perfect pixel size. Amp glow is not an issue with proper darks.

[@sreeshab4093]

I am planning to go for the new zwo 2600mc DUO with edge 8. do u think it would work well for autoguiding?

[@KopLamp]

I’ve heard a few promising success stories. It would prevent the need for an OAG.

[@CDigata]

We are still waiting for your F10 image of M1 Mr Martin 🤫

[@KopLamp]

You are right. Lots of video work is overdue. I hope to pick up my paces again. I have uploaded one other image to my telescopius profile though which was also with the f/10 setup. You can find it here: telescopius.com/pictures/view/141216/deep_sky/HCG/56/galaxy-cluster/by-schoenmaker

[@sreeshab4093]

This is great tutotial my friend. I want to setup OAG for my Edge HD 8. I like to go for zwo OAG-L, but I don't have a mini camera. I do have a 174mm standard camera which I believe would have challenges to achieve finespot focus with the helical focuser? Do you advise me to buy a mini? If so which do you advise - 174mm mini or 290mm mini? Also, is there a FB acct or email I can keep in touch with you? Thanks

[@KopLamp]

The 290 mini works too, but I did find that (especially on f/10) finding guide stars can be hard. With the 174 mini I did not run into issues yet. I would first try it with your regular 174mm though.

[@sreeshab4093]

@@KopLamp thanks. Should i still go for zwo OAG-L or you think Playerone FMG-OAG max or Celestron OAG is better? I am in zwo ecosystem for all my needs in general? Any email ID I can keep in touch with you? Or a fB acct?

[@KopLamp]

Non electronic parts are ok to go for stuff outside the ZWO ecosystem. I bought the Celestron OAG due to it being tailored for my EdgeHD and having a big prism. I don’t have experience with the others you mention, so I am unable to give advice which to pick. My email you can find in the about section of my channel.

[@sreeshab4093]

@@KopLamp thank you martin

[@sreeshab4093]

@@KopLamp thanks once again. can u pls let me know if the 174mm standard ver would have any issues for focus with celestron OAG? sorry asking again, since standard 174mm is not a barrel desgin like the 174mm mini... so am unsure if i will have a challenge with the helical focuser.

[@aerozg]

I assume you are using the Celestron OAG here, it looks like it? Could you maybe share the total weight of the whole assembly/imaging train, both with the 0.7x reducer and without? I would like to know if my CEM26 could handle it. Thank you so much!

[@KopLamp]

I would have to put it on the scales. Have not yet done that.

[@aerozg]

@@KopLamp no worries, i have investigated a bit and it seems that i would come in around 9kg total.

[@RedsRhetoric]

Any tips on how to set backfocus with a 2X barlow?

[@KopLamp]

I am afraid I am not completely sure. I have no experience with a Barlow in my system.

[@KopLamp]

I remembered getting a similar question once on a different video titled "Backfocus with an ZWO Cooled Camera". Back then I had come to the conclusion that a Barlow is only affecting the magnification of the telescope and will not affect the flatness of the field. You will also use a Barlow without a reducer/flattener in the optical train. Because of that, the backfocus is not so much a constraint or parameter you need to keep in check. As long as you can achieve focus of course. If anyone reading this has additional information, feel free to add a comment too as I unfortunately have no experience with a Barlow in my image train.

[@glennvanrooij5571]

Hi Martin, should the sensordepth for the asi2600mm be 12,5 instead of 6,5? tnx

[@KopLamp]

The video shows the ASI294MC Pro, which has a sensor depth of 6.5mm. For the ASI2600MM it would depend on whether or not you also use the tilt adapter plate on the camera. The specs from ZWO show that the 2600MM has a sensor depth of 12.5mm without tilt plate. And 17.5mm with the tilt plate on the camera.

[@glennvanrooij5571]

Thx! Great video. I finally got it right. 👍

[@charlesowillford2474]

Hope you are still taking comments. Your videos are all well done. Waiting for part 2?. Did you ever do a video showing the focusing of the mini camera? Is it's BF also 55mm??? What adapters did you use/buy. This part is still unclear. Thank you.

[@KopLamp]

Hi and thanks for your comment. I try to answer all questions I get. Even on the older videos (My channel is pretty small still, so it is very manageable still :p) The backfocus of the guidescope should (in theory) be exactly the same as the backfocus for the main camera. On the EdgeHD that depends on which EdgeHD you have and if you use the reducer or not. See the sheet I shared in the video description. I did not do a video on focusing the guide camera yet indeed. I should do that. Thanks for reminding. The video description has a link to the adapter I used. All other adapters, rings and stuff either belonged to the Celestron OAG kit, or the camera.

[@charlesowillford2474]

@@KopLamp Thanks for responding. A 4 yo UT video by James Lamb has the aswers to my question. It's the only one I have ever seen that does. I estimated 65.5mm from the prism both ways and he found 65.75mm. So I'm happy. Again, thanks for helping us rookies.

[@charlesowillford2474]

Koplamp I was in error; the James Lamb video did NOT cover the Edge HD. Can you tell us if you had to buy an extender for the mini scope and how long was it. Or do the video, HAAAAAAAA

[@KopLamp]

@@charlesowillford2474 I have the video on my todo list. In regards to the camera I think I did mount the black extender ring that came with the camera in order to get enough distance to get in focus. ZWO lists it as a 22mm extender. astronomy-imaging-camera.com/product/asi174mm-mini-mono/

[@charlesowillford2474]

@@KopLamp That was my guess, also. I tell you soon; waiting for delivery today of the Edge 8

[@andrewweller5119]

I have always been stressed out by the .3mm of the 105.3mm. I mean why?! Why not 105 dead. And it comes from the first section of the OAG @ 25.3. Is this an allowance for filters?

[@KopLamp]

I think there is some leeway. If you Google for “celestron backfocus whitepaper” you’ll find a document stating “For best results, the image sensor should be located within +-0.5mm…”

[@andrewweller5119]

@@KopLamp Thanks Martin. i feel less stressed. :) Great video BTW

[@Fantaisia]

Bonjour, la première bague de 50mm (en réalité 49,5mm) s'appuie sur le bord du filetage de la grosse bague du c8 et non au fond de la bague. Mais à la fin fin vous mesurez 134,5 mm depuis le fond de la bague ce qui fait une différence de 10mm. Celestron préconise 133,35mm mais impossible de savoir depuis ou. Qu'est que vous en pensez? Hello, the first 50mm ring (actually 49.5mm) rests on the edge of the thread of the large c8 ring and not on the bottom of the ring. But at the end you measure 134.5mm from the bottom of the ring, which makes a difference of 10mm. Celestron recommends 133.35mm, but it's impossible to know from where. What do you think?

[@KopLamp]

Bonsoir. Yes it is somewhat ambiguous how to measure it. Celestron says that for the 8inch EdgeHD you need to measure from the end of the baffle tube locknut. I got my info from this Celestron white paper: s3.amazonaws.com/celestron-site-support-files/support_files/edgehd_whitepaper_final.pdf

[@Fantaisia]

​@@KopLamp Merci beaucoup! Je vais faire comme ça! Thanks a lot! I'm going to do just that!

[@guntergeorgi1347]

Hi Martin. I have similar setup and get good images but I don’t Know why. That sounds strange but by the number my camera ist about 10 mm farther out than it supposed to be. I think it difficult to discuss that here in KZbin. I would rather like to send you an email but could not find your address here. Maybe you have any idea if my setup is so forgiving or I don’t fully understand the issue. Thank you for the videos. Gunter

[@KopLamp]

The effects of incorrect backfocus are strongest in the corners of the image. So if your camera has a sufficiently small field of view you can get away with some deviation. At least that is my understanding of the subject. My email address can be found in the about section on my KZbin profile.

[@Goldiney]

It's a shame those .7x reducers are as rare as hens teeth these days. Can't find them anywhere. 1

[@KopLamp]

519 euros at Ganymedes.nl with a 1 to 3 days delivery

[@Goldiney]

@@KopLamp Thank you friend!