AstroAF - Back Focus Made Simple | EdgeHD 8, Celestron OAG, Astroasis EFW, Player One Artemis-M Pro

[@larrychristianson2244]

Nice to see the actual assembly of an image train. Although, I guess, it's pretty much a pre-determined operation I have never seen it actually done in a video. Educational for me anyway.

[@AstroAF]

Hi Larry! Glad you got something out of this! It’s pretty straight forward but different scopes, OAG (or not), filter drawer, wheel, or not, and camera sensor back sets can have different dimensions and back focus requirements. E.g. my refractor has a 55mm back focus requirement vs the 133.3 on this scope. When I swap out the t-adapter for reducer the back focus will change again (topic of another video). I’ve developed quite a collection of spacers and adapters 😂 Cheers! Doug

[@robinbrown3896]

Don't worry too much about tilt. It is an issue inherent to Meade and Celestron cassagrain type telescopes as the primary mirror moves in the telescope for focus causes a slight tilt. Sometimes known as 'Mirror flop'. The other areas that cause tilt is created is in the focal train and possible, what's known as camera tilt. As you use threaded connectors, you should not have any issues other than the rotating OAG, this can cause tilt as well. As for the camera tilt, it will have zero tilt. A tilt adaptor for the camera only purpose is to eliminate tilt out of the focal train. If the focal train is 100 percent threaded, then a tilt adaptor is not required and can be removed from the system if required. Which would be my choice. Just a note: On threaded connectors, The female thread needs to be deeper than the male thread that is being inserted, otherwise there is a possibility of threaded tilt issues. The Celestron Telescope are very well-made not like the Meade when it comes to mirror flop but can still suffer from the issue. So, when focusing manually on the last movement of the focuser one would move the mirror back to try and flatten the mirror as match as possible, eliminating any likelihood of tilt. A little more difficult when it comes to autofocus, but this can be set in NINA. Don't worry about tilt, it is not an issue right now. Collimation and particularly back focus is more important. Do your collimatian on a medium bright star, it is a lot easier this way. Once you have sorted Collimation and back focus, you will find that tilt is no longer an issue, as it will most likely have been eliminated from getting sharp focused stars. Get this right without using reducers and such. As for filter offset, just add 0.5 to 1mm if you feel it is needed. Great, take a look at the video link as it will cover every thing you want to do. --------------------------------------------

[@AstroAF]

Hi Robin! Sorry I missed this comment reply! I did some checking on my image train and it seems that the tilt is coming from my Celestron OAG (now another reason I don’t like it very much). That OAG is problematic with the helical focuser causing guide camera tilt as well due to the locking screws not having a compression ring. Their single points of contact move the camera within the focuser body. I’ve had to add paper shim to compensate. After testing without OAG my sensor tilt was within about 4nm which is very good. Thanks for all your insight and resources. Much appreciated! Cheers! Doug

[@robinbrown3896]

I took a look at your video link you sent me on 'Back Focus'. Did you take into consideration the two adopters attached to the filter wheel? These would add about 2mm each side, adding to 4mm. I can't determine the actual thickness, so 2mm is only a guess. When you put the OAG onto the filter wheel it overlaid the adaptor slightly, A little hard to see in the video. You need to measure the distant between the filter wheel and the OAG. Depending on the thickness of your filters, you should add 1mm to your overall back focus measurements. There is also a protective glass in the camera that will also affect back focus by about 0.5mm. I'm a little confused in your drawing of the adaptor between the OAG and the 50mm adaptor is only 3.3mm. Is this correct. So instead of all my rambling, I remember while back someone had put out a very extensive video that covered all aspects of back focus scenarios for the Celestron 8HD. So searched around until I found it, you may have already seen it nevertheless, here it is. kzbin.info/www/bejne/ap6ygaSBqbmhqLs -----------------------------------------

[@AstroAF]

@@robinbrown3896 Hello! Thanks for your comment! Yes, the two adapters sit in a recess on the filter wheel which makes them take up 0mm. I measured the OAG adapter with digital calipers to find 3.3. This was a discrepancy to Celestron spec where they did not factor in the adapter recess into OAG body. The filter thickness is 1.85mm which would need a compensation added of .61mm. The camera back focus spec from manufacturer includes the AR glass. I was +/- 1mm of spec which will have no appreciable effect on the field. Also, I’ve not done the video yet but I was getting the same results with the .7x reducer back focus which I’d different than native and uses a different OAG adapter. Thanks for the link, I will check it out! At this time I don’t have any data that eludes to a back focus problem, however, I don’t discount anything. I will get back focus data when I do the tilt correction and if that shows a greater amount than should be adjusted by tilt (should be nm) then I’ll look at other areas of the train again. Cheers! Doug

[@KJRitch]

The Celestron OAG user manual states the M42/M48 female adapters are 4.5mm. Did your measurements come to 3.3mm? With the weight of your current image train and with the added weight of the focal reducer are you going to add some weight on the OTA dove tail near the corrector plate? Will you be adding counterweights onto the mount or are you purchasing a strain wave/harmonic mount? For the Astro Oasis C8 adapter did you order the clamp also or is it supposed to come with the adapter. It's supposed to be 30mm for the C8/9.25. I ordered an Astro Oasis autofocuser a month ago from a Canadian dealer and it didn't come with the clamp. I finally got one delivered to my daughter's house but I also ordered one from First Light Optics in the UK as I wasn't sure I would ever get one from the Canadian shop. So now I have two.

[@AstroAF]

Hi KJ! I also have a 4.5mm in the box. Yes, my digital calipers read out 3.3mm on it. I am adding both an additional counter weight as well as an ADM v-series counter balance weight on the mounting plate on the front under the corrector. The Astroasis C8 adapter does require the clamp, I think it’s 30mm. I had one already as it’s the same one in use on my refractor. This will let you move one Focuser back and forth between scopes. Cheers! Doug

[@KJRitch]

One of the issues I'm having with my C8 is plate solving. I use NINA also and use ASTAP and I downloaded the D80 star database. I used ASTAPs color graph with the resolution spec of my ASI071MC figuring the D80, a larger database, may be better. But recently, I've been having intermittent issues with plate solving. It seems to have gotten worse since updating to NINA 3.0. Sometime in TPPA plate solving will fail during one of the mount position changes prior to the manual adjustment phase. Sometimes in the middle of the manual adjustment while adjusting an axis it will start failing yet the previous adjustment didn't on the same axis. Then I have to start over and eventually I finish TPPA. You may not encounter this issue because you are permantly set up. I've also noticed some GoTo issues which I didn't have prior to NINA 3.0. I've had encountered several times a star is centered for focus buy NINA doesn't think its centered and it slews away. I will be interested in your experiences with NINA and PHD2 at the higher focal lengths. I've been battling these issues even when I started with ASIAir. Longer focal lengths seem to be a challenge. Thanks

[@AstroAF]

Hi KJ! In my first testing last night I also experienced ASTAP solving issues during TPPA. I also experienced issues in PHD2 finding and keeping locks on guide stars. I do not have any answers yet but will be working on it. I feel like I need a larger sensor for guiding. I have configured Stellarium Oculars with my scope, camera, and guide camera and intend to use rotation of the OAG to try and get stars into its FOV. Hopefully we can figure it out, let me know if you come up with anything in the interim! As for ASTAP in NINA, I’m on nightly build. I am going to see if I have same issues with other databases tonight. Cheers! Doug

[@KJRitch]

People on Cloudy Nights report ASTAP doesn’t like light polluted skies or moon glow. I’m using a Antlia Quad Band filter hoping to counteract this issue. With PHD2 and my AVX mount I’m experimenting with PPec algorithm. One night I was able to take test images of the Leo Triplet from 2, 3, 5, 6, 7, 8, 9, 10 minutes all with good shaped stars. I had PHD2 sent for 95% gain and 1.5 sec exposure. SNR was about 13 but PhD2 through my Celestron OAG held onto the star. Most of the time total RMS was 1” or below which for an AVX is great. That was a Bortle 3 Sky but half moon. This is despite PHD2 complaining about my calibration results. With the full moon now the Bortle 3 sky looks like I’m in big city light pollution. I may give it a go again soon.

[@AstroAF]

@@KJRitch Hi! FWIW, I am trying the D80 ASTAP database instead of D50. I haven’t gotten to guiding setup yet, I’m over in electronic focuser setup land right now. I’ll be moving to guiding following.

[@KJRitch]

I would like to see a video of you setting up your Astro Oasis focuser in NINA. I have one but without the 30mm clamp but will picking it up soon from my daughter when we visit her in early May. I’ve never used an auto focuser. Thanks

[@AstroAF]

Hi! I’m sure I’ll have one, or at a minimum it will be a chapter of a larger setup topic.