Changes to Off-Axis Guider View Settings in Stellarium v23
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- เผยแพร่เมื่อ 25 พ.ย. 2023
- ALERT! Stellarium changed the settings we use to set up the field of view for the off-axis guider in the new Version 23. Let's take a look at the changes and how to measure the dimensions we need to define the field of view. We'll also take a look at the trade-offs for aligning the long dimension of the guide camera sensor with the axis of the scope VS aligning the short dimension of the camera sensor with the scope.
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Keep ‘em coming!
Very nice video - thanks.
One major thing that can mess you up with the OAG is that, depending on your scope type, the actual image orientation of stars that you see in PHD2 is either inverted or mirrored when compared to the main scope image.
It would be wonderful if PHD2 had an option to flip / invert the image - it would make life so much easier at 1:00 in the morning.
Thanks, James! Yes, after I updated Stellarium to v23 I had to make some changes to my oculars as well, so it was good to see this. Actually, there are still things that are wonky in the new version of Stellarium that I haven't found a work-around for yet, but as you said it's an awesome piece of free software, so I'll just be grateful. Thanks again for the update!
Never found the need to rotate the off axis guider to search for guidestars so far so good
Makes life simpler. What focal length are you imaging at?
@@Aero19612 @1280mm
Not sure what's easier than leaving it alone
Hi James.
What is the blue part on your guide camera and what is it's purpose?
I've been using my Celestron OAG on my C8 for a few months now. I noticed during focus adjustment the helical focuser wasn't smooth throughout the focus range. It would be smooth then resistance was felt. When I removed the guide camera (ASI174MM) the helical focuser was smooth throughout the range. I notice the OAG guide camera barrel is a bit oversized for the guide camera. The two locking screws cause the guide came to push against the focuser tube that moves up and down. I guess it's not a big issue if you can start the guide camera near the backfocus point then only have to move a couple of millimeters to tune in the focus. I do wonder if the locking screws can cause the guide camera to tilt a little that might affect focus so that one part of the sensor is in focus and another isn't. I see what appears to me to be some stars in focus an others out of focus in PHD2. I have a ZWO helical focuser that can screw onto the top of the Celestron OAG focuser. The ZWO users two screws but a brass ring is used to clamp onto the guide camera body. The focuser is smooth throughout its travel range. It works with the Celestron focal reducer and its 105mm back focus but not with the Starizona focal reducer's 90.3 mm back focus. You can't get the guide camera sensor close enough to 90.3mm, 96mm.
That blue ring as a par focal ring from Farpoint (bought on Amazon):
Parfocal Ring for 1.25" Eyepieces, FP500
I don't think the two set screws will cause rotation since one screw pushed the camera against the helical focuser wall and the other set screw will push the camera against the focuser wall 90 deg away. That said, there can be some issues. I've had decent luck with the Celestron OAG. I have a later video that looks into the backfocus for the Celestron reducer. I got elongated stars at 105 mm and better results at shorter back focus (~85 mm). Thanks for watching!
Hi James
I have a similar setup with my Celestron SCT 9.25 scope and Celestron OAG guider with ASi174mm camera.
Always get a lot of helpfull information for checking my setup or tweaking it.
I had watched your youtube videos of creating a FOV indicator in Stellarium for the OAG .
"Using stellarium "markers" to setup an off axis guider.
" Changes to Off-axis guider view settings in stellarium v23"
One thing I noticed, you seem to have changed your Mirror distance from the bottom of the OAG housing to the bottom of the prism.
It went from 47mm to 45.5mm.
Did you find something in your analysis of the setup that lead to the change?
I run with 2 different cameras on my SCT.
A ASI2400MC pro , full frame and a ASI2600MC pro APC imager.
Right now I have the prism set at 49 mm from bottom of the OAG housing to (I think) prevent too much intrusion into the Full frame imager FOV.
Does this seem reasonable to you?
Thanks for any help on this.
Always enjoy your videos.
Take care
Steve
Haha. I see what you’re trying to do! You want me to go back and watch all of my videos. No way! I’ll try to go from memory rather than endure the torture.
There are a coup,e do things going on…
1. Stellarium v23 - they changed the CCD/prism distance from (before v23) center of optical axis to BOTTOM of prism to (v23 and higher) center of optical axis to CENTER of prism. So that’s a 6.25 mm (for the Celestron 12.5mm prism) change just to make the OAG image the same from v22 to v23.
2. I also have a video (pre v23, I think) where I define an OAG “bull’s eye” and use Stellarium “markers” to place the main scope at a RA/DEC so that the guide star is in the bull’s eye. If it’s off, I make changes to the CCD/prism distance in the Stellarium Oculars settings so that the star will be in the center of the bull’s eye. That may be the source of one change you’ve seen.
3. And I’ve also changes to the physical distance from the center of the scope axis to the center of the prism to try and get more round guide stars (reduce the distance) without suffering too much of an OAG stalk shadow (increase the distance).
So those are the things I’ve been exploring in the various videos. If your star patterns as seen in PHD2 look like Stellarium’s OAG view AND you’re not plagued with a significant OAG stalk shadow, then no need for any changes! Thank for watching, Steve….so I do t have to
@@Aero19612 hi James
I wasn’t sure if you paid attention to the peanut gallery commenting on your postings. I always seem to find something of interest in your posting s. Probably because my setup matches yours , such good taste we have. Ha I obviously fell behind on watching your videos. Was sidetracked getting ready for eclipse. Sigh . Traveled to one of the mostly cloudy areas. Thanks for your postings and in depth explanations. Take care. Steve
@@stevekaiser4959 I always try to reply but some comments do slip by me from time to time.
@@Aero19612 James. You always do a great job. I look forward to your videos since they are detailed and well presented. As a retired ME design engineer (robotics & machine vision) you keep my attention with the details. Thanks, take care
@@stevekaiser4959 robotics and machine vision? What a perfect skill set for this hobby! Nice
Thanks. Obviously, I can’t do simple math. I got mine working now. Question, why didn’t you get Hyperstar for your 9.25 vs two refractors. Did you have those before your SCT? I’ve been playing around with Stellarium and FOV is limited at F/10 or F/6.3. I plugged in my C8 with at 390mm and I can frame the North American nebula in one shot. I figure getting all the goodies for a refractor it would be cost effective for Hyperstar. I’d have to attach a guide scope but at F/2 you could get away with a smaller lighter one than you had before your OAG.
A hyperstar is an attractive approach. I find dealing with refractors to be much more convenient than handling the bulky/heavy SCT. Also, you can’t use a filter wheel in the hyperstar configuration, so if you go mono then you have to go with a filter drawer and changing filters is a pain. Operating at F/2 generally requires special filters. Focusing works better with the refractors without the mirror movement.