Using Stellarium "Markers" to Set Up an Off-Axis Guider
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- เผยแพร่เมื่อ 2 ธ.ค. 2024
- Galaxy Imaging = Long Focal Length = Off-Axis Guider = Confusion
We demonstrate the DAYTIME procedure I use to set my imaging camera and my off-axis guider for galaxy season. We'll use the "Markers" feature in Stellarium to position our imaging camera so that a very bright star is in the field of view of our guide camera and then we can use a Bahtinov mask to focus the guide camera. No more wasting time trying to find a guide star in the OAG field of view!
James, your channel is criminally underrated. I love it and I learn a lot :)
Haha. Well, maybe if I had a dog that would run in slow motion through a lawn sprinkler instead of a self-important cat that stares at me like I’m an idiot when I go outside to monitor a meridian flip in progress…and still expects to be fed at 6:00am sharp. No respect.
Another great video...whenever I get a notification that you have a new post, I know that I better be sober and ready to learn! Always informative and so helpful!
Good balance. Whenever I sit down to put a video together, I pour a glass of bourbon. Thanks for watching...and saving the bourbon for me!
Really useful work here. We need all the help we can get to avoid the dreaded “No guide-star found” during critical capture time. Setting up the tiny guide camera sensor to identify the center is ingenious. Thank you.
Thanks for watching. I hope it works out for you!
Very good. A really good high-end application in Stellarium. I'm always telling people, it's not just eye-candy.
Very true. Stellarium is an essential tool for this hobby. I use it all of the time. Thanks for watching, Blake!
Thank you for this video. I have almost the same set-up and I didn't know Stellarium could show the OAG. Thanks!!!
Sure enough. It's an indispensable feature for those of us using an OAG with a long focal length scope. Thanks for watching, David!
I'm just starting the mind numbing process of learning how to do astrophotography and, even though I had to stop at minute 17 due to my brain going offline from information overload, this is a fantastic presentation and very helpful. I have yet to capture a single image, so this will be more helpful later once I graduate from imaging the moon a few times. :) I’ve subscribed and will be watching some of your other videos right now. Thanks.
Hi Erik. Welcome to the hobby and thanks for watching the video(s). The video you’re commenting on here gets way into the weeds, so don’t think you have to understand or even do what I’m discussing. An off axis guider is a topic for experienced astrophotographers and fine tuning the view within Stellarium is something probably most people won’t worry about. To make matters worse, Stellarium came out with a new version (v23) that changes the OAG values you need to enter (I have a later video that covers that). Good luck!
Thank you for this James. I have never een able to get my OAG focused or get a guide star centered. Now I think I know how. Jus need some clear skies in Oregon.
Good luck, Pat!
James, thanks so much for your analysis of guide star selection. I am trying to image Siamese Twins and guide stars are difficult to find before and after flip. I followed your example, made measurements and created a spread sheet. Now my guide stars are perfectly centered! I’m am using the Celestron OAG and ASI 174 with Edge 11. Narrow FOV and critical guiding at 1960mm. I always appreciate your detailed analysis of issues.
Great, Sid! Glad it worked out for you. You’ve got a real challenge with that Edge11. The Siamese Twins are on my list. I have the focal reducer on my C9.25 so I could fit them and M58 in the field of view (1318 mm). Even at my shorter focal length, there are just a few stars suitable for guiding. A shame the weather sucks so bad during the peak of galaxy season. Can never seem to knock out targets this time of year. Hope your weather is better!
On my 8” Meade I’m using a 70ED for guiding and the asi120mm-s haven’t had an issue with finding guide stars and get good guiding. Keep up the great videos.
Right, Mike. With a 400mm focal length, you should have a much larger field of view than you get through an off axis guider prism at 1300mm to 2300mm. Plus, your sensor is uniformly illuminated whereas the illumination of the guide sensor in the OAG is maybe 70% illuminated. The downside to the guidescope is higher inertia for the RA axis to deal with and larger guide cam pixel scale. If it’s working for you, don’t change a thing! Thanks for watching!
Another brilliant compact, concise video..
Thank you for the knowledge share and the effort to produce the video.
One thing thst popped out for me was how much you may gain (or lose) with the match of prism size (OAG selection) to imaging camera and telescope and guide camera match to prism size to get sll you can out of the prism FOV..
The questions of which OAG and which guide camera are quite common. Here you demonstrate a means to take a systems approach to optimize the choices. I guess that's bonus content maybe worthy of another YT video?
Take care. Clear skies (and less wind)!
M
Thanks for watching, Mike! I bought the ASI174 for its large sensor. It has helped, but I was surprised to see the uneven illumination over the sensor. Probably only getting 60% of the benefit.
Thanks James and great timing for Galaxy season.
I followed along this past weekend -with C9.25 EdgeHD / Celestron Reducer / ZWO OAG-L /174mm mini / ZWO Filter Wheel / 2600mm pro and set the orientation with the guide scope on the right and lettering on the 2600 on the left.
Went to M106 (on the East side of the Meridian) and NINA reported rotation as 182 degrees (I was expecting something close to 0). When I used Pixinsight to ImageSolve, it reports 178 (which is 360 - 182 as you indicate).
So, it would appear that in order to set 0 degrees to agree with Stellarium, in my set-up, the guide scope would be pointing to the left and not as you have it at 8:48. In this case - there is a difference between 0 and 180 due to trying to get the Guide Scope image to be in sync with Stellarium.
For the life of me - I cannot figure out why my set-up with be 180 off from yours...could it be using a Reducer - or - ???
Appreciate any insight you might have.
I guess the solution is just to set the guide scope on the left and adjust per NINA to plate solve at 0 and go from there!
You are right - this OAG stuff can be confusing!
Interesting! I suppose ZWO could have wired the 2600 sensor different from the 1600 and 294 sensors so that my sensor bottom is closest to the lettering whereas your sensor top edge is closest to the lettering. Or was M106 on the west side of the meridian when you checked the image angle? Or does the Edge flattener mirror the image? My vote is for #2. Let me know what you find out.
@@Aero19612 Confirmed that for the 2600MM Pro on a C9.25 EdgeHD (with Celestron 0.7X Reducer) that for NINA to platesolve (ASTAP) to show 0 degree rotation - the lettering on the camera is to the right and guide cam on the left (using ZWO OAG-L which is bolted to EFW/camera). Actual image orientation agrees with Sellarium (I used Whirlpool Galaxy which is easy to tell), So - it appears it is opposite. I am using NINA 2.2. FYI.
I learnt a thing today! I was completely unaware of markers in Stellarium, really useful for doing this - much better than my random moving of targets in NINA to see if I can accidentally find a guide star or two.
Thanks for the video
They’re very useful and don’t cost a thing! Enjoy!
This is very helpful. I just switched from guiding with a 80mm guide scope to an OAG for my 8" Meade SCT to reduce the load on my HEQ5 Pro. Haven't encountered an issue with finding guide stars so far even with the smaller 178MM but I have been wondering how to set up my OAG view in Stellarium to get the best framing rotation angle for guiding. Thanks a lot!
Glad you could get something out of the vid! Thanks for watching.
Thanks James! Great info!
Thanks for watching!
Once again, Great Work , thank you
Thanks for watching, James!
Great video -- and dense. But I learned some Stellarium stuff today! I have an SCT which I use with a full-frame camera (ASI2400). In that situation, there is less flexibility in modifying the position angle of the OAG so as to not eclipse the sensor with the prism. On the other hand, I've found that a some eclipsing, and reduced FOV, may be necessary to find a good guide star.
Ahh. I wasn’t sure the SCT provided an image circle large enough for a full frame camera. I know it worked with my APS-C sensor on my DSLR. I wasn’t using an OAG at that time. Haha. Yeah, the video is a bit dense. May have to watch it a couple of times if it’s completely new. Nobody said astrophotography was supposed to be simple! Thanks for watching, Richard!
Well I leant a lot from that. So far i have always managed to get a descent guide star in the OAG and since the OAG is bolted to the EFW which is bolted to the camera, I have no ability to rotate the OAG relative to the camera. Not a problem if i’m imaging a single galaxy and can effectively have any main camera rotation for the galaxy (in the centre) until I get a descent guide star but definitely a problem if I’m doing something like you demonstrated for imaging, say, a triplet where orientation becomes a lot more critical. Great video.
Thanks Logan! A lot of people tell me they have no issues with finding guide stars for their OAG, so I'm wondering if I'm crazy. I must be shooting the wrong targets.
James, thank you for another very insightful and useful video. What’s your experience when changing filters when using an OAG? I quit using mine since the focus is not the same and PHD2 gets lost after a filter change. Maybe there is a way to add shims to bring the focus closer. Thanks
I don't have any issues. First, the guide camera being a little out of focus is fine (PHD2 authors actually suggest a little out of focus is beneficial). Second, if you're trying to adjust focus while guiding, the torques generated by the focus motor will generally cause PHD2 to lose its star. Select the option to "stop guiding when performing an autofocus" and you won't have that problem. Thanks for watching, Marcelo!
I agree... well done. I'd like to use one of your diagrams that shows the optical path for the Celestron OAG in posts regarding back focus. I did modify it (e.g., removed the filter wheel) and added my own dimensions. OK? If you want to see what I am referring to, I can send you a message with the image through Cloudy Nights (G.Hatfield).
No worries. That’s fine with me, George.
Hi James! Always love the videos you make for your channel. I was wondering, at 8:48, you show that 0 degrees rotation angle and 0 degrees position angle has the camera at 90 degrees compared with "up" (the direction away from the table top surface). How did you come to that (i.e. why is there a 90 degree CW rotation from "up" for your start position?)? I have always thought of "up" from the 294 camera POV to be where the writing "ASI 294MC Pro" is the correct way up when the scope is lying on it's dovetail on a flat table/surface, and I call that 0 degrees and when I setup my ocular settings in Stellarium - and this seems to match reality. What am I missing?
Hi Greg. Hmm. Assuming the angles we're talking about are coming from Stellarium, the only way to get a 90-deg difference is if you entered the smaller number of pixels in the "x" resolution and the larger number in the "y" resolution (I have the larger number of pixels in the "x").
@@Aero19612 ahhh yes, I think you're right! Silly mistake by me! I'll give that a go but I think you've nailed it! Cheers!
Whew. You don't have to change your settings though. They're fine.
Hello Jay, I'd like to ask you whats the image circle of your SCT? I use a Celestron Edge HD 800 @F7. This has a dramatic reduction of this circle. @F10 it is 42mm but @F7 is shrinks down to 26.7 mm. This is critical for my OAG setup. Even if I set the prism as close as possible to the camerasensor there is still a shadowed area on the guider camera.
Hey Gunter. My non-EdgeHD has an image circle suitable for APS/C sensors with no vignetting. I don't think it will support a full-frame camera without giving badly shaped stars in the corners and probably significant vignetting. I've never used it with a full frame camera though. I believe your EdgeHD should support a full frame sensor but you may have to work on tilt and back focus to get the best results. Some shadowing is OK and can be calibrated out with flats. While your EdgeHD may support full frame sensors, you'll need to verify that the inner diameter of the various adapters and gadgets do not block the light. If you have a full frame sensor, it may be difficult, if not impossible, to use an OAG without casting a shadow or blocking light altogether. Very challenging.
And, like Paul Harvey would say, that is the rest of the story….
Thank you.
I consulted Damien peach on this issue and if he had one; he uses C 14’s for his planetary.
His answer-he is so temperature oriented and its effects inside the scope, doesn’t even believe in dew straps; he’ll use a blow dryer when necessary.
Of course, he’s a planetary guy, so he can afford to do it in the short time he is outside actively imaging .
Thanks again, I feel I’ll be safe installing mine.
I’ll have you know that I did wait for this video before installing it ….. 😊
Haha. Sorry for the long wait. Don’t worry, there’s more dew out there
Hi Jay, at 14:40 min you mention the offset between Stellarium angles and Pixinsight by 360degrees. I’m not sure what you exactly mean by that. For example 355 deg - 360 = -5 deg. This only means the difference between clockwise and counter CW, right? Is it that what you mean? Thanks Gunter
Hi Gunter. Yes, your example is exactly what I'm talking about.
Thanks so much for another terrific video, James! I've learned an incredible amount watching your channel. I apologize if I missed a video between "Setting Up An Off-Axis Guider" and this one, but did you decide to change the orientation of the ASI174 from what you stated in "Setting Up An Off-Axis Guider"? I notice that the height and width numbers you entered in the Stellarium Oculars plugin seem to be swapped (and they're a bit different) in this video than the previous one. Perhaps I'm misunderstanding or misinterpreting the orientation image you showed in this video.
Hi Greg. Thanks for watching! Yes, I did change the orientation. I would prefer to orient the long side of the guide chip parallel with the scope axis because that gives me the largest "doughnut" to find guide stars. But that first video was put out before I used the OAG. Two videos later I showed my first outdoor experience with the OAG and found that the center tube in the SCT was cutting off light to the top of the guide sensor, so I wasn't actually getting the whole doughnut. That's why I rotated the camera. That means the CCD/Prism width and CCD/Prism height are swapped. Before Stellarium v23, they wanted you to put in the distance from the center of the scope to the bottom of the sensor, so that number changes as well. Note that in v23, they want the distance to the center of the prism instead and that's screwing some people up.
@@Aero19612 Thanks so much, James! I appreciate you taking the time to reply/explain. I actually started watching that updated video but never finished for some reason! I watched it in its entirety a little while ago. I also was using the previous version of Stellarium and updated to v23 -- always fun. Got everything working again and entered the revised length/width in the Oculars plugin. In spite of having my ASI174MM mini oriented with the long side of the guide chip parallel with the scope axis, I don't think I had as big a shadow as you did. Not sure why. Perhaps the size of the tube relative to the scope is different in the EdgeHD 8? I'm going to check things a bit more systematically, though. Thanks so much again! (Now it's on to your video about star distortion when using the Celestron Dew Heater...always something, right?)
@@Aero19612 I didn't realize this, James, but I was getting a shadow (about 1/8 of the frame) on the guide sensor. I decided to do a daylight test so I could see how the sensor is illuminated and saw the shadow. I reoriented the guide cam (short axis of sensor now parallel to the light path) and the shadow seems to be gone. IF I ever get some clear skies, I'll test it out at night and correlate the stars in the guide cam field to what I should be seeing. Big IF, though... 🙄
@@Aero19612 Hi James. Hope I'm not being a pest. So, using the Celestron OAG and ASI174MM mini, should the Prism/CCD distance in Stellarium v23 be changed to 16.75mm, the height 7.1mm and the width 11.3mm? I entered these into the Oculars plugin for v23 and it looks correct, whereas when I used the old numbers I had, things just didn't look right.
If the long side of the sensor is perpendicular to the axis of the scope then your Prism/CCD height and width are correct. Your 16.75mm for Prism distance should be the distance from the center of the optical axis to the center of the prism so if that number came from measurements you made to where your prism is located, then that should be good. I've moved my prism, but my number is in that ballpark.
My oag is above the long edge of the 268m. If the oag points up when the scope is in cwd/Polaris position, is the camera in the 0, 90, or something else position?
If the long edge of the imaging camera sensor is parallel with the ground in CWD position AND you entered the larger dimension of the sensor in the first box of the Stellarium oculars settings, then the Stellarium angle for the imaging camera is 90 deg or 270 deg and the OAG is either 0 deg or 180 deg. Hope that makes sense…
it also depends on the dimensions of the imaging camera sensor.
Absolutely. Generally speaking, you can probably get away with a smaller sensor when using a high magnification SCT and that would allow you to lower the OAG prism to make sure it's getting light over the guide cam sensor while not shadowing the imaging sensor.
I have tried to replicated your example for the c9.25 scope (FL 2350mm and Diameter 235mm), ASI294MC w/ASI174 and ASI294MC w/ASI174 Bullseye Sensors and the Lens f/6.3 Reducer with a 0.57x Multiplier. Stellarium’s (Version 23.2) ASI294MC w/ASI174 sensor’s values for the Dimensions are 49.02 X 33.36, the X scale value is 0.7097”/px, and Y scale value is 0.7094”/px. These values do not match the values in the video. Also Stellarium’s inner circle is smaller cutting off the corners of the image rectangle. In the video the inner circle is outside the image rectangle. I have checked all the Sensor ASI294MC w/ASI174 values and they match the values I see in the video. What am I doing wrong?
Hi Bob. Yes. I've been meaning to put out a "warning" video about this. Some dumba$$ changed the way Stellarium wants input for the OAG measurements for Version 23. Now, they want the distance to the center of the prism instead of to the bottom of the prism. This will throw off the OAG field of view If you're following along with my pre-v23 videos. I haven't - and may not - make the jump to v23. If you add half the prism height to your OAG prism distance, the circle should move out. Who knows, there could be other changes too.
Thanks for the reply.
I noticed changing the Prism/CCD distance would fix the problem by I did not know why. I thought it might be a bug in 23.2.
Thank for the video. I like to be able to plan ahead to help avoid problems during an imaging session.
What about getting Pegasus rotator, Pegasus motorized OAG, and Moonlite focuser. Then, NINA will take care everything.
Why in the world would I spend $3000 to address an issue that only requires a $30 solution? Any idiot can spend a ton of money, especially in this hobby. I'm trying to apply a little intelligence instead.
@@Aero19612 1500. Maybe less if you buy used. Not everyone is strong in math like you.
I guess we have tons of idiots in this hobby.
What about making everything, including telescopes and mounts yourself.
NINA only does what you tell it to do. If you expect good results from NINA you need have good intelligence going in.
If you spend $3k on remote control gear it's only because the scope is hours or days away at a remote observatory.
You will definitely need to be proficient at what James just went over in this video to be able to translate it into parameters to control it all remotely. It gets really tough when it doesn't go as expected and you don't have an outside reference to determine the relative orientation of equipment. Figure that out backwards then find out what you did wrong to get there.
So I hope the commenter was a being faciousus.
@@hbmike47 Sorry, it is not entirely correct. Rotating OAG allows you to find suitable stars for guiding very simple way. You are correct, NINA does not do it for you. You search it remotely rotating OAG, and you don’t need calculations and don’t need Stellarium as well. Take a 1-2 sec picture, if no star , then rotate 30 degree and repeat 1-2 sec exposure, etc. it take 2 min at worse to find suitable star(s). You will be opening Stelarium for 1 min.
By the way, I don’t use remote observatory; just backyard.
On QHY cameras with oag, the oag can’t rotate independently.
Yeah, that’s the way my smaller ZWO OAG is. There is basically no way to rotate the OAG with the filter wheel attached. That’s ok for me since I only use that OAG with shorter focal length scopes. I like the Celestron OAG because it gives me independent rotation of the guide cam and imaging cam which is essential for long focal lengths.
Hi James, and thank you for your video. My name is Richard Williams and I live in Astor, "Central Fla.", Florida, just west of Daytona Beach. Anyway, I'm new to Astrophotography and what you just went through seems EXTREMELY complicated to me. Is there any other procedure that a Neophyte, such as myself, can use to approximate what you just did in the last 20 minutes. Because, I think, in real life this procedure would take hours to figure out and then assuming there were no errors in my calculations and measurements, maybe I'd get it right. Surely there must be another way that a beginner can use to make this process much simpler. I appreciate all the complicated, to me, and time consuming work you just did to show us this but, I'm afraid this procedure is way over my head. Any other ideas come to mind?
Thank you James and I enjoy your channel.
Sincerely, Rich Williams
Astor, Florida 32102 USA!
Haha. Welcome to the hobby, Rich. Well, astrophotography IS complicated. If you’re starting out with an SCT and an OAG, then it’s really complicated. At first, anyway. You’ll get the hang of everything. As for the procedure I show in the video, if I knew of an easier approach, I would have made the video about that. It will seem “extremely” complicated the first time. Go through the process a couple of times. It will make sense eventually.