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Clear night, but no plate solving.

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#26 StephenW

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Posted 28 March 2020 - 03:25 PM

>I have to wonder though....what is the "fudge factor"? I've only done "lazy math" for obtaining the focal length and image scale for my other OTAs

 

The best approach is to take an image with your set-up and upload and solve it at https://nova.astrometry.net/upload

 

That will tell you exactly what your image scale is and you can reverse engineer your exact focal length from that



#27 zakry3323

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Posted 01 April 2020 - 07:09 PM

Things are looking clear, going to try it out again tonight! Thanks for the suggestions folks!



#28 NuclearRoy

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Posted 02 April 2020 - 01:52 PM

There is a setting in PS2 that limits the stars used for the solve. I forget exactly what it is called but I think the default is 6. I never had a problem solving until I put an f/4 lens on and then it wouldn't solve anything. I changed that number to 12 (I think) and viola' worked just fine. Problem is it limits how bright of a star it uses.

I'll try to find the setting. (I think it is in PS2 itself, not in the host program - I use APT)

If your other ideas don't work, look for that.

 

OK, I got my 'working-from-home' butt out of the chair and went to look :)

MaxStar is the parameter. And I was right about 6 and 12.

Since the reducer would raise the exposure a lot, that might be the issue.


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#29 Comatater

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Posted 02 April 2020 - 02:17 PM

Here is your problem and how to fix it. I just went through the exact same issue myself when I changed my image train because of new equipment. Nebulosity has given you the big clue and how to find the problem. Your pixel scale is not what you expected. Nor is it what you thought it would be. This is not lazy math, it is just that things are not what they always appear.

 

That focal reduction amount from your focal reducer assumes a precise spacing from the back of the reducer lens to your camera sensor. If your distance is spot on, you will get the advertised reduction and the expected focal length. However, if your spacing is off, even a little bit, your reduction factor will not be as advertised and your focal length will be different from what you thought it should be.

 

If the spacing is too close, your reduction will be less than advertised, and your focal length will be more than you thought. If your spacing is too far, your reduction will be more than advertised, and your focal length will be shorter than you thought. This is what is reflected in your astrometry numbers. Even a slightly off focal length can kill your plate solve. (PS2 seems to be a little more forgiving than ASPS)

 

You can be off a little bit and still get a good focus and reasonably flat stars in the corners. However, if you are even a little bit off, your focal length will be changed due to different than expected focal reduction. If you are OK with the quality of your stars, then don't change it. Just use the "actual" focal length. Again, you can get this from the setting assistant in ASPS and Astrometry. If you want the advertised performance, and the expected focal length, then carefully measure and adjust the distance between the back edge of your reducer glass and your camera sensor.


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#30 zakry3323

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Posted 02 April 2020 - 05:51 PM

Last night turned mostly into a learning experience all about fine adjustment of the imaging train as pertains to dialing in the flattest field possible. After removing an extension from the reducer/flattener, my backspace should be right around 68mm- giving me room to install the Gerd Neumann tilt adjustment unit. My setup is now FF/FR--> OAG --> adjustable M48 threaded spacer --> Tilt Adjuster --> FW --> Camera. After a few hours I ended up pretty close with the main sensor, I've probably got about a millimeter or so left to adjust, but I think it's probably good practice to start dialing in the tilt adjuster before making more precise adjustments. 
 

There is a setting in PS2 that limits the stars used for the solve. I forget exactly what it is called but I think the default is 6. I never had a problem solving until I put an f/4 lens on and then it wouldn't solve anything. I changed that number to 12 (I think) and viola' worked just fine. Problem is it limits how bright of a star it uses.

I'll try to find the setting. (I think it is in PS2 itself, not in the host program - I use APT)

If your other ideas don't work, look for that.

 

OK, I got my 'working-from-home' butt out of the chair and went to look smile.gif

MaxStar is the parameter. And I was right about 6 and 12.

Since the reducer would raise the exposure a lot, that might be the issue.

Thanks so much for checking for me! I didn't end up attempting a plate solve last night, but I should have the opportunity tonight and I'll dig into PS2 settings and make the changes you've recommended. 

 

Here is your problem and how to fix it. I just went through the exact same issue myself when I changed my image train because of new equipment. Nebulosity has given you the big clue and how to find the problem. Your pixel scale is not what you expected. Nor is it what you thought it would be. This is not lazy math, it is just that things are not what they always appear.

 

That focal reduction amount from your focal reducer assumes a precise spacing from the back of the reducer lens to your camera sensor. If your distance is spot on, you will get the advertised reduction and the expected focal length. However, if your spacing is off, even a little bit, your reduction factor will not be as advertised and your focal length will be different from what you thought it should be.

 

If the spacing is too close, your reduction will be less than advertised, and your focal length will be more than you thought. If your spacing is too far, your reduction will be more than advertised, and your focal length will be shorter than you thought. This is what is reflected in your astrometry numbers. Even a slightly off focal length can kill your plate solve. (PS2 seems to be a little more forgiving than ASPS)

 

You can be off a little bit and still get a good focus and reasonably flat stars in the corners. However, if you are even a little bit off, your focal length will be changed due to different than expected focal reduction. If you are OK with the quality of your stars, then don't change it. Just use the "actual" focal length. Again, you can get this from the setting assistant in ASPS and Astrometry. If you want the advertised performance, and the expected focal length, then carefully measure and adjust the distance between the back edge of your reducer glass and your camera sensor.

Excellent, very useful advice, you and Nebulosity (and I'm really grateful for everyone who's taken some time to help me out!). I'll attempt a solve again after I've got my reducer and the tilt adjustment set. Hopefully that will be tonight, but we'll see! F/4.5 is way more touchy than F/6 :)



#31 zakry3323

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Posted 02 April 2020 - 10:15 PM

Deets tomorrow, but PS2 is now solving for me just fine!
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#32 zakry3323

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Posted 03 April 2020 - 02:36 PM

To sum up!

PS2 settings-> set from 6 stars to solve to 12

SGP Frame and Focus-> set from 5 seconds to 2 seconds

Recalculated image scale and focal length saved to SGP

 

There were some other issues last night, but there are bound to be after completely reconfiguring my existing imaging train and adjusting for a flattish field. I'm still not where I want to be, but I'm getting closer, and I still haven't made any adjustments with the the tilt adjustment as of yet. 

 

BUT, after resetting alignment on my CEM60 and recalibrating, I had no issue slewing to targets, plate solving with PS2 with a nice big 6 degree FOV, and achieving precise targeting. The only thing I wasn't able to do was autoguide...but I have plans for getting the OAG camera and the main camera parfocal soon-ish. With my light pollution, short unguided LRGB subs will do me just fine. Just a single shot, 30 seconds, no calibration. 


M84_30sec_1x1_lum_frame30.jpg
 

 

I could spend tonight dialing in the reducer/flattener even more, and perhaps start working on that tilt....but I can do that under less than great conditions. The Moon might wash it out, but tonight I'm going comet hunting! I plugged HIP 36528 into SGP's Mosaic Wizard and already have my target ready to go smile.gif


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#33 Noobulosity

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Posted 03 April 2020 - 04:04 PM

Nice job!  This can be challenging stuff to get configured correctly.  I'm glad to hear you have things functioning properly.  Can't wait to see some of your images!


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#34 zakry3323

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Posted 04 April 2020 - 06:25 PM

Nice job!  This can be challenging stuff to get configured correctly.  I'm glad to hear you have things functioning properly.  Can't wait to see some of your images!

Images with this setup are still going to be a while off, I think. I got close fixing the tilt last night with the Gerd Neumann....only to find that there was additional tilt in the drawtube! 

Today I received the autofocus system for Rigelsys that I've been waiting for to get my Edge up and running, so that's going to be the imaging priority while I go over my SVX with a fine toothed comb. 




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