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Checking tilt on ASI071MC Pro

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#1 t-ara-fan

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Posted 19 July 2019 - 06:31 PM

I want to check the tilt of my ASI071MC Pro  for the first time.  I have CCDInspector, which I have used to inspect old images.  I has some nice displays that show tilt and curvature very clearly.

 

I think it makes sense to use my Orion ED80DT CF refractor with a Moonlite focuser and the Orion Flattener for Small Refractors.  I don't want to confuse the issue with possible collimation errors with my other scope which is an EdgeHD 8.   Does that make sense?

 

Any tips on what to do?

 

My plan is:

  • find a FOV with lots of stars out to the corners
  • take a few shots, look at them with CCDInspector, to see it there is tilt and it appears consistently in all the images
  • rotate the camera (not the whole focuser) 90°, take another shot, and see if the tilt moved with the camera

If the tilt rotates with the camera, I will assume the tilt is in the camera.  Then play with the tilt screws to reduce the tilt, then rotate again and see if the tilt is very minimal in all positions.

 

If the tilt doesn't rotate, I guess it is somewhere else in the image train.  The Moonlite can rotate, I guess I could rotate the Moonlite and the camera together, and see if the tilt shows up there.

 

Should I rotate 90° or 180° between shots?  Or maybe 90, 180, and 270 and back to 0 to really scope out the situation. (No pun intended!)

 

Comments? Advice? Thanks in advance.

 

Pics below show CCDI  curvature and 3D plot BEFORE I worked on my camera.

 

H8JsUEJ.jpg

 

AvkSHLh.jpg

 

                                                                          

Backstory:  While reassembling my ASI071MC Pro after drying the desiccant, I realized I didn't mark the orientation of the tilt adjuster at the front of the camera. I did mark the orientation of the red part with the AR window, although its orientation is obvious because of the pins for the window heater.  So I said some four letter word, probably "darn".  So anyway, I have a 1/3 chance of getting the tilt adjuster on the right way.   I will assume the tilt was quite accurate coming from the factory.


Edited by t-ara-fan, 19 July 2019 - 06:41 PM.


#2 hoxca

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Posted 20 July 2019 - 08:21 AM

Just a simple note.

 

I doubt that the tilt could be a limiting factor in the ccdi image with a 25% curvature on the field.

 

If you can turn the camera by 90°, i deduce that you are not in a full threaded system ?

With this type of coupling in the setup, in my case it will be difficult to get a consistent tilt on subsequent accouplement.

(I'm a nomad astronomer, i travel to dark skies)



#3 H-Alfa

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Posted 20 July 2019 - 10:34 AM

You have 0.1 and 0.1 tilt. It seems good enough. Do you see defocussed stars on the corners?
You can try shooting various images and average them, then introduce the averaged in CCD Inspector and measure it, or measure various images and select them, then click on curvature map to let the software make the averaging. You will notice that on various images you will have different measured tilt.

Enviado desde mi MI 5X mediante Tapatalk

#4 t-ara-fan

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Posted 20 July 2019 - 03:20 PM

I doubt that the tilt could be a limiting factor in the ccdi image with a 25% curvature on the field.

 

If you can turn the camera by 90°, i deduce that you are not in a full threaded system ?

With this type of coupling in the setup, in my case it will be difficult to get a consistent tilt on subsequent accouplement.

(I'm a nomad astronomer, i travel to dark skies)

25%?   The middle isn't too bad, the corners get bad fast.  This my entry level ED80T CF refractor (USD950) with a modest flattener (USD125).  Just curious, have you checked your Tak with CCDIspector? If so, how flat is the TAK?

 

The refractor has a Moonlite CF 2" focuser that only has a 3-screw brass compression ring to hold the optics in place.  Probably not perfectly repeatable, but at least it is short FL.  

 

My EdgeHD8 has a Moonlite CHL 2.5" focuser with threaded connections. 

 

I am hoping I can verify that the tilt is acceptable using my refractor, then check it with my EdgeHD 8 which of course has more collimation variables that make checking tilt trickier.



#5 t-ara-fan

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Posted 20 July 2019 - 03:23 PM

You have 0.1 and 0.1 tilt. It seems good enough. Do you see defocussed stars on the corners?
You can try shooting various images and average them, then introduce the averaged in CCD Inspector and measure it, or measure various images and select them, then click on curvature map to let the software make the averaging. You will notice that on various images you will have different measured tilt.

Enviado desde mi MI 5X mediante Tapatalk

Those pics were my "before" tilt and curvature, before I took apart and reassembled my camera.    I know the flattener is entry level, so in the corners the stars are a little oblong. 

 

Good idea - I will go back through my old images and see how the tilt varied from night to night.



#6 Akwilliams

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Posted 20 July 2019 - 03:26 PM

I’d just be adding or taking away spacing to get that 3D plot flat... or near as I could.  The first image for tilt looks ok.



#7 hoxca

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Posted 20 July 2019 - 03:48 PM

t-ara-fan with my tak i'm happy when the curvature is evalued between 7 and 10 with the ASI071.

If it's > 12, i try to get a better focus as the curvature of the field evolve more rapidly than the fwhm ;)

For sure it was more difficult with my old venerable the fullframe Canon 6D 

 

My impression is the tilt in your previous ccdi shoot could be OK, specially with brass compression ring.

You maybe could get better field curvature with your flattener as Akwilliams said check your spacing between the flatener and the sensor.

 

I cannot help you more on getting some insight on expected curvature with your setup, i don't remember the value i get from my SW80ED and the APS-C sensor.

 

Yeah, it always in the corner, and we can also crop anyway if it's become dramatic !

 

We are all struggling with Orthogonality and Focus, specially with short FD ratio.

Those are our nightmare beasts and we all try to not feed them !

 

Remember also that ccdi is not a perfect superhero, it's just an indicator ;)




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