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INDI Library v1.9.9 Released (30 Nov 2022)

Bi-monthly INDI Library released with new drivers and bug fixes.

Astrophotography with wedge

  • Posts: 11
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Dear all,

I am still struggling to get a half-decent pic and I am positive I am missing something very obvious due to inexperience.
I have:
  • Celestron NexStar 6SE
  • Wedge
  • Focal reducer f/6.3
  • Canon EOS 2000D
  • StellarMate
SkyAlign apparently doesn't support the wedge, so I used the "2 known starts" alignment.
The wedge is pointing towards North and set to 51 degrees as I am in London.

I pointed the scope to M 81, and it seems to be able to find it and track. When I take a pic with a 20-25 sec exposure I get this:
File Attachment:


When increasing the exposure, e.g. 60 secs:


Did I do something wrong in setting the wedge?

According to KStars:
Last edit: 1 year 9 months ago by Mirko Grewing.
1 year 9 months ago #69935

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Replied by Gene N on topic Astrophotography with wedge

Hi Mirko,

What method did you use for polar alignment? Any idea how far off the pole your current alignment is/was?

I would not expect any consistency in successful captures of anything much over 45/60 seconds with a SE type mount unless you are guiding the exposures, even on a wedge, expect to throw away 50%.

I did a back of the envelope calculation on your star trail length and rounded shorter exposure to 30 seconds, the trail length between the two was about 2X as long + roughly 10/15 arcsec difference.

Also be advised the rear cell opening of the C6 is quite small, you are going to need good flats to remove the gradient and even then only the center of the image will see the full 6 inch aperture even with your F.63.reducer. See the stretched image attachment. 
 
1 year 9 months ago #69956
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Thanks for your answer - which gives me evidence of how much I have to learn.
I will repeat the operation, this time checking how far off my polar alignment is.
1 year 9 months ago #69959

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Replied by Gene N on topic Astrophotography with wedge

There are many ways to polar align and tutorials available.

One quick thing to look at is deviation trendlines in PHD2

Configure PHD2 to use your INDI camera then let it do a quick mount calibration (turn off DEC guiding else will start playing with SE mount ALT backlash issues).

pick a star near meridian and DEC = 0

After calibration, start guiding, do a View -> Display Graph and enable Trendlines

Yes, there is a learning curve that will become second nature over time! :-)

Gene
1 year 9 months ago #69963

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Replied by Gene N on topic Astrophotography with wedge

This is a link to the method I use to final tweak in my permanent mounted scope, I find it faster than a drift align and can be done using any planetarium program that can link to and control the INDI mount.
It is all manual and requires you to be able to find an center a star near the local meridian and 0 DEC and sync the mount to that star

3-star align

There are automated methods to perform the same function, take a look at the Ekos Alignment module in 'legacy' alignment mode when you do not want to use polaris as the sync star with the camera hanging off the back and bumping into the mount to get there.

 
1 year 9 months ago #69968

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Thanks man!
Yesterday I followed Celestron instructions to the letter:
  1. Pointed the wedge towards the North with a compass
  2. Performed an EQ North alignment (I used the two stars method)
  3. Done a polar alignment adjusting the wedge instead of using the directional control
  4. Re-done the EQ North alignment
At that point, I noticed that my StellarMate was acting out after an update - couldn't connect either with VNC or SSH. So I missed my chance to check how good my polar alignment was based on your instructions... 
I had spent 2 hours doing all alignments so I decided to take some pics anyway with the DSLR camera (this time with the light pollution filter). I pointed the scope at M81 - without any indication on the accuracy beside what Sky Guide on my phone was showing. :P

30 seconds at ISO400:


30 seconds at ISO1600:


I was very much out of focus, but I didn't notice on the spot. Looking at the glass half full, at least I have learnt how to do a polar alignment (hopefully it will become faster as I go), and I have taken a mental note to check that all the equipment is working after any update.
Now I also know that the laptop's battery won't last long enough if StellarMate doesn't work.



 
1 year 9 months ago #70090

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