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Using different camera sensors for narrower FOV

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#1 rjhat3

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Posted 05 April 2020 - 01:33 PM

I recently acquired an Orion 10" Astrograph. I was shocked at how quickly it gathered enough data to produce a great image, however I was disappointed that the FOV wasn't norrower. I tried to capture Sombrero Galaxy, only to realize that with my current configuration, it was too small to be processed into a usable image. My camera is a Canon T6s.
Last night I was doing some reading since the clouds rolled in about sunset. The topics were pixel scale, fov, etc. I came across astronomy tools and entered my info with data calculated from my reading and Sombrero as my subject. No surprise, same result. My calculated FOV was 78 arcminutes if I remember correctly. But my reading suggested that maybe a camera with a smaller sensor would help. I entered the figures for my guiding cam as my main sensor. My FOV was reduced greatly!
For a test, I actually used my Canon vs my ZWO ASI 120mm this morning on a distant target. Sure enough, my Field of view was narrowed by (just guessing) 3X. This would definitely allow me to photograph Sombrero.
I do have a few questions about this.
1) Does using the smaller sensor affect light gathering ability?

2) Am I sacrificing the ability to crop my images in processing. (Losing resolution)

3) My ASI 120MM is not cut out for a main imaging cam. Which smaller sensor astro cam do you guys recommend on a budget?

Thanks in advance!

Edited by rjhat3, 05 April 2020 - 01:57 PM.


#2 rjhat3

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Posted 06 April 2020 - 08:55 AM

*Update*
Last night I attempted to use the ZWO ASI 120mm as my imaging camera. The results were frustrating at best. With such a narrow FOV, any movement or contact with the mount resulted in vibrations that lasted 15 seconds or more. Attempting to do a 3 star alignment was next to impossible. Having moved the ZWO to the primary position left me with no camera on my spotting scope. I failed to complete the alignment successfully.
I believe this FOV has exceeded the ability of my skills and possibly my equipment. So, I would like to add a question to my post.
What is the ideal FOV to aim for tho photograph Sombrero and maintain some stability?
My current configuration yielded a focal ratio of 3.94 and a resolution of 0.77 arcseconds per pixel. My FOV is 0.27x0.21 degrees.
With the canon T6s as imaging cam, my FOV changes to 1.27x.85 degrees. I feel that this configurations FOV is not narrow enough for my target, while using the ZWO created a FOV that it too narrow for me or my equipment to manage.. what do you guys think?

#3 Madratter

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Posted 06 April 2020 - 09:05 AM

I recently acquired an Orion 10" Astrograph. I was shocked at how quickly it gathered enough data to produce a great image, however I was disappointed that the FOV wasn't norrower. I tried to capture Sombrero Galaxy, only to realize that with my current configuration, it was too small to be processed into a usable image. My camera is a Canon T6s.
Last night I was doing some reading since the clouds rolled in about sunset. The topics were pixel scale, fov, etc. I came across astronomy tools and entered my info with data calculated from my reading and Sombrero as my subject. No surprise, same result. My calculated FOV was 78 arcminutes if I remember correctly. But my reading suggested that maybe a camera with a smaller sensor would help. I entered the figures for my guiding cam as my main sensor. My FOV was reduced greatly!
For a test, I actually used my Canon vs my ZWO ASI 120mm this morning on a distant target. Sure enough, my Field of view was narrowed by (just guessing) 3X. This would definitely allow me to photograph Sombrero.
I do have a few questions about this.
1) Does using the smaller sensor affect light gathering ability?

2) Am I sacrificing the ability to crop my images in processing. (Losing resolution)

3) My ASI 120MM is not cut out for a main imaging cam. Which smaller sensor astro cam do you guys recommend on a budget?

Thanks in advance!

I'm surprised you got no answers on this. Sorry I missed it.

 

1) No. You are losing light (photons), but it is only for stuff you evidently don't care about. You still gather all the photons you would have before of the object within the new FOV. There is a small caveat. Different cameras are more or less efficient at capturing light (it is called QE, Quantum Efficiency). Most modern cameras are quite good.

 

2) You aren't losing resolution when you crop. If you have an image scale of .69 before you crop you will still have an image scale of .69 after your crop. If you can separate two stars before you crop, you can still do so after you crop. If you print, you might find things look more blocky than before you crop. I suspect that may be what you are worried about.

 

3) I'll leave this to others.



#4 tomwall

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Posted 06 April 2020 - 09:12 AM

I've been struggling with this narrow fov issue with my asi224 camera and various mounts and scopes. I've found a few things that help:

- Stay within smaller areas of the sky. Typically, I'll stay within one constellation.

- Do your alignments with your eyepieces and get things centered up using increasingly higher powered eyepieces. I like to swap out my eyepieces until I'm down to the 6mm eyepiece. This approximately matches your camera's field of view. 

- "Sync" to a star near your target.

- Use precise goto to find your target.

- Practice on the brightest DSOs, first. They are the easiest to find. M42 was a good choice. M81 and 82 are good choices now. 

- Patience, Patience,Patience, and a sense of humor :-)

 

Tom,

Tucson




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