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Does "full illumination" mean zero vignetting?

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#1 betelgeuse91

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Posted 06 April 2020 - 12:41 PM

Hi, I was reading the about this telescope which says "Camera sensors up to full-frame size are completely illuminated."

 

TS-optics sometimes rephrase it to something like "full illumination up to ..." as well.

 

I am wondering if this means that there won't be any vignetting. I'd be surprised if such thing is possible!

 

Thanks :) 



#2 TOMDEY

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Posted 06 April 2020 - 01:17 PM

The connotation is that a full field 43mm diameter is entirely unvignetted. The 2.5" focuser operating at F/7 should accommodate that comfortably. If a 2" Star Diagonal is used, it will badly vignette; their Corrector Groups... you would need to select their second one, designed for full format >>>

 

"TSFLAT25Del - the big brother of the TSFLAT2. The corrector is designed for full format sensors. The working distance from the M48 thread to the camera sensor is 55 mm. The flattener fits directly to the M68x1 internal thread of the Apos." My guess is that will vignette the corners somewhat.

 

Once you have the complete system in-hand, there's an easy way to check for vignetting. Make a rectangular thru-hole mask or reticule the same size as your sensor, and place it at the final focal plane. Look through it at a bright wall or sky. Get ten inches or farther back from that mask. Move your head laterally (one eye). You should see the entire exit pupil of the telescope from all locations around the edge of that thru-hole. That's a quick and easy test.

 

[I quantitatively formalized that vignetting-check approach to certify (giant!) imaging satellites for buy-off and delivery. A painstakingly difficult test. A perfectly/critically-baffled system is a thing of beauty --- and quite rare!]   Tom



#3 betelgeuse91

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Posted 06 April 2020 - 01:29 PM



The connotation is that a full field 43mm diameter is entirely unvignetted. The 2.5" focuser operating at F/7 should accommodate that comfortably. If a 2" Star Diagonal is used, it will badly vignette; their Corrector Groups... you would need to select their second one, designed for full format >>>

 

"TSFLAT25Del - the big brother of the TSFLAT2. The corrector is designed for full format sensors. The working distance from the M48 thread to the camera sensor is 55 mm. The flattener fits directly to the M68x1 internal thread of the Apos." My guess is that will vignette the corners somewhat.

 

Once you have the complete system in-hand, there's an easy way to check for vignetting. Make a rectangular thru-hole mask or reticule the same size as your sensor, and place it at the final focal plane. Look through it at a bright wall or sky. Get ten inches or farther back from that mask. Move your head laterally (one eye). You should see the entire exit pupil of the telescope from all locations around the edge of that thru-hole. That's a quick and easy test.

 

[I quantitatively formalized that vignetting-check approach to certify (giant!) imaging satellites for buy-off and delivery. A painstakingly difficult test. A perfectly/critically-baffled system is a thing of beauty --- and quite rare!]   Tom

 

I see... Well since I have a camera, if I have a complete system in-hand, I can just take flat frames to see how much vignetting it has. 

 

Thanks for the reply!



#4 TOMDEY

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Posted 06 April 2020 - 01:54 PM

Cool! Sure looks like the manufacturer did their due diligence, with the 2.5-inch focuser and bigger corrector. The Flats will also comprise correction for cosN drop-off effects, which classify differently, in order to differentiate it from overt pupil-clipping aka vignetting. The cosN effect  should be miniscule, far less than 1%.  I'm guessing that your flats will come out very nice, compared with many other systems, especially those incorporating 2-inch focuser, undersized corrector, or 2" diagonal.   Tom



#5 Kevin_A

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Posted 06 April 2020 - 01:56 PM

full coverage never means no vignetting.... 




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