Quote:
Originally Posted by rally
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I am looking into paper...
The math mentioned in the paper is suggesting that for the extended objects F-ratio is more important than aperture (we all know that).
Also, according to their math (and our experience) the spatial resolution of the earth based telescope is limited by atmosphere turbulence, so 25cm aperture is the same as 2 metres (if there is no adaptive optics involved).
I am still trying to complete the whole thing in my mind, but my question still remains: what is the difference (apart from saving time) between stacking subframes taken by array of telescopes and stacking frames taken sequentially by a single telescope?
We all know that SNR is the key factor for detecting the low surface brightness objects... and because of LP and sky glow etc. SNR can be improved by two ways: imager dynamical resolution depth (number of bits per pixel) and stacking a as large number of subframes as it is possible (stacking is essentially averaging process). Then, aggressive stretching can bring out the extended objects which brightness is lower than sky glow (so their contribution is small). Currently, their achieved dynamical depth (detectability of extended objects) is 28 m/arc.sec.
Now, stacking of frames taken by other telescopes (from array) can average out differences between them (and between sensors as well), thus increasing the SNR (in the next couple of days I will try do do some math of my own to understand this in more detail).
Now about Canon lenses, 400mm f/2.8 in particular...
This is a very big lens, it is not cheap (2-5k$ second hand), very rare these days... and it is very heavy - my specimen (FD, from '80s) weights 5.5kg.
EF model is a bit lighter, ~3,5kg.
(some more details
here).
Marcus Keniath told me only ~2500 specimens were manufactured.
So, using this lens (or EF model) is somewhat strange (expensive!) choice for Dragonfly.. unless Canon decided to give them what was left from the sales of those models or what was returned for refurbishment...
BTW, to reduce internal reflections, I had to remove the two front elements from my specimen - they were just flats (coated of course) and used for mechanical protection of the inner ED element.