Astro Imaging Channel Tonight (7/7/24): The Quest for Aperture: Why are big telescopes better? Other · John Hayes · ... · 32 · 2035 · 3

John Hayes:

Arun H:
But, my question is: what is the real disadvantage of using small pixel cameras with large scopes, so long as you are covering a desired FOV? You can always bin/resample in software and essentially get the same signal as you would if you'd used a larger pixel in the first place. Isn't the real disadvantage just processing and storage?

Yes, the real disadvantage is in processing and storage.  I've noticed that BXT seems to do a bit better with unbanned data so in spite of starting with a lower SNR (wrt binned data) I tend to get a better looking image with sharper features from unbanned data.  This all falls apart somewhat if you are talking about a telescope that would require say 4x binning.  Big scopes such as the CDK1000 from Planewave with an EFL over 6m are reaching the point where they benefit from bigger pixels to better match the seeing conditions.  I didn't say it in the presentation but in reality, as the size of the telescope gets larger, everything gets harder!

John

John Stone:
Hi,

I'm looking at  the attached spreadsheet and I'm a little confused about the numbers used counting the lens surfaces between the GTX130 and the DR350 / DR500.

The Delta Rho 350 has two exposed mirrors and a lens group with 3 elements (https://astronomytechnologytoday.com/2022/09/02/planewave-delta-rho-350/) so it's entry in the spreadsheet of 2 dirty  mirrors, 5 clean lenses and 1 dirty lens seems correct.  (I'm guessing the dirty lens to be the one facing the secondary mirror).

The GTX130 is listed as having one clean lens surface and one dirty lens surface, but this is a triplet refractor with a field flattener.   Wouldn't that be 6 lens surfaces in the telescope (3 lenses / 2 surfaces per lens) and then another 4-6 surfaces in the flattener (4 for a 2 element flattener, 6 for a 3 element flattener)?  i.e. 1 dirty lens surface, 11 clean surfaces (presuming a 3-element flattener).

I'm using the spreadsheet to help me pick a new telescope by comparing it to a telescope I own and looking at the difference in performance so it's important to me that the calculations be accurate as possible.