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Questions about the Exposure Calculator
#1
Hi Greg,

When I use the Exposure Calculator (EC) on faint targets it sometimes reports: 'Unable to reach target SNR' in the 'Calculate Required Exposure Time' section, followed by a number in parentheses like this: 'Unable to reach target SNR (4)' and sometimes: 'Unable to reach target SNR (2)'. What do the numbers mean? I didn't see an explanation in the EC help description. Maybe I missed it. Naturally, reducing the SNR requested can eliminate the message. Sometimes a bright target will also cause the 'Unable to reach target SNR' message. The camera is a DSLR (Canon 7D Mk2).

When the EC is called from the Target Selection page with a 'Camera Only' Imaging System, the camera lens selected on the Target Selection page may or may not be the lens that appears in the EC. For whatever reason the EC will open using the 100mm f/2.8 lens at f/1.4 despite the Target Selection page being set to the 400mm f/5.6 lens. Changing the 100 mm to 400mm sticks, but when I change the f-stop from 1.4 to 5.6 the focal length usually reverts to 100mm. Seems like the f-stop setting must be changed first followed by the focal length. The Help page doesn't say much about operations with a camera + lens Imaging System. Again, maybe I missed something important. The EC is quite an impressive piece of code. I just haven't got all the quirks sorted out yet.

TIA,

Phil
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#2
Hi Phil,

I apologize for missing this post until now. The system no longer seems to be reliably informing me of new messages! One more thing to look in to.

This is code that I added for debugging purposes when we were beta testing so that I could discern between the possible causes of the message. There are two conditions under which the message is displayed, and I see that in looking at the code, this is in the less common case so I didn't notice it myself. Here is what the numbers mean:

2 = signal is blooming
3 = signal is overflowing (large than can be stored as ADU given the number of bits)
4 = not enough signal

I will add code to make the messages say what they mean.

I will look into the lens issue. Thank you for the very clear description of the problem!
Clear skies,
Greg

SkyTools Developer
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#3
Hi Greg,

Thanks for the explanation of the codes. That's very useful info. I also saw a code of (0) in some instances. I can't remember the exact circumstances now.

Another issue with the Exposure Calculator. I have defined 3 imaging systems. One uses a telescope as the camera objective and the other 2 use a camera with separate camera lenses as the objective lens. All 3 systems use a Canon DSLR as the camera. When I switch among the systems in the EC, if I switch from a camera-only system to the telescope system all is fine. When I switch back to one of the camera-only systems, the f-stop drop down button does not come back at the top of the EC window. If I switch to an IS with a CCD camera that has the binning button at the top and then switch back to one of my camera-only IS the f-stop button reappears where the binning button was. Since my telescope based IS uses a DSLR camera, it doesn't have a binning button and the EC won't fill the gap with the f-stop button when I switch back to a camera-only IS.

Hope this description of the issue makes sense,

Phil S.
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#4
Hi Phil,

I'm working on understanding what's going on with that message, so take it with a grain of salt. It may be that those codes don't really mean anything after all.

Wow! I have been trying to understand other reports regarding problems with the f-stop, and this gives me some major clues.

Thanks!
Clear skies,
Greg

SkyTools Developer
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