SharpCap Forums

Robin, not sure if this is user error, a lack of understanding or what.
29th Jan was my first clear night for a couple of months so I thought I'd have a crack at the Moon terminator with my ASI1600 using an ROI of 1920x1080 at the prime focus of a Celestron C11 (f/l 2800mm).
Acquired Moon, focussed etc and then tried to set exposure, I usually use the linear histogram to get ~60% saturation, but tonight - moon completely whited out at < 10%, checked with the logarithmic setting and was even lower .

Exposure was also much lower than when I last shot the moon back in November (now - 0.0001 with gain 75/offset 15 as opposed to 0.07 with gain 139/offset 21 in November).

I was able to eyeball the exposure and seem to have got some half decent results, but I will admit that the videos look more grainy than last time.

Any ideas? I've upload both the camera settings files and histogram files from both sessions.
Note that I had to re-calibrate the camera for your latest version - might this be causing a problem?
Regards
Neil

Missed an attachment - sorry

Hi,

in the most recent capture you have a fairly strong display stretch specified - this brightens the shadows of the image and explains why the moon seemed to white out when the exposure was too short. This doesn't affect the output files, so your output files will be under exposed.

In the mini-histogram on the right are two buttons - lightning bolt does an auto level stretch and the anti-clockwise undo cancels any level stretch.

So basically the histogram was telling you the true story. The screen was far brighter than normal because you'd previously set it that way. The default now is for camera control value to be re-loaded automatically when you re-open a camera (which I think is generally a good thing), but in this case I expect the re-load of the level stretch tripped you up. You can turn off auto reload of values completely in the settings if you want.

cheers,

Robin

Robin,

thanks for that - that stretch was probably left over from some DSO imaging I did back in November. I'll reset tomorrow night and add an aid-memoir to my startup routines to check it.

Surprisingly, I'm quite pleased with the lunar images - a bit underexposed, but nothing a stretch couldn't fix.

Neil