Complete darkness

[nfoldager]

On the 16th and 17th I was out photographing the Sun and the Moon.

On the 16th, the recordings were as expected, except for the last 2 of the Moon: there, one recording was completely black, the other very, very dark.
Only change before the last 2 was the insertion of Barlow. No disconnection of the camera.

On the 17th I took a series of the Sun: all totally black.

How is it possible that I see satisfactory images on live view, while what is downloaded is completely black?

What do I miss?

Best regards,
Niels

[admin]

Hi Niels,

check the 'display histogram stretch' on the right and see if you have stretched the displayed image in SharpCap, which can make it look OK when in fact the image coming from the camera is very dark. See https://docs.sharpcap.co.uk/4.1/#Display%20Stretch

Adding a barlow will reduce the image brightness by a factor of 4 (2x barlow) - if you corrected for that using the display stretch rather than by increasing exposure/gain then that would explain it.

cheers,

Robin

[nfoldager]

Thank you very much for your kind reply.

I compared the log files from a dark and a light recording.
Here are the significant differences:

DARK RECORDING:

Gain=143
Exposure=5,0000ms
Display Black Point=0,0859375
Display MidTone Point=0,109165882561641
Display White Point=0,99609375
TimeStamp=2024-05-17T10:27:50.6856652Z
Duration=17,842s
FrameCount=1000
ActualFrameRate=56,0476fps
------------------------------

LIGHT RECORDING:

Gain=315
Exposure=5,0000ms
Display Black Point=0
Display MidTone Point=0,5
Display White Point=1
TimeStamp=2024-05-17T10:42:31.3867216Z
Duration=17,298s
FrameCount=1000
ActualFrameRate=57,8091fps

That shows that your diagnosis is correct, right?

But I'm wondering about one thing: I didn't notice a black display before I clicked Autostretch.

If the operator can make such a mistake with Autostrech, maybe it would be a good idea if there was some kind of warning (color or something) when Autostrech is "on"? I lost a whole day's footage because I thought the display always shows what is being recorded.

But OK; I am a newbie.

Thank you again.

Best regards,
NIels

[admin]

Hi Niels,

yes, you are correct in your reading of the capture settings files - you had quite a strong stretch in the 'dark' file, which looks like it made you adjust the gain downwards from 315 to 143, leading to the dark images.

I quite like the idea of a warning about the stretch being on - perhaps when starting to capture at relatively short exposures (<0.5s or so) - you would expect stretch on for deep sky, but not for solar/lunar/planetary. I will try to add that soon.

thanks,

Robin