SharpCap Forums

Hello,
I am currently experimenting with a different plate-solving solution - and I noticed something about sharpcap I hand't noticed before

The equipment setup is a 200mm Guide-Scope with 50mm aperture coupled to a ZWO ASI120mm (monochrome) camera

I am experimenting with various settings in SharpCap for the purpose of reliable snapshots to be used for plate-solving.
The exposure time is set to 1 second
The gain is set between 10-20
The offset is set to about 8

What I am observing - I find very surprising!

When looking at SharpCap's main display of the sky in live view - I might see one or two stars visible on the display.
I am concerned that there are not sufficient stars visible for plate-solving to be successful.
But I take a snap-shot of that just to see what it will look like.

Surprisingly - the image SharpCap has taken contains perhaps 30 or more very recognizable stars.
I am wondering if I am setting something wrong in the main display - such that it is not displaying what the camera is actually seeing?

Secondly - on the image taken - I was expecting to see the stars as tiny white or semi-white pixels - sitting in background of totally black pixels.
But there are no totally black pixels in the image.
Instead of black pixel elements - the image contains elements which are various shades of grey
I am wondering if I am setting something wrong here as well?

Would greatly appreciate if anyone can advise?
Sincere thanks

Hi

This all sounds about right.
With my SharpCap captures I maybe see 5 or 6 stars but when I stack my captures (I use DeepSkyStacker or SiriL), there are anywhere between 30 and 300 stars recognized, depending on what's in my FOV.
Also the grey scale sounds right. This is what I have here too. At least in single captures when viewed for example in SiriL. Not after stacking though.

The whole how and what is maybe explained better by someone else. My English is okay but the more "technical" aspect like debayering and such, is sometimes bit too difficult

Menno

Thank you Menno555
Greatly appreciate! :-]

Hi,

it's possible that you have adjusted the display stretch in SharpCap in a 'negative' way that is making things darker on screen - this would involve moving the middle line of the three vertical yellow lines to the right (it's more usual to move it to the left to brighten things). See https://docs.sharpcap.co.uk/4.0/#!2!Min ... %20Stretch for more info.

You will never have totally black backgrounds because of light pollution, and also because most cameras add a small value to every pixel called an offset to ensure that random variations in pixel values near to total black do not try to produce negative pixel values. Even so, often there are many dimmer stars that are not easily visible to the native eye that *can* be detected by stretching the image to brighten it.

cheers,

Robin

Yes!
Thank you very much Robin!

I did play with the histogram located on the camera panel
And I did move the left control line over to the right in order to darken the image
I first noticed the peak-band (if that is what you call it) on the histogram - was located completely to the left
If I understand sharpcap that means there is not enough gain on the camera
So I adjusted the gain up in order to move that peak-band up - in order to locate the middle line at its base
But I was worried that that amount of gain was going to hurt the contrast of the snapshot image
So I lowered the gain and started to play with the middle line
Moving it to towards the extreme right made the image darker - so I thought that would work.

But if I understand you - you are saying - that probably had the effect of blocking stars on the main live view display?

Hi,

yes, adjustments to that control will just be affecting the display in SharpCap and not the saved files. For now, reset it to the default by using the reset button (a circular arrow pointing anti-clockwise), which will make the display in SharpCap look the same as the saved files.

To make adjustments that actually really affect the image rather than just the display of the image, tinker with the gain and exposure values instead. With the 120MM the gain range is fairly limited, so even with a pretty high gain you will still get reasonable images. Some cameras have very large gain ranges and the images at maximum gain can be incredibly noisy, but not for the 120MM/MC

cheers,

Robin

Thank you Robin!