How to adjust contrast for live viewing

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Lunamare
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Joined: Thu Jan 03, 2019 6:19 am

How to adjust contrast for live viewing

Post by Lunamare » Thu Jan 03, 2019 7:21 am

Hi Robin and Friends,
Thank you for providing this site. I am an old (69 years) visual observer in Perth West Oz and I really struggle to use computer technology. My main interest is Lunar surface processes. My aim at this stage is simply to achieve a good quality "live viewing" image of the moon for educational purposes. I purchased a SKYWATCHER MONOCHROME SOLAR SYSTEM IMAGER" which I realise is a more basic camera but one I was advised that will :roll: :roll: be quite adequate for monochrome live viewing of Luna. The camera has a maximum rate of 50 FPS.

I purchased a brand new therefore "clean" and capable HP PC with two 3GB terminals and sufficient capacity to run more advanced cameras than the solar system imager.

I have had a mate help me to install Sharpcap onto the PC after a dud run with Amcap. We then managed an image of the moon albeit with obvious contrast imbalance...the daylight side of the terminator is whited out obviously overexposed, the nightside and near terminator features obviously underexposed. Pressing many buttons we came across a header titled "contrast" I think, which gave us a live screen or... histogram??.. which seemed to be actively working but despite looking up and down on the screen we could not see a further header or control which would allow us to adjust the contrast, or gain. I am told "gain" is essentially contrast.

My apologies for such a tedious basic post but it is sometimes hard for older people to utilise this kind of technology. The problem is simply that computer terminology uses what is essentially another,completely foreign language.

I would appreciate any leads on how to correct the live image. The screen also shows images being taken at a rate of knots though I have not learned to access them. I presume they are somewhere in the files of the new PC. Thank you for any directions.

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Re: How to adjust contrast for live viewing

Post by admin » Thu Jan 03, 2019 6:50 pm

Hi,

so you have a couple of options to try and adjust things to give you the best view. Firstly you can adjust controls on the camera to change the way that it captures images. The primary controls that you would want to adjust are exposure and gain. Now, it sounds like you the camera you have bought is essentially working as a web cam, so it's unclear whether there will be exposure and gain controls available to you (some web cams do have that sort of control and some web cams do not).

Exposure is just the amount of time that each frame collect slight for, while gain is more like an amplifier level – how much the light collected is amplified by before being converted into an image. You may have other controls for the camera on the right-hand side and SharpCap such as brightness and contrast. These are secondary controls and usually should be left in their default positions. The brightness control typically makes everything in the image brighter by the same amount, while the contrast control acts like a crude version of gain – making the bright things brighter without making the dark things brighter too. Because these secondary controls are applied after the image has been turned to a digital form that is usually better to leave them alone. (Note that the brightness control – sometimes known as offset or black level – does have a useful purpose for more serious Astro cameras when doing long exposures, but can typically be ignored for WebCam imaging)

SharpCap also has an option (which should be preferred to the use of the contrast control) to apply an adjustment to the image as viewed on screen (i.e. to brighten it or increase its contrast) without affecting images and save to capture files. Documentation on this feature can be found here – https://docs.sharpcap.co.uk/3.2/#Mini%2 ... %20Stretch

When you start up SharpCap it acts like a video camcorder when it is turned on – so it shows the image being collected by the camera on the screen but without saving those images anywhere. In order to save the images you have to press one of the buttons that will start to capture. You will find full documentation about how to start captures in various ways starting in this documentation here –https://docs.sharpcap.co.uk/3.2/#The%20Tool%20Bar

I think that the issue you are observing that it is difficult to get good exposure on the bright side of the moon and near terminator at the same time as to be expected – there is a big brightness difference between these 2 areas and your camera is not capable of dealing with both of high brightness area of the fully illuminated area of the moon and the much dimmer area of near the terminator with the same settings. This is pretty much like you could not take an image at noon and an image in a darkened room with the same exposure and aperture on a traditional camera.

Hope this helps, Robin

Lunamare
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Joined: Thu Jan 03, 2019 6:19 am

Re: How to adjust contrast for live viewing

Post by Lunamare » Sun Jan 06, 2019 3:42 am

Thank You Robin. I'm not sure Monochrome Solar System, a basic imager shows all these controls or it may be more likely, the operator . As I understand it you are correct in saying that the camera is operating as a web cam. Pretty basic device I think.

I am sure I had to press "START CAPTURE" to get the live screen image. I looked for a long time but did not find a specific control which said or indicted "LIVE VIEWING' or similar.

I have printed out the links you have posted and your post in reply and will read them thoroughly. Much obliged.

PS... Before buying the new PC to run the above imager I looked at the basic end of the Mallincam video cameras as they seemed to be more suitable for simple live Lunar viewing. However after reading more on the net it seemed that video cameras require just as many layers of management as the "digital" types!

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