How to Zoom webcam?

Somewhere to ask questions about the best way to use SharpCap
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How to Zoom webcam?

Post by unn » Sat Apr 13, 2019 1:54 am

Hello, I am absolutely new to astrophotography with telescope. I have taken photos of the moon with my compact camera and DSLR directly and some with the telescope. Yesterday I used webcam for the first time and was blown away.

So I got a cheap Chinese "telescope webcam" for $8. It came with no instructions. The cam is printed with "f=3.8, 5mm 10X digital zoom megapixel". I am assuming it is a 1 megapixel camera and a CMOS.

My telescope is a 700X76mm reflector. When I take a photo with Canon DSLR with adapter with 20mm eye piece in it, the moon fills less than half of the camera's 3" screen.

So, I inserted the above webcam in telescope. Turned sharpcap on. scanned and connected the "USB 2.0 PC camera". Focused it with the telescope's manual control. I got a huge well focused moon on the PC screen. Only part of the moon is seen. I have never seen such a huge close up of the moon. The moon is so large that I can see the actual motion of the moon on the screen. The moon leaves the field within a few seconds.

NOW THE PROBLEM I NEED HELP WITH: Because of neck problems, I have hard time looking through the finder scope to locate the target, even the moon. I was hoping to use the webcam for that, however the huge magnification makes it impossible to find the moon or I suppose any other landmark easily. Under the "camera controls" in Sharpcap there is n=only one item: frame rate limit. There are no other controls there. Resolution is set at 640X480.

How do I change the size of the moon? The camera is "digital 10X zoom" but how do i reduce it to 1X or less so I have a wider field of view? There is "zoom" control on the top of Sharpcap. But changing that only changes the size of the screen to small or large, for example at 175% zoom setting the image size is almost 12X8 inches while 16% (lowest available) reduces the window to about 1.25X1". Changing the resolution does the same thing.

So, how do I get a much wider view of the sky? Thanks for the help.

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Re: How to Zoom webcam?

Post by admin » Sat Apr 13, 2019 9:31 pm


If you look at the sensor on the WebCam that you have bought you will see that is much smaller than the sensor on your DSLR. This means that your WebCam has a much narrower field of view (or if you want to look at it another way is much more zoomed in) then the DSLR. If you say that the moon roughly half fills your DSLR screen then that also means that the moon covers roughly half of the DSLR sensor. Now imagine the tiny sensor on the WebCam and you can see why it only sees a small fraction of the moon at one time.

So, unfortunately, there are no changes that can be made in the software that will let you zoom further out, since in order to see more of the moon you need to either have a camera with a bigger sensor or a telescope with a shorter focal length.

Hope that makes sense, Robin

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