FOV in digital eye piece, not able to see

[ju1234]

I am not sure if this question should be in "equipment" or "observing". The administrators, if you think it is in wrong forum, please move it.

I am a novice. I have a cheap 700X76 manual telescope with 20mm, 4mm eye pieces, altazimuth controls. It does not have a sky tracker.  I recently also got a cheap 0.3MP digital eye piece (web cam USB 2.0 from China. This has a "10X" written on the front of the device. I use Sharpcap to view with this.  I can center the moon easily and it shows beautiful images of moon in huge magnification, so much that only about 1/4 of the moon is visible in the field at 640X480. And the moon is moving very fast, disappears from the view totally in just a few seconds.

I tired to view Jupiter with this. My problem has been to centering it in the camera. Here is how I go about it: I set up the telescope with the finder scope, 20mm lens and center Jupiter in the view. Switch to 4mm and center with that.  Then I switch to the webcam. And there is nothing. I look around by adjusting the telescope with the micro controls. No luck so far being able to see it through the webcam. May be it is the brightness and it is there but I dont see it. But through the scope (with 200mm eyepiece and not the webcam) I can see numerous stars that I do not see at all with the naked eye.

Is there a way to change the magnification/ FOV in Sharpcap? Or is there another way I can find the target in the webcam first before I enlarge it or other suggestions. Thanks.

[Peter Drew]

I think you are going about the procedure in the correct way but are encountering the almost unavoidable problem of locating the object with a small sensor camera. The focus of the camera will be in a different position to that of the eyepiece, if Jupiter is well out of focus it may well disappear.  Welcome to this forum and good luck.  😀

[lenscap]

I managed to get some images of Jupiter with a webcam & my first scope which was similar to yours.

As Peter says the webcam & eyepiece come to focus at different positions, so by the time you change from one to the other & try to refocus, the target has moved out of the tiny FOV. I suggest you leave the webcam in place & try to locate your targets using the finder scope only.

Align the finder as accurately as possible in daylight using the tip of a distant church spire or electricity pylon & set the focus to produce a clear image on the screen, then leave the focus as it is. Now at night, when you find your target in should be in, or very close to focus.

You will then need at least 2 pairs of hands to keep nudging the scope, tweaking the focus, and altering the sharpcap settings . 😀

The FOV is the ratio of the physical size of the sensor and the effective focal length of the scope. You could increase the FOV with a Focal Reducer but I'm not sure if it would be worth the outlay with your set-up.

Have fun!

 

[Cosmic Geoff]

When you have the Moon in focus with the camera, mark the focus barrel with a pencil (etc) and use this mark to get a first focus on Jupiter.  Use your finder to acquire Jupiter - it will have to be accurately set up.

[Waldemar]

10 minutes ago, Cosmic Geoff said:

When you have the Moon in focus with the camera, mark the focus barrel with a pencil (etc) and use this mark to get a first focus on Jupiter.  Use your finder to acquire Jupiter - it will have to be accurately set up.

Or use parfocal rings:  https://www.teleskop-express.de/shop/product_info.php/language/en/info/p581_Baader-FR-4-1-25--parfocal-ring-for-eyepieces-and-adapters.html