Help a newbie, please?

Newbie to webcam astrophotography, looking for focusing advice on the following optical train (listed in order):

Celestron 9.25 SCT
JMI 2" SCT focuser with Motor (and 1.25" adapter)
Televue 2.5x Powermate
1" Tele-extender
Phillips ToUcam Pro II 840 Webcam

If I remove the Powermate, the cam comes to focus with no problems.

With the PM in, nothing - the power meter (K3CCDTOOLS) shows 0, no fuzzy blobs, nada on the screen.

If my thinking is right, adding the PM should increase the size of the image as well as making it much dimmer, but leaving the overall "power" nearly the same. I still should be getting something through the camera though.

So, what gives? Does adding a Powermate radically change the focal point? Or is there something else I need to know?

Bill,

First...heck of a nice setup!! Second, when you go from prime focus to the powermate, the focus point changes considerably. Set the gain all the way up and exposure to 1/25, then put the powermate in and try again. You should see a "donut" like object, focus on that. Re-adjust gain and exposure time after getting a rough focus. It's best to make sure your object is centered at prime focus before adding the powermate as the field of view (FOV) is much less. For me when I go from prime focus on my C8 to the 2.5x powermate, I have a fairly large refocus.

Good luck!!
Paul Maxson

Yes, the focal point will change. On my 9.25 it is a turn or 2 (on the SCT) different between no powermate and powermate in. If you're even a little out of focus it will be very difficult to see anything in the image window. You might try centering the planet first without the powermate in then putting the powermate in the path and adjusting focus. Once you find the focus, remove the camera and carefully insert an eyepiece in the 7mm-10mm range and slide it in and out of the powermate until you achieve focus. Mark this position on the eyepiece barrel. Next time you would center and focus visually with the eyepiece then swap in the camera and Voila! your ready to image.

Hi Bill.

Using a low power eyepiece to line up your object will help considerably. Also the addition of a flip mirror system might help. I use a 2.5 PM with a ToUcam as well. Keep in mind the FL of your scope will increase by 2.5, thereby decreasing your FOV which means wou will have to centre the object first before replacing the camera. Also, I find the use of a 9mm ill. ret. eyepiece (Meade) helps considerably with focus. If you can get the planet in focus and centred while looking through the 9mm with the 2.5 PM, you should be pretty close to seeing the object on screen. Also, you might want to increase the gain and brightness levels to very high settings until you find what you're looking for. Reduce them to normal levels when you have the object in sight.

I hope this helps,

Derrick.