Help please - disappearing Mars!

[DanDare]

Had my first attempt at imaging Mars last Monday, using my polar aligned ETX 105, Toucam with UV/IR filter and 2x Barlow.

Eventually centred Mars accurately enough to get an image on my laptop, then took out the webcam inserted the barlow in the drawtube, put back the webcam and hey presto! no Mars. Tried re-centering Mars (a number of times) as best I could using a 10mm eyepice with the Barlow, but still no joy. Each time I got an image using the webcam but as soon as I added the Barlow, Mars had gone.

In my desperation I captured 1500 frames (150s @ 10fps) without the barlow, but have just ended up with a white disc - no features showing at all, although this may have been because I didn't take much time setting the brightness, gain etc on K3CCD tools before capture as I knew my laptop battery was running near very low.

Any suggestions gratefully received.

Roy

Thanks

Roy

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[Sam]

Roy,

I know what you're talking about I had a similar problem when I first tried to get Mars. I think it disappears because it's gone out of focus - because the barlow has changed the focal point - on mine it moves it about 3/4 of a turn out with the webcam. The best way, IMHO, is to crank up the gain and drop the frame rate so Mars is really bright. This will then show Mars as a donut like thing when you put the barlow in (mines a reflector so the donut has the secondary mirror vanes visible as well) just then refocus until it's a crisp disk again and drop the gain and speed up the frame rate until Mars goes dimmer.

hope that helps

cheers

Sam

[DanDare]

Thanks Sam - I'll give it a go.

I should have mentioned that I did try to refocus - I know exactly what you mean about the donut! (sometime I feel like the donut )

I wondered if it was because I hadn't centred the image exactly enough and putting the barlow in was just enough to throw it out.

Roy

[Sam]

I wondered if it was because I hadn't centred the image exactly enough and putting the barlow in was just enough to throw it out.

Roy,

Good point! it only takes a slight knock when putting the barlow in to move it out off the screen - done that heaps. I have a HEQ5 mount and I lock it tight when I'm putting the barlow in now. Also, if the polar alignment isn't good enough the planet will move in the time it takes to put the barlow on and get back to the computer, especially if not centred that well. It takes a while to settle on a method that works. Someone mentioned a while ago that the webcam is the equivalent of a 6mm eyepiece and with a 2 X barlow that would make it like a 3mm - a tiny FOV so it doesn't take much to knock it off target.

cheers

Sam

[daz]

You may find that there is not enough focus travel for the barlow and it won't come to focus.

Try it in daylight to see. If this is the case, an extension tube may help.

[DanDare]

You may find that there is not enough focus travel for the barlow and it won't come to focus.

Try it in daylight to see. If this is the case, an extension tube may help.

Thanks Daz, I'll give it a try in daylight, though there is quite a lot of focus travel on the etx.

Cheers

Roy

[jcm]

Yep , tricky to get the magnified image on the screen. As Sam said if push the gain right up it is often possible to see the out of focused image even if it is just beyond the edge of the frame on the laptop screen. A quick "nudge" with the hand controller ( if you have motor drives) should centre the image , then you can refocus.

John