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Webcam and Barlow - can't get focus


rwg
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Hi folks,

I was trying to image the moon and mars last night with my logitech Fusion webcam (lens removed and 1.25 eyepiece nose attached) - results with just the webcam were reasonable.

When I tried using a 2x barlow (Skywatcher cheapo, as supplied with my Skymax 127), I couldn't bring the image to focus. What I saw was a donut of light on the camera view which didn't resolve to an image however I adjusted the focussing. I tried the same during the day today when at least I have brightly lit extended objects to focus on and got the same result - can't get a focus with the barlow in place.

The only thing I can think of is that maybe the sensor is set so far back from the barlow due to the way I've mounted it that it is somehow beyond the point where the barlow can bring the image to a focus. Does this make any sense? Am I missing something blindingly obvious?

The scope I've been using for this is the SkyMax 127 Mak.

cheers,

Robin

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You might need to try and squeeze some extra outward travel-try pulling the w/cam out of the barlow while still ensuring it is secure and try to focus.

Barlows push the focal point out

To test it pull the cam out of the barlow whilst viewing the image, if the doughnut gets smaller -yippee if it gets larger then the chip needs to get closer as you have suggested.

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Hi,

I tried pulling the webcam out of the barlow when I was testing this afternoon, and it didn't seem to help bring it into focus :)

Guess I'm going to have to work over the mounting of the camera in it's little box to pull the sensor forward. I expect I can gain 5 or more mm if I try.

thanks for the response,

Robin

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Hi folks,

well I moved the sensor forward about 7 or 8 mm by changing how the pcb is mounted in the project box. I expect that the sensor is roughly at the level of the top of the drawtube when the eyepiece nosepiece is in the focuser/barlow.

Unfortunately, I *still* can't bring an image to focus on the Mak with the barlow in, although oddly I can get a focused image using the barlow on my Nexstar 102 SLT (650mm f/6.5 refractor). I can also use the barlow and an eyepiece on the mak and get a focused image just fine.

I'm going to put it down to one of those things for the moment - I probably could move the sensor forward another 2-3 mm, but it would be a fair bit of hassle and I'm not sure it would help. I fancy getting a better barlow soon anyway, as the skywatcher one gives a fairly mushy image, so maybe that will help.

Ron, do you have any hints for planetary imaging with the fusion webcam? I've been getting some OK lunar images, but I've been finding it hard to get decent images of mars. It seems to me that the threshold between practically no signal on one hand and the image saturating on the other is very fine. I've also had software troubles as the logitech capture software just freezes when I try to record. Using Amcap or wxAstroCapture got round that though.

cheers,

Robin

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You could read this tutorial on webcam Imaging by MartinB. It is mainly for the Toucam, but some of it will cover other cams too.

http://stargazerslounge.com/primers-tutorials/40665-primer-planetary-imaging-toucam.html

What Capture Software are you using? Open Capture is quite good. You can download it from here. I think Version 1 is a free download.

http://www.008soft.com/

I have not used my cam on anything other than terrestrial targets.

I was inspired to convert the Fusion after seeing lunar mosaics made by GazoC, which were superb. I've been busy with so many other things, actual practical astronomoy has taken a back seat.

That will hopefully change soon.

Ron.:)

Edited by barkis
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Well, I'm pleased to report that I managed to get out this evening with my adjusted webcam and image mars using the barlow lens. My previous test when I'd moved the sensor forward was in daylight on an object only about 15m away - maybe that makes a difference? According to this (http://www.brayebrookobservatory.org/BrayObsWebSite/BOOKS/BarlowLens.pdf) article, the if the barlow lens is placed inside the prime focus by more than its focal length, you won't achieve focus with it, although whether this was happening to me or I was just being rubbish at focusing I don't know ;)

Anyhow, the seeing was poor going on cloudy, so I don't expect my images will come to much, but I had a round orange disk which is better than my last try :)

thanks,

Robin

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