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bus_ter

Bahintov Mask webcam focussing video

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I'm trying to improve my focussing using a Bahintov mask. Using my C9.25 and a 3x barlow, and my SPC900 webcam I get the following view.

Is this what it should look like? I tried using 'bahtinov grabber' to help me focus, but it didn't seem to give me any meaningful info. The data just jumped all over the place,

http://s85.beta.photobucket.com/user/bus_ter/media/bahintov.mp4.html

EDIT: This was focussing on the star Aldebaran in preparation for Jupiter imaging.

Edited by bus_ter

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Yep, that's it. Doesn't look like seeing was great so you are getting a lot of movement. The centre line looks a little low on that sequence. If you can convert to B&W it is sometimes easier to see what's going on.

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Is it possible to tell the difference between bad seeing and collimation error from the video? I'm still trying to perfect my collimation.

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Yes, that's very bad seeing - I got the same when I tried to focus a couple of nights ago. It was dreadful :(

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It could maybe also be looking like that if you're scope wasn't cooled down to surounding temperature. If the scope is warmer, like right after you take it out and set it up, you'll get pictures looking like that. or at least i did...

However, to average it out, i recommend to use as long shutter speed as possible. Set it to 5fps in the philips camera settings, then i like to use PHD for example and set it to 1-2 sec, and then use the grabber to adjust focus.

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The scope had been out for several hours so it should have cooled down. Despite the bad seeing I produced an okay image.

post-8564-0-68047400-1353078227_thumb.jp

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That's a nice pic. Can't say anything about collimation from that vid. Using MetaGuide with your webcam will get any collimation issues sorted.

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I spent an hour last night trying to collimate with Metaguide. I don't think I properly understand how to use it. The red box that's supposed to show you which way to collimate just jumped all over the place. I tried to find a video online showing Metaguide being used in practice, but couldn't find anything.

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First set up on a star as high as possible to try and beat any poor seeing and set stacking to 50. De focus and adjust collimation to get concentric circles. Then focus the star as best as you possibly can and reduce the exposure down so that the little graph on the left is ~2/3 up the left hand side. For me this is ~1/200 sec exposure at medium gain but will obviously be cam/scope specific. Set "starstacking" under settings to "peak". Now look at the righthand box and adjust so that the red dot is in the centre. It will jump around a little due to seeing. Hope that helps.

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Thanks Freddie, that helped a lot. As I was imaging Jupiter last night I was setting collimation on Alderbaran. I should have gone for something higher up as you say. I also read today that I should have picked a dimmer star. I had all the settings as default, I'll try setting the stacking as you have described. I read about setting the left hand side graph to 2/3, however instead of getting a peak on the left that quickly falls down (like the documentation I was reading) I was getting the graph going most of the way across. Anyway I'll try again on the next clear night!

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