Using a bahtinov mask with a webcam

[DaveGarland]

Can anyone solve my problem? I've just bought a bahtinov mask to help me focus on my webcam. Now, when I look through an eyepiece and use the bahtinov I get the proper criss-cross shape over the star/planet and all is well and groovy. BUT! When I put the webcam in and look at my laptop screen, I'm not getting a criss-cross, more of an oval blur!

Any ideas folks?

Dave.

[lukebl]

You need to focus it with the webcam in position, not the eyepiece.

[tbird]

I have the same thing Dave, but I found is still produces a diffraction pattern without the spikes which I can focus with Thats with exposure and gain turned up on the webcam..

[DaveGarland]

Ha ha! Yeah I'm not quite THAT daft lol. Yeah, the webcam is in place so that the image on my laptop is coming in through the mask.

[mallorcasaint]

I think what lukebl meant is that you will need to re-focus once you insert the webcam. As you probably know this will be a very different focus point.

[DaveGarland]

Yeah I did that too. I focused it on screen so I could see Jupiter and then put the mask on for fine tuning. Could it perhaps be that Jupiter is a relatively large source of light instead of a find point like a star?

[Demonperformer]

Dave

Is it something to do with the sensitivity of the webcam? I know when I am using my focussing mask with the canon, I sometimes need to up the exposure quite a lot to get the diffraction spikes.

HTH

EDIT: Yes, you need to focus on a point source (star) with a mask, rather than a planet

[Stargazer Jack]

I got that if you are describing what happened to me. It is all fine with planets and stars with the eyepiece but as soon as you put the webcam in, you don't get the spikes/they don't show very well. Quite weird.

[DaveGarland]

Demonperformer, I'll have a little tinker with that next time I get a clear sky.

[Freddie]

Yep, up exposure and gain to increase brightness and you will definitely need to focus on a nearby star and when you have focus move across to the planet.

[Pete Presland]

perhaps you try it on one Jupiters moons first,not sure whether they will be bright enough though

[StuW]

I found I needed to use a star or other similar "point source" of sufficient brightness. Try focussing on a nearby star then locking the focus.