Help required with CCD Web Cam

[Anonymous]

Hi all,

I need some help with CCD Photography using a web cam.  I recently plugged my Vesta onto my ETX70 and took some shots of the moon.  To my surprise, even thought the telescope was indoors pointing out of an open window over a sink of hot water (could it get worse) I got the thing in focus (well nearly) and took a few frames of the moon (results not attached I can't see how you can add pictures here?).

The thing is, after taking the web cam outside and setting things up correctly i.e. not above a sink with hot water etc.  I got slightly better results; so I thought I chuck on a Barlow lens and he presto, the thing was then impossible to focus properly.  Has anyone else had the same problem?  I'm not sure if it's the camera of the telescope where I'm having focusing problems, but I will say the ETX70 is not very good with any eyepiece above 9mm and I believe the CCD effectively increases the magnification of the telescope.

If possible before modifying the web cam for long exposures I like to try it on a better scope, if anyone can help with that I'd appreciate it.  After all before I start running along here I want to get the basics right.

Thanks


Chris

[Rick]

You'll run out of resolution at some point, but I suspect the barlow focus problem is more likely because it will have shifted the focus quite a way from where it was before.

Rough guide for maximum usable resolution is take the diameter of the objective in millimetres and don't exceed that as a magnification. If the optics are excellent then it tends to be a bit of a conservative estimate though.

Magnification is the ratio of the focal lengths of the primary optics and the eyepiece. 1200mm focal length primary and a 12mm eyepiece give a magnification of 100x.

[Rocket Pooch]

Well I suppose kicking myself would help, I just noticed the resolution of the web cam was set very low.  Bugger!!!!!

Going outside for another try in a minute (not with the moon though).

[Ian]

things get a little complicated with ccd imaging and resolution. very loosely based on Nyquist, you need to find the theoretical resolution limit of the telescope, and ensure that the resolution of camera and stuff is at least twice.

and to complicated it even further, working out the theoretical resolution isn't easy. You can investigate the dawes limit, but some of the imaging being done currently indicates this is too conservative.

When you add a barlow, the focus point moves out. If you can't reach focus, you may need to use an extension tube. Or if you are putting the camera on the "straight through" hole at the back (I'm sure it has a proper name, just can't think what it is) try putting it where the eyepieces go.

I'll be at the obs tomorrow, we can play then.

[Rocket Pooch]

Well it's all academic now I've broken my web cam whilst doing some soldering

Never mind there's bound to be another out there somewhere.....

[Ian]

is it bad? it's surprising what you can repair on those, they are remarkably resilient.

[Rocket Pooch]

I don't actually think so, if you know the mod on a vesta you have to connect to three of the pins.  One of the pads under pin ten seems to have gone bye bye and pin 13 dropped off ƒ¼ but I can solder to what¡¦s left.  

My eyesight is not as good as it used to be and I can't see where to stick the wire.  

I'm going to get a magnifying glass and have another go.  But if you're acceptable to a bribe of beer you're more than welcome to have a pop at it.

Strangely enough the camera almost works with half the control chip in bits