webcam magnification

[astro_dog]

hope everyones gettin clear skies!

I got my hands on a phillips spc900nc and was wondering what the manification of the cam is: i.e equilavent to using what mm eyepiece.

Also is there any way to increase the magnification and reduce it. I have a 3x antares barlow that is up ok up to a point when used for visual observing, but when coupled with the webcam, it is difficult to focus and seems to less light through, the gain is turned right up, but the image is still darker.

Can u use barlows with cam effectively? Is 3x pushing the limits of my scope skymax127 f.l 1500m.

Are there any simple ways to increase and decrease the mags when using a webcam?

Any advice pls

[dtr42]

seem to remember it's equivalent to a 6mm eyepiece [that may be the modded xbox live one ]but think it's 6mm for both

[malc-c]

Can u use barlows with cam effectively? Is 3x pushing the limits of my scope skymax127 f.l 1500m.

Are there any simple ways to increase and decrease the mags when using a webcam?

Any advice pls

The only way to get a bigger image of the target is to use barlows to effectively increase the focal length. However increasing the focal length then makes for less resolution, so the image will appear darker and will require longer exposures to get the detail. Also, with the longer focal length the target will drift out of the field of view quicker, especially if your polar alignment is not 100% spot on.

2x barlow would (IMO) be the max you'll get away with on a MaK127, and that would be on a night with really decent seeing where the air is still and very transparent.

[DOBBY]

Have a read of this thread.... http://stargazerslounge.com/primers-tutorials/40665-primer-planetary-imaging-toucam.html

[JamesF]

It's said that the size of image you get with a webcam is about the same as you get with a 6mm eyepiece, but magnification is a bit misleading when it comes to imaging as a webcam doesn't magnify anything.

Using barlows (sometimes with an extension tube after them) is a common way to change the image scale when imaging and there are plenty of us doing just that with our 127 Maks, but by the time you push the focal ratio out to ~f/35 with a 3x barlow you're working with a tiny patch of sky and even breathing near the scope is enough to make the image wobble. You're also spreading a limited amount of light over a comparatively large area making the image dim and hard to get accurately focused.

At the moment I think Mars is a feasible target with a 3x barlow. It's very bright and there's plenty of light. It's a different story with Saturn though. It's dimmer, lower in the sky and an altogether more challenging target. I have a 2x Revelation barlow, 2x Celestron Ultima that's reckoned to be nearer 2.3x and a 2.5x Revelation. Last time I tried (a couple of weeks ago) I couldn't get an image bright enough to be worth capturing with anything but the 2x.

I've written up some information about focal lengths and so on that you might find helpful, or at least enlightening, here:

Focal Ratio and Capture Length for Planetary Imaging | www.tanstaafl.co.uk

James

[Tinker1947]

I just tested the xbox live on my scope prime focus, thats the webcam into the focusor and this is the result, my first image, and my first pressing of Registax buttons (all of them).....

[JamesF]

2x barlow would (IMO) be the max you'll get away with on a MaK127, and that would be on a night with really decent seeing where the air is still and very transparent.

For imaging it is possible to push it further than that depending on the seeing and the target. I've used my TeleVue 3x on Mars successfully, and my Revelation 2.5x with an extension that gives me a slightly larger image than the 3x barlow, but equally I've had nights when I've abandoned my imaging plans because the seeing wasn't good enough. Mars does provide a lot of light to work with at the moment though.

It's possible that 4x might be achievable on a really good night, but would require excellent polar alignment and tracking as well as a certain amount of luck. There's a small amount of mirror shift when changing the focuser travel direction on the Mak, but at 4x it's amplified to the point where the image can be shifted across the entire camera sensor.

The same probably applies for Venus, but when it comes to Jupiter and Saturn I think there's probably just not enough aperture to allow working at the same kind of scale and you have to bring the focal length down a bit to get a usable image.

James

[JamesF]

I just tested the xbox live on my scope prime focus, thats the webcam into the focusor and this is the result, my first image, and my first pressing of Registax buttons (all of them).....

Looks like a good start to me. I feel such an astro geek now. I even recognise where on the moon it is

James

[astro_dog]

thanks for all the replies guys!

now i just need a few clear nights to put your advice to the test, and hopefully get some better images.