What magnification am I getting with XBox webcam

[DBushell]

Okay, so I've done the xbox live cam mod, fitting an eyepiece adapter to it. What I'm trying to determine is what magnification am I getting with my 650mm focal length Astromaster 130eq and 2x barlow?

Reason being I'm trying to see if it's worth getting a 3x barlow for, or whether there is anything else i can do/buy to bring a larger image to the chip.....

Thanks in advance!

[Capricorn]

If you have removed he front lens from the camera than magnification is not applicable.

You would be getting an image size defined by the object you are looking at and the scope focal length.

If you are imaging the moon - 1/2 degree then you have an image of about 5.6mm, the 2x barlow would increase that to 11.2mm.

If the lens is still in then no idea as I do not know wht the focal length of the built in lens is.

[jgs001]

As Capricorn said, with a camera, the magnification isn't relevant... however, as an approximate guide... if you're using a webcam with a VGA sized sensor (640 x 480 pixels) then you can consider the field of view to be approximately that of about a 6.5mm eyepiece.

As an alternative to buying the 3x barlow at this time, if you can move the camera back away from the barlow lens a way, you will decrease the FOV (increase the magnification) accordingly, and it'll give you some idea of the view you would get.

[DBushell]

As Capricorn said, with a camera, the magnification isn't relevant... however, as an approximate guide... if you're using a webcam with a VGA sized sensor (640 x 480 pixels) then you can consider the field of view to be approximately that of about a 6.5mm eyepiece.

As an alternative to buying the 3x barlow at this time, if you can move the camera back away from the barlow lens a way, you will decrease the FOV (increase the magnification) accordingly, and it'll give you some idea of the view you would get.

Will give that a go the next time the clouds part!

The original webcam lens is not attached, only the webcam 1.25" adapter is attached to the camera.

The reason I'm trying to find out is because I keep seeing here that the maximum useful magnification unless I'm really lucky with seeing is 200x - but when the webcam is attached i have no idea what the webcam plus adapter attached to a 2x barlow gives towards the aim of 180-200x

[jgs001]

It's less of an issue with a camera. Ibises my 80mm refractor with a 5x Barlow impossible visually but worked nicely with my webcam.

[JamesF]

When you're imaging it's more relevant to consider the image scale (how much of the sky fits on how much of the image sensor) and how the camera pixel sizes relate to the resolution of the scope rather than worrying about magnification. Part of the issue with maximum magnifications is that you need to get enough light into your eye fast enough to make a sensible image. Up to a point the same applies with cameras, but you have the option of increasing the exposure time with a camera to help get a brighter image.

Image scale is easily calculated as 206265 / focal length in arcseconds of sky per mm of camera sensor. So for your 130EQ that's just under 320 arcseconds per mm, or about 5.25 arcminutes per mm. The Xbox LIve camera sensor is about 4mm wide from recollection, which means across the entire frame you can fit 21 arcminutes. By comparison the full Moon is 30 arcminutes wide and Jupiter at its closest point to Earth is around 50 arcseconds wide (from memory).

If you have a nice bright image then you can combine the camera with a barlow, but again you don't worry about magnification. A 2x barlow effectively increases the focal length by a factor of 2, which in turn changes the image scale and would give you about 10.5 arcminutes across the sensor instead of 21.

If you only have one scope and one camera then there's not much point worrying too much about resolution. Just get on with it and have fun

James