Extension tubes???

[cosmicdonkey]

Hi there:) I have a skywatcher supatrak 127, focal length 1500. I have recently started imaging saturn and the moon with a Phillips toucam and 2x Barlow. While looking at other peoples planet images I notice they are using an extension tube. What exactly does an extension tube do? And what affect would it have on recording avi's and the overall image. I also hear people say that they have unscrewed the lens from a Barlow and used that as an extension tube. Does an extension tube have to be of a certain length depending on telescope?

I have looked around the forums for answers but there is a lot of posts:)

[Pete Presland]

an extension tube allows me to focus correctly on my ed80 if i have run out of outward travel.

[lw24]

An extension tube increases the magnification, as the further away the webcam is from the lens of the barlow lens, the more magnification there is.

I've been debating whether or not to get one aswell

[glowjet]

Basic use of ex/tubes is where you have placed an optical device in your telescopes system which changes the point of focus beyond the range of the focus draw tube and eyepiece, also used to good effect with cameras to increase magnification, always a useful item to have in your kit especially in the 2"dia variety to help prevent vignetting HTH

[cosmicdonkey]

Thanks guys for the explanation very helpful.

[jgs001]

From the point of view of being able to achieve focus, you shouldn't need one with the Mak... The range of movement of the primary is huge, and on the Skymax 102 there is no problem. If you wanted to increase the magnification of a barlow, then one will work there. As has been said you put the tube between the barlow and the camera, the further back the camera, the greater the magnification effect. You can make a 2x barlow into effectively a 4x barlow without adding any additional glass. Bear in mind that for each 2x magnification, you need 4x the exposure, so boosting gain/iso or exposure time.

[chemtom24]

surely moving the webcam further out using an extension tube will result in you not being able to focus, since the webcam sensor is too far out?

can someone help me out with this? i would like a bigger image of saturn with my neximage, already using a barlow but not big enough, will an extension tube help?

[Merlin66]

As John said, the moving main mirror on your Mak scope gives you a tremendous range of focus. You shouldn't have a problem.

[jgs001]

surely moving the webcam further out using an extension tube will result in you not being able to focus, since the webcam sensor is too far out?

can someone help me out with this? i would like a bigger image of saturn with my neximage, already using a barlow but not big enough, will an extension tube help?

Depends on the barlow, there's a couple of expensive ones that this trick doesn't work with, but otherwise, yes it will. I can't honestly remember, but I think the focus point actually moves inward a little.