'Bigger' Barlows

[CSM]

With my 6ins f/10 NexStar SE the 2xTelevue Barlow that I have works very well

with the Phillip SPC900 webcam. I am wondering whether a 2.5 or 3x Barlow would

improve still further, or is that stretching things too far?

I also have a 1.6 Barlow which came with my Binoviewer. Quite small and I could screw that into the 2xBarlow. Wondering whether that might work and what the effective magnification would be? Too cloudy to try anything!

[brantuk]

If my maths is correct you have a focal length of 1500mm or thereabouts. Barlow stacking has been done by some members in the past with varied results but bear in mind the image will be dimmed a fair bit. The effect of a 2x barlow is to "halve the eyepiece focal length" or "double the scope focal length". So stacking a 2x and a 1.6x barlows gives a focal length of 4800mm. Pop a 6mm eyepiece in for example and you get a magnification of 800x. Dunno how that looks to a camera but hope it helps a bit.

[JamesF]

With my SPC900 and 127 Mak I regularly used to do planetary imaging at effective focal lengths of getting on for five metres, so in theory there's no reason it wouldn't work. I achieved that by combining a 2.5x barlow with an extension though. I don't know how well it would work combining two barlows. Obviously there's far more glass involved if you do it that way.

James

[CSM]

Had a chance to try stacking the 2 Barlows last night. Result which you can see here was basically a larger rather fuzzy image. Yes - it may be the extra glass that causes the problem, but I suspect that a 2.5 Barlow is probably the limit for good definition with this scope.