Which extension tube?

[matt]

Guys ... in the never ending quest for more image scale in my astro pix I'm seeking your advice.

I'm looking at 2 extension tubes for sale over at Bintel: 50mm and 35mm.

Which would be best... or should I just buy the pair?!

Asi... you'd have an opinion on this since we've got the same scope.:D

Thanks

[Robert_T]

Matt, were you planning on using this with the 2.5xpowermate or have you got another barlow? Not sure if you're aware that adding extension to the 2.5powermate will actually reduce the image scale - a peculiarity of it's design....

cheers,

[asimov]

As Robert says re the 2.5X barlow/powermate.

I can only tell you what I know. I use the 2X barlow with one extension tube if the seeing is below 4/10 seeing & add another extension tube to that setup if the seeing is better.

One extension tube is 85mm & the other is 90mm....which means nothing: the distance between the barlow element(s) & the camera chip is the thing to take notice of I assume.

[matt]

Yes. That is a strange quirk. DP has recently made me aware of that.

I've got a 2x Celestron Ultima Barlow. I'm also about to order a 3x Televue Barlow which might be as much focal length as I can use in the 9.25 in Canberra's seeing?

Maybe an ext tube with the 2x... and on rare occasions use with the 3x???

Any suggestions most welcome.

And a quick question: what's the image train order? Barlow-ext tube-ToUcam?

Cheers:thumbsup:

[asimov]

I forgot to add I have once added a diagonal (just another way of extending the distance) in the train. Needs to be great seeing though.

I'd suggest trying all possible image scales to determine which is best on the night of capture.

Train order: scope-barlow-ext.tube(s) camera, yup.

So in my case: anything below 4/10 I go the 2X barlow & only one ext. tube. Works for me.

[davidpretorius]

paul haese basically stopped at 3x, and rob_t has done the odd 4x on the c9.25.

4x powermates are 2" and reallllly expensive, so a good 3x would be worth it

http://televue.com/engine/page.asp?ID=42

1/2 way down shows how the powermates change with distance

WELL WELL WELL

http://televue.com/engine/page.asp?ID=41

I say, go the 3x barlow, not powermate and with a range of extension tubes you can from 3x to 5x.

very handy for later in the year for smaller planets ie saturn or next mars or even neptune and uranus etc

[iceman]

Get a 10" newt and a 5x powermate, and then some extension tubes :)

[gbeal]

I'll second that. And a firewire/CFW combo.:lol:

[matt]

The Aperture Monster is back amongst us:rofl: :scared: