Quality Barlow?

[Aenima]

I've already voted once in this thread for the Revelation 2.5x as well. It's one of my regular pieces of kit for planetary imaging. The Ultima (which I also have) is indeed very good, but be aware that it is far closer to 2.3x or 2.4x than 2x.

James

I had forgot this thread was deciding a barlow, was a bit puzzled by the focal length instead of which type.

Still missing a bit - I think it was a formula - but if the last post was correct, that my F/no of 5 woud be F/10 at x2 barlow.....? then I at least know what x barlow to use? If for my cam it needs f/20 then a x4 would be right?

then I get lost...

So its two things I dont know and they are which type and what number x for my particular scope and cam....

Thank you for the help so far, sort of getting the idea.

Aenima

[Naemeth]

I had forgot this thread was deciding a barlow, was a bit puzzled by the focal length instead of which type.

Still missing a bit - I think it was a formula - but if the last post was correct, that my F/no of 5 woud be F/10 at x2 barlow.....? then I at least know what x barlow to use? If for my cam it needs f/20 then a x4 would be right?

then I get lost...

So its two things I dont know and they are which type and what number x for my particular scope and cam....

Thank you for the help so far, sort of getting the idea.

Aenima

Yes, a x2 Barlow on an F/5 scope would make it F/10. An x5 Barlow would make it an F/25.

Focal Ratio = Focal Length / Aperture in mm

With Barlow:

Focal Ratio = (Focal Length * Magnification of Barlow) / Aperture in mm

[Aenima]

The bit I do follow I am happy with, thank you.

Honestly, maths my weak point , especially astronomic size numbers.

Cheers.

Aenima

[JB80]

That Nyquist formula would make a good app, thanks for explaining it.

I hope you don't mind me asking this here as I'm going through similar motions.

Is there a big difference between the Orion Shorty and Celestron Omni x2s?

They are both priced similar and are a touch above the Tal in price but are they any better than the Tal?

I only ask as I'm going to task Mrs P with the job of upgrading my SW x2 for Christmas so I have to kind of second guess who she'll order from and if the Tal is out of stock then I need a different option. I already have the Tal x3 and I'd like a decent x2 now.

I can find a little bit of info on the Shorty stating they used to be Japanese but are now out of Taiwan and was wondering if that made much difference but in general the Shorty had good reports.