Barlow a zoom is it any benefit?

[Rogering1]

I'm sure this must have been covered before.

Shortly I will purchase a Baader zoom ep & I'm considering barlow to suit my F5 10 Dob, but I don't think there is a benefit and am happy to be corrected.

The zoom EP has:

24mm, 20mm, 16mm,12mm, & 8mm, If I were to use a 2 x Barlow the result is

12mm, 10mm, 8mm, 6mm & 4mm,

12mm-8mm already exist on the zoom & from my understanding 6mm to 4 mm could be next to useless.

Should I consider a smaller barlow or a larger or none.

If I were to use 3 x Barlow:

8mm,6.6mm 5.3mm,4mm & 2.6mm.

Input greatly appreciated.

[John]

Your assumptions are correct. My main concern is that, with the 10" F/5 (or F/4.7 as many of them are) dob being a fast scope and pretty demanding on eyepieces, you would need to be using a high quality zoom and a similarly high quality barlow to get satisfactory results.

Of the focal lengths achieved through your proposal, the 4mm (300x) would not get a lot of use although it could be used on very good nights for the Moon, binary stars and, say, Mars. The 2.9mm (414x) would be too much magnification to be any use, in my view.

Personally I stick to fixed focal length eyepieces in my 10" F/4.8 newtonain.

[Rogering1]

Thanks John good point, is the Baader MK3 the correct zoom for that scope, if not can you suggest?

[John]

Thanks John good point, is the Baader MK3 the correct zoom for that scope, if not can you suggest?

The Baader is a good zoom but, having used a Mk II, I prefer fixed focal length eyepieces. There have been some reports here of the Baader Mk III's seizing up - use the "search" feature to find out more.

[Rogering1]

Yes I'm aware of the seizing up problem, hopefully by now they have corrected the situation.

I also did read that they were more suited to slow scopes, but I don't understand why?

[jabberwocky]

there is also the williamoptics zoom which isnt a clickstop zoom which i assume is the reason the baaders lock up, i have one and love it, yes individual eyepieces are better but zooming in on saturn takes some beating

[knobby]

I have the same, if not similar setup. I find the Barlow is useful on good seeing nights but its pretty poor to use below about 6mm (¹²mm barlowed) so may be a bit of a waste!

So much so that I've bought a Baader 5mm for those 'special nights '

Good luck with your choice

Sent from my Nexus One