8" refractor?

[YKSE]

What do you people think of this one?

http://www.astrobuysell.com/uk/propview.php?view=76615

A 8" f12.

Something seems hard for me to understand:  about 10kg for this beast, and tube length of 1.55 meter.

[ScottS]

Lightweight carbon fibre.

[MartinB]

203mm objective F12 = focal length 2436mm.  I would be interested to know how they get the tube length down to 1.55m.  

[dweller25]

It's a folded refractor

[emadmoussa]

10Kg...how is that possible? My 6" f/5.9 refractor is 11.8kg.

[Scott]

how do you get an f12 203mm into 1.55mtrs ? not saying it can't be done, just that I don't know how

edit: too slow (my post, not the refractor)

[DaveS]

It's a folded design. I recall seeing an article about this in AN sometime last year (Can't remember the issue).

I *think* it uses a singlet objective lens with corrections applied further down the optical path with smaller lens groups, but my memory might be faulty and I'm happy to be corrected on this.

Either way, an 8"n unobstructed telescope for that sort of money is very attractive.

Good job I'm broke .

[ScottS]

I'm not so clued up on refractors, but is this not REALLY cheap for an 8" apo.

[YKSE]

Folded design may result in shorter tube, but I suppose it should add more weight?

As Emad mentioned, most 6" f6 refractor weigh over 10kg.

[davew]

It's a folded design. I recall seeing an article about this in AN sometime last year (Can't remember the issue).

I *think* it uses a singlet objective lens with corrections applied further down the optical path with smaller lens groups, but my memory might be faulty and I'm happy to be corrected on this.

Either way, an 8"n unobstructed telescope for that sort of money is very attractive.

Good job I'm broke .

Correct. Just a singlet out front and correctors in the tube.

Not that heavy.

Dave.

[DaveS]

Ah, thanks for that.

Yes, that's pretty much as I remember, though not in as much detail!

[davew]

That's a diagram of another size he made but I'm assuming it's the same.

He's been producing very " Different " designs for some years now. I've never looked through one.

Dave.

[John]

It's based on the design used by John Wall for his famous 30 inch refractor at Hanwell. It was the largest refractor ever made by an amateur and equal 5th largest refractor in the world:

http://www.flickr.com/photos/edhiker/3288412346/

Interestingly the TAL 125 Apolar apochromat uses a singlet objective lens design and 5 further elements in 2 groups much further down the light path but thats not a folded design. 

[YKSE]

Nice to know, always something to learn.