Could this be used to make a monster achro refractor?

[Chris]

I was doing a bit of Ebay surfing when I came across this interesting item:)

http://www.ebay.co.uk/itm/MASSIVE-VINTAGE-TELESCOPE-LENS-21cm-Diameter-5-5-Kilos-/280932969664?pt=UK_Collectables_Scientific_MJ&hash=item4168e8ecc0

I'm not sure about the focal length, the seller doesn't know much about the lens so I've sent him/her a message explaining an easy way to calculate the focal length, I also asked if they know if its a doublet or not but I assume so if its in a cell.

If this lens focal length is quite long it would make for a truly massive scope! too much for me but someone might be interested in it?

Chris:)

[Merlin66]

Hmmm

Not sure it's an achromat doublet....could be just a single lens from an illuminator/ old lantern slide projector?

[astrofox]

I agree it looks like the condenser lens from an old photo enlarger. I had something similar, very short focal length circa 105mm

[Chris]

Thanks guys, it would make a truly awful scope then with a single lens and a very short focal length, the CA and field curvature would be shocking:)

[fwm891]

If it was a telescope objective from a reasonable maker the optical details would be inscribed on the lens cell (I would have thought)

[Chris]

Hmmm well I can't see anything written on the lens cell so its more evidence for it not being suitable for a scope. People seem to be bidding on it, I wonder what they plan on using it for? I guess it would make an interesting manly ornament:D

[Gina]

It looks like a condenser lens to me. I think if it was a telescope lens you would be able to see a bit of the table slightly magnified. Condenser lenses were usually two lenses back to back - flat on the outside faces and spherical on the inner ones. Overall focal length would be something like 20 or 30cm (8-12") so that light from a limelight or whatever would be converged into a parallel beam.

[Chris]

Thanks Gina, thats interesting to here, I learn something everyday on here:)