Magic Lantern Lens, a reversed petzval?

[jimmyp]

Hi,

I just picked up a couple of Magic Lantern style brass lenses. One is an A.T. Thompson Importers with a focal length near 11" and a diameter about 2 inches. This one has some pencil writings on the elements, but I can't get them out to read it.

The other one is curious(er). It's a no name with a brass lensboard, but it seems to be reversed. The front elements have a spacer and the rear elements are the cemented ones. It's also about 11" focal length and the diameter of the glass is just over 2 inches.

Are some of the petzvals set up backwards, with the spaced elements in the front? Or is that normal?

Thanks,

[Steven Tribe]

Some pencil marks are "for internal use only" - and don't identify the maker. Lens work, brass work and assembly were done by different people in the same or adjoining workshop.

The second lens could be either a wrong assembly (if front and rear threads are the same!) or a design that has this construction (A Triplet, for e.g.).

[Richard Rankin]

I see incorrectly assembled petzvals quite often. Most likely, some curious owner unscrewed the elements and then put them back in the wrong set of threads. If the threads are the same, just move them. Or, if there is an outer barrel and a focus knob, some past person may have removed that and put it on backwards. And, I've also seen some lenses where the person thought the part that was the front was actually the rear when it was originally mounted on a magic lantern..

If the spacer between the air-spaced elements is small, as in under a cm, then it is most likely a petzval. If it is larger, like 4-5cm, then it is probably a triplet. In between the two, there suddenly seems to be a controversy as to what they are...

Cheers, Richard

[jimmyp]

Thanks for all the comments. The spacer in the front group is about 2mm. I can't see how the front group could become the back group, just because of the shade on the front end.

[jimmyp]

Interesting what the search will turn up:

http://www.largeformatphotography.in...ad.php?t=66626

So my lens is like Dan King's lens.

[DanK]

Interesting what the search will turn up:

http://www.largeformatphotography.in...ad.php?t=66626

So my lens is like Dan King's lens.

Jimmyp,

I'm convinced mine were just assembled backwards over time....

This thread has some good info on orientation of the elements...

http://www.largeformatphotography.in...hlight=petzval

I've only had the time to play with the darlot (magic lantern), but I rearranged the elements according to the above thread...then flipped the rear element (as many have suggested - more convex side to the rear) which increased the 'swirl' by quite a bit...

Thanks,
Dan