Building a steinheil periskop out of close up`s

[Drew Bedo]

This is not a trivial project.

If it was easy to design and build a lens that is sharp, well corrected and "fast" in the equivalent of a home workshop, the history of lens development and photography in general would have been very different—from 1840 to the present.

[Amedeus]

well, that´s not particulary true, most designs from the past were purely empirical (petzval were the first to calculate extensively) and good replicas of those lenses can be easely made... i´m not trying to make an amazing lens, just A long lens for a process that is mainly blue sensitive and is not for enlarging...

As Garrett already stated, most, if not all, lenses after Petzval were computated. I have a decent background in optics and have access to optical modeling programs + custom lens building. What you're trying to do is not straightforward, by no means. Yes, you can put to meniscus lenses or two achromats together and get something that resembles a periscope or rectilinear but since you're relying on available lenses you don't have control over either curvature nor refractive indexes. This said, you can combine them and get "acceptable" results (insert your own definition here) if you follow few empirical guidelines.

For starters, use lenses with identical focal length and diameter. If you're chasing a 1000 mm design, then get two 2000 mm focal length lenses. They're pretty hard to find in large diameters. Once you have the lenses, space them between 1 to 2 diameters apart, play within this range. Put the stop in the center and play with the distance between the lenses while observing the different aberrations at play. This is purely empirical. Different lenses, different compromises. When stopped down though, you can expect results like Mark was showing. The more you stop down the better the performance and the longer your exposure will need to be. The latter is not something you want to hear for wet plate ... but you know that already. You will have to improvise a simple optical bench. It doesn't have to be complicated ...

just searching for some empirical and practical experience, lens taxonomy is another business, and lens makers and designs apart, i´m trying to make something out of simple things...

this search started when i started to look for a 1000mm or so lens to make big collodion´s in a trailor... i know that there are some lenses with this focal leghts around... but where? and at what price?... this way i will do it

I understand the need for simple things because when you start looking for the 1,000mm and longer lenses to make large wet plates in a trailer ... well, that's another endeavor. There are indeed few lenses around that will do what you want to do but they all come at a price and you'll have to be patient ... very patient. There are a decent amount of 1200mm lenses around but there's hardly anything that is longer ... I know quite a few people looking for > 1500mm lenses to do large wet plates ... I'm one of them and the message is: be patient and be willing to invest one way or the other. Making large wet plates in a mobil set-up is a relatively expensive habit ... you might find the cost of the lens one of the smaller problems.

Good luck in your search and evaluating lenses, I'm down the path quite a distance now ...

[ruilourosa]

well... i´m not getting such bad results judging by the projections on a ground glass... corners are soft... but nothing to worry about... 2 leica 0,75 achromats are doing a nice job towards a periskop tipe lens, aperture at 11 to 16 seems ok by now... one of my worries was the lack of contrast but so far so good.


cheers and thanks for your help!!!


Rui Lourosa