View Full Version : Silly Petzval Question

4-Dec-2010, 19:24

This may (or may not) be a silly question.

But I thought I would ask anyway.

I have a Petzval lens in magic lantern mount. It slides easily in the lantern sleeve using the existing worm gear.

However, I noticed the lens barrel is symmetrical and can be reversed. A simple procedure by taking out the pinion mount screws, reversing the barrel, and replacing the screws. Then the Petzval projection lens is in backwards.

So now to the silly question: I get great images looking through in either direction. To my eye they don't look much different. Has anyone done this and found any benefits shooting with the lens backwards?

And feel free to punish me if this is a truly idiotic question. But my inherent knowledge of Petzval design is essentially nil.

Cheers. Bob G.

Richard Rankin
4-Dec-2010, 21:01
I don't see any difference when I reverse them either. I have often shot my old Darlot with the rear cone backwards when it fit into the camera better that way. I've never made any proper scientific inquiry into it though, just gone with the ground glass.

5-Dec-2010, 06:00
You will get a pretty good image backwards, but the light photons will be all confused. Seriously, a petzval is usually a little bit sharper the correct way, is the most noticeable difference.

5-Dec-2010, 06:04
Richard: thanks for your note on empirical observation.

Seems that way to me too but I haven't tried taking any photos with it that way yet.

But with the lens reversed I then have the benefit of being able to use the lens-threads to mount screw-on filters. And that is an advantage.


Mark Sawyer
5-Dec-2010, 11:54
The lens is probably sharpest and at its best field curvature and abberation-wise in its intended original orientation. How it changes when reversed probably varies significantly between different Petzvals, as there was quite a bit of variation in glass, spacing, etc.