Combining two Petzvals, would it make sense?

[erian]

I have been thinking about what would happen when one would combine rear and front elements from different Petzvals.

Would this produce an usable image?

What happens when different focal lengths are combined?

[Tin Can]

Who knows what you have?

Front and rear of any lens may be different

There are casket sets that mix and match a big variety

Use all combinations and report back with images

Usable images are another topic...

[Nodda Duma]

The field lens group of a Petzval corrects coma and balances astigmatism of the objective group. So mismatching the the objective group and field group will result in degraded off-axis performance. You’ll likely lose the swirly bokeh effect and replace it with something less pleasing. Or you may get lucky and increase the effect. Of course, it depends on the specific cells you want to combine.

[karl french]

I'm currently engaged in such nefarious activities... If the groups are of from lenses of similar focal lengths it can work out quite well. I have a 11.25" f3.6 Voigtlander with an awful front group. I replaced it with a nice front achromat from a no name 12" f4 petzval. The resulting lens seems very sharp, but I haven't shot with it yet, so the final verdict is still out.

[Pere Casals]

You’ll likely lose the swirly bokeh effect and replace it with something less pleasing. Or you may get lucky and increase the effect. Of course, it depends on the specific cells you want to combine.

Just a reasoning... not sure if it's right...

IMHO it's easier that the swirl increases or stays the same, supose that we place a front group with an smaller entrance pupil, this may increase the swirl. Instead if we substitute the front group by one with a larger entrance pupil then probably we would get the same swirl, as anyway the rear group would be trimming the aperture disc in the OOF. Suposing that the Petzval has balanced entrance and exit pupils then swirl can only increase an smaller pupil in the front or in the back.

[Nodda Duma]

Changing pupil size has little to do with what I was talking about. Rather, I’m speaking to what the OP was asking.

[Pere Casals]

Changing pupil size has little to do with what I was talking about. Rather, I’m speaking to what the OP was asking.

OP asks:


What happens when different focal lengths are combined?


I'm speculating that the Franken_Petzval may easily produce a swirl even at larger apertures and more to the center when wide open. With also stronger fall-off. This would be beyond the off-center performance loss you mentioned, of course.


You are the master optician, correct me if I'm wrong... I've only Franken-interchanged front cells of a convertible Symmar 150 and Symmar 210, both resulting Frankens (210-150 and 150-210) deliver a swirl in the OOF, which was not present with the right assemblies, and this should be because size-position of pupils.