Using a Petzval portrait lens

[lungovw]

Let us say that you have a half body portrait to make and you want to use a Petzval lens. According to your composition the sitter’s face is not at the center of your frame (where you get Petzval’s optics best performance with no more than 15º angle of view for that part – lens fully open) How do you go about it? Just get the best focus you can while keeping your lens’ axis centered in your frame, no movements, or, do you move your lens or camera back in order to have its axis crossing your sitter’s face? Or something else?

Asking because with modern lenses (I may be wrong about that) if the scene has only one point of interest and composition is OK, I just focus that spot and shoot. But with a lens so uncorrected, that is probably not the best strategy. I will do some tests, but would like to know how others face this situation.

[Pere Casals]

Let us say that you have a half body portrait to make and you want to use a Petzval lens. According to your composition the sitter’s face is not at the center of your frame (where you get Petzval’s optics best performance with no more than 15º angle of view for that part – lens fully open) How do you go about it? Just get the best focus you can while keeping your lens’ axis centered in your frame, no movements, or, do you move your lens or camera back in order to have its axis crossing your sitter’s face? Or something else?

Asking because with modern lenses (I may be wrong about that) if the scene has only one point of interest and composition is OK, I just focus that spot and shoot. But with a lens so uncorrected, that is probably not the best strategy. I will do some tests, but would like to know how others face this situation.

As you say, if the lens has an image circle that is larger than the sheet you can use shift and rise/fall movements to displace the center of the image circle from the center of the sheet to the place were you have the face. This will also move the center of the swirl bokeh a Petzval may have from the center of the sheet to were you place the center of the image circle.

IMHO it is more important to displace the center of the swirl than the best image quality area.

It's time to remember that the swirl is generated by entrance/exit pupils limiting the the aperture...

Regards

[Jac@stafford.net]

Front rise is your friend, still keep in mind that the swirl effect is largely due to the distance from the subject to background, so if your subject is at zero perspective controls no movements are likely necessary. ... all presuming you have a background, probably an outdoors image.

[lungovw]

My problem is that I am using a Linhof Tecknika 13 x 18 cm with 4x5" back. This camera has so little lens fall (for faces on the upper part of the frame) that I will have to use angles: tilting the lens board and film backwards. I have to do some math. For me it is impossible to guess with angles.
I am not very much after swirl, I just want the eyes perfectly in focus. I want them very sharp and the rest more blurred, not necessarily with swirl.

[Steven Tribe]

I do not recall seeing "swirls" on studio portraits fom yesteryear. There must be some outdoors photos with distant greenery here somewhere. The old motto was to focus on eyes and the rest of the face will be OK. I have seen a few examples of apparently smart use of the curving focal plane where the photographer has managed to include some very sharp costume details/flowers/hands etc.

[cowanw]

Also, Petzvals with a longer than you might think Focal Length were used with smaller than you might think film sizes. So that you would be farther away from the subject and the film would "crop" the central good part of the image.

[ScottPhotoCo]

Here is an example of an 8x10 Wollensak Portrait Lens Series A (Petzval) shot on 8x10 film at f11 with the subject off center. I just focused on the closest eye and made the image. No rise, fall or any other adjustments.

https://farm5.staticflickr.com/4563/38569954501_660f2df82c_b.jpg (https://flic.kr/p/21Li6Hx)Anna L, Actor, 2017 (https://flic.kr/p/21Li6Hx) by Tim Scott (https://www.flickr.com/photos/themdidit/), on Flickr

[lungovw]

Scott, that is what I want, thanks for sharing. What I still don't know is whether with the lens fully open, f/3.7, aiming the lens axis to where one wants sharpness, would provide a significant improvement, compared with just focusing on the same spot with lens centred. At f/11 you corrected a larger share of spheric aberration, the remaining out of focus is coming more from depth of field... I guess.

[Two23]

Scott, that is what I want, thanks for sharing. What I still don't know is whether with the lens fully open, f/3.7, aiming the lens axis to where one wants sharpness,


That's what I always do with portraits. Must have the eyes as the sharpest part of the image.


Kent in SD

[Pere Casals]

I do not recall seeing "swirls" on studio portraits fom yesteryear. There must be some outdoors photos with distant greenery here somewhere. The old motto was to focus on eyes and the rest of the face will be OK. I have seen a few examples of apparently smart use of the curving focal plane where the photographer has managed to include some very sharp costume details/flowers/hands etc.

Hello Steven,

Field curvature and swirl can be both in a Petzval shot, but these two effects are of different origin, one may be present independently from the other. The swirl comes from the entrance and/or exit pupil limiting aperture, so I guess it is possible that some Petzval lenses are simply not able to provide the swirl even when wide open. Perhaps somebody knowing optics would be able to clarify it better.

Also if OOF background is smooth then swirl won't be noticed.

This is a Derogy Petzval 6" F/3.75

https://www.flickr.com/photos/vitalityname/11914265283/in/photolist-aCuQqD-baUtQ6-pJ5YZ8-nru6gF-r8LfsB-nuovpS-dv15b7-cr8Y27-j9PHYX-nqiYYk-aTbFrM-gZR5AZ-fsRNEB-jwnZ1c-eaurjM-cPkho7-czoCos-jwu4PN-cPv5Y3-cB6piA/

Regards

[alex from holland]

While using a smooth backdrop you will never see swirl. Even when using it wide open.
You will only see it when the background has a certain pattern or outside when there is a background with leaves or so.

[lungovw]

Pere Casals, beautiful picture!!! It is intriguing how come that the lens could focus on the girl and also on the bushes that seem to be half the distance. Otherwise it illustrates the rule of 1/3 of focal length being sharp at image centre.

My point at the opening of this thread was, in different words, that if you focus on the lens axis you get a circle of sharpness, but if you focus on a peripheral point, in theory, you get not a circle but a ring of sharpness, due to the field curvature. But I don't know whether this is a noticeable effect on the final picture. I will definitely do some tests.

[Pere Casals]

Pere Casals, beautiful picture!!! It is intriguing how come that the lens could focus on the girl and also on the bushes that seem to be half the distance.

There is a swing, if you observe the plants that are just at left and right of the girl you see that at left plants are out of focus, while at right are sharper. The plane of focus (sphere of focus in this case :) ) passes by the plants in the left-bottom corner and by the girl.

Also there is some tilt (I think), as girl is more out of focus near feet.

Also I feel that placing the swirl in the right place is powerful...

It looks magics, some "pixel lovers" would have said that a good photoshop work was there ! :)

I also like it because what is in the back of the girl it is OOF, what she can see in front of his face it is sharp. It suggests me some kind of subject self awareness, just a personal impression.

https://www.flickr.com/photos/vitalityname/11914265283/in/photolist-aCuQqD-baUtQ6-pJ5YZ8-nru6gF-r8LfsB-nuovpS-dv15b7-cr8Y27-j9PHYX-nqiYYk-aTbFrM-gZR5AZ-fsRNEB-jwnZ1c-eaurjM-cPkho7-czoCos-jwu4PN-cPv5Y3-cB6piA/

LF is great ! I love it !!!

[lungovw]

I tested it. The attached images show a portrait made with a Derogy Rapide nº4, Petzval type, 223 mm focal length, fully opened, serial number 40022. I used FP4 9x12 cm. First of them I just kept the lens axis centred on film while for the second I shifted lens 2 cm to the left and tilted film and lens board, backwards, in order to get the equivalent to 3 cm lens fall. In both cases I focused the eyes using a loupe. It confirms that there is a noticeable effect of aberrations acting upon the overall impression of sharpness on the off center parts of the image. We can focus on a peripheral part of image and compensate field curvature but this does not correct aberrations that will always be there. When lens axis points to the spot we where we want the best image quality, then we get the best performance the lens can yield. The only way to improve those portions far from center in regards to aberrations is stopping down the lens, as Scott did in his above posted portrait.
Portrait:
172293
Eyes with lens axis pointing to film center:
172294
Eyes with lens axis pointing to subject's eyes:
172295

[jnantz]

thankfully the only petzval lenses i have used were
a focal length longer than my format and i never got the swirls
they give me a headache and nausea ..

[DrTang]

I think yes.. the bottom or long side of the pix will go progressively crazy out of focus - because of the physics of the curve of the lens

might be cool though