Shortest focal length Petzval barrel lens with back focal distance >= 105mm?

brianssparetime · Feb 19, 2025

I'm looking to figure out what focal length petzval lens I should buy to mount it on a camera that has a minimum flange distance of about 105mm.

I understand that the flange distance of a simple (i.e. non-retrofocus or telephoto design) lens scales with, and is approximately the same as, it's focal length. However, I understand that the focal length is generally measured from the optical center of the lens, so I can't just assume that, for example, a 6" inches will have 6" of rear clearance.

If anyone has a petzval in the 4.5-6 inch focal length range, I'd appreciate knowing what the back focal distance for it is (when focused to infinity of course).

koraks · Feb 20, 2025

Comparing Petzvals to Petzvals, I don't expect you're going to see much difference in rear clearance between lenses of the same focal length. Same design, after all!

Since you have a minimum clearance, can't you pick any old Petzval and make a hat-style lens board for it that puts it a little further away from the film plane?

Ian Grant · Feb 20, 2025

koraks said:
Comparing Petzvals to Petzvals, I don't expect you're going to see much difference in rear clearance between lenses of the same focal length. Same design, after all!

Since you have a minimum clearance, can't you pick any old Petzval and make a hat-style lens board for it that puts it a little further away from the film plane?

No, not all Petzval's are of the same design, J H Dallmeyer redesigned and improved the Petzval in 1860 re-configuring the rear cell, and Patented the change. This was to correct spherical aberrations, so there's no swirly effects with my 2B. I also have a Squire Carte de Visite Petzval that is well corrected. One other effect of Dallmeyer's change is shortening back focus, compared to earlier Petzval lenses.

My 10x8 camera is setup permanently so I just fitted the f3 2B focused on a wide window frame about 20 ft away, adding tape to mark the edges on the screen. I then switched to an un-named f6 swirly Petxval, size wise almost the same in terms of length, and position of the Waterhouse stop slot, I had to extend rear focus by an inch. The angle of view was almost identical. I then added my 210mm Symmar and the angle of view matched, not surprising as the 2B is listed by Dallmeyer as having an Equivalent focus of 8¼”.

So yes, there can be a significant difference in terms of back focus. Just checking the Squire which is approx 6” focal length, the rear of the barrel is approx 11cm / 4¼” from the focus screen when focussed at Infinity, the Squire just covers 5x4.

An important question to @brianssparetime spare is what camera/format do you want a Petzval to cover, and what does he expect from it.

Ian

koraks · Feb 20, 2025

Thanks for setting the record straight @Ian Grant; I had not realized that! So effectively you saw something like a 5% difference (slightly less) in rear focus distance between the 2B and the unnamed f/6 'swirly' lens?

Ian Grant said:
An important question to @brianssparetime spare is what camera/format do you want a Petzval to cover, and what does he expect from it.

Certainly, and whether the slight difference that can apparently be expected is meaningful in that context.

Ian Grant · Feb 20, 2025

With two lenses of the same "Equivalent" 8¼ inch Focal Length, and a difference of back focus of 1" at Infinity, then the swirly Petzval has just over 16.6% longer back focus that's the difference between 6" & 7". (Or 14.2% the other way around). I just double-checked the distances at Infinity.

Now my 8¼" 2B is listed as having a back focus of 6" and covering 5x4, the 6" 1B is listed as having a back focus of 4½" and covering Quarter plate. In practice, like my 6" Squire, there's a bit more coverage.

I measured the Illuminated circle of the 2B on my 10x8 camera screen, and it was 9" at Infinity.

That's tight for 7x5, no room for movements, but for portraits that image circle increase with closer focussing. A 6" lens like my Squire is just as tight with 5x4.

Ian

brianssparetime · Feb 20, 2025

Thanks for all the feedback here.

Ian Grant said:
An important question to @brianssparetime spare is what camera/format do you want a Petzval to cover, and what does he expect from it.

A little more context here....

I'm interested in sticking this lens on my Bronica S2, which has a flange distance of ~102mm (with a few mm for an adapter, I arrive at 105mm) and a 6x6 film plane.

I'm interested in Petzval lenses specifically for their defects. Ideally, I'd like aggressive swirl, strong astigmatism, barrel distortion, vignette, and field curvature; I'm willing to tolerate whatever other aberrations come along for the ride.

koraks said:
Since you have a minimum clearance, can't you pick any old Petzval and make a hat-style lens board for it that puts it a little further away from the film plane?

Yes, I could. However, the longer the focal length, the larger the image circle, and the more likely it is that the "fun" parts of the image are outside what my 6x6 captures. Also, ceteris paribus, I'd like a focal length that isn't super long relative to the format (we're already in the ~85-100 FFEFL range). In fact, I did take a chance on a Darlot lens at a great price from a listing that had basically no info on it. Turned out to be a 12" lens, which will be cool for another project, but is completely impractical for this one.

FWIW, I'm exploring a few other avenues for this as well.

I've already adapted a bunch of old folder lens assemblies (Kodak 616, Kodak Premo, Buster Brown 3a) that are generally about 120-135mm. These are fun, but they are generally too good for what I'm ideally looking for.

I'm currently experimenting with adapting early lenses meant for 35mm cameras in the 135-150mm range. I learned that a front aperture ring is key through failure with a Asunuma 150mm, and I have a partially disassembled Triotar 135mm f4 with front aperture ring that needs to be unseized. My thought here is that since these lenses were designed for 35mm film, I'm hoping the extra image circle I'll be capturing is more "wild" than the 35mm crop.

Finally, I've been considering projector lenses. But I have some of the same questions as re: Petzval - it's hard to figure out whether a 135mm or 150mm lens will have enough BFD to clear my mirror, and overshooting to something like 200mm is suboptimal.

I was going to post it in a separate thread later on, but any suggestions for modifying existing lenses to achieve my "so bad it's good" look would also be much appreciated.

MattKing · Feb 20, 2025

I have a friend who has done fun things with a matched pair of those "Wide Angle" auxiliary lenses used on fixed lens cameras - the ones he has been playing with are for 35mm cameras, but there are also units for medium format TLRs.
He does have machine shop skills, and he has combined them a barrel that turns them into a reversed pair.

brianssparetime · Feb 20, 2025

MattKing said:
I have a friend who has done fun things with a matched pair of those "Wide Angle" auxiliary lenses used on fixed lens cameras - the ones he has been playing with are for 35mm cameras, but there are also units for medium format TLRs.
He does have machine shop skills, and he has combined them a barrel that turns them into a reversed pair.

I've been slowly educating myself on optical design and have been interested in trying something like that as well. I currently have a few larger lenses on backorder from China to play with, plus a nice box of lens elements from bargain bin finds. That project is moving slowly though due to current geopolitical conditions, as well as focus on these other options.

I've been studying the Pencil of Rays website, picked up a few books on optical design, and anything else I can get my hands on. But the glass I can find rarely has sufficient information on it (e.g. curvature diameter, index of refraction), and I'm trying to make a bad mostly-uncorrected lens rather than a good fully corrected one.

FWIW, I've also played a bit with a Sankar fisheye converter, which fits on the Nikkor-P 75mm. It does vignette heavily (basically keyhole), but it's a cool effect nonetheless.

Finally, I have a spare trashed Nikkor-P 75mm which I was going to try reversing the front element or possibly doing some element substitution on, but I want to have some theory guiding my experimentation instead of just doing it monkey style.

OAPOli · Feb 20, 2025

About the Bronica. Due its peculiar mirror movement, it has generous clearance for back focus distance. If your Petzval lens has a small enough ID to fit in the helical, you can bypass the 102mm restriction. The helical mount (or tube for the S version) has a 57x1mm threaded section for an adapter.

brianssparetime · Feb 20, 2025

OAPOli said:
About the Bronica. Due its peculiar mirror movement, it has generous clearance for back focus distance. If your Petzval lens has a small enough ID to fit in the helical, you can bypass the 102mm restriction. The helical mount (or tube for the S version) has a 57x1mm threaded section for an adapter.

Thanks.

I'm familiar with the removable helicoid and the ability to sit lenses further back into the camera. I've measured the decreased flange distance from removing the helicoid, and I've found it to be about 85 (i.e. from the front of the helicoid, lenses can extend about 3cm backwards).

Keeping the helicoid mounted is handy for lenses that lack a focusing mechanism (e.g. projector lens or 35mm lens where I've stripped off the lens's existing helicoid), but I'm very open to modifying a body cap or using my bellows to handle a lens that protrudes back within allowance if it has its own focusing mechanism (as most petzvals do).

The S2a and EC/EC-TL also have the 57mm thread on the inside of the helicoid. I've been using adapters from RAFcamera.com to adapt that to M42, so I can use an additional M42 helicoid to adjust the flange distance and common adapters for sticking the folder leaf shutter lenses (which I mentioned above) on. I've also had some fun sticking regular M42 lenses on for macro shots (e.g. 1, 2, 3)

Nonetheless, I need to know the approximate BFD (and mount diameter if I'm recessing it) for a given FL petzval so I'm reasonably sure it will fit before I buy it.

reddesert · Feb 20, 2025

brianssparetime said:
Thanks for all the feedback here.

A little more context here....

I'm interested in sticking this lens on my Bronica S2, which has a flange distance of ~102mm (with a few mm for an adapter, I arrive at 105mm) and a 6x6 film plane.

I'm interested in Petzval lenses specifically for their defects. Ideally, I'd like aggressive swirl, strong astigmatism, barrel distortion, vignette, and field curvature; I'm willing to tolerate whatever other aberrations come along for the ride.

Yes, I could. However, the longer the focal length, the larger the image circle, and the more likely it is that the "fun" parts of the image are outside what my 6x6 captures. Also, ceteris paribus, I'd like a focal length that isn't super long relative to the format (we're already in the ~85-100 FFEFL range). In fact, I did take a chance on a Darlot lens at a great price from a listing that had basically no info on it. Turned out to be a 12" lens, which will be cool for another project, but is completely impractical for this one.

FWIW, I'm exploring a few other avenues for this as well.

I've already adapted a bunch of old folder lens assemblies (Kodak 616, Kodak Premo, Buster Brown 3a) that are generally about 120-135mm. These are fun, but they are generally too good for what I'm ideally looking for.

I'm currently experimenting with adapting early lenses meant for 35mm cameras in the 135-150mm range. I learned that a front aperture ring is key through failure with a Asunuma 150mm, and I have a partially disassembled Triotar 135mm f4 with front aperture ring that needs to be unseized. My thought here is that since these lenses were designed for 35mm film, I'm hoping the extra image circle I'll be capturing is more "wild" than the 35mm crop.

Finally, I've been considering projector lenses. But I have some of the same questions as re: Petzval - it's hard to figure out whether a 135mm or 150mm lens will have enough BFD to clear my mirror, and overshooting to something like 200mm is suboptimal.

I was going to post it in a separate thread later on, but any suggestions for modifying existing lenses to achieve my "so bad it's good" look would also be much appreciated.

Some ideas:

If you want exaggerated out of focus areas, "swirls" (which IMO are often uncorrected astigmatism) and so on, you typically have to use a fairly fast aperture. Which means you might not need the aperture control after all. One of the reasons the lenses out of an old folder are "too good" is that they're probably slow, like f/6.3 or slower. Many basic Brownie-type cameras used single-element meniscus lenses, yet delivered acceptable snapshot type results (off-axis sharper than you want) because they were working around f/8-11 and not enlarged.

For individual lenses or lens elements, you typically won't have any information on the optical makeup and optical design is quite exacting (even for an ancient design like a Petzval), and not easy to teach yourself.

One approach you could take is just to get a single element meniscus lens or an achromat, but make it fast, like f/3 or f/4. For example, go to Surplus Shed's website, achromats here: https://www.surplusshed.com/category/Achromats
and get a 125mm focal length, 35mm diam coated achromat (about f/3.6), mounted in a cell, for the princely sum of 8 US dollars. It should be relatively free of chromatic aberration, have a bit of spherical on-axis, and plenty of curvature of field and astigmatism off-axis.

You can also get a positive meniscus lens (use their Lens Finder) fl=114mm and diam=34mm for $4.50, mount it somehow, and have the world's only f/3.4 Bronica Brownie. Mount the concave side forward. Reinhold Schable sells even faster meniscus lenses like this: https://re-inventedphotoequip.com/reinventedphotoequip/Home.html
for MF, LF, ULF, and while I've never seen one, people seem to like them.

Finally, if you want to adapt a long-focus 35mm lens, there are a few rangefinder lenses where the front unit screws off the focusing tube. The one I know about is the older Leica 90/4 Elmar, but I think there are others. This would make your life much easier with mounting it.

brianssparetime · Feb 20, 2025

Thanks - I appreciate your thoughts here.

reddesert said:
If you want exaggerated out of focus areas, "swirls" (which IMO are often uncorrected astigmatism) and so on, you typically have to use a fairly fast aperture. Which means you might not need the aperture control after all. One of the reasons the lenses out of an old folder are "too good" is that they're probably slow, like f/6.3 or slower. Many basic Brownie-type cameras used single-element meniscus lenses, yet delivered acceptable snapshot type results (off-axis sharper than you want) because they were working around f/8-11 and not enlarged.

I agree. Specifically, I agree that there is a strong relationship between astigmatism and swirl (hence my listing astigmatism first and foremost in my list of desired attributes). And I agree those older lenses aren't fast enough to do that.

Speaking of Brownies, I like the look of hawkeyes with a reversed front element (or reversed lens perhaps? I don't have one to try it on). Same with the reversed front element of the helios 44 (examples).

But back on track, I think you're right I want a fast lens.

reddesert said:
For individual lenses or lens elements, you typically won't have any information on the optical makeup and optical design is quite exacting (even for an ancient design like a Petzval), and not easy to teach yourself.

Yeah. I've played with lens design spreadsheets a little bit and agree here too.

reddesert said:
One approach you could take is just to get a single element meniscus lens or an achromat, but make it fast, like f/3 or f/4. For example, go to Surplus Shed's website, achromats here: https://www.surplusshed.com/category/Achromats
and get a 125mm focal length, 35mm diam coated achromat (about f/3.6), mounted in a cell, for the princely sum of 8 US dollars. It should be relatively free of chromatic aberration, have a bit of spherical on-axis, and plenty of curvature of field and astigmatism off-axis.

So I alluded above to having ordered some lenses, by which I meant I'd ordered two 120mm FL and 120mm diameter biconvex lenses. I figured I'd just go straight to f1 and stop down as needed.

I've looked at surplusshed a little bit, but I wasn't sure if those achromats would be either fast enough or poorly adjusted enough to work. But I'm game to give it a try for that price! EDIT: that lens, and a few others, are now on their way to me. Excited to see how it looks. Thank you.

reddesert said:
You can also get a positive meniscus lens (use their Lens Finder) fl=114mm and diam=34mm for $4.50, mount it somehow, and have the world's only f/3.4 Bronica Brownie. Mount the concave side forward. Reinhold Schable sells even faster meniscus lenses like this: https://re-inventedphotoequip.com/reinventedphotoequip/Home.html
for MF, LF, ULF, and while I've never seen one, people seem to like them.

I did not know about the lensfinder. That's makes this much easier. I already have the world's first Bronica Buster Brown 2A (with a Martini aperture) shown here taking a self-portrait (of the lens, not me), so having the fastest brownie around sounds fun.

I hadn't run across Reinhold Schable though - that's awesome. Thank you.

I have, however, run across the Ivanichek Petzval. I haven't emailed him yet, but I likely will at some point to ask about the BFD of the lens without the helicoid.

reddesert said:
Finally, if you want to adapt a long-focus 35mm lens, there are a few rangefinder lenses where the front unit screws off the focusing tube. The one I know about is the older Leica 90/4 Elmar, but I think there are others. This would make your life much easier with mounting it.

Yes - I've been looking at the 135mm Hektor, which I believe also has a removeable lens head, and the 135mm Elmar, which I'm not sure does. Great suggestions. I'll likely pursue this at some point just for the hell of it, but I don't think these will satisfy my desire for a really weird distorted lens.

The projector Hektars of about 135mm though I think may have more potential.....

MattKing · Feb 21, 2025

brianssparetime said:
I hadn't run across Reinhold Schable though - that's awesome. Thank you.

He is a member here!
He even has a Classifieds listing!
https://www.photrio.com/forum/threads/fs-125mm-lens-for-the-creative-photographer.209604/

brianssparetime · Feb 21, 2025

MattKing said:
He is a member here!

Great to know - thank you!

Shortest focal length Petzval barrel lens with back focal distance >= 105mm?

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Shortest focal length Petzval barrel lens with back focal distance >= 105mm?

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