Flat Field Focus on LF Lenses?

[Angstrom]

So I recently bought a laser rangefinder for measuring distance, in order to perfectly get the hyperfocal distance and other uses. (And to use in conjunction with focus calculator apps like Lumariver DoF).

However, I'm not sure if I should use the rangefinder in Line-of-sight mode (the straight line distance) or the 'true range' mode that tells you just the horizontal distance (using an angle sensor and basic trigonometry).

I know modern lenses are designed to be 'flat field' so the focal plane is actually a flat plane parallel to the lens plane. But naturally, an uncorrected lens will actually create a focal field that is curved like a sphere. But I'm not sure if this is the case for older lenses like those for large format.

Does anyone know if most large format lenses are corrected to have a flat focal plane or not?

This would only make a difference if photographing things that are well above or below the camera when it's being pointed horizontally, which could be the case if photographing a building, or from on top of a hill.

Specifically, the lenses I have are:

Nikon 90mm f/4.5 NIKKOR-SW (4x5)
Schneider 240mm f/5.6 Apo-Symmar (8x10)


Update: After doing some additional reading, it seems like most lenses should be corrected for field curvature. There are lenses that are specially designed to be extremely flat, called 'flat field' lenses but I don't think they really exist for large format photography.

This wiki page describes what I'm talking about: https://en.wikipedia.org/wiki/Petzval_field_curvature

A notable thing from there is that apparently stopping down the lense will reduce curvature, so if you're stopping down to like f/32 or f/64 that should help. Also it says that shorter focal lengths have a lot more curavture. Though I'm not sure if that's in absolute terms, or 35mm equivalent focal lengths. If not, it would seem the longer focal lengths used in LF would make it not as much of a problem.

Finally the best evidence I found is from Nikon's old brochure of large format lenses: https://galerie-photo.com/manuels/nikkor-lenses-for-large-format%20cameras.pdf

On page 3 where it talks about Nikkor-W lenses, it says "Distortion, curvature of field and chromatic aberration are corrected to the high standards you'd expect from nikon". The way I read that, is that means some degree of field curvature is designed into basically all their lenses, but it's pointed out as being particularly good in that range of lenses.

Considering most large format lenses often have just as many lens groups as other more modern lenses, there surely must be field curvature correction in there.

[Havoc]

Roger Ciala gave some method of determining it yourself. Must be somewhere on the lensrentals blog I think.

I have no clue what you are going on about the line of sight and true range distance. An optical rangefinder working on the principle of matching 2 images with a given baseline will always work with trigonometry and it will always give you the distance when viewing along the plane formed by the straight line through baseline and along the main optical axis.

[Dan Fromm]

Does anyone know if most large format lenses are corrected to have a flat focal plane or not?

Um, er, ah, lens designers aim for flat fields. Some lenses are better than others. For practical purposes, all of the lenses you mentioned have flat enough fields.

For flatter fields, use a good grade of process lens.

[ic-racer]

So I recently bought a rangefinder in order to perfectly get the hyperfocal distance a]

You realize that you will also need a ruler to perfectly position your eye from the print for it to be that exact.

I focus at infinity because the prints look better to me that way. Otherwise you can read about it here too:

http://www.trenholm.org/hmmerk/TIAOOFe.pdf

[Angstrom]

An optical rangefinder working on the principle of matching 2 images with a given baseline will always work with trigonometry and it will always give you the distance when viewing along the plane formed by the straight line through baseline and along the main optical axis.

I should have been more clear, I don't mean a rangefinder camera, I mean a laser rangefinder, like that used in shooting.



You realize that you will also need a ruler to perfectly position your eye from the print for it to be that exact.

I focus at infinity because the prints look better to me that way. Otherwise you can read about it here too:

http://www.trenholm.org/hmmerk/TIAOOFe.pdf

Hm that looks like a book I'll have to definitely read through. I guess I don't mean 'perfect' hyperfocal, but if the calculator said something like I'd need to focus at say 18 meters, I could do it much more easily with a laser rangefinder than eyeballing it (and I'd probably focus a bit past it for safety).

Basically I'd plan to use it when I want to focus "not quite" at infinite and at least get a bit extra closer in focus than normally.

[Luis-F-S]

Update: After doing some additional reading, it seems like most lenses should be corrected for field curvature. There are lenses that are specially designed to be extremely flat, called 'flat field' lenses but I don't think they really exist for large format photography.

You can get enlarging lenses mounted in shutters which are quite flat field. Most process lenses also fall into this category. Also, too much reading will only confuse you.

L

[Bob Salomon]

You can get enlarging lenses mounted in shutters which are quite flat field. Most process lenses also fall into this category. Also, too much reading will only confuse you.

L
You might have to reverse mount enlarging lenses for best results as a taking lens.

[Dan Fromm]

You might have to reverse mount enlarging lenses for best results as a taking lens.

Wrong. Enlarging lenses are optimized for big print in front of the lens, small negative behind the lens. Taking lenses are optimized for big subject in front of the lens, small negative behind the lens.

Big front, small behind in both situations.

[Drew Wiley]

Not necessarily if you classify duplicating lenses among enlarging lenses, since they are potentially mounted on enlargers, and tend to be tweaks of similarly named series, for example, Apo Rodagon D (duplicating) versus Apo Rodagon N. But that's the exception rather than the rule. And there are symmetrical process lenses which basically do it all quite well, regardless of 1:1 clear to out infinity, potentially usable on either an enlarger or copy camera, or as a taking lens on a view camera. And there are macro and close up optimized view camera lenses. Both G Clarons and Fujinon A's are close-corrected plasmats also excellent at infinity.

Unrelated : In today's technology, a pro laser distance meter will be more accurate than an optical rangefinder. Just don't buy a toy one at Cheapo Depot. The good ones can be found at survey equip suppliers. They can be small enough to fit in a shirt pocket, no bigger than a light meter.

[Dan Fromm]

Yeah, yeah, yeah, but what sensible person would use an Apo Rodagon D as a general purpose taking lens? Now that I've posted this, I expect that a few creatures will come out of the woodwork to announce that their Apo Rodagon Ds are the best general purpose taking lenses they've ever used.

[Richard Wasserman]

Yeah, yeah, yeah, but what sensible person would use an Apo Rodagon D as a general purpose taking lens? Now that I've posted this, I expect that a few creatures will come out of the woodwork to announce that their Apo Rodagon Ds are the best general purpose taking lenses they've ever used.

Not quite. I have a 150mm Componon in a Compur shutter that I bought because it was cheap and looked like it had never been used. The lens works well at close distances, but is weaker at infinity where the Plasmats do better.

[Drew Bedo]

Just spit-balling on this but:

Pick a sunny day. Go somewhere where there is a flat lawn.. .a golf course, soccar field or similar. Set up you camera and lens and focus at various distances wide open. Maybe you will be able to see the thin DOF in the grass by looking on the Ground Glass. Perhaps a football field with straight lines will help. You might have to expose a few sheets of film to see if the zone of focus is curved or flat.

Am I way off on this or will it work?

[Drew Bedo]

Yeah, yeah, yeah, but what sensible person would use an Apo Rodagon D as a general purpose taking lens? Now that I've posted this, I expect that a few creatures will come out of the woodwork to announce that their Apo Rodagon Ds are the best general purpose taking lenses they've ever used.

You are probably right: Other lenses may very well be more suitable for general photography.

I may be overly defensive, but I'd point out that when I broke into LF photography, it was on a shoe-string . . .a frayed one at that. At that point in my life, the best general photography lens was the uncoated 135mm something in a dial-set Compure shutter marked in German . . . .from the 1930s I think. It was the best lens for me because it had come on the Pre-Anniversary Speed Graphic beater I'd been able to snap up at the Houston Camera Show for what I had in my pocket that Saturday.

The best lens to use for a shot is the lens you have. If you have more than one lens . . .great . . . figure out which one is better for the shot you have in mind.

Now, there is a guy I know who has two stand-up roll-around Snap-On tool chests that hold much of his small camera gear. There are drawers and drawers of lenses that if sold off could probably pay for my grandson's first year of non-Ivy League college. He can pick and choose the "best" lens for about shot.

[Alan Klein]

Just spit-balling on this but:

Pick a sunny day. Go somewhere where there is a flat lawn.. .a golf course, soccar field or similar. Set up you camera and lens and focus at various distances wide open. Maybe you will be able to see the thin DOF in the grass by looking on the Ground Glass. Perhaps a football field with straight lines will help. You might have to expose a few sheets of film to see if the zone of focus is curved or flat.

Am I way off on this or will it work?

Sounds great. PLus the lines with have the yards marked on the ground for reference.

On a separate issue, I'm thinking about wide-angle lenses like the 90mm. Ordinarily, you want a center filter to account for the fall-off towards the edges. Does that falloff have any effect on the OP's project?

[Drew Wiley]

Dan - I actually knew someone like that. Jewelry maker by trade, miniaturist photographer as hobbyist. Prints were displayed with a gooseneck magnifying glass in front of them. I sometimes do macro shots of natural subject, but rely on versatile lenses not only specially close corrected, but good clear out to infinity too, like G-Clarons and Fuji A's. Those can be hypothetically used on enlargers too (I've tested em), but aren't quite as well corrected as real deal apo process lenses for critical applications.

[Dugan]

Big front, small behind .

I'm ok with that. :)

[LabRat]

Tape a page of newsprint to a wall, focus camera to it full frame, and examine image on GG and neg with good magnification to see how even focus is...

Steve K

[Greg]

Years ago was involved in a long term project for a Historical house that was turned into a walk through Museum. Project was to shoot 4x5 Chromes of many original documents. Chromes were archivally stored, but before that they were scanned. From the digital files. 1:1 double sided prints made on thin archival paper. Ragged edges and holes in the paper very carefully cut with a Xacto knife. Then the paper was "beat up" on a stiff rug. The resulting prints could be easily mistaken for the original documents. They were left on desks and tables in the Museum. If they were stolen the Museum was only out a few bucks, and the perpetrator would have been in for a rude surprise. Camera used was a 4x5 Sinar Norma. After testing out several lenses, we used a 210mm Repro-Claron (not a G) at f/16 or f/22 I seem to remember. Flat field focus was exceptional. Had to leave my photo equipment in a separate new modern "workshop" building on the grounds for several weeks. At first I was skeptical of doing that, but then I was shown their elaborate alarm system.