macro configuration for maximum DOF

[scott russell]

Hey,

So i've got myself interested in this macro project and now I can't stop thinking about it till i figure it out. For simplicity sake, the objects i'm photographing are 3D and are about half the size of a 4x5 frame. Filling the whole frame would be 2:1. My goal is to get a 4:1 ratio while maintaining a lot of DOF and have some working distance between the lens and the object. I know enlarger lenses of short focal length will be able to achieve a more magnified ratio, but wont it also give you an extremely narrow depth of field? My "view camera technique" book says that "perspective is often less attractive with 3d subjects when the camera to subject distance is small". Does that mean that the longer focal length you use will make a better image? If I combine two cambo cameras with 21" rails, adding a second tripod, i would be able to get more than 1000mm of extension. What would be the best size lens to use with that much extension. Fuji makes a nice 180mm F9 that might seem to fit. I know a 1:1 ratio requires twice the focal length of the lens, but do you just add 180mm for each increase in size? Would 900mm of extension give you a 4:1 magnification?

[Dan Fromm]

Scott, nothing personal but you're doomed. Doomed. There is no way to get much DoF at 2:1 on film, let alone 4:1.

A few obnoxious facts:

At the same magnification on the negative and same aperture set, DoF is the same for all focal length. Only extension and front node-to-subject distance vary with focal length.

Getting the same magnification on the negative with a long lens requires more extension than getting it with a short lens. The relevant magic formula is: lens rear node-to-film distance = (1 + m) * f where m is magnification and f is the lens focal length.

If the lens if mounted normally (front of lens towards subject), DoF is given by:

2*(CoC*aperture set *(1 + m/p))/m^2. You'd use this formula with, e.g., a Luminar.

If the lens is reversed (front of lens towards film), DoF is given by:

2*(CoC * (M + 1/p))/m^2

CoC is the desired circle of confusion, m is magnification on film, p is the lens pupillary magnification (diameter of entrance pupil/diameter of exit pupil). ^ is the "squared" operator. Most of the time people ignore p, but it matters in a big way for, e.g., retrofocus lenses.

The diffraction limit (can't get better resolution than that) is approximately 1500/effective aperture. Some use 1600.

Before you try to do the impossible and get very frustrated, buy a book. Two books, in fact.

Lefkowitz, Lester. 1979. The Manual of Close-Up Photography. Amphoto. Garden City, NY. 272 pp. ISBN 0-8174-2456-3 (hardbound) and 0-8174-2130-0 (softbound).

A thorough discussion of getting the magnification, lighting, and exposure. Especially good on working above 1:1. Extensive bibliography.

Gibson, H. Lou. Close-Up Photography and Photomacrography. 1970. Publication N-16. Eastman Kodak Co. Rochester, NY. 98+95+6 pp. The two sections were published separately as Kodak Publications N-12A and N-12B respectively. Republished in 1977 with changes and without the 6 page analytic supplement, which was published separately as Kodak Publication N-15. 1977 edition is ISBN 0-87985-206-2.

Gibson is very strong on lighting, exposure, and on what can and cannot be accomplished. His books, although relatively weak on getting the magnification with lenses made for modern SLR cameras, provide a very useful foundation for thinking about working at magnifications above 1:10 and especially above 1:1. Extensive bibliography.

Gibson gets very forceful about what can't be done, reading his book will curl your hair.

Good luck, have fun, lower your expectations, curb your enthusiasm,

Dan

p.s. I regularly shoot in the range 1:1 - 2:1 with my little 2x3 Graphics. It can be done, but requires very exacting technique.

[Ralph Barker]

Dan's advice is good. Expressed in a different way, what the focal length giveth (at first glance, shorter focal lengths would seem to give greater DoF), the CoC taketh away. That is to say, we're still stuck with the realities of the optical physics and the role of magnification in the process.

One aspect that is omitted from the formulas is that some LF lenses are optimized for close-up work, and will produce somewhat sharper images at macro distances. The formulas, however, still trump lens design.

[scott russell]

interesting. I think i'm going to end up buying both of those books once this amazon gift certificate i'm getting comes in the mail. If what you say is correct, then I guess it would be most practical to mess around with some dirt cheap enlarger lenses before i go and spend money on a modern lens optimized for macro. The problems with enlarger lenses though, would be figuring out how to get one on a lens board, and even possibly fitting a shutter. Being that typical enlarger lenses don't stop down past 22, wouldn't adding a shutter like a copal with a variable aperture that goes down to 45 or 64 fix that?

[David A. Goldfarb]

You don't need a shutter, really, because at the apertures you'll be using at those magnifications (I try to be around f:22), you'll either be using strobes and probably multiple pops or a long exposure, and you can just pull the darkslide and put it back at the end of the exposure, or if it's under 10 seconds use a black card in front of the lens.

Exposure factor at 2:1 is 3-1/3 stops.

[Dan Fromm]

Scott, there are many ways to bodge a lens onto the front of a shutter. One can also have an adapter made.

And then there's the really easy way, and it involves an ok and usually inexpensive lens. Look for a 105/4.5 Schneider Comparon. Not Componar, Comparon. There are lenses that are better in the range 1:4 - 4:1 but the Comparon isn't bad. And its cells are direct fits in a #0 shutter. One of the nice things about the #0 is that it is symmetrical, so reversing a lens in one requires simply swapping the cells front to rear and rear to front. I got one in #0 from a Sirchie ID camera.

I suggest the Comparon because per Schneider it is better in the range of magnification you want than the Componon or Componon-S. I don't use mine much, as I said there are better lenses. But the humble enlarging Xenar is good enough.

David, opinions differ and so do goals, but for my purposes f/22 is too small at 1:1 for 35 mm, let alone higher magnifications. On larger formats, with less enlargement needed, the limit is lower.

Scott, the basis of disagreements over how small an aperture is too small is intended enlargement. There's a rule of thumb to the effect that a print has to resolve at least 8 lp/mm to pass close scrutiny. If you buy that, and not everyone does, then an "N" times enlargement requires at least 8N lp/mm in the negative. The smallest effective aperture that can possibly give that resolution is 1500/8N.

I shoot 2x3, print to 8x10, so enlarge roughly 4x. At 1:1, the limiting effective aperture is around f/45. This corresponds to aperture set to f/22. At 2:1, the limiting effective aperture set is f/16. And so on.

I agree with David that using flash illumination for closeup work makes life much easier. I don't agree with him on which flashes/geometry to use. Perhaps because I started shooting closeup with 35 mm and don't have studio flashes, I use tiny little flashes, often with ND gels taped on them, mounted fairly close to the lens. In truth, there are many ways to get much the same shot.

Do the arithmetic for yourself. Nothing personal, Scott, but you're toast.

Cheers,

Dan

[scott russell]

well the actual goal is macro photography, getting a lot of DOF with it was just the curious part that kept coming up in stuff i read. The main idea of my project was wanting to shoot small-ish things that bear a resemblance to things that are much larger in real life. The two things i that seemed to be important were to have a good amount of DOF and figuring out a perspective that would make the objects not just look like something under a microscope.

Dan,

The comparon was the exact lens i was looking at to use for this. As far as a shutter goes, i don't really see needing the actual shutter part of it, but was hoping to use the aperture diaphragm so i could stop the comparon down to 64 instead of its max f32 on the lens, but since your saying 22 or 32 might be the limit it might be unnecessary.

[Dan Fromm]

Scott, with flash the shutter is very useful. With available darkness, sometimes essential.

By the way, please understand that I'm toast too.

Also understand that in general, and that includes the very fine Nikon, Rodenstock, and Schneider macro lenses made specifically for LF closeup work, lenses made by the major companies' photographic objectives divisions aren't the best for working above 1:1. Zeiss West's microscope division made Luminars, Zeiss East's microscope division made Mikrotars, Reichert made Neupolars (100/6.3 great, 50/3.5 so-so) that are all better in their design ranges than the macro lenses. So are Leica's Photars, the Olympus and Canon RMS-mount lenses (exceptions, not, AFAIK, made by the microscope divisions, in fact Canon doesn't make 'em and Leica's is a separate company).

The biggest sleeper I've yet found among enlarging lenses is the 4"/5.6 Wollensak Enlarging Pro Raptar. With the emulsions I use, its as good as a known good (careful, not all used lenses are as good as they were when they left the factory) 100/6.3 Luminar and nearly as good as my 100/6.3 Neupolar from 1:4 to 4:1 mounted normally. It must be pretty nearly symmetrical.

Mind you, the Comparon isn't shabby. I was so taken with my 105/4.5 that I got a 150/5.6 when the getting was really good. I find the Neupolar, for which I have an adapter to #1, too hard to use much of the time; the diaphragm ring is at the front with the markings facing forwards. And for a long time I wasn't willing to have an adapter made for front-mounting the Enl. Pro Rapter. I should have done that in the beginning, would have saved time and money.

Cheers,

Dan

[Maris Rusis]

There are at least two ways to get essentially unlimited depth of field at any repro ratio no matter how high. Neither is easy or cheap but I've done both in a laboratory context.

Scanning electron microscopy uses a fine electron beam to scan the surface of an object and during the scanning process secondary electrons are produced. These electrons are collected and the varying current is used to modulate a monitor picture. The final picture is achieved by photographing the monitor. This image is made up of a combination of topographical contrast and atomic number contrast. Resolution and depth of field are amazing. Magnifications from 3x and up are usual but different models of SEM may have different capabilities. A good SEM may cost $200 000 but buying time on one may be a way forward.

Confocal photography is another way. I used four slit lamp projectors with intersecting beams to form a very thin light plane. The camera is focussed on this plane in an otherwise dark room. The subject is supported on stepper motor driven table jack that advances the subject through the light plane. Since the only part of the subject that is visible to the camera is in the light plane/focal plane ordinary depth of field limitations don't apply. The final image is the accumulation of the successive optical sections that register on the film. Down side problems include perspectiveless rendition, hollows that never get light never register, dust in the slits come out as lines on the image, calibrating everything is tedious, and a well equipped optics research lab environment is hard to get into.

In ordinary lens based imaging the laws of optics have not been repealed and the nasty trade-offs between resolution, contrast, and depth of field cannot be circumvented.

[Emmanuel BIGLER]

I may add to the previous discussion : if you accept to post- process your images digitally, there is a commercial software named Helicon Focus that allows you to cheat with the physical limitations of optical DOF.

The idea is to record several images at different focus and let the software blend those various frames to extract the best focus of all.