Caltar II-E 210 Lens & Depth of Field

[Brandon Draper]

I am starting to explore table top photography with a Calumet Cadet camera and a Caltar II-E 210 f6.8 lens. Which came with the camera. I am having problems with my depth of field not being very deep. The most I can get with my softbox and light is F22 then I have to open up 1.5 stops for my bellows extension. (ISO 50 transparency film). And I can't get the entire item I am photographing to be completely in focus. Which is just a 90mm LF Lens. I need at least a F64 to get the entire lens in focus. Without going to a higher ISO film. Is this just a characteristic of a compact lens? Which I assume this one is. Which kind of lens would be ideal for product style photography?

Thanks

[David Karp]

Hi,

Its not the compact lens, its the focal length.

A 210mm is a standard lens for tabletop photography. No need to change unless you feel you need a lens with a larger image circle than the 210mm Caltar II-E. The depth of field on a more expensive Caltar II-N or other lens will be the same as the lens you already have.

You need to work on learning how to swing and tilt your front lens standard. This changes the plane of focus, and helps to make up for the lack of depth of field. Remember, you would not expect a 210mm lens for 35mm photography to have a lot of depth of field. A 210mm lens for 4x5 photography has exactly the same depth of field characteristics as the lens for 35mm. The advantage of the 4x5 camera is its movements, including swings and tilts.

There is some good information on this at http://www.largeformatphotography.info/how-to-focus.html.

There is also some valuable information on selecting an f/stop at http://www.largeformatphotography.info/fstop.html. You can skip the details if you want and go right to the table at the end of the article.

Also, another good reference is Using the View Camera, by Jim Stone.

I hope this helps.

[Leonard Evens]

The general (approximate) formula for the total depth of field in the close-up range is

2Nc(1+M)/M^2

where N is the f-number, c is the chosen circle of confusion, and M is the magnification or scale of reproduction. Note that the formula is independent of focal length, although what is considered close-up isn't. That is usually taken to be within 10 times the focal length. With a 210 mm lens, the close-up range would be work out to about 2 meters, so it seems likely it would apply in your case.

A value of c = 0.1 mm is a common choice for the coc for 4 x 5. You don't say what the scale of reproduction is. Let's assume you want something like 1:2, so M would be 0.5. Then the DOF at f/64 ends up being about 76 mm, which should be enough for your lens. On the other hand at f/22, it would end up being about 26 mm which probably wouldn't be enough.

If you reduced the scale of reproduction to 1:5, so M =0.2, the total DOF at f/22 is 132 mm which is enough, but then the subject would be fairly small in the frame.

This is basic optics, and there doesn't seem to be any good way around it for large values of M except either increasing the intensity of illumination (for flash) or increasing the exposure time, which might preclude flash.

[Leonard Evens]

David,

I've never thought about this, and I don't have a lot of experience with close-up photography in different formats, so perhaps there is something I'm missing. But it seems to me that if you go from 4 x 5 to 35 mm, you have to use a smaller value for the coc and a smaller value of M in the same proportion. For example, suppose we take a factor of 4 by comparing 96 mm to 24 mm. Then instead of using c = 0.1 mm, we would use c = 0.025 mm and instead of using M = .5, we would use M = .0.125. That would produce dramatically different results for the answers because you are squaring M in the denominator.

What is wrong with my analysis?

[Dan Fromm]

Leonard, remember that the smaller the format, the less magnfication is required to fill the frame with the subject. Therefore, at the same relative aperture and desired circle of confusion, the more depth of field the smaller the format. The killer is that the smaller format requires more magnification to get the desired print size. So film resolution can limit the gains from shooting smaller and enlarging more.

Cheers,

Dan

[Dan Fromm]

Brandon, if use of movements to position the plane of best focus won't save you, you're cooked.

Sorry,

Dan, who just took some horrible shots of a tiny, tiny orchid bloom at f/4 and 20:1. What a silly idea that was!

[Eric Jones]

Since your shot is static you could stop down and trigger your flash twice therefore double exposing to arrive at the proper exposure. Just another option.

[Paul Moshay]

If you need more depth of field, just stop down to what you need. If it is one stop more than metered, just pop the flash once more, in a darkened room without the modeling lights of course. If you have to go down two stops, just pop the flash four times, if three stops, pop the flash eight times. You will have to make tests with the two and three stop pop shots because of the intermitantcy effects. But that's the way it works for me.

[Jim Galli]

What Eric said was the first thing in my mind. Stop down to what you need and do multiple pops to expose. That can multiply quickly into a lot of flashes. Why not put the 90 on the camera and make a picture of the 210?? Seriously, you might play with enlarger lenses you already have and get great results. You don't need a shutter for this kind of photography.

[Leonard Evens]

Dan,

I believe all your comments are subsumed in the formula. Again, total DOF in the closeup region is given closely by

2 Nc(1 + M)/M^2

where N is the focal length, c is the circle of confusion, and M is the magnification. If you reduce c by say a factor of 4, and also reduce M by a factor of 2, you end up multiplying the DOF by a factor a bit less than 4.

Jim,

In the closeup region, the DOF is close to being independent of focal length. The only difference is how the closeup region is defined. For a 90 mm lens, it would be defined as about 900 mm, or close to a meter. But in any case, it is the scale of reproduction that really counts. In closeup photography, one aims for a certain size image. Thus if, for 4 x 5, 1:2 would be right with a 210 mm lens, it would also be right for a 90 mm lens. You would have to put the subject much closer to the 90 mm lens for the same scale of reproduction, but that doesn't affect the calculation of DOF. Moreover, the calculation assumes the lens is a point, using the front nodal point to measure distance from. If you get too close, and the subject is fairly large, you could bump into the front element of the lens. Working distance issues like that make a longer lens more appropriate.