Shallow depth of field on 5×4

Today I was looking for a lens to put on my MPP 5×4 to shoot a still life in the studio, and I picked out a 150mm f2.8 lens which originally came from a photocopier. The reason I know it’s origins is because about 15 years ago, a slightly eccentric neighbour was breaking up an old photocopier outside my house, so I asked him if he would give me a lens if he found one inside. I got it and I’ve had it sitting in a box of odd lenses and unusual bits of glass since then. Putting it on the camera, I really liked the shallow focus and beautiful soft background, but with a fixed aperture of 2.8, I had to find some way to control the exposure. I decided that some very slow X-Ray film and a diffuser over my tungsten light would give me a manageable exposure which I could time in seconds. I cut some strips of X-Ray film and put them in a dark slide, then did a couple of test shots, one at the exposure I expected and one with more exposure. The second one gave me the kind of negative I was after, so I cut a piece of film to the full 5×4 size and exposed it. I took it into the darkroom and processed it in a tray of paper developer for a minute and a half, gave it a quick stop and fix, then washed it. The negative looked much softer in the background than it looked on the focusing screen (this is something I’ve noticed a lot) and I thought it would make a nice print. Then I remembered that somewhere in my studio I had a 150mm f2.8 projector lens which gave really nice out of focus softness, probably better than this one I’d just shot, so I thought I’d expose a second shot through it and compare them.

I had a faint idea that I’d read somewhere that two lenses with the same focal length and aperture should produce the same depth of field, so I was interested to see if it was so. After shooting and processing the second sheet of film through the projector lens, I could see immediately that they were quite different. The projector lens had a much shallower focus and was far softer in the out of focus areas, so I must have misremembered the thing about comparable focal lengths.
Anyway, I present the two images here for comparison.

Screen Shot 2015-01-14 at 18.42.54 Screen Shot 2015-01-14 at 18.42.17

Screen Shot 2015-01-14 at 18.42.02  Screen Shot 2015-01-14 at 18.41.45

2 Comments

  1. Keith

Posted 21/11/2014 at 7:22 am

This makes me want to get my old MPP Mk VIII out of the box and take some still-life.
I only have a 150mm Xenar lens though.

  1. Thomas Binsfeld

Posted 27/11/2014 at 5:38 pm

Could you give some advice how to attach the lens to the camera and e.g. which lens to which camera?
Kind regards,
Thomas

2 thoughts on “Shallow depth of field on 5×4

  1. Paul.

    If a lens is f/2.8, it will always give the same depth of field as another lens at f/2.8. However, some manufacturers are a little creative when they quote the maximum aperture. I have one lens that claims to be f/7.7, but if the iris is removed and measured, the actual aperture is aproximately f/9.

    Perhaps what you have is one manufacturer quoting the theoretical aperture and the other giving the actual.

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    Reply
    1. andrewsandersonphoto Post author

      That was my understanding too Paul, but the difference was more extreme than a slight error of labelling would account for. Also, the negatives were almost identical, and a different ‘real’ aperture would have give a negative of different density.

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      Reply

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