Decreasing Minimum Focus Distance and DoF

[Project7]

I have a quandary that I was hoping I might get some help on. I’m planning a series of portrait shots, and I’d like them to be tightly cropped head shots with very narrow depth of field. I have two Hasselblad lenses to work with, an 80mm and a 250mm. The problem with the 80mm is that I have to get right up in the subject’s face and I still can’t get as tight as I’d like. The 250mm allows me to place a little more distance between the camera and the subject, but I’m still not getting a tight as I’d like, nor is the depth of field as dramatic as I’d like to see. The minimum focus distance is right around 9 feet. Ideally I’d like to be able to get a little tighter on the subject and end up with a depth of field that provides a noticeable loss of focus between the eyes and the back of the head. Is this something that can be achieved with a Proxar or an extension tube perhaps? Is there another method?

For those LensWork readers out there, the current May-June issue features a portfolio by Hiroshi Watanabe. His shot that is featured on the cover approximates what I’m talking about. The rapid loss of focus from the subject’s shoulder to her neck is a good example of what I’d like to achieve.

Any thoughts would be most appreciated. Thanks!

 

[David A. Goldfarb]

I'd use an extension tube in that situation.

 

[HerrBremerhaven]

Definitely an extension tube, on either lens you own. You can set it for infinity focus, then walk towards your subject (or move your tripod), until the parts you want are in focus. With an extension tube, and infinity focus, anything beyond the in-focus distance will be very out of focus.

I have mostly used this trick on a 180mm f2.8 on a Nikon body with a very short extension tube. The look is quite unique.

Ciao!

Gordon Moat
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[Project7]

Any thoughts on an appropriate length for the extension tube if I use the 250mm lens?

 

[Roger Hicks]

Or a weak Proxar.

Cheers,

Roger

 

[Helen B]

There's a slight catch to using close-up lenses (dioptres/diopters). The focal length of the prime+diopter is shorter than that of the prime alone, so you end up closer to the subject than you would for the same framing with an extension tube. I put some numbers to it (there was a url link here which no longer exists).

Best,
Helen

 

[Roger Hicks]

Dear Helen,

True, but not a problem with the 250 (or even 150) in my experience. Nevertheless, (as always) a useful reminder.

Cheers,

Roger

 

[Chan Tran]

I only wish that I have your problem. I always feel that I don't have enough depth of field.

 

[David A. Goldfarb]

For tight portraits with a 250mm lens on 6x6, you probably want a tube on the order of 15-20mm.

 

[Sirius Glass]

A few months ago I posted websites and information about DOF and image size. Please search for them and follow the links.

In summary, for a given image size, f/opening, and blur circle, the DOF will be the same regardless of the focal length. This is a theoretical limit that cannot be improved on. The DOF will be the same for a 40mm, 50mm, 60mm, 80mm, ... 250mm for the object image of the same size. Only the prespective will change. Therefore, while the close up lenses and extension tubes will allow you to get a closer cropping of the image, the DOF will be the same.

What can you do about this?
Aren't you glad you asked?
1) Change the laws of optics
2) Use faster film at the expense of granularity, or
3) Increase the illumination

#1 is highly unlikely. #2 is a possibility. #3 also a possibility. Did you ever wonder why movie studios use such bring lights?

I recommend that regardless of the lens/close up lens/extension tubes you use, that you increase the intensity of the lighting. Of course #2 would still be an option, but I think that you will find that #1 is probably not worth your time.

Steve

 

[Project7]

Thank you all for your input. This has been very helpful!

 

[John Koehrer]

I recommend that regardless of the lens/close up lens/extension tubes you use, that you increase the intensity of the lighting. Of course #2 would still be an option, but I think that you will find that #1 is probably not worth your time.

Steve

He's attempting to decrease the DOF not increase it.

 

[Sirius Glass]

He's attempting to decrease the DOF not increase it.

Ok, slower film and reduce the light.

Steve

 

[Sirius Glass]

He's attempting to decrease the DOF not increase it.

Ok, slower film and reduce the light [ND filters].

Steve

 

[eddie gunks]

steve,
i thought that DOF comes from focal length and is also dependent on how close you focus. the DOF becomes smaller the closer you focus, at a given F stop. so if i am correct, if you use and extension tube and focus closer your DOF should become smaller. isn't this correct?

eddie

A few months ago I posted websites and information about DOF and image size. Please search for them and follow the links.

In summary, for a given image size, f/opening, and blur circle, the DOF will be the same regardless of the focal length. This is a theoretical limit that cannot be improved on. The DOF will be the same for a 40mm, 50mm, 60mm, 80mm, ... 250mm for the object image of the same size. Only the prespective will change. Therefore, while the close up lenses and extension tubes will allow you to get a closer cropping of the image, the DOF will be the same.

What can you do about this?
Aren't you glad you asked?
1) Change the laws of optics
2) Use faster film at the expense of granularity, or
3) Increase the illumination

#1 is highly unlikely. #2 is a possibility. #3 also a possibility. Did you ever wonder why movie studios use such bring lights?

I recommend that regardless of the lens/close up lens/extension tubes you use, that you increase the intensity of the lighting. Of course #2 would still be an option, but I think that you will find that #1 is probably not worth your time.

Steve

 

[Sirius Glass]

Eddie,

When you are dealing with comparing DOF of different lenses on the same camera body for a constant image size on the focal plane it is focal length independent.

When I used extension tubes, the DOF did decrease, but that was in part do to increasing the image size on the focal plane.

The results that I stated in the original post are based on the same size image as the final result for each lens. If you increase the image size the DOF will decrease.

Steve

 

[eddie gunks]

thanks steve,

i missed the "same size" from your post. thanks for clearing that up. i had not thought of the increased image size.

i am not understanding what you mean by "constant image size on the focal plane it is focal length independent." i am not sure about the focal plane part of it.

cheers

eddie

 

[Sirius Glass]

thanks steve,

i missed the "same size" from your post. thanks for clearing that up. i had not thought of the increased image size.

i am not understanding what you mean by "constant image size on the focal plane it is focal length independent." i am not sure about the focal plane part of it.

cheers

eddie

Eddie,

Please check out the websites as they were well written and clear. Basically, if you are taking a photograph of a flower and you want the flower covered from the outside on the left to the outside on the right and similarly top and bottom, and you set up each lens to frame exactly the same way, then you have a constant image size. Then every lens shows the same depth of field.

After I graduated and brought a series of lenses for my camera [long since passed to a better world] I would set up a photo of a flower, a portrait, or even a detail of some other object(s) and I wanted a better DOF, I would progressively go to wider and wider angle lenses. Then I would try my zoom telephoto at several different focal lengths. Now matter what I did, the DOF would not improve!

For years, this bothered me. No one could explain why and very few had noticed it. When I went to work at Kodak my boss ordered a large assortment of optical textbooks and sent me to optics classes. Every night after a 10 to 12 hour day I would study optics. Once or twice a week I would come in with an optics question [Why there is recipocity failure at very shoot shutter speeds?]. My boss always knew who to send me to get a complete and clear answer.

This particular question was posed and I was told put the depth of field question on the white board from Smith's book. Put such and such equation about image size on the focal plane under it. Solve for ..., substitute ..., group terms ... The next to the last line had focal length in every term and was divided out. The final equation did not have focal length in the depth of field equation. I wish that I had kept a copy of the derivation. Maybe PE can show us.

Steve

 

[kunihiko]

Hi, Project7

What you shold look at first is this PDF from Hasselblad.
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