When doing a still life (DOF) question

mark · Oct 23, 2005

I have had this problem with each of my cameras so I know the problem is with me not them.

When doing a still life at a decent magnification I knwo the DOF will be reduced. Is there a rule of thumb out there that will get the greatest DOF.

What I have been using is this:

Focus on a part of the subject that is 1/3 of the way in and stop way down.

This worked great for everything behind but not for what is in front.

It is kind of getting frustrating.

jmdavis · Oct 23, 2005

Mark,

With LF, some tilt can help too. But it's not always easy to get enough DOF without stopping down and using LONG exposures. The clasic was (I think) 90 minutes for Weston's peppers. Maybe it was longer. But between f64, some tilt and careful planning, you can get it.

With MF you can try fast film, daylight and stopping to f32-45.

Mike Davis

mark · Oct 23, 2005

I use the tilts the issue really pops up when I am shooting straight down. It is not so bad when shooting at an angle but still there.

Andy K · Oct 23, 2005

If you are working in a controlled environment, ie you are set up with tripod etc. I would go with minimum aperture and a long exposure. I would also move back from the subject a little to bring the closer edge of the DOF to a point between the camera and subject. But that is from the point of view of a 35mm/mf shooter. The rules may be different for lf.

jp80874 · Oct 23, 2005

We probably need to have more details to help you, but we would like to help. For a start tell us about what equipment you are using and describe more specifically the scene. Are the lenses you are using designed for close up or macro work? How far is the lens from the still life and the focal point? How deep is the still life What f stop and speed are you using? For an experiment put an easily read ruler down the line of exposure with 1/3 on the camera side of the focal point. When you look at the negative or print the picture if the negative is too small, what inch or mm points are reasonably in focus? Where does it go out of focus? Perhaps it is a simple as moving the focal point to meet your expectations. With more detail we can probably give you more help.

John Powers

jmdavis · Oct 23, 2005

mark said:
I use the tilts the issue really pops up when I am shooting straight down. It is not so bad when shooting at an angle but still there.

You can tilt the front standard even when shooting straight down. Because the subject likely isn't completely flat, you may need the combination of small stops and tilts to make it work.

Mike Davis

mark · Oct 23, 2005

jmdavis said:
You can tilt the front standard even when shooting straight down. Because the subject likely isn't completely flat, you may need the combination of small stops and tilts to make it work.

Mike Davis

I tried this but it through another part of the image out of focus

Here is the info John asked for

Right now I am usinfing a Sinar F1 and a 210mm rodenstock. Not a macro lens. I am not working one to one but close though. Both are at f64 the smallest aperature

Straight down subject is a small pinon pine cone three inches high with pine nuts in it on a bed of pine nuts. The pine cone would be off center towards the upper right of the image.

Angled Subject is three pine cones at different stages of being open with the last fully open and spilling it's seeds onto a white back ground going from left to right with the nuts spilled toward the camera on the right side of the image

As for the measurement it is clearly going out of focus on the upper third of the cone on the straight down image

Meausrements on the other are dot possible as the wind blew my set up over after I made my two shots. I would have to set it up again.

It is not as bad on the angled image as I am able to use the DOF calculator on the Sinar but it is still not perfect. Should I not set the focus that deep? Should I shoot right at the top of the cone. The bed of pine nuts is only three inches away from the top of the cone.

MichaelBriggs · Oct 23, 2005

mark said:
Is there a rule of thumb out there that will get the greatest DOF.

What I have been using is this:

Focus on a part of the subject that is 1/3 of the way in and stop way down.

This common rule of thumb is exact for only one subject distance, and can be quite wrong for other subject distances. If you must work in subject distances and want to know the optimum distance to focus on, then there is no simple rule, you have to consult a depth of field table, or equations. (Or on small cameras look at the graphical lines on the lenses.)

But since this is a Large Format question, there is a simple rule that works very well. Instead of working in subject space, work in image space. Focus the rear standard on the farthest object you want in focus and note the focus position. Repeat for the nearest object. Refocus the standard to halfway between the two positions. This is a rule that is a good approximation for studio shots and for landscape distances. This is easiest if your camera has a ruler scale for the focus position. If it doesn't, probably you can attach one.

Depth of field will still be small for closeups, but at least this way you can start at the best focus position. If the depth of field isn't what you want, the goal of using tilts or swings is to reduce the focus spread.

Here are two articles on these topics: http://www.largeformatphotography.info/how-to-focus.html and http://www.largeformatphotography.info/fstop.html

MichaelBriggs · Oct 23, 2005

Mark, the Sinar DOF calculator uses the image-space method I described. I've never used one so I can't give detailed directions, but the proper procedure should arrive at the best focus position. You shouldn't be trying to guess depth into subject as the way to set your focus position. The Sinar calculator wheel should help you implement the procedure that I described. Maybe someone can point you to directions for using the Sinar DOF calculator.

mark · Oct 23, 2005

I have the instructions thanks. It is still awkward for me to use though.

jp80874 · Oct 23, 2005

Mark,

You said Straight down subject is a small pinon pine cone three inches high with pine nuts in it on a bed of pine nuts. The pine cone would be off center towards the upper right of the image.

Again I am not clear what distance the lens is from the subject. Are you enlarging or must you use what you get as in a color slide or positive? You mention 210mm Rodenstock. The Rodenstock APO Sironar S has a flange focal distance of 202mm or about 8. The 210mm Geronar has 195mm. I use a Rodenstock 180mm macro which has a ffd of 176mm. At distances that close I have a dof of about 3/8. Put in this perspective a three inch pine cone would be a bit of a giant challenge.

To obtain that dof in a b&w print I take advantage of the quality in a 4x5 T-Max 100 negative, move back from the subject until I have the dof wanted, and expand to fill the picture in the enlarger. This gives me the dof needed. It also allows me to use f45 instead of f64. This should lead to higher resolution.

Hope this helps.

John Powers

Smudger · Oct 23, 2005

It seems to me that if you are shooting straight down that the film may be sagging slightly in the holder.
This would bring at least part of the film slightly closer to the lens, resulting in the true focus being further away than the focused image would indicate..
If that is the case DOF calculations may not help.
It might be worth checking a holder with a scrap sheet to see if the film sags,even slightly. If so, you would need to incorporate a "fudge factor" when focusing.

jadphoto · Oct 24, 2005

Part of your problem could be that when shooting close-up the distribution of the depth of field is no longer 1/3rd in front and 2/3rds in back of the point of focus as when you are shooting at more normal distances such as scenics.

At 1:1 or so the distribution of DoF is 50/50. So you should be focused half way into the subject not 1/3rd as most have suggested.

Joe Dickerson

mark · Oct 24, 2005

Thanks for the help folks. This has been an education.

When doing a still life (DOF) question

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