Help!!! no DOF at all????

[Gary Tarbert]

I have recently toyed with 8x10 , i am aware that dof is reduced at the same aperture
the bigger the format, but my results have very shallow DOF even at f27/f32.
There only seems to be 1 plane of focus!! , I have exsperience with 5x4 so it's not as if i have never used LF.
I have discussed this with dealer who sold me the camera and he suggested it could be a fault with the lens, which is a 240 symner s and offered to loan me a lens to see if this is the problem ,any thoughts or is it just my technique.cheers Gary

[Nick_3536]

A lens is a lens is a lens. A 240mm doesn't know what's behind it. What changes with format is the amount of enlargement you're likely to do. Plus you'll use longer lenses to achieve the same thing. If you like a 240 on 4x5 you might use a 450mm on 8x10. The 450mm would have less DOF then the 240mm did.

http://www.schneideroptics.com/info/depth_of_field_tables/index.htm

[Robert A. Zeichner]

Actually, there is only one plane ever in perfect focus. Depth of Field is what enables us to achieve an acceptable condition of sharpness on either side of that plane. How much DOF we have to work with is a function of aperture and magnification (magnifiction being a product of focal length and camera to subject distance). A 240mm lens should provide about the same DOF at say 50' and f22 as a 480mm lens would at 100' and f22. At the greater distance, there is less image magnification (the field of view would appear the same).

As to why you sense there is so much less DOF, I would guess that with 4x5 you were used to a focal length of maybe 150mm. If you were to put that focal length on the 8x10, you would have the same DOF characteristics, albeit with a much wider view of the world. You will need to use smaller apertures with a 240mm to achieve similar results.

[Walter Calahan]

Gary, were you focused on some at infinity or 5 feet away?

Read Nick and Robert, they are on the money.

Focusing on a subject at 5 to 10 feet away, using my Nikkor 240mm stopped down to, say, f/22, I don't have a lot of apparent depth of field either. My 240 is my favorite lens on 8x10 for full length portraits. You can see some results here: http://www.walterpcalahan.com/Cheers/Carroll%20County.html

Welcome to 8x10. You'll get use to it. 10-8 is a much more exacting way of seeing in my humble opinion.

[Frank Petronio]

Think of it as an advantage, not a problem!

If you want long DOF just stick to long horizon, focus at infinity and tilt until the foreground comes into focus... boring shots.

[Helen Bach]

If you produce two prints of the same size, same perspective and same final magnification (or same angle of view), one from 4x5 and one from 8x10, each shot at the same f-stop, the 4x5 will have greater depth of field.

For distant scenes the depth of field can be approximated to 2 x u^2 x N X C / f^2

where u is the distance from the lens (front node) to the object, N is the aperture, C is the diameter of the acceptable circle of confusion and f is the focal length.

If you hold u (same perspective) and N (same f-stop) the same, the depth of field varies with C/f^2. For the case above f for 4x5 needs to be half that of f for 8x10 (same angle of view), so f^2 for 8x10 is four times that for 4x5. The 4x5 needs to be magnified two times more than the 8x10 (same print size), so C needs to be half that for 8x10. Therefore the overall effect is for the depth of field for 8x10 to be half that of 4x5 under the conditions described.

Best,
Helen

[Jim Jones]

There is one way of comparing DOF between different formats that is so simple that even I can understand it. When prints from different formats are enlarged so the subject is the same size, the apparent DOF is determined only by the linear diameter of the entrance pupil. Print viewing distance affects our perception of DOF. In the dark ages before electronic calculators it took me quite a while of wrestling with pencil, paper, and basic lens formulae to learn this. It was effort well worth while.

[Brian Ellis]

Depth of field is a function of the size of the circles of confusion in front of and behind the plane of focus (which is represented by points rather than circles). The size of the circles of confusion (and hence depth of field) is affected by three things and three things only - aperture, focal length of lens, and distance from subject. Once a print is made all sorts of variables come into play that affect how "sharp" the photograph appears to be - degree of enlargement, viewing distance from the print, lighting conditions, visual acuity, etc. etc. Those are the variables that you can control to some extent after the negative is made that affect "acceptable sharpness" but the outer limits so to speak of "acceptable sharpness" are established by the negative and the size of the circles of confusion.

If all the variables affecting acceptable sharpness in the print remain the same (degree of enlargment, viewing distance, etc.) depth of field doubles as the f stop number doubles, depth of field quadruples as the distance from the subject is doubled, and cutting the focal length in half quadruples depth of field. I haven't done the math but I believe (or hope) that if you apply the formula Helen has provided those are the results you'll obtain. If they aren't then blame Ansel Adams, I learned this from one of his books.

A 240mm lens is a long focal length lens. If you were using it a short distance, e.g. five feet, from the subject then those two factors would tend to promote a shallow depth of field and to offset them you'd need to stop down well below f22.

[Gary Tarbert]

Thank you all for your help:) , I think the problem may be where i am focusing ,i only have about a metre of acceptable sharpness!! @ f27 ,this lens only stops down to f45
so there is only 1.5 stops to play with, cheers Gary

[Gary Tarbert]

:o Well the penny has dropped the problem is with the operator (but we knew that all along:) )Just did a dry run & had sharp focus from 2mtrs to infinity @f32.
The mistake i made is thinking this is just a bigger 5x4 & did some shots in very
subdued lighting at a location i had shot before on 5x4, i should have done some dry run practices first & when i first used it in the field gone for brighter conditions until i familiarised myself with the camera lesson learnt now for some more practice & pretty soon some good photographs.cheers Gary