Help With Bokeh

[Helen B]

" Again, focal length, subject distance and aperture control depth of field. Nothing else."

Fred,

Please explain the formula you are referring to that only uses focal length, subject distance and aperture for depth of field.

Here is the simplified one that I believe is correct enough for all but close-up subjects, ignoring pupil magnification:

T = 2 u^2 N C / f^2

Where T = depth of field,
u = distance from first nodal plane to subject
N = f-number
C = maximum acceptable diameter for the circle of confusion
f = focal length

Are you suggesting that the maximum acceptable diameter of the c-o-c has no effect on depth of field?

I have never seen a formula for depth of field that ignores the c-o-c.

Best,
Helen

 

[nossie]

Try putting the camera in portrait mode to see how far it'll go by itself. That's usually the icon of a persons head in profile.

 

[fmw]

" Again, focal length, subject distance and aperture control depth of field. Nothing else."

Fred,

Please explain the formula you are referring to that only uses focal length, subject distance and aperture for depth of field.

Here is the simplified one that I believe is correct enough for all but close-up subjects, ignoring pupil magnification:

T = 2 u^2 N C / f^2

Where T = depth of field,
u = distance from first nodal plane to subject
N = f-number
C = maximum acceptable diameter for the circle of confusion
f = focal length

Are you suggesting that the maximum acceptable diameter of the c-o-c has no effect on depth of field?

I have never seen a formula for depth of field that ignores the c-o-c.

Best,
Helen

Ah. Well perhaps the problem is that none of my lenses have a circle of confusion control ring on them.

 

[JerryPH]

Ah. Well perhaps the problem is that none of my lenses have a circle of confusion control ring on them.

LOL... sorry, in the right light (pardon the pun), that *was* humorous.

 

[Helen B]

Humorous - perhaps as a last resort. Inaccurate - definitely.

Ah. Well perhaps the problem is that none of my lenses have a circle of confusion control ring on them.

You do have control over the maximum acceptable diameter of the circle of confusion, and you probably use it even though you are blissfully ignorant of it. Do you make contact sheets? Do they look sharper than enlargements? Do you ever crop? Under what circumstances do you get less D-o-F when you crop, and when do you get more? Do you use more than one format? There's a brief, simple discussion on the different factors affecting D-o-F between formats here.

Best,
Helen

 

[fmw]

Helen, calm down. No need to cause the thread to become a circle of confusion. CoC is a measure of resolution. It is controlled by focusing the lens. It is used in the formula you included in your post as the determinant figure for focus. It is the part of the formula that defines the focus itself. Yes it is necessary to calculate depth of field by formula.

I've been talking about controlling depth of field photographically, not the formula for calculating it. Again, depth of field is controlled by subject distance, focal length and aperture. Your formula says the same thing. Take care.

 

[moliver]

Since you mentioned you're shooting sports I'll throw this in.

I've heard if you use the fastest possible shutter speed and follow your subject with your camera, and snap the shot as the camera moves, then you should end up with a blurry background and a frozen subject... I've never tried it, but it can't hurt to try I suppose.

 

[Helen B]

Helen, calm down. No need to cause the thread to become a circle of confusion.

Fred,

You will have to try a lot harder than that to make me lose my legendary cool, but it is nice to see someone else playing the game.

This discussion isn't going anywhere. You are resorting to personal comment and snide remarks, maybe to avoid a simple technical discussion. You see a disconnect between a formula and practice, I see something that adds to my ability to decide on the best way of achieving exactly what I or the client wants. You will continue to use your three factors (I know that you do your work very well), I'll continue to use five (we haven't mentioned pupil magnification, which comes in to the game for close-up work).

Best,
Helen

 

[fmw]

Fred,

You will have to try a lot harder than that to make me lose my legendary cool, but it is nice to see someone else playing the game.

This discussion isn't going anywhere. You are resorting to personal comment and snide remarks, maybe to avoid a simple technical discussion. You see a disconnect between a formula and practice, I see something that adds to my ability to decide on the best way of achieving exactly what I or the client wants. You will continue to use your three factors (I know that you do your work very well), I'll continue to use five (we haven't mentioned pupil magnification, which comes in to the game for close-up work).

Best,
Helen

I tried to have a little fun with you. You didn't like it. I apologize. I agree, this discussion is going nowhere. Take care.

 

[Helen B]

I tried to have a little fun with you. You didn't like it.

I'm not bothered by it at all. It is easy to see that you were having fun, but the nature of it is less obvious. The mildly tongue-in-cheek nature of a lot of the stuff I write gets misinterpreted as well. I have a lot of respect for your work, both technically and aesthetically, and for your very valuable contributions to this forum, so I have high expectations that you had better live up to. Or else.

Best wishes,
Helen