f stops and printing

[Gary Holliday]

I was talking to a printer a few years ago who stated that when she printed nudes for example; the model's back could have a hard or soft edge depending on which f stop she used on the enlarger lens.

I didn't think that f stops could alter an image.

Is there any truth in this?

Thanks

 

[w35773]

Sure, similar to a camera lens, if you open it up all the way, you get some sloppiness. This depends a lot on the lens and the light source, too.

 

[Gary Holliday]

Define sloppiness? unsharpness?? But surely a negative is flat so there is no depth of field.

 

[smieglitz]

Lenses tend to be sharpest about two f/stops closed down from wide open (e.g., f/5.6 for a lens with maximum aperture f/2.8). So, the entire print would be sharper at that sweet spot but depth of field would not be an affected factor in the image. It is set when exposed in the camera. A similar effect, depth of focus, does exist in an enlargement situation, but increasing it by using smaller apertures again only affects the overall print sharpness for example by bringing the edges of the print to greater apparent sharpness when one has actually focused on the print center. It is the apparent sharpness range of the print image, but has nothing to do with the subject depth of field.

At some enlargement f/stop, this sharpness all falls apart due to diffraction. You can observe that effect by looking through a grain magnifier as you progressively stop the lens down after initially focusing the grain in. It will sharpen up to a specific aperture and then turn to mush beyond that.

Joe

 

[Ole]

I was talking to a printer a few years ago who stated that when she printed nudes for example; the model's back could have a hard or soft edge depending on which f stop she used on the enlarger lens.

I didn't think that f stops could alter an image.

Is there any truth in this?

Thanks

Unless the enlarging lens sufferes from an unusual amount of field curvature (=soft corners), it's bullsh*t.

 

[w35773]

Yes, I was thinking more of my situation where my lens and enlarger were made during the flintstone age and the abberations in my lens are somewhat soothed by stopping down some.

 

[Ole]

Yes, I was thinking more of my situation where my lens and enlarger were made during the flintstone age and the abberations in my lens are somewhat soothed by stopping down some.

While my enlarger is not exactly "flintstone age", one of my lenses is - flint and crown glass; an Aplanat. Not even that shows enough field curvature to give a visible difference!

 

[w35773]

Is it possible to get a focus shift when changing aperatures on a enlarger lens? Maybe that is my problem?

 

[Dave Miller]

Is it possible to get a focus shift when changing aperatures on a enlarger lens? Maybe that is my problem?

If you do, then it's time to chuck the lens.

 

[Jim Jones]

Is it possible to get a focus shift when changing aperatures on a enlarger lens? Maybe that is my problem?

I struggled with such a lens for too long. Dodging and burning had to be done very close to the paper, too. Despite that, the prints were reasonable sharp. Like Dave says, chuck the lens. Good ones are affordable now.

 

[Saganich]

I also read that sharpness changes for papers more sensitive to blue light, ie multicontrast papers, and tests should be made. On print dead on via magnifier, and two slightly off in either direction to see if there is shift.

Chris

 

[Dave Miller]

I also read that sharpness changes for papers more sensitive to blue light, ie multicontrast papers, and tests should be made. On print dead on via magnifier, and two slightly off in either direction to see if there is shift.

Chris

Just goes to show - shouldn't believe every thing you read.

 

[Arvee]

Thornton and Ctein spoke of 'smear' when some enlarging lenses are used wide open which I am sure would contribute to some apparent softness that might be used to one's advantage.

Fred

 

[Ole]

I also read that sharpness changes for papers more sensitive to blue light, ie multicontrast papers, and tests should be made. On print dead on via magnifier, and two slightly off in either direction to see if there is shift.

Chris

Chromatic aberration? That shouldn't be a problem with any undamaged enlarger lens made after 1900 (with the possible exception of the Voigtländer W.Z., which was designed to be soft).