Please Help an Enlarger Newbie

[SilverGlow]

Folks,

I'm not new to shooting film, but I am new to processing and darkroom processes with film/printing.

What's with enlarger lenses? 35mm film uses 50mm enlarger lenses, longer focal length for bigger negatives. Ok, I think I get this part, but...

What about F-stop's on an enlarger lens? Why F2.8 and not F4 or smaller?

Please advise, and thanks...and if there's anything else you think I should know, please do advise me.

 

[bdial]

There are f4 lenses around, and slower ones, especially in the longer focal lengths. Faster lenses make it easier to focus though you'd rarely use an enlarger lens wide open. For most the optimum sharpness is around f8 or 11.

 

[Bob F.]

The f-stop of the lens is only the largest available: you can stop down as you would with a camera lens to reduce the light reaching the paper.

Generally (and you will see arguments about this but it holds as a general rule I believe) you use an enlarger lens stopped down by one, two or three stops as most are not at their sharpest wide open. If this gives you too short an exposure time, say under 8-10 seconds or so, do not be afraid to stop down further.

Focus with the lens wide open as it gives the narrowest focus on the paper, providing more "snap" when it is focussed and, of course, it is brighter... Then close down to a suitable aperture for the exposure.

 

[SilverGlow]

Everyone, thanks for the information. So then the aperture and the time the light is on effect exposure....just like a lens on a camera...ok, I think I've got it. For some reason, I thought an enlarger's lens was fixed in f-stop, as well as focal length....I guess I know better now...

 

[Kevin Kehler]

You have a grasp now: the shorter the focal lens, the less of a negative that can be projected at any one time; thus, 35mm film is fine with a 50mm enlargement lens but medium format film needs a 70-90mm enlarger lens to be able to project the whole image. A general rule of thumb is whatever the "standard" lens is for your film size should be the size you use for enlarging. I sometimes use a 50mm lens on a 6x7 negative but only because I want to crop the image to 8x10 without having the enlarger raised to the roof.

What the f-stops are doing is: (1) reducing the amount of light reaching the paper, which allows for more controlled developments (once you start burning/dodging, you need more seconds to do your work than for a contact sheet); and (2) giving a depth of field for the projected image (if your enlargement lens is set at f/4, you might only have several millimeters of projected vertical image. If your paper surface is not smooth or level, you could have sections of the projected image out-of-focus even though the negative is in focus; using a smaller aperture gives more vertical focus but it will still max out in under a centimeter).

 

[SilverGlow]

You have a grasp now: the shorter the focal lens, the less of a negative that can be projected at any one time; thus, 35mm film is fine with a 50mm enlargement lens but medium format film needs a 70-90mm enlarger lens to be able to project the whole image. A general rule of thumb is whatever the "standard" lens is for your film size should be the size you use for enlarging. I sometimes use a 50mm lens on a 6x7 negative but only because I want to crop the image to 8x10 without having the enlarger raised to the roof.

What the f-stops are doing is: (1) reducing the amount of light reaching the paper, which allows for more controlled developments (once you start burning/dodging, you need more seconds to do your work than for a contact sheet); and (2) giving a depth of field for the projected image (if your enlargement lens is set at f/4, you might only have several millimeters of projected vertical image. If your paper surface is not smooth or level, you could have sections of the projected image out-of-focus even though the negative is in focus; using a smaller aperture gives more vertical focus but it will still max out in under a centimeter).

Kevin, and everyone, thank you very much!

 

[Vaughn]

With 50mm enlarger lenses, those starting at f2.8 are usually of higher quality than those starting as f4. I believe the f2.8 lenses are 6 element and the f4's are usually 4 element lenses. The 6 element design allows for more correction of the various distortions lenses can have. So if you have the choice, go with the f2.8's.

Vaughn