i'm pretty new to doing my own printing and have done everything so far at f/5.6 or f/8 but i'm wondering what effects (more or less contrast is my guess) changing the f-stop on the enlarging lens has?

thanks for any info joe

btw- i do understand the effects with camera lenses

-- Joe H (joe1013_@excite.com), February 28, 2001

Answers

Stopping down the enlarging lens has no effect other than increasing the exposure time and giving a bit more focus latitude.

-- Pete Andrews (p.l.andrews@bham.ac.uk), February 28, 2001.

thanks, so does stopping down not result in more contrast from the longer exposure? i guess it's best to just continue using the "sweet spots"?

-- Joe H (joe1013_@excite.com), February 28, 2001.

Most decent enlarging lenses are diffraction-limited a couple of stops down from wide open, or iow, stopping down more than two or so stops will cause image quality to _decrease_ because of diffraction. The reason for stopping down a couple stops from wide open is that that cleans up aberrations that limit quality at wider apertures.

The extension enlarging lenses are used at result in an effective aperture somewhat smaller than what you set on the lens.

-- John Hicks (jbh@magicnet.net), February 28, 2001.

Joe:

Are you asking about the possibility of contrast increase caused by the additional increases in exposure necessary to compensate for reciprocity law failure? This type of thing is quite common at the camera when we have to deal with low-light situations, especially when we have to stop down to obtain adequate depth of field. Is that what you are suggesting when you say that you "understand the effects with camera lenses?"

Today's printing papers don't suffer from reciprocity law failure nearly as bad as they did 20 years ago and more. With the faster papers and brighter enlarger light sources, such problems are a rarity today, at least for me. Its been so long since I have had to deal with such a thing, that I don't recall if I used to have to adjust contrast as well as exposure when large increases in exposure were necessary, such as when changing from a very small print size to a large size.

Other than the optical problems mentioned above by John Hicks, increases in exposure times resulting from stopping the lens down should have no noticable effects on the image.

-- Ken Burns (kenburns@twave.net), February 28, 2001.

i think your 1st paragraph summed up what i was thinking as far as stopping down effecting contrast....

as for the 20 years ago stuff, i believe i may have one of those enlargers, it's a bogen 22b and i've come up empty on info for this thing..... anyway, thanks for the advice

joe

-- Joe H (joe1013_@excite.com), March 01, 2001.

Joe, a twenty year old enlarger is not going to act any differently from a new one of similar type.

chris

-- Christian Harkness (chris.harkness@eudoramail.com), March 01, 2001.

See my enlarger f-stop test at home.flash.net/~brownt/optical.htm

-- tim brown (brownt@flash.net), March 06, 2001.

There are problems with the URL I gave in the last post. They will be fixed in the next day.

-- tim brown (brownt@flash.net), March 06, 2001.