Changing Time vs Aperture When Making Enlargements?

[tkamiya]

For 8x10 prints that I usually do, going full open doesn't seem to make the final image any softer. I use 6 element EL-Nikkor.

Typically, I do whatever it takes to keep the exposure time reasonable. Make it too short, dodging/burning accurately becomes an issue. Make it too long, my arm gets tired.

One thing I ran into is that using whatever the formula/system gets the exposure close, but if the image size is changing as much as double in area, our perception of the images change. I often have to make significant changes to make them "look right". That involved as much as 20 to 30% change in exposure and half a grade in contrast.

[artonpaper]

Middle grade lenses like Componars, perform best about 1-1/2 to 2 stops down. My 50 mm Componar came with a recommendation for use between f5.6 and f8. That said, when making small prints, lower magnification, it's less critical. Larger prints, much more critical. APO lenses are better corrected for flat field and often perform well wide open. I attended a lecture given by a Leitz optical technician. He said, all photographic lenses are sharpest wide open, but in the case of enlarging lenses, they may not be sharp out at the edges. Stopping down a stop or two will crisp up the edges at a minimal loss of overall sharpness. I certainly saw this phenomenon while photographing circuit boards for ITT. When I first began, I always used f45 on a 135 mm lens on a 4 x 5. This was true macro photography, where the image on the ground glass was same size or larger. I was a little disappointed in the results. ITT had several optical engineers working there. Don Taniguchi was the guy that made the photo resists for the tiny circuit boards. He said, try f16, and bingo, like night and day. Too small an aperture when doing close focusing, which is what most enlarging is, can create diffraction causing a loss of sharpness. I use f5.6 mostly and change the time.

[artonpaper]

For 8x10 prints that I usually do, going full open doesn't seem to make the final image any softer. I use 6 element EL-Nikkor.

Typically, I do whatever it takes to keep the exposure time reasonable. Make it too short, dodging/burning accurately becomes an issue. Make it too long, my arm gets tired.

One thing I ran into is that using whatever the formula/system gets the exposure close, but if the image size is changing as much as double in area, our perception of the images change. I often have to make significant changes to make them "look right". That involved as much as 20 to 30% change in exposure and half a grade in contrast.

BTW, the above statements are wise and considered. Especially the thing about about "looking right." Size matters.

[Tom Stanworth]

yes, and print size can impact how a print is agitated, speed of developer across the paper etc. There's the maths and then using the Mk I Eyeball for any adjustments required.

PS On the comment earlier about going from 8x10 to 20x16 and running out of stops, no way. If using F5.6 at 8x10, you'd be on F11 at 20x16. I never use area, but caculate new exposures based on height between the easel and the lens rim.

[Photo Engineer]

When using VC B&W papaers, if you change the time and if there is any reciprocity failure, you can "create" a bump in the mid tones that changes the contrast as a function of size, right where you do not want problems. So, this potential problem is to be found in B&W as well as color.

The problem is more evident today in economy priced papers which do not have the sophisticated emulsions that the high end papers have.

PE

[RPC]

I tend to agree with those who change aperture instead of time. I try to keep exposure times around ten seconds or less but will change it to avoid a wide open or closed down aperture. I use an exposure meter to make it easy.

Really, I don't practice color processes because the chems don't keep 6 months. When it's a hobby, color doesn't give much "time" in the darkroom for the price.

This is a myth. I have had both C-41 and RA-4 developers, stored in full, glass containers last three years or more and give results which matched fresh developer. During that time the developer hardly changed color. Storing this way prevents oxididation. Others here on APUG have posted similar experiences.

[Bill Burk]

This is a myth. I have had both C-41 and RA-4 developers, stored in full, glass containers last three years or more and give results which matched fresh developer. During that time the developer hardly changed color. Storing this way prevents oxididation. Others here on APUG have posted similar experiences.

Thanks for that potential door-opening feedback.

[Photo Engineer]

I have been able to store C41 and RA4 working solution for months in Jobo 5 L plastic bottles and 1 L plastic bottles when they were full. In fact, I have had the unopened concentrate go bad almost as fast as the working solution which surprised me.

PE

[ic-racer]

Best to change the intensity of the light with a non-diffracting aperture or density filter. Many color heads have some mechanism to facilitate that.

[Nicholas Lindan]

My experiments show very little to no reciprocity failure with Ilford MGIV RC. I'm sure it holds for the rest of the Ilford range.

http://www.darkroomautomation.com/su...ermittency.pdf

As noted in the application note, the range of exposure times in the darkroom is very narrow - 4 seconds to 64 seconds is equivalent to changing the shutter speed on a camera from 1/4th to 1/60th of a second. NBD.

But unless you have some way of precisely measuring light and controlling exposure the whole reciprocity issue is moot.

For color you need to hold exposure time constant if you can.

When changing magnification the ((M + 1)/(m + 1))^2 formula works very, very well -- see the sticky thread at the top of this forum.