Changing Time vs Aperture When Making Enlargements?

Tom Taylor · Apr 1, 2012

In making B&W enlargements going from, say, 8x10 to 11x14, 16x20, or 20x24, is it best to keep the aperture constant and change the time or keep the time constant and change the aperture? Or does it matter?

Thomas

Ian C · Apr 1, 2012

Most enlarging lenses give best image quality closed 2 stops. For this reason most of us prefer to fix the aperture and alter the time to suit for different print sizes. Its the same for color or B&W.

This and similar ideas were discussed here.

(there was a url link here which no longer exists)

Dan Henderson · Apr 1, 2012

I agree with Ian. Use the aperture that the lens is designed to render sharpest whenever you can. Then if the exposure times get too long or too short, go up or down a stop. One stop either side of the ideal aperture will not make a hugely noticable difference as long as you don't get too close to wide open or all the way down.

wildbill · Apr 1, 2012

i very often use neutral density gel filters over the light source on my colorhead because it's just too bright even on low output and f16 on the lens. you can get these in large sheets (nd 1.5, 3, 6 for about $6 from lee or rosco.

Photo Engineer · Apr 1, 2012

This is all very true if your paper has low or no reciprocity failure.

If there is reciprocity failure than speed and/or contrast may change if you change the time.

In my professional work, I was taught to change the aperture while keeping the exposure time constant! Of course, you pick the center point with time so that lens sharpness is optimal but you have a stop or so on each side of "perfection" to work with between 8x10 and 16x20.

PE

Tom Stanworth · Apr 1, 2012

Change one, or both as it suits you.

You may wish to stop a lens down three stops for a small test print to keep the time sufficient to allow dodging and burning. When you make a bigger print, you may in fact open it up a stop and make a further change to exposure time to make your next print. I often want exposure times to be 'long enough' but not too long.

vpwphoto · Apr 1, 2012

Its not linear anyway... you'd run out of apertures going from 8x10 to 16x20.

Bill Burk · Apr 1, 2012

Photo Engineer said:
This is all very true if your paper has low or no reciprocity failure.

If there is reciprocity failure than speed and/or contrast may change if you change the time.

In my professional work, I was taught to change the aperture while keeping the exposure time constant! Of course, you pick the center point with time so that lens sharpness is optimal but you have a stop or so on each side of "perfection" to work with between 8x10 and 16x20.

PE

Thanks for the reminder. I learned this from datasheets for reversal color print papers, I think the aim was 10 seconds... Bought a 2.8 lens for the purpose... Threw it out because it wasn't sharp enough...

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.

But I can see how this might pertain to B&W paper if "contrast" or "speed" changes due to reciprocity failure. It makes sense to keep the time consistent as possible. If you have to pick another time for a different print size, then re-evaluate exposure and contrast for that print.

In practice, I change my aperture from around f/11 to f/22 to keep my 11x14 print times around 32 seconds. But I also keep other relevant variables constant too for example I stick to print size 11x14 and print full-frame. I'll throw in a 2 stop ND filter when making smaller prints.

Thomas Bertilsson · Apr 1, 2012

Don't be afraid of using your lens away from that 'magical' two stops down optimum.

If you use a 50mm f/2.8 and usually print at f/5.6 aperture, don't be afraid of f/4, f/8, or even f/11 to get reasonable printing times. Will there be a difference? Probably. In my world, though, it's better to be at a comfortable printing time where the paper stays consistent (avoiding reciprocity failure) than having a wee bit better sharpness. Use what's practical and don't worry about it. That's my advice.

- Thomas

Ian Grant · Apr 1, 2012

For colour work you're better to change the aperture & keep the exposure times constant, reciprocity with colour papers affects the colour balance and contrast.

In the days before minilabs in professional labs the colour roll-head printers were set up and calibrated and the aperture ring locked so that regardless of the lens used on the turret the exposure remained constant - the degree of enlargement was dependant on which lens was used. This was important because it meant that regardless of the size all machine prints had identical colour correction (and exposure).

With B&W this is less important but it's still useful to keep times similar as it also helps with dodging and burning at different sizes.

Ian

tkamiya · Apr 1, 2012

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 · Apr 1, 2012

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 · Apr 1, 2012

tkamiya said:
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 · Apr 1, 2012

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 · Apr 1, 2012

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 · Apr 1, 2012

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.

Bill Burk said:
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 · Apr 1, 2012

RPC said:
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 · Apr 1, 2012

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 · Apr 1, 2012

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 · Apr 1, 2012

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/support/appnotereciprocityandintermittency.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.

Thomas Bertilsson · Apr 1, 2012

Nicholas,

Your test shows even gray density over a wide range from 1s to 256s, which is great news for Ilford users.

However, did you also test for contrast, to see if it was affected by exposure time?

Thanks.

- Thomas

Nicholas Lindan said:
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/support/appnotereciprocityandintermittency.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.

Nicholas Lindan · Apr 2, 2012

Thomas Bertilsson said:
did you also [do a reciprocity] test for contrast, to see if it was affected by exposure time?

Not as part of that series. But you are right, I should add the results of a test for contrast to that application note.

artonpaper · Apr 2, 2012

Back in the 70s, I took George Tice's printing class at The New School. He had the best visual aids ever. He brought in a set of prints, I think were 11 x 14, and each print was printed of the same negative at every aperture on the lens. If my memory serves me they were from a 35 mm negative. I don't remember what lens he used, but I seem to recall he liked Schneider Componons. He always used a longer focal length than the recommended one. So for 35, he used an 80mm, for 2-1/4 he used 135mm, and for 4 x 5, he used 150mm. Of course he adjusted the exposure time by the equivalent of one stop. There was a noticeable loss of sharpness on the smallest apertures. That I remember well. Some loss of edge sharpness when wide open. There was very little difference in print density, minimal really. I do not recall what paper he used, but in those days Agfa Brovira was a favorite of his, although he used a host of different papers. I always avoid the smallest apertures and I use ND filters under the lens when exposure time become too short.

Changing Time vs Aperture When Making Enlargements?

Tom Taylor

Ian C

Dan Henderson

wildbill

Photo Engineer

Tom Stanworth

vpwphoto

Bill Burk

Thomas Bertilsson

Ian Grant

tkamiya

artonpaper

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Tom Stanworth

Photo Engineer

RPC

Bill Burk

Photo Engineer

ic-racer

Nicholas Lindan

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Thomas Bertilsson

Nicholas Lindan

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Changing Time vs Aperture When Making Enlargements?

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