Exposure calculation for enlarging

[chassis]

Hello,

I want to improve my skills in arriving at the proper exposure, starting from a contact print and moving towards an enlargement. The way I have been doing this involves test strips and test prints, which seems inefficient time and material wise.

Here is the scenario. I know the exposure and contrast filter I want for a 4x5 negative, based on a contact print. When the contact print is made, I have the enlarger head set at a height appropriate for an 8x10 enlargement, with the lens adjusted so the negative would be in focus, if there was a negative in the holder.

If I remove the negative from the contact printer, and place it into the negative carrier, can I keep the same exposure and contrast filter? I imagine there might be small adjustments to exposure (maybe a 1/2 stop or so) but I think I would be pretty close. Let me know if I am off base here.

Thanks for any input.

[Jim Noel]

To answer your question simply, No. The exposure will change and the contrast might because of the lens.
A full sheet test strip is still the most effective method. If you can find a copy of Gene Nocon's book, "Photographic Printing" you will learn more about making effective test strips and beautiful prints than any other source. Basically his test strip method is based on "F" stops and uses a full sheet of paper rather than a little strip. Using times each of which is twice as long as its predecessor rather than steps of equal time, like 5 second increments, produces much more information and results are easily seen. Try 5,10, 20, 40 and 80 seconds as a starting point.
Others may respond to buy automatic timers, etc. All of the f-stop based timers are based on the ones Gene designed and had built several years ago.

[Andrew O'Neill]

I have a predetermined time for print sizes. They usually get me into the ball park and then I go from there. I don't like test strips.

[bob carnie]

If the enlarger height , time, filter,and lens apeture are the same and all you are doing is putting the negative in a holder rather than a contact, then yes you are correct there will be very little change. you are not off base.


Hello,

I want to improve my skills in arriving at the proper exposure, starting from a contact print and moving towards an enlargement. The way I have been doing this involves test strips and test prints, which seems inefficient time and material wise.

Here is the scenario. I know the exposure and contrast filter I want for a 4x5 negative, based on a contact print. When the contact print is made, I have the enlarger head set at a height appropriate for an 8x10 enlargement, with the lens adjusted so the negative would be in focus, if there was a negative in the holder.

If I remove the negative from the contact printer, and place it into the negative carrier, can I keep the same exposure and contrast filter? I imagine there might be small adjustments to exposure (maybe a 1/2 stop or so) but I think I would be pretty close. Let me know if I am off base here.

Thanks for any input.

[cowanw]

Interesting. so far 1 no; 1 yes
Being Canadian, I am going to go for the moderate approach. Aperture and time will stay the same but contrast will change some (which may change aperture and time some) as you go to a bigger print.

[Leigh]

If I remove the negative from the contact printer, and place it into the negative carrier, can I keep the same exposure and contrast filter?
Yes.

The main factor controlling exposure is the distance from the negative (in carrier) to the paper.

Assuming proper focus, the intensity of the light reaching the paper varies according to the inverse square law as you change print sizes.

As long as the negative carrier to paper distance remains unchanged, the exposure will be the same regardless of where you put the negative.

- Leigh

[jeroldharter]

I have tried many times to automate printing in various ways.

Of course, it depends on what you want. if you are trying to crank out a number of good enough prints, then standardizing works. If you really want to workout a fine print then shortcuts don't work. You have to put the time and effort into it.

I would try to work out a conversion factor so that when your enlarger height is a fixed height you can convert the contact print exposure into the base exposure for an enlarged print. Then I would use that as the center around which I expose the full sheet test print.

[Shen45]

A very simple solution is buy an RH Designs Analyser Pro and the money you will eventually save on wasted time and paper you can spend on film, yourself or someone else. I recently got one secondhand off *bay and while it is the very first model they made with limited features it only took a minimal amount of time to calibrate and the results are amazing. The latest version must be outstanding.

[ataim]

I use an ilford em10exposure meter. It works ok after some calibration. It has already saved me the cost in paper within a couple of prints

[ic-racer]

In a low - flare situation (multicoated enlarging lens, masked negative edges, etc) and a diffusion head, the exposure and contrast should be similar.

What I do is just skip the contact part and go right to the enlarged print, however.

[chassis]

Well, it worked. Starting from a contact print exposure, and noting the negative stage height and lens aperture, I put the negative into the carrier, then raised the head to enlarge to my desired image. Noting the height change of the negative carrier, and considering the enlarger lens was opened one stop, I calculated the exposure.

The result was spot on. Another way to say it is, the results are acceptable to me at this stage of my reentry to the darkroom. There are plenty of boo-boos in the final print, but I was able to get done what I wanted to get done, using basic exposure calculations from a contact print. I will use this basic method to get print exposures in the right ball park.