How to use characteristic curve to enlarging

Hi everyone
Can I ask how to use characteristic curve to caculate the expouse time(for enlarging)
I know the characteristic curve use Log(E), but How can I transfer the log(E) to actual time?
On the negtive, we have many different density, which match different expouse index, in final step of enlarging, which expouse index should I use?

Make a test strip or two.

If you follow Phil Davis Beyond the Zone System paper speed is calculated along with film E.I as part of the process using a his magic wheel and later apps for the old Palm Pilot and later smart phones. Other use enlarging meters, as yya I make test strips.

You can read the density of film, and you can read the reflectance of paper -- with a meter or eyeball. Same thing really, just one is transmission, the other reflectance. You can get as involved/accurate as you want. Check out Richard Henry's book -- Controls in Black & White Photography.

This doesn’t answer the question as stated, but comments on practical ways to deal with the underlying question, “How do we determine the correct exposure time in enlarging.”

As a matter of practicality, the characteristic curve of an enlarging paper is not particularly useful for most individual users. One of the “Cut-and-Try” methods is generally most practical for home-based users.

We must test each package of paper by exposing and processing a small representative sample of paper from the package from which we intend to print.

This can be done in several ways:

1. Making a series of test exposures at progressive times on a single strip of paper and evaluating the results to find the approximate best exposure time. A 1” x 8” test strip uses 8 square inches of paper.

2. Making a 60-second exposure through a Kodak Projection Print Scale onto a 4” x 5” test sheet (uses 20 square inches of paper). The KPPS is no longer made, but can be found in decent condition used.

https://www.ebay.com/sch/i.html?_fr...nkw=kodak+projection+print+scale&_sacat=69323

Also, the similar Delta 1 Projection Print Calculator is still available.

https://www.bhphotovideo.com/c/product/15711-REG/Delta_12610_Projection_Print_Calculator_Scale.html

3. Estimating the initial time based on the intensity of the projection and using your experience to make a single exposure “test patch” of some convenient size (I use 1” x 2”). Use that result to adjust the time of the next test. Repeat until you find the best time. I can usually find the correct exposure within 3 or 4 test patches, sometime fewer. This uses 4 to 8 square inches of paper.

It’s also possible to use the Ilford EM-10 Exposure Monitor in conjunction with an exposure test to arrive at the correct exposure. Methods 1, 2, and 3 above are generally easier.

Once you’ve found the exposure time that gives you the required density, you can alter your filter choice to fine-tune the contrast. Some workers might have devised some variations on these ideas that they wish to share.

X axis is exposure, Y axis is density.

Read your spot on the projected negative with a meter and using the curve, calculate the exposure needed to get the density you want for that area on the print.

Usually one uses the method in post #2 above.

yya said:

Hi everyone
Can I ask how to use characteristic curve to caculate the expouse time(for enlarging)
I know the characteristic curve use Log(E), but How can I transfer the log(E) to actual time?
On the negtive, we have many different density, which match different expouse index, in final step of enlarging, which expouse index should I use?

Click to expand...

Just like with film speed, paper speed needs to be determined individually -- if you want the best results. I won't shoot the same film at the same ISO as you, and you won't shoot the same paper at the same speed as me. While Ansel Adams deals with THE NEGATIVE (Book #2) before he deals with THE PRINT (Book #3), Richard Henry takes the opposite approach -- you can't determine how to create the best negative until you figure out how to make the best print. Here's the first page of his book's table of contents. The negative isn't even on it!!!:

yya said:

Hi everyone
Can I ask how to use characteristic curve to caculate the expouse time(for enlarging)
I know the characteristic curve use Log(E), but How can I transfer the log(E) to actual time?
On the negtive, we have many different density, which match different expouse index, in final step of enlarging, which expouse index should I use?

Click to expand...

If you include a step wedge on your print adjacent to the test print, then you can determine the exposure change needed to get from the test print time to a reasonable proof print time.

For you may have a tone on the step wedge that is what you would like for a part of the picture that shows up looking like a different step.

You only need to count the steps from what you got… to what you want and multiply the number of steps times the step density difference.

If you use a T2115, with steps of .15 difference, two steps is a stop.

Bill Burk said:

If you include a step wedge on your print adjacent to the test print, then you can determine the exposure change needed to get from the test print time to a reasonable proof print time.

For you may have a tone on the step wedge that is what you would like for a part of the picture that shows up looking like a different step.

You only need to count the steps from what you got… to what you want and multiply the number of steps times the step density difference.

If you use a T2115, with steps of .15 difference, two steps is a stop.

Click to expand...

Bill
thank you for your reply
Yes, this is the method I have been using, but as far as I know, some people can get the exposure parameters directly through the log operation and the characteristic curve

xkaes said:

Just like with film speed, paper speed needs to be determined individually -- if you want the best results. I won't shoot the same film at the same ISO as you, and you won't shoot the same paper at the same speed as me. While Ansel Adams deals with THE NEGATIVE (Book #2) before he deals with THE PRINT (Book #3), Richard Henry takes the opposite approach -- you can't determine how to create the best negative until you figure out how to make the best print. Here's the first page of his book's table of contents. The negative isn't even on it!!!:

View attachment 347117

Click to expand...

Thank you for your reply, I will read it again now

Paul Howell said:

If you follow Phil Davis Beyond the Zone System paper speed is calculated along with film E.I as part of the process using a his magic wheel and later apps for the old Palm Pilot and later smart phones. Other use enlarging meters, as yya I make test strips.

Click to expand...

Thanks for your reply, sorry I just saw it now

xkaes said:

You can read the density of film, and you can read the reflectance of paper -- with a meter or eyeball. Same thing really, just one is transmission, the other reflectance. You can get as involved/accurate as you want. Check out Richard Henry's book -- Controls in Black & White Photography.

Click to expand...

Thanks for your reply, sorry I just saw it now!!!!

ic-racer said:

X axis is exposure, Y axis is density.

Read your spot on the projected negative with a meter and using the curve, calculate the exposure needed to get the density you want for that area on the print.

Usually one uses the method in post #2 above.

Click to expand...

Thank you for your reply, this is also the way I can think of, the light meter is necessary in this process

Yes

xkaes said:

Yes

Click to expand...

Thank you

yya said:

Bill
thank you for your reply
Yes, this is the method I have been using, but as far as I know, some people can get the exposure parameters directly through the log operation and the characteristic curve

Click to expand...

Ah so you’re going to want someone who knows calculus… derivatives…

Counting steps only gets you within a half stop if you’re lucky.

Are you taking densitometer readings of the test print? Maybe you could plot a graph and plan exposure changes graphically.

xkaes said:

Just like with film speed, paper speed needs to be determined individually -- if you want the best results. I won't shoot the same film at the same ISO as you, and you won't shoot the same paper at the same speed as me. While Ansel Adams deals with THE NEGATIVE (Book #2) before he deals with THE PRINT (Book #3), Richard Henry takes the opposite approach -- you can't determine how to create the best negative until you figure out how to make the best print. Here's the first page of his book's table of contents. The negative isn't even on it!!!:

View attachment 347117

Click to expand...

Hi xkaes
If possible, can you recommend me some similar books?

I've never run across a book like Henry's "Controls in Black & White Photography", but there are plenty of books about how to process your film or darkroom enlarging. The entire point of Henry's book is to have you run your own tests on your paper FIRST to figure out how to process it. These tests will depend on what gear you have -- and your preferences. They can be simple and eye-ball-based, or as complex as you want to get. Then he goes on to have you do the same thing with whatever film you are using -- to match it to what you've determined the paper is capable of.

And, of course, if you change anything -- the paper, the film,, the developer, etc. -- you need to test again, because that changes everything.

xkaes said:

I've never run across a book like Henry's "Controls in Black & White Photography", but there are plenty of books about how to process your film or darkroom enlarging. The entire point of Henry's book is to have you run your own tests on your paper FIRST to figure out how to process it. These tests will depend on what gear you have -- and your preferences. They can be simple and eye-ball-based, or as complex as you want to get. Then he goes on to have you do the same thing with whatever film you are using -- to match it to what you've determined the paper is capable of.

And, of course, if you change anything -- the paper, the film,, the developer, etc. -- you need to test again, because that changes everything.

Click to expand...

Okay! Thanks!

Years can be spent trying to figure out the sensitometry and acquiring the right kind of equipment, to equate to what can be done with a simple test strip in a few minutes, plus a bit of experience. I have done hundreds of densitometer plots, so do understand the analytic method. But for basic black and white printing, it can be an awfully tortuous way to simply get from Point A to Point B.

Incidentally, old fashioned curve plotting paper was based on log units. Density itself is. Understanding the implications of those specifics curves, however, takes a lot of experience, regardless. It makes a lot more sense to spend some time shooting a ball at the basket rather than trying to start out designing basketballs based on blackboard equations. There are just way too many potential variables.

DREW WILEY said:

Years can be spent trying to figure out the sensitometry and acquiring the right kind of equipment, to equate to what can be done with a simple test strip in a few minutes, plus a bit of experience. I have done hundreds of densitometer plots, so do understand the analytic method. But for basic black and white printing, it can be an awfully tortuous way to simply get from Point A to Point B.

Incidentally, old fashioned curve plotting paper was based on log units. Density itself is. Understanding the implications of those specifics curves, however, takes a lot of experience, regardless. It makes a lot more sense to spend some time shooting a ball at the basket rather than trying to start out designing basketballs based on blackboard equations. There are just way too many potential variables.

Click to expand...

Yes! you are right! Thanks! I just keep to do the test strip