PDA

View Full Version : Enlarging from 5x7 to 8x10 to 11x14



Jfnphotography
10-Jul-2006, 13:12
I have just started developing and enlarging my 4x5 B&W negatives. Last night I made a few test prints. I used 5x7 R.C. Glossy paper that came with my enlarger. I was able to make nice looking B&W prints after about 8 test prints, I would like to try making larger prints that are 8x10 and 11x14, my question is, how do I determine how much time I should add or what f stop I should go to, to print this size. Here is the technical information. Omega D-5 pro-lab 4x5 with a Nikon 135mm lens my exposure time was
3 sec at f11 to make a 5x7 print.
Thanks, Jacob

David A. Goldfarb
10-Jul-2006, 13:47
5--8--11--16

Recognize those numbers? Indeed, they're about the same as the f:stop series, so as long as you're using the same paper, each step in standard paper size requires one more stop of exposure, either by time or by aperture--at least as a starting point. You might find that as you enlarge, you need more contrast, and reciprocity could become an issue with very long printing exposures.

Jfnphotography
10-Jul-2006, 14:27
David,
Sounds easy enough, I will give it a try.
Thanks, Jacob

Barry Trabitz
10-Jul-2006, 16:59
David'

Thanks for your comment. It is so obvious that I ( and I suspect WE ) lose sight of this when going larger.


Barry

Brian Ellis
10-Jul-2006, 20:50
I'm not sure that simply doubling the exposure as you move from one standard paper size to the next is going to get you real close to a correct exposure. First, moving from 5x7 to 8x10 to 11x14 to 16x20 to 20x24 paper sizes obviously doesn't represent a doubling of the previous size. Second, the inverse square rule of light fall off, which tells us that the intensity of light doesn't decrease in direct proportion to increases in distance (or something like that) affects the new exposure on larger paper. Then there's the fact that as you move from one standard paper size to the next the printed image has to be changed to some extent (except when going from 8x10 to 16x20), which requires its own adjustment of the height of the enlarger head. Finally, some enlargers such as the Beseler MX series have canted center columns so that there isn't a direct correlation between changes in image magnification and changes in the distance the head travels on the center column.

When I printed in the darkroom I used a book published by Kodak called "The Kodak Darkroom Guide" or something like that. It contained a little wheel that could be used to determine the correct exposure (or close to it) when going from one magnification to another. Once you knew the correct exposure at one magnification and knew the magnification factors involved in moving from one print size to another you could use the wheel to determine a more or less correct exposure for the new magnification. I don't know if Kodak still publishes that book but if not it should be readily available used. There must be other methods but that's the one I used and it worked pretty well.

Bill_1856
10-Jul-2006, 21:09
It's not exact, but the easy way (besides the Darkroom Dataguide that Brian recommends) is to compare the ratio of the area of the prints. 11x14=154. 5x7=35. 154 divided by 35= 4.4. Multiply this by the correct exposure time for a 5x7 print (3 seconds). 3 times 4.4= 13.2 seconds. So try 13 seconds. 8x10=80. 80/35=2.3. 2.3 times 3 equals 6.9, so try 7 seconds.
Incidentally, those are awfully short times. There must be some way of cutting down the amount of light that your enlarger produces.

robc
10-Jul-2006, 21:10
there is a rough calculation which is :

T2 = ((W2/W1)^2) * T1

where:

T1 = time for smaller print
T2 = time for bigger print
W1 = long side of smaller print
W2 = long side of bigger print

It never works exactly, but will get you fairly close without changing fstop.

more accurate is to measure the difference in height of the enlarger head and using the inverse square law you can calculate the difference in time.

Also, if you have a spot meter, you could take a reading from a piece of white paper or baseboard at smaller enlargement size. Then move enlarger up and take another reading. Then convert the difference in stops to time.

Jfnphotography
11-Jul-2006, 10:40
When you use a spot meter. If I took a reading of F11 with my exposure time of
3 sec. for a 5x7, then increased the size to a 8x10 and took another reading of f8 would my new time be 6 sec. for exposure?

Jacob

robc
11-Jul-2006, 11:02
When you use a spot meter. If I took a reading of F11 with my exposure time of
3 sec. for a 5x7, then increased the size to a 8x10 and took another reading of f8 would my new time be 6 sec. for exposure?

Jacob

That ones easy because its exactly one stop difference so its double the time, so 6 secs would be correct at the same enlarger fstop as your first print. Just make sure you take the two readings from the same angle and position/distance.

What you really need is a formula for when its not exactly one stop. I've forgotten what the formula is. Will work it out and report back shortly, unless someone else chimes in with it in the mean time.

People forget they have a handy lightmeter which they can use as an enlarger exposure meter if needs be.

Keep a record of the exposure differences between the enlargement sizes because you can then just refer back to the difference for future prints. Infact, if you do it for all the different paper sizes you expect to use in one go, then you will have a handy look up table for future use. It may not be exact, but it will be pretty darn close.
Often when changing print size, the print looks diifferent and you find that you also want to change print contrast or where the emphasis in the print is. Because of that, the times you calculate for the bigger print never seem to be exactly spot on.

Donald Qualls
11-Jul-2006, 11:50
Hmmm. Maybe it's just me, but I usually just make a new test print when I change sizes -- I split filter, and test both filters on the same test exposure, so I need only one test print to get both exposure and contrast (at least to the stage of a good working print).

Once you have this time, you can apply any dodging and burning as a percentage of the total working from your notes on the smaller print -- that way, if (for instance) you changed the lens aperture to keep the printing time reasonable when you changed magnfication, you don't add to the complexity of the task, or increase the likelihood of a miscalculation leading to one or more completely wasted prints. It's also pretty quick to do -- a couple minutes to make the test exposures, maximum five minutes souping the test print, and a minute or two under the inspection light picking the best area in the grid...

robc
11-Jul-2006, 12:14
OK I thought about it.

formula is:

for calculating time for bigger print size from original

T2 = T1 * 2^Fdiff

where:
T1 is original print time.
T2 is new print time
Fdiff is fstop difference in stops.

for calculating time for smaller print size from original
Fdiff should be made negative. i.e.

T2 = T1 * 2^(Fdiff * -1)

that should do it if you use your fstop meter to meter fstop difference at different enlargements/magnifications.

Jfnphotography
11-Jul-2006, 12:30
I made a test print.
I used Kodak Projection Print scale, put it on the paper set the enlarger lens to f11 then exposed for 1 minute. My paper was black, so I cut the time down until I was happy with the results. My end time was f11 at 3 sec. for a nice print. Do I have something set wrong on the enlarge? My exposure time is real short. Should I be at a higher f-stop to use the projection print scale?
Thanks, Jacob

robc
11-Jul-2006, 12:36
if you are printing to only 5x7 from a 4x5 neg size then enlargement factor is very small, so head will be close to paper and very bright. You may need to use some neutral density, at that scale, to increase the print time.

Brian Ellis
11-Jul-2006, 19:09
robc's mention of an exposure meter reminded me that Ilford makes (or used to make) a very inexpensive ($30 or so) enlarging exposure meter. I had one and it worked very well but I found the wheel in the Kodak book quicker to use so the Ilford meter sat in a drawer. However, I had a table of magnification factors for my Beseler MXT enlarger at any given height that was created by Daryll Nicholas and that table really made the Kodak wheel easy to use. Without such a table (or more math ability than I possess) the Ilford meter probably would have been the easier of the two.

robc
11-Jul-2006, 19:51
using the formula I gave, you can calculate a factor to be used for magnification from any size to any size. This only needs to be done once. But there is a problem with all of these formula and look up tables. Say you have worked out a time factor for magnification from 5x7 to 10x8. The factor will only be accurate if your neg crop area is exactly the same as used to calculate the factor and when you upsize to 10x8 you also use the exact same crop area as when calculating the factor. In practice from one neg to another, this won't be the case, so the factor won't be 100% accurate.

Only if you meter(or measure height difference) for each usage will the formulas be accurate. That also includes focus being set at both heights before metering or measuring height difference. For that reason, its often easier to just take an approximation and make a test strip. Therefore the original formula I gave is accurate enough as a starting point for a test strip. But since the question was asked an answer was given although it may not be the most practical option. It will however be accurate if done on a neg by neg basis.

Jfnphotography
12-Jul-2006, 16:29
Made an 5x7 then a 8x10 last night, I found that from F22 if I went up to F16 and added 2 sec the print came out just like the 5x7, I didn’t get a chance to try the spot meter. I will have to try that next time.
Thanks for everyone help.
Jacob