How calculate exposure time in function of distance light to paper

Hi,

 

I want to expose Ilford RC Multigrade paper.

In order to do so, what are correct exposure times in relation to Fstop of the enlargers lens?

Also in relation to the distance of the light source of the enlarger to the exposed paper?

 

How to measure this?

 

thanks

If you don't have an exposure meter for your enlarger, you guess the exposure time and fstop, then do a test strip of about an inch wide. With experience, you can get the number of test strips down to no more than two. But I'd recommend to buy an exposure meter

Familiarise yourself with something called the 'inverse square law', which basically says that light intensity changes according to the inverse square of the distance from the light source.

 

Usually this only works exactly for a point source of light spreading out into a 360 degree solid angle, but in the case of light emitting from an enlarger lens, it also holds almost exactly.

 

So, if you double the enlargement size, then the exposure needs to be increased by 4 times (= 2 stops). A 1.4 x increase in enlargement needs a 2x increase in time, or a 1 stop opening of the lens aperture.

 

You can relate this directly to lebs aperture by simply multiplying or dividing the aperture number by the change in magnification factor. I.E. Twice the magnification requires the aperture number to be divided by 2. Half the magnification needs the aperture number to be multiplied by two. 3 times the size of enlargement needs the aperture number divided by 3, or the time to be increased by 9x.

 

"How to measure this?"

 

- The same as any other light intensity; with an electronic meter.

 

Some lightmeters, such as my Minolta Autometer IVF, can be fitted with an accessory mask to convert them into an enlarging meter. This usually also requires a diffusing filter to be placed under the enlarger lens. Otherwise the reading will be very dependant on where in the image the meter is placed.

 

With other designs the meter is placed looking down on the baseboard, which automatically gives an average or integrated reading.

 

However, no metering method is 100% accurate, since pictures vary greatly in their distribution of light and shade. The most accurate assessment of printing exposure still remains the test-strip; taken from the most important part of the image.

 

For colour work I would strongly recommend finding a device called a 'colour analyser'. These used to be immensely expensive, but these days they're sold for peanuts... that's if they haven't already been scrapped or thrown away.

Edited September 28, 2018 by rodeo_joe|1

'Lebs aperture' should have been lens aperture of course.

If you don't have a meter, you can get something like this:

 

Delta Projection Print Scale | Freestyle Photographic Supplies

 

I still have the one given to me by my grandfather for my 10th birthday.

While the design is for a 4x5 print, 2x3 is enough, sort of centered

on the middle of the circle.

 

You give it a fairly long exposure, such as 60 seconds, and the different

wedges have equivalent exposure much less. Still useful even with

a meter, as you have to calibrate the meter to something.

 

Even with an enlarging exposure meter, you have to select the place

to put it. I usually pick a face, if there is one.

 

But otherwise, as above, once you have a good idea of the exposure, if you

raise or lower the enlarger head, to change the print size, the inverse square

law works.

'Lebs aperture' should have been lens aperture of course.

 

Hmm... "lebs aberjure" in

Great Ape slang is "banana

daiquiri"...

http://bayouline.com/o2.gif

Here's the thing . . . This is all great and accurate advice but it seems to ignore the real issue going on . . .

 

The right exposure is the one that gives you image that you want from the negative that you want to print with. This is the expressive portion of printing your own pictures.

 

It sounds like you want someone to give you the equivalent of a "sunny 16" rule but it doesn't work that way. The exposure you need depends on the light source you are using, the lens AND the aperture, the paper, the enlarger height and THEN the negative. An over exposed or over developed negative may take more time to expose but, the image that you want may not require that. An under exposed or under developed negative may take less exposure but again . . . It might not.

 

I have two completely different enlarger, several lenses and different papers that I print with. From memory, some of my favorite negatives have required exposures under one second and others have required two to three minutes.

 

After a while, you will get a feel for how your work prints. It take practice and we have ALL wasted a lot of paper over the years.

Also to be considered when setting a "proper" time for the print is you will need some time for dodging / burning during the print session. I would always work for a medium time of 30 seconds to start. With my negatives, that "usually" was with f11 set on the enlarging lens (condenser enlarger). Worked well for me over 40+ years of wet lab work. Bill

Hmm... "lebs aberjure" in

Great Ape slang is "banana

daiquiri"...

http://bayouline.com/o2.gif

 

-Then pour me a big f/1.4 lebs aberjure Gingey!

 

BTW, I completely agree with Ed and Bill's comments. But that wasn't the question the OP asked.

Edited September 28, 2018 by rodeo_joe|1

This is just the same as getting a correct exposure in your camera, except you don’t have a light meter in your enlarger. You change the aperture, and the time, to whatever is required, to get a good exposure. As you have no light meter, then only way you can tell what is good, is to do tests, with small bits of paper, at different times and apertures. Try you tube videos of ‘how to make a test strip’ and go from there.

A test strip can be exposed multiple times by covering each exposed section as they're done. It's done in easily remembered exposures by changing the aperture one stop at a time. This can often save time, paper and chemicals

In order to do so, what are correct exposure times in relation to Fstop of the enlargers lens?

Also in relation to the distance of the light source of the enlarger to the exposed paper?

 

It's tough to dive into these complex and difficult topics, and I hope you won't take offense, but a lot of your questions are complicated versions of what are really basic knowledge in photography.

 

In this question, for example, you need to get a decent, basic book on darkroom procedures. It's really the same problem as exposure of the film itself, except that you have to actually understand how to set everything by yourself without automatic this and that.

 

Eventually you want to work up to Ansel Adams' classic photo books, but those are pretty high level for a beginner. You want to start with a beginner's handbook and I really have no idea what is now on the market in that regard. There may very well be internet sources, especially on YouTube.

 

By the way, much of what you are asking will be on data sheets that either come with the paper, or can be downloaded.

There may very well be internet sources, especially on YouTube.

 

- I would be very wary of some of those internet 'instructional' videos. There's poor advice and technique galore shown in some of those. They seem mainly to be made by 'newbs' themselves; anxious to show off their newly acquired lack of knowledge and skills!

 

Old skool paper books at least have an editor, and generally give better advice. It doesn't matter if they're years old either, since darkroom techniques haven't changed in 60 years to my knowledge.

 

'Enlarging' by C.I.Jacobson - focal press, springs to mind, but there are dozens of other books on the subject.

Since you're using Ilford paper, I'd start with the folded piece of paper that comes in all their boxes of paper and also read this - Making a Black & White Print - Exposure Testing . They have several other pages on their site with good info about developing film and making prints.

 

One of the most important things is to be consistent. The paper should be in the developer for the same amount of time for each print (with Ilford RC and Ilford MG developer at 1:9 that's 1 minute), stop bath for the same amount of time for each print, and fixer for the same amount of time for each print. If you vary those, you can't compare two prints made with different times.

To summarize the comments here - there are many variables that contribute to 'correct' darkroom exposure time. As a result, there can be no simple formula.

 

Instead, the ONLY way to proceed is to make a test print, and then adjust the exposure time and contrast filtration to get the results YOU want. Understand that as you spend more time working in the darkroom, you will develop the skill to sense the adjustments you need to make, so it s not quite as random as pure trial and error.

 

The other point here is that YOU have to determine what YOU want the final print to look like . Different photographers can make prints form the same negative, and get widely different final images - because the image they produce is their vision of what that final print should look like.

 

As others have noted, it is helpful to reduce the number of variables - use the same f/stop on the enlarging lens and adjust exposure only by changing time, use the same paper, developer, development time, and temperature, etc. That said, after you acquire darkroom skills, you may find yourself tinkering with some of those variables to achieve specific objectives.

 

The best reference on the subject is a now-out-of-print book by David Vestal called 'the Art of Black and White Printing' - and the title of that book tells a lot. The process is really an art, and not a science.

Hi,

 

I want to expose Ilford RC Multigrade paper.

In order to do so, what are correct exposure times in relation to Fstop of the enlargers lens?

Also in relation to the distance of the light source of the enlarger to the exposed paper?

 

How to measure this?

 

thanks

Have tried an app enLARGE on iphone has worked pretty good with 50mm lens on enlarger, lets you work out exposure times for different sized prints