ilford em 10 meter

[el wacho]

hi,

has anyone derived a meaningful scale for this enlarger meter. i know it was designed for comparator-style usage but am curious as to whether the linear scale on the knob could tell me more ( sounds like user incompetence ! )


any thoughts/help would be appreciated.

 

[DWThomas]

I recall someone here posting a plot to relate the numbers to density -- maybe a year or so ago. But I suspect the units are not calibrated to a common standard; that is a reading of 57 on mine might be considerably different from 57 on yours. That would suggest a scale would have to be devised for each individual unit.

DaveT

 

[Nicholas Lindan]

has anyone derived a meaningful scale for this enlarger meter

It can be done. You have to calibrate your own meter as no two meters read alike.

The calibration isn't very stable. The meter uses a 'logarithmic' volume control potentiometer / knob of the type used in old transistor radios - with use the potentiometer can be become erratic and noisy.

You can calibrate it to a step wedge in the enlarger. The problem here is the step wedge is calibrated for use in a densitometer and the Callier effects and flare generated by the enlarger will change the effective densities of the wedge.

If you have an El-Nikkor enlarging lens you can use the aperture of the lens to calibrate the meter. El-Nikkor apertures, after the first stop, are accurate to better than a 1/10th stop. Rodenstock and Schneider enlarging lenses do not have very accurate aperture calibration.

Place the meter in the center of the illuminated field and tape it down or lock it in an adjustable easel so it can not move. When making readings, move your hand away from the meter and verify the meter stays zeroed (green led on, both red ones off). The meter can see light reflected from your hand and can also pick up electrical interference. A white shirt can sometimes give problems.

You can 'paste' together aperture sequences to calibrate the meter over a greater range (assuming a 50mm f2.8 El-Nikkor, if you use an f5.6 then you start at f8, and so on.).

1. Set the head low and the aperture at 4.0 and note the first dial reading.
2. Close the lens down one stop and note second reading
3. Continue to f16, note the reading and keep the knob at this setting
4. Now open the lens back to f4.0 and raise the head so the meter zeros
5. Continue stopping the lens down and noting the reading.
6. When you get to f16 and you are not out of the meter's range then raise the head and open to f4.0 - repeat as needed.
7. You can also use fogged film or a VC filter to cut the light down instead of/in addition to raising the enlarger head

If you are going to be using a calibrated enlarging meter for real darkroom work you will be better served using the real thing - click on Darkroom Automation link, below. Calibrating and using an EM-10 as a meter should be limited to recreation: it is one of those things that can be done, but there are better ways to do it.

 

[el wacho]

thanks to all,


Nicholas, how would an enlarger meter respond to negs made with cachetol where density is related to the stain (VC) ?

 

[Nicholas Lindan]

how would an enlarger meter respond to negs made with cachetol where density is related to the stain (VC) ?

It is possible to use an enlarging meter or densitometer with pyro negatives. However calibration is a major issue and has to be done individually. To complicate matters, the stain produced by pyro changes with film, developer and processing and each combination will require its own calibration.

Because the stain color changes and the response of MG paper changes with stain color and the effect of the stain changes with the head's contrast filtration, it is impossible to make an enlarging meter that will work with pyro negatives in the same manner as it works with conventional negatives.

We have many customers who use the meter with pyro negatives but they each use it in a different way as an aid to determining exposure.

 

[Ole]

The nice thing with the EM-10 is that it seems insensitive to filtration, so that the same reading for a "light grey" will give the same density from all yellow to all magenta with Ilford MG.

Stained negatives complicate this quite a bit.

 

[el wacho]

thanks to all.

 

[Nicholas Lindan]

The nice thing with the EM-10 is that it seems insensitive to filtration, so that the same reading for a "light grey" will give the same density from all yellow to all magenta with Ilford MG.

That is a function of the filtration and not so much the meter.

Ilford has designed its filtration and its papers so you get the same light grey with the same exposure with all filters 00 - 3.5. The filters have a neutral density component to balance the exposure times and the meter responds to this just like the paper does. The Ilford filter system is also made to pass red light unfiltered, so the #2 filter has a pink tint to it - it’s really a grey with no red attenuation.

The grades 4-5 filters have had the neutral density component altered, so that although they are a stop slower when printing, they are not visually darker but about 0.2 - 0.3 stop lighter. The color also shifts to the yellow as the 'pink' tint that was used for neutral density is removed.

Ilford’s published settings for color heads carry through the neutral density component - the light for #2 grade isn’t white but a 50Y/25M or thereabouts.

The Darkroom Automation meter reads similarly with filtered light, but like all high precision systems it is used without filters - reading through the filter just introduces one more source of error into the system. The Ilford EM-10 will read close to a 1/4 stop of error over the filtration range if the light is read through the filter.

 

[Ole]

Nicholas, I don't use Ilford filters. I use a colour head with one enlarger, and AGFA CC filters with the other. One enlarger uses a halogen light source, the other a CFL bulb. So I can assure you that it is a function of the meter and not the filtration.

 

[el wacho]

...so is it true that the filters add or subtract a 1/6 of a stop at the top and bottom per 1/2 grade shift?

 

[Ole]

No idea.

I go by the "that looks a little hard - add 20 yellow next time" or "way too soft - 130 magenta pronto" method.

Then I adjust aperture and/or neutral filtration to give me exactly the same reading in a light grey area, and print away.

 

[Nicholas Lindan]

Nicholas, I don't use Ilford filters. I use a colour head with one enlarger, and AGFA CC filters with the other. One enlarger uses a halogen light source, the other a CFL bulb. So I can assure you that it is a function of the meter and not the filtration.

I thing it depends on how much you adjust around the filter settings. If you start at #2 and then remove all magenta I think the trick will not work.

In any case, you can do the same thing with any meter. The response of the meter is the response of the CdS cell, and all CdS cell meters will respond in the same manner - give or take a little bit. Modern meters based on Silicon photodiodes may respond a bit differently.

 

[Nicholas Lindan]

...so is it true that the filters add or subtract a 1/6 of a stop at the top and bottom per 1/2 grade shift?

The reality is not very pretty when it comes to multigrade papers:

MGIV FB HD graphs

The horizontal axis is in stops.

The grade spacing isn't even, and although one can take the spread of speeds accross the grades at arrive at ~1/7 of a stop in the highlights and 1/4 stop in the the deep shadows, these numbers should be used with caution.


At 0.1 OD 1/7 stop/grade
At 2.0 OD 1/4 stop/grade

However, the grade spacing isn't even.

At 0.1 OD there is a ~ 1 stop spread over 7 grade intervals and 1.7 stop spread at 2.0 OD.