What exposure correction?

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Dave
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I've developed my first film for several years. I wanted to use my 50/60s rangefinder cameras, one Voigtlander CLR and the older Baldina.
I'd exposed one 35mm 36exp film between the two cameras, using metering of an app on my mobile phone.
I compared the app to the readings given by my Fujifilm XQ1 compact and adjusted the app to match it (-1 stop). Surprisingly, the onboard metering on the CLR agreed well with the app, so a few frames were shot using the camera's metering.
The image attached shows a sample of the scan of the negatives on my flatbed scanner. Frame #6 (lump of concrete) was an exposure guess and came out well exposed (I think), frames 4 & 5 were affected by direct sunlight onto the camera meter "window" and caused it to read a lower value, making them nearer the right exposure. The frames on the top row are as per all other frames on the roll, pretty heavy exposure, giving quite a dense negative.
Since developing the film, I have resurrected my Nikon F70. Checking the exposure values that this gives against the app & digital camera shows that the F70 gives a reading one stop lower exposure. As I tend to trust the F70 over the other means of metering, it seems that my film could have been over exposed by one stop, but most frames are so heavy, I wonder if i should adjust for more change than one stop?
Is there a more reliable way to analyse the overexposure (and save me one more film and disappointment)?

Fomapan 100 in Ilfosol3 (1+9), 5 mins at 20c (with presoak).
filmscan.jpg
 
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Hi Dave,

The first thing I thought of when reading your post above is, are you sure the actual exposure times of the camera are close to the settings on the exposure time control? I.e., is the exposure time of the 1/30th control setting actually close to 1/30th (for example), or is it out? My thinking is that, if you guessed #6, then this is out of the running. #4 and #5 as you say were artificially under exposed due to direct light on the meter. #1 through #3 look as though the sun was to the side of you, or behind you based on the shadows, so the these are fairly easy to meter for.

A 1 stop over exposure shouldn't give that level of over exposure at the processed negative in my experience. However, if the shutters are dragging, or the timing in the camera is out, a 1 stop under reading combined with a shutter problem could start to explain the negative density. For cameras this old, if they have not been used in decades, the lubricants can become viscous or gum up. A CLA by a decent camera engineer can easily solve this.
 
Neither of the OP's cameras have any lubricant in the shutter mechanisms. Both cameras have leaf shutters which are designed to run dry. The Nikon F70 is another matter as that camera has a focal plane shutter and that does have lubricants in key places.
 
I agree with Woodsy - one stop over should be negligible with a negative film. In the absence of a densitometer, and assuming that shutter speeds and apertures on the camera are correct, then all I can suggest is getting a good scan of number 6, locking the exposure, and scan the ones which are too dense. The eye dropper in Photoshop may then let you estimate how far off you are.

If you don't mind using more film, bracket. Start at three or four stops under the suggested exposure and increase up to the suggested exposure.
 
Afterthought, and as a matter of interest. Did you vary exposure by changing the shutter speed, or the aperture? I'm just trying to see if the shutter could be slow or inconsistent. With a hand held camera, I fix the shutter speed (1/250th or faster); with large format, it's the aperture I fix (f/16 or smaller).
 
john.margetts said:
Neither of the OP's cameras have any lubricant in the shutter mechanisms. Both cameras have leaf shutters which are designed to run dry. The Nikon F70 is another matter as that camera has a focal plane shutter and that does have lubricants in key places.
Click to expand...

Fair point. Surely the shutter timing mechanism is not designed to run dry though?
 
Woodsy said:
Fair point. Surely the shutter timing mechanism is not designed to run dry though?
Click to expand...
Yes it is. Any oil or grease would attract dust which would both stiffen the movement and cause wear. The leaf shutter mechanism is basically clockwork but the needs of the camera means that the mechanism cannot be sealed like a watch would be so it is easy for dust to get in - the dust needs to get out again as well, not be stuck to the moving parts.
 
Thanks for your input guys... It's right to question if the shutter speeds are off. I had found that the two RF cameras gave very similar results in the density of their negs.. and so made the rather large leap in logic to think that they are both OK, rather than to consider that they may be both lagging.
 
Today, I received my order of a low power laser diode and a receiver. I used these on an Arduino that simply counts the number of microseconds of the flash duration as I operate the shutter.
I ran it on my two leaf shutter cameras. The results were quite heartening. For the range 30/60/125/250/500 I measured 20/39/82/157/260. Both cameras gave similar figures. I don't expect the shutter speeds to tally exactly, the way that shutter works in opening and closing will give longer opening times. Based on these figures, I will run another film in them, this time testing for exposure varaitions due to shutter lag. My old Praktica PLC3 should have given results that tallied quite well with the selected shutter speed.... this was all over the place and not particularly consistent on one speed. I can leave that in the cupboard.
 
This is essentially what I did with my LF shutters a while back, with the exception that I had access to an oscilloscope from work. Precisely the same principle though, of course.

So your shutters are, rounded for ease to the nearest 1/3rd of a stop, 2/3 of a stop slow (over exposing) for the first three speeds, and a stop slow for the last two. Couple this with the 1 stop over exposure you compensated for, I can start to see the density in your negatives showing signs of correlation. As @StephenM alluded to above, if you're aperture is perhaps 1/3 of a stop out (I'm assuming the aperture on these cameras is set in 1 stop intervals - apologies, I've no specific working knowledge of these cameras, as pointed out above re the leaf shutter :D), then yes, 2 stops over exposure on B&W film could well start to look like this in my experience.
 
Compur and Prontor leaf shutters were designed to be +/- 20% of the set speed and that is measured from when the shutter is fully open. Your measuring device is measuring from when the shutter has barely started opening.
 
It depends on how much the beam fills the lens to begin with and also how collimated it is. Further, how long does it take for the shutter to fully open?
 
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We're now getting in to the realms of shutter efficiency. At small apertures, the full exposure will start with the shutter barely open, and continue until the shutter is fully closed. At large apertures, full exposure will require the shutter to be fully open. From memory, leaf shutter speeds were set for a specific aperture (f/16?) and were less accurate at wide apertures. Again from memory, about 30% error. My figures are easily checked and corrected if anyone cares to :)
 
And the really important thing here is it does not really matter. For normal film photography, half a stop exposure is not really either here or there.
 
All this makes perfect sense. In my test, the laser beam is set up to run (very close to the lens) directly through the centre of the lens to the centre of the film gate. I guess that this is actually measuring the shutter speed at a small aperture, hence can be expected to give longer open times than might be expected of an "instantly opening/closing" shutter.
For my use, the test has shown some consistency. That is probably all I can ask for. If I reduce the exposure by one stop from the metering given by my F70 camera (which itself is around one stop less exposure than is reported by my digital camera), then maybe I will be in the right ball park. As always the fastest speed can be a little slower than indicated, so I will try to avoid that.
One camera/film has had a few exposures this morning (using my "new" metering). A series of exposures in good light of the same subject at 500th/250th/125th/60th with aperture changes to give the same exposure, then a short series of exposures at one speed giving +2,+1, 0, -1, -2 stops just for my education in seeing what these exposures look like on the developed negative. I'll remove the film and finish it in the F70, so the resulting negs will have all been through the same dev process. ..... fortunately, it's still fun.
 
Thanks for your pointers... My second film was processed recently, Fomapan 100 in Iflosol3.
The vintage rangefinder I used seemed to have similar shutter timing to my Baldina, so I only used the Voigtlander CLR for this test.
All test shots of a wall for a dozen shots with the metering as per my F70 less one stop (which is two stops less than my digital camera measures).
All worked well. Shots at a metered scene, then +one stop, then +two stops showed that my originals were pretty much all two stops over exposed. These new exposures came out well.
A test which maintained an exposure over several shutter speeds does show a slight extra exposure when at 1/500 which is expected.
The remainder of the film was shot in my Nikon F70. All of these were good exposures (poor subject matter for my tests).
Now to find suitable scenes for film (although most of the exercise was simply to play with old (consumer level) cameras).

CLRwall.jpg
CLR test shot, nice neg density.


Benchf70.jpg
F70 shot of "my" bench (work in progress).
 
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