Calibrarting an exposure meter of one camera from another

As you may have noticed from my other posts, I normally use a Canon
300D. However a friend wants to play with 35mm and developing it
himself. This is something that I used to do long ago so I dragged
out an old and dusty Canon T70 to have a go myself. I remember one
problem of this camera, the auto-exposure seems to be miscalibrated.
My vague memory is that it overexposes by 1 or 2 stops but I am not
sure. I used to solve the problem by setting a higher ISO than was
really loaded. I was wondering if I could use the 300D to calibrate
the T70. The T70 will have 100 ISO black and white film. Can I set
the 300D to 100 ISO, point them both at the same scene (ensure an
equivalent focal length on the 300D), choose similar programs (e.g.
TV), set the same shutter speed, and the compare which aperture the
cameras select? If so, what subject would be best? Maybe a plain
white wall, maybe deliberately out of focus? I had a brief go and it
seemed to confirm that the T70 was overexposing but the results were
not consisent. They varied from agreement to 2 stops higher on the
T70.

This would save me blowing a roll of film just to sort the issue out.
Also, since I will be out of practise with developing, if the film
comes out wrong, I won't know whether to blame the camera or the
processing.

--
Seán O'Leathlóbhair

On May 3, 7:28 am, Seán O'Leathlóbhair <jwlaw...@yahoo.com> wrote:
> As you may have noticed from my other posts, I normally use a Canon
> 300D. However a friend wants to play with 35mm and developing it
> himself. This is something that I used to do long ago so I dragged
> out an old and dusty Canon T70 to have a go myself. I remember one
> problem of this camera, the auto-exposure seems to be miscalibrated.
> My vague memory is that it overexposes by 1 or 2 stops but I am not
> sure. I used to solve the problem by setting a higher ISO than was
> really loaded. I was wondering if I could use the 300D to calibrate
> the T70. The T70 will have 100 ISO black and white film. Can I set
> the 300D to 100 ISO, point them both at the same scene (ensure an
> equivalent focal length on the 300D), choose similar programs (e.g.
> TV), set the same shutter speed, and the compare which aperture the
> cameras select? If so, what subject would be best? Maybe a plain
> white wall, maybe deliberately out of focus? I had a brief go and it
> seemed to confirm that the T70 was overexposing but the results were
> not consisent. They varied from agreement to 2 stops higher on the
> T70.
>
> This would save me blowing a roll of film just to sort the issue out.
> Also, since I will be out of practise with developing, if the film
> comes out wrong, I won't know whether to blame the camera or the
> processing.

Starting backward, it would probably be better to use a roll of color
slide film to test whether your exposure compensation is correct, as
slide film has much less exposure latitude than negative film, and
with slides you get WYSIWYG results to look at, whereas unless you are
experienced at reading b/w negatives, you will have to judge the
exposure from a b/w print, and in that case you introduce the further,
significant variable of the way the negative is printed. Either way,
you are only going to "blow" something like US $15 at most for both
film and processing.

If the sensor in the film camera is not functioning properly, it could
be malfunctioning on a non-consistent basis; i.e., it might be
accurate at some EVs but not at others, or inconsistently accurate
across the range of EVs. I had this problem on a used camera once.
Therefore, setting your ISO to compensate might not be a complete
solution. One way to test this is to go through the full range of
shutter speed/aperture combinations, and check whether you
consistently meter a twofold reduction/increase in shutter speed for
every f/stop increment, and a one f/stop difference for every doubling/
halving of the shutter speed.

Any uniform subject would probably suffice for metering, but if I had
to do this I would go with something more toward the middle tones,
like a gray card or just plain grass, which in my experience usually
has a reflectance very close to neutral grey, since this is what
meters are designed to interpret.

HTH.

--
YOP...

On 3 May, 16:24, Nervous Nick <nervous.n...@gmail.com> wrote:
> On May 3, 7:28 am, Seán O'Leathlóbhair <jwlaw...@yahoo.com> wrote:
>
>
>
>
>
> > As you may have noticed from my other posts, I normally use a Canon
> > 300D. However a friend wants to play with 35mm and developing it
> > himself. This is something that I used to do long ago so I dragged
> > out an old and dusty Canon T70 to have a go myself. I remember one
> > problem of this camera, the auto-exposure seems to be miscalibrated.
> > My vague memory is that it overexposes by 1 or 2 stops but I am not
> > sure. I used to solve the problem by setting a higher ISO than was
> > really loaded. I was wondering if I could use the 300D to calibrate
> > the T70. The T70 will have 100 ISO black and white film. Can I set
> > the 300D to 100 ISO, point them both at the same scene (ensure an
> > equivalent focal length on the 300D), choose similar programs (e.g.
> > TV), set the same shutter speed, and the compare which aperture the
> > cameras select? If so, what subject would be best? Maybe a plain
> > white wall, maybe deliberately out of focus? I had a brief go and it
> > seemed to confirm that the T70 was overexposing but the results were
> > not consisent. They varied from agreement to 2 stops higher on the
> > T70.
>
> > This would save me blowing a roll of film just to sort the issue out.
> > Also, since I will be out of practise with developing, if the film
> > comes out wrong, I won't know whether to blame the camera or the
> > processing.
>
> Starting backward, it would probably be better to use a roll of color
> slide film to test whether your exposure compensation is correct, as
> slide film has much less exposure latitude than negative film, and
> with slides you get WYSIWYG results to look at, whereas unless you are
> experienced at reading b/w negatives, you will have to judge the
> exposure from a b/w print, and in that case you introduce the further,
> significant variable of the way the negative is printed. Either way,
> you are only going to "blow" something like US $15 at most for both
> film and processing.
>
> If the sensor in the film camera is not functioning properly, it could
> be malfunctioning on a non-consistent basis; i.e., it might be
> accurate at some EVs but not at others, or inconsistently accurate
> across the range of EVs. I had this problem on a used camera once.
> Therefore, setting your ISO to compensate might not be a complete
> solution. One way to test this is to go through the full range of
> shutter speed/aperture combinations, and check whether you
> consistently meter a twofold reduction/increase in shutter speed for
> every f/stop increment, and a one f/stop difference for every doubling/
> halving of the shutter speed.
>
> Any uniform subject would probably suffice for metering, but if I had
> to do this I would go with something more toward the middle tones,
> like a gray card or just plain grass, which in my experience usually
> has a reflectance very close to neutral grey, since this is what
> meters are designed to interpret.
>
> HTH.


Thanks for the suggestions.

I think that the error is consistent. It is not second hand, it is my
camera but I have not used it for about 20 years. I remember that I
needed to adjust the ISO and once I did, the results were fine.
Mostly colour print but sometimes slide. The problem is that I have
forgotten the necessary adjustment. Of course, the camera could have
degraded in this long period of neglect, does anyone know if this is
likely? I was rather surprised that the battery still had some life
in it.

I did already shoot and process one roll of ISO 100 black and white.
I started with a shot of a court yard (maybe not a good choice), first
with the correct ISO set and an auto-exposure program. I noted the
shutter speed and aperture and then switched to manual, set the same
speed, shot the same scene with a series of wider and narrower
apertures. Then I dialled in my guessed 2 stop correction (i.e. ISO
400) and finished off the film. It was very hard to interpret the
test shots. So much so that I was beginning to doubt my notes of the
settings used since they did not seem to fit what I was seeing. The
shots made at ISO 400 were reasonable and there were a few nice
photos. They were probably a bit underexposed. 2 stops may have been
too much of a compensation. Maybe my memory was wrong and the correct
compensation was two steps (i.e. 2/3 of a stop) rather than 2 stops.
Alternatively, my development may have been faulty, it is a long time
since I have done it. I did not print the negatives traditionally. I
scanned them, converted to positive by the scanner's software, and
continued in Photoshop.

So, I want to repeat the test in a more effective way. I actually
have a grey card, I feel a bit stupid for not thinking of it. It was
not available at the time of the first test but I should have thought
of it for the repeat. One idea of mine was to write the exposure
settings on a card and include it in the photo so that there is no
doubt which photo was taken with which settings.

Judging from your suggestions, you don't appear to like the comparison
against the other camera. I need to shoot and process some film,
preferably slide, to do this job well? It is a good idea to test at
different EVs and I will do it but, as I said, the error used to be
consistent. I will forget the flash. I can't be bothered with the
old manual flash. If the shot wants flash I will use the 300D and
580EX (but see my other question of today).

There is the separate question of whether to bother anyway. My
research is beginning to convince me that for most purposes (including
anything that I do), digital is as good as or better than 35mm.
Nonetheless, I liked some of the 35mm black and white shots, they
seemed somehow more artistic in a way I could not quantify.
Obviously, I could use my 300D and post process to black and white.
This has possibilities but somehow, the results don't seem quite the
same. It may be just a question of lenses, I have a 50mm f/1.4 on the
T70 which can give plenty of bokeh but only a 50mm f/1.8 on the 300D
which has rather less bokeh potential. The shots that I liked from
the T70 were head and shoulders taken wide open in a poorly lit cafe
without flash. The background is well out of focus and it gives the
shots a nice feel.

--
Seán O'Leathlóbhair

I frequently cross check cameras and exposure meters.
I don't see why you need to run off film to do this, unless you want to
check the shutter and apertures. If you keep a record of the exposure for
each frame then issues with processing of the film should be cancelled out.
Unless you process your own film under tightly controlled conditions you
will see differences in density that you will likely interpret as due to
exposure issues when it is really a processing issue.
One problem if you observe differences metering complex scenes has to do
with the fact that different camera brands use different evaluative
algorithms. However the differences should be within fractions of an f-stop.
I believe camera manufacturers even twenty years ago assumed most people
would be shooting negative film with its wider latitude anyway.
Theoretically transparency film sent to a reliable, high quality lab should
be less subject to variations in development but not necessarily.

On 3 May, 23:38, "babaloo" <fac...@hotmail.com> wrote:
> I frequently cross check cameras and exposure meters.
> I don't see why you need to run off film to do this, unless you want to
> check the shutter and apertures. If you keep a record of the exposure for
> each frame then issues with processing of the film should be cancelled out.
> Unless you process your own film under tightly controlled conditions you
> will see differences in density that you will likely interpret as due to
> exposure issues when it is really a processing issue.
> One problem if you observe differences metering complex scenes has to do
> with the fact that different camera brands use different evaluative
> algorithms. However the differences should be within fractions of an f-stop.
> I believe camera manufacturers even twenty years ago assumed most people
> would be shooting negative film with its wider latitude anyway.
> Theoretically transparency film sent to a reliable, high quality lab should
> be less subject to variations in development but not necessarily.

The real question here is whether the cross check is reasonable
considering the very different technology. A 1980s 35mm SLR and a
relatively new digital SLR. Do they really mean the same thing by ISO
100? I guess that the 35mm SLR should aim to be correct since the
film is produced separately from the body. On the other hand, since
the meter and sensor in the digital cannot be separated, they may only
be a nominal ISO 100 and as long as they agree with each other, it
would not matter too much if they were actually some way off 100.
When I first used a digital SLR, I was very surprised by the ISO
setting. Since the sensor was not interchangeable (unlike the film in
the old days), I had expected that it would have a certain sensitivity
and that was that. I did not expect to see ISO except maybe buried
deep in the technical specs. It took a while to get used to the
possibility of changing the ISO from shot to shot. I still forget
this possibility sometimes and struggle in low light with the ISO
still at 100 (where I tend to leave it for normal purposes). More
annoying is leaving the ISO high and taking shots that did not need it
to be so high.

The old SLR used to work well except for what appeared to be a
consistent overexposure so I am not too worried about shutter
operation, aperture control etc and don't plan to test them. If they
turn out to be defective, it will go in the bin. The one roll that I
have already shot recently, does not suggest a problem in this area.

I will probably go for a compromise. Start the next roll with a more
carefully planned and executed series of test shots. Then do the
cross check with the digital to calibrate the camera for the remaining
shots.

--
Seán O'Leathlóbhair