Underexposure with an ND filter

[Andi_77]

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Hello! As I was mentioning in another thread, after the theft of my M9 and lenses, I re-bought a camera (M9P) and three lenses (35, 50, 90). In the last few days I took many pictures, and the only problem I've had was my B+W ND filter.

The weird thing is that the images were all underexposed (a lot). As if the metering was not TTL (???!).

The only way to solve this was to use a +2 exposure compensation.

 

Any idea of the possible cause?

 

Thanks a lot!

A.

[tobey bilek]

Exposures without ND are ok ?

 

Repeat same time, same place, one with, one without ND. Use manual exposure, then try A so you can isolate the problem.

 

Shutter speeds correct? Maybe slower speeds are running fast.

[Andi_77]

Exposures without ND are ok ?

 

Yes, they're perfect...

 

Thank you for the tips, I'll definitely try them!

[250swb]

You don't say what strength your ND is but I find the greater the strength the greater the exposure compensation if metering with my MM. I have a three stop and no compensation is necessary, but I have a ten stop and about two stops are necessary. I simply assume that the meter progressively under reads the denser the filter.

 

Steve

[Andi_77]

Good point as well.

It's a 1000x by B+W, the darkest available (10 stops if I remember correctly their scale).

Now that I think about it, I always leave my camera with a -0.7 compensation, so that didn't help either, I guess. But even at +0.0 the pictures were still dark. I ended up overexposing by 2 stops, more or less.

Glad to know this is common.

[sm23221]

I just completed some long daylight exposures with a stacked 1,000 B+W and deep red filter on my Monochrom. Setting the dial to "A" produced black frames at any aperture. I ended up using Bulb and guessed the exposures with lots of latitude according to the histogram. Typical exposures were up to about 30 secs. I've never had problems with 3-stop ND's though.

[jip]

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I think it just is 'too dark' for the camera to make a accurate exposure measurement.

 

Haven't tried it on the M yet.

[250swb]

Glad to know this is common.

 

It is common to all meters. The best way to get an idea of the exposure you need is to take a reading without the filter and then add a ten stop adjustment, or a neater way is to use a good hand held meter (by good I mean it may even have enough latitude to factor in a ten stop adjustment on the display or dial without you having to use your fingers or toes). The thing to remember is that if you use the camera on Auto Exposure the shutter is limited to 32 seconds anyway, so use the B or T settings which allow up to 240 seconds.

 

 

 

Steve

[tobey bilek]

The proper way to use any colored filter is to meter without the filter, then add the filter and manually add more exposure according to the filter factor for the particular filter.

 

Yellows will meter fairly close right thru the filter, but as you get into the darker ones like red, the meter will not read properly. It is overly sensitive to red if I remember.

 

I neve no experience with ND except for polas which are only 1.5 to 2 stops.

 

I have worked extensively with really dark IR filters and I used to set a false film speed and meter thru the lens. This was to compensate for the metering deficiency at low light and to compensate for the lack of blue color.

 

To find the filter factor , meter a grey board in the same light as your photos, find the correct exposure, add the filter, and then find the new correct exposure. It will be around 3 stops with #25 red, more with #29 red.

 

10 stops may be getting the camera metering out of the designed range of light metering specially if you add 3 stops more red.

 

I would find the correction factor with a grey board for the combination and use that as a starting point from now on. There may still be issues based on subject color as the meter does not see all colors equally which is why you can not or should not meter thru a colored filter and why the filter factor factor is made with white or grey board as a test. Old grey blacktop road will work ok.

 

There are lots of factors involved here and that is why you need to meter without the filters.

[honcho]

Good point as well.

It's a 1000x by B+W, the darkest available (10 stops if I remember correctly their scale).........

 

As a rule of thumb, with film increase your exposure by one stop from your calculated reading with reciprocity compensation per each 8 stops of neutral density. As an example, If your metered exposure tells you that 1 minute is correct with a 3.0 nd, you need to increase your exposure to 2 minutes as a starting point. Forget trying to meter through a 3.0 nd or stronger combination with your camera ttl meter, you need to use a hand held meter for long exposures.

 

Your camera is possibly limited to a maximum timed exposure of about 240 seconds which is not is long enough for 'long' exposures but is long enough to smooth out water and blur some cloud movement if that is the effect you are trying to achieve. To remove traffic and people from urban scenes you will need much longer exposure times which are beyond your camera.

[jaapv]

The proper way to use any colored filter is to meter without the filter, then add the filter and manually add more exposure according to the filter factor for the particular filter.

 

Yellows will meter fairly close right thru the filter, but as you get into the darker ones like red, the meter will not read properly. It is overly sensitive to red if I remember.

 

I neve no experience with ND except for polas which are only 1.5 to 2 stops.

 

I have worked extensively with really dark IR filters and I used to set a false film speed and meter thru the lens. This was to compensate for the metering deficiency at low light and to compensate for the lack of blue color.

 

To find the filter factor , meter a grey board in the same light as your photos, find the correct exposure, add the filter, and then find the new correct exposure. It will be around 3 stops with #25 red, more with #29 red.

 

10 stops may be getting the camera metering out of the designed range of light metering specially if you add 3 stops more red.

 

I would find the correction factor with a grey board for the combination and use that as a starting point from now on. There may still be issues based on subject color as the meter does not see all colors equally which is why you can not or should not meter thru a colored filter and why the filter factor factor is made with white or grey board as a test. Old grey blacktop road will work ok.

 

There are lots of factors involved here and that is why you need to meter without the filters.

 

A bit puzzled by this as my M8 measures correctly with an 093 filter on (Far Red and IR pass).

The problem with using filter factors is that they do not take the spectral range of the light falling onto your subject into account.

[Andi_77]

Anyway, I was a bit puzzled because I was used to my 5D that could handle the same type of filter (same factor) with no issues and no need to compensate.

If this is normal, then no worries, I'll simply try to find the right compensation. As long as my camera isn't faulty, I'm OK

[honcho]

It's likely the 3.0 nd filter is sometimes too strong for the maximum timed exposure your M9p is capable of, so you are limited to using it in full daylight beyond dawn or dusk unless you use weaker nd filters such as 1.8, 1.2, 0.9 etc to keep within the camera's exposure limits.

 

For truly long exposures you'll need to use a camera or back that is up to the task, such as an IQ260.......or film.

[farnz]

Sounds to me like a combination of a very dense ND filter, reciprocity failure, and not enough time available with Bulb. Try using a less dense ND filter to put your exposure back in the usable range.

 

Pete.

[Andi_77]

Thank you but... we're talking about 4 or 5 seconds exposures, so still within a normal range.

I simply think it's a combination of those factors:

- the M9P doesn't handle low-light metering perfectly (as I said, I'm used to a 5D Mk III which gave me no problems in the past with an identical filter)

- my standard setting (-0.7 stops compensation) ruined the first shots...

- ...and probably the best setting for this type of light and filter is around +1/+2 compensation

 

[jaapv]

Sounds to me like a combination of a very dense ND filter, reciprocity failure, and not enough time available with Bulb. Try using a less dense ND filter to put your exposure back in the usable range.

 

Pete.

As far as I am aware digital cameras have no reciprociy failure - exclusively on film.

[Andi_77]

As far as I am aware digital cameras have no reciprociy failure - exclusively on film.

 

That's what I thought as well.

[honcho]

The problem is not reciprocity failure. It's the OP's camera technique, especially the metering method, which is questionable.

 

What is the rationale behind using a constant -0.7 stop 'compensation'? Deliberately underexposing with a 3.0 nd filter makes no sense.

 

Again, forget the M9p ttl meter and set your compensation to +/-0. Ideally you need a hand held meter for calculating long exposures with anything stronger than a 0.3 nd.

 

From 2.0 nd, increase your calculated reading by 1 stop and work around this as a starting point, with a 3.0 nd you may need 2, 3 or more stops increase especially if using wide angle lenses. You will only find out by experimenting in a controlled way but you won't learn much by leaving it to a rudimentary ttl centre-weighted M9p meter and arbitrary -0.7 compensation.

 

If you don't have a suitable hand held meter, try using your Canon meter on matrix (unfiltered) and transfer your calculated settings to your Leica as a starting point.

[Andi_77]

What is the rationale behind using a constant -0.7 stop 'compensation'? Deliberately underexposing with a 3.0 nd filter makes no sense.

 

The -0.7 exposure compensation is my standard setup without the ND filter.

 

The rationale is that this leads to less clippings when I'm in a hurry and I take a quick snapshot without having the time to think about the exposure.

 

I explained this point because it partially explains why the first shots with the ND filter were too underexposed.

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Hallo,

Look here: Leica M

[jaapv]

Your exposure meter must be out of adjustment. I don't use any compensation and my exposures are normally spot-on. If it is meant as safety buffer, you are throwing away nearly one stop of dynamic range.