Light Metering with ND filter

Charles Topp · May 22, 2018

Hey. I have just got a mamiya RZ67 with 110mm lens and want to shoot at the maximum aperture to get great portraits. I'll need an ND8 (3stop) filter but don't know how to get accurate light meter readings with the ND filter on as the light meter will not have the same 3 stop difference and so will be 3 stops inaccurate.

I would put the same filter on my digital lens but it doesn't go down to 2.8.

Mainecoonmaniac · May 22, 2018

Readjust the ASA of your light meter (If it's external) accordingly. For example, ASA 400 will be ASA 100 if my math is correct. That's 3 stop difference between ASA 400 and 100.

bdial · May 22, 2018

You can meter through the filter if you're using a reflected light meter. Or else just set the camera for 3 stops more than what the meter says.
Also, some meters let you dial in a compensation factor, in which case you just meter normally and use the setting it shows. (But don't forget to reset the compensation when you're done with the filter). Finally, you could set the meter for a film speed that's 3 stops slower than whatever film you're using, assuming the meter lets you go down that low.

Paul Manuell · May 22, 2018

Charles Topp said:
Hey. I have just got a mamiya RZ67 with 110mm lens and want to shoot at the maximum aperture to get great portraits. I'll need an ND8 (3stop) filter but don't know how to get accurate light meter readings with the ND filter on as the light meter will not have the same 3 stop difference and so will be 3 stops inaccurate.

I would put the same filter on my digital lens but it doesn't go down to 2.8.

Not sure I understand this bit. What won't it have the same 3 stop difference as? Are you going to be taking a light meter reading with the filter ON the meter or off it? However you do it, it should be pretty simple to set the correct settings on your camera. If you're taking the reading with the filter ON the meter, set your camera's settings to whatever the meter says (assuming you're putting the filter onto the camera after taking readings with it on the meter). If you're taking meter readings with the filter OFF the meter, simply over expose by 3 stops when transferring the reading to your camera. So for instance, if the filterless meter says 1/125th at f 11, set either 1/15th at f11 or 125th at f3.5

tomkatf · May 22, 2018

Mainecoonmaniac said:
Readjust the ASA of your light meter (If it's external) accordingly. For example, ASA 400 will be ASA 100 if my math is correct. That's 3 stop difference between ASA 400 and 100.

Isn't that 2 stops? 400-200-100...400-200-100-50 should be three...

Charles Topp · May 22, 2018

bdial said:
You can meter through the filter if you're using a reflected light meter. Or else just set the camera for 3 stops more than what the meter says.
Also, some meters let you dial in a compensation factor, in which case you just meter normally and use the setting it shows. (But don't forget to reset the compensation when you're done with the filter). Finally, you could set the meter for a film speed that's 3 stops slower than whatever film you're using, assuming the meter lets you go down that low.

Thanks for the reply!! Do you have any recommendations of any light meters that allow for compensation?

Charles Topp · May 22, 2018

bdial said:
You can meter through the filter if you're using a reflected light meter. Or else just set the camera for 3 stops more than what the meter says.
Also, some meters let you dial in a compensation factor, in which case you just meter normally and use the setting it shows. (But don't forget to reset the compensation when you're done with the filter). Finally, you could set the meter for a film speed that's 3 stops slower than whatever film you're using, assuming the meter lets you go down that low.

Also do you mean I can just put the filter infront of the light meter? Would that give an accurate reading as the filter may not cover the whole light meter sensor

moto-uno · May 22, 2018

I've had good luck simply putting the filter in front of the light meter and taking the reading . ASA on meter
set the same as the film and I've been good to go . Worst case scenario is you do a test roll . Peter

Charles Topp · May 22, 2018

Mainecoonmaniac said:
Readjust the ASA of your light meter (If it's external) accordingly. For example, ASA 400 will be ASA 100 if my math is correct. That's 3 stop difference between ASA 400 and 100.

Does this not effect the quality of the image? Or does it not change anything?

MattKing · May 22, 2018

Charles Topp said:
Does this not effect the quality of the image? Or does it not change anything?

The only thing that a film's ISO speed tells you is what to set your meter at.
The ND filter doesn't change the film or camera at all, it just decreases the light that reaches the film (and the viewing screen, if you are using an SLR).
If your film has an ISO speed of 400 and you are using a separate hand meter, you need to take the ND3 filter into account by setting a different reading - an Exposure Index or "EI" - on your hand meter.
Set your hand meter to 50 (100 would be the setting for an ND2 filter).
Then set your camera to what the meter tells you.
If you are using a meter that is built into the camera and reads light after it goes through the filter, then set the ISO on the camera to 400 - reading through the meter compensates for its affect.

bdial · May 22, 2018

The Gossen Luna-Six (Luna Pro here) meters have filter factor compensation. Lots of other "pro" meters do as well, though I'm not sure of which specific ones off hand.

Most meters have a fairly small light sensor, so most filters will completely cover the sensor area, the filter doesn't need to fit tightly against the meter to be useful for this. But you would need to use the filter in it's reflected light mode as opposed to using an incident mode (Luna-sixes can be used both ways).

Mainecoonmaniac · May 22, 2018

Charles Topp said:
Does this not effect the quality of the image? Or does it not change anything?

Nope. Readjusting your (external) meter just "syncs" your meter with your combination of film speed and ND filters.

Chan Tran · May 22, 2018

Charles Topp said:
Hey. I have just got a mamiya RZ67 with 110mm lens and want to shoot at the maximum aperture to get great portraits. I'll need an ND8 (3stop) filter but don't know how to get accurate light meter readings with the ND filter on as the light meter will not have the same 3 stop difference and so will be 3 stops inaccurate.

I would put the same filter on my digital lens but it doesn't go down to 2.8.

Many ways to meter with the ND filter. You can put the filter in front of the meter if you use reflected mode. You can set the ISO 3 stops slower than your film. You can simply mentally increase exposure by 3 stops from what the meter read. They all give you accurate enough reading.

Sirius Glass · May 24, 2018

If the meter is behind the lens, then the meter will adjust for the filter. Otherwise reset the light meter for three stops slower [ISO 400 ==> 100, ISO 100 ==> 25].

MattKing · May 24, 2018

Sirius Glass said:
If the meter is behind the lens, then the meter will adjust for the filter. Otherwise reset the light meter for three stops slower [ISO 400 ==> 100, ISO 100 ==> 25].

Actually, ISO 50 is the end point.
400 - 200, 200 - 100, 100 - 50.

jwd722 · May 24, 2018

Check this out...http://www.alexwisephotography.net/blog/2009/07/23/neutral-density-reference-chart/

Marco Gilardetti · May 25, 2018

I have always thought that this idea of marking the exposure corrections on filters with "X-times" multiplying factors was - in a word - stupid. The only thing even more stupid than that is that it was never changed, since decades and decades and decades.

The surprising amount of mistakes and wrong figures reported in this thread confirms my opinion that using "X-times" multiplying factors is indeed a stupid idea in first place, which leads to frequent errors, and makers should change it immediately as there is no real reason not to change it to "number and/or fractions of stops".

msage · May 25, 2018

Marco Gilardetti said:
I have always thought that this idea of marking the exposure corrections on filters with "X-times" multiplying factors was - in a word - stupid. The only thing even more stupid than that is that it was never changed, since decades and decades and decades.

The surprising amount of mistakes and wrong figures reported in this thread confirms my opinion that using "X-times" multiplying factors is indeed a stupid idea in first place, which leads to frequent errors, and makers should change it immediately as there is no real reason not to change it to "number and/or fractions of stops".

Been using the "x-times" and "stops" methods for may years now. Simple and it works, never thought it was "stupid".

Sirius Glass · May 25, 2018

Sirius Glass said:
If the meter is behind the lens, then the meter will adjust for the filter. Otherwise reset the light meter for three stops slower [ISO 400 ==> 100, ISO 100 ==> 25].

MattKing said:
Actually, ISO 50 is the end point.
400 - 200, 200 - 100, 100 - 50.

But 100 ==> 50 is only one stop. I should have posted 100 ==> 12.5.

.

MattKing · May 25, 2018

Sirius Glass said:
But 100 ==> 50 is only one stop. I should have posted 100 ==> 12.5.

Or 400 --> 50 (not 100, as you posted)

Sirius Glass · May 26, 2018

MattKing said:
Or 400 --> 50 (not 100, as you posted)

Yes, I guess I am having a bad decade.

Light Metering with ND filter

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Light Metering with ND filter

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