Wrong metering with Neutral Denstiy Filter, compensation required?

[emlee]

hi,
I recently got myself a neutral density filter and tested it. I can't help but noticed a few differences between shots with and without the filter on the same scene/lighting/time:
1) the colour balance is slightly different (expected)
2) the camera metered settings are 2-3 stops higher. e.g. shutter at 1/400 without the filter became 1/100 with the filter (expected with ND8 filter)
3) the metered outcome, however, is about 1.5 - 1.7 stop darker than the picture without the ND filter. i.e. I have to adjust the RAW image by increasing the exposure by 1.5 - 1.7 stop to achieve similar lighting (unexpected)

[used the ND8 on top of the UV filter, didn't think it'd make any difference]

My question: do you also experience wrong camera metering when using ND filters? Is it common to have to compensate for lighting when using ND filter?

thanks in advance for your advice/comments.

 

[zac08]

hi,
I recently got myself a neutral density filter and tested it. I can't help but noticed a few differences between shots with and without the filter on the same scene/lighting/time:
1) the colour balance is slightly different (expected)
2) the camera metered settings are 2-3 stops higher. e.g. shutter at 1/400 without the filter became 1/100 with the filter (expected with ND8 filter)
3) the metered outcome, however, is about 1.5 - 1.7 stop darker than the picture without the ND filter. i.e. I have to adjust the RAW image by increasing the exposure by 1.5 - 1.7 stop to achieve similar lighting (unexpected)

[used the ND8 on top of the UV filter, didn't think it'd make any difference]

My question: do you also experience wrong camera metering when using ND filters? Is it common to have to compensate for lighting when using ND filter?

thanks in advance for your advice/comments.

The camera metering is TTL. Thru the lens, so whatever you add in front of the lens will affect the metering values.

But it should not be darker unless you are not using the correct metering mode. Which mode are you using? And the shooting mode as well... ?

 

[emlee]

The camera metering is TTL. Thru the lens, so whatever you add in front of the lens will affect the metering values.

But it should not be darker unless you are not using the correct metering mode. Which mode are you using? And the shooting mode as well... ?

my thoughts exactly. I tried using Av and P, both produced same results. Evaluative metering. The settings will change (e.g. slower shutter, bigger aperture), but the result brightness of the picture should be the same. But all my test shots require adjustment of +1.5 to +1.7 stop in RAW format for the picture to have the same brightness as the shot without the filter. :dunno:

 

[LittleWolf]

1) the colour balance is slightly different (expected)

Not expected... the "N" in "ND" means "neutral".

2) the camera metered settings are 2-3 stops higher. e.g. shutter at 1/400 without the filter became 1/100 with the filter (expected with ND8 filter)

ND8 should attenuate the light by a factor of 8, or 3 stops. Assuming that the filter really does what is it supposed to do, if the metered exposure changes by only 2-3 stops, the resulting picture will be 0-1 stops less exposed (underexposed) compared to the picture without ND filter.

3) the metered outcome, however, is about 1.5 - 1.7 stop darker than the picture without the ND filter. i.e. I have to adjust the RAW image by increasing the exposure by 1.5 - 1.7 stop to achieve similar lighting (unexpected)

What type of camera/metering system are you using? If the filter is not strictly neutral (see point 1), and the image sensor of the camera has a different spectral response than the metering sensor, you could get such strange effects. I could think about the filter not doing its job properly in the deep red/infrared region. Since you mentioned a different colour balance, do the pictures taken with the filter look a bit more "warm" (reddish)?

 

[Splutter]

Depending on the brand of your ND filter, the attenuation might not be that even. I'm pretty sure it won't be a perfect 3 stops too. Also, colour shift is common, unless you are using super expensive brands like Singh Ray or Lee.

 

[zac08]

my thoughts exactly. I tried using Av and P, both produced same results. Evaluative metering. The settings will change (e.g. slower shutter, bigger aperture), but the result brightness of the picture should be the same. But all my test shots require adjustment of +1.5 to +1.7 stop in RAW format for the picture to have the same brightness as the shot without the filter. :dunno:

Btw, was the aperture opened up to the max already??

 

[alexj]

Hmm... 1/400 to 1/100 is 2 stops. Yours is a 3-stop ND; would expect 1/50. Another possible, but I suppose rare situation would be the filters stacking caused internal reflections (from the sunlight entering the lens at particular angles; assuming the filters are not parallel due to manufacturing or whatnot), so your evaluative metering took into account of that too... like I said, Rare..

ND filters require fixed exposure compensation; ND8 is 3-stops, and shouldn't be 2-3 stops. Other filters like polarizer require 1.5 to 2 stops due to variance in the amount of polarization you require...

Would suggest bringing back to where you bought it and test it on other cameras.

 

[night86mare]

not sure, for nd filter you *should* be getting good meterings or at least close. the disparity here is too large.

but in any case, usually when a camera behaves a certain way with a certain filter.. you'll be sure that it will happen all the time in the same way given similar conditions.

perhaps, if you have a picture to show what sort of lighting condition were prsent during the time of shooting?

 

[psychobiologist]

hi,
I recently got myself a neutral density filter and tested it. I can't help but noticed a few differences between shots with and without the filter on the same scene/lighting/time:
1) the colour balance is slightly different (expected)
2) the camera metered settings are 2-3 stops higher. e.g. shutter at 1/400 without the filter became 1/100 with the filter (expected with ND8 filter)
3) the metered outcome, however, is about 1.5 - 1.7 stop darker than the picture without the ND filter. i.e. I have to adjust the RAW image by increasing the exposure by 1.5 - 1.7 stop to achieve similar lighting (unexpected)

[used the ND8 on top of the UV filter, didn't think it'd make any difference]

My question: do you also experience wrong camera metering when using ND filters? Is it common to have to compensate for lighting when using ND filter?

thanks in advance for your advice/comments.

ya, when there is less light coming in, the metering for the lens often goes awry if its on a slow lens. even focussing screen also affects if you change it to an el-cheapo MIC one ;(

 

[emlee]

thank you all for the comments. here are 2 test shots:
with filter
1/100
f/5.0

without filter
1/800
f/5.0

the pictures were taken 20 secs apart for removing the filter.
no process here except converting from RAW to JPG.

 

[grantyale]

Did you leave the viewfinder exposed when metering? Or, was your face pressed against the camera?

 

[emlee]

Did you leave the viewfinder exposed when metering? Or, was your face pressed against the camera?

my eye was peering through the viewfinder.

 

[grantyale]

So that takes out the possibility of stray light from VF affecting metering.
What was the metering mode and which AF point(s) was used?

 

[catchlights]

what is your purposes of using ND filter to shoot? what effect you want to archive?

 

[night86mare]

the pictures were taken 20 secs apart for removing the filter.
no process here except converting from RAW to JPG.

hrm, the condition looks the same to me.

well if this is the case, then be grateful for immediate feedback, i guess.. no camera is perfect.

 

[LittleWolf]

the pictures were taken 20 secs apart for removing the filter.
no process here except converting from RAW to JPG.

Interestingly, the metering of the camera reflects the nominal difference (factor 8) the filter should make.

How reproducible is the effect on the pictures when you take several pictures in a row? Does it also happen when you open the aperture all the way? I've seen lenses where a bad aperture mechanism resulted in random exposure variations...

Edit: If the EXIF tags are to be believed, the first picture was taken at 1/125s, not 1/100s, which would make only 2.7 stops difference. Also, as grantyale points out in the post below, make sure you don't use evaluative metering - it is pretty much a random number generator.

To determine the effect of the filter, you could try a series of different exposures in manual mode. That should make it clearer what part of your troubles can be attributed to the filter, and what part to the camera/lens.

 

[grantyale]

If the camera was set in AF-point auto selection, probably the slight difference in composition has caused the camera to pick up different things and thus affecting AE.

Anyway... does this happen consistently or just for these two photos?

 

[calebk]

If the camera was set in AF-point auto selection, probably the slight difference in composition has caused the camera to pick up different things and thus affecting AE.

Anyway... does this happen consistently or just for these two photos?

IIRC, the only camera that spot-meters to the AF point is the 1D series with a certain custom function enabled. Otherwise, spot meter is to the center circle of the viewfinder. Not sure if TS is on a 1D though...

 

[grantyale]

Doesn't have to be spot metering. Evaluative is linked to active AF point anyway.

 

[calebk]

Doesn't have to be spot metering. Evaluative is linked to active AF point anyway.

But only on 1-series cameras, right?