ND settings question

Sydh

Sydh

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Syd
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Brand new member to the forum (filled in the welcome post) so here is my first question.
Just recently bought my first 10 stop ND and I have found a strange result. Setting the camera to aperture priority, the metering recommended around 20 second exposure, but the result was under exposed, despite the camera probably tried upping the ISO. I then removed the filter and took a standard reading using the same aperture, changed to manual and bulb, calculated the exposure as around 2 minutes, and got a perfect photo.
So am I right in assuming the meter can be fooled by ND filters? It's a Nikon D7100 so presumably a decent metering system.
Further to that, I will also be using a 3 stop 0.9 ND. Is this OK with metering or should this also be done manually with a quick calculation?
Thanks for any advice.
 
A 10 stop won't give you satisfactory results in Aperture Priority. Use Manual. I now know that 1/100th without is about 20 seconds with when using my particular ND110 - B+W.

I'm pretty certain I have used my 3 stop before in Av - I may be wrong though.... If not just Manual mode that one too - It's only a few clicks ;)
 
Cameras will have an upper limit on how long a shutter speed they will set in things like Aperture Priority - not sure about the Nikon but for example my EOS won't go over 30 seconds in Av even if this leads to under exposure. So as has been said work out the correct exposure without the filter and then calculate the shutter speed you need with it in place and use either manual or bulb depending on how long the shutter needs to be open if this is longer than the camera can set for itself in Av. That's the way for a Big Stopper type filter where you're likely to run into these very long exposures.
It's likely to be less of a problem with a 3 stop as it cuts the light down to an eighth so you're less likely to get the very long exposures so as long as it's within the range your camera can set in Av then it should work OK - otherwise if it's longer use the manual/bulb approach.
 
Thanks guys. The camera will go up to 30 seconds, but even when it exposed at 20 seconds with presumably an adjusted ISO, it was under exposed compared to my manual shot of 2 minutes at 100 ISO. Hence I wondered if even at 20 seconds maybe the camera was not a good judge while looking through a 10 stop. Seems I will use the 10 stop on manual as you recommend. I will play around with the 3 stop the same way for the same comparison. Whoever said photography was an exact science with all this technology. Once again, thanks for your time.
 
Syd, you're right in taking a reading without the filter then calculating manually or using a phone app. The sensors can't work correctly with the filter in place in the same way that you won't be able to see clearly through the viewfinder.


Just watch your exposure calculation in variable (early/light) light. At dawn you will need to reduce your times and dusk extend it as the light will change across the duration of the long exposure (not so much so for your 20 sec example above)
 
It's also worth noting that some 10 stop filters can actually be darker than 10 stops, it can vary a lot. I know my Lee 10 stop is probably closer to 11/12 stops. If I use a 10 stop calculation with it, it'll be underexposed.
 
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