Author Topic: ND and ND Grad Filters  (Read 4539 times)

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Offline Faldrax

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ND and ND Grad Filters
« on: June 25, 2011, 11:26:16 PM »
For the experts at using ND and Grad filters, I though I'd just ask a quick Q on how you actually use them, in terms of the sequence of events in taking a shot.

So, as I understand it;

For ND Grads you meter the bright area (typically the sky) an meter the dark area, and figure out the difference (in stops) - this gives you the strength of Grad to use (assuming you have a choice).

For ND filters you meter without the grads (in the dark area if subsequently combining with Grad filter), calculate the number of stops required for the shutter speed you want, this gives the strength of ND filter you want.

The sequence (I am guessing), is then

1) Compose shot.
2) Set focus (either manual of AF).
3) Switch to MF to lock the focus.
4) Switch to manual, set exposure for dark area, then adjust for ND's
4) Slot in Grad & adjust height.
5) Slot in ND.
6) Take shot, review, adjust expose and re-shoot as required.

Does this sound right, or is a different sequence better?




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Offline Rob aka [minolta mad]

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Re: ND and ND Grad Filters
« Reply #1 on: June 26, 2011, 11:22:28 AM »
1)  Yes
2)  Yes, though i always use MF
3)  If using MF this is not needed. If using a 10 stop ND you will have to MF as the camera will keep hunting for focus
4)  Switch to Manual and set exposure for dark area
5)  Slot in ND grad(s) adjust to correct height and take an image to check for exposure, add remove ND Grads as required
6)  Take note of correct exposure and slot in ND. Calculate the exposure difference depending on strength of ND
7)  Yes.

Bear in mind if using a 10 stop ND around or just after sunset that the light is changing all the time and if you have calculated a 100 sec exposure and its say 2 stops underexposed, that by the time you have taken another exposure of 120 (est) (to allow for the 2 stops of underexposure) this image could still be underexposed as the light could have dropped in those 2 Min's by another 1-2 stops.

What i tend to do is that if i have taken an image of 100 secs and it was 2 stops underexposed is add the 2 stops more exposure and allow another 20%. So if you had a 100 sec exposure and added another 2 stops (say 20 secs for argument) i would then add another 25 seconds (20 % error, as i call it)

Hope this helps.


Rob

Offline Faldrax

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Re: ND and ND Grad Filters
« Reply #2 on: June 27, 2011, 09:12:53 AM »
Thanks Rob, good to know I was on the right lines.

Useful note about changing light when taking a long exposure - I suspect it would be easy to assume I had made the wrong adjustment or calculation for exposure in such a circumstance, and so repeat the same 'mistake' on the next attempt.
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Offline Rob aka [minolta mad]

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Re: ND and ND Grad Filters
« Reply #3 on: June 27, 2011, 10:08:50 PM »
The changing light is something that catches a few people out, myself included.
I took some images recently with the 10 stop ND of 300 ish seconds and they were underexposed, so made a recalculation and come up with 580 sec exp, so 580 seconds later the image was just as underxposed as the 300 second one.

I then gave up and took some 'normal images'


Rob