ND filter
- Thread starter adamg
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Adam, 1 minute exposure in what sort of light?
The Sunny-16 rule says that in bright sunlight the correct exposure is normally the reciprocal of your ISO value at f/16. In other words, at ISO 100 - the least sensitive you can make your 400D - you'd need 1/100th at f/16. You probably don't want to stop down smaller than f/16, because you'll start to lose sharpness. So in bright sunlight, 1/100th is the slowest you can go without an ND filter.
If your filter reduces the light coming into the lens by one stop, your shutter speed will be 1/50th. Two stops: 1/25th. And so on. By my calculation you need to reduce the light by about 12½ stops to get to a 1-minute exposure.
The extended Sunny-16 rule in that Wikipedia article I linked to suggests that slight/normal/heavy overcast conditions offer about 1/2/3 stops less light than sunlight. So in those conditions your ND filter only needs to take out about 11½/10½/9½ stops.
If you go to a shop like this one (not necessarily recommended - just the first one I found on Google) you'll find ND filters in a range of strengths. Remember to get the right size for your lens, which I believe is 52mm.
The Sunny-16 rule says that in bright sunlight the correct exposure is normally the reciprocal of your ISO value at f/16. In other words, at ISO 100 - the least sensitive you can make your 400D - you'd need 1/100th at f/16. You probably don't want to stop down smaller than f/16, because you'll start to lose sharpness. So in bright sunlight, 1/100th is the slowest you can go without an ND filter.
If your filter reduces the light coming into the lens by one stop, your shutter speed will be 1/50th. Two stops: 1/25th. And so on. By my calculation you need to reduce the light by about 12½ stops to get to a 1-minute exposure.
The extended Sunny-16 rule in that Wikipedia article I linked to suggests that slight/normal/heavy overcast conditions offer about 1/2/3 stops less light than sunlight. So in those conditions your ND filter only needs to take out about 11½/10½/9½ stops.
If you go to a shop like this one (not necessarily recommended - just the first one I found on Google) you'll find ND filters in a range of strengths. Remember to get the right size for your lens, which I believe is 52mm.
Messiah Khan
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The B+W Neutral Density Filter 110 that StewartR linked to is the one you want. I have the 52mm version, and have just bought a 77mm version to fit my 10-20mm. 
cheers for your help mate. its for taking photos at dusk mainly. i think 1min is a bit OTT, more like 20seconds...
The B+W Neutral Density Filter 110 that StewartR linked to is the one you want. I have the 52mm version, and have just bought a 77mm version to fit my 10-20mm.
cheers mate. i have changed my mind and think i will go for a 20/30second exposure. is it still worth getting the 110 or should i go for something else? also, this is probs a stupid question but because it says its a b&w neutral filter does that make the image b&w becuase i want to take the photos in colour. cheers!
Messiah Khan
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There are several ways of doing it; Getting the 110 and upping the ISO to 200, which would halve the exposure time. Or get a 9 stop filter. Im not sure if B&W do a 9 stop filter though. You mention shooting "at dusk". This will very much affect the exposure time, and you could quite probably get a 30second (or longer) exposure by simply stopping down to f22 and using ISO100 at dusk. What is the reason you want to extend the exposure time? Is it to smooth water, or blur people out of scenes etc? B&W doesn't mean its black and white by the way. It stands for Biermann and Weber (The makers). The filter will however create a quite strong redish cast over the whole image, which is inevitable through such a strong filter.
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I've given you all the tools you need to work out the answer to that question, or any variant of it, yourself ...
(Teach a man to fish, and all that.)
Well dusk isnt too bad but I also wanted it for just after sunrise when there is morning fog. Its usually too bright for any exposure longer than a few seconds. I also wanted it for blurring the clouds during daylight.
alright cheers mate