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I am a beginner to nd filters. Im still debating if i need a variable filter or not. If i buy a 6 stop filter nonvariable or a 10 stop filter couldn't i just turn the iso up if its too dark. Why would i get a 6 stop or 3 stop. Could a single 3 stop be emulated by a 10 stop with a higher iso? What woild be the difference.

Also if they would be the same why would one need a variable nd filter. If he could buy a 10 stop and control the iso to move up to a 6 stop or 3 stop

Sorry for the beginner question.

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ISO isn't magic. When you turn up the iso you're increasing the gain on an amplifier that is amplifying an analogue signal – the light hitting the sensor – and when you amplify a signal you amplify the noise. Remember that opening up a stop is a doubling the light intensity. To get ten stops of gain on a camera with native iso of, say 200, you'd have to go to iso 204800. So whacking a 10 stop ND (also known as a 'Black Filter' because you could literally use it as welding goggles) on the front would mean that all you'd get is noise soup.

A 10 stop ND is really only useful for the harshest sunlight with a fast lens with a wide open aperture, or for still and time-lapse photography if you want extremely long exposures. It's certainly not the first filter I would buy as a beginner.

A Variable ND filter allows you to change the exposure in bright conditions without affecting other picture characteristics. Increasing the f-stop increases your depth of field, which may be undesirable, and increasing the shutter speed (i.e. reducing the exposure time) reduces motion blur, which may mean more strob-y motion (as you often see in sports coverage), again, this may not be desirable.

So a variable ND changes the exposure without changing the feel of the shot as the other ways of reducing exposure do. One thing to be aware of is that some variable ND filters do cause colour shifts across their range. So if you go for a bargain basement one off ebay buy a Macbeth card at the same time because you will have to compensate in post.

  • Nice answer. Just for the sake of argument, if you need to use a cinema camera with a base ISO of 800 and a wide aperture on a sunny day, you might easily require 10+ stops of ND. – Duvrai Nov 27 '16 at 15:05
  • Good point, but I somehow don't think the OP is shooting on a Red Dragon with a Schneider Xenon on the front. – stib Nov 28 '16 at 8:49
  • He could just be using a Blackmagic Cinema Camera with a Sayang lens... – Duvrai Nov 28 '16 at 22:02
  • I use a BMCC, and I was going to say I've never needed more than 6 stops of ND, even shooting in the Australian outback, but then I checked my variable ND and it's 8 stops. So I'm completely wrong there. With faster glass than my usual Canon 16-35 I might just need a 10 stop ND. I'll edit the answer. – stib Nov 29 '16 at 0:43
  • Get one ND filter and one A7SII ... :) – A.J. Hernandez Nov 29 '16 at 3:49

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