Answers.Body: <p>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. </p>
  
  <p>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.</p>
  
  <p>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.</p>
  
  <p>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 <a href="http://nofilmschool.com/s/12969/149228" rel="nofollow noreferrer">compensate</a> in post.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-27T15:05:03.647Z
Answers.Text: 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.
Answers.UserDisplayName: Duvrai
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-28T08:49:56.313Z
Answers.Text: Good point, but I somehow don't think the OP is shooting on a Red Dragon with a Schneider Xenon on the front.
Answers.UserDisplayName: stib
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-28T22:02:12.630Z
Answers.Text: He could just be using a Blackmagic Cinema Camera with a Sayang lens...
Answers.UserDisplayName: Duvrai
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-29T00:43:17.157Z
Answers.Text: 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.
Answers.UserDisplayName: stib
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-29T03:49:55.123Z
Answers.Text: Get one ND filter and one A7SII ... :)
Answers.UserDisplayName: A.J. Hernandez
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-29T05:27:53.550Z
Answers.Text: @A.J Urgh XAVC? No thanks. I'll stick to my BMCC - who needs to expose correctly when you're shooting dng?
Answers.UserDisplayName: stib
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-29T05:33:54.903Z
Answers.Text: My previous comment was half sarcastic and half real... but external recorders record .mov out of HDMI if you're super concerned, plus the benefit with the A7SII is that it is the best low light camera EVER. Just because you shoot in dng doesn't mean you don't have to have the "right" settings or camera for a given situation.
Answers.UserDisplayName: A.J. Hernandez
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-23T12:52:46.610Z
Answers.LastActivityDate: 2016-11-29T00:51:27.543Z
Answers.LastEditDate: 2016-11-29T00:51:27.543Z
Answers.UserDisplayName: stib
Body: <p>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.</p>
  
  <p>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</p>
  
  <p>Sorry for the beginner question.</p>
  
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2016-11-24T18:18:29.307Z
Comments.Text: This question is better asked on http://photo.stackexchange.com/
Comments.UserDisplayName: Nayuki
Tags: <lenses>
Title: ND filters. Why variable?
UserDisplayName: TreeKing
ThreadText: # ND filters. Why variable?
  
  (Asked by: username_0 on 2016-11-23)
  
  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.
  
  **Tags:** lenses
  
  > **Comments:**
  > **username_1**: This question is better asked on http://photo.stackexchange.com/  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_2 on 2016-11-23. Score: 4 | Accepted answer
  
  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](http://nofilmschool.com/s/12969/149228) in post.
  
  > **Comments:**
  > **username_3**: 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.  
  > **username_2**: Good point, but I somehow don't think the OP is shooting on a Red Dragon with a Schneider Xenon on the front.  
  > **username_3**: He could just be using a Blackmagic Cinema Camera with a Sayang lens...  
  > **username_2**: 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.  
  > **username_4**: Get one ND filter and one A7SII ... :)  
  > **username_2**: @A.J Urgh XAVC? No thanks. I'll stick to my BMCC - who needs to expose correctly when you're shooting dng?  
  > **username_4**: My previous comment was half sarcastic and half real... but external recorders record .mov out of HDMI if you're super concerned, plus the benefit with the A7SII is that it is the best low light camera EVER. Just because you shoot in dng doesn't mean you don't have to have the "right" settings or camera for a given situation.  
  
  ---
  
  