Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-07-2014, 04:28 PM   #1
Veteran Member
whk1992's Avatar

Join Date: Aug 2014
Photos: Gallery
Posts: 715
Questions about the Mechanics of a Variable ND Filter

Hello all,

I'm thinking about grabbing a variable ND filter for hiking. Sometimes, the sunlight is just way too bright, especially when I'm using slow-sync flash too.

I read an article related to variable ND filters: The Best ND Filter Guide | NDFilters.org
QuoteQuote:
These [variable ND filters] work by effectively sandwiching two polarizing filters together. The rear polarizer will cut out light in one plane, whilst the from element can be rotated, effectively reducing the light in the other plane. By using this technique you can control the amount of light reaching the sensor with almost infinite control.
This is interesting. I've never used a variable ND filter before.

1. I own a CPL filter; does it mean I can just grab another CPL filter somewhere and make my own variable ND filter?
2. Does it have adverse effect on shooting electronic devices, such as LCD monitors (which have a built-in polarizer), or at a vehicle (some windows are polarized)?
3. Does it affect the camera's autofocusing system and metering system like a linear polarizer would do?

Thank you.

09-07-2014, 04:47 PM - 1 Like   #2
Veteran Member
psychdoc's Avatar

Join Date: Jul 2010
Location: Bham
Photos: Gallery | Albums
Posts: 949
Here is an article on how to build an nd filter with cpl filters. I did not try it myself as I have a variable nd filter already.

How to Build a Cheap and Simple Variable Neutral Density Filter
09-07-2014, 04:54 PM   #3
Veteran Member
whk1992's Avatar

Join Date: Aug 2014
Photos: Gallery
Posts: 715
Original Poster
QuoteOriginally posted by psychdoc Quote
Here is an article on how to build an nd filter with cpl filters. I did not try it myself as I have a variable nd filter already.

How to Build a Cheap and Simple Variable Neutral Density Filter
Thanks for the nice tutorial! I'm scouting a CPL online now... I'll let you guys know if it works nicely.
09-07-2014, 05:20 PM   #4
Veteran Member




Join Date: Jun 2014
Posts: 340
Unfortunately there is a problem with his application. A circular polarizer has a polarizing element on one side and a randomizing element called a quarter wave plate on the other. This quarter wave plate randomizes the polarized light, so the camera can correctly use it. This means that the light coming into the second polarizer is randomized and it will not have any effect. You can see this effect and test your CR polarizer by holding it up to a flatscreen monitor or TV. A flat screen monitor/TV emits polarized light. Hold the polarizer of toward the TV/monitor and rotated approximately 90. A good polarizer will have a dramatic affect on the light. Flip the polarizer around and repeat, a good polarizer will have little if any effect on the light that passes through it. A standard polarizer or a bad circular polarizer will have a similar effect in either direction.

What you need is one circular polarizer attached directly to the lens, and one standard polarizer attached to the first Circular polarizer. Now you can vary the polarized light by turning the second polarizer In relationship to the first polarizer. This will give you a variable neutral density filter that will very light from approximately 1 stop down to nearly completely dark.

Hope this helps.

Stay safe and have fun.

Joe.


QuoteOriginally posted by psychdoc Quote
Here is an article on how to build an nd filter with cpl filters. I did not try it myself as I have a variable nd filter already.

How to Build a Cheap and Simple Variable Neutral Density Filter


09-07-2014, 05:29 PM   #5
Veteran Member
whk1992's Avatar

Join Date: Aug 2014
Photos: Gallery
Posts: 715
Original Poster
QuoteOriginally posted by promacjoe Quote
Unfortunately there is a problem with his application. A circular polarizer has a polarizing element on one side and a randomizing element called a quarter wave plate on the other. This quarter wave plate randomizes the polarized light, so the camera can correctly use it. This means that the light coming into the second polarizer is randomized and it will not have any effect. You can see this effect and test your CR polarizer by holding it up to a flatscreen monitor or TV. A flat screen monitor/TV emits polarized light. Hold the polarizer of toward the TV/monitor and rotated approximately 90. A good polarizer will have a dramatic affect on the light. Flip the polarizer around and repeat, a good polarizer will have little if any effect on the light that passes through it. A standard polarizer or a bad circular polarizer will have a similar effect in either direction.

What you need is one circular polarizer attached directly to the lens, and one standard polarizer attached to the first Circular polarizer. Now you can vary the polarized light by turning the second polarizer In relationship to the first polarizer. This will give you a variable neutral density filter that will very light from approximately 1 stop down to nearly completely dark.

Hope this helps.

Stay safe and have fun.

Joe.
Hmmm... Just a recap: Instead of following the tutorial, should I mount an unmodified CPL to the lens first, then put a linear polarizer? Thanks.
09-07-2014, 07:54 PM   #6
Veteran Member




Join Date: Jun 2014
Posts: 340
Yes, that is correct. You do not need two circular Polarizers. You do not meet to take one circular polarizer apart and flip it over. One circular polarizer on the lens, the second linear polarizer goes on next. Use good polarizers. If you don't you could get some odd colors from it.

Stay safe and have fun.

Joe.


QuoteOriginally posted by whk1992 Quote
Hmmm... Just a recap: Instead of following the tutorial, should I mount an unmodified CPL to the lens first, then put a linear polarizer? Thanks.
09-07-2014, 09:05 PM   #7
Veteran Member
Imageman's Avatar

Join Date: Dec 2013
Photos: Albums
Posts: 461
The circular polarizer is there because the modern camera doesn't work well with a linear polarizer.


A circular polarizer does nothing it simply changes the polarized light that passes through a linear polarizer so the camera can use it.


A circular polarizer is then a linear polarizer and a circular polarizer sandwiched together


To make a variable ND - polarizer you fit a circular polarizer to a lens, and fit a linear polarizer on the front of the circular polarizer.

09-07-2014, 09:09 PM   #8
Veteran Member
whk1992's Avatar

Join Date: Aug 2014
Photos: Gallery
Posts: 715
Original Poster
QuoteOriginally posted by promacjoe Quote
Yes, that is correct. You do not need two circular Polarizers. You do not meet to take one circular polarizer apart and flip it over. One circular polarizer on the lens, the second linear polarizer goes on next. Use good polarizers. If you don't you could get some odd colors from it.

Stay safe and have fun.

Joe.
Meh. I just paid 2 bucks for a made in Japan CPL. Glad that I was being cheap and didn't buy a pricy one
09-10-2014, 03:10 AM   #9
Junior Member




Join Date: May 2014
Location: Luanda, Angola
Photos: Gallery
Posts: 48
If you have the polarizes in hand or can obtain them cheaply, this could be a fun experiment. However, I recently bought a variable ND filter and was quickly frustrated with the banding that occurred at high density and wide angles which is how I most wanted to use it.
09-10-2014, 03:30 AM   #10
Veteran Member
whk1992's Avatar

Join Date: Aug 2014
Photos: Gallery
Posts: 715
Original Poster
Banding? What does that mean? The neutral density wasn't applied uniformly?
09-10-2014, 11:00 AM   #11
Veteran Member
narual's Avatar

Join Date: Jun 2013
Location: South Bend (Notre Dame), Indiana
Posts: 1,977
It's a lot easier and cheaper to just buy a cheap variable ND filter than two CPLs. Some of them have that banding issue at their highest setting -- here's an example of what it looks like:


Some of them don't. I have them in 77, 67, 55, and 49mm sizes and IIRC I've only had the problem with the 55. If you run across one with the problem, return it and get a replacement. If you have the problem with the replacement, try a different brand. It's not necessarily a problem inherent in the design, so far as I can tell... just something with bad batches or misaligned filters or something.

That said... they're not at their best at the darkest setting. I *mostly* use mine as sunglasses for my f/1.2 lens since it does really strange things to my camera in live view when it's in too much sun, and as a general replacement for a 1/2/3 stop or so filter. For heavy filtering, I picked up a Haida ND 3.0 / 1000x filter for $28 to use with my 15mm ltd.

Last edited by narual; 09-10-2014 at 11:06 AM.
09-10-2014, 11:28 AM   #12
Veteran Member
whk1992's Avatar

Join Date: Aug 2014
Photos: Gallery
Posts: 715
Original Poster
QuoteOriginally posted by narual Quote
It's a lot easier and cheaper to just buy a cheap variable ND filter than two CPLs. Some of them have that banding issue at their highest setting -- here's an example of what it looks like:


Some of them don't. I have them in 77, 67, 55, and 49mm sizes and IIRC I've only had the problem with the 55. If you run across one with the problem, return it and get a replacement. If you have the problem with the replacement, try a different brand. It's not necessarily a problem inherent in the design, so far as I can tell... just something with bad batches or misaligned filters or something.

That said... they're not at their best at the darkest setting. I *mostly* use mine as sunglasses for my f/1.2 lens since it does really strange things to my camera in live view when it's in too much sun, and as a general replacement for a 1/2/3 stop or so filter. For heavy filtering, I picked up a Haida ND 3.0 / 1000x filter for $28 to use with my 15mm ltd.
That's lots of info! Thanks for the tips. I'll test it out later this week.
09-11-2014, 07:05 PM   #13
Junior Member




Join Date: May 2014
Location: Luanda, Angola
Photos: Gallery
Posts: 48
I think in general the banding happens at high density on wide angles. Is your lens that has a 55mm diam a wide angle lens?
09-11-2014, 07:17 PM   #14
Veteran Member
narual's Avatar

Join Date: Jun 2013
Location: South Bend (Notre Dame), Indiana
Posts: 1,977
Has nothing to do with angles. You can even see it with your naked eyes if you hold the filter up to a light source. The banding from wide angles with polarizers is different, and happens with any polarizer, not just variable ND filters. The 55mm filter I have that does this exhibited it on my Porst 55mm/1.2 lens. The photo I linked wasn't a shot I took, just the result of a quick google search.

This is what polarizer banding on a wide angle shot looks like: (again, not one of my photos - I don't tend to post the ones that have issues)
09-12-2014, 01:11 AM   #15
Veteran Member
whk1992's Avatar

Join Date: Aug 2014
Photos: Gallery
Posts: 715
Original Poster
QuoteOriginally posted by kthornsberry Quote
I think in general the banding happens at high density on wide angles. Is your lens that has a 55mm diam a wide angle lens?
Please refer to Ken Rockwell's webpage for explanations of banding related to wide angle photos.
How to Use Filters
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
control, cpl, filter, filters, light, nd, plane, polarizer, system, tripod, variable
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: Tiffen 77mm Variable ND filter and T1 Infrared filter ploetzlich Sold Items 0 12-24-2013 09:14 PM
3 Piece Hoya ND filter set or Tiffen variable??? nms_photog Pentax Camera and Field Accessories 9 10-18-2011 11:07 AM
Nature Ice art - K20D with variable ND filter (8 images) newmikey Post Your Photos! 4 02-23-2011 08:03 AM
Variable ND Filter - Fader ND mark II yusuf Pentax SLR Lens Discussion 2 11-16-2010 11:39 AM
A noob-like question about lens mechanics Pwn4g3_P13 Pentax SLR Lens Discussion 7 01-06-2009 05:43 PM



All times are GMT -7. The time now is 03:55 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top