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Photography Question 
Alex T. Mizuno
BetterPhoto Member Since: 3/28/2007
 

Filter for slow speed shooting


If I shoot moving water (water falls or river) in the daylight with a slow shutter speed and I need to cut down the light, which filter works better, neutral density or polarizer?


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7/4/2007 11:38:23 PM

 
Pete H
BetterPhoto Member Since: 8/9/2005
  Alex;

It all depends how "slow" you want to shoot.
Generally; a polorizer will reduce light about 2 stops, rarely enough in a brightly lit scene.

The scene you describe is best handled by a ND; or even better, a split ND.
Most outdoor nature photogs will carry more than one.
A few companies sell (variable) ND's..and they rock..a little pricey, but well worth it.

All the best,

Pete


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7/5/2007 7:18:35 AM

 
Alex T. Mizuno
BetterPhoto Member Since: 3/28/2007
  Pete,

I really appreciate you for giving me such detailed information. This helps me a lot! Nature photos are my biggest interest but I'm still new in this field. I'll check out some ND filters at my local photographers supply.

Thank you again!!


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7/6/2007 1:29:53 AM

 
Alan N. Marcus   Hi Alex,

Neutral Density Filters: Filters used to reduce the amount of light passing through your camera lens. ND filter will not alter the rendition of colors. While most photographers use screw-on glass filters, one can buy ND gels. Gelatin filters are made in thin bendable sheets and are dyed to the desired color and shade. Gels are manufactured by Kodak and others. These sheet filers are available in various sizes; you will want 3 or 4 inch square’s. The ND’s by Kodak are known as Series 96, available in a verity of strengths. Gels are normally inexpensive and because they are optically flat their mounting position and orientation over the lens is not critical i.e. you can hand hold them in front of the lens. Gels can be stacked to achieve any desired value.

What you need to know:
Table of labeled values as related to reduced exposure in terms of f/stops.
0.10 = 1/3 stop – 0.20 = 2/3 stops – 0.30 = 1 stop – 0.40 = 1 1/3 stop – 0.50 = 1 2/3 stop – 0.60 = 2 stops – 0.90 = 3 stops – 1.20 = 4 stops. Sometimes the decimal is omitted thus a 0.30 may read on the package as 30.


What you don’t need to know:
ND’s by tradition are labeled using a unique unit known as “Density”. The value as labeled is cryptic. The value is the filter factor expressed in logarithmic notation. Further, the value as written is only the exponent portion of the log. The base of the log is omitted but understood to be 10. As an example: ND 0.30 translates to 10 elevated to the 0.30 power. This works out to be ordinary number 2. Thus a 0.30 has a filter factor of 2 meaning is stops half or 50% of the light thus yielding a one f/stop reduction. The Density unit is also used to express the strength of colored filters. As and example: A yellow filter block mainly the passage of blue light. Thus a 0.30 yellow filter has a blue light filter factor of 2 In this case, the yellow filter stops 50% of the blue light from being transmitted while the red and green primaries are transmitted largely unhindered. .

I only give marginal technical advice you didn’t ask for.

Alan Marcus
Ammarcus@earthlink.net


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7/6/2007 8:29:12 AM

 
Alex T. Mizuno
BetterPhoto Member Since: 3/28/2007
  Hi Alan,

Thank you so much for even more detailed information! This is very educational for me. I did not know I could use gels as an alternative method. If I need variety of strength, it's definitely an inexpensive way to collect them.

I'm going to keep the factors you gave me. It's certainly useful when I buy either filters or gels.

The logarithm is a bit beyond me but it's also educational. And I do appreciate the opportunity to learn more about filter factors. At least I'm more equipped with knowledge before I go to a local camera store.


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7/7/2007 1:55:13 PM

 
Alan N. Marcus   A filter factor is a value stated by the filter maker. When a filter is mounted on a camera, the filter blocks some light thus the exposing light is caused to reach the film/chip at a reduced intensity. So if a filter is mounted it is necessity to take it into account otherwise an under exposure will result.

Not to worry: Most modern cameras determine exposure (camera settings) using sensors mounted at the end of the optical path. These sensors read scene brightness after the energy has transversed a mounted filter. Thus the cameras exposure logic nicely compensates for the filter.

Should the photographer choose to use a hand-held meter, the burden of exposure compensation falls to the photographer. Filter factor to the rescue. Exposure adjustments are generally made by changing the shutter speed or lens aperture or both. The adjustment is generally made using a 2 x increment. The f/numbers (lens aperture) 1.4 – 2 - 2.8 – 4 – 5.6 – 8 -11 – 16 - 22 used are a number set based on a 2 x increment of change. Moving the aperture one number to the left causes the size of the aperture to enlarge thus allowing twice as much light to enter the camera. Moving two numbers to left yields a 4 x change. Moving three numbers to the left results in an 8 x change.

Shutter speed changes follow this same logic. The shutter speed values are a number set based on a 2 x increment of change. 1/1000 – 1/500 – 1/250 – 1/125 – 1/60 – 1/30. These are fractions of a second. Moving right, one number allows the light to play on the film/chip for twice as long. Film and chips can accumulate light energy thus doubling the amount time, doubles the exposing energy. Moving two numbers to the right gives a 4 x increase. Moving three numbers to the right yields an 8 x change.

When presented with a filter factor, we need to compute how we will use this value to make a manual exposure adjustment. Try this method: count out the value on your fingers in powers of 2. The sequence is 2 – 4 – 8 – 16 – 32. Each falls on a finger. Now say you mount a filter with a filter factor of 8. We count on our fingers 2 – 4 – 8. That’s three fingers. We now know we must make a 3 f/stop adjustment. Say we were shooting at f/8 without filter. When we mount a filter with a factor of 8 we must open up three f/stops to f/2.8. Same logic with shutters speeds. We were at 1/500 before mounting a filter with a factor of 8. To compensate by shutter we move the shutter setting three increments right to 1/60.

Sorry photo math is not that easy and perhaps I am a poor explainer. That’s the burden I must suffer when I give marginal technical advice. Maybe someone can present this with better clarity.

Alan Marcus
ammarcus@earthlink.net


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7/7/2007 10:37:03 PM

 
Alex T. Mizuno
BetterPhoto Member Since: 3/28/2007
  Wow! Who can explain better than this! I had to read it twice but I understand the logic. Alan, thank you again for further information! Thank God I live in the time of digital technology. I don't have to use a lightmeter each time I use a filter!

Your explanation about filter factor in relation to f stop using fingers is a great way to figure out the amount of light cut down by each filter factor. I find it very useful and helpful for a novice like me.

Again, this is very educational. It's like I took a free photography class :) Are you a photography teacher by any chance?

Alan, I really appreciate your kindness and generosity. Molto generoso and domo arigato gozaimasu!!


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7/10/2007 10:20:39 PM

 
Alan N. Marcus   How to handle a filter factor? Assumes you are manually setting your camera.

1. Count on your fingers in powers of 2 i.e. 2 – 4 – 8 – 16 – 32. Each finger (digit) corresponds to one f/stop (2x) compensation. .

2. Divide ISO by the filter factor. Reset exposure meter to this revised value.

3. Multiply exposure time by filter factor. Reset shutter to this revised value. Most difficult because most are not handy multiplying fractions. Example: say your shutter speed was 1/500 second and the filter factor is 4. 1/500 x 4 = 1/125.

I am a retired. My 50 year career was mainly manufacturing photographic devices and teaching color print & process.

doo itashimashite
prego

Alan Marcus
ammarcus@earthlink.net


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7/11/2007 7:15:58 AM

 
Alex T. Mizuno
BetterPhoto Member Since: 3/28/2007
  Alan, thank you for the handy formulas again!! I'll carry them in my camera bag whenever I go out for taking photos.

No woder you are so knowledgeable. You have a half century career in this field! That's amazing!

Thank you very much again for your kindness, Alan.

PS. I'm impressed you know Japanese :)


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7/13/2007 2:19:19 PM

 
Bob Cammarata
BetterPhoto Member Since: 7/17/2003
  Boy, all this talk of waterfalls makes me want to get my feet wet again!

Seriously though...if you can, get in really close to the action on smaller falls on tiny streams.
Even at mid-day it's usually possible to find shaded areas where you can shoot filter-free and veil the falls with shutter speeds up to 1 full second at 100 ASA.
You will be so close that you need to worry about water splashing onto the front of your lens but it's a cool way to spend a hot summer day.

Bob


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7/13/2007 5:23:13 PM

 
Alex T. Mizuno
BetterPhoto Member Since: 3/28/2007
  Bob, thank you so much for your advice!! I take your word and start shooting from a small waterfall (I don't have a big waterfall in my neighboring area anyway). If I'm able to slow down to 1 second, that would be slow enough to capture a silky water flow.


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7/20/2007 12:29:37 PM

 
Bob Cammarata
BetterPhoto Member Since: 7/17/2003
  Actually Alex, you won't really need a full second to imply motion.
Shutter speeds that long are indeed possible in deep shade but vertical falls will blur nicely from 1/8 second and slower when you're real close to the action.
You can see an example of a blurred falls on a tiny creek at 1/8 second here.

(...just remember to bring your wet-wading shoes.) :)

Bob


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7/20/2007 3:28:27 PM

 
Alex T. Mizuno
BetterPhoto Member Since: 3/28/2007
  Wow, that's a nice waterfall shot!! If that was shot with a 1/8 second speed, it's slow enough to make water smooth and silky. Great tip!! Thank you, Bob! I will try it at my nearby park. I will bring beach sandals.


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7/20/2007 3:42:47 PM

 
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