Getting into Long Exposures - Which ND Filter?

jaieger · 12-01-2010, 07:03 PM

With a new lens, the DA15, comes new things I want to try, one of them being long exposures - sunsets, flowing water, etc. And I've read up enough on filters and the like to know that I want a neutral density filter. The only thing is though, can anyone shed some light on strength of a filter I should get? I was mainly thinking 2 or 3 stops, but I'm not sure if that'll be strong enough - I'm thinking of doing exposures at around 30 seconds, maybe up to a minute or so (baby steps

). But I don't know whether this'll be during the day, or at night, or both. The next step-up in strength as far as filters go that I can find is a 1.8 (6 stops?) and a 3.0 (9...? or 10), and with those, I'm worried that they'd be too strong.

Obviously, the simple solution would be to get both, but, like I said, baby steps first. Got my TV remote that happens to trip the IR on my K-x and tripod at the ready

newarts · 12-01-2010, 07:28 PM

one solution is using a pair of polarizing filters to create a variable ND filter.

Put a circular polarizer on your lens.
Stack a linear polarizer on it (or stack a reversed* circular polarizer on it.)

You should get from 1 to 8 or more stops as you turn one polarizer with respect to the other.

Dave

*reverse it with a reversing ring, or remove the glass element, turn the element up-side down & replace the element.

Eruditass · 12-01-2010, 07:41 PM

This guy got around 8 stops before his color shift:
Using Crossed Polarizers for a Variable ND Filter Digital ImageMaker

jaieger · 12-01-2010, 07:57 PM

Hmm, this definitely looks pretty interesting, but.... Just one polarizer would be more expensive than a 3 stop ND from B&H, and $10 less than the 1.8 one ! =/

krp · 12-01-2010, 08:52 PM

Originally posted by Eruditass

This guy got around 8 stops before his color shift:
Using Crossed Polarizers for a Variable ND Filter Digital ImageMaker

That's pretty interesting. I was about to buy a 10 stop nd filter but I might have to give that a try. I downloaded his 9+ stop image and photoshop's "auto color correction" fixed it easily. So that would mean I could use a filter combination like this to get rid of 3-9+ stops of light without ruining the picture. The only thing I'm hesitant about is people always say stacking filters reduces image quality.

krp · 12-01-2010, 08:56 PM

Originally posted by jaieger

Hmm, this definitely looks pretty interesting, but.... Just one polarizer would be more expensive than a 3 stop ND from B&H, and $10 less than the 1.8 one ! =/

That's true but this would be like having multiple nd filters from 3-9 stops. Looking around I think I could get a Tiffen linear polarizer and a Hoya circular polarizer for about $30 total. In the 58mm size at least.

imtheguy · 12-01-2010, 09:50 PM

Originally posted by newarts

Put a circular polarizer on your lens.
Stack a linear polarizer on it (or stack a reversed* circular polarizer on it.)
.

I tried stacking screw-on filters with a da15 and got significant vignetting. Maybe the extra thin filters could work for you though. I have no thin style to test with as I typically use a Cokin-P system.

alohadave · 12-01-2010, 11:03 PM

Originally posted by krp

That's pretty interesting. I was about to buy a 10 stop nd filter but I might have to give that a try. I downloaded his 9+ stop image and photoshop's "auto color correction" fixed it easily. So that would mean I could use a filter combination like this to get rid of 3-9+ stops of light without ruining the picture. The only thing I'm hesitant about is people always say stacking filters reduces image quality.

I've used this technique myself, and it works great. Be sure to use the eyepiece cover on long exposures during the day so you don't get stray light in your shot.

About stacking filters, it's more of a general rule. If you are going for a specific effect, you sometimes have to make a judgment about what is more important, composition or fine detail quality. In most cases, you probably won't notice that much degradation, but it's something to be aware of, not afraid of.

RioRico · 12-03-2010, 10:15 PM

At a hardware store, a 4x5" piece of welder's glass costs maybe US$5.
Take some useless UV filters of various sizes and remove the glass.
Take welder's glass and empty filter rings to a local glazier for cut and fit.
Congratulations! You now own a set of ND 666 filters! And cheap, too.

newarts · 12-04-2010, 05:40 AM

Originally posted by krp

......The only thing I'm hesitant about is people always say stacking filters reduces image quality.

People say many imprecise things; people might better say "stacking filters may reduce image quality".

Even one poor filter will reduce image quality while two good ones may have no detectable effect.

Coated filters will minimize flare & contrast loss, but cleanliness is likely most important.

Lloydy · 12-04-2010, 11:13 AM

Welders mask lenses fit Cokin P filter holders. To fully light seal the glass you can use thin slivers of weathersealing sticky back foam such as used for draught proofing doors.

The glass lenses come in different grades of colour density for different types of weldiing, and should be good quality flat glass as the welder has to look through the lens all the time he's welding.

Some of the glass lenses have safety edges, but most are plain cut and sharp. I use a diamond dust knife sharpener to remove the sharp glass edges.

I have this all set up and ready to try, but the last few months have been hectic and I haven't had a go at it yet.
But there's a few groups on Flickr that have some good info and images that are worth looking at.

12-01-2010, 07:03 PM	#1
jaieger Veteran Member Join Date: Jul 2010 Photos: Gallery \| Albums Posts: 586	Getting into Long Exposures - Which ND Filter? With a new lens, the DA15, comes new things I want to try, one of them being long exposures - sunsets, flowing water, etc. And I've read up enough on filters and the like to know that I want a neutral density filter. The only thing is though, can anyone shed some light on strength of a filter I should get? I was mainly thinking 2 or 3 stops, but I'm not sure if that'll be strong enough - I'm thinking of doing exposures at around 30 seconds, maybe up to a minute or so (baby steps ). But I don't know whether this'll be during the day, or at night, or both. The next step-up in strength as far as filters go that I can find is a 1.8 (6 stops?) and a 3.0 (9...? or 10), and with those, I'm worried that they'd be too strong. Obviously, the simple solution would be to get both, but, like I said, baby steps first. Got my TV remote that happens to trip the IR on my K-x and tripod at the ready

12-01-2010, 07:28 PM	#2
newarts Inactive Account Join Date: Dec 2008 Location: Ames, Iowa, USA Photos: Albums Posts: 2,965	one solution is using a pair of polarizing filters to create a variable ND filter. Put a circular polarizer on your lens. Stack a linear polarizer on it (or stack a reversed* circular polarizer on it.) You should get from 1 to 8 or more stops as you turn one polarizer with respect to the other. Dave reverse it with a reversing ring, or remove the glass element, turn the element up-side down & replace the element. Last edited by newarts; 12-04-2010 at 05:52 AM.*

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12-01-2010, 07:41 PM	#3
Eruditass Veteran Member Join Date: Jul 2009 Photos: Gallery Posts: 2,207	This guy got around 8 stops before his color shift: Using Crossed Polarizers for a Variable ND Filter Digital ImageMaker

12-01-2010, 07:57 PM	#4
jaieger Veteran Member Join Date: Jul 2010 Photos: Gallery \| Albums Posts: 586 Original Poster	Hmm, this definitely looks pretty interesting, but.... Just one polarizer would be more expensive than a 3 stop ND from B&H, and $10 less than the 1.8 one ! =/

12-01-2010, 08:52 PM	#5
krp Veteran Member Join Date: Oct 2010 Location: Illinois Photos: Gallery Posts: 470	Originally posted by Eruditass This guy got around 8 stops before his color shift: Using Crossed Polarizers for a Variable ND Filter Digital ImageMaker That's pretty interesting. I was about to buy a 10 stop nd filter but I might have to give that a try. I downloaded his 9+ stop image and photoshop's "auto color correction" fixed it easily. So that would mean I could use a filter combination like this to get rid of 3-9+ stops of light without ruining the picture. The only thing I'm hesitant about is people always say stacking filters reduces image quality.

12-01-2010, 08:56 PM	#6
krp Veteran Member Join Date: Oct 2010 Location: Illinois Photos: Gallery Posts: 470	Originally posted by jaieger Hmm, this definitely looks pretty interesting, but.... Just one polarizer would be more expensive than a 3 stop ND from B&H, and $10 less than the 1.8 one ! =/ That's true but this would be like having multiple nd filters from 3-9 stops. Looking around I think I could get a Tiffen linear polarizer and a Hoya circular polarizer for about $30 total. In the 58mm size at least.

12-01-2010, 09:50 PM	#7
imtheguy Site Supporter Join Date: Mar 2009 Location: Virginia Beach Photos: Gallery \| Albums Posts: 2,950	Originally posted by newarts Put a circular polarizer on your lens. Stack a linear polarizer on it (or stack a reversed* circular polarizer on it.) . I tried stacking screw-on filters with a da15 and got significant vignetting. Maybe the extra thin filters could work for you though. I have no thin style to test with as I typically use a Cokin-P system.

12-01-2010, 11:03 PM	#8
alohadave Veteran Member Join Date: Jan 2008 Location: Quincy, MA Photos: Gallery \| Albums Posts: 2,024	Originally posted by krp That's pretty interesting. I was about to buy a 10 stop nd filter but I might have to give that a try. I downloaded his 9+ stop image and photoshop's "auto color correction" fixed it easily. So that would mean I could use a filter combination like this to get rid of 3-9+ stops of light without ruining the picture. The only thing I'm hesitant about is people always say stacking filters reduces image quality. I've used this technique myself, and it works great. Be sure to use the eyepiece cover on long exposures during the day so you don't get stray light in your shot. About stacking filters, it's more of a general rule. If you are going for a specific effect, you sometimes have to make a judgment about what is more important, composition or fine detail quality. In most cases, you probably won't notice that much degradation, but it's something to be aware of, not afraid of.

12-03-2010, 10:15 PM	#9
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	At a hardware store, a 4x5" piece of welder's glass costs maybe US$5. Take some useless UV filters of various sizes and remove the glass. Take welder's glass and empty filter rings to a local glazier for cut and fit. Congratulations! You now own a set of ND 666 filters! And cheap, too.

12-04-2010, 05:40 AM	#10
newarts Inactive Account Join Date: Dec 2008 Location: Ames, Iowa, USA Photos: Albums Posts: 2,965	Originally posted by krp ......The only thing I'm hesitant about is people always say stacking filters reduces image quality. People say many imprecise things; people might better say "stacking filters may reduce image quality". Even one poor filter will reduce image quality while two good ones may have no detectable effect. Coated filters will minimize flare & contrast loss, but cleanliness is likely most important.

12-04-2010, 11:13 AM	#11
Lloydy Veteran Member Join Date: Aug 2007 Location: Shropshire, UK Posts: 1,114	Welders mask lenses fit Cokin P filter holders. To fully light seal the glass you can use thin slivers of weathersealing sticky back foam such as used for draught proofing doors. The glass lenses come in different grades of colour density for different types of weldiing, and should be good quality flat glass as the welder has to look through the lens all the time he's welding. Some of the glass lenses have safety edges, but most are plain cut and sharp. I use a diamond dust knife sharpener to remove the sharp glass edges. I have this all set up and ready to try, but the last few months have been hectic and I haven't had a go at it yet. But there's a few groups on Flickr that have some good info and images that are worth looking at.