The Filters We Need With Digital...

Started Oct 5, 2008 | Discussions
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BorisK1 Veteran Member • Posts: 5,381
Re: Continuous ND?

Whoops, didn't read your post until after I wrote the one below.

IMHO, this works best with two linear polarizers. Yes, you'll get flare and other problems - but it's the only way to smear movement in broad daylight.

Ninety degree angle should give nearly complete blackness.

Boris

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JensR Forum Pro • Posts: 17,620
Re: Or two of them...

To smear grass that's waving under the wind in broad daylight, stack
two polarizers and get a variable neutral density filter. The
polarizers have to be color-neutral though - any color cast will be
greatly magnified.

And usual crossed polarisers act as a defacto IR pass filter, because they are almost transparent in IR, but very dark for visible light. This creates a further colour cast. As a positive aspect, they can be really cool on an infrared-modified camera. You need two linear polarisers or one linear and one circular for this.

Jens

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BorisK1 Veteran Member • Posts: 5,381
Re: Or two of them...

JensR wrote:

And usual crossed polarisers act as a defacto IR pass filter

I knew this applied to gel filters, but thought the ones made out of glass weren't IR-transparent. Good to know, thank you!

Boris

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JensR Forum Pro • Posts: 17,620
Re: Or two of them...

Hi Boris!

And usual crossed polarisers act as a defacto IR pass filter

I knew this applied to gel filters, but thought the ones made out of
glass weren't IR-transparent. Good to know, thank you!

Here's how I found out
http://www.jr-worldwi.de/photo/polarizer.html
It is not very technical, but the pics and data should be okay.

If you research in a catalogue for optical componets (Edmond Optics for example), you will see that polarisers that really work in IR cost quite a lot.
I assume this has both technical reasons and economy of s(c)ale ones.

Cheers
Jens

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Joseph S Wisniewski OP Forum Pro • Posts: 34,123
Sometimes it works, sometimes it causes problems...

Henrik Andersson wrote:

Thanks for all the info in this thread.

You are quite welcome.

Is there a good way to get a strong continuously variable ND?

There's a device called a PLZT, but it's expensive even at small sizes...

Like putting a linear polarizer followed by a circular (linear plus a
quarts plate?) in front of the lens and then turn the first filter 0
to 90 degrees to get 1.5 (?) to "many" stops of "ND-filter effect"?

That can be problematic...

More in a minute.

... or will there be a lot of reflections from the polarizers,
destroying the contrast if the image at the focal plane?

Yes, this technique increases the problems with reflection. It also causes three other things to go wrong...

1) Any type of transparent deposit on the polarizers (skin oil, typically) decreases the uniformity of the neutral density effect when the polarizers are crosses.

2) The polarizers get more blue and less neutral as you approach maximum density. Typically, they're noticeably off by the time you're 4 stops down, and get worse as you go farther.

3) Crossed polarizers let lots of IR and UV through. The UV may cause overall haziness, the IR will definitely cause problems for older cameras. Shots taken with an old Nikon D100 and crossed polarizers look remarkably like IR filter shots.

... or use two linear ones?

Not necessary: the circular polarizer has a linear polarizer for the first layer. A good circular is fine for the rear polarizer, only the front has to be linear. One of the filter companies (I think it's B+W) now lists linear polarizers as "top" polarizers, specifically for stacking applications.

I don't need the mirror or phase-AF for my applications ...

Use a circular for the rear polarizer, and don't worry...

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Joseph S Wisniewski OP Forum Pro • Posts: 34,123
Contrast "reducing", for film only...

BorisK1 wrote:

First off, thank you for a great refresher!

You are quite welcome.

I've seen many companies advertise "contrast enhancing" filters, like
this one:
http://www.adorama.com/TF58UC3.html

Those are actually contrast reducing filters. I have the original set of Tiffen Contrast 1, 2, and 3 in the film days...

Never actually tried one. Do they actually work, or is it good old
snake oil?

They worked back in the film days. They "scatter" light, letting light from the highlights fill in the entire image, producing the same effect as the lens flaw called "veiling flare", but doing it in a more predictable way. This "veiling" lifted the shadows up a bit, preventing them from falling below the "relaxation threshold" of the film, or even lifted them up over the "toe" of the film sensitivity curve to give the shadows a very different look. The problem was that they were very unpredictable, you'd never be sure until you saw the film which filter was the right one...

They have no effect with digital. Digital, at low levels, is linear, so we try to lower shadow levels as much as possible to make better use of the A/D converters. Every now and then some smarmy snake oil salesman does try to sell us on veiling as a way of improving digital, but fortunately, in the internet age, they're quickly shot down.

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Gary J Jensen Senior Member • Posts: 2,204
Re: Crossed Polarizers getting blue...

Joseph S Wisniewski wrote:

[snip]
2) The polarizers get more blue and less neutral as you approach
maximum density. Typically, they're noticeably off by the time you're
4 stops down, and get worse as you go farther.
[snip]

This effect depends a lot on the quality of the particular polarizing foil used in the polarizer.

The "blue" effect is most pronounced with cheap polarizers and those that use a "dye" polarizing layer rather than a high quality foil.

Rosco polarizing film [as one example] has a definite blue/violet transmission tint at maximum density.

I've found that the Heliopan LP/CP lens filters [and also their LP "sheets" for lighting] use a high quality foil that maintains neutrality and achieves a near-zero transmission at maximum density.

Of course, I don't use them as "variable ND" filters; but they're outstanding when working with cross-polarization lighting techniques.
Hope you find this useful.
And, thanks again for your excellent filter summary.

Joseph S Wisniewski OP Forum Pro • Posts: 34,123
All polarizers are "gel", sort of...

BorisK1 wrote:

JensR wrote:

And usual crossed polarisers act as a defacto IR pass filter

I knew this applied to gel filters, but thought the ones made out of
glass weren't IR-transparent. Good to know, thank you!

Polarizers aren't actually glass, nor are they really "gel", but they are "gel like". They're actually a vinyl polymer, loaded with shards of iodine crystals. Single solid optical grade iodine crystals big enough to make a decent polarizer would cost a simply insane amount.

Edwin H. Land figured out that if you put a bunch of microscopic crystals in a polymer, and applied physical stress (stretching) or an electrical field as the polymer hardened, the crystals would all orient themselves along the field, and you end up with enough of them stacked on top of each other so that you have nice, uniform polarizer with no holes...

To make them easier to handle, the vinyl is glued between two sheets of optical glass, which is what you see when you handle the polarizer. They're typically PVA, and that absorbs water and swells, gets gooey and sometime cloudy. And the glue fails, because it's difficult to do a good job gluing dissimilar materials like PVA and glass. That's why B+W makes such a fuss about their Kaeseman polarizers with the sealed edges...

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J1000 Senior Member • Posts: 1,339
Answer me this, filter man...

Do they make small filter attachments that make them easy to snap on / snap off the lens?

An example might be the spring-loaded filter mounts used for the Raynox closeup lenses. They are not what I'm looking for though, because they are huge due to supporting a wide range of lens thread sizes, and it only supports small filters (because these are for closeup lenses, which typically operate at telephoto lengths, so wide angle vignetting is OK).

And thank you for your posts!

Iliah Borg Forum Pro • Posts: 19,786
Re: I find them problematic...

Dear Joseph,

I found many architectural and landscape shots to be impossible without magenta filter (in a single-shot mode). It takes little to have a filter with me and shoot twice, once with a filter and once without it.

In studio I filter lights, not the lens.

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Iliah Borg Forum Pro • Posts: 19,786
Re: Something I forgot to mention...

Dear Joseph,

One more type of filters that is worth discussing IMHO is light filters. Those are:

  • filters for flash, balancing it closer to incandescent or fluorescent ambient light when shooting indoors;

  • filters for the studio lights, especially when using incandescent light sources.

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GregGory Veteran Member • Posts: 4,249
Nice summary

Should be made a sticky, but won't happen I know.

DaSigmaGuy Forum Pro • Posts: 12,299
Re: The “Non-Filter” You Need, and the Filter You Don’t

Joseph S Wisniewski wrote:

The Protection Racket

Well, what about the “protection” filter: be it the traditional “UV”
or “haze” filter, or a so-called “digital” filter? The camera store
salesman told you that you need one. He may even have said you won’t
get a warranty if you don’t have one (a lie the smarmiest sales
people have been using for decades).

Funny you should bring up this subject Joe. I have just bought a Tamron SP 300mm f2.8 LD IF and while searching for sites with more info about it I came across a lens test with a remarkable finding...As you probably know, Tamron used to offer an optional 112mm "normal" filter for the front of the lens. I dont know what a "normal" filter is but apparently the tester has found his Tamron 300/2.8 to be considerably sharper with this filter on the lens than without it!!!

He has even posted MTF graphs to show the difference, with and without the 112mm normal filter.

If you have time, perhaps you would like to read his article to try and work out whats going on. After reading it I now feel perhaps I should try to get one of these filters or my lens wont be as sharp as without one.
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Gregory King Veteran Member • Posts: 7,322
Re: The “Non-Filter” You Need, and the Filter You Don’t

DaSigmaGuy wrote:

Funny you should bring up this subject Joe. I have just bought a
Tamron SP 300mm f2.8 LD IF and while searching for sites with more
info about it I came across a lens test with a remarkable
finding...As you probably know, Tamron used to offer an optional
112mm "normal" filter for the front of the lens. I dont know what a
"normal" filter is but apparently the tester has found his Tamron
300/2.8 to be considerably sharper with this filter on the lens than
without it!!!
He has even posted MTF graphs to show the difference, with and
without the 112mm normal filter.
If you have time, perhaps you would like to read his article to try
and work out whats going on. After reading it I now feel perhaps I
should try to get one of these filters or my lens wont be as sharp as
without one.

I have one of these...it came with the filter. I can run this test if you like (minus the MTF graphs.

Good info to know!

Greg

DaSigmaGuy Forum Pro • Posts: 12,299
Re: The “Non-Filter” You Need, and the Filter You Don’t

Gregory King wrote:

DaSigmaGuy wrote:

Funny you should bring up this subject Joe. I have just bought a
Tamron SP 300mm f2.8 LD IF and while searching for sites with more
info about it I came across a lens test with a remarkable
finding...As you probably know, Tamron used to offer an optional
112mm "normal" filter for the front of the lens. I dont know what a
"normal" filter is but apparently the tester has found his Tamron
300/2.8 to be considerably sharper with this filter on the lens than
without it!!!
He has even posted MTF graphs to show the difference, with and
without the 112mm normal filter.
If you have time, perhaps you would like to read his article to try
and work out whats going on. After reading it I now feel perhaps I
should try to get one of these filters or my lens wont be as sharp as
without one.

I have one of these...it came with the filter. I can run this test
if you like (minus the MTF graphs.

Thats would be great Greg but can you please make sure you also do a with/without the front filter test and also a with/without the rear 43mm filter too, because I've noticed a difference when I take the rear filter out of mine.
Thanks.

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Joseph S Wisniewski OP Forum Pro • Posts: 34,123
Alf, I'd love to see that article...

DaSigmaGuy wrote:

Joseph S Wisniewski wrote:

The Protection Racket

Well, what about the “protection” filter: be it the traditional “UV”
or “haze” filter, or a so-called “digital” filter? The camera store
salesman told you that you need one. He may even have said you won’t
get a warranty if you don’t have one (a lie the smarmiest sales
people have been using for decades).

Funny you should bring up this subject Joe. I have just bought a
Tamron SP 300mm f2.8 LD IF and while searching for sites with more
info about it I came across a lens test with a remarkable
finding...As you probably know, Tamron used to offer an optional
112mm "normal" filter for the front of the lens. I dont know what a
"normal" filter is but apparently the tester has found his Tamron
300/2.8 to be considerably sharper with this filter on the lens than
without it!!!
He has even posted MTF graphs to show the difference, with and
without the 112mm normal filter.
If you have time, perhaps you would like to read his article to try
and work out whats going on. After reading it I now feel perhaps I
should try to get one of these filters or my lens wont be as sharp as
without one.

That sounds interesting. I'd love to see that article.

Clear glass, either in front of the lens or behind it, affects several optical properties, including spherical aberration and astigmatism.

But it's unusual for a telephoto, even a fast one, to be seriously affected by clear glass. It's much more common for wides, fast normals, and macros to be thrown off by clear glass in front of the lens.

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Ciao! Joseph

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Iliah Borg Forum Pro • Posts: 19,786
Re: The “Non-Filter” You Need, and the Filter You Don’t

I have just bought a
Tamron SP 300mm f2.8 LD IF and while searching for sites with more
info about it I came across a lens test with a remarkable
finding...As you probably know, Tamron used to offer an optional
112mm "normal" filter for the front of the lens. I dont know what a
"normal" filter is but apparently the tester has found his Tamron
300/2.8 to be considerably sharper with this filter on the lens than
without it!!!

I had a similar experience with Canon 1D MkII and long lenses. A UV filter improved AF performance of the camera.

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Tiffles Veteran Member • Posts: 4,970
Re: The Filters We Need With Digital...

Great informative summary. But where is the ND grad filters? And where can I get a neodymium enhancement filter?

Cheers
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Joseph S Wisniewski OP Forum Pro • Posts: 34,123
Thank. And ND grad and neodymium...

Tiffles wrote:

Great informative summary.

Thank you. Glad you enjoyed.

But where is the ND grad filters?

Number 6 on the "big six" list.

http://forums.dpreview.com/forums/read.asp?forum=1018&message=29592787

And
where can I get a neodymium enhancement filter?

At B&H, they're listed under "filters" in the "enhancing and intensifying" category.

Tiffen sells it as an "enhancing filter". B+W calls it the 491 "enhancer" or "redhancer". Hoya calls it a either an "enhancer" or an "intensifier", depending on the mood they're in. They also have a "blue field" and "green field" variation that I've never tried.

Among the square Cokin style filter manufacturers, Lee calls it an "enhancing" filter, Singh-Ray calls it a "color intensifier" filter.

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Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

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Joseph S Wisniewski OP Forum Pro • Posts: 34,123
Now that is just weird...

Iliah Borg wrote:

I have just bought a
Tamron SP 300mm f2.8 LD IF and while searching for sites with more
info about it I came across a lens test with a remarkable
finding...As you probably know, Tamron used to offer an optional
112mm "normal" filter for the front of the lens. I dont know what a
"normal" filter is but apparently the tester has found his Tamron
300/2.8 to be considerably sharper with this filter on the lens than
without it!!!

I had a similar experience with Canon 1D MkII and long lenses. A UV
filter improved AF performance of the camera.

Iliah, that is just plain weird. Not that I'm doubting you, I've seen enough weird stuff in this world to know that "weird happens".

But I can't imagine how, unless the AF system was unusually sensitive to UV, so that whatever was making it through the lens was enough to drift the AF system off a bit (since the lens isn't corrected for near UV, or even for violet). Even then, a long lens should block pretty much as much UV as a filter...

Were you using a stronger UV filter, a UV(1) or something that cuts off near (or even above) 400nm, like those 415nm UV filters I use for blacklight sessions...

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

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