The Filter thread.

[timmyquest]

I got a few filter questions.

1.) I see images from IR filters and aside from being stunned many of the times, i often wonder if there are differnt types of IR filters because some just look very differnt in some respects.

2.) Are there "black and white" filters

3.) How do polorized filters work? It is my understanding that the term "polorized" means it filters "half" the light "waves" (when in this instance light is working like a wave and not a particle). Yet that doesnt seem to be what it does in photography, nor would it makes sence to need a filter to do that.

[CyberDyneSystems]

I can only answer Number 2...

"B&W" is a very high quality brand name of German manufacture.. they are ocnsidered to the "best" manufacturer of filters. There is no "black and white" filter.

[iwatkins]

1. Yes, there are many different IR filters. There are ones that block everything but pass red and infra-red, there are ones that block all visible but pass infrared, there are ones that block everything but only pass a narrow band of infra-red etc. etc.

The common IR filter is called an R72 so called as is doesn't pass anything with a lower wavelength than 720 nanometres. Well, it actually lets through stuff a little shorter than that, but total blockage from 700 nm downwards (Ian searches around the 'net for the graph):

http://www.hoyaoptics.com/img/color_filter/r70_lg.gif

For loads more information on the various IR filters, check out Hoyas Page here (http://www.hoyaoptics.com/color_filter/ir_transmitting.htm)

2. No such thing as a black and white filter as such. However, there filters that are used when using black and white film, but these are coloured. These block or reduce certain colours so that the image captured on black and white film is changed to suit.

There is a widget you can buy that looks like a little eye-bath on a stick. You hold it up to your eye and look through it. It removes almost all the colour from the scene. However, with all the colour removed it is easy to concentrate on the tones in the scene. This is used by black and white photographers to get a good idea of what the scene will look like on B&W film.

It is called the Monovue Contrast Viewing Filter and it is mentioned on page of 2 this article (http://www.photographymonthly.com/samples/ACF1F.pdf) (PDF document)

3. Some good links in the "Best Links" sticky. I don't pretend to understand polarisers but I like the effect they give. :)

Cheers

Ian

[timmyquest]

Thanks alot...now i gotta go do some research :roll:

And now i know that when i decide to get an IR filter it's going to be a pain in the ass :cry:

[iwatkins]

And now i know that when i decide to get an IR filter it's going to be a pain in the ass :cry:

Hoya R72 is a safe bet. Comes in many sizes.

Anything higher and you will have to find out first whether the upper limit of sensitivity of the sensor you are using is below that of your prospective filter or not

E.g. the 10D may have an upper limit of 900nm (does anybody know ?) so no point having an IR filter that only starts to pass at 910nm.

Actually, report back when you are done. I'm interested in doing some IR work myself. :lol:

Cheers

Ian

[timmyquest]

And now i know that when i decide to get an IR filter it's going to be a pain in the ass :cry:

Hoya R72 is a safe bet. Comes in many sizes.

Anything higher and you will have to find out first whether the upper limit of sensitivity of the sensor you are using is below that of your prospective filter or not

E.g. the 10D may have an upper limit of 900nm (does anybody know ?) so no point having an IR filter that only starts to pass at 910nm.

Actually, report back when you are done. I'm interested in doing some IR work myself. :lol:

Cheers

Ian

Wont be for a while, i've only got two crap sigmas and the kit lens with my 300D, my first lens is going to be the 50mm F/1.8 then the 100-400mm Neither of which would i buy an IR filter for, rather that will go on my 28-135...i have a veyr long road to look down ;-)

[Scottes]

I'll take a stab at polarizers...

Polarizers work by allowing in only the light that is at a particular angle. So that light coming into the lens at an angle (like glare) won't be allowed in, and is blocked by the metallic(?) particles set in the glass somehow at very specific angles.

OK, OK, it's magic, and just leave it at that. :)

Seriously, I don't know if I explained it well, but that's how they work. Imagine a picket fence - when you're at a 90-degree angle to it then it's easy to see through the fence. But position yourself at a sharp angle to the fence and you can't see through it very well. Basically that's polarization.

[timmyquest]

I'll take a stab at polarizers...

Polarizers work by allowing in only the light that is at a particular angle. So that light coming into the lens at an angle (like glare) won't be allowed in, and is blocked by the metallic(?) particles set in the glass somehow at very specific angles.

OK, OK, it's magic, and just leave it at that. :)

Seriously, I don't know if I explained it well, but that's how they work. Imagine a picket fence - when you're at a 90-degree angle to it then it's easy to see through the fence. But position yourself at a sharp angle to the fence and you can't see through it very well. Basically that's polarization.

Nope, makes alot of sense and is pretty much what i thought. My physics teacher once showed us "polarizers" and if you stacked two on top of eachother at the right angles 0 light would get through. I was just wondering how this worked with photography.

[CyberDyneSystems]

Scottes,. thans for that.. very "simple to the point we can all understand it" answer!

Now I know :)

[GPR1]

I believe the 10D has an IR filter in front of the sensor -- most digitals do. That makes IR photography difficult with a digital, because you put the IR filter in front of the lens, limiting the visible light that passes, then your IR filter in front of the sensor blocks most of that light you just let through.

There's a company on the web who will retrofit your camera by removing the factory-installed IR filter, but then you have an expensive IR-only camera.

If you want to experiment with IR, I'd suggest picking up a cheap film body (they're a dime a dozen now), buy some IR film, get the filter, do a little research (exposure is tricky), and have some fun. The images can be amazing.

Greg

[Volatile]

I thought I read that digital sensors are not affected by UV light, so there's no need to filter it. Don't forget that even the best UV filters block 10% of visible light. Wouldn't you want that extra 10% to hit the sensor?

Also, I believe that the glare from sunlight on water is polarized horizontal to the water's surface, so a polarized filter rotated to the vertical would block out the glare and possibly help you get a better overall exposure of your subject.

I'm not a photographer, but I did stay at a Holiday Inn Express last night.

[Laziferous]

Also, I believe that the glare from sunlight on water is polarized horizontal to the water's surface, so a polarized filter rotated to the vertical would block out the glare and possibly help you get a better overall exposure of your subject.
I knew there was a reason I bought a circular polarizer rather than a linear one :D

[Ikinaa]

Found this about polarizing filters...

http://www.colorado.edu/physics/2000/polarization/index.html
rather easy to understand...

[stopbath]

I can only answer Number 2...

"B&W" is a very high quality brand name of German manufacture.. they are ocnsidered to the "best" manufacturer of filters. There is no "black and white" filter.
Well, it depends on the definition of "Black and white" filter...
Yes there are no filters that desaturate colour out of an image while retaining the value of the light.
But there are lots of filters used in black and white photography.
These can be refered to as black and white filters as they are used almost exclusively in black and white photography and are almost useless in colour photography except for special effects.

A solid red filter will block non-red light waves and thus lighten the reds in a black and white image. Red is useful for deepening the sky in black and white photography.

Filters like warming filters (light orange cast) have more use in colour photography and not in black and white.

Effect filters such as star, or soft image filters are useful in both colour and black and white...

[w10d]

A solid red filter will block non-red light waves and thus lighten the reds in a black and white image. Red is useful for deepening the sky in black and white photography.


Reminds me of the time at college when a first year came to me for help whilst printing....

They had been away for 3 days, 2 days travelling and one day shooting landscapes with a 5x4 camera, large tripod and a stack of dark slides. They had (half) paid attention during the previous week's theory lesson covering the use of filters for black and white. They had used a red filter on all shots, to enhance the blue sky. Now they had a problem printing the pictures - no matter what they tried they couldn't get rid of the strong red cast in all the contacts...

(Well, we all have to learn).