Why this effect?? Who Can Explain It!

I purchased a Cokin P series holder and ND 8x (3 Stop) filter the other day. I had read the comments regarding these filters throwing a red tint into pictures, but I figured I'd try it anyway. Well,lo and behold, I got a red tint. Local camera store where I purchased it didn't believe me so they asked me to take some shots and let them see them.

So I ventured outside and took some, then came inside and took some of my bathroom sink. Properly exposed without the filter @ f8, no flash, 1/8 SS but the red tint showed up again with the filter in place and the camera stopped down 3 full stops, still at f8, no flash 1 sec SS. So I decided to see what would happen if I stopped down further. Much to my surprise the tint almost disappeared @ 1'8" sec.

Folks at the camera store where shocked over the tint and then couldn't explain why it would almost disappear when stopping down further.

Any of you guys want to take a stab at an explaination?

That's weird. I wonder if you might be getting a light leak with refraction around the edge of the filter.

That might have been a fluke. Did you try longer speeds?

Most ND filters aren't truly ND so they tinge off one way or another, especially over longer exposures as the light isn't as bright and as such the gel effect shows through more due to being visible longer - your best bet is to shoot a white card with the ND filter mounted to compensate for the filter, or just adjust WB in post.

huntersdad wrote in post #9952581
I purchased a Cokin P series holder and ND 8x (3 Stop) filter the other day. I had read the comments regarding these filters throwing a red tint into pictures, but I figured I'd try it anyway. Well,lo and behold, I got a red tint. Local camera store where I purchased it didn't believe me so they asked me to take some shots and let them see them.

So I ventured outside and took some, then came inside and took some of my bathroom sink. Properly exposed without the filter @ f8, no flash, 1/8 SS but the red tint showed up again with the filter in place and the camera stopped down 3 full stops, still at f8, no flash 1 sec SS. So I decided to see what would happen if I stopped down further. Much to my surprise the tint almost disappeared @ 1'8" sec.

Folks at the camera store where shocked over the tint and then couldn't explain why it would almost disappear when stopping down further.

Any of you guys want to take a stab at an explaination?

You tried the ND indoors and the tint almost disappeared by 1'8"? Were you under artificial light or natural light?

My guess would be that either the light source (if artificail) was giving out less red light (normal flourescent can render green with AWB) or that your windows are cutting down the portion of red light transmitted (glass bears a slight green tint).

Bear in mind that no glass is 100% transparent- they all absorb certain wavelengths of light by varying amounts.

I should mention that the tint shows up even when outside, though the degree varies. Pictures were taken under fluorscent light, but I have tried the same experiment in sunlight with similiar but less drastic results. I just thought it interesting that the tint would go away by increasing length of the exposure.

Guess I have some more testing to do.

huntersdad wrote in post #9955845
I should mention that the tint shows up even when outside, though the degree varies. Pictures were taken under fluorscent light, but I have tried the same experiment in sunlight with similiar but less drastic results. I just thought it interesting that the tint would go away by increasing length of the exposure.

Fluorescent lighting can be extremely frustrating for a photographer who does not understand it. If the fluorescent lights are operating at the power line frequency (and not all do, especially the compact fluorescent lamps that screw into ordinary light bulb sockets), there will be problems related to the shutter speed chosen.

The problem is that both the intensity and color of the light from fluorescent lights changes at their operating frequency. Those lights that are operating at power line frequency are particularly nasty for photographers, as faster shutter speeds can and will capture some really odd-looking lighting of the subject.

The solution is to use a shutter speed that is twice the speed at which the power line voltage is changing. For example, with 60Hz power, 1/120 second is the fastest shutter speed you can reliably use (and get uniform intensity and color in your image).

You can use shutter speeds that are slower than the max I mentioned as long as they are even multiples of the power line frequency. For 60Hz power, the list of shutter speed choices would be 1/120, 1/60, 1/30, 1/15, and so forth.

SkipD wrote in post #9956157
Fluorescent lighting can be extremely frustrating for a photographer who does not understand it. If the fluorescent lights are operating at the power line frequency (and not all do, especially the compact fluorescent lamps that screw into ordinary light bulb sockets), there will be problems related to the shutter speed chosen.

The problem is that both the intensity and color of the light from fluorescent lights changes at their operating frequency. Those lights that are operating at power line frequency are particularly nasty for photographers, as faster shutter speeds can and will capture some really odd-looking lighting of the subject.

The solution is to use a shutter speed that is twice the speed at which the power line voltage is changing. For example, with 60Hz power, 1/120 second is the fastest shutter speed you can reliably use (and get uniform intensity and color in your image).

You can use shutter speeds that are slower than the max I mentioned as long as they are even multiples of the power line frequency. For 60Hz power, the list of shutter speed choices would be 1/120, 1/60, 1/30, 1/15, and so forth.

I'm pretty sure I understand what you are saying, however, if no filter is properly exposed, shouldn't filtered properly adjusted produce the same exposure? Does the line power change up and down?

huntersdad wrote in post #9956360
I'm pretty sure I understand what you are saying, however, if no filter is properly exposed, shouldn't filtered properly adjusted produce the same exposure? Does the line power change up and down?

A neutral density filter would change your shutter speed, all else (available light level, ISO and aperture selection) being equal.

The point I was making is that fluorescent light can make shutter speed choice a critical factor in getting a decent image.

I thought about fluorescents at first, too - but the shutter speeds were 1/8 second and 1 second. Plenty long enough to average out the flicker.

Strange.

-js

number six wrote in post #9957838
I thought about fluorescents at first, too - but the shutter speeds were 1/8 second and 1 second. Plenty long enough to average out the flicker.

You are right. I missed the bit about the slow shutter speeds in the first post.