When does a hot mirror filter make a difference?

akptc

akptc

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Read somewhere that all digital sensors register some IR "light" which can negatively affect image quality. Hot mirror filters are supposed to help. I've had an opportunity to try a Tiffen hot mirror filter on my R-D1, did not see any effect on the images. The 1st link below is general info, the 2nd appears to prove that hot mirror filters are pretty much useless. I wonder if anyone has tried using one of these filters on the R-D1 (and noticed any positive results)?

http://whatdigitalcamera.com/help/article.php?id=65833
http://dpfwiw.com/ir.htm#hot_mirror
 
Andy,

I would surmise that they would be useless as stated in the article, due to the fact that most digital sensors have intergrated IR filters. Canon makes a special model of the 20D for recording IR. It does not have any IR filters over the sensor.
 
I've just obtained a B+W 486 UV-IR cut filter for the 50mm 1.4 Nokton. I'm hoping it will eliminate the slightly reddish blotchy skin I sometimes get on portraits taken with incandescent light. (The light is strong in IR which penetrates the skin showing surface blood vessels if the camera has significant residual IR sensitivity.)

I haven't had time to evaluate the filter yet. I believe the R-D1 uses the same sensor as the Nikon D70. If you google D70 and "hot mirror" you will find many references to the problem, including photographs. For example, some fabrics reflect strongly in the infra red resulting in a reddish magenta cast. The severity of the effect is strongly dependent on the amount of IR in the ambient illumination.

Bob.
 
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Hot Mirror on a 20Da

Hot Mirror on a 20Da

kbg32 said:
Andy,

I would surmise that they would be useless as stated in the article, due to the fact that most digital sensors have intergrated IR filters. Canon makes a special model of the 20D for recording IR. It does not have any IR filters over the sensor.
Click to expand...

I actually have that special Canon 20D without the IR filter. Its called the 20Da (for astrophotography). It's made to capture dim emmission nebelues which emmit most of their light in the infrared. Its not really made for everyday use but by putting a hot mirror filter on the lens, you can use it for ordinary use. It actually works OK without the hot mirror by compensating in Camera Raw.
I'm not surprised that a hot mirror would be useless on a regular camera that already has a built in IR filter.

A neat feature of the 20Da is, it is the only DSLR that you can "live view" on the LCD screen. This is so you can manually focus the camera thru a telescope, but I use it occassionally for macro shots and other manual focusing chores.

Rex
 
It seems that in some digicams a hot mirror filter can be useful. In this review of Nikon D2h, Thom Hogan says "Others on the net have noted that use of a hot mirror filter (filters out near IR) changes the camera's noise and color tendencies with certain fabrics and objects. Well, they're right. It appears that any object that reflects near IR has a tendency to run up the blue channel response in the D2h, which in turn makes for slight color shifts and increased noise. Note that flash emits a great deal of near IR and IR light, and I've indeed run into the problem more often indoors using flash than elsewhere. A hot mirror filter does seem to eradicate the problem, at the expense of small light loss overall."
 
Bob Parsons said:
I've just obtained a B+W 486 UV-IR cut filter for the 50mm 1.4 Nokton. I'm hoping it will eliminate the slightly reddish blotchy skin I sometimes get on portraits taken with incandescent light. (The light is strong in IR which penetrates the skin showing surface blood vessels if the camera has significant residual IR sensitivity.)

I haven't had time to evaluate the filter yet. I believe the R-D1 uses the same sensor as the Nikon D70. If you google D70 and "hot mirror" you will find many references to the problem, including photographs. For example, some fabrics reflect strongly in the infra red resulting in a reddish magenta cast. The severity of the effect is strongly dependent on the amount of IR in the ambient illumination.

Bob.
Click to expand...

Bob
The filter I use on my Canon 20Da is similar to your B+W 486. Mine is a Heliopn ES 77 UV/IR blocker. Its a very exotic looking multicoated filter, that cost about $200 in the 77mm size. Because of the cost, I only have one. That's how I discovered that you don't really need it on every lens as you can compensate in CS2 Camera RAW. Basically, what you have to do is build a custom profile using the Greta Macbeth color checker as outlined by Bruce raiser in his book "Real World Camera Raw".

I used the same procedure on my RD1 and it definitely improved the color balance especially with regards the greens. Its true the reds are a little hot on both the RD1 and its sensor cousin, the Nikon D70.

Every camera is a little different,but if you want I can send you the settings that worked on my RD1. Or you can go thru the Bruce Frazer routine which has avery steep learning curve but is very interesting. I know more about color space and
balance because of learning the process.

Rex
 
rvaubel said:
... Every camera is a little different,but if you want I can send you the settings that worked on my RD1. ...
Rex
Click to expand...
Rex, I'd love to try your settings as well, if that's ok. - Thanks!
 
akptc said:
Rex, I'd love to try your settings as well, if that's ok. - Thanks!
Click to expand...

AKPTC
O.K. Your milage may vary. However its easy enough to set the defaults back to 0 if they don't work for your RD1. The results are pretty subtle. They are most visible in greens whick get a little more vibrant. And keep in mind these settings are only for the CS2 Camera Raw plug in version 2.4

Here we go. In the Camera Raw Window open a RD1 file and click on Calibrate
Then set the sliders as follows

Shadow Tint 0
Red Hue 0
Red Saturation 0
Green Hue +6
Green Saturation +50
Blue Hue +9
Blue Saturation -5

Don't forget to Save New Camera Raw Defaults under the hidden arrow @ Settings:

This particular setting balances out my Gretagmacbeth Color Checker to almost perfect values for the Pro Photo color space. I like the looks of it a little better than Adobes default for the RD1 but that may be just my individual sample.

I just started getting into this. My light source was natural sunlight which can be more variable than a controled artificial source. I'm going to do another sample this weekend and see if I get consistent results.

Rex
 
akptc said:
Rex, I'd love to try your settings as well, if that's ok. - Thanks!
Click to expand...

AKPTC
O.K. Your milage may vary. However its easy enough to set the defaults back to 0 if they don't work for your RD1. The results are pretty subtle. They are most visible in greens whick get a little more vibrant. And keep in mind these settings are only for the CS2 Camera Raw plug in version 2.4

Here we go. In the Camera Raw Window open a RD1 file and click on Calibrate
Then set the sliders as follows

Shadow Tint 0
Red Hue 0
Red Saturation 0
Green Hue +6
Green Saturation +50
Blue Hue +9
Blue Saturation -5


This particular setting balances out my Gretagmacbeth Color Checker to almost perfect values for the Pro Photo color space. I like the looks of it a little better than Adobes default for the RD1 but that may be just my individual sample.

I just started getting into this. My light source was natural sunlight which can be more variable than a controled artificial source. I'm going to do another sample this weekend and see if I get consistent results.

Rex
 
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