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Old Aug 29, 2008, 9:27 AM   #1
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From another post, those awful purple streaks in low light, off lamps etc or in bright light off reflections etc, if this can be overcome would be amazing yes?

I dont know why I've never stumbled on this before, I've never ever heard of it but it's called a hot-mirror, see below, been around a while and used on earlier Nikon dslrs. Anyway, I'm not sure but this could be what is causing purple streaking and smearing on ccd's, ie no "hot-mirror" or it's not good enough. Interestingly SK filter group, B+W have this, just imagine you could cut that awful ccd smear, maybe this is the answer? worth a try anyway, how would you fit it thought permanently to a 12/15?


hot mirror filter cuts IR light. According to Kodak's site it greatly reduces near-infrared light, resulting in less noisy and more color-accurate images. Basically it blocks light in the 700nm to 920nm wave length. This light passes through the Bayer filter and exposes your sensor.

The Bayer layer is needed because All image sensors are grayscale devices that record the intensity of light from full black to white. To add color to a digital camera image, a layer of color filters is bonded to the silicon using a photolithography process to apply color dyes. Typically, an RGB camera would have three image sensors with color filters, as well as an optical prism and a special optic capable of sending the incoming light to the three different color sensors. Each image sensor will then create 'red' 'green' or 'blue' digital samples. However, to lower the cost of an RGB camera, a new approach was developed to simplify the camera's optics such that only one image sensor is needed instead of three. This approach uses color filter arrays (CFAs) in order to capture RGB images.

A Bayer filter uses a checkerboard pattern with alternating rows of filters. The Bayer pattern has twice as many green pixels as red or blue and takes advantage of the human eye's tendency to see green luminance as the strongest influence in defining image quality.

What the Hot Mirror filter does is prevent the IR (or near IR 700nm and up) from reaching the CCD. It seems that the Bayer layer allows IR to pass through the red and blue layers (thats why it looks purple).

As for the Neutral Density (I assume you are asking if it effects your exposure), the answer is - yes, you loose 20% of a stop (give or take) or roughly 2/3rds of 1/3 of a stop. I'm not sure that you even lose that in the visible portion of the light. (If the IR is adding to the amount of light exposing your ccd and you cut it out - I guess the image looks less bright, but more testing is needed as to if that loss is of any benefit.)

The D1H seems to have less of a problem in this area (although the D100 seems to be effected more then the D1H and less then the D2H). All cameras made today should have a hot mirror (or other IR blocking) filter installed between the lens and sensor (CCD, CMOS, LBCAST).

As for leaving it on the lens all of the time - I do. Any filter(or any glass in front of your lens) can reduce your quality and sharpness. They are prone to flare (more places for the light to bounce around in). The advantage I seem to experience with the hot mirror is the images seem sharper. I'll believe that this is because IR light focuses at a different point then visible light, so most of the IR is out of focus light anyway.
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Old Aug 29, 2008, 4:48 PM   #2
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I have ordered one for my Canon HF100. I will report results when it arrives

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Old Aug 29, 2008, 5:00 PM   #3
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why I preferre Cmos LOL thanks for the info
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Old Aug 29, 2008, 11:33 PM   #4
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The CMOS in my Canon still responded to the infra-red remote, but without overloading with 'blur', like the CCD.

I have often wondered why I am unable to get decent sharp images from video projection screens, I will bet this is the reason.. That's why I ordered a filter for my Canon, and we will see what happens then...

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