Re: B+W 77mm UV/IR Cut (486M) MRC Filter
Re: B+W 77mm UV/IR Cut (486M) MRC Filter
- Subject: Re: B+W 77mm UV/IR Cut (486M) MRC Filter
- From: Robin Myers <email@hidden>
- Date: Sun, 26 May 2013 10:23:05 -0700
UV light should always be filtered out at the source not just to control fluorescence, but more importantly to eliminate damage to the subject. UV is high energy light that breaks molecular bonds, altering the artwork. It can easily fade more fugitive colors, degrade optical brighteners, can cause chemical changes, and much more.
The issue of fluorescent colorants is not solved by eliminating UV illumination because these pigments are excited by UV AND visible light. Eliminate the UV, there will still be the visible light induced fluorescence.
As for which lights produce the least UV, LED illumination is very good. Tungsten lights still produce UV, including Solux lamps, although at lower levels than other technologies. All the mercury based lights produce UV, that is fluorescent, HMI, HID, CDM, etcetera. Flash units also produce lots of UV. Since UV can be blocked easily with filters such as UF-3, OP-3, UF-4 and others, when shooting artwork I recommend always placing a UV blocking filter in front of the lights, for any light source.
There are also big issues with flash units in their exposure and color variability. It is more by luck than design that some may be acceptable for fine art imaging, most are not, and I do not recommend their use.
For my artwork imaging I use North Light Copy Lights, which use CDM lamps. These lighting units are shipped with a UV blocking filter installed.
IR filtration at the camera may be needed, depending on the camera's optical system. Electronic sensors are extremely sensitive to IR light, and many pigments, and most dyes, reflect large amount of IR light. If your camera insufficiently blocks IR light, there will be color shifts in the image. Some of the visible effects include blues turning purple, blues turning pink, greens appearing gray, blacks becoming pink, and more. There is a paper at http://rmimaging.com/information/color_accurate_photography.pdf which describes the science behind these color changes.
Using lights with high IR emission exacerbates these observer metamerism failures. This is one reason I do not recommend using tungsten or tungsten-halogen lights for fine art imaging. Additionally, the high IR output cooks the subject potentially damaging it.
Of all the light technologies, LED holds the most promise, but it is not good enough for all fine art imaging, yet. Their spectral output, while low in UV and IR, is often deficient in red and cyan wavelengths. This can make some colors hard to reproduce. There are LED lighting fixtures that are adequate for small artworks, but not yet for large ones.
Not mentioned is the issue of cross-polarization, which is sometimes necessary. For that you will need about 8 times more light than an unpolarized exposure. LED and tungsten lighting do not work well, if at all, under these demands.
Robin Myers
rmimaging.com
On May 26, 2013, at 7:25 AM, Hal Hinderliter wrote:
> OK John, I'll bite - which type of studio lighting emits the least IR? (LED?) But what about UV, isn't that more important to reduce at the light source? And if so, what type of lights produce the least UV?
>
> Hal
>
> On May 26, 2013, at 2:00 AM, John Castronovo <email@hidden> wrote:
>
>> Does it help? The right place for filtering u.v. is at the light source. Once the artwork is fluorescing from u.v. light you can't filter the problem out at the camera. More IR filtration at the camera can help with some art, especially if you're using hot lights on a subject having colorants prone to metameric failure but it's still better to use lights that emit less IR in the first place.
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