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Photo Forum / Digital Photography / DSLR Cameras / August 2006Filters
Other than polarizing filters, has digital post-processing made most filters obsolete? This occurred to me as I was looking through my old film camera bag and came across with my disused collection of Cokin filters and adapters... > Other than polarizing filters, has digital post-processing made most filters > obsolete? > > This occurred to me as I was looking through my old film camera bag and came > across with my disused collection of Cokin filters and adapters... There some specialized filters such as soft focus, graduated neutral density and so on that are still useful. I don't see much for the black and white filters such as red, yellow, etc.  SignatureBill in Lake Charles >> Other than polarizing filters, has digital post-processing made most >> filters [quoted text clipped - 7 lines] > density and so on that are still useful. I don't see much for the black > and white filters such as red, yellow, etc. Last review of the 20D b+w mode was that genuine red,yellow etc had ever so slightly better effects than the software red yellow etc. As for polariser for enriching colour hue and saturation slide bar are better than losing 1.5 stops of light. If you want to cut down water or metallic reflections then keep using a real polariser. I keep a proper UV filter on my lenses mostly for protection. As for starbursts and things it comes down to your photoshop skills. If you are already proficient filter user then keep using them rather than learn to use photoshop. At that point its down to personal taste, convenience and skill level. > Other than polarizing filters, has digital post-processing made most filters > obsolete? Not if you want to avoid post-processing. > Other than polarizing filters, has digital post-processing made most filters > obsolete? 8< To an amateur probably. However, the camera's image sensor records the Red, Green and Blue channels in differing intensities. To quote an extract from an article on the sensor of the Kodak professional DSLR range: "In the raw silicon, there's about a two-stop difference in sensitivity between the red and blue channels. When you combine this with the heavy color cast of incandescent light sources, the total variation in response can reach four or even five f-stops." http://www.imaging-resource.com/PRODS/SLRN/SLRNA.HTM It is therefore preferable to correct the *incoming* light before it hits the sensor, than to compensate for it afterwards by software, as other undesirable anomalies can creep in, such as extra channel noise. Fascinating...So then, what filters should we be using to correct the incoming light? Are you talking about something similar to the filters we used to use to correct color film for fluorescent lights? Does it have something to do with equalizing that two-stop difference? I've never heard this discussed, but I've never been happy with digital photos taken under tungsten lights, or mixed flash and tungsten, for that matter. >The camera's image sensor records the > Red, Green and Blue channels in differing intensities. > It is therefore preferable to correct the *incoming* light before it > hits the sensor, than to compensate for it afterwards by software, as > other undesirable anomalies can creep in, such as extra channel noise. > Fascinating...So then, what filters should we be using to correct the > incoming light? Are you talking about something similar to the filters [quoted text clipped - 3 lines] > photos taken under tungsten lights, or mixed flash and tungsten, for > that matter. You can equalize it out somewhat with a magenta filter (particularly good on a flash), but at the cost of losing light (flash will drain faster, or you'll have to use a slower shutter speed). The practical benefit of doing so, assuming you have the photons to spare, is reduced shadow noise. This only works if you shoot RAW, of course. SignatureZed Pobre <zed@resonant.org> a.k.a. Zed Pobre <zed@debian.org> PGP key and fingerprint available on finger; encrypted mail welcomed. > Fascinating...So then, what filters should we be using to correct the > incoming light? Are you talking about something similar to the filters > we used to use to correct color film for fluorescent lights? Yes, pretty much. > Does it have something to do with equalizing that two-stop difference? I've > never heard this discussed, but I've never been happy with digital > photos taken under tungsten lights, or mixed flash and tungsten, for > that matter. When shooting outdoors, or with a flash use a (e.g.) Magenta CC40M which will require an additional 2/3 eV of exposure. The spectral power distribution of the light is adjusted relative to the sensor's response curve. As result exposure can be increased and will then achieve the same response from all channels. Without the magenta filter, you will have either underexposed Red/Blue channels or properly exposed Red/Blue and whilst simultaneously overexposing the Green channel. For Tungsten lighting, use a Cyan filter, and for high altitudes use a Yellow one. The precise grade of each will depend on the sensor you have in the camera. >> Fascinating...So then, what filters should we be using to correct the >> incoming light? Are you talking about something similar to the filters [quoted text clipped - 19 lines] > Yellow one. The precise grade of each will depend on the sensor you have > in the camera. I'd overlooked basic colour correction. I take white balance for granted. I still use the colour photo menu in photoshop the same way i'd use the real numbered filters. I had also used the eye droppers in level to select the black and white points. Depending on what you choose also affects the final colour balance. I noticed this more once i'd bought a spyder two screen calibrator. Canon auto white balance is shite. shooting raw and then selecting the appropriate one is quite good. The custom one works well too.I'd also found selecting outdoor cloudy/overcast a good 'one size fits all' setting that more than one source have recommended. I've been playing with that for a while. That works pretty well except for flash work which surprisingly produces slightly warm results rather than cool blue ones. As i don't have a set of each correction for each lense size i will continue down the software route. Though i should really practice using the custom calibration function. 8< > That works pretty well except for flash work which surprisingly > produces slightly warm results rather than cool blue ones. The Magenta filter works well here too. > As i don't have a set of each correction for each lense size 8< There's the rub. |
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