BetterPhoto Q&A
Category: Camera Filters

Digital Filters

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February 16, 2004

The only real difference between "digital" and "film" filters is what normally is the size and the coatings. The size being 20-42mm for the typical "digicam" and "digital camcorder" filter sizes. Usually 37mm or so.

With film and prosumer digital cameras, the filter sizes are in the 42mm+ range. 49mm-72mm is typical.

The other difference would be the type and number of coatings to reduce things like Chromatic aberration which is a much bigger issue in digital photography than film photography due to the difference between film based capture and sensor based capture of light.

Basically, for your 10D, it is a moot point since you will be using some pricey EF glass which is already coated for high end optics. Filters you would use for "film" and "digital" would essentially be the same.

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February 16, 2004

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February 17, 2004

I've used filters without incident on an Olympus C2100UZ and on my current Minolta Dimage A1.

I'm curious to know what kind of issues you encountered while using filters with a digital camera. Which camera model and filter combo
produced a problem?

Below, I've listed my experience with filters on digital cameras, whether there was an issue and a workaround, and whether photoshop can be
used to replicate the effect.

- Polarizing filters:
Use a circular polarizing filter. Standard "straight" polarizing filters will mess up the auto-focus system on a digital camera. The
circular polarizer will cut down the light, but not affect the autofocus system as much.

Glare that polarizers filter out cannot be corrected for in photoshop easily(or at all in some cases). The intensifying characteristic of
polarizers for the sky can be mimicked, but at a potential loss of image information when changing saturation of the picture unless you
are working with RAW/16bit mode.

- Color balancing filters:
Redundant in the digital system. Auto White balancing or custom white balancing will resolve the light coloration issues. What the camera
doesn't catch, you can fix(to a degree) in photoshop later. Unless you are shooting in RAW and correcting in RAW, you will lose image data
when you perform a color correction if it pushes the color information past what the bit allocation for that color channel can handle.

- ND Filters:
Whether this is redundant will depend on your shooting style. You can apply a ND or a graduated ND filter to stop down an overly bright
scene or a grad-ND to tone down part of a scene. However, you can also take 2 pictures exposure balanced for the 2 extremes and blend
them back in photoshop. Either way works. The blending method may result in imperfect blends if the shots were hand-held.

You can correct for a certain amount of over or under exposure, but in many cases, doing so will also pull out alot of shadow noise.
There are only so many bits of data used to store information about each color channel. When you push it beyond that, you get data
clipping which results in unnatural color/noise/lighting.

- Macro/CloseUp Lens:
Works fine. The only issue to bear in mind is increased chromatic aberration(colors not focused, causing fringing). I've used up to +10
close-up lens and while CA crept in at the edges and corners, the majority of the image was still sharp and clear. This would be a problem
on a film setup as well.

This cannot be mimicked in photoshop without serious software cropping and resampling. At which point, your image will lose the actual
resolution and become less and less sharp.

(end of part I)

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February 18, 2004

- Soft Focus Filters:
These can be emulated in photoshop, but having used this filter with my digital gear, it doesn't pose a problem. The overlaying of a
blurred version and a sharp version in photoshop does a good aproximation, but isn't a replacement for a soft focus lens. Light flares
and other natural artifacts of using a soft focus filter will not be present. This applies to selective soft focus filters as well.

- Intensifiers/Color shifter filters
Basically, you don't suffer a penalty in using these filters. The effect can be mimicked in photoshop, but with the above color channel
data loss to be kept in mind. You can augment the hue of the image to simulate the color shifting and up the saturation/luminosity to
mimick the intensifiers, but the effect won't be quite the same. (See below about auto-whitebalance issues.)

- Starburts/multi-image filters:

Basically, they perform the way you would expect them to. No workarounds were required. With photoshop, there are filters you can get
which will key in on luminosity values in the image and render a star burst or lens flare or multi-image composite.

- Wide Angle lens filters/fisheyes:

One a camera which uses IR autofocus, the wide angle can block the camera's ability to focus. This made the filer/lens unuable on my old
digital camera without resorting to manually focusing. On my current camera which uses contrast auto-focus, this is no longer a problem.
For my old camera, what I would do is shine an infra-red flashlight at the target to illuminate it for the focusing and turn off the
flashlight when I was ready to shoot.

Short of applying a spherical distortion filter to your image, you really can't get a "wide" shot effect from just photoshop alone.

- ND filters (for long long exposures)
The problem I encountered here had more to do with the CCD/CMOS sensor's noise level than the filter. Basically, taking a digital camera
(with the exception of the 1D,1Ds,D60,D30,10D,S2Pro,etc pro cameras), the noise renders the image unusable. This was also true when using
#87 type filters for IR photography. What you will get is ALOT of noise and grain in your final exposure in digital.

Neatimage and other noise removal programs can help, but you'll probably also be filtering out alot of the image as well. :

- AWB(Auto White Balance) interference.
Color filters are rendered mute if one does not turn off the auto-white balance of most digital cameras. You can set the WB of the camera
to AWB or fixed to some type(sun/cloudy/flourescent/tungsten/etc). When you can't you've basically negated the ability to effectively use a
color filter. This can be worked around by white balancing against a known object without the filter, then locking that setting in place
before putting on the filter.

- Teleconvertors (1.4x, 1.5x, 1.6x, 2x)
Not replicatable in photoshop. Negatives include loss of light and loss of sharpness. But this would have been the case regardless of
whether you were working with film or digital.

(End of part II & response)

Sorry for the 2 parted answer... the system was complaining that my post was too long. ^_-

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February 18, 2004

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February 18, 2004

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February 20, 2004