Originally posted by Kitty I'm curious about the B&W and CC, closeups lenses, etc. I don't know what IR-pass filters are.
Ash and Salty are dead-on. As for the other stuff:
* There are two sorts of close-up/macro adapter lenses (strap-ons): 1) complex, corrected adapters like the Raynox products, and 2) simple cheap filter-like +dioptre meniscus close-up lenses. Both (1) and (2) shorten the working distance; (1) correct for aberrations, while (2) degrade image quality somewhat, especially at the image edges. If edge sharpness isn't important, they're cheap fun. I'll use a +1 on a slow lens to drastically thin the depth of field (DOF).
* I mention those +dioptre strap-ons because they also come in split versions similar to graduated or HalfChrome filters, where half the 'filter' is clear glass (or blank) and the other half is the close-up meniscus. This can apparently thicken the DOF -- focus on a near subject through the lens portion, and on a distance through the clear/blank portion. As with any gradated or split filter, be careful where that terminator line goes!
* IR-pass (aka IR) filters block some or all visible light and only allow InfraRed frequencies to pass through to the camera. These filters work best with a camera that has been modified to remove its internal IR-block hot.filter. An unmodified camera requires long exposures with most IR filters.
B&W (Red, Yellow, Orange, Green, Blue) and CC (color-correction) filters are mostly irrelevant on unmodified digital cameras -- their effects CAN be replicated in PP. Exceptions:
* I have read that a Red filter increases sharpness slightly when shooting B&W on a digicam. This has to do with the construction of microfilters built onto the camera sensor. I haven't verified this yet.
* A Yellow filter when shooting garish neon lights at night gives strange color renditions. Since used sets of B&W filters are cheap, this can be more cheap fun.
* B&W filters can be stacked on modified digicams for interesting tonal effects. I use these on Sony NightShot P&S's, which are pre-modified to disable the internal IR-block hot-filter.
* I use a Blue B&W filter or a Violet CC filter as wayback machines. The earliest photo emulsions only saw Actinic light (UV, Violet, Blue) and were blind to green, yellow, orange, red, and IR. Blue and Violet filters let me replicate pre-1875 photo visions.
Using these tinted optical filters is Spectrum-Slicing. More sophisticated variants are the filters used in forensics and scientific work, where narrow bands of the EMF spectrum can be closely examined. Shooting in UV slices can require special (rare, expensive) lenses, beyond my budget. Ratz...