Are photoshop/aperture etc. B&W conversion filters exactly the same as a real filter?

I think that perhaps they aren't and B&W conversion filters still may have a place...or maybe you can teach me a new technique.


Situation:
You want a B&W with red filter effect.

There is a larger dynamic range in the scene than the sensor can capture.

RGB is not evenly dispersed through the dynamic range, for this example, lets say that the blue channel is way to the right of the red channel, so you cannot capture all the detail of the reds and blues in one exposure.

In this case, you couldn''t use the channel mixing to create a good image with software filters, because you would lose large chuncks of image data regardless of which filter you choose, either losing the highlight detail or shadow detail, or losing the middle and getting way to mich contrast.


So woudn't putting on a real filter allow the sensor to then be re-exposed to capture all the deatil in the scene pertinent to your desired final image, because it is filtering real light, and not restrited to the small dynamic range of each ridgid one-color channel in the RAW file?

In scenes where each channel occupies a similar dynamic range, I think software filters are good, but sometimes the light is just crazy, and filtering out real light with real glass could help the camera better capture the data specific to your end product, this making it valuble to still keep on hand some B&W conversion filters.

Or am I crazy?

I started to write a long response but changed my mind.

By putting a filter on the lens you are altering the relationship of the primary colors much like the different lighting situations you illustrated.

Unless the sensor is not equally sensitive to R + G + B, you would not be capturing a true representation of the scene by putting a colored filter on the lens, limited DR, aside.

It depends what you want. Lots of different filters for B&W photography were available which have become, imo, obsolete with the advent of digital cameras and the fact that they capture in color only. Do it in post unless there is some technical or artistic requirememnt to capture detail throughout the entire image and get around the limited DR of digital camera.

NatDeroxL7 wrote in post #10706656
Or am I crazy?

I think you're probably worrying too much about the details.

In the days of black & white film, we used colored filters to control contrast. We knew that some films were more sensitive to one color or another, but nobody know precisely how much and usually we didn't care. Unless we used colored filters a LOT, we just had an idea what various colors of filters would be likely to do for us. It was always a trial-and-error type of thing.

I believe that using colored filters on a DSLR and having the camera make the monochromatic image would be as much of a crap-shoot as we used to have in the old days. I would much prefer to be able to make a hundred different monochromatic images from the same RAW image using post-processing tools because the process lets me produce the image I had in my mind much more easily than being locked into one combination and having to guess right.