Using filters for digital B&W

Kev M

Kev M

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I've recently been having problems with image quality (or at least perceived image quality) when taking B&W photos with my DSLR. It's mostly in the form of posterization in the transition between tones and it looks crap.

I know about the argument for taking a striaght colour photo and then applying filters but there's a good reason I've been using coloured filters at the taking stage. I've started using coloure filters more in my B&W film photography and have been using the DSLR as a sort of Polaroid/backup. I test which filter is going to suit the scene best from the playback on the LCD, double check the exposure and then stick the filter on the film camera. When it comes to editing the digital photos the problems start.

This weekend I was doing some portraits and using an orange filter to give me the contrast I wanted, when I imported the photos into lightroom and desaturated them the problems started.

I sent a copy of the RAW file to a friend who immediately said "there's no blue data in the image, when you then try and desaturate it rapes the image because of the lack of data".

Ah-ha! says I. Could this be because I used an orange filter?

The only thing I found last night was something saying that orange filters make blue skies go dark. Could this be the key to my degraded image quality?

Has anyone else found problems when using coloured filters with digital cameras?

Are there any alternative methods to converting to B&W in lightroom than using the desaturate method?
 
Do it all in the software as your friend is correct if you start putting colour filters in front of the camera it doesn't act the same as using bw film.

I dont use lightroom, but the bw styles in capture one are brilliant, I'm sure there are Lightroom ones you can download.
 
I beg to differ. It does make a difference.

I made some comparative tests last year and I've found an improvement in image quality using a Cokin P002 orange filter compared with a digital 'filter' in PP (Lightroom, Photoshop and Canon DPP).

More at the level of detail than at a larger level with posterisation. Something else is going on there.

http://www.talkphotography.co.uk/forums/showthread.php?t=239064

The flip side is that you lose a lot of flexibility in PP and have longer exposure times.
 
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The problem may be that the sensor in your camera is designed to capture an image as colour i.e. RGB. If you put a colour filter on your lens, you are affecting the colour recorded by the sensor, which may not be the same affect that the filter would have on a medium that is designed to record the varying tones in the scene.
 
I'll admit it would work better with something like the Kodak DCS-420m.

I do keep my eyes peeled at car boot sales, just in case I fancy using a 1.5 mpx monochrome DSLR :)
 
One better way to get black and white in Lightroom is to make a preset that sets all the saturation sliders on the HSL palette to zero (nothing else) now you can use the luminance sliders to ajust the tones.
 
Convert to B&W at the RAW stage, you'll be amanzed at the difference. I shoot digital with a red filter, converted in raw straight to B&W it looks perfect. Export the colour one and try it with differing conversion options an dit never looks right.

Which is which, film or digital?

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Cheers for the responses chaps. As soon as I've got time I'll reply to all your points, unfortunately work is getting in the way of internet time (and everything else at the moment).
 
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