Re: OT: Digital SLR's

Huge <Huge@xxxxxxxxxxxxxxxxxxxx> wrote:

On 2008-03-05, Tim Streater <tim.streater@xxxxxxxxxxxx> wrote:

At this point I'm more interested to understand film response vs. sensor
response to different light levels (not sure of a good term here -
transfer function?). At my wedding, on a bright September day, the DSLRs
appeared to have trouble with the cake (icing) and the bride's dress -
both very white. The official photog with his large format film jobby
had no trouble. Of course, it could just be that he's a pro, but I am
curious about whether there's a difference in the behaviour of
film/digital in this respect.

This is definitely something I noticed recently, while trying to photgraph
the Taj Mahal in bright sunlight. My D50 was *way* overexposing it on
auto. I think I ended up underexposing it by about 3 stops.

There's not a digital camera that can match the dynamic range (I think
that's the term you're after) of old film. If you want to start learning
how to deal with this, then you'll need to learn about histograms. These
can tell you a lot about exposure.

If you check one for an old film photo (in Photoshop, or Gimp for
example), you'll see that the data is usually spread across the entire
width of the scale (of that does depend on how good your scanning is
too). If you look at images from DSLRs, you'll usually see that they
don't quite reach the ends of the scale. Typically a DLSR is a couple of
stops short on DR than film. Compacts are even worse.

This is where you see people harping on about HDR (High Dynamic Range)
now, where they'll use techniques to regain that lost data. This can be
done by bracketing a shot, and then merging them later (OK if you
haven't got a moving subject), or with RAW you can make sure the
original shot hasn't been blown at either end of the scale, and then
process the image twice to allow for exposing each end of the scale.

With RAW images it helps a lot to slightly underexpose anyway - I
usually set my Olympus DLSR to -0.3ev. THis usually maintains highlight
detail, and the shadows rarely get dropped off either.

--
Andy Hewitt
<http://web.mac.com/andrewhewitt1/>
.

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