Originally posted by BoredomFestival Please help an SLR newbie with some lens advice. I just ordered a K-5 (my first interchangeable-lens camera of any sort)... up to now I've been sticking to high-end P&S cameras, as my interest is in the rather niche area of cave photography (where you really don't want to schlep around more gear than you have to, so size & weight matters a lot).
Based on my P&S experience, the bulk of cave photography wants a fast lens (duh), but also pretty wide -- my current go-to cave camera (Canon S90) has a fixed lens at f/2.0, 28mm (equivalent) at wide open. It's pretty rare that I need anything longer than 50-60mm equivalent.
Now, the K-5 is obviously gonna have waaaaaay better high ISO performance (which is kinda the reason I got it), so I can make do with a less-fast lens, but it seems that those excellent Pentax pancake primes tend to be significantly slower than I would have thought.... the DA21 is f3.2, and the DA15 is f4, and since the only light around is the light I bring in, I need all the photons I can get...
And just to throw one more wrench into the mix: as mentioned here, size and weight are nontrivial considerations here (i.e., a pancake prime is waaaaaaay preferable to a heavy zoom); similarly, WR is preferable to non-WR (as dusty/muddy/wet conditions are the norm, not the exception). While neither of these are deal-breakers, they are definitely tiebreakers...
I'm going to initially be experimenting with the 35mm f2.4 prime, even though it's not as wide as I'd like, mainly because it's fast and cheap (and augmenting it with the 18-55WR lens, mainly to have at least one WR lens available for sloppy conditions), but I'd love to find a wider lens that is "fast enough" for darker-than-usual conditions. While I'm not expecting to find many cavers chiming in here (though that'd be great), I'd love to hear advice from anyone who has had to do shooting in other sorts of dark, enclosed spaces.
A number of years ago I did a project documenting a gold mine, including the underground workings, shortly before it shut down. The underground part happened on very short notice, so I had to move quickly and shoot a lot of pictures with a minimum of equipment.
I went with a solid but failry light tripod, a Nkon F90 and SB25 flash, and a Sigma 20/1.8. Existing light ranged from widely spaced, dim light bulbs to total darkness. My strategy was to use flash for bare bones documentation. To capture the underground ambience, I decided to use existing light or combined flash and existing light as appropriate. I also experimented with illuminating some shots by painting with the miners's lamp on my helmet, in some cases combined with other existing light. I worked at a variety of apertures, depending on the circumstances of the particular shot.
I relied on manual focus as it was more reliable than AF under those conditions.
The 20/1.8 was very useful. In particular, the fast speed made focusing and composition much easier. I was able to do weird things like use illumination from the AF assist beam on the flash to focus on things that were too far away to see properly with my rather dim miner's lamp.
The miner's lamp shots worked out remarkably well, by the way.
I know there have been lots of reports of inconsistent build quality with the 20/1.8. I had a very good sample that was quite sharp through its aperture range. I was even able to use it for very high-quality copy work with a full-frame DSLR ina a pinch, with excellent corner-to-corner sharpness at f/8.
John