Originally posted by Augustus58 How long do the exposures for IR photography take? I can only go up to 30 seconds on the K-X as far as I can figure out. Is this enough? Is there any way to make my exposures longer (I am also interested in astrophotography)?
I imagine some of our astro.friends will chip in on that subject. For long exposures, your mode dial has a B (for bulb) setting. Plug in a wired remote (preferably one that latches) and the shutter stays open as long as you want. Here's how to make a DIY Pentax DSLR cable release:
booleansplit.com DIY Pentax DSLR cable release
The exposure time for IR depends on how deep a filter you use, as well as f-stop and ISO. Since most or all visible light is blocked, only the red pixels on your cam's sensor (1/4 of the total) gather light, so your effective resolution drops from 14.6mpx to 3.65mpx, and you lose 3/4 of the sensitivity. That's why digital IR shots are usually rather grainy. IR film is another story, but why fret...
A mild IR filter like a 680nm or 720nm (or for less money, a red R25A filter) lets you shoot hand-held, lens wide open. My deepest 1000nm filter requires several minutes on a tripod, up to many minutes if I use a small aperture and a ND4 or darker to eliminate all motion.
For your amusement, here are a couple references.
Shooting IR with a normal unmodified DSLR is a 2 step process:
https://www.pentaxforums.com/forums/559973-post33.html
Using DSLRs for Astronomical Imaging:
Digital SLR Astronomical Imaging
(note: w/Pentax interval shooting, Canon remote isn't needed)
Books on digital IR exist. Some can be found in torrents. (Did I say that? Shame on me!) Other IR guides exist online. Spectrum-slicing is great fun and not all that hard, once you get the concepts and tools. Enjoy.