long exposures with K100D

[jlemire]

I am looking to someday soon get a Pentax DSLR - most likely the K100D. I'm

curious about its ability to shoot long exposures. Is the digital sensor

capable of capturing a high quality image with multi-second exposures? How about

multi-minute? Hours? Where, if any (beyond battery life), is the limit?

[phule]

Digital sensors are affected by temperture. The longer the exposure, the more noise you will see. CCD sensors in consumer cameras can be particularly troublesome with exposures longer than a minute or two. CMOS sensors, on the other hand, handle longer exposures much better, but still are sensative to temperture.

 

Astronomers using CCD sensors for image capture typically cool their equipment with liquid nitrogen in order to reduce noise.

 

If you're planning on exposures under 20 minutes, a DSLR with a CMOS sensor would be the better choice, and even then you should shoot these when it's cold out. If you're planning on longer exposures, you should stick with film.

 

For long exposures (10-20 minute) with a 20D and 5D (both CMOS sensors) see http://notraces.com

 

Another option for long exposures is to take many short exposures and stack them together with some image stacking software.

[josphy]

http://www.tawbaware.com/imgstack.htm

[jlemire]

thanks for the info so far.

 

would a CCD sensor be OK with a few minutes exposure time? Something useful (on the long end) for blurring water motion?

 

Thanks!

[phule]

<<would a CCD sensor be OK>>

 

I'm not sure I understand what you mean by "OK." The amount of noise you see in the image would be related to the time the sensor is exposing, the ambient temperture, the inherent level of noise in that particular sensors design, and whether or not your camera allows you to do a dark-frame subtraction (called Noise Reduction by most manufacturers).

 

You could simply try it and see.

[jlemire]

I guess I am looking for a more "descriptive" ("practical"?) answer, such as "I have taken 2 minute exposures with the camera (or the like) and have had wonderful success" or "I have found that anything beyond 30 second exposures are unacceptable"

 

I understand that matters of taste, levels of what is acceptable, what the final image will be used for will all vary. I also understand (now) that temperature is a factor as well. Before I buy this camera I would like to know how people have found longish exposures.

 

THanks.

[Jochen_S]

I can't help. I haven't been testing into this long exposure stuff with digital yet. The only 30 sec exposure I ever did revealed lots of greenish noisy nothing at 3200 ISO.

 

OTOH: if you want to expose for hours for which artistic reason ever; why don't you just grab a film body and a affordable scanner? - At these exposure times the additional hassle with film shouldn't count at all.

[jlemire]

I plan on using my K1000 for super-long exposures, for star-trails for example. I am just hoping not to have to use film for blurring waterfalls and waves.

[donnie_strickland]

I don't know if they use the same sensor; I don't have a K100D, but I've done 2-minute exposures with my *istDS on ISO 400. There is definitely a little noise. If I was doing more of these type shots I think I'd use film.

[josphy]

For the amount of time it takes to blur waterfalls and waves and streams -- a few seconds is plenty -- don't worry about it. You asked about multi-second, -minute and -hour. But if blurred, milky water is your main objective, then you'll be golden. Stick to film for the star trails though.