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03-30-2013, 01:03 AM   #1
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Pentax K-x more than ISO 1600 in bulb mode?

Has anyone found a way to set a Pentax K-x to more than ISO 1600 in bulb mode? I.e. some debug mode operation or similar? Anyone who know why this limitation? Is it similar in K-30, K-5, K-5 II?

03-30-2013, 01:32 AM   #2
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It might have been limited because it gets very noisy. The K-5 doesn't have that limit ?
03-30-2013, 01:55 AM   #3
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QuoteOriginally posted by Falke Quote
It might have been limited because it gets very noisy. The K-5 doesn't have that limit ?
It might be a reason. But has anyone tried? I find this limitation a barrier for night scape photography with moving stars in the scene. Both with, and without a mount for tracking the stars. I have a theory that the limitation is there for preventing the sensor from overheating at higher iso:s during longer exposures than 30 sec. But as far as i know, the camera has a built-in heat protection sensor who shuts the camera down when reaching critical temperatures (in live-view that is so). When outside temperature drops below freezing point, one should be able to exposure more richly in bulb if this is the case.

Also found now that K-r, K-5, K-5 II and K-5 IIs has the same limitation. K-30 I still don't know about, but probably likewise.

I guess I'm not the only one who would benefit from some kind of work-around for this problem. Though, I'm somewhat specialized in night-time photography. The word problem means "before a solution is found", I hope this can bee the case here.

Last edited by Nokturner; 03-30-2013 at 02:01 AM.
03-30-2013, 02:01 AM   #4
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QuoteOriginally posted by Nokturner Quote
It might be a reason. But has anyone tried? I find this limitation a barrier for night scape photography with moving stars in the scene. Both with, and without a mount for tracking the stars. I have a theory that the limitation is there for preventing the sensor from overheating at higher iso:s during longer exposures than 30 sec. But as far as i know, the camera has a built-in heat protection sensor who shuts the camera down when reaching critical temperatures (in live-view that is so). When outside temperature drops below freezing point, one should be able to exposure more richly in bulb if this is the case.

Also found now that K-r, K-5, K-5 II and K-5 IIs has the same limitation. K-30 I still don't know, but probably.

I guess I'm not the only one who would benefit from some kind of work-around for this problem. Though, I'm somewhat specialized in night-time photography. The word problem means "before a solution is found", I hope this can bee the case here.
I think that the limit is there because ISOs above that are beyond the sensor's native operating range- but that's just my guess. In any case, if you're planning on using long shutter speeds, why not shoot at ISO 100 to begin with for the best IQ?


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03-30-2013, 02:10 AM   #5
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QuoteOriginally posted by Adam Quote
I think that the limit is there because ISOs above that are beyond the sensor's native operating range- but that's just my guess. In any case, if you're planning on using long shutter speeds, why not shoot at ISO 100 to begin with for the best IQ?
This is no problem without moving stars in the frame. In this case lower ISO in combination with longer exposure times is a good option and the best solution for good nightscapes. But with moving stars in the frame the only option is to crank up the ISO. A star-tracker blurrs the landscape, and there are several other reasons that one likes to keep the exposure times down by rising the ISO. Exposure times get long enough anyway to start getting problems with changing scenery during the exposure.
03-30-2013, 03:44 AM   #6
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Strange. I just checked on the K-5 and I had no problem taking a shot in Bulb mode with infrared trigger and set to ISO12800. But in the manual - as you stated - they say maximum ISO sensitivity is 1600.

If I could be bothered I would pull out my old K-x, put in batteries and try the same as above. It might be a mistake in the manual... as in the K-5's.
03-30-2013, 04:15 AM   #7
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Can't get any of my two K-x:s to reach higher than ISO 1600 in bulb mode, with firmware 1.01 and 1.02, with, or without ir-remote-setting. Was that ISO 12800 on your K-5 really in bulb mode? Than there is a wrong statement in the specs/manual as you say. Wonder about the K-30 in this case?
03-30-2013, 04:30 AM   #8
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ISO1600 is "native" top iso of the sensor, all the rest including is done by software anyway, so shoot in RAW and lighten up and you get the same shot actually.
Same is true for the K5

03-30-2013, 05:11 AM   #9
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QuoteOriginally posted by Anvh Quote
ISO1600 is "native" top iso of the sensor, all the rest including is done by software anyway, so shoot in RAW and lighten up and you get the same shot actually.
Same is true for the K5
Might be so, but my actual tests of ISO-noise suggests that rising the ISO in the camera always gives better results than lightening in post, both in RAW and JPG. Especially att higher ISO:s. This contradicts the theory, but it is my findings.
03-30-2013, 06:25 AM   #10
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above ISO1600 the camera aplies noise reduction to the RAW files, if even you turn off noise reduction.
So nothing is contradicted yet.
03-30-2013, 07:31 AM   #11
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Oh yes! That might be the solution! Haven't thought of that noise reduction is aplied on the higher ISO RAW:s. Dug into my archive and made a preliminary test, can be as you are saying. Will do a field test to night and see what happens when comparing exposures of different ISO:s and applying gently NR in post to the 1600-ISO:s to compare when I lighten them in post to same level as the higher ISO:s. Hopefully they are equivalent and I don't have to bother about higher ISO in bulb than 1600, the camera is already doing all that it can for me so to say I just continue shooting and post-processing as before.

Will come back and tell my findings here
03-30-2013, 01:08 PM   #12
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the NR on the computer is often more sophisticated so it might be able to do a better job with a little bit of work.

this is also still on my test chat to do, so would be very interesting to see your result.
03-30-2013, 05:28 PM   #13
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Made the field test exposures now to night: Comet PANSTARRS, Andromedagalaxy, aurora and astroscapes. Exposures ranging from ISO 1600-12800. Will make the comparison tomorrow I hope. Now time is 01:30 local time and time for sleep after a beautiful evening and night out in the forest
03-31-2013, 05:09 AM   #14
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Comparison made

Time consuming comparison made. And my findings are... equivalense! If I use Pentax own rawconverter Pentax Digital Camera Utility 4 there is a perfekt match between an ISO 1600 image lightened 3 steps in post and an ISO 12800 image straight out of the camera. All there is need for is to set the EV to +3 and turn all noise reduction to off in the programme (!). If I use Adobe Lightroom, things get a bit more complicated when one has to compensate with fill light, brightness, color temperature, contrast, some noice reduction and also color balance in HSL and maybe some more setting. But Adobe LR also does a good job, and I prefere the rendering of the image out of LR over PDCU4 and also LR:s convinient adjustment possibilitys and tools. I now has stored my settings in LR as presets, converting ISO 1600 to 3200, 6400 resp 12800. Remains to see how well they work on different kinds of images.

So, there is no longer a need for me to feel that ISO 1600 in bulb hampers my creativity in low-light conditions My problem had a solution, and a very simple one

Images (too small to really see, but I'm saving on my storage space here), ISO 1600 to 12800 in LR. The first is ISO 12800 straight out of the camera, the second ISO 1600 to mimic ISO 12800 with Adobe LR, the tweak coul'd bee better done by some more adjustments, but I find it good enough for now. 25 sec exposures at f/2,8. Notice that the aurora has changed between the images, it is more intense green on the first image, it's not the image rendering:
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Last edited by Nokturner; 03-31-2013 at 05:23 AM.
03-31-2013, 06:26 AM   #15
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Good to see this confirmed with these great shots =]

You could make presets in lightroom to push your 1600iso photo up the stops you want.
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