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02-26-2010, 03:28 AM   #1
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K-x longest successful exposure?

Hi, I was trying to get some star trails tonight, so using very long exposures. I'm curious, whats the longest exposure time people have successfully got with their K-x in Bulb mode?

The longest I have managed so far is 2 minutes. So far anything longer and I end up with my K-x in a funny state - I hear half the shutter noise at the end of exposure and camera never comes back even after waiting many times the exposure period (also will not turn off - have to remove batteries). Not sure if this is a common experience or not?


Last edited by kiwi_jono; 02-26-2010 at 04:41 AM.
02-26-2010, 02:10 PM   #2
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Your camera is doing something called "dark frame subtraction noise reduction". On long exposures, the sensor heats up and adds noise to the image. To compensate for this, the camera takes a second shot with the shutter closed, for the same length of time as the real photo. Then it subtracts the noise in the second image from the first.

You'll have to read your manual to find out the exact details and whether it can be turned off. I think on your camera, after a certain length of exposure, it can't be disabled.
02-26-2010, 02:26 PM   #3
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I did a few star trails at approximately 20 minutes. The camera then did 20 minutes of dark-frame exposure and then went back to normal. I don't know why yours wouldn't be coming back to its normal state after the DF exposure.
02-26-2010, 02:58 PM   #4
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QuoteOriginally posted by Just1MoreDave Quote
Your camera is doing something called "dark frame subtraction noise reduction". On long exposures, the sensor heats up and adds noise to the image. To compensate for this, the camera takes a second shot with the shutter closed, for the same length of time as the real photo. Then it subtracts the noise in the second image from the first.

You'll have to read your manual to find out the exact details and whether it can be turned off. I think on your camera, after a certain length of exposure, it can't be disabled.
Ahh yeah I knew that and yes I have read the manual a couple of times. As I said I was waiting for 3 times the exposure time after it finished and it does not come back.
Sounds like it might be a problem with my camera or possibly batteries (although I made sure they are charged and have tried two sets).


Last edited by kiwi_jono; 02-26-2010 at 03:14 PM.
02-26-2010, 09:20 PM   #5
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Are you using alkalines? Your safest bet for longer exposures are lithiums (A single set of the cheaper variety of energizer lithiums handled the star trails I mentioned along with two more weeks of heavy use... sometimes I forget the little thing actually requires fresh batteries from time to time).
02-26-2010, 11:28 PM   #6
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QuoteOriginally posted by kiwi_jono Quote
Ahh yeah I knew that and yes I have read the manual a couple of times. As I said I was waiting for 3 times the exposure time after it finished and it does not come back.
Sounds like it might be a problem with my camera or possibly batteries (although I made sure they are charged and have tried two sets).
Sorry, can't read.

I would suspect a power problem of some kind. There have been a few complaints about the K-x and batteries. The expensive idea is an AC adapter - at least if you buy the Pentax one. A pack of non-rechargeable lithiums is cheap, and they should be better than NiMH rechargeables because they have a higher voltage. If you haven't upgraded your firmware, that will help with battery issues too.

If you were in this hemisphere, temperature might be an issue. Probably not in NZ, right?

My camera (*ist DS) started randomly firing its shutter many times after each shot. Cleaning the battery contacts fixed it, and it's been fine for months. A longshot in your case, with a much newer camera.
02-27-2010, 12:37 AM   #7
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QuoteOriginally posted by Just1MoreDave Quote
Sorry, can't read.

I would suspect a power problem of some kind. There have been a few complaints about the K-x and batteries. The expensive idea is an AC adapter - at least if you buy the Pentax one. A pack of non-rechargeable lithiums is cheap, and they should be better than NiMH rechargeables because they have a higher voltage. If you haven't upgraded your firmware, that will help with battery issues too.

If you were in this hemisphere, temperature might be an issue. Probably not in NZ, right?

My camera (*ist DS) started randomly firing its shutter many times after each shot. Cleaning the battery contacts fixed it, and it's been fine for months. A longshot in your case, with a much newer camera.
Its quite alright - I am posting in the beginners corner after all and most of the time it is a case of RTFM (Read The *Fine* Manual). Yes it is quite warm here at the moment
Yes I do have the latest firmware (in fact needed it to run my camera NiMH for any reasonable period). You have both made a good point - time to break out those Lithiums - if they solve the problem then fine I will keep them handy for long exposures. Will report back on how I go. Thanks.

Cheers

Jonathan
02-27-2010, 04:35 AM   #8
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That was the issue

It appears that when I run with Lithiums the problem goes away. Just did a 15 minute exposure without any issues.
So although I am not have any other issues with NiMH, they are an issue for long exposures.

Cheers

Jonathan

02-27-2010, 04:56 AM   #9
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What kind of NiMH batteries do you use?
I'd recommend Sayo Eneloops or Panasonic Infiniums. I use Infiniums with my K-x and I've had no problems whatsoever. Even stratrailing with minus 12 celsius (15 minute exposure).
02-27-2010, 08:01 AM   #10
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I've been using Eneloops with good results, but I just got a couple sets of Ansmann low-discharge batteries from Thomas Distributing. They seem to last a bit longer than the Eneloops and work just as well. Here's the link:

ANSMANN 2500 AA LOW DISCHARGE NIMHFOUR BATTERIES PER PACK - ..
02-27-2010, 01:38 PM   #11
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Thanks everyone, but I'm already using high quality low leakage NiMH batteries - including one new set of Sony batteries but I still have the problem. Some day will give other types a go too.

I think an acceptable work around for me at the moment is to use NiMH for everything but very long exposures where I will need to use Lithiums.

Thanks Jonathan
02-27-2010, 10:37 PM   #12
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My longest exposure was 35 minutes. Of course, that was with a K-7, not a K-x, and the lithium ion battery has no trouble at all with such long exposures. However the 35 minute wait for the stupid dark frame was a pain... 70 minutes to take one stupid picture, and it turned out a good 5 minutes too bright... I wish it was possible to turn that feature off
02-27-2010, 11:01 PM   #13
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QuoteOriginally posted by GoremanX Quote
70 minutes to take one stupid picture, and it turned out a good 5 minutes too bright... I wish it was possible to turn that feature off
70 minutes
I must admit I was planning on posting the results of 15 minute exposure but same thing - got the exposure a bit long! It is a very slow process!
02-27-2010, 11:28 PM   #14
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QuoteOriginally posted by kiwi_jono Quote
70 minutes
I must admit I was planning on posting the results of 15 minute exposure but same thing - got the exposure a bit long! It is a very slow process!
it's annoying is what it is. You could take your own dark frame once, save it, and then use it in post-processing yourself to remove the sensor noise from the long exposure. That one dark frame could be used for dozens of pictures. But instead, the camera insists on taking a dark frame after EVERY SINGLE SHOT that's longer than 30 seconds. So in essence, you're being reduced to taking only half the pictures in a given amount of time. Complete waste of time.

There's an online petition here to have Pentax add an option to disable the auto dark frame feature. That's definitely something I'd like to see in a future firmware upgrade.
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