Advice: Long exposure on K-5

[JohnFHY]

Hi,

I need some input from gurus here. I understand hot pixel are inevitable when it comes to long exposures, but what level of it is consider normal? I've started to take long exposures (~5 mins iso400-800) on my k-5 for my study project. I noticed that there hot pixel which are normal but what gets me wondering/worrying is that aside from the scattered hot pixels, i would have a obvious cluster of hot ('hotter' if i may say haha) in the center region of the photo. at the moment i'm unable to post the photo due to t&c of my project. i would try to take some blank photos soon.

My question is, is the cluster normal or is it something i should send to have it looked at? anyone could share their raw long exposure shots? thanks

[wtay0001]

I do not know the spec/ tolerance as to the amount is considered acceptable. But I assume it's something that will be there and will continue to increase as time goes thus the reason why Pentax has Pixel Mapping option in the menu. You can always run Pixel Mapping in your K5 and see if it helps.

[dwRK]

Pixel mapping to fix dead pixel...dark frame subtraction to fix hot pixel

If there is no hot pixel during normal condition...most likely nothing wrong... ccd n cmos heats up during long exposures...

Back in the good old days...my long exposures are 45-90mins

[vinsant]

Without an idea of just how big your clusters of hot pixels are, it's really hard to tell. In general they are very easy to ignore, or pixelmap.

[JohnFHY]

Thanks for your inputs so far. I'll post up a photo within these few days. the reason i'm asking is also because my machine is still under warranty, n if its not normal it would be wonderful to have it fixed. don't wanna end up making wasted trip to KL to be told its normal haha its kinda annoying at times because depending on my WB settings (especially under tungsten), the cluster may make the specific location look like there is a blue tint over it.

[JohnFHY]

i finally came back with a photo. i'm not sure whether you're able to see it but it was more obvious on my k-5 screen then my laptop screen. took this with the lens cap on at iso800 for 3 mins. i have another worse photo which was at 6mins iso400. note that i just started taking long exposures ~20 shots in total and they were noticeable the moment i started it. Also i did a little PP as i couldnt see it on screen. increase the midtones slightly
IMGP6460.jpg

[wtay0001]

I couldn't see anything. Perhaps you can circle them for us.

[vinsant]

I see you've got a nice little constellation there. That might be a little hard to pixel map, but the results are what matter more - is it noticeable if you were to do a real world exposure?

If so, it might be time for a service.

[JohnFHY]

I couldn't see anything. Perhaps you can circle them for us.

I've circled it in the image below, but only use it as a reference to the location on the cluster in the image below. I dont have the original photo with me now to edit, so i just saved the image above and edited.
IMGP6460.jpg

I see you've got a nice little constellation there. That might be a little hard to pixel map, but the results are what matter more - is it noticeable if you were to do a real world exposure?

If so, it might be time for a service.

Yeah. good thing i wasnt catching stars, if not i would have been mislead by it. it does matter, due to the location of the cluster and severity (when longer exposure) it affects the result of the sample i'm taking. As my warranty is still valid, would i have problem trying to get it fixed or it could be regarded as a normal prob? what fix could it be, a sensor change?

thanks

[JohnFHY]

I see you've got a nice little constellation there. That might be a little hard to pixel map, but the results are what matter more - is it noticeable if you were to do a real world exposure?

If so, it might be time for a service.

Yeah. good thing i wasnt catching stars, if not i would have been mislead by it. it does matter, due to the location of the cluster and severity (when longer exposure) it affects the result of the sample i'm taking. As my warranty is still valid, would i have problem trying to get it fixed or it could be regarded as a normal prob? what fix could it be, a sensor change?

thanks

[Jeremy.S]

I'd say if you try to cover up your viewfinder and do it again. See if still exists..

[JohnFHY]

I'd say if you try to cover up your viewfinder and do it again. See if still exists..

thanks for the advice. have yet to try it yet. shall do it tonight. but i wouldve thought that wouldnt be affected because i had my whole system in a closed unlit cabinet in a dark room. it would still have effect is it?

[dwRK]

wow...thats a nasty cluster...doesn't look like the usual dead/hot pixels...could it be sensor overheating issue...

[JohnFHY]

Tried covering the viewfinder but it is still the same. overheating because of the long exposure?anything to do that would avoid it?or that my unit has problem?

[kittykat46]

Please check your menu whether you have Long Exposure Noise Reduction turned on.
The feature is exactly meant to counter such sensor built-in noise during long exposures.
Alternatively, you can do it through software by by merging your Start shot with a deliberately made black exposure like the one you did above.