[Sevilla]

Hello eveybody,
I found out that my Pentax K1II shows a few hot pixels in long exposures probably do to overheating of the sensor. Some are automatically remapped by the processing application I am using (Affinity Photo) but some escape the remapping. they can be easily removed in post processing but the phenomenon is making me curious?

1 is this normal?
2 what about other cameras?
3 any experience or recommendation?

[photoptimist]

1. Yes it is normal -- it's why cameras have slow shutter speed noise reduction (aka dark-frame subtraction)
2. It varies. Sony apparently had a solution so aggressive it was known as a "star eater"
3. Frequent pixel mapping but dark-frame subtraction is the real solution. You can use the in-camera version (easy but it doubles the time the camera spends taking the shot) or collect your own dark frames as part of a shooting session and subtract them in post.

[FozzFoster]

(easy but it doubles the time the camera spends taking the shot) or collect your own dark frames as part of a shooting session and subtract them in post.

To do proper manual dark frame subtraction would take the same time as in-camera dark frame subtraction, no?

[Aaron28]

To do proper manual dark frame subtraction would take the same time as in-camera dark frame subtraction, no?

yes....the dark frame is equal in all settings as the exposed framed.......the difference being in camera a 30 second exposure would require the 30 seconds immediately following the original exposure making for 1 minute of lapsed time........taking your own dark frames you can take original exposure after original exposure with minimal lapse in time then take the dark at the end of your exposure set (if taking multiple/consecutive exposures) and use a program such as deep sky stacker or starstax to create a master dark frame to subtract from all the original exposures..........reckon it depends on yer subject matter but thats my process for star trails and milkway projects

[FozzFoster]

taking your own dark frames you can take original exposure after original exposure with minimal lapse in time

thank you for that explanation

[Aaron28]

thank you for that explanation

you bet! ......i failed to mention that the dark frame is with the lens cap on.......and typically i will take 10-15 dark frames for a master dark frame.....

[Mooncatt]

I haven't had a chance to work on long exposures with my K3 II yet to know how Pentax sensors may work, but I had this issue on an Olympus DSLR. What I noticed is the hot pixels were not the same from shot to shot. That meant pixel remapping and standard dark frame based editing didn't work. The only reliable method was to use the in camera slow shutter noise reduction. Even that wasn't perfect, but the best I could get sense the hot pixels weren't given a chance to cool and the sensor was in the same heated state.

[Aaron28]

but I had this issue on an Olympus DSLR

pretty much the same (E-510)......it helped having multiple dark frames to create a master dark frame.......oh the noise and hot pixels with that poor worn out sensor in low light/long exposure........did quite well with working light tho

[Sevilla]

Thank you, but confused on how to do that dark frame...

[Aaron28]

but confused on how to do that dark frame...

the dark frame is taken with the lens cap on with the identical settings of the original...........if your work is not time sensitive you can use in body noise reduction and other corrections

[Mooncatt]

pretty much the same (E-510)......it helped having multiple dark frames to create a master dark frame.......oh the noise and hot pixels with that poor worn out sensor in low light/long exposure........did quite well with working light tho

E-500 here, and yes it did work well in good light. Once I learned about light painting, fuggetaboutit.

[stevebrot]

Thank you, but confused on how to do that dark frame...

Dark frames are mostly used for subtraction with stacked images. The process can be simple (a single exposure of n-number of seconds with the lens cap on) or very complex (not as simple). Both methods require software to do the subtraction. In-body subtraction is often adequate as long as the time required is not a problem. Where things get strange is when one is not committed to doing the full-on astro approach. I have done it a few times (don't do much astro stuff) and it works well.


Steve

[Wasp]

yes....the dark frame is equal in all settings as the exposed framed.......the difference being in camera a 30 second exposure would require the 30 seconds immediately following the original exposure making for 1 minute of lapsed time........taking your own dark frames you can take original exposure after original exposure with minimal lapse in time then take the dark at the end of your exposure set (if taking multiple/consecutive exposures) and use a program such as deep sky stacker or starstax to create a master dark frame to subtract from all the original exposures..........reckon it depends on yer subject matter but thats my process for star trails and milkway projects

My Samsung NX1 does that all by itself with very long exposures. It's a bit annoying - having to wait before you can do the next shot - but it's for the greater good.

[Aaron28]

My Samsung NX1 does that all by itself with very long exposures. It's a bit annoying - having to wait before you can do the next shot - but it's for the greater good

can relate.....a GE500 something i have does the same thing.....no turning it off......did purdy good fer a simple bridge camera

[MJKoski]

I do not bother with DFS when doing daytime long exposures. K-1 mk2 already reaches 5min with no sweat. If there are some hotties around in the end, I'll do noise removal layer in Photoshop which is a flattened and noise filtered final image. Then, I just mask the filtered layer where it counts (smooth dark shadows and backgrounds). This way, real details in textures etc. are kept intact and they usually mask lone hotties on their own.