[Nass]

What are you talking about? This has nothing to do with noise, the dark frame is used to remove hot pixels, not noise. Slow Shutter Speed Noise Reduction is an option in the Custom Menus, and I can already turn that off.

It's the same thing - they just call it that. And that can be turned completely for <30 secs exposures, but not for >30 secs.

[Nass]

It's not just hot pixels. The noise level would be unacceptable to 99% of users.
Astro is a very unique and small percentage of their sales.

Yep I appreciate that, but we'd still like the option to completely turn it off for >30 secs

[wildlifephotog]

Read up on cmos sensors in long exposures. Heat is higher, noise is higher. Dark frames are to remove noise, and any hot pixels.
Battle of the Imagers - CCD vs CMOS

[GoremanX]

Here's an oddity; I don't even get hot pixels anymore. I just used the "Pixel Mapping" feature in the Setup menu, and now even 30-second long exposures in Manual mode don't generate any hot pixels.

And yet the camera still insists on taking the stupid dark frame for any exposure longer than 30 seconds... what a pain!

[Nass]

Read up on cmos sensors in long exposures. Heat is higher, noise is higher. Dark frames are to remove noise, and any hot pixels.
Battle of the Imagers - CCD vs CMOS

Yes, wildlifephotog is quite correct, CMOS is noisier. Hence the enforced DFS at >30secs.

An enforcement, though, that whilst terribly kind of Pentax, we'd quite simply prefer to do without . And for those that want it, they just keep the option on!

Everyone happy!

[Nass]

Here's an oddity; I don't even get hot pixels anymore. I just used the "Pixel Mapping" feature in the Setup menu, and now even 30-second long exposures in Manual mode don't generate any hot pixels.

And yet the camera still insists on taking the stupid dark frame for any exposure longer than 30 seconds... what a pain!

Total pain.

Probably not a big deal to others, and to each their own I say... but for some of us it's a ballbreaker.

[GoremanX]

Read up on cmos sensors in long exposures. Heat is higher, noise is higher. Dark frames are to remove noise, and any hot pixels.
Battle of the Imagers - CCD vs CMOS

wrong, the dark frame is solely for removing hot pixels, not noise. Hot pixels and noise have nothing to do with each other. Slow Shutter Speed Noise Removal is a completely different thing. Again, it's clearly a separate option in the menu. I can turn it on or off.

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Last edited by GoremanX; 02-24-2010 at 12:16 PM.

[wildlifephotog]

If you never had a hot pixel it would do DFS. It is programmed into the cmos processing procedure. CMOS sensors in DSLR's are known for heat issues. Many astro nuts have built peltier coolers for their cameras.

[GoremanX]

If you never had a hot pixel it would do DFS. It is programmed into the cmos processing procedure. CMOS sensors in DSLR's are known for heat issues. Many astro nuts have built peltier coolers for their cameras.

I'm not saying CMOS sensors aren't noisier for long exposures due to heat, what I'm saying is the dark frame has nothing to do with that. The dark frame is to remove single pixels which get clipped much faster than others. These could be considered "defective pixels", and every CMOS sensor has a few of them. They show up as a single bright-coloured pixel in a picture that was taken with long exposures. They're always fully clipped (one of their values is 255), and they always exist all by themselves in a sea of normal pixels. Those are what the dark frame helps remove. Again, nothing to do with noise.

[wildlifephotog]

Wrong.
From the DeepSky Stacker manual.

"Dark Frames and Dark Flat Frames
The Dark Frames are used to remove the dark signal from the light frames (or the flat frames for the Dark Flat frames).
With DSLRs and CCD Camera, the CMOS or CCD is generating a dark signal depending of the exposure time, temperature and ISO speed (DSLR only).
To remove the dark signal from the light frames you use a dark frame that contains only the dark signal.

The best way to create the dark frames is to shoot pictures in the dark (hence the name) by covering the lens.
The dark frames must be created with the exposure time, temperature and ISO speed of the light frames (resp. flat frames).
Since the temperature is important try to shoot dark frames at the end or during your imaging session."

[Nass]

If I have the terminology wrong then I need to correct that.

My understanding is that the NR at >30 secs ( page 92 of the manual) is actually DFS taking place, so the same thing. I forget who or where I got this from.

[GoremanX]

Hey, you're right! Go figure

Except of course (and I quote):

"Visible fixed-pattern noise is most often caused by hot pixels – pixel sensors with higher than normal dark current. On long exposure, they can appear as bright pixels."

[GoremanX]

If I have the terminology wrong then I need to correct that.

My understanding is that the NR at >30 secs ( page 92 of the manual) is actually DFS taking place, so the same thing. I forget who or where I got this from.

no you have it totally right, I'm just arguing semantics

I still think being able to turn off the DFS would be preferrable. Again, I can easily make my own dark frame and apply it in PP. That would save me countless time and allow me to take twice as many pictures. If I can turn off NR, I should be able to turn off DFS. End of story.

[Nass]

@wildlifephotog So DFS is a bit of a wrong assumption then, what I should simply request is that noise removal be turn offable at > 30 seconds too.

^^ is that correct/better/clearer?

Appreciate that's tricky, might make for icky results, but that's a choice I'm prepared to live with!

[Nass]

@GoremanX Love it when I post a reply after the reply has already been posted

Maybe I should just update that petition to be completely clear