[petercrane]

I dare you to team up with a fellow Canon or Nikon photographer some night for a photo marathon (as you are already aware, there is a whole other world to photograph at night).... you might feel a little inadequate next to them. Comparing relatively similar cameras with similar IQs.... you and your Pentax are going get far fewer photos by the end of the evening when compared to the non-Pentax photographers.

Every DSLR I've ever owned has been a Nikon, and I've used almost every Canon known to man for work purposes. I wouldn't have bought the K7 if it had made me feel inadequate. Sure, a certain Nikon might have the potential to shave a second or two off processing time, but the Pentax range have their benefits also, with the K7 being everything I want and need in a single package. It's all about what's important for the user. I suppose I'm just not in much of a hurry to get shots at night.

[lunelson]

Since it would obviously be very easily to program a preference to disable this, I'm assuming Pentax is trying hard to hide something bad about their sensor(s). I guess I can see why they might want to do so -- imagine a review that shows a long exposure shot compared to other cameras where the Pentax fell short. I would guess it could hurt them more than the complaints about being unable to disable the automatic DFS.

However, DFS isn't magic, so if it was really that bad I would think it would show in degraded quality on long exposure shots anyway. Who knows what their thinking really is?

[pentaxmz]

Since it would obviously be very easily to program a preference to disable this, I'm assuming Pentax is trying hard to hide something bad about their sensor(s). I guess I can see why they might want to do so -- imagine a review that shows a long exposure shot compared to other cameras where the Pentax fell short. I would guess it could hurt them more than the complaints about being unable to disable the automatic DFS.

However, DFS isn't magic, so if it was really that bad I would think it would show in degraded quality on long exposure shots anyway. Who knows what their thinking really is?

RiceHigh was one of the first Bloggers to discuss this Pentax K20D flaw, he stated the same theory that Pentax was hiding the fact that the Samsung sensor was flawed by becoming too hot during longer exposures. Hence, the reason for the forced DFS. Check out the replies to his postings regarding this (both here and on his site), you will see that many Pentax fanboys shot him down for that.

I completely agree with your statement.

There are two possibilities:

1. Pentax is hiding the fact that noise would be so great that it would be an embarrassment. I suspect this because in long exposure tests (15 minutes or more) of tracked star fields, the DFS is actually removing stars, as though they are noise! In other words, the K20D flaw goes beyond just being annoying because of the DFS waiting time.

2. Pentax doesn't really give a flying flipper for the estimated thousand or so complaints about this problem. I actually have no idea how many have complained but there has been some chatter about this. I also know that Pentax's stupidity in regards to this problem has swayed a huge number of photographers AWAY from Pentax products.

[nostatic]

2. Pentax doesn't really give a flying flipper for the estimated thousand or so complaints about this problem. I actually have no idea how many have complained but there has been some chatter about this

"the estimated thousand or so complaints..."

"I actually have no idea how many have complained..."

I have identified your true calling - politics! Just add, "I have no recollection of saying that" and you're all set

[pentaxmz]

"the estimated thousand or so complaints..."

"I actually have no idea how many have complained..."

I have identified your true calling - politics! Just add, "I have no recollection of saying that" and you're all set

Well, at least, I was honest that I don't actually know. I was writing as I speak.... I made a statement and then realized that I couldn't back it up with fact. Give me a break, I was guessing... but if I were a betting man, I would bet that my number is close.

Are you in this thread to haunt me?

BTW, What the heck are you talking about? I never wrote that!

[nostatic]

Are you in this thread to haunt me?

BTW, What the heck are you talking about? I never wrote that!

Just consider me part of the 24 hour news cycle.

Senator PentaxMZ, did you know that model was underage? And can you see Russia from your front porch? And have you inhaled?

How am I doing so far?

[pentaxmz]

Just consider me part of the 24 hour news cycle.

Senator PentaxMZ, did you know that model was underage? And can you see Russia from your front porch? And have you inhaled?

How am I doing so far?

I think you should turn off your TV and go take some photos.

[ManuH]

There are two possibilities:

It's rather simple, DFS can be turned off completely on the cameras based on the Sony sensors. The K-7 improved a little and now force DFS only in Bulb mode after 30 seconds. As I rarely do exposure of more than 30s that's really not a big deal and I still have a K-m in case I would need it.

[hagla]

Im not sure i understand what you are after, but using the K-7 and a shorter than 30 second exposure times many, without the Auto EV adjustment, would that get it right? The Multi-exposure setting would allow for > 30 sec exposure without DFS kicking in... (As an example: 25 seconds x 5 exposures = 125 seconds total exposure with the help of the Multi-exposure setting)
It should even be possible to configure for a one button press for all 2-9 exposures also...

Would that help?

[pentaxmz]

Im not sure i understand what you are after, but using the K-7 and a shorter than 30 second exposure times many, without the Auto EV adjustment, would that get it right? The Multi-exposure setting would allow for > 30 sec exposure without DFS kicking in... (As an example: 25 seconds x 5 exposures = 125 seconds total exposure with the help of the Multi-exposure setting)
It should even be possible to configure for a one button press for all 2-9 exposures also...

Would that help?

On the K20D, outside bulb mode, DFS only kicks in after 15 second (I think). But the K20D 'only' allows for 9 multiple exposures. That is a total of 2 minutes and 15 seconds, which is not nearly enough for much. Beside, multiple exposures increase the chance of de-registration (due to camera shake, movement).

Unfortunately, that won't work... :-(

[Jonson PL]

I'll step in, since I am the biggest instigator of this issue, lately.

The problem is that the K20D and the latest K7 share a serious limitation when taking long exposures in Bulb mode. Every exposure taken will effectively double in length. It's not really a serious problem for shorter (measured in seconds) exposures, however, 1 minute, 5 minutes, and longer exposures will surely ruin your enjoyment with these cameras.

The reason why the exposures time is doubled is because these cameras have a mandatory noise reduction (more specifically known as DFS or Dark Frame Subtraction). Every exposure is followed by a dark frame of equal length, any hot pixels found on the dark frame are algorithmically removed from the actual exposure. This ensures a relatively noise-free exposure. Every other DSLR allows the DFS algorithm to be switched off because either the photographer is not concerned about additional noise, or the photographer will apply their own DFS at a later time.

In my previous posting, I attached a photograph of lightning. This was taken with a Canon camera. In order to get this type of photo, the camera is opened in Bulb mode (aperture slightly stopped down) and exposed until lightning is captured. Sometimes, the exposures are more than 2 minutes long.

Not quite, the noise is not actually random. In long exposures, a certain number of pixels will begin to go hot after a certain amount of time. That is the entire point of the second equally long exposure. The same pixels will go hot again, then the camera subtracts those hot pixels the first exposure.

As mentioned numerous times, the DFS doesn't need to take place immediately after a long exposure. Most/all photographers prefer to do the DFS after they are done taking photos. Unfortunately, if you own a K20D or K7, this is not an option.

thanks, good explanations

Kenyee,

I appreciate your attempt to help me, but I really don't understand what the problem is. In fact, I have no background with Pentax cameras at all. What is this long exposure problem. Can you be a bit more specific about it? Also, how does one deal with the long exposure problem?

Bulb mode, is for exposures longer than 30 seconds, where you have the camera on a solid (expensive) tripod, and use a wire remote.

If you do not shoot longer than 30 seconds, then it is a non-issue for you. And if you just need a few shots, than usually it will not be a problem either



For long exposures, there was a user who had extensive experience with it, who recommended Pentax and the K7. It can stand more massive cold than other cameras, this will help get less noise. And it is completely gasketed, so no trouble with moisture formation.

I couldn't be happier with the k7 and it's long exposure capabilities.

This was one of the first long exposures I took when I got the camera. Shutter was open for around 2 minutes.

Wheel of Brisbane on Flickr - Photo Sharing!

Great shot.


I thought my K10 had automatic DFS ? I guess I would prefer that it had. I seldom use bulb mode, and when I do, I would prefer that I can’t go wrong and the camera will help me out.
Anyway, if some shooting situation is important to me, I would usually plan on bringing along two bodies.


More important to bulb mode, I think I prefer that they work on up to 60 seconds in automatic longer shutter mode.

[kittykat46]

Sorry for resurrecting this old post (old wounds ? ), but I'd like to update a new development.

I took the K-7 out last night for some harbour shots - its very pretty with all the harbour and ship lights. I mostly shot Manual Mode, but I did try the Bulb mode, for the first time since updating to Firmware 1.01.

I was pleasantly surprised when the camera responded instantly after closing the shutter in Bulb mode - no Long Exposure Noise Reduction i.e. no DFS.
Happy to say the Long Exposure at low ISO - 100/200 is of very good quality, no noise, even with NR off.

Too bad, it still forces DFS at 30 seconds or more. There is a way around this by stacking the shots in PP, but I'd have to shoot e.g. 10 times for a 5 minute exposure.

Looks like Pentax did act on user feedback that the Bulb mode NR behaviour did not match what was stated in the Operating Manual.

For the rest of the DFS issue....well...hopefully their engineers would at least look at it...

[JackBak]

Too bad, it still forces DFS at 30 seconds or more. There is a way around this by stacking the shots in PP, but I'd have to shoot e.g. 10 times for a 5 minute exposure.

I'm not sure if you meant by this you would have the equivalent of a single 300 sec exposure because you would not. You would have a 30 sec exposure of your subject with great signal to noise ratio. And this is the problem with not being able to turn off DFS. I do astrophotography with my K10D and regularly shoot single 240-300 sec exposures. After the shooting session I take my dark frame exposures and subtract them from my night's shots.

I think when Pentax moved from CCD sensors to CMOS sensors the astrophotography Pentaxians lost out.

[kittykat46]

I'm not sure if you meant by this you would have the equivalent of a single 300 sec exposure because you would not. You would have a 30 sec exposure of your subject with great signal to noise ratio. And this is the problem with not being able to turn off DFS. I do astrophotography with my K10D and regularly shoot single 240-300 sec exposures. After the shooting session I take my dark frame exposures and subtract them from my night's shots.

I think when Pentax moved from CCD sensors to CMOS sensors the astrophotography Pentaxians lost out.

Sure you can. Its a breeze with the K-7 - you can do up to 9 in multi-exposure.
If you need more than 9, you'll have to do it in Photoshop or other PP software.

Here's a simulation with a 2 second exposure of a darkened room. Way under-exposed.


This is a stack of 9 x 2-second exposures. It looks like a normal photo now.
This is not a "pushed" PP, the individual exposures are cummulatively adding more light to the final photo.

Sorry, the shots are not so sharp, I was doing manual focus in semi-darkness. If you use an IR or cable remote, you won't need to touch the camera.

Scale this up to 9 x 29 seconds, there you have your 261 seconds exposure, without DFS.

[JackBak]

Sure you can. Its a breeze with the K-7 - you can do up to 9 in multi-exposure.
If you need more than 9, you'll have to do it in Photoshop or other PP software.

Interesting. I have never tried stacking non-astro shots. The way I have always thought of it is, lets assume you have your camera (sensor) mounted on a telescope mount that counteracts the motion of the earth. Thus, each cell of the sensor will capture the same photon stream coming from the stars. Now that photon stream (flux density) is constant for each point source of light (star). This means for each 30 second exposure each cell in the sensor obtains no more photons than subsequent 30 second exposures.

This would mean that by averaging multiple exposures (stacking) you are getting no more information of your subject. You are however averaging out random noise which is different for each exposure. This is what we all call increasing the signal to noise ratio. Not because we are increasing the signal but because we are decreasing the noise.

Again this has been my experience with constant flux density (astro) shots. Maybe I still don't get it though.