turn off DFS with your K20D and K7

After a bit of to'ing and fro'ing about whether this was a fault or not I've just received a disappointing reply from pentax support

Dear Sir,

Thank you for your enquiry.

We just got an answer from our software-engineers regarding switching off the NR on the K7:

For technical reasons and sensor management reasons, they had to make the choice of switching automatically the NR on for long exposure-times. So indeed it is not possible to switch it of for exposures longer than 30 seconds.

I just can't understand the "technical reasons" why they can't let the user make the decision as to whether he wants to turn off NR in bulb mode or not. Can't help but feel I'm being fobbed off

Any opinions?

The most likely thing is in the phrase "sensor management reasons" which possibly means heat. I doubt that it's a Diabolocal Plot!

Thanks John
Yes, could very well explain what they mean

So is heat buildup (I presume this introduces noise) a known issue on long exposures for other makes of DSLR or is it only these pentax sensors that exhibit poor performance in this particular aspect?

All sensors generate heat and the longer they are active the more heat they generate. Heat=noise=reduced quality.

The Samsung sensor in the K20D/K7 is not the best for noise, so DFS would definitely be required. But what people are annoyed about is that they cannot do the dark frame subtraction themselves in order to combat this noise, instead of having it done automatically after every single shot.

The advantage of doing it yourself is that you only need to shoot one dark frame for several shots, and the results ought to be the same. Perhaps Pentax are worried about what people would think if they saw the shot before DFS was carried out, but I'm sure a lot of users would be able to steel themselves for the horror of that experience if it made shooting long exposures much more convenient.

That's a bit strange if you ask me...
Because it builds up heat with 30 second exposure it would be a great idea to do the same exposure of a 30 second afterwards for the DFS, wouldn't that just heat up the sensor more?

it depends upon the rate of dissipation of the heat I guess.

So if you turn a sensor on for 30 seconds it gets warmer than you turn it on for 1 minute, can you tell me how that works?

I don't think anyone said the DFS had anything to do with reducing heat :

No one said it was for reducing heat indeed and i don't claim someone said that.

But it was said that the DFS is on with longer exposure because of heat build up.
That's what i find a bit strange, why force a sensor that gets warm to do DFS it will only get more warmer right?

Perhaps so, but it will be able to map the noise and banding on a blank shot and then eliminate it from the original shot... if I'm correct in my understanding of how DFS works? OK the sensor will stay warm, there's no way round that, but it's probably got as warm as it's gonna get during the original exposure. If there was no DFS would probably be shooting your next image soon after anyway.

As an aside, I wonder if anyone has experimented with cooling the back of the camera to help dissipate heat from the sensor?

that's what I was commenting on about heat dissipation. tehre will reach a point where the power the sensor is drawing that's converted to heat will equal the amount of heat dissipared and heat equilibrium will be achieved. Otherwise it will just keep getting hotter and hotter and melt

I suspect that the heat factor is only small issue though and it's more to do with the fact that at such low light levels the S/N ratio is marginal and the noise that builds up is almost as much as the wanted light build up.

Mind you The K10D doesn't suffer with it's NR off. Different sensor though

Perhaps the K20D/K-7 is just a bad era in pentax sensors

Anyone had any negative effect from doing this to there K7?

Didn't think this actually worked on K-7?

Thank you Anvh K7 stuck in debug mode googled for help and came across this post, using the link provided by you managed to turn it off. Cheers david