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11-22-2009, 04:07 PM   #1
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Pentax K-7 and 1hour 20 minutes night exposure

I have made long exposure test with my K-7.

Parameters:


ISO 100
Sigma 10-20/4-5.6 lens at f10
1hour 20minutes exposure time

Result is here:


Name:  LongTime.jpg
Views: 2632
Size:  20.0 KB

Iīm very pleased with result, as there are no purple areas, as I have read something about chip overheating.


After capturing the image camera was performing Dark Frame Substraction, I was expecting it will do it about same time (1h 20min).
But it took only about hmm 20 minutes? I donīt know exactly.
Do anybody know how DFS time depends on shooting time?

11-22-2009, 04:15 PM   #2
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hot damn! thats awesome, nice work!
11-22-2009, 04:40 PM   #3
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how did you manage to get 1 hour 20 min exposure?
11-22-2009, 05:04 PM   #4
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QuoteOriginally posted by kent Quote
how did you manage to get 1 hour 20 min exposure?
Bulb with the remote or something similar, I would assume.

Is there any way to view a larger version of the image? It's hard to really get much out of such a small, compressed image but what I can see certainly looks promising.

11-22-2009, 05:14 PM   #5
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QuoteOriginally posted by er1kksen Quote
Bulb with the remote or something similar, I would assume.

Is there any way to view a larger version of the image? It's hard to really get much out of such a small, compressed image but what I can see certainly looks promising.
I concur 123456...
11-22-2009, 05:43 PM   #6
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I've reviewed this result and your comment with interest therion.
I'm more keen to see the image in better JPEG quality posted in a larger resolution linked to a photo hosting site for more detail. Reason being that at this quality and low resolution, there is no way of telling how well the K-7 performed in controlling noise for this long exposure.

You mentioned a short DFS time, which indeed does seem unusual. It does appear that the exposure time you reported is right (judging by the FL you used and arcs created by the stars) but there isn't any explanation I can think of to understand the quick DFS processing time - unless somehow the K-7 accelerates DFS exposures (anyone attest to this phenomenon?)

My interest is in finding a way to create controllable noise in low-ISO long exposure images from the K20D/K-7 CMOS sensor, as it has not been a positive point for these cameras (cf. the K-x, which seems to do reasonably well).

My paltry attempt at long exposure with the K20D failed miserably (excuse the blur):

https://www.pentaxforums.com/forums/post-your-photos/74773-night-country-trai...iso-noise.html

Even with strong NR performed, I couldn't get results even close to those from my CCD-driven K10D:
This by the K20D:


This by the K10D:
11-22-2009, 05:51 PM   #7
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WOW....Fantastic.....
The Aussie night shots are quite interesting with the circular motion of the stars...

11-22-2009, 06:47 PM   #8
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QuoteOriginally posted by Ash Quote
You mentioned a short DFS time, which indeed does seem unusual. It does appear that the exposure time you reported is right (judging by the FL you used and arcs created by the stars) but there isn't any explanation I can think of to understand the quick DFS processing time - unless somehow the K-7 accelerates DFS exposures (anyone attest to this phenomenon?)
I've done a ~90 minute exposure with my K-7 and IR remote, although nothing worth showing here as cloud cover came in partway through, so I only continued the exposure out of mild curiosity. Pretty sure my DFS was identical in length to the main exposure, though. Can't see how they could accelerate it, as dark frame noise is dependent on shutter speed - so if the DFS frame is shorter, the noise pattern won't entirely match.

I'm wondering if one of two things happened here: Either the OP ran low on battery and hence the camera terminated the DFS exposure early so the file could be written before the camera powered off, or (less likely) the sensor passed the overheating threshold during the DFS frame and terminated the exposure for that reason.
11-22-2009, 06:52 PM   #9
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okay so i know how you did it in practise, but HOW on earth do you know that you need 1h 20mins of exposure.
is there some sort of calculation? i thought remote-bulb shots were hit and miss. but how can you afford to take a +1hr picture not knowing if its even going to come out properly.
11-22-2009, 07:01 PM   #10
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QuoteOriginally posted by therion Quote
I have made long exposure test with my K-7.

After capturing the image camera was performing Dark Frame Substraction, I was expecting it will do it about same time (1h 20min).
But it took only about hmm 20 minutes? I donīt know exactly.
Do anybody know how DFS time depends on shooting time?
Your observation is correct.

I noticed the change after upgrading to Firmware V1.02

Prior to this, and for all previous Pentax cameras, DFS time = Actual Exposure time.
I think Pentax has tweaked the V1.02 firmware with some "intelligent" algorithm assessing how much DFS time is actually needed for noise control, and it usually comes out quite a lot less than Actual exposure time
But Pentax didn't mention anything about it

I took several rounds of Bulb Mode shooting to confirm that, but I think that's right.
Some results I got
Exposure 10 secs , 3 Secs DFS
Exposure 1 minute, 20 Secs DFS
Exposure 10 minutes , 3 minutes DFS

I know the theory is that you have to match the exposure time for DFS to match the noise pattern, but the "accelerated DFS" doesn't seem to have hurt the image quality.

Last edited by kittykat46; 11-22-2009 at 07:07 PM.
11-22-2009, 07:51 PM   #11
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QuoteOriginally posted by PNTXFTW12 Quote
okay so i know how you did it in practise, but HOW on earth do you know that you need 1h 20mins of exposure.
is there some sort of calculation? i thought remote-bulb shots were hit and miss. but how can you afford to take a +1hr picture not knowing if its even going to come out properly.
There's nothing really to calculate.

In pitch black darkness, ambient light is negligible and at low ISO barely registers in the scene. What matters is the stars etching their path on the sensor, and this may require a relatively large aperture, but their brightness will not be dependent on shutter speed, but rather the ISO and aperture.

Foreground exposure will then be determined by whatever little ambient light there is available - or you can create your own.

Last edited by Ash; 11-22-2009 at 10:34 PM.
11-22-2009, 07:52 PM   #12
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QuoteOriginally posted by kittykat46 Quote
Your observation is correct.

I noticed the change after upgrading to Firmware V1.02

Prior to this, and for all previous Pentax cameras, DFS time = Actual Exposure time.
I think Pentax has tweaked the V1.02 firmware with some "intelligent" algorithm assessing how much DFS time is actually needed for noise control, and it usually comes out quite a lot less than Actual exposure time
But Pentax didn't mention anything about it

I took several rounds of Bulb Mode shooting to confirm that, but I think that's right.
Some results I got
Exposure 10 secs , 3 Secs DFS
Exposure 1 minute, 20 Secs DFS
Exposure 10 minutes , 3 minutes DFS

I know the theory is that you have to match the exposure time for DFS to match the noise pattern, but the "accelerated DFS" doesn't seem to have hurt the image quality.
Now that's interesting - and a welcome improvement (if indeed it gives the same results as an equal DFS to exposure time).
11-22-2009, 08:35 PM   #13
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I think he may have been more concerned with the exposure of the ground as opposed to the stars.
11-23-2009, 12:37 AM   #14
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I have measured right exposure by this procedure:

I have set K-7 to ISO 6400, f4 aperture on Sigma, tried several exposure times, I was most happy with 15sec

So here is calculation:

First ISO:

6400 3200 1600 800 400 200 100
15s - 30s - 1min - 2min - 4min - 8min - 16min


and now aperture:

f4 f5.6 f8 f9.5
16min 32min 1hour 1hour 30min

I have used external programmable cable release, set time to 1hour 20min (I would like have it darker). Set to Bulb a and fired.

(I have updated K-7 to fw 1.20 before.)

After 1hour 20min I have taken camera home and thought I will wait long time, as K-7 should perform DFS the same time. But I was surprised very much when about 20minutes it has finished.

So it really seems so Pentax has changed DFS to shorter, more accaptable way.


OK I will post full image.
11-23-2009, 02:41 AM   #15
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QuoteOriginally posted by therion Quote
I have measured right exposure by this procedure:

I have set K-7 to ISO 6400, f4 aperture on Sigma, tried several exposure times, I was most happy with 15sec

So here is calculation:

First ISO:

6400 3200 1600 800 400 200 100
15s - 30s - 1min - 2min - 4min - 8min - 16min


and now aperture:

f4 f5.6 f8 f9.5
16min 32min 1hour 1hour 30min

I have used external programmable cable release, set time to 1hour 20min (I would like have it darker). Set to Bulb a and fired.

(I have updated K-7 to fw 1.20 before.)

After 1hour 20min I have taken camera home and thought I will wait long time, as K-7 should perform DFS the same time. But I was surprised very much when about 20minutes it has finished.

So it really seems so Pentax has changed DFS to shorter, more accaptable way.


OK I will post full image.
Interesting... I thought I updated my firmware before my long exposure, but maybe it was the other way around. Time to do another long exposure, methinks.

Elegant way of figuring out a suitable exposure time, btw!
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