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05-01-2012, 07:41 AM   #16
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QuoteOriginally posted by alunfoto Quote
I experimented with really long exposures this winter, and found that the 645D sensor is sensitive to what the astronomers call "spurious noise".
Thank you for those interesting tidbits. I'm assuming they are a minor pain and pretty easy to clone out, much like sensor dust in most cases. Before I print, I always zoom into 100% and scan the image for any problematic dust, etc. and do a little cloning.

05-01-2012, 07:48 AM   #17
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QuoteOriginally posted by jwoodland Quote
<<That is your dark-noise frame which you can subtract from your actual exposure and can be done in post processing.>>

How do you actually subtract the dark frame in Photoshop? Thanks....
In Photoshop, you can subtract images in the layers palette. Simply set the layer to be subtracted from the image below it. There is a drop-down menu to set that in the palette.
05-01-2012, 08:07 AM   #18
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Got it - thanks! I never noticed "subtract" on the list before!
05-02-2012, 08:46 AM   #19
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QuoteOriginally posted by Ryan Tischer Quote
Thank you for those interesting tidbits. I'm assuming they are a minor pain and pretty easy to clone out, much like sensor dust in most cases. Before I print, I always zoom into 100% and scan the image for any problematic dust, etc. and do a little cloning.
The effect is cumulative, and In my experience it got annoying with exposures at 8 minutes and longer. But I suppose the amount of spurious noise accumulated will depend on many things. At my latitude there are sometimes auroras. It seemed to me that the spurious noise became more abundant then, but it may have been a coincidence.

Hope for your sake that you continue to be un-annoyed. Apart from the spurious noise, the image quality is certainly soothing.

05-03-2012, 11:36 PM   #20
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Hi guys, can someone confirm the NR system on 645D, i have downloaded latest FW from site and updated camera.

The NR still takes another DARK exposure, i CANNOT turn it off, ie take one exposure at 60 secs,(BULB MODE) it auto takes another(Dark) when first one is taken fro same or similar time. !!
I have tried changing the NR settings in the menu but to no avail.. no matter wether switched on or off it does the same thing..

Any help or feedback is much appreciated.

Cheers.
PS i thought i had read somewhere becuase of sensor type and the heat it generates it was not possible to turn tis feature off , but then why have the option. ??
05-05-2012, 09:38 AM   #21
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QuoteOriginally posted by Bigvern1263 Quote
Hi guys, can someone confirm the NR system on 645D, i have downloaded latest FW from site and updated camera.

The NR still takes another DARK exposure, i CANNOT turn it off, ie take one exposure at 60 secs,(BULB MODE) it auto takes another(Dark) when first one is taken fro same or similar time. !!
I have tried changing the NR settings in the menu but to no avail.. no matter wether switched on or off it does the same thing..
I can confirm that my camera does the same thing. In "B" mode, the camera will do a dark-frame after every shot no matter what.

I think the workaround is to take multiple 30-second shots and stack them in the computer afterwards, using astrophoto software. Some plugins for Lightroom or Photoshop may also do the job, I think.

I have tried to use multi-exposure too, but the camera is not as good as computer software at separating true detail from noise.
05-06-2012, 10:42 PM   #22
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Many thanks Alunfoto, i would be interested to hear what any others have to say on this matter? re the B mode and Dark exposures on anything over 30 secs . Ie NR cannot be turned off ..

Cheers Guys.

05-09-2012, 07:15 PM   #23
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Hi, in regards to post above, have any other 645D users switched there camera to BULB mode and taken an exposure over 30 secs ??? if so does it take another DARK exposure for NR purposes ? can you turn off NR ?? Or i will rephrase that, SW says you can turn it off, but does it actually turn off ? i have latest FW and my 645D continues to take a NR exposure regardless of settings....

Cheers.
05-11-2012, 07:22 AM   #24
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I was doing some 4-8 min exposures the other night using B. I can confirm the camera does take a similar length dark exposure immediately after. I haven't tried turning it off though, so I'm not sure long exposure noise reduction is on or off. I'll take a look when I get home tonight.

Jeff
05-11-2012, 07:05 PM   #25
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I have posted about this before and have spoken to pentax europe about it. Pentax Europe had no clue about it whatsoever. I won't be calling them for advice in future! I'm still waiting for my 645D to be repaired but it was up to date and the NR frame happened regardless of what I had set in settings
05-11-2012, 10:19 PM   #26
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Why does your 645D need repair?
05-12-2012, 01:11 AM   #27
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There is a whole thread on it! Impact damage so expensive repair although not a major repair
05-12-2012, 05:11 AM   #28
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QuoteOriginally posted by Bigvern1263 Quote
Hi, in regards to post above, have any other 645D users switched there camera to BULB mode and taken an exposure over 30 secs ??? if so does it take another DARK exposure for NR purposes ? can you turn off NR ?? Or i will rephrase that, SW says you can turn it off, but does it actually turn off ? i have latest FW and my 645D continues to take a NR exposure regardless of settings....

Cheers.
I tested my camera. Slow shutter speed noise reduction only effects exposures <= 30 sec. If you take an exposure over 30 sec (using B) it will do a dark frame regardless of the setting.
05-12-2012, 09:00 AM   #29
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QuoteOriginally posted by jwjohnson Quote
I tested my camera. Slow shutter speed noise reduction only effects exposures <= 30 sec. If you take an exposure over 30 sec (using B) it will do a dark frame regardless of the setting.
One more; Thanks jwjohnson.

Dunno what it is about his own camera that Bigvern doesn't trust...
05-12-2012, 11:30 PM   #30
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Thanks guys, i was curious thats all, as i do a few LE seascapes etc, which can run into minutes, and all the while the sky etc is changing, so the extra dark frame is more a pain than anyhting.
If it cant be turned off why have it in the software suggesting you can ?
And also in this earlier thread some posters had suggested it didnt do a dark exposure ??

Thanks itshimitis, can you point me to the thread you started on this? cheers.
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