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Author Topic: iq 180 noise after heavy use?  (Read 6363 times)

Bart_van_der_Wolf

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Re: iq 180 noise after heavy use?
« Reply #20 on: November 02, 2011, 08:53:15 pm »

The reality is going back to the Op's question is any CCD sensor will create noise when it gets hot or very warm. The question is when does that happen.

Hi Guy,

It's not really a "when" does it happen question. CCD sensors typically double their so-called dark count for each six degrees Celsius (or Kelvin) increase in temperature. So there will be noise, especially with increased temperature.

Whether it will be noticeable depends on how much noise there is (which varies between sensor designs), but also in relation to the actual signal (the exposure) level (hence my earlier remark about the almost 2 stops 'underexposure' for the ISO value). As the above link says, "Having lower dark count is always desirable, but there comes a point when other factors such as shot noise or S/N supercede dark count considerations".

So there are 2 factors that matter, CCD sensor temperature controlled by cooling, and the absolute amount of dark count during the 'exposure' time versus the actual exposure level.

Cheers,
Bart
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EricWHiss

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Re: iq 180 noise after heavy use?
« Reply #21 on: November 03, 2011, 01:16:37 am »

Bart,
Thanks for the info.  Is that true for both Dalsa and Kodak sensors?  I'm not remembering any grain in the kodak sensor based backs that I've shot with (at base ISO), and only now notice it with the Aptus 12.


And regarding dealers - I had a prob with my Aptus back and my dealer went to bat for me on getting it sent in for service, but I ended up with the e-mail and phone numbers of nearly everyone at Leaf and a few guys in the tech dept at Phase too.  They will talk to you on the phone if you can get to them. That was helpful I guess.  Good dealers usually have tech guys, but these guys spend their time getting to know the software mostly. But having written the above - anyone notice the Hasselblad web store?  I ended up buying my CF-ii-39MS direct from Hasselblad and did so for much less than the dealers I spoke to could offer.   The opportunity to eliminate the dealers is out there to be seen - I mean HB already provides tech support and service directly, and phone sales as well as web sales.   

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Bart_van_der_Wolf

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Re: iq 180 noise after heavy use?
« Reply #22 on: November 03, 2011, 05:16:48 am »

Is that true for both Dalsa and Kodak sensors?  I'm not remembering any grain in the kodak sensor based backs that I've shot with (at base ISO), and only now notice it with the Aptus 12.

Hi Eric,

AFAIK it's a property of silicon based image sensors. Do note that we're not talking about total noise, but only the "dark count" component of noise. In addition we'll have read noise and then photon shot noise. As always, when the signal to noise ratio is high enough we won't notice the noise floor because the absolute amount of shot noise becomes significantly higher than the floor.

When I look at the Maker notes in my camera's EXIF data with Phil Harvey's EXIFtool, there is a field that holds the camera temperature. I don't know where inside the camera it's recorded, and maybe not all manufacturers record it.

Cheers,
Bart
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ced

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Re: iq 180 noise after heavy use?
« Reply #23 on: November 03, 2011, 06:33:02 am »

Why not post 2 samples (crops) 1 of the first few images and 1 of the last few images of the series you were shooting so we may get an idea of what you see.
What exposure time were you using or were you shooting a fashion setup that required rapid shooting?
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