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  #31  
Old November 1st, 2017, 10:33 AM
Ted Cousins Ted Cousins is offline
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Originally Posted by Doug Kerr View Post
Hi, Ted,


Ah, but to get that recommendation, we would have to feed the exposure meter an exposure index, normally expected as the ISO speed of the imaging system, however we have it "set". So how would we do that?
Got me there, Doug. All those orphaned L-398s (you have or had one, I think). I like mine, it says "ASA" on it. :)

Quote:
No. It is that the so-called "well" is charged when the sensor is initialized, leading to an initial voltage on the well "electrode" (typically positive). Then each effectively captured photon annihilates one electron, leading to a progressive discharge of the "well", and a decrease of its (absolute) voltage.
Major oops on my part. I've seen the 3T circuit many times and never realized the significance of where the reset FET is !! Ah cain't hardly believe it. :(

So the photo-diode capacitance is charged on reset and discharged by electron/hole flow in the depletion region, if I understand correctly. That makes the term "well full" and those pretty pictures of buckets filling up with photons or elctrons quite misleading, IMHO. Never liked them any way . .

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Well, that sensitivity in uv/e is presumably the absolute value of that parameter. The actual number is negative.
Understood, thanks.

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You may find this paper interesting:
http://dougkerr.net/Pumpkin/index.htm#CMOS-APS
Best regards,

Doug
Excellent paper, thanks again.

best,

Ted
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  #32  
Old November 1st, 2017, 12:44 PM
Doug Kerr Doug Kerr is offline
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Hi, Ted,

Quote:
Originally Posted by Ted Cousins View Post
Got me there, Doug. All those orphaned L-398s (you have or had one, I think). I like mine, it says "ASA" on it. :)
Indeed, and it also had the DIN "degree" scale.

But its successors, the L-398M and the L-398A (I happen to have my L-398A in front of me) say "ISO" (and that of course means ISO speed).

You can follow that here, if you care to:

http://dougkerr.net/Pumpkin/index.ht...irector_meters

Quote:
Major oops on my part. I've seen the 3T circuit many times and never realized the significance of where the reset FET is !! Ah cain't hardly believe it. :(
Easy to do. We hear the folklore and come to think that really describes how something works! And we see circuits many times but somehow think they show what we think! Been happening to me for 70+ years!

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So the photo-diode capacitance is charged on reset and discharged by electron/hole flow in the depletion region, if I understand correctly.
Yes.

Quote:
That makes the term "well full" and those pretty pictures of buckets filling up with photons or elctrons quite misleading, IMHO.
Quite.

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Excellent paper, thanks again.
Thanks so much.

Best regards,

Doug
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  #33  
Old November 1st, 2017, 04:14 PM
Asher Kelman Asher Kelman is online now
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I was taken by surprise here:

"
Quote:
So the photo-diode capacitance is charged on reset and discharged by electron/hole flow in the depletion region, if I understand correctly.
Yes.

Quote:
That makes the term "well full" and those pretty pictures of buckets filling up with photons or electrons quite misleading, IMHO.
Quite."

It does make sense when the mechanism is revealed.

It reminds me that in Hebrew a cemetry is "bet chayyim" (house of the [eternal] life!

Also tax cuts for the rich are not called "welfare" as allocation of funds to the poor!

Asher
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  #34  
Old November 1st, 2017, 04:43 PM
Ted Cousins Ted Cousins is offline
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Quote:
Originally Posted by Doug Kerr View Post
Hi, Ted,



Indeed, and [the L-398] also had the DIN "degree" scale.

But its successors, the L-398M and the L-398A (I happen to have my L-398A in front of me) say "ISO" (and that of course means ISO speed).
Assuming that means Saturation-based . . now we get to wonder about SOS relative to that, apropos of your findings as a Canonista which have read about somewhere ;-)

Quote:
You can follow that here, if you care to:
http://dougkerr.net/Pumpkin/index.ht...irector_meters
I wish I had a buck or two for the number of times I've read that article , Doug!

best,

Ted
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  #35  
Old November 1st, 2017, 04:45 PM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post
I was taken by surprise here:
"
Yes.

Quite."

It does make sense when the mechanism is revealed."
Well, I was surprised too when I discovered that (about 11 years ago).

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It reminds me that in Hebrew a cemetry is "bet chayyim" (house of the [eternal] life!
Of course, auf Deutsch it is friedhof, which one could translate as "house of peace".

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Also tax cuts for the rich are not called "welfare" as allocation of funds to the poor!
I don't follow that. Maybe a word or two got left out.

Best regards,

Doug
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