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11-11-2013, 11:22 PM   #16
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QuoteOriginally posted by Mutters Quote
I can almost see your place from here - Croydon - except for the dirty great hill in the way, and the magnificent glow of your K-3!

It's funny how the dealers aren't getting anything yet.

I was going to order straight from CRK, but my local dealer freaks when I do.lllll

Get some good shots of this rain!

AB
Mutters, I moved back up to the hills last year after living in Moorolbark for 7 years or so.Even closer to you. (We have 5 acres of Horse poo factory now)

Go see Paul at Kirks in Ringwood, tell him Wayne - yep, that Pentax nutter- sent you and see what he can do for you. Or go see Dean Jones at Croydon Camera House. Probably less he can do though.(Yep, go see Paul, I feel guilty for not buying it from him, but then again, I spent about $500 in his shop on a large memory card and a good CPL filter just last week....so not tooooo guilty)

Rain? but, but..wont my camera get wet????? LOL

QuoteOriginally posted by saladin Quote
Good thread. I'm really pleased that there is at least one k-3 on the loose in my general area. I'm holding off to see what CRK do with the price of K5iis, as I'd kinda decided it might offer the value for me, but the 3 just sounds better and better.
G'day Saldin, Thanks for reading the thread. I think there are lots of K-3's around if what I heard from CRK is true. They were just overwhelmed by the response.I think their whole first shipment has been sent to pre-purchasers like me, or to the Camera Shops.

QuoteOriginally posted by rod_grant Quote
Hey Wiz' Glad to hear your thoughts. But my question has to do with your K2000d; Where in Melbourne (or even in a much wider region) did you find a salesman who steered you towards Pentax?? You obviously live in a different part of the universe to me!
Actually Rod, it was Hans, who no longer works at the same Kirks Camera's in Ringwood. He was a Pentax shooter too, but switched to Canon for some reason I dont recall (lack of taste possibly?) So he was biased towards HIS brand, and gave me a steer in that direction. Very glad he did.

Dunno if the outer Eastern 'burbs is that much different from Central Vic. I tend not to buy much from the Camera strip in Elizabeth St. I like my outer suburbs people.

Maybe you should give Paul at Kirks a call and see what he can do for you too, when the K-3 bug bites (and it will......)

11-11-2013, 11:32 PM   #17
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Jason has apparently also left Kirks. fair old staff turnover recently, lots of long-termers have moved on.
11-11-2013, 11:33 PM - 1 Like   #18
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QuoteOriginally posted by bobmaxja Quote
Still it's was not native, it was firmware base. The sensor was not rated at ISO 80.
I've not seen the actual base sensitivity stated for the Sony IMX071 sensor (the one used in the D7000, and presumably the K-5). Where was it published? Just because Pentax, Nikon & Sony chose to use ISO100 as their Base ISO for this sensor, does not mean it's the lowest the sensor can go.

The extension in Base ISO in the K-5 is real, not fudged.

The formula for the Base ISO is:

Base ISO = 78.57 * Rg / Nsat (aka FWC)

where Rg is the Reponsivity in the green channel, the number of photo-electrons outputted as the exposure, (the result of the scene luminance, f-stop & shutter speed - measured in lux-seconds, lx-s), varies.

Excepting the Aptiva sensor design, (used in the Nikon V1), the responsivity (related to the conversion gain) is fixed in a sensor. The conversion gain/responsivity of the sensor does not change as you increase the ISO sensitivity - what changes is either the analogue gain between the sensor & the ADC, or the scaling of the digital number (DN) after the ADC (digital gain change).

For example, with the K-5 at ISO80 (ISO70 measured), using the Sensorgen.info data for Pentax K-5 data (derived from the DxOMark Full SNR & ISO Sensitivity curves):

Responsivity = Base Sensitivity (measured) * FWC / 78.57
= ISO70 * 47159 e- (electrons) / 78.57 = 42 ke-/lx-s
Comparing this with the K-5's ISO100 (ISO91 measured):
ISO91 * 36512 / 78.57 = 42 ke-/lx-s

So, as I said, sensor responsivity does not change with the ISO80 base extension.

That really only leaves Nsat/FWC. FWC does not change with increasing ISO. FWC is only achieved at the true Base ISO. At higher ISOs, (than the Base ISO), what happens is that the system "saturates", instead of the sensor. What is happening is that the digital number (DN) reaches its max. value and can go no higher. So Sensorgen's FWC column should really be titled either "Apparent FWC" or "Nsat."

Now compare the D7000 (Sensorgen.info data for Nikon D7000) at ISO100 (ISO83 measured):
ISO83 * 49058 / 78.57 = 52 ke-/lx-s

and the A580 (Sensorgen.info data for Sony A580) which is believed to have the same sensor as a D7000:
ISO75 * 44983 / 78.57 = 43 ke-/lx-s

Comments:
1. A580 has a similar responsivity to the K5, while the D7000 is different. This may be a measurement funny from DxOMark or a curve-fit anomaly (Sensorgen does a curve-fit on the published DxOMark Full SNR curve data, which apparently DxOMark smoothes, to solve equations to derive FWC and Read Noise values).
2. The 3 sensors have similar FWCs at their lowest ISO (measured), but the D7000 is furthest from the K-5 in FWC. Perhaps a measurement anomaly?

A570 @ ISO75: 44983 e-
K-5 @ ISO70: 47159 e-
D7000 @ ISO83: 49058 e-

Since FWC is set in the sensor design (capacitance in the sensel), and since it's unlikely that there would be differnt versions of this chip in these cameras (all released around the same time), I think the FWC would be the same for all 3 sensors.

3. However, a similar FWC in the K-5, when compared to the other cameras, occurs at ISO80 (manufacturer). At ISO100 (manufacturer) the FWC is only 36512 e-. So why the low FWC at ISO100? One possibility that occurs to me, is that the sensor performance was restricted by 12-bit raw. The K-5 is the only camera of the 3 mentioned here to use 14-bit raw. So Pentax engineers calibrated its metering system for optimum performance at ISO80 (manufacturer), where it's real FWC is revealed, but chose ISO100 (manufacturer) as the default, because it was more standardised and expected. So at ISO100, the DN is maxing out before the real FWC is reached.

4. The other possibility is that standard P&S & DSLRs have linearly-responding sensors. Perhaps the linearity degrades as FWC is approached. So instead of experiencing the non-linearity, the sensor manufacturers specify an FWC value that is a little lower. But the Pentax engineers thought that they could get a bit more out of the sensor by continuing to operate further up into this region, and then correcting the non-linearity afterwards (before storing the data to an image file).

Dan.

Last edited by dosdan; 11-12-2013 at 05:37 PM.
11-11-2013, 11:49 PM   #19
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QuoteOriginally posted by wizofoz Quote

Go see Paul at Kirks in Ringwood, tell him Wayne - yep, that Pentax nutter- sent you and see what he can do for you.
Ha! Paul. That's exactly who I'm talking about. I bought a 16-50 directly for CRK, and he did not like it!

Maybe he's trying to punish me, because my name's on one of his stock to be.

I've been going to Kirk's since it was - err, Kirk's! If you know what I mean.

EDIT: Hans is still at Kirks btw - just spoke to him the other day.

AB

11-12-2013, 12:02 AM   #20
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QuoteOriginally posted by saladin Quote
Jason has apparently also left Kirks. fair old staff turnover recently, lots of long-termers have moved on.
I wondered why I hadn't seen him recently. Very smart fella and good to have a chat to (for a canon shooter, that is...)
11-12-2013, 12:04 AM   #21
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QuoteOriginally posted by Mutters Quote
EDIT: Hans is still at Kirks btw - just spoke to him the other day.
He's back? Last I heard he was living up north somewhere. I'll have to drop in and see the old fella.
11-12-2013, 12:12 AM   #22
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QuoteOriginally posted by wizofoz Quote
He's back? Last I heard he was living up north somewhere. I'll have to drop in and see the old fella.
You're not thinking of Mel, are you?

Hans lives just around the corner.

AB
11-12-2013, 12:37 AM   #23
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QuoteOriginally posted by Mutters Quote
You're not thinking of Mel, are you?

Hans lives just around the corner.

AB
Yes, of course I am.
Mel, not Hans.
Thanks Mutters.

11-12-2013, 08:45 AM   #24
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QuoteOriginally posted by LaurenOE Quote
+100 about ISO80.
I miss that a great deal.
I hope a firmware update gives it to us.
+1,000,000 about this as well. I really hope they bring this back somehow. I wish they would have gone to even further to ISO50, in stead of of taking 80 away.
08-15-2014, 12:56 PM   #25
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QuoteOriginally posted by dosdan Quote
. The other possibility is that standard P&S & DSLRs have linearly-responding sensors. Perhaps the linearity degrades as FWC is approached. So instead of experiencing the non-linearity, the sensor manufacturers specify an FWC value that is a little lower. But the Pentax engineers thought that they could get a bit more out of the sensor by continuing to operate further up into this region, and then correcting the non-linearity afterwards (before storing the data to an image file).
To see how the "FWC" value is set when a certain amount of non-linearity is reached, and that this limit is "soft", as compared with ADC clipping which instead limits the imaging system capacity at higher ISOs, and where the limiting is "hard", see this November 2013 blog entry from Prof. Albert Theuwissen, and in particular the 2 comments about it:

November

Dan.
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