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12-17-2011, 11:16 AM   #1
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K-5 sharpness at ISO80

It seems to me that sharpness of K-5 at ISO80 is less than at all other ISO (I've checked 100-800).

I've tried to shoot at ISO80 with K-5 - it seems to me - VERY good film like photos, not soft, but even ISO800 is sharper than ISO80 with the same settings in C1Pro.
ISO80 is very good for portrait IMO. No problem.

If you shoot at ISO80 - you could think that K-5 has stronger AA filter than K200D or K10D....
But...I've compared picture at ISO100-800 and I can see that K-5 can offer rather sharp picture, just a bit worse than K10D with weak AA filter.

maybe, it's illusion...I will try to check my conclusion about ISO80...Of course...

Can the user of K-5 confirm it or deny?


Last edited by ogl; 01-04-2012 at 12:16 PM.
12-17-2011, 11:27 AM   #2
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I really haven't noticed that. Not in either studio shots or outdoor shots. Also, without knowing the specifics, especially shutter speed, between the sharp 100+ shots and the not-as-sharp ISO 80 shots, it's hard to draw any conclusions.
12-17-2011, 11:52 AM   #3
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QuoteOriginally posted by areidjr Quote
I really haven't noticed that. Not in either studio shots or outdoor shots. Also, without knowing the specifics, especially shutter speed, between the sharp 100+ shots and the not-as-sharp ISO 80 shots, it's hard to draw any conclusions.
ISO80 is not native ISO for 16 MP APS-C sensor...
I've tried FA77 and FA43. Shutter speed is good. 1/160 and 1/200 and e.tc. or 1/100 for FA43 and shorter...
12-17-2011, 12:08 PM   #4
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QuoteOriginally posted by ogl Quote
ISO80 is not native ISO for 16 MP APS-C sensor...
I've tried FA77 and FA43. Shutter speed is good. 1/160 and 1/200 and e.tc. or 1/100 for FA43 and shorter...
Just trying to rule out any non-ISO related phenomenon.

Even though ISO 80 isn't a native ISO, the tests show that ISO 80 is better than ISO 100+ in all DXO Mark tests for the sensor and, quite honestly, I'm at a loss to see how a change in ISO between 80 and 100 can effect sharpness in any way at all if shutter speed is eliminated as a source of the softness.

12-17-2011, 12:12 PM   #5
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ogl,

I didn't actually compare resolution between ISO 80 and above, esp. not between ISO 80/100 or ISO 80/200.

However, I did run all my resolution tests at ISO 80. I didn't even bother to use ISO 100. Unfortunately, from where I am ATM I cannot access my archive. Otherwise, I would show crops from ISO 80 test shots. But I can comment how they look: they look razor-sharp if everything else is ideal (e.g., using a DA 70 Ltd. with flash). Detail at the Nyquist frequency is clearly fully resolved at ISO 80 and that's as much as you can ask for.

Of course, one should always apply sharpening when doing the raw conversion in order to compensate for softness introduced by the process of AA filtering and demosaicing. In LR 3, I suggest to increase the 25% value to 100% at low ISO like below ISO 200 and if the overall sharpness is otherwise excellent.

This "reversing AA sharpening" however is ISO dependent: at higher ISO, it doesn't work anymore due to mathematical reasons and the extra noise introduced isn't tolerable. I.e., the amount of sharpening to apply is ISO dependent: High at low ISO and low at high ISO.

I can imagine that C1Pro applies this kind of processing in an automated way (AFAIK, DxO does and LR doesn't). After all, it is expert knowledge which the raw converter software can provide to users.

So maybe, there is a bug in C1Pro: that sharpening defaults are taken from a table which lacks an entry for "80" which is a value not normally met. Or where the 80 entry has a lower value than the 100 entry. Try to override defualts to find out.

Otherwise, I see no way to explain your observation.
12-17-2011, 10:52 PM   #6
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I will make several tests and put crops here.
12-17-2011, 11:21 PM   #7
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Crops comparing Lightroom 3, DxO, C1, DCU4, and maybe Raw Therapee output @ ISO 80 would be very interesting.

Here's a decent resolution test target...
http://media.pentax.de/media/de/is/microsites/K7/siemensstern_pentax.pdf
12-18-2011, 01:46 AM   #8
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Not to take the thread off-topic, but can someone tell me how to expand sensitivity on the K-5? I received mine yesterday, dutifully downloaded the manual and read it while patiently waiting for it to be delivered, but for the life of me I can't find it in the manual. Thank in advance for your assistance.

12-18-2011, 02:30 AM   #9
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MENU / Custom (C) tab 1 item 3 "Expanded Sensitivity".
12-18-2011, 02:35 AM   #10
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QuoteOriginally posted by ogl Quote
ISO80 is not native ISO for 16 MP APS-C sensor...
I've tried FA77 and FA43. Shutter speed is good. 1/160 and 1/200 and e.tc. or 1/100 for FA43 and shorter...
Is that not in the range of the shutterblur?
Maybe you could test it at higher and lower speed than those to see if it has any effect.
12-18-2011, 02:46 AM   #11
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Jolepp, thanks very much! Mission accomplished.
12-18-2011, 02:55 AM   #12
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Well I only use iso80 on a some occasions, so no idea to this. But I'm reading it.
12-18-2011, 05:58 AM   #13
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I don't know how ISO 800 noise on the K-5 looks like but I know that some noise can increase perceived sharpness.
12-18-2011, 08:07 PM   #14
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QuoteOriginally posted by falconeye Quote
In LR 3, I suggest to increase the 25% value to 100%
Which setting are you referring to? I assume you mean the first slider under sharpening- "amount", but wanted to confirm.

Thanks
12-19-2011, 02:20 AM   #15
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QuoteOriginally posted by JamieP Quote
Which setting are you referring to? I assume you mean the first slider under sharpening- "amount", but wanted to confirm.
Yes, I meant "Amount" but didn't go into detail on purpose. 100% Amount is a good first guess at low ISO.

What I really do is this:
- try 100% Amount
- for a good image (low iso, good overall sharpness), I reduce Radius and increase Detail to see if it reveals further detail.
- for a worse image, I may reduce Amount and/or increase the Radius. Or replace Sharpening by Clarity (which is mild sharpening with a very large radius).
- Eventually, esp. if I used Fill Light, I apply some Noise Reduction in LR. The slider is right below for a reason ...
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