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05-04-2015, 12:57 PM   #1
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K3 "optimum" ISO?


I just purchased a K3. I'm a long-time Pentaxian, this being at least my fifth Pentax DSLR...

My question is: Have other K3 users found an "optimum" ISO? I'm someone who wants to shoot as sharply as possible with my equipment, and am wondering if those of you who have been using this camera for some time have found an ISO sweet spot for it. Yes, I can do the testing myself, but it's also very informative to hear/read about others' experiences.

Thanks and looking forward to your input,


05-04-2015, 01:01 PM   #2
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I don't think ISO has a "sweet spot" like lens aperture. The lower the better. So ISO 100.

Everyone's tolerance for noise is different so you can test to see what you can live with and correct with your PP. For me I shoot @100 if possible and I'll go to 400 if I have to. If the shot requires higher than that I just don't bother. But I know others here shoot it at 1600 and 3200 with no problems. YMMV.
05-04-2015, 01:06 PM   #3
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Yes, lowest ISO means lowest noise. But the K-3 should be good even with ISO that was considered high only a few years ago.
If you shoot jpeg, you should look at the in-camera NR. If you shoot raw, look at the raw software's NR settings. I use very low NR for low ISO, and then progressively stronger. I don't really worry about ISO when its lower than 400. Above 1600 I take extra care.

The main thing with ISO is that it needs to be high enough to avoid handshake blur, while allowing the DoF you want (aperture).
05-04-2015, 01:17 PM   #4
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Some brands of cameras native ISO is 200 but can amp things down to 100 or 50, etc... I've heard it can reduce image quality but I have no evidence myself to back that.
It certainly hasn't seemed to bother the myriad of professionals that use those brands.

I believe ISO 100 is native for Pentax sensors. You *can* see a slight negative difference with ISO 200 under some conditions, but in reality it ain't gonna matter a heck of a lot.

Basically, as already said, getting the shot matters more than lack of noise.
Of course if you have the luxury of still life/studio, use ISO 100 when possible.

05-04-2015, 01:22 PM - 2 Likes   #5
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The best way to think of ISO is an inverse mapping to maximum print size for the gear at hand (obviously dependent on whatever lens+body combination you are currently using).

For example, if at ISO 100 you determine that your gear can make a quality 22"x33" print, then at ISO 400 the same scene might max out at 16"x24" print size, likewise at ISO 1600 it might max out at 10"x15", and finally at ISO 6400 might max out at 4"x6". My suggestion is to simply shoot different subjects at all different ISO values, then print them out at different sizes and see what your gear is capable of (and your tastes will allow). You might find you LIKE the look of noisy images, in which case you can print bigger (and you can safely ignore ISO settings altogether)!

05-04-2015, 01:49 PM   #6
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Iso 100 is the best, but I get decent results up to iso 800. Higher than that would not be my preference, although you can get decent snap shots up to iso 6400.
05-04-2015, 02:28 PM   #7

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Optimum ISO is the lowest ISO that exposes correctly for the required aperture and shutter speed. If you need high shutter speed to freeze action, don't worry about upping the ISO, but if you can shoot at ISO 100 and still get the shutter speed and aperture you need for the shot, that's best.
05-04-2015, 03:04 PM   #8

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Remember with DSLR's to look outside of the regular exposure triangle (of ISO <> aperture <> shutter speed).

With DSLR's I think you need to make the 'triangle' a 'square' by adding 'software' as the fourth reference point. The software you use (in-camera, DxO, Lightroom, C1 etc) and how you use it (shooting RAW, JPEG only, NR applied etc) needs to be taken into account too nowadays.

A correctly exposed ISO 100 shot, with everything done right according to the exposure triangle, could still look different (visually, and according to the histogram) depending on which RAW or JPEG image processor was used to form the image for display.

Returning to the original posters question: 'Have other K3 users found an "optimum" ISO?', I find it hard to isolate optimum ISO outside of the other features of the exposure 'square'. A dark and blurry ISO 100 image shot as a low-res '1 star' JPEG on the K-3, for example, doesn't tell me that ISO 100 on the K-3 is better than ISO 800.

As a final note: why has no one mentioned DxOMark yet The DxOMark K-3 measurement charts are required study for examining the optimal performance of the camera sensor.

05-04-2015, 03:15 PM   #9
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I agree there is no sweet spot, as low as you can is best. I also agree with the size of the print affects how high you might wish to go.
Photo of female cardinal was taken at 3200 ISO, with 10 out of 100 applied in lightroom for noise reduction and screen medium sharpening applied at jpeg export.
Photo of nuthatch was taken at 800 ISO, with 3 out of 100 applied in lightroom for noise reduction and screen medium sharpening applied at jpeg export.
Photo of woodpecker was taken at 400 ISO, with 0 out of 100 applied in lightroom for noise reduction and screen medium sharpening applied at jpeg export.
I have acceptably printed all of the above 13x19"(from the original dngs in lightroom not the resized for web jpegs here), although the Cardinal was a little grainy(a term used in the old film days meaning the same as noisy).
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05-05-2015, 12:00 AM   #10
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my formula

> iso = < prints size

at iso 100/200 with K3 you can print at 30 x 40 inches, and probably more... !
at iso 3200, 8 x 10 inches prints are good for my personal experience (sometimes I printed test shot taken at 6400 iso with good result)

normally, if I have little light, I use iso 1200-2000 without problems, sometimes also iso 3200, and work a little in postp.
05-05-2015, 12:46 AM   #11

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This is not a direct answer to the question but with some my older cameras I was using the ISO suggested by the site DXO Mark as the ISO in their "Sport & Wildlife" use case. I understand that this translates to the highest ISO with no visible noise and satisfactory dynamic range (no postprocessing/ no noise redcution in the camera needed). However the value given by DXO might be just a tad conservative with 24 MP sensor as you not often use that much MP in reality.

Look at this:
Tests and reviews for the camera Pentax K-3 - DxOMark
05-05-2015, 05:26 AM   #12
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I don't have a K3 so I can't speak to that specific camera but I've had a few Pentax DSLR's (*ist, K-x, K30, K5II ) and my personal preference is 800 or lower. I know Pentax DSLR's can do 1600, 3200 and above fairly well but for me anything above 800 just gets too noisy and I don't go there unless I absolutely have to. I normally shoot at 100-400, bump up to 800 if I need to, that's it. Very rarely do I take it above that even though you can. Shots at 1600, 3200 they're just too grainy for me unless that's an effect I am going for intentionally...
05-05-2015, 07:12 AM   #13
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While I agree with others that certainly ISO 100 is the cleanest, dynamic range is going to be your greatest concern. Shooting RAW, you will benefit by a nearly full f/stop of DR by utilizing Highlight Compensation which will raise the floor ISO to 200, under-expose by one stop, and apply a gentle roll off curve to highlights. (This can be set to use very conservatively as Auto mode.) Unlike the older CCD sensors, ISO is not as critical in the newer cameras (on the under-exposure side that is). You lose a lot of DR but not as much deterioration of detail and increase of noise with the new cameras.

We used to worry about native ISO for sensors, and the Nyquist Limit for lens resolution. Great theories to debate, but in practical application neither terms have a tangible impact.
05-05-2015, 07:23 AM   #14
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QuoteOriginally posted by ScooterMaxi Jim Quote
dynamic range is going to be your greatest concern
The key being that not every photograph NEEDS lots of dynamic range. Heck the old Kodachrome 64 didn't have a lot of "dynamic range" yet still was able to produce excellent imagery in the hands of an artist.


05-05-2015, 01:20 PM   #15
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You all have provided some great and thoughtful responses and I appreciate it!

I typically shoot at the lowest possible ISO, which has mostly been 200 in the past with my K20D and 645D, at "middle" apertures and with a tripod. Now that I have the K3 in my hands with a different type of sensor, I didn't know if users had noticed significantly different results with the CCD vs CMOS sensors at the lowest ISO settings. There's a part of me that still thinks of film and that there was a modestly noticeable difference between ISO 64, 100, 125 and 200 films.

Again, thank you all,


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