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08-21-2010, 11:15 PM   #1
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Color saturation--iso vs. shutter time

I've been an amateur photo bug, shooting with Pentax since 1963. I went digital about two years ago with the K-10 welded to a FA 100 macro. I've gotten into a groove with my shooting, producing some excellent scientific photography. Plants in macro on a tripod account for 99% of my shots. Just recently, a visiting friend and fellow plant nut caught the Pentax bug and bought a new K-7 with a DFA 100 WR macro. In lieu of a tripod, his hand held approach has been to use higher iso (400/800) so he can use f/16 or higher for good DOF. Since I am tripoded, I always use iso 100. I figured it will give me the highest quality (as did Asa 55 Velvia film) and what's a few seconds more with the shutter open? Also, in an early test of my K-10 using f/16 in all iso levels, anything over 200 didn't seem so great. But I have to continually question my approach in the quest for unattainable perfection. When I look at my friend's recent 800 iso shots, the quality seems much better than on my K-10. Is this just a sub-conscious desire for a new K-7 or is the CCD actually that much better? Also, when I'm shooting at long exposure times, i.e. 3-10 sec. +, are there color saturation or other technical issues that might actually decrease the quality of the shot?

08-21-2010, 11:53 PM   #2
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Something I learned fairly recently is that with long exposures over 1s, you can get stray light coming in and reaching the sensor from your viewfinder, causing loss of contrast and other yucky flare-like effects, if you don't cover the viewfinder with the included cap.
08-22-2010, 12:52 AM   #3
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This sure is a rather complicated question. There are several factors influencing the outcome at different ISO settings. Your basic assumption about image quality deteriorating at higher ISOŽis right when comparing results from a certain camera. All the key things, dynamic range, colour rendition, noise etc are at their best at low ISO settings. However, different cameras exhibit different characteristics. In some cameras this IQ deterioration takes on earlier than in others. Typically more recent models are better in this respect. The K-10 has a CCD sensor, while the K-7 has CMOS one. This structural thing also has some effect on the visible characteristics.
The K-10 is capable of producing excellent results. However, to get everything out of this camera you had better shoot in RAW.

I used to have a K-10, bought a K-7 last summer. At low ISO settings the CCD sensor of the K-10 produces very pleasant colours, while post-processing is more often needed with the output of the K-7. Once you inrease the ISO setting, the K-10 gradually loses this advantage and from ISO 800 onwards I would say the K-7 is clearly superior. The other thing is that when comparing to the latest competitors, even the K-7 does not exactly excell at noise handling above ISO 1600 .
No matter which camera you use, post-processing makes a big difference, especially at high ISOŽs. Levels adjustment for all the colour channels compensates many of the harmfull effects and pushes the limits a lot furher. The same goes for dedicated noise removal tools such as Noise Ninja orTopaz DeNoise.

Last edited by PePe; 08-22-2010 at 01:28 AM.
08-22-2010, 03:35 AM   #4
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I would say that over iso 400, the K7/K20 is going to look better. At iso 100, however the K10 is hard to beat, very sharp with amazing little noise, even with long exposures. If you always use a tripod, then it is no big deal. However, if you want to shoot higher iso, you may look at one of the newer cameras.

08-22-2010, 11:03 AM   #5
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Also, you don't say if you are shooting JPEG or RAW or if you've experimented with different settings as far as NR or sharpening (which is inextricably linked to the appearance of noise). Chances are very good your K10D is perfectly capable of results much better than you may be remembering, if you optimize your shooting and PP technique.
08-22-2010, 11:15 AM   #6
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QuoteOriginally posted by RawheaD Quote
Something I learned fairly recently is that with long exposures over 1s, you can get stray light coming in and reaching the sensor from your viewfinder, causing loss of contrast and other yucky flare-like effects, if you don't cover the viewfinder with the included cap.
I was told not so long ago, rather bluntly, that this cannot happen since the Mirror is up and the viewfinder area is essentially light sealed. The only reason for covering the viewfinder I was told, was for metering. I won't argue the point either way because I don't care and it isn't important for me to do so. However, when doing long exposures, I tend to cover the viewfinder with a towel, hat, or something similar. The cap is too much of a pain to use because you have to remove the eye piece to do so..

08-22-2010, 08:51 PM   #7
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Thanks all for your comments. I shoot only raw and use Aperture 3 software. Never knew about the
possibility of light leakage, but will keep in mind for long exposures. Noise has never been a problem in
my shots due to the low ISO. Thanks Pepe for the insight in differences between the K-10 and K-7.
08-22-2010, 10:47 PM   #8
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QuoteOriginally posted by JeffJS Quote
I was told not so long ago, rather bluntly, that this cannot happen since the Mirror is up and the viewfinder area is essentially light sealed. The only reason for covering the viewfinder I was told, was for metering. I won't argue the point either way because I don't care and it isn't important for me to do so. However, when doing long exposures, I tend to cover the viewfinder with a towel, hat, or something similar. The cap is too much of a pain to use because you have to remove the eye piece to do so..

The mirror isn't opaque. It is semi-transparent and will let light through if no precautions are taken.

08-23-2010, 09:44 AM   #9
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QuoteOriginally posted by wjjstu Quote
The mirror isn't opaque. It is semi-transparent and will let light through if no precautions are taken.
All I'm stating is what I was told, on these very forums. I didn't say I believed it.

08-23-2010, 11:18 PM   #10
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QuoteOriginally posted by JeffJS Quote
All I'm stating is what I was told, on these very forums. I didn't say I believed it.


I have a half a dozen shots that prove, without doubt, that light gets in through the viewfinder without caps.
08-24-2010, 02:10 AM   #11
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QuoteOriginally posted by RawheaD Quote
I have a half a dozen shots that prove, without doubt, that light gets in through the viewfinder without caps.
I believe you. I am not arguing with you. It would be nice though if we could make up our minds when answering somebody's questions about it. One poster says it Can, the next, says it Cannot (light pass through the viewfinder to the mirror box when the mirror is up).

08-24-2010, 04:43 AM   #12
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QuoteOriginally posted by john mood Quote
Since I am tripoded, I always use iso 100. I figured it will give me the highest quality (as did Asa 55 Velvia film) and what's a few seconds more with the shutter open? Also, in an early test of my K-10 using f/16 in all iso levels, anything over 200 didn't seem so great. But I have to continually question my approach in the quest for unattainable perfection. When I look at my friend's recent 800 iso shots, the quality seems much better than on my K-10. Is this just a sub-conscious desire for a new K-7 or is the CCD actually that much better?
His shots are better in what way exactly? More detail, mre contrast, better colour? Are you using the same lens? Are you processing the same way? Viewing on the same screen? Any of these contribute as much or more than the camera.

I assume the plants are being photographed in a lab or studio? Are you sure there's no air movement or floor vibration that is causing micro movement? Foot traffic can be deadly in a building.

Most importantly, are you using the 2s delay feature on the shutter?
08-24-2010, 01:21 PM   #13
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QuoteOriginally posted by JeffJS Quote
I believe you. I am not arguing with you. It would be nice though if we could make up our minds when answering somebody's questions about it. One poster says it Can, the next, says it Cannot (light pass through the viewfinder to the mirror box when the mirror is up).


Well, perhaps we can agree that when answering somebody's question, it is always best to speak from experience, rather than hearsay :-)

I'm not confronting you, by the way. It's just that your post appeared to make this point equivocal (or at least tried to do so), when it is not. And you should care one way or another, actually, because now you can say with confidence which is the correct answer.


Of course, to be consistent, it is best to see for yourself. If you have a really dark ND filter (like ND400), try shooting with the sun behind you for the longest duration possible (shoot F22, ISO100). If you can stack NDs or a polarizer, the better. Take two shots, one with the cap (or hat) off and one on. The difference will be astonishingly great if the exposure is any longer than a few seconds :-)
08-24-2010, 01:58 PM   #14
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Does anyone have any info on the Kx in regards to ISO level and its effects on saturation, clarity, etc.?

Last edited by jwiles; 08-24-2010 at 01:59 PM. Reason: Correct spelling
08-24-2010, 03:56 PM   #15
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The K-x is no different than any other camera - the higher the ISO, the worse the IQ. and that applies to resolution and color accuracy as well as it does to "noise" per se.
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