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a900 ISO: 100 vs 320

peterv

New member
Lately there's been some talk on this forum that 320 ISO would be an interesting ISO setting for the a900. Kind of a 'sweet spot' for the right exposure and noise. I compared 100 to 320 ISO and here are some screenshots of in-camera jpgs. It looks like 100 ISO shows more detail, saturation, better contrast and also less noise.

There's some purple fringe in the 320's that not visible in 100. Probably makes sense with the higher sensitivity, but it may be one more reason to stick with 100 ISO.

What are your thoughts? Why use 320 ISO?

320 is on the left, 100 right.
 

peterv

New member
I think the comparison needs to be done in raw though. ISO 100 does look sharper.
Hi Carsten, I agree, raw must compared too. Interesting thing here: in RD standard settings things look different... Now 320 seems to look better. 320 is still noisier though.

again, 320 on the left, 100 on the right.

(will do more testing/developing tomorrow, bedtime in Amsterdam :eek:)
 

douglasf13

New member
ISO 100 is a +1 EV exposure comp of ISO 200, and there is no gain difference between the two. You essentially exposed the ISO 100 one more stop than the ISO 320 shot. Try this again in raw with ISO 200. Also, the reason for ISO 320 is that doesn't clip and blob out shadow detail. This may or may not make things appear very slightly more noisy overall than ISO 200, but it's worth it in most situations, IMO. ISO 200 destroys shadow detail, which is easily checkable with Rawanalyze.
 

fotografz

Well-known member
Okay, this made me curious. So I just ran a controlled test in studio.

Available but constant light (Profoto modeling lights in soft boxes, no variable)

A900, 24-70 @ 70/5.6 on a tripod to keep it a constant. RAW.

Walked through all ISOs from 100 through 3200.

Batch sync processed in CS4 Bridge-ACR.

Opened as 16 bit tiffs in CS4, viewed at 100% on screen.

ISO 320 clearly shows more micro detail than 100 which seems to suppress it, (see the crop where a finger print is more clearly visable in the 320 shot).

320 shows a bit more noise than 100 but not a lot more, and in most practical applications would be a non issue. Color looked a bit better at ISO 320.

No surprise, ISO 200 records more nano detail than 100 but not quite as well as the 320, while exhibiting the noise level very close to the 100.

In all but the most huge enlargements I'd agree that 320 is the optimal balance between recording detail with acceptable noise levels when working at the lower ISO end.

The question is how much sharpening with 100 works, and how much selective noise control for 320 works, and in the end which is better? I suspect that if you sharpen 100 to gain back the detail the noise will be enhanced, so you may as well have shot 200 or 320 in the first place.

I would only resort to 100 if trying to control shallow DOF in extraordinarily bright conditions, or to produce a slow shutter speed, but not for IQ.

HIGH ISOs

I detected very little applied difference between ISO 1250 and 1600. There is some, but the noise structure is very similar.

But when compared to ISO 1000 it was clear that 1000 was the best high ISO because it did not exhibit a salt 'n pepper type grain structure apparent in 1250 and 1600.

Plus, ISOs 1250 and above (but not much in 1250) increasingly showed blue blotches in the solid black areas. ISO 1000 showed no signs of this at all.

My working conclusion would be that 1000 is highly usable on this camera if exposed with the usual care needed for any high ISO application. 800 is better, and 640 even better ... with 640 being the optimal balance between detail and noise in mid range ISOs. But 800 is no slouch.

-Marc
 

Terry

New member
Marc,
Will this test now change your basic setting to 320? Based on the long thread this weekend and an email from Jono that is where I set it.

terry
 
H

hardloaf

Guest
Each sensor model in digital cameras has one sensitivity and this is a basic physical property of the sensor. All in-camera ISO adjustments cannot change it - they work through internal analog/digital processing when information is extracted from the sensor after image is captured, kind of internal push/pull in film terms. So whatever it captures is going to be the same as long as shutter and aperture are same, ISO doesn't matter at this stage.

When you compare two shots at ISO 100 and 320 you essentially gave sensor 1 2/3 stops more light in case of ISO 100, so no wonder it's less noisy.

Regarding ISO 320 - just make a shot at ISO 200 and 320 with good colored shadow details and process them identically in IDC f.e. Shadows will be different and at ISO below 320 they can get weird tint like greenish or purplish and also they'll get clipped. It's easier to see if both shots are equally underexposed.

Even Sony warns about limited DR for ISOs below 200 and they are not kidding. I'd never recommend anybody to use those actually :)
 

Terry

New member
Each sensor model in digital cameras has one sensitivity and this is a basic physical property of the sensor. All in-camera ISO adjustments cannot change it - they work through internal analog/digital processing when information is extracted from the sensor after image is captured, kind of internal push/pull in film terms. So whatever it captures is going to be the same as long as shutter and aperture are same, ISO doesn't matter at this stage.

When you compare two shots at ISO 100 and 320 you essentially gave sensor 1 2/3 stops more light in case of ISO 100, so no wonder it's less noisy.

Regarding ISO 320 - just make a shot at ISO 200 and 320 with good colored shadow details and process them identically in IDC f.e. Shadows will be different and at ISO below 320 they can get weird tint like greenish or purplish and also they'll get clipped. It's easier to see if both shots are equally underexposed.

Even Sony warns about limited DR for ISOs below 200 and they are not kidding. I'd never recommend anybody to use those actually :)
So, If you are in a bright situation and you max out on shutter speed you are better off with an ND filter than going lower on ISO?
 

Guy Mancuso

Administrator, Instructor
Now that is a PITA to deal with. Must be a way to draw out a better base 100. Not so sure I am seeing the contrast lower in the ISO 100 shots. Can we not add some clarity to the 100 shots to draw out more detail. Seems to me this maybe a higher DR that is flattening out the file at 100 and the 320 shots we are seeing the contrast higher because it is shortening the DR. Has anyone actually measured the DR difference between these two ISO's. I have a tough time going with a base 320 on any cam. 200 is more reasonable
 

Terry

New member
Guy,
I'm not saying I would always do this but just following the thought all the way through to see what the "best" answer is vs. making a decision about the practical answer.

terry
 

Guy Mancuso

Administrator, Instructor
I realize that but I am seeing some DR difference here and it is affecting the micro contrast by lowering the contrast on the ISO 100 shots. Some small adjustments in the raw conversion like clarity can bring that right back in line with micro contrast.
 
H

hardloaf

Guest
So, If you are in a bright situation and you max out on shutter speed you are better off with an ND filter than going lower on ISO?
If you want to stay wide good ND will be the best option quality wise, but usually I just prefer to step down.
 

SeattleDucks

New member
I realize that but I am seeing some DR difference here and it is affecting the micro contrast by lowering the contrast on the ISO 100 shots. Some small adjustments in the raw conversion like clarity can bring that right back in line with micro contrast.
Guy is right, the 100 ISO crop clearly shows greater dynamic range. Notice ISO 100 has MORE shadow detail in the dark tones top left just below the gray patch, and overall tonality is smoother (compare the orangish color patch, in the ISO 320 crop it's going blotchy).

Last month I spent 5 weeks on a road trip in the West shooting the A900, much of the time at 100 ISO, and the files processed in Raw Developer are simply superb, with way more DR and shadow detail than my 4x5 Velvia chromes and a very natural filmlike look. In my landscape work the reported clipped shadows at less than ISO 320 is simply not showing itself. If someone has measured such with their camera sample, cool, but for me the result in 20x30 prints is all I care about and there is zero visible issue for me. Before I left on the trip I carefully ran an indoor test comparing every ISO in 1/3rd steps from 100 to 800, and 100 definitely shows the lowest noise on my A900.

Cheers,
Ross
 

jonoslack

Active member
Hi There
Well, I think this is all extremely interesting, however, personally, after 6 months shooting at ISO 200 (which Sony say is native) I've found no problems with shadow areas, and I also find it convenient for most circumstances. (which, of course, is not to say that it is the best, just that it is okay).

Marc - I found your comparison between ISO 1000 and 1250 really useful

The nice thing about this is that I no longer have any qualms about using ISO 320, if I really couldn't shoot wide enough open with ISO200 I would use ISO100 without any worries either - using an ND filter adds all sorts of other variables into the mix anyway.

I know we all want the best out of our kit, but sometimes this gets dangerously close to angels dancing on the heads of pins - I'll settle for the lovely files out of the A900, and I'll use whatever ISO seems appropriate at the time (in the knowledge that the cameras only obvious compromise is that it's not a high ISO machine).
 

peterv

New member
The question is how much sharpening with 100 works, and how much selective noise control for 320 works, and in the end which is better? I suspect that if you sharpen 100 to gain back the detail the noise will be enhanced, so you may as well have shot 200 or 320 in the first place
-Marc
I agree, this is THE question. I'd like to know the answer and get on taking pictures with this wonderful camera. I plan to work with this system for two years and don't want to end up with a large archive full with 100 ISO shots regretting I didn't shoot 320, or vice versa.

The results so far seem to suggest that the difference between 100 and 320 is not such big deal, but than again every bit of more detail and less noise is a nice bonus to the already very pleasing results we get from this camera.
 

peterv

New member
I realize that but I am seeing some DR difference here and it is affecting the micro contrast by lowering the contrast on the ISO 100 shots. Some small adjustments in the raw conversion like clarity can bring that right back in line with micro contrast.
Guy, I was thinking along those lines too, so I brought the 100 ISO shot into RD again and took down exposure 0,59 and added contrast + 0,20 to match the 320 ISO that was developed with standard settings.

Now there doesn't seem to be much difference, really. Obviously 320 is still noisier though.

BTW What do you guys think about the color fringe on the letterbox in the 320 shot?
 
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