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Camera conference General and model-specific E-System camera chat.

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  #16  
Old 12th April 2009
PeterD PeterD is offline
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Re: Native ISO?

Quote:
Originally Posted by Nick Temple-Fry View Post
I think we have been scared of high iso, perhaps because of all the review comments about poor high iso performance. And there is some truth in these comments, higher iso settings can be a weak point of the sensors in olympus cameras. But noise can be managed both in pp and whilst you are taking the shot.

A better shot with decent dof and good exposure at a higher iso will beat hands down a shot you've squeezed out of the camera with exposure tending to the left and a too shallow a dof (or a lens too open to be happy). And of course if you take a noisy image at iso 800, then it's hard to realise that at iso 1250 with a well balanced histogram you will actually get a better/cleaner image.

I'll regularly shoot at iso 1000 or 1250 (Canon 1600 equivalent) if it means a good shutter speed and a good exposure. So with the later sensors (at least) look at the histogram you are getting as well as the iso and the shutter speed. A good exposure opens up the higher iso values.

Nick
Thanks for this Nick. I knew this thread would be useful. When I first tried wildlife shots I went for shutter priority and auto ISO. The results were not too bad most of the time but using a long lens on a dullish day caused the camera to select very high ISOs with the result that I got very noisy images. In some cases, I could not deal with the noise. This put me off high ISOs. I now have Neat Image so I may try pushing up to ISO 1600 again and see what happens.

Peter
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  #17  
Old 13th April 2009
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Re: Native ISO?

Looking at this thread I put together http://e-group.uk.net/forum/showthread.php?t=5146
I get the impression that the native ISO for the E400 is about 100ISO as colour noise appears to be introduced above that
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  #18  
Old 15th April 2009
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Re: Native ISO?

Some interesting thoughts.

Crimbo, your examples certainly sem to show ISO 100 best in that example. I think I'll do some testing of my own.

In the wrotniak article it seems to me that ISO 200 is just as good. But a different situation and camera.

Anyway, I shall be more prepared to wander from the ISO 100 standard.
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  #19  
Old 15th April 2009
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Re: Native ISO?

An interesting thread,

I tend to keep my iso set to auto but with it 'capped' at 400 so I don't actually shoot with any larger numbers than I intend to.

This is an option on the E3 but I'm not sure about other models.
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  #20  
Old 15th April 2009
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Re: Native ISO?

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Originally Posted by ndl0071 View Post
An interesting thread,

I tend to keep my iso set to auto but with it 'capped' at 400 so I don't actually shoot with any larger numbers than I intend to.

This is an option on the E3 but I'm not sure about other models.
Auto ISO in the E400 is 100ISO and only changes when flash is used...dont know if this changed for later models
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  #21  
Old 16th April 2009
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Re: Native ISO?

Just to follow up on Ian's comments from a few days ago:

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Originally Posted by Ian View Post

Where there is some growing consensus is that ISO 200 is the optimun setting because people are seeing more over-saturated highlights at ISO 100 compared to when using ISO 200. It's a grey area, really. I haven't seen any evidence for the ISO 200 argument in technical tests (like DxoMark, for example).

Ian
I see that the DP Review of the E30 shows about half a stop more usable range overall at 200ASA compared to 100ASA, with over 1 stop difference being in the highlights. This presumably would explain what folk have been finding in practice.

Anyone got an explanation for this? I guess it must have something to do with the relative amounts of sensor noise and amplifier noise, but I can't grasp why this doesn't have a greater impact in the shadows rather than the highlights.

Ian
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  #22  
Old 16th April 2009
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Re: Native ISO?

A bit of Googling has revealed an answer to my own question! What I found was:

"Any digital sensor has a floor ISO sensitivity which is the readout of
the charge collected in its photon wells without any amplification.
Higher ISO settings is achieved by amplyfying the analogue readout of
photon wells. This makes the sensor appear more sensitive, but also
amplifies any noise present in the signal.

Setting ISO below this floor serves no purpose. The photon wells
will simply overflow, resulting in a reduced dynamic range.
"

That makes sense. The highlight range would be significantly restricted, but in setting a gain of less than one (i.e. to reduce sensitivity from the native 200ASA to 100ASA) would also reduce sensor noise as well as the signal (so long as the amplifier itself doesn't contribute much noise), and so contribute to the extended shadow 'tail' of the response curve.

Surprising what can be found on the web

Ian
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  #23  
Old 16th April 2009
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Re: Native ISO?

But do we know what these 'floor ISO's are for the Olympus sensors or are there practical tests we can do to determine them?
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  #24  
Old 16th April 2009
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Re: Native ISO?

I think that the straight answer is 'no', but one could surmise from the likes of DP Review data that the base ISO for the E30 is above 100ASA. The same result is observed in the Nikon D700, D3 and D3X reviews for example, but in those cases Nikon has indicated what the base ISOs are and has prefixed slower speeds by 'L'. I can't imagine that Oly will be forthcoming on this, but Ian might be able to get some inside info. At any rate, it is perhaps sufficient to be aware that the better DR appears to occur at 200ASA and not 100ASA. What happens between 100 and 200ASA is anyone's guess.

Still, what does impress me, if DP Review's data are anything to go by, is that the E30's approach to clipping is much gentler, for speeds of 200ASA and above, than with my E510 (or even the E3 for that matter). Much more film like I think. It will be interesting to see if the E620 has the same characteristics.

Ian
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  #25  
Old 16th April 2009
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Re: Native ISO?

In this week's Amateur Photographer Barney Britton tests the E620 and finds that the camera has one whole EV stop of dynamic range more at ISO 200 compared to ISO 100 which leads him to believe that the native ISO is 200.

Whether this relates to all Olympus cameras I don't know, but if it does it would seem that ISO 100 is best avoided unless you particularly want to achieve the lowest possible shutter speed, for example when attempting to create some artistic blurr or subject movement.

It could also explain why other models in previous tests have revealed slightly worse DR than the competition; if the test has been conducted at ISO 100 the sensor could have been at a disadvantage of 1EV compared to how it would have rated at ISO 200.

It would also make sense to have ISO 200 as the native setting. If you think about it, noise is bound to increase with each stop that ISO is increased beyond the native value, therefore if this was ISO 100 then higher ISO values would automatically be worse than on competitor cameras with a native ISO of 200 - quite apart from any other differences in sensor performance.
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  #26  
Old 17th April 2009
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Re: Native ISO?

That's good to know about the E620.

I don't think it does apply to the other models. Looking at DP Review data (for consistency if nothing else - I don't have any affiliation ) for the E510, E520, and the E3, there is nothing to suggest that the native ISO is anything other than the lowest setting. DR isn't seen to increase as the ISO is bumped up from 100 to 200.

Interestingly, I see that the data for the G1 shows no such effect either. That means that the native ISO for the G1 sensor is 100, rather than 200. If these characteristics are indeed inherent in the sensor itself, then it does suggest that the G1 and E30/620 sensors are not as similar as might at first be thought. Also, the response characteristics of the G1 give a much more abrupt approach to clipping than does the E30, more reminiscent of my E510 (albeit with a slightly larger DR). Intriguing.

Ian
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