Three Quick Questions vs The Enjoyment of Photography

Started Jan 2, 2013 | Discussions thread
richarddd
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Re: Three Quick Questions vs The Enjoyment of Photography
In reply to Great Bustard, Jan 2, 2013

Great Bustard wrote:

richarddd wrote:

1) Some are interested in technical information for its own sake.

Absolutely.

2) For others, there should be practical implications. The practical implication of the entire equivalence issue comes into play when you are deciding between cameras with different sensor sizes...

Yes.

...and might have believed there are differences that don't actually exist.

You lost me with that. As a side, if one believed that, for example, f/2.8 1/100 ISO 200 and f/5.6 1/100 ISO 800 had the same exposure, then they would have to conclude that FF has the same exposure as mFT for Equivalent photos.

If you're trying to decide between different formats, it would be helpful to know if you are likely to see differences in image quality when talking "equivalent" photos.

3) In that thread you said "Except the ISO setting doesn't change the "sensitivity to light" -- it merely applies a gain to the signal, which we can do in post just as well as we can in camera. The advantage of changing the ISO in-camera is that higher ISOs result in less read noise than lower ISOs for many sensors"

Yes.



For the E-M5, you can not do it in post just as well as in camera. Boosting ISO in camera works better up to about ISO 1600 compared to processing in post. I started a thread on this subject recently.

The EM5 is essentially ISOless beginning at ISO 800:

http://www.sensorgen.info/OlympusOM-D_E-M5.html

See below



That seems a more practical bit of info than a question which turns on whether one is using the dictionary meaning of exposure or a meaning in common usage.

In the end, it's the final photo that matters. But to maximize the IQ of the photo, it helps to know what exposure is and what the ISO setting on the camera actually does.

Here's a particulary practical example. f/2.8 1/100 ISO 800 and f/2.8 1/100 ISO 3200 have the same exposure (for a given scene) since they result in the same density of light falling on the sensor.

Let's assume that the ISO 3200 pic gives the desired brightness. Why use ISO 800 and push two stops in post? The answer is because the ISO 800 pic will give two stops more DR (since elements of the scene will be pushed outside the bit-depth of the recorded file), and thus the photographer has greater lattitude in the tone curves they can successfully apply to the photo with virtually no noise penalty, since the EM5 is essentially isoless at and beyond ISO 800.

The disadvantage, of course, is that the image playback will be dark (a simple firmware fix for all cameras -- to give an option for the playback brightness to be at the metered brightness), and, if shooting jpg, the tone curve has already been applied to the photo, so no help there.

In any case, whether or not you are going to make use of knowing what exposure is and what the ISO setting on the camera does, is another matter all together. But, as I said, these are technical forums, and, well...



For the E-M5, you are better off increasing ISO in camera than increasing in post, subject to a few conditions. See for example http://forums.dpreview.com/forums/thread/3352455  From what I've read, this would not be true for current Nikon DSLRs

Knowing this seems more valuable for an E-M5 user than knowing whether "exposure" includes ISO.

I like technical information, both for its own sake and to aid in taking pictures.  Problems arise when technical info is used to play gotcha games.

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