ISO 1600 vs correcting exposure in photoshop

[Chuck Lee]

Daniel,

Emil has a chart of the read noises (including tweeners) in his Noise, Dynamic Range and Bit Depth in Digital SLRs essay:

Looks like the link is dead.


Do you havea copy you could post?


Thanks,


Chuck


P.S. Madison quit cause I called him a tool. I feel really bad. I was just jok'n around. He's European. woops.

[bob williams]

Thanks, that is very helpful. I appreciate the feedback Dan.





Bob

[Daniel Browning]

Looks like the link is dead.


Do you havea copy you could post?

Here ya go:

[Chuck Lee]

Thanks

[Johnny Rasmussen]

Very interesting topic and I totally agree. Take a look at this Norwegian site where you can see examples. I have run it through google translate so I hope the link is working.


Testing 50D and exposure:


http://translate.google.com/translate?prev=hp&hl=no&js=y&u=http%3A %2F%2Fwww.foto.no%2Fcgi-bin%2Farticles%2FarticleView.cgi%3FarticleId%3D412 81&sl=no&tl=en&history_state0=





Testing D90 and exposure. This example shows that ISO 6400 + 1.3EV can look as good as ISO 1600 if the exposure is right:


http://translate.google.com/translate?prev=hp&hl=no&js=y&u=http%3A %2F%2Fwww.foto.no%2Fcgi-bin%2Farticles%2FarticleView.cgi%3FarticleId%3D413 16&sl=no&tl=en&history_state0=





PS! I dont know how to make a hyperlink. Copy and paste and look at Exposure and ISO properties.








Johnny

[Chuck Lee]

Jonny,


Thanks for the links. To add a hyperlink to anything just select those words and click on the little chain icon (4 left of the happy face) and paste the url in the appropriate box. Just remember the "http://" has to be in front of the "www"


Like this: Canon Rumors


Voila, as the French say

[Dumien]

First, I'm very impressed with google translation, it's pretty darn accurate, isn't it?


As for the pictures: TOTALLY AWESOME...see, I tried to do a little test with my XSi, but I guess that i'm going to see better results when I'll take pictures in real life...


thanks Johnny...(btw, that's my nickname! Everybody calls me johnny at school..well, used to: i'm finally done with highschool hahaha)


Andy

[peety3]

(By the way, they have the same "exposure" but different "brightness". The idea that ISO is a part of exposure is a common misconception.)

In a purely digital world, you may be right. In the days of film, f/4 and 1/500th might underexpose some film and overexpose other film. Otherwise, Bryan Peterson must be wrong in calling it the Exposure Triangle...and he's certainly sold a lot of books calling it that.

[peety3]

The short answer is to use the highest ISO you can without blowing important highlights. High ISO reduces noise.

Here's the long answer. ETTR (Expose To The Right) means to increase exposure (f-number, shutter speed, etc.) as much as possible without blowing the highlights you care about. ETTR is the best technique for reducing noise. A single stop of exposure (e.g. f/2.8 instead of f/4) can make more of a difference than 2 stops of ISO (e.g. 400 -> 1600). That doesn't mean ISO is unimportant, just that exposure is more important.

But there is a cost associated with high ISO. That cost is clipped highlights. For every doubling of ISO, one stop of highlights are lost. That is why I advise folks to use ITTR: ISO To The Right. That is, increase ISO as much as you can on every shot, without blowing important highlights. But don't go over 1600, as I said above, unless you need the convenience features.

This took me a long while to digest and interpret. What I finally figured out is that you're suggesting that we shoot in manual mode, starting at ISO 100 "for every shot", and choose "exposure" (using your definition of exposure) values such that the desired image is (hopefully) captured while also maximizing the light upon the sensor, without so much light that important highlights are lost. If it's impossible to achieve the desired image via aperture and shutter values (i.e. slowing the shutter will result in a blurry image, or opening the aperture will thin the DoF too much), it's best to increase the ISO to maximize the light upon the sensor, without so much light that important highlights are lost.


My translation of all of that is that it's best to achieve a right-justified histogram (using appropriate margins for the details we wish to keep) by prioritizing the widest artistically-reasonable aperture and the slowest artistically-reasonable shutter, and then the minimum amount of ISO increase. My initial interpretation was that I should set my camera to ISO 1600 and lock that in, which I don't think is the desired interpretation.

[Daniel Browning]

In a purely digital world, you may be right. In the days of film, f/4 and 1/500th might underexpose some film and overexpose other film. Otherwise, Bryan Peterson must be wrong in calling it the Exposure Triangle...and he's certainly sold a lot of books calling it that.

There's nothing wrong with calling it the Exposure Triangle: that does not imply that changing ISO (without changing f-number or shutter speed) is changing exposure. I do not recall Bryan Peterson ever using the incorrect definition of exposure in "Understanding Exposure".

This took me a long while to digest and interpret. What I finally figured out is that you're suggesting that we shoot in manual mode,

I did use manual for illustration, but it's possible to use the "ETTR then ITTR" technique with autoexposure as well.

starting at ISO 100 "for every shot", and choose "exposure" (using your definition of exposure) values such that the desired image is (hopefully) captured while also maximizing the light upon the sensor, without so much light that important highlights are lost. If it's impossible to achieve the desired image via aperture and shutter values (i.e. slowing the shutter will result in a blurry image, or opening the aperture will thin the DoF too much),

Yep.

it's best to increase the ISO to maximize the light upon the sensor, without so much light that important highlights are lost.

Increasing ISO doesn't change the light on the sensor at all. It increases brightness and decreases read noise.

My translation of all of that is that it's best to achieve a right-justified histogram (using appropriate margins for the details we wish to keep) by prioritizing the widest artistically-reasonable aperture and the slowest artistically-reasonable shutter, and then the minimum amount of ISO increase.

That will result in the same settings (Tv/Av/ISO) that I am suggesting.

My initial interpretation was that I should set my camera to ISO 1600 and lock that in, which I don't think is the desired interpretation.

Correct. ISO 1600 always has less noise for a fixed exposure, but that doesn't mean we should always use it. High ISO has a price: clipped highlights. That price is always far too high to pay, except when we are in low light, and we no longer need the normal amount of highlight headroom.