A few thoughts about ISOless (continued).

Started Jul 11, 2013 | Discussions thread
ForumParentFirstPreviousNextNext unread
Flat view
Great Bustard
Forum ProPosts: 24,681
Like?
A few thoughts about ISOless (continued).
Jul 11, 2013

This thread is a continuation from this thread:

http://www.dpreview.com/forums/post/51788461

OK, first up, what is an ISOless sensor? It is a sensor where the read noise does not change as a function of the ISO setting. For example, the read noise for the D800 sensor remains at right around 3 electrons throughout the ISO range:

http://www.sensorgen.info/NikonD800.html

whereas the read noise for the Canon 6D sensor continually lowers from 26.8 electrons / pixel until around ISO 3200, where it remains at around 2 electrons / pixel from there on out:

http://www.sensorgen.info/CanonEOS_6D.html

Thus, the 6D sensor is non-ISOless up to ISO 3200, and ISOless from 3200 on.

OK, so what?

Well, the so what is that the two primary sources of noise are due to the total amount of light collected the sensor (photon noise) and the additional noise added by the sensor and supporting hardware (read noise).

The total amount of light collected by the sensor is the product of the exposure, the sensor size, and the QE of the sensor:

Total Light Collected = Exposure x Sensor Size x QE

where the QE is the proportion of light falling on the sensor that gets recorded (a QE of 50%, which is right where most modern sensors are at, means half the light falling on the sensor gets recorded).

Let's say we have two cameras, one with an ISOless sensor, the other with a non-ISOless sensor. Let's also say that the LCD playback and OOC jpg brightness are tied to the cameras meter, and that the meter is zeroed for f/2.8 1/100 ISO 1600 for a particular scene. We then take a pic with each camera at f/2.8 1/100 ISO 100 and f/2.8 1/100 ISO 1600.

For the camera with the non-ISOless sensor, the ISO 1600 photo will be a bit less noisy than the ISO 100 photo (see here for an example), but will have more blown highlights for the same reason as the ISO 1600 photo from the ISOless camera.

For the camera with the non-ISOless sensor, the ISO 1600 photo will be a bit less noisy than the ISO 100 photo (see here for an example), but will have less blown highlights for the same reason as the ISO 100 photo from the ISOless camera.

Thus, for cameras with non-ISOless sensors, there's still reason to set the ISO manually, depending on whether noise or blown highlights matter more. On cameras with ISOless sensors, there is no reason to use anything other than base ISO (assuming, once again, that the LCD playback and OOC jpg brightness were tied to the meter).

In practice, the ideal use of ISOless photography would be the same as shooting in M mode with Auto ISO and the appropriate safety shifts for aperture and shutter speed, except if the camera had an ISOless sensor, there would only be one ISO (base), and the LCD playback and OOC jpg brightness need to be tied to the camera's meter (and any dialed in EC), which is a simple matter in firmware.

What does ISOless shooting offer the photographer? Basically, it's not unlike RAW vs jpg. By not pushing brighter portions of the scene outside the bit depth of the image file, the ISOless shooter will have a greater range of tone curves to apply to the photo. It's not unlike asking what advantages does a camera with 14 stops of DR have over a camera with 11 stops of DR -- for most scenes, no advantage at all. But occasionally, the advantage would be substantial.

In any case, ISOless shooting is more "natural" -- that is, the photographer concentrates on exposure, and applies processing after the fact. With non-ISOless shooting, the photographer is committing to a particular amount and type of processing when they choose the ISO.

I hope this is helpful.

Canon EOS 6D Nikon D800
If you believe there are incorrect tags, please send us this post using our feedback form.
ForumParentFirstPreviousNextNext unread
Flat view
Post (hide subjects)Posted by
ForumParentFirstPreviousNextNext unread
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark post MMy threads
Color scheme? Blue / Yellow