Dynamic Range -- what it is, what it's good for, and how much you 'need'

Started Oct 17, 2011 | Discussions thread
Great Bustard
Forum ProPosts: 24,681
Like?
Entirely 'quite'
In reply to boggis the cat, Oct 22, 2011

boggis the cat wrote:

Great Bustard wrote:

boggis the cat wrote:

The difference between systems in terms of light collecting ability for lenses using the same f-ratio and photos displayed with the same area is quite simple:

  • 4/3 vs 1.6x: log2 (332/225) = 0.56 stops more light on the 1.6x sensor.

  • 4/3 vs 1.5x: log2 (372/225) = 0.73 stops more light on the 1.5x sensor.

  • 4/3 vs FF: log2 (864/225) = 1.94 stops more light on the FF sensor.

Not quite, because of the efficiency of the aspect ratio.

That, and the rest of my post, was 100% correct.

These calculations ignore the additional aspect ratio efficiency of 4:3 over 3:2, which is roughly 4%. This changes e.g. the Canon APS-C to FT ratio from 0.55 to 0.49 "stops", and the 135 to FT ratio from 1.94 to 1.89 "stops".

They ignore nothing. You simply don't understand what they are saying (a familiar story). Here -- I'll spell it out to you. For the figures above, the assumption is that we are taking a pic of the same scene with the same exposure, so that the area of the scene in the focal plane is the same for both systems.

Remember that the aperture is the diameter of the image circle...

That's wrong, right from the start. The aperture is most certainly not the diameter of the image circle.

...so the closer to 1:1 the aspect ratio is the more of the light from the image circle is being used (efficiency).

This ends up being 4:3 having 4% greater efficiency than 3:2.

No. A 4:3 rectangle inscribed in a circle with the same diameter as a 3:2 rectangle will have 4% more area. This does not mean "4% greater efficiency" unless the final photo is displayed at 4:3 or more square. If the photo is displayed 3:2 or more wide, then the 3:2 rectangle is "more efficient". This has been explained to you multiple times, but you still lack the cognitive capacity to understand it.

My point is...

...simply incorrect. My post was completely correct, as written. Whether you understand that or not, however, is another matter entirely.

Reply   Reply with quote   Complain
Post (hide subjects)Posted by
MathNew
You.New
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark post MMy threads
Color scheme? Blue / Yellow