D.P. Explain please :)

[CGrieves]

From another thread-

Furthermore digital sensors really don't respond wel to ultra fast apertures. there is a strong decline in efficiency as lenses get faster than around f/2.2. So much so that an f1.2 lens doesn't really provide any more light than a f1.4 lens and an f1.8 lens is not really noticible lower.

Could you shed some more light ( ) on this? As I enjoy low-light stuff, I was planning to go for the 50mm 1.2L over the 1.4, thinking it was worth the money for the extra aperture....

 

[CGrieves]

Yep, vignetting, DOF and make/model aside, I'm just intrigued by the suggestion that a f1.4 doesn't let in roughly twice the light of an f1.8... I'd like to know why, otherwise I'll just get another plastic fantastic

 

[CGrieves]

Hehee, thanks chaps, but you're missing the point, my fault for being vague

Not bothered about the actual model of lens, I'm interested in D.P.'s assertion that higher apertures don't actually provide measurably more light or better performance. If so then extra money for bigger apertures might be a waste in my case. I'm interested in the reasoning and physics behind it.

 

[CGrieves]

Very interesting, cheers, have now got some reading to do....

 

[CGrieves]

Nor should it, it is one of the best lenses Canon makes. Nothing anyone has said has been to criticize the 85L, I am very surprised that it ended up so heated and Raymond taking it very seriously. The thread is just about an explanation of a physical phenomena that results in diminishing returns for light gathering capability at ultra fast apertures that effect all manufacturers equally.

I am interested in the technical side of photography no more than I am interested in the technical side of anything I do. i am a scientists, i have a PhD, I like to know how things work and why, I spend how on Wikipedia just learning anything and everything from biology, chemistry, physics, history, economics, etc., etc. I far prefer to be out in the mountains hiking and taking photos but monday-Friday I am in the office all day so that isn't possible. What is possible is reading articles that interest me in a 5 min coffee break.

I'm also not sure why this got so heated. Exactly as asked, you've clarified interesting information I didn't know, and given me another dimension to consider when choosing equipment. Personally, I'd much rather know than not....

I'm guessing that as sensor technology and efficiency advances, the off-axis sensitivity might also increase? If so, from that standpoint, going for the largest aperture possible could still be viewed as a good long-term investment. Unlike computing technology, and one could argue to a certain degree camera bodies, lenses aren't prone to becoming obsolete over the short term.

Even knowing this limitation, I'd still consider the 50 f1.2. Performance and build quality aside, while I hate to admit it, the consumerist in me still gets satisfaction from pulling an L out of the bag

 

[CGrieves]

To be fair, D.P. never asserted that we should or shouldn't be worried about this effect, or even called it an "issue". He merely stated in another thread that digital sensors don't necessarily realise the light gathering potential that one might assume from the focal ratio of a lens. I then asked for an explanation here, and he clarified the facts, nothing more. The argument about whether we should be concerned or not blew up pretty much on its own!