Is my thinking about equivalence right?

Started 3 months ago | Questions thread
Bassam Guy Veteran Member • Posts: 3,036
My mistake

James Stirling wrote:

Bassam Guy wrote:

jwilliams wrote:

Muster Mark wrote:

Hi all, I realize this is NOT the topic everyone loves to discuss and I totally understand. I hope no-one feels annoyed by this post. That said, after some investigation I have come to the conclusion that "traditional" equivalence math is only useful as a rough heuristic to get a sense of what DOF will be and NOT a reasonable way to compare individual lenses or judge cost/performance of lenses in different systems.

No, not really. Equivalence is more than DOF or even mainly about DOF. I'll not go into any long winded discussion, but here's an article on this site that is a good read on the subject.

Equivalence is useful if you have any interest in light (and as a photographer, you probably should): Digital Photography Review (

That is not true. 'Equivalence' implies at least two things. If 43 is your only sensor size then equivalence is meaningless.

Facts are facts whether you use them or not and it applies equally to all systems . People who buy the the £1100 40-150mm F/2.8 pro as opposed to the £195 40-150mm f4-5.6 , presumably appreciate the abilities that two extra stops of light gathering bring at the long end. Or perhaps they just like carrying larger heavier gear.

Perhaps, then, I don't understand 'equivalence' in digital photography. I thought it was about differences between various sensor sizes, not about differences between different apertures, like the $99 plastic fantastic at 5.6 and the 40-150 pro at 2.8 (which seems to me like common blasé knowledge).

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