Quote:
Originally Posted by rogerg
Thanks Susan for the very useful information, particularly this pieces above. I have wondered where the line is between a lens that focuses close and a lens that is truely a macro lens.
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It's all in the optics...
To focus close, all you need to do is move the whole lens further away from the focal plane and any lens can do that.
But to get really good image quality, you need to optimise the lens for close focusing, and macro lenses have had this done.
Other lenses have usually been optimised for other things...
The Canon 50 mm f1.2 for speed, (and stuff the cost!)
The Canon 50 mm f1.8 for low cost, (and stuff the build quality - although image quality is very good)
The Canon 50 mm f1.4 for an excellent all round good compromise,
The Canon 50 mm f2.5 macro for excellent image quality at all distances and fantastic image quality at 0.5 - 1 x magnification, (cost and F/ratio compromised)
Something like a 28 - 90 (or worse, an 18 - 300) mm zoom is optimised for focal range, (with the image quality, f-ratio compromised, unless you pay big bucks for something like some of the Canon L-series lenses.)
(Most of the other lens makers do just the same thing - I just gave Canon as an example as that's what I use.)
To put in pseudo-macro crap zoom by allowing a lens to focus closely is a cheap, easy gimick. It's a bit like the old maxim:
"We do cheap, fast and good. Now choose any two..."
The only real drawback with a true macro is that the f-ratio is compromised - they are usually no faster than f2.5 or so. My old Olympus 50 mm macro was f3.5, but the image quality - and the resale price - was much, much better than any the 50 mm f1.4 or f1.8. The 1.8 these daze goes for about $10 on eBay, the 1.4 for maybe $50, but the macro still gets a few hundred.
This is what Canon say on their website about the 50 mm macro:
"Lightweight and compact macro lens for close-ups up to 0.5x. Floating system for superior delineation at all focusing distances. With a large f/2.5 aperture, true and beautiful background blur is possible."
1st point - True
2nd point - Yes - the 'floating' optics is what makes it a macro and gives the super-good image quality
3rd point - This is stretching the truth a bit....