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03-02-2009, 07:44 PM   #1
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Why no fast 50mm macro lenses?

I notice that there are no fast 50mm (or 55mm or 60mm) macro lenses. The fastest I've seen is f/2.8 while even the cheap "non-macro" 50mm is f/2. F/1.7 and f/1.4 are not at all uncommon.

Is it because it's difficult (and thus costly) to make fast 50mm macro lenses?

It doesn't seem to be a problem with longer focal length, however. There are plenly of 90mm - 135mm macro lenses with f/2.8, which is about as fast as their "non-macro" counterparts.

I'm just curious.

03-02-2009, 07:49 PM   #2
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It may be possible, but it's probably a wasted extra expense. The depth of field at f1.4 isn't going to be useful at macro distances and magnification. It would make the lens more useful for general purposes, of course.
03-02-2009, 07:50 PM   #3
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I'm just not sure what the point would be exactly. As a walk around lens? Because for macro even f/2.8 has incredibly narrow dof and isn't really usable.
03-02-2009, 07:51 PM   #4
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QuoteOriginally posted by SOldBear Quote
I notice that there are no fast 50mm (or 55mm or 60mm) macro lenses. The fastest I've seen is f/2.8 while even the cheap "non-macro" 50mm is f/2. F/1.7 and f/1.4 are not at all uncommon. Is it because it's difficult (and thus costly) to make fast 50mm macro lenses? It doesn't seem to be a problem with longer focal length, however. There are plenly of 90mm - 135mm macro lenses with f/2.8, which is about as fast as their "non-macro" counterparts. I'm just curious.
I'm just ~guessing~ (as an "armchair optical engineer" - <g>) that it is very difficult to make a 50-ish lens that is very fast and has a flat field at the same time.

03-02-2009, 09:16 PM   #5
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The priority for a macro lens is flat field, low abberations, corner to corner sharpness and good depth of field.
Trying to get all of these and also have a large maximum aperture would be making the lens too expensive and large and heavy. Macro lenses are specialist lenses, optimised for close-up work.
General purpose lenses like 28, 35, 50 and 85mm lenses are usually available in fast versions with large maximum apertures for use in low light and obtaining shallow depth of field.
Making a multi-purpose lens results in compromises in one or more areas.
03-02-2009, 09:40 PM   #6
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it would be useless. My guess is that to work effectively in macro, you need a lens that is optimized around f8, and it is exactly what Pentax D FA macro lenses seems to do. Any wider than f2.8 gives such a shallow DOF that it is practically un-useable in the vast majority of situations.
03-02-2009, 09:46 PM   #7
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Well, it could be done mechanically in some way. The 50/1.4s do not have a very flat field, but the 50 1.7s generally are okay on an extension tube. There must be a way you could ratchet the assembly out. Not that it would be practical necessarily, beyond being a good walk around/ macro shooter. Which is exactly what I like. Hmm!

It is nice to use a fast lens on extension tubes so that you have enough light by which to focus before stopping down. At least, that's how I do it.
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