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02-25-2009, 09:19 AM   #1
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What makes a macro lens a macro lens?

What is the benefit of getting specific macro lens as opposed to shooting macro with any other lens? I see some lenses are zoom and macro.... some aren't....

What's the difference?

Thanks,

Ken

02-25-2009, 10:13 AM   #2
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QuoteOriginally posted by Javaslinger Quote
What is the benefit of getting specific macro lens as opposed to shooting macro with any other lens? I see some lenses are zoom and macro.... some aren't....
A lens that is not a macro lens won't shoot macro, plain and simple. Where "macro" is defined as allowing you to shoot extremely "close up" pictures, where the size of the object on the sensor is close to or larger than life size. Since the sensor is about an inch wide, a macro lens would allow you fill the frame with an object that is about an inch wide, like a quarter.

The difference between a macro lens and a non-macro lens of a given focal length is in how close they allow you to focus. So a non-macro 100mm lens might force you to be several feet away from your subject, which won't result in a very "close up" image - the quarter wouldn't come close to filling the frame. A macro 100mm lens might let you focus mere inches away. Same focal length, but the mere fact that you are closer means the image with be far more "close up".

Zoom lenses advertised as "macro" let you focus closer than other zoom lenses, but they usually aren't "true" macro - they won't focus as closely as an actual macro lens. So you won't get as "close up" of a picture as you would with, for example, the DA 35 or D-FA 100 macro lenses. The quarter might fill only half the frame, for instnce.

Now, for lenses that are *not* advertised as macro lenses, you might still be able to shoot close-up if you buy an attachment that helps them focus closer, like the Raynox 150 or 250 lens that clips on to the front. These are not expensive ($50 or less) and work very well. There are even cheaper "closeup lenses) that screw on to the front of a lens like a filter, but they are usually *much* worse in quality, and not *that* much cheaper.
02-25-2009, 01:28 PM   #3
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Extension tubes and bellows allow one to make macro (1:1 or greater magnification) photos with non-macro lenses as well. If for example you have a 50mm lens with a 1:2 magnification factor and you attach 50mm of extension tube to it you will achieve 1:1 magnification.

The basic formula for calculating extension tube magnification is this:
M = (F + X) / F

Example:
Lens Native Magnification (M): 1:2
Lens Focal Length (F): 50mm
Extension Tube Length (X): 50mm

M = (50mm + 50mm) / 50mm = 2:1 magnification factor applied by the extension tube.

To calculate the total magnification simply multiply the extension tube magnification factor by the lens' native magnification factor:

Total Magnification = 2:1 * 1:2 = 2:2, or 1:1 ("pure" macro).

My understanding of what really makes a true "macro lens" special has more to do with the optical properties of the lens itself. True macro lenses generally have a very flat (planar) field of focus across the breadth of the lens - more so than most "regular" lenses at least.
When doing macro work your depth of field even stopped down is extremely thin, so it is very desirable that the focus distance be precise from edge to edge on the lens.
Most regular lenses have an at least slightly convex field of focus; the focal point at the edges is slightly closer than at the center of the lens.
While it is rarely noticeable at "normal" shooting distances, in the macro world 0.05mm can make a huge difference.
02-25-2009, 02:05 PM   #4
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Magnification ratio and minimum focus distance are the two big factors. A zoom that says macro on it won't usually have a very high magnification ratio. Some should more accurately call themselves close-focus. It's more of a marketing term on these lenses.

A dedicated prime macro lens will also be sharper and have a flatter field. They either have a 1:1 or 1:2 magnification ratio. They sometimes have features important to closeup work like a focus limiter. The maximum aperture is usually slower than non-macro primes in simialr focal lengths, because very wide apertures are not that useful for macro. Often these lenses can be used at normal distances as well, and still be very good, but their main job is up close.

02-25-2009, 02:08 PM   #5
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QuoteOriginally posted by Venturi Quote
Extension tubes and bellows allow one to make macro (1:1 or greater magnification) photos with non-macro lenses as well.
True. One reason I didn't mention these is that it is pretty hard to find any that worth with DA lenses (or other lenses that lack an aperture ring). But extension tubes are indeed another way to get a lens to focus more closely. Also reversing rings designed to mount a lens reversed to the body itself, and ones designed to mount one lens front-to-front against another lens that is mounted to the body normally.
02-25-2009, 02:08 PM   #6
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QuoteOriginally posted by Javaslinger Quote
What is the benefit of getting specific macro lens as opposed to shooting macro with any other lens? I see some lenses are zoom and macro.... some aren't....
In the old days, "macro" as defined as "magnification of 1:2 or greater." "1:2" means the size of the image on film (there was no sensor back then) is 1/2 of the actual size. Many macro lenses can go to "1:1" (image having the same size as actual object).

Then marketing department took over.

They call any lens that can do better than 1:10 "macro."

But calling a lens "macro" does not necessarily makes it so. The user just needs to look at the magnification spec.

Not just magnification, most macro lenses are better at controlling distortion. When taking photo of a flat object (e.g. a document), this becomes significant.

Of course you can still use a macro lens to take photos at "normal" distances. Most macro lenses have very high quality optics.

A macro lens achieves great magnification by moving the optical elements away from the camera body (same way as extension tubes work) at the same time as controlling the focus. At great magnification (close focus), the lens becomes significantly longer than at infinity focus.

Below is an example of a macro lens, Mamiya 60mm f/2.8. It is probably the first lens that could achieve 1:1 magnification without auxiliary lens:

At infinity focus:



At 1:1 magnification:

02-26-2009, 06:49 AM   #7
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I'm just curious about a thing: does a "natively" macro lens be used also as a "normal" prime? If so, what will be the difference?
For example: could I use the Pentax D FA 50mm F2.8 Macro also as a 50mm prime?

Bye
Jenner
02-26-2009, 11:19 AM   #8
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QuoteOriginally posted by ntx Quote
I'm just curious about a thing: does a "natively" macro lens be used also as a "normal" prime? If so, what will be the difference?
For example: could I use the Pentax D FA 50mm F2.8 Macro also as a 50mm prime?

Bye
Jenner
Absolutely. The D FA 50mm F2.8 Macro will produce slightly different images than the FA 50mm f1.4. It's definitely sharper at comparable aperture settings. The dedicated macro lenses are bigger and heavier than general photography lenses, so you might not want to carry the macro around if you have something lighter at the same focal length.

02-26-2009, 12:37 PM   #9
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adding to all the very good points above (or summing them up?):

a macro lens is designed (optics) to perform well at magnifications close to 1/1. the way a lens "behaves" in such conditions as opposed to 1/many (as in infinity focus, when objects in real life in the plane of focus are much much bigger than the image on sensor) is very different. a "normal" (general purpose) lens used as a macro lens with extension tubes will generally not be quite as nice as a lens designed for ratios close to 1/1 (though some can be close). one notable example is said to be the pentax kit lens (18-55) which gets "dreamy" close up (even if it's more like 1/4 at minimum focus). it is also said that most macro lenses will not do so well at infinity focus as "normal" lenses (can somebody confirm, i have yet to play with a true macro lens; i hear the new 35mm macro is an exception to this btw)

for practical puprposes, if what you want is macro on the cheap, i suggest starting with a cheap (old) prime (i prefer long lenses for macro, so i like to use 135 lenses or such), with extension rings. you will have to do manual focus, watch your distance (because your focus range will be very limited), and generally be patient, but it can be fun, and sometimes the results can be amazing. another hint for bringing price down is that you can use m42 lenses, with m42 extension rings (which are much cheaper) and an m42 k mount adapter on the rings, the main downside is that the m42 adapter will not be tight into the mount on the body in such conditions, and with a long (and longer with the extension tubes) heavy lens the wobble can become unbearable -- the reason for this is obvious once you try it, but no point to get into that here.

a better option, which requires a bit more work though, is to try a good enlarger lens instead, they are specially designed for these kinds of magnifications, and they tend to do very well, but they almost never include a focus helical (or any focusing mechanism for that matter), thus requiring more work (either using bellows, or some focusing rail on the tripod -- which is really changing the distnace to subject, if i understand correctly, not the focus itself). another issue is that they tend to come in m39 screw mount, so you need an adapter to mount them which is not so common (i myself am still stuck at this point, i got one for a ridiculous price a few months ago, i still didn;t get around to mount it). a plus side is that they tend to be dirt cheap (especially the not-so-famous ones), because "nobody uses enlargers anymore" and they are small and light (as the only mechanics needed consist of the aperture)

good luck, and i hope this sheds some light.
02-26-2009, 01:12 PM   #10
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QuoteOriginally posted by nanok Quote
for practical puprposes, if what you want is macro on the cheap, i suggest starting with a cheap (old) prime (i prefer long lenses for macro, so i like to use 135 lenses or such), with extension rings. you will have to do manual focus, watch your distance....
Note that with a 135mm lens, you will need a long extension tube to get decent magnification.

Roughly, a 50mm extension tube will give you 1:2.5; a 100mm extension tube will give you 1:1.25.

On the other hand, a 50mm extention tube and a 50mm lens will give you 1:1 magnification. The sensor-object distance will be significantly smaller than the case with a 135mm lens, however.
02-27-2009, 02:31 PM   #11
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correct. it does depend on the lens somewhat, though, and the distance to work with is precisely what i like so much about long macro lenses. however it is true most will choose a fast fifty to use extension rings with, for macro on the cheap.

interestingly enough, worth noting is that dof, unlike what one might think, is actually not that different between focal lengths at macro range (unless i am mistaking?), as the dof "optics" go completely insane when going into macro realm

edit: very interesting explanation here:
http://en.wikipedia.org/wiki/Depth_of_field#Close-up_2

excellent "scientific" explanation, but to keep with the "for practical reasons" logo: a longer lens will mean longer working distance, so dramatically (?) flatter perspective. so when it comes to the look you want to get, the only reason to choose a focal length over another should be the perspective (how flat you want/accept it to be), along with, perhaps, the fact that you can use smaller apertures on a long lens before diffraction kicks in (because diffraction is mostly related to the physical size of the opening, so for a given size which you can consider safe for diffraction, you will have a smaller -- higher f number -- relative aperture, thus, according to the link, more dof at the same magnification, when using a longer focal length while avoiding diffraction, which is actually quite a twist, come to think of it )

Last edited by nanok; 02-27-2009 at 02:47 PM. Reason: added useful link
02-27-2009, 03:06 PM   #12
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Reproduction ratios between 1:1 and 10:1, flat field, well corrected, optimised for close-up work.
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