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07-30-2007, 09:37 PM   #1
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100mm f/2.8 macro lens?

There are several medium-telephoto focal length primes for the Pentax DSLRs that are advertised as "macro" lenses: the Tamron 90mm, Pentax 100mm, and the Sigma 105mm. All are f/2.8 and all advertise a 1:1 magnification ratio.

I've never owned a lens like this and I'm confused by the designation "macro" -- not by the positive meaning of macro but by the possible implication that the lens can't be (or aren't expected to be) used for anything else.

I have never been interested in macro photography, but I think I understand the benefits of being able to get maximum magnification without having to squish the bug with the front of the lens.

But what I'm not so sure about is whether these lenses can be used "normally," as a fast telephoto lens useful, say, for shooting candids in a park or playground, perhaps for indoor sports, perhaps even for portraiture.

These focal lengths (especially the Sigma 105mm) do seem a tad long for portraiture on a Pentax digital SLR, where the 35mm film equivalent focal length = around 150 or 160. My guess is that these lens could perfectly well be used anywhere a medium-distance telephoto lens would be useful, but that these focal lengths, on digital SLRs, are somewhat less useful for normal telephoto purposes than they would be on a film SLR, so the manufacturers push the lenses mainly as macro. How far off am I? Am I missing something big?

Anybody own one of these lenses? What do you use it for -- shooting bugs and flowers and postage stamps, or do you shoot pets and people, too?


07-30-2007, 10:07 PM   #2
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I have used my Kiron 100mm f/2.8 (1:1 Macro) for portrature, and it does an amazing job. It was a great telephoto for any kind of photography. However, it is also larger and heavier than a normal 100mm and has an extremely long focusing range, which may be a problem if you want auto-focus. If you do not plan on doing macro work, a normal 100mm, or one with close focusing (1:2/1:4) ability is probably a better solution.
07-30-2007, 10:08 PM   #3
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Macro lenses are specially made lenses that allow you to focus on very close objects. they can also be used as regular lenses.

A true macro lens will give you a 1:1 magnification ratio. Basically, this means that if a bug is 17mm long, it will record on the sensor 17mm long. A 1:1 ratios means life size, even though when you print out your photos, the image will be far larger.

Macro lenses are sharp because they have to record very fine details. By definition, one could argue that macro lenses have the highest definition and resolving power of all lenses.

Macro lenses come in varying sizes; from 50mm to 180mm seem standard at the moment. Because they need to focus accurately at such close distances, their focusing track tends to be on the long side. In other words, you may have to turn that lens barrel a full 360 several times to go from closest focus to infinity focus. On a macro lens, this is a good thing. It allows you a finer control over focusing. The downside is that auto-focus is very slow, even on the faster motored variants. This is due to that long focusing throw.

The larger telephotos give you greater working distances, perfect for skittish bugs and live things. Shorter macros are perfect for flowers and other inanimate objects. You can still use them on live things; you just need the patience of a saint. A 50 to 70mm macro is also a good candidate for portraiture on an APS-C camera.

Macro lenses work very well doing other things. You can use them for anything a like focal length lens would be used for. However, if you’re interested in a macro for portrait work, you may need to use a soft focus filter, or do some post processing to blur blemishes in your subjects. Their phenomenal sharp detailed results can make your best looking model not so good looking.

To wrap it all up, macro lenses tend to be super sharp, can focus very closely to life size, and have slow auto-focusing due to their design (most macro work is done manually focusing anyhow).
07-30-2007, 10:15 PM   #4
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The macro lenses you mention are "true" macro lenses...that is to say they were designed specifically for 1:1 magnification. This is different from a lens, often a zoom, which can sometimes carry the 'macro' label, usually zooms such as the Sigma 70-300 or 17-70. These lenses are 'close focus' lenses but not true macro, and this becomes an important distinction.

True macro lenses have a very long focus throw and require the movement of all the elements in the lens, and as such the autofocus speed is often slower than an equivalent non-macro lens. If the autofocus hunts, it has a longer distance to go before it stops and reverses direction. Lens manufacturers often put in a focus limiter for this reason, which speeds things up a bit. Slower AF is less of a factor in the faux 'macro zooms'.

To answer your question, there is nothing wrong with using a macro for the purposes you mention. These lenses are among the sharpest in their focal length, and aside from the slow AF are fine for any of the types of shooting you mention, although macro lenses would be least suitable for sports due to this limitation. They are marketed as macro lenses because that's what they're best at and it's what other lenses can't do...and frankly manufacturers have other lenses they want you to use for portraits, sports, candids, and so on

Some people think that a macro is too sharp for portraits, because it reveals even the smallest flaws in the subject. I don't subscribe to this theory, because I like to capture as much detail as possible in camera and tidy things up in post if need be. That being said, lenses which are less sharp than macros are no less suitable for each her or his own.

I have a 100/2.8 macro for my minolta, and used to have a 100/2. I shoot an 85/1.9 takumar now, and I like both of these lengths for people shots because of working distance. I know many people who use 90mm macros as all-round lenses and are quite happy!

** for the record Chako, I was writing my reply as you posted yours...our arguments seem identical in content and structure!

07-30-2007, 11:42 PM   #5
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Hi Will,
The previous posts answer your question quite well.
I have the Pentax DFA 100mm and it gets a lot of use, often being the lens left on the camera.
I can concur with the comment on the slow auto focus, but the quality is something else.
Anne & I are travelling to the US later this year and I am toying with the idea of just taking the sig EX24mm on one body, the dfa 100 on the other and carry the 135-400 for the long shots.............and leave the p 18-55 & sig 18-125 at home, as I think I would be better off with the speed option rather than the zoom convenience.
I have used the 100 for portrait type shots and landscapes.
07-30-2007, 11:50 PM   #6
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What I don't understand is, take the Sigma 17-70 "macro" for example, @70mm & closest focus distance 8", it's 1:2.3 (=0.44x) magnification. Now take the Pentax 50mm macro, closest focus distance is also around 8", 50mm being wider angle than 70mm yet it gives 1:1 magnification !!

Would someone educate me please, is it because at macro distance the 50mm has *smaller* fov than when it's at normal distance? Thanks.
07-31-2007, 03:32 AM   #7
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there will be so little distance variation between the 50 and 70 that you would probably have to set them up on tripods to get an acurate measurement of distance from subject. also the 17-70 is not a macro lens. it's a close focus lens..
07-31-2007, 05:36 AM   #8
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100mm Macro f/2.8

Another question regarding true macro lenses vs close-focusing "pseudo-macros". What about the depth of focus for a given amount of light and a given shutter speed? I've used the "macro" feature of my Sigma 70-300 APO DG f4-5.6 lens on several occasions, and my non-professional eyes are quite impressed with the IQ. The DOF, however, is extremely narrow which is normal for macro photography. I'm just wondering if one of the 100 mm f2.8 lenses would give me any extra DOF under identical circumstances. Thanks for your response.


07-31-2007, 05:46 AM   #9
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QuoteOriginally posted by roy Quote
there will be so little distance variation between the 50 and 70 that you would probably have to set them up on tripods to get an acurate measurement of distance from subject. also the 17-70 is not a macro lens. it's a close focus lens..
If this is in reply to my question I think I need to phrase it again.

If we put a certain object at 8" from the sensor plane, then normally it would look smaller thru a 50mm lens compared to a 70mm lens, correct? Then what makes it 1:1 magnification with 50mm while only 1:2.3 (0.44x) with 70mm?

More accurately, what "clicks" the 50mm's smaller image into 1:1 magnification, is there a macro switch on the lens, or is it linked to the focusing ring, or .... ??

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