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12-13-2012, 10:53 AM   #1
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Understanding the controls on Pentax FA100mm f2.8 Macro lens

Hi Experts, Today I got a used Pentax FA100mm f2.8 macro lens and this's the first time i'm using the macro lens on my K-r. There're two controls(knobs) 'focus range' and 'clamp' on this lens. I hardly understand why they are ans how to use them? I couldn't even find a useful info on net. Can anybody explain clearly about this lens and its controls. I'm a beginner and can understand moderate technical terms. Also, I couldn't find any difference between this macro lens and a standard 105mm takumar lens, when I test few shots.
Thanks in advance,

12-13-2012, 11:03 AM   #2
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QuoteOriginally posted by vass Quote
Hi Experts, Today I got a used Pentax FA100mm f2.8 macro lens and this's the first time i'm using the macro lens on my K-r. There're two controls(knobs) 'focus range' and 'clamp' on this lens. I hardly understand why they are ans how to use them? I couldn't even find a useful info on net. Can anybody explain clearly about this lens and its controls. I'm a beginner and can understand moderate technical terms. Also, I couldn't find any difference between this macro lens and a standard 105mm takumar lens, when I test few shots.
Thanks in advance,
I believe its minimum focus is closer than a standard lens, hence the term Macro.

Also the one control is a focus limiter to prevent hunting, based on my reading about the newer version that failed to include the limiter.
12-13-2012, 11:03 AM   #3
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clamp simply almost lock the focus ring, no idea about the other one.
12-13-2012, 11:31 AM - 1 Like   #4
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I think thats it. The clamp makes the focus ring harder to move so it wont get accidentally changed. And the limiter limits the distance where AF will go, so the lens won't waste time looking for a focus in the wrong place (macro vs. non-macro use)

12-13-2012, 12:06 PM - 2 Likes   #5
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Congratulations! Its a lovely lens and definitely one of my favourites.

Optically FA 100 is better than most other lenses in the range (that I have used anyway) because:
1. Its sharp across the frame at most settings
2. Basically zero distortion
3. low CA
4. Pretty sharp even wide open at f2.8 (as long as you have the focus right)
5. Its a 1:1 macro so at minimum focus distance you see a lot of detail!

I find the focus limit is brilliant and is something that is missing from later DA macros. Macro lenses have a longer focus travel (from a very close focus distance through to infinity). You limit in two zones (just roughly focus then set dial to "limit"):
  • Close / Macro focus
  • Normal telephoto distances focus
When using the limit the auto focus is much faster because it does not have to hunt through the whole focus range. So if you are doing normal telephoto work (or even portraits!) set the limit focussed towards infinity and its auto focus performance is better than later macro lenses.

The clamp can be useful. For normal AF work set it to "Off" (less work for AF to do). When using the lens in Manual Focus it can be useful to set the clamp to on because this gives manual focus ring a better feel (damped) which makes it a bit easier to focus.

Have fun!
12-13-2012, 12:45 PM   #6
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Spot on Jono. The damped feel of the focus ring on clamped mode does also allow for more precise minute movements. This is one of my favourite lenses.
12-13-2012, 12:54 PM   #7
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Thanks for all the inputs. Special thanks to kiwi_jono and Na Horuk. NOw I got it. Also I understood that, if I want to shoot a macro within a limited distance. Shooting far subjects doesn't make a big difference as compared with standard lens of same focal length(say, M100mm f2.8)-correct me if i was wrong. Can somebody put some light on how to get better pictures using this lens.
12-13-2012, 01:54 PM   #8
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"Macro" simply means it allows close focusing, which makes the subject appear huuge (or magnified). So macro will only be when subjects are close to you, if subjects are further away, it will be like any other 100mm lens. Except that macro lenses are usually sharper, have a flat area of focus, but have a slower max fstop/aperture. So macro lenses are usually great, provided you can deal with the focusing and don't need them in very low light.
Maybe get a hood for this lens, use high f-stop number when shooting macro (for bigger DoF), maybe even a tripod to avoid movement blur. If not shooting macro, the lens is great as is. Have fun with it

12-13-2012, 02:42 PM - 1 Like   #9
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This lens is great stopped down - use apertures of f/5.6 for relatively distant subjects and f/8-22 for closer subjects, and see some shining results.
12-13-2012, 05:18 PM   #10
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Agree with Ash, f5.6 is a sweet spot (f8.0 is very nearly as good).

Also the image quality is still surprisingly good right to f16 (normally diffraction reduces image quality significantly with apertures f11 - f22+) and still usable at f22 for macro / close up work.
12-13-2012, 08:37 PM   #11
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The focus limiter is useful for both macro and for more normal-distance shooting. Let's say you're taking some portraits. Since 100mm is a relatively long lens, there's no need to use the close-focus range. Using the limiter cuts down on AF hunting because less of the whole focus range is available for the lens to hunt through.
12-14-2012, 02:21 PM   #12
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I have this lens, it's a beauty. All the advice above works.
I also have an LED Ring Light which has a slide plate which screws in place to help take pictures of insects in the evening.

Keep your shutter speed highish, f8ish, and ISO in a good range and be prepared to shoot lots of images if you're chasing bees etc.

12-17-2012, 03:19 PM - 1 Like   #13
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Thanks for all the suggestions and letting me know the sweet spot of this lens. Quite surprised with Ash's comments, ' wide aperture, for distant subjects and small aperture for close-up subjects'. I use to reverse the settings on a standard lens. Quite interesting. I'm attaching few pics with this lens.
Attached Images
     
12-18-2012, 06:12 AM   #14
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I usually use f11 or f13 when using this lens. But I guess as long as you have a good lighting when shooting, it should be able to produce wonderful pictures.

Here is a sample that I took using the same lens


12-18-2012, 06:47 AM   #15
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WOW! Amazing!
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