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Old Mar 6, 2007, 5:26 AM   #1
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The focus ring on this lens continues to move when it reaches the end of the range. I have never seen a lens do this before. Is this normal?

thanks

John
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Old Mar 6, 2007, 9:45 AM   #2
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I'm not familiar with this lens (I think there have been a couple of different Pentax 100mm macro lenses), but I do have an A*300 that goes beyond infinity (is that what you are asking?). And I've heard of other lenses that do this, so while it isn't normal across the board (I have an M 50mm 1.7 that is older than the A lens I have, and doesn't do it).

Hope someone who has this lens can answer your question.
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Old Mar 7, 2007, 8:46 AM   #3
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John

Would you specify which 100mm macro. It could be F, FA or DFA version as well. Also there is a FA100mm macro F3.5 as well. If it is the older F or FA version, I am not surprised that it may be loose somewhat.

Daniel
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Old Mar 7, 2007, 8:55 AM   #4
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It's DFA Macro 100mm f2.8
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Old Mar 7, 2007, 9:48 AM   #5
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Now I was wondering, what is the optical difference between this lens that you are talking about (DFA 100mm 2.8 macro) and the P-FA 100mm F2.8 Macro lens. I have checked stans pentax regarding the P-FA 100mm and they claim the lens is optically very impressive. Is it worth the extra money for the DFA?? Thanks for any suggestions...
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Old Mar 7, 2007, 10:46 AM   #6
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I have not used the other lens and seem to be having a problem with this one so I can't answer your question. At this point I am dissapointed in that I am not getting the sharpness I was getting with my Olypmus C5050.


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Old Mar 7, 2007, 11:30 AM   #7
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John,

If it is DFA 100macro, bring that to Pentax for warranty repair . I suppose it is relatively new. That lens is pretty sharp (reputation-wise). When you do macro, test it with a tripod and step it down to at least F10 or below. That is the norm for macro work.

Daniel
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Old Mar 7, 2007, 11:43 AM   #8
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JohnF wrote:
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The focus ring on this lens continues to move when it reaches the end of the range. I have never seen a lens do this before. Is this normal?

thanks

John
Hi John,

This is normal for the D FA 100 macro. the focus ring will continue to turn past either of the ends of the range, but it does not do anything extra once it's reached the stop. I believe that it's an unexpected result of the focus clamp mechanism that allows you to lock in a focus distance/magnification factor.

Dedicated macros on a DSLR are sometimes not seen as being as "sharp" as digicam macros because of the comparatively razor thin DOF. They are meant to be stopped down considerably to gain any measure of DOF, and even then DOF is pretty thin. I think that when you stop down to at least f11, you'll find that the lens is sharper, captures more detail, and has a flatter field of focus than most digicams, which means that it's sharper from edge to edge if the entire frame is within the DOF. Flash is usually recommended to give you enough light to use these small apertures.

The normal focusing drill is to frame the subject with the focusing ring, then move the camera back and forth to achieve critical focus.

Scott

[Edit] BTW, there is a point at which you start to lose the benefit of greater DOF because of diffraction from too small an aperture for any lens. In the case of this lens, it's probably at @ f22.
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Old Mar 7, 2007, 11:53 AM   #9
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Hi Scott

I contacted Pentax and then said to send it in??? I will continue to work with the camera (K10D) and lens to see what I can get with it. My first digital SLR. I wanted the SLR ( many years ago used an old Spotmatic) to be able to better control focus. Don't want to use flash because I don't like the look of it.

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John
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Old Mar 7, 2007, 5:40 PM   #10
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JohnF wrote:
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Don't want to use flash because I don't like the look of it.

Hi John,

If you want to take 1:1 macros, especially of creatures, I think that you'll eventually see that flash is an almost indispensable tool. A lot of shooters dismiss flash photography, but for macros where you need to shoot small apertures for DOF, and the tiniest movement causes motion blur, flash has made things worlds easier for me. There's a whole world of flash techniques (different ways to bounce and diffuse, and use the flash off-camera) to soften or eliminate shadows and harshness. My guess is that if you want to pursue this field, and especially if you get into shooting critters, you'll change your mind. If you normally shoot flowers or other stationary items, flash is less important, but still offers some opportunities for isolating your subject from the background and freezing flowers blowing in the wind, even when the natural light is good.

Of course, YMMV

Scott
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