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09-12-2014, 08:08 PM   #1
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What's the next FL?

I have a K5 and the FA 50mm 1.4 but still need to get a longer FL. I want to get at least a 77m but I really want a 100mm, must be autofcus. What are my options? I've been lens hunting for too long and all the info is jumbled in my head. My budget is $600. I do portraits of families and their quick moving children

I like this guy Pentax SMC-FA 100mm f/2.8 macro but this paragraph below confuses me. I though it was AF but then it says it's not.

Pentax SMC-FA 100mm f/2.8 macro - Review / Lab Test Report
The FA 100mm f/2.8 has no internal AF motor and relies on a slotted drive screw operated by the camera. It takes quite a while if you feel the need to AF from infinity towards 1:1 magnification. In other words - the AF is a bit lame, prone to hunting and fairly noisy. However, macro users often prefer manual focusing anyway and for mainstream applications you can take advantage of the focus limiter. When restricting the AF to a range between 0.6m-infinity the AF speed is actually very fast and leaves nothing to be desired here.

09-12-2014, 08:28 PM   #2
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Pentax has two different types of AF. The FA lenses use what is commonly refereed to to a screw drive motor located in the body and mechanically drives the lens to auto focus. The newer approach is using the SDM and CF (? - if I remember correctly) that uses a motor in the lens itself (with a second set of interfaces in the lens mount for control). All the K dSLRs have the screw drive built into the body. All the bodies starting with the K100D Super have the SDM interface. The SDM lenses have the SDM designation in their names.

The FA 100 that you are looking at uses the screw drive approach. This has proven to be extremely dependable.

09-12-2014, 08:32 PM   #3
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QuoteOriginally posted by interested_observer Quote
Pentax has two different types of AF. The FA lenses use what is commonly refereed to to a screw drive motor located in the body and mechanically drives the lens to auto focus. The newer approach is using the SDM and CF (? - if I remember correctly) that uses a motor in the lens itself (with a second set of interfaces in the lens mount for control). All the K dSLRs have the screw drive built into the body. All the bodies starting with the K100D Super have the SDM interface. The SDM lenses have the SDM designation in their names.

The FA 100 that you are looking at uses the screw drive approach. This has proven to be extremely dependable.

That I understood, Thanks! From waht you said is it safe to day that the 100mm I am looking at will work similarly to the 50mm I already have?
09-12-2014, 08:53 PM - 1 Like   #4
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QuoteOriginally posted by julbelle Quote
That I understood, Thanks! From waht you said is it safe to day that the 100mm I am looking at will work similarly to the 50mm I already have?
Yup!! Personally, I prefer the screw drive to the SDM. There are advantages to the SDM in terms of speed and being quiet. But, it adds complexity and additional items to fail. Also, most of the DA lenses are screw drive.

One thing that folks have been asking for is that if the SDM fails for any reason, that the screw drive takes over (in particular on the DA 16-50). Pentax has never done that, but there is a debug mode work around that disables the SDM and has the lens use the screwdrive. This would be something really nice for Pentax to implement.



09-12-2014, 11:14 PM - 1 Like   #5
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I'd think about used Sigma 50-150mm F2.8 II EX DC APO HSM (discontinued, unfortunately) for your intended purposes.

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09-13-2014, 12:25 AM - 1 Like   #6
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The 100mm macros are great lenses, but because of their design have very long focus throw, and are liable to slow focussing as they rack in and out a long way. Try before you buy!

If the budget will go to it, the DA* 50-135 is superb, but for less money try either the DA50-200 or DA55-300 lenses. Both have a good reputation, cover the range you want, but, (there's always a but), both are 'slow' compared to your 50mm f1.4 the 50-200 being f4-5.6 and the 55-300 being f4-5.8.

There's also the DA18-135, which seems to have mixed reviews but plenty of fans.

Last edited by JohnX; 09-13-2014 at 12:30 AM.
09-13-2014, 12:58 AM - 1 Like   #7
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If you want to use a 100mm macro for general use as well, I would suggest the newer DFA100WR over the FA100. If you use the quick shift to start from infinity before activating the AF, it is actually a very quick focussing general purpose lens. For the macro end, you are best using manual focus most of the time anyway.

Mind you, if you want it primarily for portraits, the FA77 is *the* lens. The DFA100WR is almost *too* sharp for portraits. This is wide open, with flash:

09-13-2014, 07:00 AM   #8
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Macro just means the lens has an extremely near minimum focus distance, which means a high magnification. Most primes have around 0.15 magnification, but the Pentax macro lenses have true 1:1 magnification. This means the focus throw must be much longer. (focus throw is how many degrees of turning the focus ring takes from minimum focus to infinity) Macro lenses also need to allow precise manual focus (for macro purposes), so the focus throw must be even longer. All of this means the AF will take more time to go through the range. This is why some macro lenses have a focus limiter. I don't think the DFA and FA have a focus limiter, but the F version does (they are optically identical, though, just different features and construction).
All that being said, my DFA 100mm WR still has decently fast AF. On the K-01 (and live view in general) it is a little slow, but on DSLRs it is quite acceptable for most purposes. You can also use manual focus. The DFA WR has the Quickshift function, so you can focus manually without moving the camera AF/MF switch.

Your other options are the Tamron 90mm macro (slightly cheaper, but good optics, well liked on this forum) and Sigma 105mm. All of these have great optics, as do pretty much all modern true macro primes. I doubt any of these will disappoint you. We have had many threads comparing these lenses and its difficult to say. Most rank the Pentax as being the sharpest, but by a very slim margin. So you have to decide which features you want and what your budget is.
The only problem with using macro lenses for portraits is that they are very sharp lenses, they render all the detail, which can be unflattering! Macro lenses also don't have as much "character" (bokeh, colour rendition) as other primes, like the DA* 55mm (which is the modern Pentax portrait lens) or FA 77mm ltd (which is a legendary lens and also great for portraits and bokeh)

09-13-2014, 11:13 AM   #9
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Have in mind that macro lenses, like the 100mm F2.8 macro (in different incarnations) usually have a long focus throw to be very precise in close focusing distances. If they do not have a focus limiter (the modern D-FA 100/2.8 does not have that for instance) there is a possibility that it will start hunting a lot during difficult lighting conditions. How bad will be depending on what body it is used on as well. Personally I have no problem with screw-drive AF, it is just as fast and the lenses are less complicated and can be made smaller. I have the FA77 and use it mostly for portaits, but it is also a good short/medium telephoto lens for general purpose. I have written more detailed on my thought in my review on this forum.

I have tried the DA*50-135 but I found the FA77 to be that much faster, smaller and sharper that it compared very well and I never felt that I missed out on anything.
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