[LennyBloke]

There's plenty of general information about the 5 versions of the superb Pentax 100mm f2.8 Macro lens, but it's difficult to find why (and how) they evolved from the A series into the current DFA-WR model.

I find it easier to understand the change from the "film" AF models to the "Digital" models - I believe the F and FA are identical in optical design, size and weight (well almost), and these made way for the more compact pair of the DFA then the DFA-WR which have a very similiar optical design to the F and FA but were designed with a smaller filter size, optimised for Digital and of course Weather Proofing (in the case of the DFA-WR). But information on the "original" A series and why it is so different in optical design isn't too easy to find. The optical construction is very different (7 elements in 7 groups compared to 9 in 8 for the four later versions) although they all share the FREE (fixed rear element extension) design at the camera end, and it is very big for an A series lens that doesn't boast a fast aperture.

There are very few reviews of the A version, and some of them allude to this being one of the "special" lenses - possibly in the "Star" class - but I guess there are more of you who have/use this lens, and hopefully some who know a little more about the evolution of the 100mm f2.8 macro models?

[rvannatta]

There's plenty of general information about the 5 versions of the superb Pentax 100mm f2.8 Macro lens, but it's difficult to find why (and how) they evolved from the A series into the current DFA-WR model.

I find it easier to understand the change from the "film" AF models to the "Digital" models - I believe the F and FA are identical in optical design, size and weight (well almost), and these made way for the more compact pair of the DFA then the DFA-WR which have a very similiar optical design to the F and FA but were designed with a smaller filter size, optimised for Digital and of course Weather Proofing (in the case of the DFA-WR). But information on the "original" A series and why it is so different in optical design isn't too easy to find. The optical construction is very different (7 elements in 7 groups compared to 9 in 8 for the four later versions) although they all share the FREE (fixed rear element extension) design at the camera end, and it is very big for an A series lens that doesn't boast a fast aperture.

There are very few reviews of the A version, and some of them allude to this being one of the "special" lenses - possibly in the "Star" class - but I guess there are more of you who have/use this lens, and hopefully some who know a little more about the evolution of the 100mm f2.8 macro models?

My recollections of the A models is that they did not have the mechanical travel of the later models meaning that you had to reach for extension tubes, and if you pushed the envelope much
you applied the reversal ring and put the lens on backwards. The newer design marginalized the need for extension tubes, or bellows, and lens reversal.

[Adam]

I think the overall optical design and physical construction was modified starting with the F version to facilitate autofocus, though the A F2.8 version of the 100mm did support 1:1 magnification, unlike previous lenses.

[fwcetus]

My recollections of the A models is that they did not have the mechanical travel of the later models meaning that you had to reach for extension tubes, and if you pushed the envelope much you applied the reversal ring and put the lens on backwards. The newer design marginalized the need for extension tubes, or bellows, and lens reversal.

I think the overall optical design and physical construction was modified starting with the F version to facilitate autofocus, though the A F2.8 version of the 100mm did support 1:1 magnification, unlike previous lenses.

As Adam has stated, the A 100/2.8 Macro did reach 1:1 magnification. That was also true for the A* 200/4 Macro, but not so for the A 100/4 Macro, the A 50/2.8 Macro, and all previous (non-bellows) Pentax macros (I believe). [Whether the FREE design of the A 100/2.8 Macro and A* 200/4 Macro lenses aided them in reaching 1:1 magnification or not I do not know.]

Many F and FA lenses did offer redesigned optics, likely due, at least some of the time, to a desire to make successful AF lenses. Examples include the A and FA 35/2's, the A* and FA* 85/1.4's, the A and F 100/2.8 Macros, the A and F 135/2.8's, the A* and FA* 200/2.8's, the A* and FA* 200/4 Macros, and some others (including the super-tele "MF-to-AF pairs"). [Of course, some of these altered designs may have included modifications intended strictly for optical considerations.]

However, the transition to AF did not always require re-configuring the optics to allow for AF. Examples of optically identical "MF-to-AF twins" include the A and FA 20/2.8's, the A and F 20-50/4's, the A and FA 28/2.8's, the A and F 35-70/3.5-4.5's, the A and F 35-80/4-5.6's, the A and F 35-135/3.5-4.5's, the A and F 50/1.4's, the A and F 50/1.7's, and the A and F 80-200/4.7-5.6's.

So much for lens evolution thinking...

As for the A 100/2.8 Macro, I've had some experience with that design -- in fact, I (temporarily) had three of 'em --



-- but I no longer have any of 'em anymore (two went to eBay and one eventually to KEH) -- nowadays I prefer using the A 50/2.8 Macro and the Tokina AT-X 90/2.5 "Bokina" for my main macro lenses.

But I digress...

[blende8]

As for the A 100/2.8 Macro, I've had some experience with that design -- in fact, I (temporarily) had three of 'em

This qualifies you as Pentax Premium Dealer!

[LennyBloke]

Thanks for the information guys - I hadn't actually considered that there may have need to be a significant design change to make it Autofocus But that makes total sense now!

I never thought I'd see 3 of the A100's in one place - it took me several years to find one!

I haven't really had the chance to give mine a good work out yet, but I certainly got the feeling that it was a special lens just from the first few snaps I took...





The second shot hasn't quite nailed the focus, but I was still surprised at how much web detail was picked up

[fwcetus]

The second shot hasn't quite nailed the focus, but I was still surprised at how much web detail was picked up

Your pix (of course) have a very shallow DOF, but I couldn't see any EXIF info to see the aperture used. So, what was the aperture in each pic? [I am suggesting that perhaps you ~might~ be able to close the aperture down just a wee bit more to make it slightly easier to nail the focus.]

[LennyBloke]

Your pix (of course) have a very shallow DOF, but I couldn't see any EXIF info to see the aperture used. So, what was the aperture in each pic? [I am suggesting that perhaps you ~might~ be able to close the aperture down just a wee bit more to make it slightly easier to nail the focus.]

The Tomato shot was F7.1, 1/125, iso1600. The Spider with Avocado was F5.6, 1/125, iso1600.

You are of course right, the smaller aperture would improve the depth of field - but these were literally just snaps to get a first impression of the lens. I'm not great at Manual Focus - the eyes are getting on a bit - so I need to spend a lot more time on my technique if I do use MF lenses now!

Around a year ago (probably another unfulfilled New Year Resolution) I had decided that I was only going to buy AF lenses and sell off my MF collection, but since then I've bought around 10 more A series lenses (including the A100/2.8 Macro).

[fwcetus]

The Tomato shot was F7.1, 1/125, iso1600. The Spider with Avocado was F5.6, 1/125, iso1600.

You are of course right, the smaller aperture would improve the depth of field - but these were literally just snaps to get a first impression of the lens. I'm not great at Manual Focus - the eyes are getting on a bit - so I need to spend a lot more time on my technique if I do use MF lenses now!

Around a year ago (probably another unfulfilled New Year Resolution) I had decided that I was only going to buy AF lenses and sell off my MF collection, but since then I've bought around 10 more A series lenses (including the A100/2.8 Macro).

Understood.

I think it's funny (not "ha-ha funny", but "interesting funny") that, as you were posting your reply (the one I quoted above), I was posting my own reply in another thread (where I'm selling an A 20/2.8 because I've switched to using an FA 20/2.8 for vision reasons). Now I'm not bringing up that thread here to try to "advertise" the sale, and I certainly won't ask you to read through the long For Sale description (etc.), but I did say, in the first post in that For Sale thread (the description and conditions, etc., post), the following:

[In case you might be wondering why I might be selling this lovely FF MF lens, my old eyes had voted 2-to-0 that I had to replace it with an optically identical (and just recently acquired) FA 20/2.8 AF lens.]

And then, in my reply to a comment from another Pentaxer (who had compared the build qualities of the A lenses and the FA 20/2.8), I said:

Yes, my FA 20/2.8 is not built quite as nicely as is this A 20/2.8, but "time marches on..."

However, they do seem optically the same (as they should), and I am getting used to using the FA version with AF -- "it's easy on the eyes", so to speak.

I still use MF with a number of "cult classic" lenses and also for my macro shots (such as for the pix showing this A 20/2.8, for which I used an A 50/2.8 Macro), but most of those lenses are tele lenses (which I find a little easier to focus manually nowadays), and I often use my backup body (a K20D equipped with a split-image Katzeye screen, which is what I used for these A 20/2.8 pix) when I want MF.

I do find that Live View works nicely for MF on my K-3 (with just the stock screen) when it's on a tripod, but I find using Live View when hand-holding (which is what I do 99% of the time) a bit annoying.

Oh well...

So, as you can see, I am also dealing with "older eyes", too, making compromises when I have to in order to carry on with my LBA.

Getting more back on topic (such as shooting with your A 100/2.8 Macro), I will simply mention that I often shoot macro pix at f/11 (or even f/16, etc.) when I want to increase my chances of nailing the focus and/or getting as much of an object into focus as possible, but, when testing out a new lens (such as what you were doing), I often shoot wide open or at least close to it, "just to see what the new toy will do"...

[monochrome]

^^ I generally use f/11 with my Series 1 105 and AD-2 90 macros. I can get by with a much larger aperture using my FA50, especially with the K-3 AF. I haven't yet extensively tested the 'new' Tokina 90, but smaller apertures are quite likely. I guess we need deeper fields.

[8540tomg]

Thanks for the information guys - I hadn't actually considered that there may have need to be a significant design change to make it Autofocus But that makes total sense now!

I never thought I'd see 3 of the A100's in one place - it took me several years to find one!

I haven't really had the chance to give mine a good work out yet, but I certainly got the feeling that it was a special lens just from the first few snaps I took...


https://www.pentaxforums.com/lensreviews/SMC-Pentax-A-100mm-F2.8-Macro-Lens.html


The second shot hasn't quite nailed the focus, but I was still surprised at how much web detail was picked up

Hey Len,

I think you will really like your A 100/2.8 macro. It does take some time and effort, like everything else, to get good results however. I've had mine for over 20 years now and my review of this optic can be found in the lens review area. I'm not sure why there are only 5 reviews but that is all we have thus far.


I use it for portraits as well as macro work and find it to be a most versatile lens. As you would expect it is uber sharp. The rear element protrudes a bit and is prone to damage when mounting the lens if you are not careful. Some respected forum members (Wheatfield, arpaagent) have noted sensor reflections when using it wide open on digital. To be honest I had not noticed this until it was pointed out to me. This is a non-issue if you stop down a bit. I any case have fun with your new lens.

Looking forward to your images.

Tom G

[LennyBloke]

Hey Len,

I think you will really like your A 100/2.8 macro. It does take some time and effort, like everything else, to get good results however. I've had mine for over 20 years now and my review of this optic can be found in the lens review area. I'm not sure why there are only 5 reviews but that is all we have thus far.


I use it for portraits as well as macro work and find it to be a most versatile lens. As you would expect it is uber sharp. The rear element protrudes a bit and is prone to damage when mounting the lens if you are not careful. Some respected forum members (Wheatfield, arpaagent) have noted sensor reflections when using it wide open on digital. To be honest I had not noticed this until it was pointed out to me. This is a non-issue if you stop down a bit. I any case have fun with your new lens.

Looking forward to your images.

Tom G

Hi Tom - Yes, I'd spotted your review, one of the more informative ones - I've used several Pentax 100 macro's and they've all been superb performers, but the main difference with this one is the "feel" of the focus ring! It's smooth yet has slight resistance - enabling an easier 'stop' at the right focus point (assuming you can see well enough ). I doubt that this lens has any more resolving power or better IQ than any of the other fine Pentax 100's, but just from that one shooting session I was surprised by how much extra detail was exposed. The tomato shot shows the texture of the skin itself (not just the hairs) which I'd never noticed before. I really do need to use it more to find out if it is really one of those "special lenses"

[LennyBloke]

....Getting more back on topic (such as shooting with your A 100/2.8 Macro), I will simply mention that I often shoot macro pix at f/11 (or even f/16, etc.) when I want to increase my chances of nailing the focus and/or getting as much of an object into focus as possible, but, when testing out a new lens (such as what you were doing), I often shoot wide open or at least close to it, "just to see what the new toy will do"...

I've generally not shot at smaller apertures than f8 or f9.5 as I expected diffraction to kick in - but you seem to be saying that f11 and f16 are good choices! Are you trading a bit more depth for a bit less sharpness, or have I set my mental minimum aperture level at the wrong f-stop?

Advice appreciated

[pathdoc]

I've generally not shot at smaller apertures than f8 or f9.5 as I expected diffraction to kick in

I've noted that the macro lenses and some of the longer primes go all the way to f/32 rather than stopping at the usual f/22 that became standard after the switch to K mount. I can certainly understand, with practical experience, why this was done for the macros - at very close range with maximum magnification and a relatively "thick" target (e.g. a small frog on a branch or lily pad rather than a spider in its web), you can run out of depth of field very quickly. I'm guessing that the designers either accepted the trade-off or are able to correct for it in some way, given the "flat field" nature of the lenses.

Lenses like the FA135/2.8, however, are another matter. I can't work out what they were thinking there. Perhaps they wanted to give the owners some DOF breathing room for very close-range portraits?

[fwcetus]

I've generally not shot at smaller apertures than f8 or f9.5 as I expected diffraction to kick in - but you seem to be saying that f11 and f16 are good choices! Are you trading a bit more depth for a bit less sharpness, or have I set my mental minimum aperture level at the wrong f-stop?
Advice appreciated

I don't have any A 100/2.8 Macro copies anymore, so I can't test your assumption about what I intended specifically, but my own assumption is that you are most likely right - ~if~ ultimate resolution is what you are most looking for.

I do shoot a lot of hand-held macro at f/10 and f/11 (and up to f/16 if I ~really~ need some DOF), but, under hand-held conditions, I am usually willing to trade a wee bit of diffraction loss to earn a more "forgiving" DOF.

However, for those less frequent occasions when I might instead be shooting macro on a tripod (and also using magnified live view as well), I'm more likely to be shooting at much wider apertures, depending mostly on the amount of DOF I might need, balanced against the resolution I might want, balanced against the quality of background bokeh I might want.

[And the above generalizations are not just for macro shots -- with sensible modifications, they can, of course, apply to a lot of shooting situations.]

So, "it all depends"...