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04-16-2015, 05:44 PM   #1
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Lens choice - Pentax D FA 100mm f/2.8 WR Macro or Tamron SP 90 mm 2.8

I am contemplating a new lens (I just realized today I have not bought a lens in over two years), I am interested in a macro lens to be used mostly for flowers and it seems like a longer focal length will be the most useful for that. I've read the comparison review in the database. and user reviews on different sites and have a couple of questions.

One Tamron user (who was very happy with his purchase) mentioned that he did not realize prior to actually using the lens for awhile that at the macro focusing distance, the widest aperture is effectively 5.6, not 2.8. The Tamron is only 2.8 from 10' to infinity. I wonder if this is also true of the Pentax, and it makes a bit of sense (at least to me) because at macro the lens will be fully extended, which seems like it would cut down on the available light reaching the sensor.

Another user noted that fully extended at macro, the Tamron front element is about 1" from the subject; a reviewer of the Pentax lens said that it was about 7" in the macro position- can anyone confirm either of these?

I also have a concern about the seller of the Pentax being offered on Amazon (at a good price), is there any way to verify if a lens is gray market prior to purchase or do I need to get it then check the serial number?

I am not certain that I'm going to get either - if the macro aperture is truly 5.6 then I may just get some extension tubes and play with the lenses I already own before plunking down so much money... although I'm sure I could come up with a good reason if I think on it awhile.

Thanks much for the help.

04-16-2015, 06:04 PM   #2
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QuoteOriginally posted by Riverlady Quote

One Tamron user (who was very happy with his purchase) mentioned that he did not realize prior to actually using the lens for awhile that at the macro focusing distance, the widest aperture is effectively 5.6, not 2.8. The Tamron is only 2.8 from 10' to infinity. I wonder if this is also true of the Pentax, and it makes a bit of sense (at least to me) because at macro the lens will be fully extended, which seems like it would cut down on the available light reaching the sensor.

Another user noted that fully extended at macro, the Tamron front element is about 1" from the subject; a reviewer of the Pentax lens said that it was about 7" in the macro position- can anyone confirm either of these?

I also have a concern about the seller of the Pentax being offered on Amazon (at a good price), is there any way to verify if a lens is gray market prior to purchase or do I need to get it then check the serial number?

I am not certain that I'm going to get either - if the macro aperture is truly 5.6 then I may just get some extension tubes and play with the lenses I already own before plunking down so much money... although I'm sure I could come up with a good reason if I think on it awhile.

Thanks much for the help.
The tamron minimum focus distance is 29cm (11 1/2 inches). The pentax is 30cm (12 inches). If someone is using the tamron closer then this they are using extension tubes which would explain why they are see the effective F-stop come down to f5.6......but you don't need extension tubes for either to be 1:1 at minimum focus distance.

I have the tamron and love it and light has never been an issue. Remember as well that if you are shooting flowers at 1:1 and at F2.8 your depth of focus is less the 1 millimeter. I am not sure of many situations where that would be desirable.

Tamron SP AF 90mm F2.8 Di Macro Lens Reviews - Tamron Lenses - Pentax Lens Review Database

SMC Pentax-D FA 100mm F2.8 Macro WR Reviews - D FA Prime Lenses - Pentax Lens Reviews & Lens Database
04-16-2015, 06:06 PM   #3
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I've got both. To the concern about the Tamron not actually being 2.8 in the macro position... I don't think it really matters. The greater the magnification, the thinner the depth of field. If you're shooting handheld at 1:1 macro distance, at f 2.8, it'll be nearly impossible to keep focus where you want it with such razer thin DoF. I rarely shoot macro at a lower aperture than f8.
Also the min focusing distance between the two cameras isn't as great as you were told. Off the top of my head the Tamron is more like 2.5" and the Pentax is more like 4.5". I don't have either of them on me so I can't test them. They're both very good lenses and I've been able to get up close and personal with bugs using both.
04-16-2015, 06:25 PM   #4
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QuoteOriginally posted by geomez Quote
They're both very good lenses...
That's the key point. They're both good lenses so there's not really a "wrong" answer here.

04-16-2015, 06:49 PM   #5
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Pentax for WR and light weight, Tamron for price/performance. They are both great lenses as far as i can tell.
04-16-2015, 07:19 PM   #6
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QuoteOriginally posted by Riverlady Quote
I also have a concern about the seller of the Pentax being offered on Amazon (at a good price), is there any way to verify if a lens is gray market prior to purchase or do I need to get it then check the serial number?
Usually the price is a fairly good indicator, plus check to see if it's sold my amazon directly, but a photo store, or by an individual seller (probably grey market).

Have you seen our comparative review?
Tamron 90mm Macro vs Pentax 100mm WR: Review - Introduction | PentaxForums.com Reviews

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04-16-2015, 08:54 PM   #7
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I used to have the tamron, and I've tried the pentax in the store. The tamron feels junky, it's just so plasticky. On the other hand, the pentax is a well designed metal tool that feels great and has a much nicer manual focus ring.

04-16-2015, 09:30 PM   #8
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It depends on the "pupillary magnification factor (P)" and whether the lens uses extension to reach higher magnification. Assuming P=1, and it uses extension only, at m=0.5 the effective aperture is reduced by 1.25 stops, and at m=1 it is reduced by 2 stops. So f/2.8 becomes f/5.6 at m=1. Fast macros tend to have P>1 and (thus) a smaller effective aperture. I don't have either of the lenses to measure P, but typically it results in 1/2 to 1 more f-stop loss at m=1.

BTW your feeling that extension reduces the available light is basically correct.Another way to think of it is extension (effectively) increase the focal length (FL) and aperture is ratio of opening diameter to focal length (and please everyone don't promptly protest that FL is only used for focus at infinity!).

Also if you have a moderate aperture 50 or 55 mm lens (f/1.7, f/1.8, f/2, etc.) and extension tubes it will do nicely (generally the more symmetrical lenses do best). Also adding a 2x TC [and extension if need be] does not degrade the image in the macro range (it actually may make it slightly worse to slightly better--and for flowers you will not see it anyway). I really like the Vivitar 2x macro TC--as it gives you an effective FL of 100 mm (w/ 50mm lens), and allows m=1 (it has variable extension)--and it is beautifully made.

As regards "minimum focus distance"--this is measured from the film/sensor plane--so the 12" is not the distance from lens objective--termed "minimum working distance". If you need more working distance you need a longer FL lens (prior to adding extension).

Last edited by dms; 04-16-2015 at 10:01 PM.
04-16-2015, 10:30 PM   #9
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QuoteOriginally posted by Mistlefoot Quote
Remember as well that if you are shooting flowers at 1:1 and at F2.8 your depth of focus is less the 1 millimeter. I am not sure of many situations where that would be desirable.
QuoteOriginally posted by geomez Quote
To the concern about the Tamron not actually being 2.8 in the macro position... I don't think it really matters. The greater the magnification, the thinner the depth of field. If you're shooting handheld at 1:1 macro distance, at f 2.8, it'll be nearly impossible to keep focus where you want it with such razer thin DoF. I rarely shoot macro at a lower aperture than f8.
Completely agree. At 100mm and only a few inches from the subject even f8 gives quite shallow DOF.

I would only use f2.8 on my DFA 100WR when using it as a medium telephoto lens. It's great fun in that role, if you can live with the eccentricity of the AF (no focus limiter and long focus throw means it goes crazy hunting at times). At least with quick shift you can help it along.

Flower macros are a lot of fun. This is handheld:

Last edited by Des; 04-27-2015 at 03:22 PM.
04-16-2015, 11:36 PM   #10
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Tamron has aperture ring, Pentax is WR. IMHO these are the main differences.
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04-17-2015, 05:25 AM   #11
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QuoteOriginally posted by Riverlady Quote
I am not certain that I'm going to get either - if the macro aperture is truly 5.6 then I may just get some extension tubes and play with the lenses I already own before plunking down so much money... although I'm sure I could come up with a good reason if I think on it awhile..
You can read about effective aperture here: Macro Camera Lenses

I have the DFA100mm, and though I've never gotten around to measuring the pupil magnification dms mentioned I expect it's close enough to 1 to not matter much. The DFA100mm at 1:1 seems to also lose 2-stops of light (or very near to it), the auto-exposure modes will compensate for it but you need to factor it in if you use external manual flashes.

The non-WR version version of the DFA100mm is a cheaper option, and includes an aperture ring. You give up rounded aperture blades, weather resistance, and nicer build.
04-17-2015, 06:26 AM   #12
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I own the 100mm Pentax WR Macro and am happy with it for what it is. I suspect that the horrific DOF at minimum range and maximum magnification is one reason why this particular lens stops down all the way to f/32. This seems odd because one would expect, from reading between the lines of some of the lens tests here, that diffraction effects would start to supervene long before this, but perhaps the optics have been designed with that in mind? The designers and optics engineers must surely know what they are doing, and it would be no skin off their noses to only provide the usual f/22 as the final stop, but they went one beyond it.

If you're getting down in the dirt with the flowers, slugs and bugs, I think WR would be the way to go (assuming your lens body and budget supports it).
04-17-2015, 03:13 PM   #13
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QuoteOriginally posted by pathdoc Quote
I own the 100mm Pentax WR Macro and am happy with it for what it is. I suspect that the horrific DOF at minimum range and maximum magnification is one reason why this particular lens stops down all the way to f/32. This seems odd because one would expect, from reading between the lines of some of the lens tests here, that diffraction effects would start to supervene long before this, but perhaps the optics have been designed with that in mind?
You can't really cheat physics. They've just given us more choice on how far we can head into diffraction land to get more in focus even if overall sharpness starts to suffer. Choose your compromise (focus stacking for the win of course, but that's another compromise of time and effrot).
04-17-2015, 03:27 PM   #14
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QuoteOriginally posted by BrianR Quote
You can't really cheat physics. They've just given us more choice on how far we can head into diffraction land to get more in focus even if overall sharpness starts to suffer. Choose your compromise (focus stacking for the win of course, but that's another compromise of time and effrot).
Remember its a full frame lens. The larger pixels on FF are slightly less affected by diffraction and CA. With my own tests, I'd say ƒ22 is about the limit for APS-c. But it is quite useful up to ƒ 22. In that case, an increase in the area of the image in sharp focus may increase enough to more than compensate for diffraction.
04-17-2015, 08:28 PM   #15
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Thanks everyone for the help - you've given me a lot of information and things to think about.
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