Review: smc PENTAX-DA* 200mm f/2.8

(2013-06-16)

 

 

Normally, I would be very reluctant to do reviews on contemporary lenses because there are already so many reviews available that are made by more competent people with better skills and gear. But sometimes one gets hands on a piece of equipment that causes the urge - for better or for worse - to share one's experiences from a simple user's point of view. So, here's my case for the smc PENTAX-DA* 1:2.8 200mm ED (IF) SDM, as this lens' full, official name goes.

 

  Figure 1
 
Design, Construction, First Impressions
The DA200,as I will call it from now, lends its optical design from the Pentax-FA* 200mm and thus, dates back to 1993. The two designs are identical as far as are concerned the smc-coating, the 9-bladed diaphragm, internal focus and 9 lens elements in 8 groups. In addition, the DA200 has got PENTAX's dirt and moisture repellent SP coating on the front lens and, if I understand correctly, the 'digital' coating on the rear element facing the camera sensor.  
  Figure 2
As with all PENTAX DA lenses, the aperture ring has been abolished and for that reason, the DA200 cannot really be used on older PENTAX SLR cameras.
 

On the mechanical side, one should first of all mention the dust and weather sealing making this lens ideal for use under harsh conditions - hence the DA 'star' designation.

 

Further, the DA200 has got an ultrasonic 'SDM' focusing motor, while the AF screw drive has been retained and thus permits use of this lens with older DSLR cameras as well. New is also the PENTAX quick-shift focus mechanism that allows for manual

 
  Figure 3
override of AF at all times. Finally, there is a dedicated switch for AF/MF operation of the lens (in contrast to the FA200 where the switching was a push-pull movement of the focusing ring).

The construction, apart from the lens hood and AF/MF switch, is all-metal and rubber, and the lens gives a reassuring 'feel' of solidity and robustness. Focusing grip and AF/MF switch are dimensioned and placed just right, the focusing movement is delicately smooth and has the right amount of travel to make manual focus a breeze. And although the lens is quite heavy (825 g) the camera-lens combination balances very well in my hands.

Thus, I don't hesitate to call the ergonomics of this lens superb. At least some will understand what I mean, when I say that holding and operating this lens gives an almost Takumar-like feeling.

My only complaint is the lack of a tripod grip ring. While the balance with handheld shooting is excellent, this is not the case with the camera mounted on a tripod. Here the combination becomes very nose-heavy and I do wish PENTAX would consider a tripod ring as an accessory for tripod mounted long exposures.

     
Do the Specifications Hold?
Verifying the focal length of a lens like this is quite easy: Take a star of known declination and let it drift across the field of view for some time - the longer, the better accuracy. From the known properties of my sensor, physical- and pixel width I can measure the length of the trail recorded on my sensor. And from the star's declination and the focal length of my lens, I can calculate the same, using a simple formula shown in Section 4 of this tutorial. So, here we have the image of star Arcturus drifting for 284 seconds over my Pentax K-5 sensor:
     

Figure 4

 

Using the dimensions of my sensor (23.6 mm / 4928 pixels) I measure the trail to be 3.86 mm and using the declination of Arcturus (+19.12 degrees) and the 200 mm FL stated by Pentax  I calculate that the length should be 3.90 mm. That is accurate within 1% and given the possible errors in timing, positioning on my screen, possible atmospheric refraction effects a.o. I should say that my  DA200 is spot on with regards to this specification

     
Now then, Pentax also states that the minimum focusing distance is 1.20 meter (quite close for a 200 mm lens) and that the reproduction ratio at that distance will be 1:5. To verify, I photograph a ruler at the very closest distance where AF will work and examine the result:
 

Figure 5

 

As can be seen, 11.8 mm of my ruler spans the entire width of my sensor, which is 23.6 mm, so I have a reproduction ratio at closest focusing distance of 118/23.6 = 5! So, Pentax didn't 'cheat' here either.

     

But hey - wait a minute! With a 1:5 magnification at 1,2 meter's distance, the simple lens formula (se for example Example 1 on this page) tells us to a very good approximation that the focal length is about 160mm. So, did Pentax 'cheat' after all?? No, it's a fact that any lens with lens groups that move relative to each other during focusing (be it zooms or primes) may vary with subject-sensor distance. And that is indeed the case with the DA200 which has internal focusing (IF). The specified FL only holds at infinity focus and may vary substantially with distance and at the closer ranges and differently from from one lens type to another. Thus, one must be careful when one compares images taken from the same, close range with different types of lenses. One example can be found in Figure 25/26 below. This is something the manufacturers hardly ever inform us about - we have to do the calculation ourselves.

 

One fact, that I cannot verify with my simple means, but which I have found at the DxOMark site, is that like most lenses there is a transmission loss of light in the DA200. Thus at the maximum aperture, (f-stop = 2.8) the T-stop is only 3.2. Apparently, the coatings of the DA200 take some toll in respect of transmission, but then the coatings have other benefits as we shall soon see.

 

     
Focus - Auto and Manual
As said, the DA200 comes with both conventional screw drive for older Pentax DSLRs and a built-in ultrasonic 'SDM' motor. Additionally the lens features a quick-shift feature, meaning that one can override AF at all settings and in all situation by merely rotating the focusing ring. Finally there is a switch for purely manual operation of the focus. I'll come back to the MF options, but first a few words about the SDM AF:

I must confess that it took me some time to get used to the SDM drive. That is because the lens in many situations seems to take ages to adapt from one range to another and hunting a bit forth and back is not unusual. I think this is because of the very generous focus travel of the barrel, about 3/4 of a full turn, from closest focusing distance to infinity. This is perfect when the lens is used in MF mode, but when one briefly looses contact with the target or, when an obstacle comes into the way re-focusing may take what is - at least felt as - a good deal of time. A focus limiter, such as one could have with the old FA* 200mm macro would truly have been a valuable feature on this lens.

That said, when you are within a decent range, the SDM is ultra fast, wonderfully quiet and, best of all, ultra precise. Even very tiny targets can readily be focused on, as shown in the example below:

 

 

 

Figure 6

 

Figure 7

 

 

 

Figure 8

 

Switching focus from the fine grass in the foreground in Figure 6 to the rails in the background in Figure 7 poses no problem for this lens on a Pentax K-5. The shift from foreground to background is fast and flawless.

 

Also, AF on the dim New Moon way down in the city smog in Figure 8 is instantly and reliably achieved. And AF can be used even on only just moderately bright stars too:

     

Figure 9

 

Figure 10

     

This is just for demonstration purposes but nevertheless: In Figure 9 we have a handheld photo, using AF, of star Arcturus and the 100% crop in Figure 10 does shows that this single point of light really was enough to provide accurate focus. In fact, with this lens I mostly do use AF to train my lens on the stars at the start of my astrophotography sessions.

 

Yes, I have got used to the SDM drive and I am a great fan of it now - but I still think the DA200 should have had a focus limiter built-in.

 

 

 

Manual focus with the DA200 is a breeze. The bright image provided by the lens in combination with the bright viewfinder of my K-5 leaves little doubt  on which part of the image is in focus and when - it literally pops out from the background when focus is achieved. Therefore, the quick shift focus is a really useful feature on the DA200.

 

Further, the generous focus travel comes to its right in purely MF operations, where the same benefits of the sharp, bright image in the viewfinder also apply. And thanks to AF/MF switch plus Pentax Catch-In-Focus, I have two options: With the lens in MF and the camera in AF.S mode I have the ideal (weather and dust sealed) camera trap; with both lens and camera in MF mode, I have total freedom to play with focus.

 

As far as focusing options are concerned, I couldn't wish for a more versatile system than the smc PENTAX DA* 200mm f/2.8 on my PENTAX K-5.

 
 
Chromatic Aberration, Purple Fringing, Softness, Contrast

One does not have to read much literature about the DA200 to discover that the most frequent complaint is that of 'chromatic aberration' (CA) or 'purple fringing' (PF). So, let's jump straight to it and examine the lens' behaviour in a very harsh situation: A relatively dark curtain against a bright blue sky. If anything can provoke CA or PF, this will.

 

And, since this is not a "scientific" test, I do the socond best thing and compare results with two

 

Figure 11

lenses that I know and trust well, namely the Tamron SP 80-200mm f/2.8, Model 30A and the Tamron 200mm f/3.5, Model 04B - both from the vintage Adaptall-2 series, but still very capable lenses from my experience. Here, I only show a few composite images at selected apertures, but the link below leads to a the complete series of images obtained. Images are taken in Av-mode, where I have set the Aperture and then let the light meter of my Pentax K-5 determine the exposure.
 

Comparisons between Pentax DA* 200mm (left), Tamron Adaptall-2 SP 80-200mm f/2.8 Model 30A (middle) and Tamron Adaptall-2 200mm f/3.5 Model 04B (right):

 

Figure 12

 

 

Figure 13

 

Figure 15

 

 

Figure 15

 
The complete series (complete f-stop range) can be found here:

link to lens comparison samples page

 
And we see indeed some PF at f/2.8 which rapidly diminishes already from f/3.2. But we also see that the DA200 maintains a consistent exposure and contrast, while the model 30A and model 04B (also with fringes but of a different hue) are slower in reaching an optimal clarity in the texture of the curtain and that comes at the expense of an overexposed sky (in particular in case of the 30A). I used the same PK/A custom mount for the two Tamrons and the difference between these lenses must be ascribed to the lens itself, not the interchangeable Adaptall-2 P/KA-mount.

Now, I am only a layman, but this fringing doesn't look like CA to me - see for example: What is Chromatic Aberration? -  neither longitudinal (different wavelengths have different focal planes) nor lateral (different wavelengths have the same focal plane but come in focus at different positions in that plane). Because: There is no halo outside the curtain; it is the subject itself that is "miscoloured" at the borderline between dark and light. I see the same feature with for example dark branches against a bright sky: The branches may be coloured, but there is - usually - no halo surrounding them.

So yes, whatever PF is, there is some with the DA200 at the widest apertures, and that does detract from the rating. But you usually has to crop tight to really see it and I tend to believe that those who discard the lens as useless because of "excessive PF" must be hardcore pixel-peepers.

And I prefer to look at pictures - not at pixels!

 
 
Distortions, Coma, Internal Reflexions, Flare

Any lens with a focal length as long as 200 mm should be fairly free of any linear distortions across the entire field and one may justifiably expect a lens with DA200's price tag to be without any such distortions. And this is indeed the case as illustrated below with the ruler form above (Figure 16) and a test chart made of 9 approximately 8 x 12 cm identical charts shot at a distance of some 4 m, (Figures 17 and 18):

 

Figure 16

 

Figure 17

     

Figure 18

 

Allowing for that I don't have a test bench to secure that sensor and image planes are absolutely parallel and perfectly centred, distortions are absolutely absent, and the charts shot at the centre and at the corners are about as identical as can be to the extent that the ideal lens formula for a 200 mm lens permits.

 

 

 

Coma is one potential aberration that is often not accounted for. Usually, in ordinary photography, one wouldn't notice coma much, but it can be annoying in low-light photography with bright sources of light involved. Actually, it is quite easy to test for: Take a shot of the starry sky and notice whether the stars near the corners of the image are stretched out like small comets with tails radiating away from the centre of the image.

Here, I test against a star field surrounding planet Jupiter (Figure 19) and as can be seen in the 100% crops (Figure 20) of that image, there is no difference in the appearance of the stars near the centre and near the corners.

 

Figure 19

   

Figure 20

     
One does notice a slight asymmetric haze surrounding the stars. This is uniform over the entire field and cannot be coma. It could perhaps be unfocused near-infrared light, but I have been unable to remove it with IR-cut-off filters and my suspicion is that we are seeing outer parts of the stars' diffraction patterns. If so, the asymmetry indicates an ever so slight flaw in the camera-lens line-up or in the lens' collimation. I shall have to await darker and cleaner skies to investigate this further....
     

Finally a look at internal reflexions, 'ghosts' and flare. Pentax boast that their coatings are very efficient in suppressing these phenomena, and true that is: The image to the right (Figure 21) of the bright Sun directly and somewhat off-axis 'should' reveal both ghost and flare, but there is only a very slight ghosting effect to be seen - well done PENTAX!

 

Figure 21

WARNING: An image like Figure 15 must NEVER be taken looking directly into the viewfinder. That can result in severe eye damage and blindness!!! The Sun must be centred by indirect means or use of a safe solar filter - or you can make the same test with the bright Full Moon.

 

 

Resolution, Contrast, Sharpness
We have already seen above (Figure 5-8 + link) how the lens renders fine detail of the curtain throughout the full f-stop range. We may also use the test chart from above (Figure 9) for a similar exercise. In Figure 22 I just show the test chart (8 x 12 cm) taken at 4 m distance at f/2.8 and f/11. You may see the full range of f-stops by clicking here:

link to f-stop comparison page

It is often claimed that the DA200 - like most other lenses - is a bit 'soft' at its widest opening(s), but, really, in terms of resolution, the DA200 does a fine job at f/2.8. Enhance contrast a bit, and there really isn't much of a "problem" left. Further, I one looks at the complete range of f-stops (c.f. the 100% crops shown in Figure 23), there really isn't much degradation at the smallest apertures, where diffraction effects might be expected, either.

 

Figure 22

 

Figure 23

 

 

 

Well, greyscale test charts may be fine for resolution tests, but as a practical amateur, I prefer as much to test my lenses against stamps. Here we have minute masterpieces of very fine engravings with subtle shades of colour. So, in Figure 24 we have a 39 mm wide stamp photographed at a distance of 2.4 meter. The stamp was taken at dusk in ambient light. It was mounted on a grey-white door some 4 meter away from the nearest windows - quite a demanding situation.

 

Figure 24

     

Figure 25

 

Figure 26

 

 

 

In the composite Figure 25 above I show a comparison of the stamp taken at the same distance (2.4 m) with the DA200 at f/5.6 (upper left) and the Tamron Model 30A at f/5.6 plus f/8 (upper right and lower left respectively). Two things, other than the flatness due to the poor lightening condition, are obvious: 1) The focal length of the Model 30A is longer than that of the DA200 at this short distance. This is not so surprising, c.f. the discussion in the Specifications Section above. 2) Nonetheless the DA200 excels in both clarity and resolution at this short distance. Enhance the contrast a bit as in Figure 26 and the differences only become more obvious. Mind you, the Tamron isn't actually bad - the stamp is only 4 cm wide - but the PENTAX is just that much better.

     
'Sharpness' is a rather difficult and subjective concept very much dependent upon how one perceives the combination of resolution, contrast and, to some extent also, depth-of-field. Furthermore, to my mind many people tend to over sharpen their pictures in post-processing resulting in un-natural edges not seen by the human eye in "real-life" situations. I suspect much of this 'sharpness' obsession can be ascribed to severe pixel-peeping addiction.
     
 

 Anyway, here are some "real-life-3-D objects" with adjoining 100% crops that ought to speak for them selves. 'Sharpness', whatever that is, isn't a thing that the DA200 is in want of.

 

Figure 27

     

Figure 28

 

Figure 29

     

One final example for this section: I bought the DA200 also with astrophotography in mind. I took delivery of the lens in April where nights in my place are already pretty bright (and mostly cloudy!) but I just and barely managed to capture this picture of the star field in Lyra surrounding the famous Ring Nebula, M57. (Figure 30, stack in Deep Sky Stacker of twelve 15 seconds exposure using the PENTAX O-GPS1 unit's Astrotracer function).

 

Figure 30

 

Figure 31

     

The Ring Nebula is fairly bright but also fairly small, being just 1.4 arc minutes wide at its longest dimension. Thus, although it can be captured relatively easy, even with shorter lenses, it will mostly be as a diffuse featureless patch of light. With a 200 mm lens the image formed will be just 0.08 mm wide and thus, occupy a mere 17 pixels on my Pentax K-5 sensor. The "empty" hole in the ring will of course be even smaller.

 

The fact that the 100% crop in Figure 31 actually does show the ring structure is one more testimony to the excellent light-capturing capability, contrast and resolution of the DA200.

 

 

Colour, Saturation, Bokeh

To my experience, the Pentax smc coating is actually more then one thing. At least, I have found that colours and saturation can be quite different from lens type to lens type, and some of these lenses actually provide too much saturation to my taste.

 

Not so, with the DA200. In almost all situations, I find colours are rendered very pleasingly and faithfully. And the 9-bladed diaphragm should and does ensure a very acceptable bokeh.

 

I have not much more to say about this, and will just let the following few samples speak for themselves.

     

Figure 32

 

Figure 33

     

Figure 34

 

Figure 35

 

 

 

Figure 36

 

Figure 37

 
     

Why 200 mm?

Judged upon the sheer number of articles and pictures on the subject, the 200 mm never seems to have been the most popular focal length for SLR and DSLR photographers. Placed between the once very popular 135mm and the still popular 300mm, the 200mm may be considered as "neither fowl nor fish" - too long for portraits and the like and too short for wildlife. Still, to me and many others, the 200mm format is a very versatile one, offering a huge variety of photographic opportunities.

 

Figure 38

 

 

 

I believe, I can best illustrate these options by referring to the slideshow below. Nature, city- and landscapes, candid portraits, converts & events, clos-ups, architectures  - used properly, this is a lens for 'all' occasions.

 

http://ggs.gyes.eu/#!home

Click on arrow to start slideshow. Click on leftmost screen icon

to view slideshow in full screen

 

 

 

Well, for all occasions? I suppose 'everyone' would agree that this is not really a lens suited for birding. And, of course, the ideal 'birding lens' is to be found in the 300 mm+ range. Yet, with the DA200 on can still capture our feathered friends in the air or on the ground - if only they come close enough or let you get close enough.

     

Figure 39 (cropped image)

 

Figure 40 (cropped image)

     

Figure 41 (cropped image)

 

Figure 42

     

 

Figure 43

 

     
     

DA* 200 and Teleconverters

So, I don't really have a 'birding lens' and it is tempting to contemplate adding a 2X or 1.4/1.5X TC to my DA200. Now I don't have a 2X K-mount TC with electrical aperture control contacts, let alone AF coupling. But I have made some tests with my excellent,

manual, 7-element Tamron SP F-series converter. It is purely manual, meaning that used on my DA200 I can only have full aperture, f/2.8 in Av-mode or minimum aperture, f/22 in M-mode. Anyway, no matter what, the optics of that TC and that of my DA200 simply don't work well together. Getting focus confirmation and using CIF is easy enough but image quality leaves a lot to be desired as can be seen in the rightmost section of Figure 44.

 

Thus I have given up more tests with 2X converters for the time being. If nothing else, this is a good illustration that you cannot expect 'each and every' TC to work well with 'any' lens, be it zoom or prime, that has separately moving lens groups built-in.

 

Figure 44

     

But I do have my Pz-AF 1.5X Teleplus SHQ Kenko teleconverter (which actually "only" gives me 1.4X magnification). The Kenko TC has both screw drive and SDM couplings.

 

AF-wise, it works very well with all of my (other) DA-lenses, whether with screw-, DC- or SDM drive. and I have tested it with my DA200 on my *ist DL (screw drive only), my K200D (SDM drive) and my K-5 (also SDM drive). Results, when it comes to AF are somewhat confusing:

 

In AF-mode, the lens doesn't really hunt a lot but finds its range and then stops with the green hexagon blinking in the viewfinder, signalling "I cannot get focus". Now press the shutter release two or three times and you have focus. And as long as you are within close range, AF will then work decently. But change the range, and the process starts all over again.

 

On the other hand, with MF and CIF, focus confirmation and -lock is swift and accurate as can be seen in the examples shown below. Figure 45 is my stamp from before, photographed under "controlled" conditions, but this time at a distance of about 4 meters, while Figure 46/47 was taken at a few hundred meters distance and Figure 48 at some hundred meters. Remembering that air turbulence can and will take its toll the longer the distance and the longer the focal length, I actually find the optical performance of the DA200-Kenko combination satisfactory.

 

Guesswork note: One could suspect that this curious difference in behaviour between AF on the one side and MF/CIF on the other is due to some dedicated DA200 focusing algorithm in the camera firmware. Focus is about right, but not in the sense that the focusing algorithms "knows" the pattern should look like?

     

Figure 45

 

Figure 46

     

Figure 47

 

Figure 48

 

Anyway, for my limited needs, I can do with my Kenko TC as long as I am prepared to use it on my DA200 in MF only. Well knowing the risk, I am going to try out my lens with another 2X TC with electrical contacts.

 

One might of course hope that PENTAX will release a dedicated TC, (which is/was on their latest road map) in the near future. But, one should also realize that dedicated PENTAX teleconverters in the past used to be costly items.......

 

Addendum 2013-09-15:

So, I did find a teleconverter, that matches this lens very well. See my review of the Pentax Rear Converter A 2X-S.

 

Conclusions

A weather and dust sealed lens, built rock-solid with superb ergonomics and silent, very accurate, and mostly very fast, focusing options. Excellent resolution, contrast, 'sharpness', colour rendition and bokeh.

 

Yes, there are minor flaws, mostly or only in respect of some purple fringing. And there are a few shortages, notably a focus limiter and a tripod collar are on my wish list.

 

But weighing pros and cons against each other, this is definitely an exquisite piece of optical and mechanical craftsmanship that places the smc PENTAX-DA* 1:2.8 200mm ED (IF) SDM in a league of its own within its class.

 

It may not be the lens with which I will take most of my pictures, but if ever I have had a one, single 'favourite lens', this is surely it.

 

Links:
smc Pentax-DA Interchangeable Lens Manual(2008)
 

 

 

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Copyright 2013 - Steen G. Bruun