Lens Spotlight: A50 Macro - Jason Doss

Lens Spotlight

smc Pentax-A 50mm f/2.8 Macro

Macro lenses again, this time the A50f2/8 version which was previously examined with the 1.4x-S TC attached. All comments that follow refer to the lens with a naked rear end. 


The lens is 220g (0.5#) and, focused at infinity, 40mm long (1.6 inches) and has 8 aperture blades and 49mm filter threads. The fast aperture of f/2.8 is about average for lenses of this focal length. The lens bears the usual aperture ring and has a rubberized grip for easy manual focusing. Minimum focus distance is 120cm (3.9 ft) producing 1:7.7 reproduction ratio (0.13x). I have been saying in many of my previous posts that "the lens focused at infinity is Xmm long."  That's because focused at infinity, the lens is as short as it gets. 

Older lenses often extend, sometimes significantly, when focused to close-up distances.  Sometimes the photographer will say, the lens is "racked out" for macro photography.  Or maybe that's just me, I don't know.  Modern lenses have "internal focusing" as a feature which means that the movement of all lens elements occurs within the lens barrel.  The overall length of these lenses is usually somewhat longer than the older lenses without this feature, but they can be shorter when "racked out" and of course, the overall physical dimensions do not change. 


Here are a couple of photos of this lens at infinity (left) and at minimum focus distance (right) to show the difference.  The line on the lens barrel at right indicates the magnification ratio numbers printed on the focusing ring.


As usual, image quality when wielded correctly from this, and arguably all lenses that are macro lenses is excellent. This correctly implies that the secret to getting good images out of this lens requires wielding with skill and aplomb. The late Michael Reichmann said in an article I read long ago and still remember that, "Most lenses are better than most photographers."  So keep in mind no lens is going to shine in the hands of a person with no skill.


A 50mm macro lens will allow in much more background image than one with a longer focal length, and most macros have longer focal lengths. Where there is more background, there is more challenge. Only the photographer can choose the right point of view from which to shoot, and sometimes that point of view might contain background matter that contrasts or somehow conflicts with the primary subject.  Think of contrasting colors, lighting, or distracting and detailed material. So for this round, I shall assault you with three new images demonstrating the optical magnificence of this lens which is at the mercy of the aptitude of its wielder.


First at top, we have another frost flower.  Previously, I mentioned that these were once-a-year phenomena, however I hope you noted that they are once-per-year-per-plant phenomena, therefore apparently a few plants hidden alongside the road were we spotted these did not erupt into frost flowers last time. And luckily, I had the A50f2.8 Macro on me at the time, so I hopped out and grabbed a few shots, this one being representative. There is lots of fine detail in the ice crystals that will be apparent if you click on the image at left to embiggen it. 


Second, the street sign, "Cedar Lane Estates," which is near to where we live. It was in the same general vicinity as the frost flower but a little less "macro." I went for a B/W image here to emphasize contrasts between dark greens and highlights in the sign, and in the background.  Perhaps this image would have worked better with a longer focal length because the highlights in the background interfere?  You tell me.


Lastly, proof positive that (a) macro lenses can be excellent landscape lenses, and (b) power lines suck.  There's no way to avoid these power lines without dangling from the Highway 7 bridge in Jasper, and I wasn't going to do that.  Nevertheless, I think we snagged plenty of interesting detail here, as the Little Buffalo approaches from the west.


Again, click any photo to see larger versions, and comments can be left on this page or under each photo if you are so inclined.


The Pentax SMC-A 50mm f/2.8 Macro is, of course, all manual with an aperture ring and manual focus ring. A-series lenses have an A setting on the aperture ring which enables aperture control on the camera. Macro lenses with a normal focal length (50mm or so) tend only to magnify to half life size, which means the smallest field of view is only 48mm x 72mm.


Macro lenses do best at close distances and have optics with minimized distortion. This lens sports a reasonably fast f/2.8 maximum. The fast aperture allows greater focus precision, however most macro photos are typically done stopped down to f/11 or smaller. This lens is one stop faster than its M-series counterpart, and in fact there is a slower f/4 A-series 50mm Macro which I think was a holdover from the M-series.


The lens is 220g (0.5#) and, focused at infinity, 40mm long (1.6 inches) and has 49mm filter threads. There are markings on the lens to indicate the magnification ratio. This macro lens has recessed front elements, therefore a lens hood is not required.


In my collection, I work thru lenses in a random order, and I treat the addition of teleconverters as a separate lens. So, here, the A50 Macro is paired with the 1.4x Pentax teleconverter of the day, which was the Converter A 1.4x-S. The teleconverter adds 0.85 inches and 5.1 ounces to the package. The fit is tight and comfortable. Magnification is increased by 1.4x without decreasing the minimum focus distance. The combination behaves as a 70mm f/4 lens with 3/4 life size magnification.

On display this time are three macro images taken at 70mm, with flash, and near the house. The boys and went in search of subjects, armed with a shoe-mounted flash, hoping to highlight the closeup performance of this combo. At top, we see berries growing on the stalk of an American beautyberry bush. These grow in dense clusters at the base of each pair of leaves, and are intensely purple. They are supposed to be easy to grow, and I'm going to test that... I've gone around my place tossing berries alongside the road, and hope to see the road lined with beautyberries next year.


A katydid poses on the outer window sash, and was a good sport tolerating a very close-up shot with flash to boot. And on the right, we have a long-snout butterfly who also co-operated with my photography attempts. Each animal posed for at least three shots, and these were the best of each series.


Flash photography and macro go hand-in-hand. It's the best way to combine hand-held photography with low light and small apertures. Plus, since the flash impulse is microseconds, then unless combined with long shutter speeds, that kind of illumination will often yield sharp detail. Don't forget to use your diffuser, or bounce the flash when possible. I could have done that with these two photos (bottom) to cut down on highlights and even out the light.


That's all I have for now... See you next time.


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