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This lens is Pentax’s offering in the popular group of circa 100mm Macro Lenses. For those interested in close up work all the SLR camera manufacturers as well as the independent lens manufacturers offer a lens in this area due to the handy working distance from the subject. We take a look at how the Pentax offering stands up against the opposition.

Specifications

• Focal length 100mm
• Aperture f/2.8
• Angle of view 24.5º (16º on *istDxx)
• Filter size 49mm
• Construction 9 elements in 8 groups
• Focus type Helical
• Closest focus 0.303m (1:1)
• Weight 0.345kg
• Dimensions 67.5x80.5mm
• Mount available Pentax KAF
• Tripod bush No
• Price(SRP) 449.99

Build and handling
Despite being comparatively small and lightweight, this lens feels well put together and up to the job. Adjacent to the mount is the aperture ring that on modern, automatic cameras is set to a fixed position. In front of this is a large distance window with measurements in metres and feet and marked with an arbitrary depth-of-field scale. Alongside this, on the right, is a handy clamp switch to clamp the autofocus, useful for close-up work. The wide (40mm) manual focus ring follows this and is reasonably although lightly torqued.

Just short of a full turn is required to travel through the entire range. Just forward of this point is where the supplied lens hood, a full cone bayonet, fits. With the hood in place it appears that the lens does not extend in use. However, the front element does extend some 45mm, shielded by the hood, which is another 12mm longer than the extending element. The front element does not rotate, making the use of filters easier. Care needs to be taken with adverse lighting though, as the hood becomes less effective as the focus gets closer.

Autofocus was quite quick and fairly unobtrusive noise wise in the normal range but took it’s time to arrive at a point of focus when used close. The large amount of travel was responsible for this and a focus limiter would have helped a lot but was sadly lacking.

Optical Quality
As with many, but not all lenses, this one benefits from stopping down to achieve the best out of it. The performance wide open is, if anything, a little disappointing. However, once stopped down a couple of stops, the results improve dramatically and as a macro lens will normally be used at smaller apertures in order to achieve greater depth of field, this should not be too much of a problem.

On the other hand, chromatic aberrations are better controlled with the lens wide open than they are as the lens is stopped down and the more we stop down, the more chance there is of the dreaded purple fringing! To be fair though, these were measured responses and fringing did not appear in any of the pictures that we took nor on the prints we made.

On the good side, distortions are reasonably well controlled, with negligible pincushion measured but not seen.
Overall, the results that we obtained from this lens were quite pleasing.

100mm is the ideal focal length for a lot of close-up photography, giving a reasonable working distance from the subject as shown here with this flower head from a Prostrate Toadflax, which is only 25mm long including the tail. Pentax *istDS. 1/60sec at f/11	The detail the lens will record can be seen here with this crop from the full frame of a crane fly hanging itself out to dry. Pentax *istDS. 1/125sec at f/11 with fill flash.
	The lens also makes a nice short telephoto lens for everyday subjects. 1/350sec at f/8 on Pentax *istDS

Click on each comparision photo below to view full size versions

Below is our lens test data. To find out how to use these graphs look at this article: How we test lenses

Verdict
In a system that boasts the compact size of it’s dSLR cameras, this lens fits well being solidly made and finished without being accompanied by a lot of bulk. The wide open performance is a little disappointing for a prime lens but improves rapidly once stopped down. For a macro lens, the peak performance is in the right area.

In summary, the positive points of the Pentax SMC 100mm f2.8 D FA Macro are
Good build and finish
Performance peaks in the right place
Lightweight in keeping with system

Negative points are:
Disappointing performance wide open
Lack of focus limiter, which is needed
Extending front element negates effectiveness of the hood.

Check the latest price of the Pentax SMC 100mm f2.8 D FA Macro here

Test by Ian Andrews www.wildaboutkent.co.uk

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