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The SMC Pentax-A 100mm f/4 Macro is the right lens at the right price. You can buy a decent used one of these for less than £100 on eBay, which is fantastic value for money if you're willing to overlook the lack of autofocus.

Whilst it's not right as a tube lens for use with infinite objectives because of the recessed front lens element, in its proper environment as a regular macro lens, it really shines.

SMC Pentax-A 100mm f/4 Macro is the right lens at the right price. Whilst it's no good as a tube lens for use with infinite objectives with its deeply recessed front element, in the field it shines.

Macro Performance

The focus ring is huge, silky smooth and has a wonderful focus throw: 340 degrees of travel from infinity to close focus (0.45 metres).

With the tiniest bit of pressure from a little finger the user can shift the focus precisely with no play at the start of end of the motion, yet it doesn't drift when there is no pressure applied.

If you want the lens exclusively for macro, then the lack of autofocus is not an issue as it's useless at macro distances and you'd have it switched off.

The focus ring is huge, silky smooth and has a wonderful focus throw: 340 degrees of travel

From f/5.6 and up the results are excellent- smooth, clean and sharp, with great colours.

The Pentax-A 100mm f/4 macro gives you super sharp edge to edge shots, and really is one of the sharpest vintage 100mm lenses around.

In terms of optics, its 5 elements give very low distortion with vivid contrast and rich colour rendering.

Dental Macro

Pentax also made a dental version of this lens, the SMC Pentax-A 100mm f/4 Dental. This is the same lens with added markings meant for close-up diopters for dentists.

But...

its 5 elements give very low distortion with vivid contrast and rich colour rendering

It only magnifies up to 1:2, but for many traditional macro subjects a 1:2 magnification is just perfect, ie butterflies, dragonflies and damselflies.

The maximum aperture of f/4 makes it quite tricky to focus in situations with less light.

Flare can be seen if shooting close to the sun even in spite of the deeply recessed front element.

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