Given Pentax’s longstanding K mount I regularly search KEH.com to see what lens produced since 1975 has popped up. A couple of months ago 2 numbers and 2 words prompted me to hit the BUY button with haste. The 2 numbers are 600 and 94 as in 600mm and $94. The two words are ‘mirror’ and ‘lens’. As opposed to mirrorless which is all the rage in France (hey, I like them, have had many and still have one too) this lens adds 2 more mirrors to the DSLR mix rather than reduce the count. I reserve this space for a history of mirror lenses in general and how they came to be, but none of that matters to me right about now. My interest is piqued solely by the empty coffee can funhouse mirrored gaping maw of these lenses like shown below ever since I first laid eyes on one of these beasts:
Would you look at that thing? Picture quality? Who gives a hoot? I determined I must own one of these on sight. Any half in focus image drawn in by it is gravy. Upshot, compact (lengthwise, not diameter) and light weight. It is after all a hollow can with some mirrors in it. Found a diagram. Want to see it? Here it goes.
I did look in to it enough to know that, as with every upside, there are downsides, namely:
- In folding the image using that mirror at the center ‘Donut Bokeh’ will be introduced wherever there is out of focus light.
- Personally I think this is neat. Depending on the circumstances this could lead to some interesting images I thought.
- Any aperture setting you want as long as that setting is f/8.
- Attributable to all mirror lens due to the nature of their design this is less of an issue in the digital era and the sky high ISO now available that was only a dream in the film era. I imagine f/8 with 400 ISO film like I commonly use (Pentax ME Super and SF10) would be an issue.
- Manual focus
- This is also due to the design, but manual focus does not bother me and I regularly use, and in certain situations prefer manual focus lenses.
- Tripod only.
- Read that with film this lens was really for tripod use only.
- Blurry.
- Also read that sharp focus was an issue with mirror lens designs.
I wondered if the Pentax K-1 would offset a couple of these:
- Being able to bump ISO up to a usable in a pinch 6400 should do a lot to ramp up shutter speeds.
- In body image stabilization that includes a 600mm setting should also do a lot to increase shutter speeds.
The question was answered recently when I decided to take this 600mm and a more traditional legacy film AF Pentax 80-320mm (used on a K-70 to get out to a FF 480mm relative field of view) lens out to a band competition to see which lens would be more practical.
A legacy battle if you will. In all honesty given the limitations listed above and the AF/non mirror design/brighter aperture I fully expected the 80-320mm to clean the 600mm lens’ clock. Later on I realized that I had accidentally turned off IS on the K-1/600mm, but it was in full effect on the K-70/80-320mm which should have given the latter an even greater advantage. The result when I got to the RAW files? In my opinion the the 600m was the lens that came out on top by a pretty good margin. Why?
- Turns out the 80-320mm, even with IS enabled and no additional mirrors to contend with, was no great shakes at creating sharp images itself. Had noticed that sharpness was hit or miss in earlier testing, but I was able to create images I liked. Also I thought the additional advantage of a bright day would favor the 80-320mm. Nope. Not bad. Seems the lens prefers static subjects. I did get some images I like. Just not as good as the 600mm.
- Standard issue. Compared to the 600mm the images appeared flat and a bit boring.
Notes and surprises with the Sigma 600mm:
- Very easy to focus. Smoooooth focus ring. With the long reach and narrow aperture I expected a dark jittery mess through the viewfinder, but with the bright Saturday afternoon sun I had no issue nailing focus at all. Chalk some of that up to Pentax’s bright and large viewfinders I imagine, but the result was a surprise. With the viewfinder there is no IS compensation or focus peaking to counteract a jittery hand like Live View would have, but I felt no need to use Live View and these aids. Oddly had I used Live View I would have likely realized that IS was off as the image on screen would not have been corrected for motion. Even with moving objects like the running cargo panted judge action I captured running through the performances.
- Handheld. No tripod or even funky camera holding techniques were used and even without IS I had no issue getting shots I liked.
- At the proper donut diameter, owing more to distance of out of focus light sources in the background, I really liked the Donut Bokeh effect. In one picture with the witch they turned out to be  a nice feature above her staff.
- Colors. I love the way this lens renders colors.
- Sharpness. Perhaps owing to my low expectations going in I was perfectly happy with the sharpness of the images. Take a look at the reflection of the field in the trombone below.
- <ahem> It was $94!!!!
Enough rambling. Below is a sample of the images I took and here is a link to the gallery I will be adding images to over time for this lens.
-ELW
Eric L. Woods 