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01-21-2008, 09:56 PM   #1
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Location: Rowlett, TX
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older Sigma 1:2.8 135mm - question

I've had my K10D for about a month now and I've obtained (for free) 8 older lenses, and rediscovered a couple of others I've had for 20 years.

One in particular is a Sigma 1:2.8 135mm in M42 screw mount. It has a feature that I'm unfamiliar with and I'm hoping someone here can explain it to me. The focusing system is a bit odd, it actually has two focusing rings. The inner/main ring will focus down so far and then you can engage the secondary/outer ring, which will allow you to focus in even further.

The main ring says "SYSTEM FOCUSING" on the outer edge. The other ring says "REPRODUCTION RATIO", and then as you rotate the outer ring, 1/5, 1/4, 1/3.

There are also two small holes on the front of the lens that I can't explain, they are visible in the first photo below.

Here's what it looks like:

When you engage the secondary ring with the fractions on it, the focus gets odd at wider apertures. The below photo is with the secondary ring engaged almost completey, f2.8, 1/30sec.

Weird eh? It's not my shaky hands making that effect, at least I don't think so. Same shot at f5.6 0.3sec, weird effect gone.

See, my hands aren't so shaky.

If you do not engage the secondary ring and only use the main ring, here's the result (f2.8, 1/10sec):

Any insight that can be provided is appreciated! Thanks.

01-22-2008, 07:38 AM   #2
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Original Poster
Is this perhaps just bokeh gone wild? It seems extreme to me.
01-22-2008, 09:29 AM   #3
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Location: Rowlett, TX
Posts: 61
Original Poster
I think I've more or less answered my own question now. I've found bits of information on the lens, some call it a "Telemax" others a "Tele-macro". It does work a bit like a macro. Basically, the outer ring turns the front element allowing you to increase the magnification further. So, uh, thanks for looking.

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135mm, effect, f2.8, focus, hands, k-mount, pentax lens, photo, sigma, slr lens
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