Focal 135mm f/2.8 closer to f/3.5

Started Nov 2, 2012 | Discussions thread
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math guy
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Focal 135mm f/2.8 closer to f/3.5
Nov 2, 2012

Until this week, the only lens I had longer than 70mm was the 55-300, which is great outdoors but not so much indoors. So I bought a Focal 135mm f/2.8 for $28 to play around with, figuring if it turned out to be a dud then not much would be lost.

Well, it turned out to be a KR mount, not a K mount, but the Ricoh pin was pretty easy to remove. And it's an A lens, so the camera can control the aperture and register it in EXIF. So overall I'm satisfied with the purchase.

However, I don't think it's a true f/2.8 lens. I noticed that after adjusting the shutter and aperture by one stop, the images seemed darker at f/2.8 than at f/4. So I tested it out, and sure enough, based on the histogram the images were about the same at f/3.5, slightly darker at f/3.2, and significantly darker at f/2.8. So essentially this is an f/3.5 lens, not an f/2.8.

I can't really complain for the money, but I was just curious whether this is a common thing with old budget lenses.

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-- Joe S.
"We make a living by what we get; we make a life by what we give." ~ Sir Winston Churchill
http://www.pentaxphotogallery.com/artists/josephschmitt

 math guy's gear list:math guy's gear list
Pentax K-x Tamron SP AF 70-200mm F/2.8 Di LD (IF) MACRO Pentax smc DA 55-300mm F4.0-5.8 ED Pentax smc DA 21mm F3.2 AL Limited Pentax smc DA 70mm F2.4 AL Limited +4 more
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