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04-19-2012, 07:33 AM   #1
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FA 100-300 4.7-5.8 Identified as 4.5-5.6 ??

I grabbed a FA 100-300 4.7-5.8 the other day, got it in the mail today, and for some reason all my bodies (K-r, MZ-6, MZ-7) identify the aperture in "A" mode as 4.5-5,6 instead?? It's indeed the 4,7-5.8 (4,7 is marked on the aperture ring) but for some reason in "A" mode, this does not seem to be the case.

https://www.pentaxforums.com/lensreviews/data/44/SMC_Pentax-FA_100-300mm_F47-58.jpg

Anyone know what this could be about? There's another FA 100-300 that actually is 4.5-5,6, but there's no way to be wrong about this, it is the 4,7-5.8 version.

The lens is sweat and everything works perfect, I dont mind having 4.5 instead of 4.7, but I wonder what it's all about...

Confused...


Last edited by JFN; 04-19-2012 at 10:33 AM.
04-19-2012, 07:47 AM   #2
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I suspect that Pentax cameras are programmed to only record specific f-stops (such as 4, 4.5, 5, etc.) and 4.7 and 5.8 don't fall in the pre-programmed array. With variable aperture zooms, just because the camera says 4.5 doesn't mean it's really 4.5. It might be 4.3 or 4.7.
04-19-2012, 07:52 AM   #3
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Very interesting, I had no idea about this!

I though at first that it was the K-r that identified the lens, and did it wrong assumingly, since there actually is another 100-300 FA as well which has just precisely f/4.5-5.6, but then when I found out that my film bodies did the same, I became quite curios about what this was..

04-19-2012, 09:02 AM   #4
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Well, the thing is, the 4.5-5.6 is supposed to be a lower grade lens.

04-19-2012, 09:11 AM   #5
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QuoteOriginally posted by Giklab Quote
Well, the thing is, the 4.5-5.6 is supposed to be a lower grade lens.
But that's another lens, other glass, etc. So?
04-19-2012, 09:29 AM   #6
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So, the camera identified it as a 4.5 instead of 4.7. I agree that the problem might lie with the "rounded" aperture values, but just pointing out since many people seem to mix them up. I know it says 4.7 on the lens.
04-19-2012, 09:42 AM   #7
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QuoteOriginally posted by Giklab Quote
So, the camera identified it as a 4.5 instead of 4.7. I agree that the problem might lie with the "rounded" aperture values, but just pointing out since many people seem to mix them up. I know it says 4.7 on the lens.
Yeah, I bet that happess, though with this lens it's not a case of mixup.

04-19-2012, 10:19 AM - 1 Like   #8
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Max aperture on K-mount lenses is communicated to the camera via the pins on the mount encoding a binary string. Each pin can either be shorted, or not (1 or 0). Pentax defined the combinations when the KA mount was created for the A-series lenses. The documentation is here: Features and Operation of the Ka Mount . As a result, lenses would odd max apertures can't be exactly specified to the camera. What will blow your mind even more as the bodies indication of max aperture will vary depending if the camera is setup for 1/2 stops or 1/3 stops!

11-07-2014, 01:43 AM   #9
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Hello...

i have almost the same question : a seller in ebay is selling this lens : smc FA 100-300. On the photo we can see the box with written FA 100-300 F4,7 -5,8 but on the photo of the lens : body of the lens is black and aperture ring starts at 4.5.
seller certify that it is the 4,7 - 5,8 version with black body...

this question is important because 4,7/5.8 version does not have same weight and optical performance than 4.5/5.6

Is it possible ? has anyone already had this problem ?

Thanks for your answer...

Lionel
11-07-2014, 02:19 AM - 1 Like   #10
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As far as I know the 4.7 only came in silver.

Ask Yves if the photograph is of the actual lens for sale.

If he says yes, it's a 4.5. If he says no ask for a photo of the actual lens he has for sale including the side which says SMC PENTAX-FA etc..
11-07-2014, 03:58 AM - 1 Like   #11
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The 4.7 also came in black, but it's a lot rarer. I have one, and I saw another one in a Shinjuku camera shop in 2012.
11-07-2014, 04:22 AM   #12
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QuoteOriginally posted by krazykat Quote
The 4.7 also came in black, but it's a lot rarer. I have one, and I saw another one in a Shinjuku camera shop in 2012.
How can you make difference between f4.5 black and f4.7black ????
Obviously on the photo in ebay i ca read on aperture ring 4.5...but seller says it is a 4.7 "black version" with a f4.7 box...strange ???
11-07-2014, 12:44 PM   #13
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QuoteOriginally posted by doudou54300 Quote
but seller says it is a 4.7 "black version" with a f4.7 box...strange ???
Very strange.

Ask for a picture from the side:

11-07-2014, 01:53 PM   #14
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QuoteOriginally posted by doudou54300 Quote
How can you make difference between f4.5 black and f4.7black ????
Obviously on the photo in ebay i ca read on aperture ring 4.5...but seller says it is a 4.7 "black version" with a f4.7 box...strange ???
If the photo shows 4.5 then it's a 4.5, my black 4.7 shows 4.7.
12-08-2014, 02:58 PM   #15
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Finally seller sent me mail : confirming that he made a mistake : it was a f4,5 usual black edition....and not a 4,7....we were all right !!!

Lionel
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