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05-08-2016, 07:35 AM   #1
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Can't get my lens to 3.8 even though it is a 3.8 -22 lens

Hi guys. I bought a used Pentax 28-200 f3.8 lens. I mounted it on my K-S2 and generally like the lens BUT ....

I cannot get it to go below 5.6. Did I limit it somewhere in the menu system or is there a way to force the camera to recognize the 3.8?

Thanks

05-08-2016, 07:54 AM   #2
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QuoteOriginally posted by Hazcat Quote
Hi guys. I bought a used Pentax 28-200 f3.8 lens. I mounted it on my K-S2 and generally like the lens BUT ....

I cannot get it to go below 5.6. Did I limit it somewhere in the menu system or is there a way to force the camera to recognize the 3.8?

Thanks
At what focal length? The 28-200 is a variable aperture lens. It is only F3.8 at the wide end (though a DSLR will see it a F4). At the long end it is F5.6 (71-200mm). From 50mm to 70mm it is F4.5.
05-08-2016, 08:14 AM   #3
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QuoteOriginally posted by boriscleto Quote
At what focal length? The 28-200 is a variable aperture lens. It is only F3.8 at the wide end (though a DSLR will see it a F4). At the long end it is F5.6 (71-200mm). From 50mm to 70mm it is F4.5.
DUH! on me but even at the 28 end it will only go to 4.0.
05-08-2016, 08:32 AM   #4
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You're using it on a DSLR, yes?

QuoteOriginally posted by boriscleto Quote
a DSLR will see it a F4
As in, it will read as f4.0 even though it is fractionally wider.

05-08-2016, 05:38 PM   #5
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QuoteOriginally posted by victormeldrew Quote
You're using it on a DSLR, yes?



As in, it will read as f4.0 even though it is fractionally wider.
Yes K-S2. Will it not read any f stop below 4?
05-08-2016, 05:47 PM   #6
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QuoteOriginally posted by Hazcat Quote
Yes K-S2. Will it not read any f stop below 4?
Yes, it will, but 3.8 is neither a full stop, half stop, or third stop, so your camera display rounds to the nearest, which is 4.

Last edited by MPrince; 05-08-2016 at 05:52 PM.
05-08-2016, 06:26 PM   #7
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QuoteOriginally posted by MPrince Quote
Yes, it will, but 3.8 is neither a full stop, half stop, or third stop, so your camera display rounds to the nearest, which is 4.
So if I had a 1.8 it would read as 2? The Camera wouldn't take the .2 in account?
05-08-2016, 06:37 PM   #8
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f1.8 is on a third stop increment so your camera would indeed read it. The full details are available on wikipedia, but it involves a lot of boring maths. In the end your display is just rounding to the nearest available amount and that lens falls in between.

05-08-2016, 06:52 PM   #9
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OK thanks!!
05-08-2016, 07:11 PM   #10
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What are your EV steps set to in the custom menu? 1/2 or 1/3? Try setting it to 1/3rd steps.
05-08-2016, 07:39 PM   #11
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QuoteOriginally posted by Not a Number Quote
What are your EV steps set to in the custom menu? 1/2 or 1/3? Try setting it to 1/3rd steps.
It is set to 1/3. Thanks.
05-10-2016, 03:20 PM   #12
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I think it'll be fine. I'm not sure I've had a 3.8 lens. It would be curious as to whether when it is wide open, does one adjustment keep it at 4.0 since it is in theory wider than 4.0.

Otherwise, how do you know that you are not at f4 or that the camera is actually opening up fully? This seems like it could be problematic if you are shooting in manual mode.
05-10-2016, 07:36 PM   #13
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I haven't had a lens with an aperture of f/3.8, but my K10D shows f/1.9 with my FA 43. It doesn't round when the aperture is all the way open.
05-11-2016, 05:22 AM   #14
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QuoteOriginally posted by builttospill Quote
I haven't had a lens with an aperture of f/3.8, but my K10D shows f/1.9 with my FA 43. It doesn't round when the aperture is all the way open.
Not sure what you mean by one adjustment. I am curious if it will be overexposed.
05-11-2016, 08:40 PM   #15
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QuoteOriginally posted by Hazcat Quote
Not sure what you mean by one adjustment. I am curious if it will be overexposed.
Sorry, I'm not sure what you mean either. But what I was trying to say is f/3.8 is odd and so is f/1.9. I have a lens with an aperture of f/1.9 when it's wide open. My camera does not round it to f/2, but instead shows f/1.9 and f/2 as two separate aperture settings. I've never heard of a camera rounding the aperture setting display, so that would surprise me if that is what's happening.

Instead I'm wondering if the camera is registering that the lens is all the way zoomed out.
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