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05-11-2009, 09:08 PM   #1
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FA 50mm f1.4 vs. F 50mm f1.7 (and DA 18-55mm f3.5-5.6 AL II)

I know they are not exactly apples to apples and this is not really a scientific test, either.

But I just wanted to test these lenses under similar conditions at the same aperture so I arbitrarily picked f5.6, and used a solid tripod and changed the lenses with utmost care to not disturb the position, placement or orientation of the camera. In all the shots, I used Spot metering and focused on the silver oval on the coffee mug shown in the pictures.

Attached are the pictures (DA, F and FA, in that order) but looking at the EXIF I was a bit puzzled at the differences in shutter speeds selected by the K20D.

Just why is that? I am just trying to understand what happened.

The camera figured that F 50mm f1.7 needed 2.5 seconds vs. the FA 50mm f1.4 which exposed the same frame for 2 seconds. Both these shots were taken just a few minutes apart at night under tungsten lighting so should have been no difference in lighting.

Just for good measure, I tossed my kit lens in at the same focal length and it came up with an exposure time of just 0.8 seconds!

All these lenses have (different) UV filters which stay on them permanently.

Thanks,

EsBee

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05-11-2009, 10:12 PM   #2
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um, what ISO and aperture for each lens?
05-12-2009, 01:09 AM   #3
axl
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as above
(damn you 10 characters)
05-12-2009, 01:12 AM   #4
axl
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OK, I found out.
so they are all at 5.6. I think we all knew that DA18-55 likes to underexpose (especialy the 1st version) but the difference between f50 and fa50 is puzzling indeed.

05-12-2009, 04:38 AM   #5
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please test

Can you please compare the SMC 50mm F1.7 and FA 50mm F1.4 at apertures from F1.7 to F3.2?

Thanks
.lars
05-12-2009, 08:57 AM   #6
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Sure, I just have to wait till the weekend to do that.
05-12-2009, 09:23 AM   #7
emr
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So inconsistent results with Pentax branded lenses doesn't give a very high quality impression of the exposure metering.
05-12-2009, 10:38 AM   #8
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oh people, pleeeease. When you meter of a shiney and reflective spot with other more shiny stuff around it all kinds of crazy things can happen.

05-12-2009, 11:55 AM   #9
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I agree, the above tests do not conclusively say anything except perhaps, raise some questions.

I will find a better subject to focus on, and also remove the UV filters when I do these tests over the weekend.
05-12-2009, 02:41 PM   #10
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QuoteOriginally posted by Stratario Quote
oh people, pleeeease. When you meter of a shiney and reflective spot with other more shiny stuff around it all kinds of crazy things can happen.
I agree. Try to meter the EV on non-reflected surface.
05-12-2009, 05:21 PM   #11
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QuoteOriginally posted by Recercare Quote
Can you please compare the SMC 50mm F1.7 and FA 50mm F1.4 at apertures from F1.7 to F3.2?

Thanks
.lars
I have tested the SMC-A 50/f1,4 and the SMC-F 50/f1,7.

I could post results if needed.

The A1,4 has a half stop more and that just cannot be beat sometimes. But at f1,8, the A1,4 looks a tiny tiny tad worse than the F1,7 at its widst (it might be subjective). Onward, they look exactly the same.

The A has a much nicer focus ring, the F autofocuses...
05-13-2009, 12:21 AM   #12
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please do

Hello bdery

Very interesting and please post the test....... they're actually equal at F2.0 and F2.8?

Kind regards
.lars
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