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05-30-2011, 09:32 PM   #1
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FA100mm f2.8 Macro Aperture Issue?

I have just received a FA100 f2.8 Macro from Trademe and at first I thought all was good. Its in lovely optical condition and good to very good cosmetic condition. However...

When using it in any camera control aperture mode (aperture ring on A), I noticed exposure to be rather uneven at different apertures. It was showing relatively good exposure at f2.8 but then getting dimmer as stopped down towards f8 and then gets brighter again at f32 (tripod, fixed ISO on same scene).

Further diagnosis:
1. Looking into the lens (with it still on the camera) I see that the aperture is not fully open when in aperture ring in "A".
2. Turning aperture ring to f2.8, it does go fully open.
3. Now with the lens off the camera,.. Looking at back of lens it all looks fine and no sign of damage (impacts, scrapes etc).
4. Looking at the back of the lens (off camera) I can operate the aperture lever on the back of the lens and the aperture fully opens / closes accordingly. Its a tiny bit stiffer at f2.8 end but does not seem to stick.

So any ideas, you might have, as to what I can do (or was is worth trying) or have I bought a bit of lemon?

Thanks

Jonathan


Last edited by kiwi_jono; 05-30-2011 at 09:43 PM.
05-30-2011, 09:37 PM   #2
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QuoteOriginally posted by kiwi_jono Quote
1. Looking into the lens I see that the aperture is not fully open when in aperture ring in "A".
Did you mean the aperture won't fully open when the aperture ring is in the "A" setting or the aperture isn't fully open when the aperture is in the "A" settings. I assume you meant the former because in the "A" position the aperture should be at it's smallest aperture (f/32 on the FA100 I think) when you have the lens unmounted from the body.
05-30-2011, 09:40 PM   #3
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Sorry that was not clear. To clarify: I mean that with the aperture in the A position AND with the lens on the camera (k-x), the aperture is not fully open (camera holds open for brighter viewfinder but its not fully - more like f3.5).
05-30-2011, 09:45 PM   #4
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Jono,
The FA is a great lens.
Is your copy sharp throughout?
The lens (and all other A lenses and above) should be fully stopped down (not wide open) when set in A position on aperture ring.
Exposure inconsistencies also occur with my copy. Wide open, EV0 is spot on, but at f/5.6-f/22 or so, I need EV -1.5 or so to get the right exposure. To me this is a great advantage for handholding macros.
If your lens requires a positive EV bias for f/8 then it may be a quirk of your own copy. Check to see if everything's OK otherwise by shooting manually, keeping exposure quotients equal as you stop the lens down. If you're not satisfied with it, you might do well to exchange it.

05-30-2011, 09:56 PM   #5
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I don't think you bought a lemon, but the rear lever wasn't properly adjusted. Mine didn't either and took me some time to figure out. You can remove the rear cover (the black plastic cover held by 3 tiny screws, but don't remove the one closet to the lever) then re-adjust the lever. Be extra careful don't let anything fell inside or you will be in a real mess disassembling the whole lens.
05-30-2011, 10:06 PM   #6
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Thanks for the reply Ash,
Yes it is a lovely lens to hold and the test images I have shot so far are stunning (if I have exposure right and the all important focus!).
It seems to be pretty sharp from about f3.5 (and probably from f2.8 but its not fully opening in A mode at the moment - see below) through to f16. If you pixel peep f22 and up up is not so good bit thats to be expected.

I will probably hang on to it anyway (they don't come up for sale very often in NZ) but I was wondering if there is anything I can do to "tweak" it or perhaps send to someone who knows what to do.

The main issue is that: With lens on camera and switched on, aperture ring in A, the aperture (I believe) should be wide open so that there is a bright viewfinder. However the aperture is not fully open (more like f3.5) - I can see by looking into the front of the lens. The aperture can be fully opened by turning the aperture ring to f2.8 (so I know it should be capable of opening that far).

Or is this a common quirk as well?

Thanks
05-30-2011, 10:11 PM   #7
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QuoteOriginally posted by wlachan Quote
I don't think you bought a lemon, but the rear lever wasn't properly adjusted. Mine didn't either and took me some time to figure out. You can remove the rear cover (the black plastic cover held by 3 tiny screws, but don't remove the one closet to the lever) then re-adjust the lever. Be extra careful don't let anything fell inside or you will be in a real mess disassembling the whole lens.
Wow thanks! I was hoping it might be something like this! I will have a look and see if its something I am confident in doing. Thanks again.
05-30-2011, 10:42 PM   #8
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Hmmm... I don't see any plastic covers on my lens?
Will google it.

05-30-2011, 10:46 PM   #9
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Ah, missed out that point of the lens being mounted and not opening up fully. Hope it works out. It's an awesome lens.
05-30-2011, 10:55 PM   #10
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QuoteOriginally posted by kiwi_jono Quote
Hmmm... I don't see any plastic covers on my lens?
Will google it.
It's the piece of matt black inner rim on the chrome mount. It looks metal but is actually plastic. Just to help you a little. You might toy with the piece of brass first for your problem. It controls how far the aperture opens up when mounted.
05-30-2011, 11:20 PM   #11
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Jonathan,

Sounds like the aperture blades are a bit sticky from f4 to f2.8. It may pay to send it to a lens repair place for a clean and adjust.

If you are in Wellington, I'd suggest Phil Jacobs in Petone.

Regards

Chris Stone
05-31-2011, 01:34 AM   #12
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QuoteOriginally posted by seventhdr Quote
Jonathan,

Sounds like the aperture blades are a bit sticky from f4 to f2.8. It may pay to send it to a lens repair place for a clean and adjust.

If you are in Wellington, I'd suggest Phil Jacobs in Petone.
Thanks Chris.
I'm in Christchurch - the city that shakes.

Im not sure if its sticky because:
1. Seems to be fairly consistent tension required on lever to open iris (although somewhat more tension is required as it opens).
2. the aperture seems to always opens to the same amount after every shot (camera A set to f2.8). Would of thought this would vary if aperture was sticky?

But I will investigate further and if in doubt will send to someone!

Cheers

Jonathan
06-01-2011, 11:01 PM   #13
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Well still have not sorted aperture but I'm now fairly sure it is an adjustment problem rather than sticking (you can rotate lens in mount and see aperture stops moving only as mount clicks into place - not because it has stuck before then).

Anyway enjoying it using it manually.

Its sharp at f2.8 if you NAIL the focus
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