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04-12-2010, 06:38 AM   #1
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Advice on FA50 1.7 focusing defect please

I have an FA50 1.7 in excellent condition - except that it won't focus sharply at long distances unless stopped right down. It's fine at close distances, which suggests to me that the focus throw is not going far enough to infinity. In other words when up against the infinity stop, it hasn't actually gone quite far enough. Is it likely that this is maladjustment of the focusing ring? I.e. easily adjusted by someone who can get inside and has the right screwdriver?

I know nothing about the inside of lenses as you can guess ...

I had it serviced recently by a guy who didn't spot this problem. If it is supposed to be easily solved I'll take it back and get him to do it for nothing.

04-12-2010, 06:47 AM   #2
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Hi, havn't come across the problem myself, but if you have a split focusscreen, you may be able to aim at a line in the distance and from min focus, manualing focusing up to it. You may be able to dentify where the focus range stops?

Just an idea, best wishes with fixing the problem
04-12-2010, 06:53 AM   #3
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At F1.7, the DOF is very thin

Any slight movement from you or the subject is enough to cause out-of-focus and this is especially true for distant objects which appear so very small

Another reason would be: the lens may just be characteristically soft wide open

I suggest you give it a try again with a tripod and focus on something stationery. You may be able to get some better results

Do remember: a 50mm isn't really a telephoto lens. You can't expect it to behave like one when you focus it on distant objects :ugh:
04-12-2010, 06:59 AM   #4
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Forgive the crappy drawing.. When the lens is at Infinity (with the plastic body FA lenses), the lens glass body should be flush with the lens body. If it is, then you may have a different focusing problem. If it sticks out then your guess is right, it won't go all the way to infinity. I had an FA100 macro that did that. Since I had just bought it though, I sent it back to the seller for a refund.



04-12-2010, 07:06 AM   #5
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QuoteOriginally posted by JeffJS Quote


Forgive the crappy drawing.. When the lens is at Infinity (with the plastic body FA lenses), the lens glass body should be flush with the lens body. If it is, then you may have a different focusing problem. If it sticks out then your guess is right, it won't go all the way to infinity. I had an FA100 macro that did that. Since I had just bought it though, I sent it back to the seller for a refund.

Not a crappy drawing at all. When the focus ring is pushed all the way to 'infinity', the filter ring projects, but the next 'step' in the body is flush with the surrounding case. Which doesn't sound very hopeful, if your diagnosis is correct!
04-12-2010, 07:07 AM   #6
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QuoteOriginally posted by Just12hvFun Quote
At F1.7, the DOF is very thin

Any slight movement from you or the subject is enough to cause out-of-focus and this is especially true for distant objects which appear so very small

Another reason would be: the lens may just be characteristically soft wide open

I suggest you give it a try again with a tripod and focus on something stationery. You may be able to get some better results

Do remember: a 50mm isn't really a telephoto lens. You can't expect it to behave like one when you focus it on distant objects :ugh:
Thanks but I have three other 50mm lenses, including an M50 1.7, so I know exactly how it should behave!
04-12-2010, 07:09 AM   #7
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QuoteOriginally posted by cps_goodbuy Quote
Hi, havn't come across the problem myself, but if you have a split focusscreen, you may be able to aim at a line in the distance and from min focus, manualing focusing up to it. You may be able to dentify where the focus range stops?

Just an idea, best wishes with fixing the problem
Thanks but .... the Katzeye screen on my K10D does not give accurate MF focusing indication - I have a replacement 'shim' set on order for that to be sorted out. One thing after another ...
04-12-2010, 07:30 AM   #8
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QuoteOriginally posted by timo Quote
Not a crappy drawing at all. When the focus ring is pushed all the way to 'infinity', the filter ring projects, but the next 'step' in the body is flush with the surrounding case. Which doesn't sound very hopeful, if your diagnosis is correct!
I'm out of obvious ideas.. It's Just THIS lens? I missed the part about where you had it serviced before. What was done? Perhaps an element didn't get fully seated.



04-12-2010, 07:42 AM   #9
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QuoteOriginally posted by JeffJS Quote
I'm out of obvious ideas.. It's Just THIS lens? I missed the part about where you had it serviced before. What was done? Perhaps an element didn't get fully seated.

Yep it's just this lens - and this was why I had it serviced/'adjusted'. To no effect, obviously. It's weird - it focuses beautifully and sharply on relatively close subjects at f1.7. You have to get to at least f5.6 before it's even usable at long distances, so it obviously isn't focusing correctly. Stopping the lens down masks the effect through the larger DOF. As I said in another post I have other 50s, including an M1.7, so I do have a good basis for comparison! It's not an AF problem, as it focuses accurately even wide open at shorter distances. Surely if an element wasn't properly seated IQ would be messed up at all distances - one would think.
04-12-2010, 09:26 AM   #10
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My theory: if this lens is simply not adjusted for infinity focus, it should focus slightly closer than a properly adjusted lens. The ring turns the same amount, so affecting one end affects the other. The theory might not work for all lenses, but for the 50/1.7 lenses, the front and rear groups all move together when focusing.

I tested my theory by setting up an infinity-focusing M50/1.7 so it is focused at the minimum focus distance. Then I adjusted the lens so that it doesn't focus to infinity. The minimum focus distance became shorter.

Since the 50mm f1.7s are all supposed to share the same optic design, you can see if there is a difference in the minimum focus distance between your M and FA models. If the FA focuses closer and the M works at infinity, I think the FA is most likely still not adjusted for infinity focus.

I have no idea if the adjustment is the same or similar on the FA series.
04-12-2010, 10:22 AM   #11
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QuoteOriginally posted by timo Quote
Yep it's just this lens - and this was why I had it serviced/'adjusted'. To no effect, obviously. It's weird - it focuses beautifully and sharply on relatively close subjects at f1.7. You have to get to at least f5.6 before it's even usable at long distances, so it obviously isn't focusing correctly. Stopping the lens down masks the effect through the larger DOF. As I said in another post I have other 50s, including an M1.7, so I do have a good basis for comparison! It's not an AF problem, as it focuses accurately even wide open at shorter distances. Surely if an element wasn't properly seated IQ would be messed up at all distances - one would think.
The reason I went to the mis-seated element was that I once had an A28 f2.8 that behaved similarly. I took it apart to see why (and blow out the internal dust) and found that the front element wasn't pressed all the way into it's flange. It was parallel to the rest of the lens elements but was out Just far enough to affect focus. It worked perfectly afterward. Before that, stopping the lens down helped but wide open, it was difficult to get a good shot with it.

In need of a proper adjustment sounds more likely though. Perhaps your service person didn't do the job he said he did.

Good luck with it..
04-12-2010, 10:45 AM   #12
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QuoteOriginally posted by timo Quote
Thanks but .... the Katzeye screen on my K10D does not give accurate MF focusing indication - I have a replacement 'shim' set on order for that to be sorted out. One thing after another ...
Yea I was gonna say that- getting another focus screen can sometimes open up a whole new can of worms! I recently installed a K3 split screen and found that my K20D front-focussed significantly. A shim replacement was required in my case too, but now manual focussing exactly correlates with AF confirmation, and accurate catch-in focus with MF lenses is now a piece of cake.

Sorry, didn't mean to thread-jack!
04-12-2010, 11:28 AM   #13
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some photos would help. please post the whole images and some crops as well. also indicate f-stops.
04-12-2010, 03:33 PM   #14
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If the camera tried to turn the lens even if it hits infinity, the lens is unable to focus at infinity. To adjust the lens for this issue, remove the retaining ring from the front using a piece of thick rubber, then the 3 screws and the filter ring. 3 tiny screws should expose and they are responsible for the focus adjustment. Loose them slightly (don't extract them), adjust the focus, then tighten. Threadlock is needed btw. You will need a #00 screwdriver for the job (or JIS 1.4 or 1.7mm). Good luck.
04-12-2010, 04:34 PM   #15
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OP, you mentioned that you had sent the lens to be serviced.
However a proper service also means having the lens collimated to ensure infinity focus. Unfortunately not all repair shops may have an optical collimator on hand. That is why opening up any lens runs the risk of such issues unless one has the correct tools. This is such a common problem because a lot of people think "opening up a lens, well there's nothing to it."
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