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09-09-2013, 02:46 AM   #1
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focus issue with Pentax-FA 1:2.8 28mm SOFT lens

Hi - my first post here!

A friend of mine recently bought the (quite rare) Pentax-FA 1:2.8 28mm SOFT lens.
It looks in excellent condition and, using it manually, the focus rings turns smoothly all the way to infinity.
However, when set to infinity, the lens is actually only focused at about 1 meter.
This has been confirmed on a couple of Pentax manual focus cameras (KX and MX) where all other
lenses focus to infinity without any problem - so it is definitely an issue with this lens only.

Does anyone have any idea what's going on here? Could it possibly be that this lens is deliberately
designed this way? But if so, why does the lens have a focus scale that indicates right up to infinity?
(I have the 85mm f2.2 soft and that doesn't even have a focus scale!)

If anyone out there has this lens, could you maybe check yours out and tell me if it is like this one
or whether you can actually focus it manually to infinity?

Thanks.

09-09-2013, 05:21 AM   #2
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I have no experience with that lens, but most of my manual lenses require that I refocus a tiny bit shorter when set to infinity.
09-09-2013, 06:37 AM   #3
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i think the lens has been opened (maybe for repair ? ) and the ring with the distance ring hasn't been replaced well.

just check if the focus actually change, as you move the focusing ring.

If it's the case, then go to a repair shop. What is your country ? maybe some members can advise you a shop in particular.
09-09-2013, 02:03 PM   #4
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Thanks for your replies.

There is no sign of this lens having been opened or tampered with at all.
It was just sent from Japan to my friend here in England but was very well packed and protected, and has no sign at all of any damage.

The focus ring seems to work perfectly and feels fine when you turn it - the only problem is that it will focus up to but not past about 1 meter (set to infinity and on a manual focus camera - I don't have an autofocus one), even though the ring turns all the way to the infinity end of the scale.

Before I send it for repair, I want to be absolutely certain that this is a fault. Soft lenses are obviously rather unlike most other lenses in design and it's very hard to get information on this particular one, which is even more unusual in being wide-angle. (Most soft lenses are in the 85-135mm range, designed for portraiture.) Is it possible this lens is designed like this? Or that it's not but came out of the factory faulty but the previous owner didn't notice? That it was damaged in transit from Japan? That someone deliberately modified it to change the focus (unlikely, surely?)? That someone opened it for some other reason (also seems unlikely because the lens looks virtually unused and the screws look pristine)?

If there is just one other person out there with a copy of this lens, they should be able to tell me all I need to know!

09-09-2013, 03:41 PM   #5
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QuoteOriginally posted by paulmdt Quote
The focus ring seems to work perfectly and feels fine when you turn it - the only problem is that it will focus up to but not past about 1 meter (set to infinity and on a manual focus camera - I don't have an autofocus one), even though the ring turns all the way to the infinity end of the scale.
I have open a bunch of lens to repair it, so let me explain this :

First : The lens focus by a simple mecanisme : some piece of glass move, some other don't. To move some piece, you just move one barrel into another by screwing-unscrewing it.

Then : The two barrels are design in order to be assembled by screwing the first into the second, like a simple mecano game.

Third : There is by design one stop (to make sure you can screw the barrels into the other so far that they separate), the other stop, to prevent the complete unscrewing is made during the assembly.

Four : If you miss something while you assemble the lens (like a complete rotation of one barrel into the other), you make the focus scale useless : either the lens while focus to close and won't go to infinity (your case), or the lens will focus after infinity and not at it's closest distance possible.

And i think that is what happened : when you focus at the infinity the groupe of lens should arrive right at the border of the lens mount



(and when you focus closer the glass go further away from the lens mount)


but your lens was badly reassembled and the groupe of glass don't come close enought of the mount.

does that make any sense ?

Last edited by aurele; 09-09-2013 at 03:46 PM.
09-09-2013, 11:48 PM   #6
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QuoteOriginally posted by aurele Quote
I have open a bunch of lens to repair it, so let me explain this :

First : The lens focus by a simple mecanisme : some piece of glass move, some other don't. To move some piece, you just move one barrel into another by screwing-unscrewing it.

Then : The two barrels are design in order to be assembled by screwing the first into the second, like a simple mecano game.

Third : There is by design one stop (to make sure you can screw the barrels into the other so far that they separate), the other stop, to prevent the complete unscrewing is made during the assembly.

Four : If you miss something while you assemble the lens (like a complete rotation of one barrel into the other), you make the focus scale useless : either the lens while focus to close and won't go to infinity (your case), or the lens will focus after infinity and not at it's closest distance possible.

And i think that is what happened : when you focus at the infinity the groupe of lens should arrive right at the border of the lens mount



(and when you focus closer the glass go further away from the lens mount)


but your lens was badly reassembled and the groupe of glass don't come close enought of the mount.

does that make any sense ?
Thanks again, aurele.

So you think there is a fault and someone opened this lens for some reason (why would they do that, I wonder?). You don't think this lens would have left the factory like this - and also that this isn't something that could happen by accident, without the lens being opened? Another thing that surprised me was how "big" this error is: although it is a wide angle lens, 1m and infinity are a long way apart on the focusing ring - so maybe the (re)assembly was "out" by a complete rotation (as you say).

(By the way, one thing I noticed as soon as I first saw this lens was that the infinity "stop" was not quite in line with the middle of the infinity sign (as it is on all my other, older Pentax lenses) - but slightly to the left of centre.)

So, it looks like I need to find someone who can fix this lens. The last time I was in a similar situation (with a Vivitar/Kiron 70-150mm zoom that wouldn't quite focus to infinity - but by a much smaller amount than with this soft lens) the person who attempted to repair the lens completely ruined it - so this time (with this much rarer and more expensive lens that belongs to a friend) I need to find someone I can trust, who knows exactly what they're doing.
09-10-2013, 01:13 AM   #7
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QuoteOriginally posted by paulmdt Quote
So you think there is a fault and someone opened this lens for some reason
No, i think, the lens is fine, but the one who opened it, re-assembled it like an ... idiot to be polite.

QuoteOriginally posted by paulmdt Quote
You don't think this lens would have left the factory like this - and also that this isn't something that could happen by accident, without the lens being opened?
No chance at all.

QuoteOriginally posted by paulmdt Quote
By the way, one thing I noticed as soon as I first saw this lens was that the infinity "stop" was not quite in line with the middle of the infinity sign (as it is on all my other, older Pentax lenses) - but slightly to the left of centre.
usually a good clue someone mess with it in the past.

QuoteOriginally posted by paulmdt Quote
So, it looks like I need to find someone who can fix this lens. The last time I was in a similar situation (with a Vivitar/Kiron 70-150mm zoom that wouldn't quite focus to infinity - but by a much smaller amount than with this soft lens) the person who attempted to repair the lens completely ruined it - so this time (with this much rarer and more expensive lens that belongs to a friend) I need to find someone I can trust, who knows exactly what they're doing.
There is no need to torn appart the whole lens to correct this.

usually it goes that way :

1/ unscrew the front plate by rotating it (tricky as you have to don't scratch the front element)

2/ the two barrels can be unscrew without limit in one direction.

3/ unscrew the mount (be carreful to not loose any piece or screw)

4/ probably have to remove the aperture ring.

5/ there it is usually. there is a piece in L or T shape, that screw in one of the barrel, and bloc the other. On the A 50/1.7 there is 2 places where you can put it : one mess the focusing, the other not. So in your case, just change the place (but be sure you don't need to rotate half or completely the barrel).

6/ just check with the distance scale, it's Ok or not.

7/ re-assemble.
(No need to disassemble any piece of glass)

I suggest you to ask for some "agreed repair shop", so go have a look on the pentax website, there is probably a list of the main repair shop for UK.

Contact them by mail to know the price.
09-11-2013, 12:01 AM   #8
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Thanks again for your reply, aurele - very helpful.

Re 6/: Isn't it necessary to check the focus of the lens on a camera after it's been adjusted? The distance scale is only "out" by about 1mm (at the infinity stop) but the focus is a long way out when the lens is set to infinity (focuses at 1 meter). So isn't it a question of adjusting the lens, reassembling, remounting on the camera, checking it focuses to infinity (but not beyond), then (if it doesn't) starting all over again, readjusting ... trial and error?

And why was this lens taken apart by someone, I wonder? A repair? To correct a fault? Curiosity? (It certainly is an unusual lens. Perhaps another lens maker was interested in its design?!) Or could it be they wanted it to focus a bit closer for some reason (unlikely?)? Or make some other kind of modification? It seems a strange thing for someone to do to a relatively rare, modern lens that appears to be in excellent condition.

09-11-2013, 11:59 AM   #9
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i bet the opening was because one of the inner element was durty or with some fungus (easy to clean with appropriate liquids).

There is usually no need for a lot of trial and error, as there is not a lot of combo possible.

Just, check with the lens around f5.6 to make sure what you consider as a faulty focus distance ajustement is not the soft focus effect (Yeah, seems completely dumb to say, but try anyway. It would be sad that you pay for a service and the shop answer back saying everything fine )

Did you check the pentax website for the repair shop ?
09-13-2013, 11:26 AM   #10
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Thanks again, aurele.

As you can imagine, we checked this lens very thoroughly (on two cameras) - we really didn't want to believe there was something wrong with it. But I've had quite a lot of experience with the Pentax 85mm f2.2 Soft, and I know that in the middle of the image it's actually pretty sharp. I imagine it's similar with the 28mm, and with the split-image rangefinder there really was no doubt that it was focused at 1 meter when it was set on infinity.

Since my last post, I contacted the seller (in Japan) and told him the problem. He was very apologetic and immediately offered a generous partial refund - hopefully enough to pay for the repair. The fact that he didn't ask any questions makes me wonder if he maybe opened the lens himself (to clean it, perhaps) and then didn't put it back together again properly. But maybe it just didn't occur to him that the focus was something that needed checking.

I did look at the Ricoh/Pentax UK website and they just recommend their own business, but I'll probably use another well-known, widely recommended Pentax camera and lens repairer instead. Ideally I'd like to take the lens there, hang around somewhere while he does the repair, then check it before I leave - but that might not be very easy to arrange.
09-14-2013, 12:27 AM   #11
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seems, you've done your homework !

for the repair, as you know 100% of the lotery winner have played the lotterie, so ask the shop and you'll.
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