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03-25-2010, 01:02 PM   #1
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DA* 300mm Aperature blades misaligned

I took out my DA*300 for the first time in a while to do some test shots of it coupled to an extension tube set I recently bought, but before I used the lens I noticed that the aperture hole was not a perfect octagonal shape. I did some test shots with it and the blades don't seem to stick or anything, they seem perfectly functional but three of the blades seem to be misaligned or dislodged.. not really sure how to explain it. Even at wider apertures the octagonal hole is "oblong", here's some photos to explain better:









I treat this lens with the utmost care ($1200 lens!!!) and has never been dropped. The only thing I can think of is maybe the sling bag it was in was bumped.

In any case, I'm going to send it off to Pentax for repair, it still has two months warranty left but not sure if this will be covered. Does anyone know if it's a simple fix or am I going to have to shell out half of it's cost for repair? Has this happened to anyone else?


Last edited by Roland303; 03-25-2010 at 01:28 PM.
03-25-2010, 02:05 PM   #2
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can't say i have seen this on a pentax lens but many third party lenses (especially older ones) do not uniformly close down the aperture but go to a distorted shape when they get down to F22 and smaller.

What does it look like at F8 and F16, It might just be tolorances
03-25-2010, 02:38 PM   #3
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Mine isn't totally regular either, but not as ugly as your's ;-). When the diafragm isn't totally closed the effect will be minor, but anycase, it should be a reason to get it improved by Pentax. Seems strange too how much some of the blades elevate above the level of the rest.
Cheers - Klaus
03-25-2010, 03:44 PM   #4
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All imho, kindly ignore if I am wrong or misinformed.

A small misalignment is one thing, but those three blades are crossed. The blade tips should be all on the one side, each overlapping the next. Those three are overlapping in the wrong direction.

um, I do not have that much experience with this issue, but maybe they've been damaged now that they have been stopped down with the three on the wrong side? Probably not if they smoothly stop down. I don't seen any damage except for the "elevation" which may only be there because the blades are designed that way, and they're free now?

I once had a A50/1.4 that was slightly misaligned but didn't impact photos (not completely octo stopped down) but all blades were overlapping properly you see.

Warning, research this problem or document your use of the lense before you send it in? if the mechanism has been designed so that crossed/wrongly overlapping blades can't happen, then they may claim that the lense has been badly knocked or opened before and badly cleaned/repaired.

EDIT: Looking at my own lenses, I do not think this can happen from a knock or drop. If you've had it cleaned, maybe they didn't put it back together properly. If it is 2nd hand then I would postulate that it has been opened before. If bought new, then factory mistake?

That really really sucks. Fingers crossed that it is a painless procedure with pentax. They've been great to me before regarding a grip I had a problem with. Goodluck


Last edited by cps_goodbuy; 03-25-2010 at 03:50 PM.
03-25-2010, 03:56 PM   #5
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. . . running to look at my lens . . . :Yikes:
03-25-2010, 04:45 PM   #6
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Thanks for the replies so far:

Lowell Goudge and Klaus: yes, I also have a couple of old lenses where at small apertures the blades don't seem to make a perfect octagon/hexagon, but in this case it was even more than what I've experienced with other lenses.

cps_goodbuy: exactly. The blade adjacent counterclockwise should overlap the top part of the blade before it, which it seems in this case the three have somehow "sprung" out.

At larger apertures the effect is less pronounced. At f/5.6 or f/6.7 one or two of the blade tips poke a little further out into the open aperture. Looking at test shots there is no effect on image quality other than out of focus point light sources having a peculiar shape. Still, this is really bothering me and I'm afraid that the blades will be further damaged if it keeps being used.

Here's one more picture to show that it doesn't close uniformly and shows the three misaligned blades:

03-26-2010, 10:13 AM   #7
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The exact shape is not always regular, but the blades should never be loose enough to become "unwoven" like that. In lenses I've worked on, a single part fits on top of the stack of blades and keeps them from doing this. That part must have moved. Eventually you could have just a pile of loose blades in there.
03-26-2010, 01:56 PM   #8
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I have now dismantled (and sucessfully reasembled) a couple of dozen aperture mechanisms but have not seen one like this (except when I tried to resemble one under the influence of alcohol). If the ring which retains the blades was lose enough to allow them to move out of position like this then they would all have dropped out or jammed by now and if you had knocked the lens hard enough to do this then some or all of the glass ould have broken. I do not believe that this could have happened any time except during assembly (maby someone on the production line had a liquid lunch...). If it is under warrenty I would send it back for repair / replacement as it looks like a manufacturing fault.

03-26-2010, 03:21 PM   #9
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QuoteOriginally posted by Just1MoreDave Quote
The exact shape is not always regular
This is good to know. I looked at my lenses and both of my DA* (the 55 and 16-50) have an irregular shape when closed all the way down like the OP. My DA L 50-200 does not though.

I did notice that my aperture blades are not misaligned like the OP's. I would definitely send it in for repair.
03-26-2010, 04:08 PM   #10
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My DA300 was irregular when stopped down also, though not near as bad. I seem to remember a thread on it a long time ago. I would send it in to get looked at if it was mine.
03-26-2010, 05:10 PM   #11
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Somebody was being sloppy along the assembling line. Irregular aperture stop down is not uncommon with modern Pentax lenses, but yours a manufacturing flaw, an human error during assembling (the tips of 3 blades being on the wrong side). My FA43 & 77 had irregular stop down too but they could be much improved by rearranging the blades. The mechanisms were kind of loose and took some patience to sort out the best arrangements, but it could be done. Factory workers however, working within very tight time frame might have to make some sacrifice.
03-26-2010, 05:19 PM   #12
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if this is indeed a manufacturing fault, then the problem has always been there, yes? I wonder why you just noticed? spending too much time looking at your equipment instead of using it? I do know, like others have stated, that irregular aperture shape can be something that happens. I have lenses both old and new that exhibit this, in both longer and shorter focal lengths. but yes, the blades in your lens seem to be in a bit of a funk there. I wonder though, if it has been operating fine so far, and has always been this way.. is it worth it to even get repaired? will the current state of the blades cause any further problems? or are you just worried about the more than normal irregular shape that it causes?

I guess under warranty, it would be wise to send it off.
03-26-2010, 07:33 PM   #13
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QuoteOriginally posted by MattGunn Quote
... I do not believe that this could have happened any time except during assembly (maybe someone on the production line had a liquid lunch...).
I often wonder how anyone could do that as a job on a schedule. I don't think I'd make it to lunch on the first day.
03-26-2010, 09:11 PM   #14
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QuoteOriginally posted by séamuis Quote
if this is indeed a manufacturing fault, then the problem has always been there, yes? I wonder why you just noticed? spending too much time looking at your equipment instead of using it?
Haha! C'mon, you don't admire your DA*/DA Ltd lenses like if they were your new born? Sad thing is that I haven't used it enough to feel justified sending it off for repairs. I noticed the problem the other day when I wanted to try the lens out with a recently acquired extension tube set. I have admired and drooled over the lens before and not noticed this problem then.


QuoteOriginally posted by séamuis Quote
I wonder though, if it has been operating fine so far, and has always been this way.. is it worth it to even get repaired? will the current state of the blades cause any further problems? or are you just worried about the more than normal irregular shape that it causes?

I guess under warranty, it would be wise to send it off.
Well, as another poster has said: if something was dislodged that holds the blades in place, further use might cause more of the blades to go out of whack. I don't want the risk of damaging it further. Tilting the lens up or down shows those three blades moving away from the rest of the group, so they are definitely loose even though they still open and close fine.

I'm just as stumped as the rest of you as to how this could happen. If it were a jarring jolt (which I'd definitely remember) I'm surprised nothing else was broken.. and yes, the SDM works fine

Pentax replied to my email within 2 hours and it's off for repairs now. Luckily I still have 2 months warranty left, should it fall under a warranty repair. Otherwise I hope it won't be too expensive to fix. I need this lens quick as spring is approaching!!
03-27-2010, 04:58 AM   #15
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QuoteQuote:
Haha! C'mon, you don't admire your DA*/DA Ltd lenses like if they were your new born?
I dont own any. but I see your point. I hope it gets a speedy service and back to you in short order.
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