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02-06-2019, 10:11 AM   #1
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Slightly visible blades at widest aperture

Hi,

Recently I have fixed solenoid in my k-50 following this and I wonder what will happen when the "metal A" part is too short? Does camera will set aperture wrong, e.g. camera show F8.0 and real is wider/narrower. I have SMC Pentax-DA L 18-55mm F3.5-5.6 AL WR and on F3.5 I can slightly see aperture blades. Is this normal?

Greetings!

02-06-2019, 10:37 AM   #2
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You shouldn't see the apertureblades wide open.
02-06-2019, 10:54 AM   #3
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The aperture mechanism is a switch (relay). If the blades are visible on the lens at 18mm then I believe this is normal. Even if it's not normal then it is still a lens issue, nothing to do with the camera.
02-06-2019, 11:47 AM   #4
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I don't see any part of the aperture blades on my 18-55 when it's mounted. If I set the aperture at f4 @ 18mm or f6.3 at 55mm and use the DOF preview, I can see the blades.

You can check the lens off camera by moving the lever.

Some fixed-aperture zoom lenses have visible blades at one end of the zoom range. They are supposed to be like that. In my experience, all other K-mount lenses should fully open the blades on the camera.

02-06-2019, 12:05 PM   #5
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For some zoom lenses, it is normal to see blades slightly closed at widest aperture at certain focal length setting. This has been discussed before at this forums. I have found quite a few lenses like this. For example, FA 28-105mm Power Zoom, 645 FA 55-110mm Zoom, etc. This being said, I have no experience with your specific lens 18-55mm.
02-06-2019, 12:33 PM   #6
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QuoteOriginally posted by olm Quote
Hi,

Recently I have fixed solenoid in my k-50 following this and I wonder what will happen when the "metal A" part is too short? Does camera will set aperture wrong, e.g. camera show F8.0 and real is wider/narrower. I have SMC Pentax-DA L 18-55mm F3.5-5.6 AL WR and on F3.5 I can slightly see aperture blades. Is this normal?

Greetings!
It's normal unless you are getting exposure issues. Sometimes the aperture blades have to close down a bit to keep the effective aperture consistent, though this mostly occurs on fixed-aperture zooms.

Adam
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02-06-2019, 12:38 PM   #7
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With a variable aperture zoom (two wide open speeds specified) the aperture normally opens completely with no visible blades.

The aperture lever on the lens may be bent or blocked.

Try moving the lever on lens with the lens dismounted as Just1MoreDave suggests.
02-06-2019, 12:49 PM   #8
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QuoteOriginally posted by Not a Number Quote
With a variable aperture zoom (two wide open speeds specified) the aperture normally opens completely with no visible blades.

The aperture lever on the lens may be bent or blocked.

Try moving the lever on lens with the lens dismounted as Just1MoreDave suggests.
This!

On some fixed aperture lenses I can see this as mentioned by Adam. I haven't seen it on variable aperture but apparently this isn't unheard of per the earlier messages in the thread. I no longer own a DA 18-55 so I can't test this myself. The off camera testing of the aperture lever on the lens seems the best idea.

02-06-2019, 01:12 PM   #9
olm
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Lever is fine. I need to specify that in mounted lens i don't see blades, but when i press the shutter (F3.5, 18mm and 1s to have time to look) aperture blades closes slightly, making ring thin like single hair. A second ago i tested my k-50 with this https://www.dpreview.com/forums/thread/4221791
and using optical preview at F3.5 has no effect, but making photo still cause thin ring as i mentioned.

Last edited by olm; 02-06-2019 at 01:24 PM.
02-06-2019, 01:56 PM   #10
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any other lenses?
02-06-2019, 05:56 PM   #11
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Do you have another lens to test it with?

How was the camera repaired? DIY or sent off somewhere?
02-06-2019, 10:58 PM   #12
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I also have SMC Pentax-DA L 50-200mm F4-5.6 ED WR.
On both lenses sometimes blades are visible at widest aperture, sometimes not.

First post has link to video which i followed during DIY repair.

Last edited by olm; 02-06-2019 at 11:06 PM.
02-07-2019, 01:59 AM   #13
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Since it was a DIY repair all bets are off as to what the problem could be, but most likely it is in the camera if both lenses display the behavior. Even worse is that it is intermittent.

If you look at the service manuals for the *stD and K100D series (available on the Pentax Hack website) there are close to three pages devoted to the aperture control block. Work on this involves proper positioning of the timing gears and specific sequences of events. If you happened to move the gears or the gears and levers weren't set in the proper sequence to begin with operation of the diaphragm and mirror could be off.

Filing and sanding the metal parts near the open camera as shown in the video probably isn't great idea with possibility of the metal shavings or grit getting into the camera.
02-08-2019, 01:17 AM   #14
olm
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I just wanted to know it is how this lenses works or it is due solenoid DIY repair. It's over a month since repairing and i can tell that this malfunction has no effect whatsoever, camera always takes well-exposed photos.

Thanks for help!
02-08-2019, 06:19 AM   #15
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If the wide open shots are off by 1/3 stop you probably won't notice it unless you compare histograms with the same shot at smaller apertures. Within 1/3 a stop is good enough in my book
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