P6x7 lenses - how 'snappy' do the aperture blades have to be?

johnha · 03-12-2018, 05:42 AM

Hi All,

I've just acquired a 6x7 S-M-C-Tak 135/4 macro lens, although described as having a 'snappy' aperture, it isn't as snappy as my other lenses (possibly a couple of visible spots of wear/oil on the blades). I have no doubt it should be snappier (the blades can be seen moving - it's not instantaneous), but for the price I paid and considering the age of the lens I'm tempted to keep it (my second body only meters stopped-down anyway). So the question is, what problems might I expect?

I can't seem to work out whether the camera holds the aperture open (letting the spring close it before exposure) or drives it closed (letting the spring open it after exposure)?

Regards,

John.

MysteryOnion · 03-12-2018, 06:04 AM

I've had a few sluggish apertures and I've tended to slide the lever to the "MAN" or manual position prior to making my shot.
Depending on reason for the oil, either someone oiled it up or it was due to age, the oil could badly coat the elements adjacent to the aperture.
If you see oil on the extended barrel, then it might be a good idea to store the lens front facing down to reduce future intrusion of oil.
It would be get to have it cleaned.
I too acquired a 135 with oil issues a few years ago and I would think it condition was due to the lens being stored in a very hot situation prior to my ownership.
The clues are the helical grease being very stiff and paste like consistency (more as a semi-dried paint) as well as oily conditions in all areas from body of the barrel to aperture cup/carrier.
It was a pain to clean it all out...major disassembly to reach all parts and not for novice tinkerers.

LaHo · 03-12-2018, 06:11 AM

Hi John,

I have just such a lens - the S-M-C Takumar 6x7 135mm/4.0 - with the same problem. As you normally focus and measure the exposure (with a TTL prism) with fully open aperture even if the aperture ring is set at a smaller aperture, the camera closes the aperture blades when you press the shutter release. With oily shutter blades the blades will not be snappy when opening afterwards. As the P6x7 does not have a motor drive, this is of little concern. The images I have taken with my lens with far from snappy aperture blades have been perfectly OK.

Camera: Pentax 67 II
Lens: S-M-C Pentax 6x7 135mm F4.0 and K2 yellow filter
Exposure: 1/350 @ F6.7
Film: Rollei RPX 400 dev. in D-76 1+1 in the Jobo ATL-1500 film processor

Bob L · 03-12-2018, 03:41 PM

If there's going to be club for folks with sluggishly apertured 135/4's then I'm also qualified to join. The blades on mine move very slowly but so smoothly that one could imagine some sort pneumatic damping is responsible......works fine via an adapter on my Z though.

Bob

Last edited by Bob L; 03-13-2018 at 12:47 AM.

sbjornda · 03-12-2018, 06:16 PM

Originally posted by johnha

Hi All,

I've just acquired a 6x7 S-M-C-Tak 135/4 macro lens, although described as having a 'snappy' aperture, it isn't as snappy as my other lenses (possibly a couple of visible spots of wear/oil on the blades). I have no doubt it should be snappier (the blades can be seen moving - it's not instantaneous), but for the price I paid and considering the age of the lens I'm tempted to keep it (my second body only meters stopped-down anyway). So the question is, what problems might I expect?

I can't seem to work out whether the camera holds the aperture open (letting the spring close it before exposure) or drives it closed (letting the spring open it after exposure)?

Regards,

John.

I had one of those sluggish 135/4's as well. I had it CLAd but it didn't help - I suspect it was a weak spring, not oil on the blades. I finally sold it for pennies on the dollar and bought one in great condition.

If the aperture blades are slow to close, you risk over-exposure: The shutter will fire before the correct aperture is reached. This problem usually is irrelevant if you switch the lens to MAN before you fire, as MysteryOnion says. As well, the MLU will close the aperture in advance. And if you're planning to shoot wide open it will be irrelevant. So there are several shooting situations where sluggish stop-down won't matter. But if you want increased depth of field and you don't want to take the time to switch to MAN or to trigger MLU, it's best to give up on this copy of the lens and to try another sample.

Regards,
Sterling

Theov39 · 03-12-2018, 07:15 PM

I have a Pentax SMC AF 18-135 lens that seems to have sluggish aperture blades but it appears that the aperture level on the lens is getting stuck rather than the blades. It doesn't close all the way to the smallest aperture (eg f/22). Is this a problem or ONLY a problem if you want to shoot at the smallest aperture?

johnha · 03-14-2018, 05:37 AM

Thanks for the replies. I'll probably keep it (it wasn't expensive) and see how it goes. It is interesting to see so many examples of the 135/4 with similar problems.

K mount note: My K mount M35/2.8 has a similar problem, this seems OK on film bodies but when using Green button metering on my K-5, it doesn't stop down fully before the meter reading is taken (using the DoF stop-down position around the release button helps though).

03-12-2018, 05:42 AM	#1
johnha Veteran Member Join Date: Apr 2012 Location: Lancashire, UK Photos: Albums Posts: 1,155	P6x7 lenses - how 'snappy' do the aperture blades have to be? Hi All, I've just acquired a 6x7 S-M-C-Tak 135/4 macro lens, although described as having a 'snappy' aperture, it isn't as snappy as my other lenses (possibly a couple of visible spots of wear/oil on the blades). I have no doubt it should be snappier (the blades can be seen moving - it's not instantaneous), but for the price I paid and considering the age of the lens I'm tempted to keep it (my second body only meters stopped-down anyway). So the question is, what problems might I expect? I can't seem to work out whether the camera holds the aperture open (letting the spring close it before exposure) or drives it closed (letting the spring open it after exposure)? Regards, John.

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03-12-2018, 06:04 AM	#2
MysteryOnion Giveaway winner! Join Date: Dec 2007 Location: beantown Photos: Albums Posts: 944	I've had a few sluggish apertures and I've tended to slide the lever to the "MAN" or manual position prior to making my shot. Depending on reason for the oil, either someone oiled it up or it was due to age, the oil could badly coat the elements adjacent to the aperture. If you see oil on the extended barrel, then it might be a good idea to store the lens front facing down to reduce future intrusion of oil. It would be get to have it cleaned. I too acquired a 135 with oil issues a few years ago and I would think it condition was due to the lens being stored in a very hot situation prior to my ownership. The clues are the helical grease being very stiff and paste like consistency (more as a semi-dried paint) as well as oily conditions in all areas from body of the barrel to aperture cup/carrier. It was a pain to clean it all out...major disassembly to reach all parts and not for novice tinkerers.

03-12-2018, 06:11 AM	#3
LaHo Pentaxian Join Date: Mar 2007 Location: Greater Copenhagen Area Photos: Gallery \| Albums Posts: 430	Hi John, I have just such a lens - the S-M-C Takumar 6x7 135mm/4.0 - with the same problem. As you normally focus and measure the exposure (with a TTL prism) with fully open aperture even if the aperture ring is set at a smaller aperture, the camera closes the aperture blades when you press the shutter release. With oily shutter blades the blades will not be snappy when opening afterwards. As the P6x7 does not have a motor drive, this is of little concern. The images I have taken with my lens with far from snappy aperture blades have been perfectly OK. Camera: Pentax 67 II Lens: S-M-C Pentax 6x7 135mm F4.0 and K2 yellow filter Exposure: 1/350 @ F6.7 Film: Rollei RPX 400 dev. in D-76 1+1 in the Jobo ATL-1500 film processor

03-12-2018, 03:41 PM	#4
Bob L Senior Member Join Date: Mar 2016 Location: La Vienne (86), France Posts: 223	If there's going to be club for folks with sluggishly apertured 135/4's then I'm also qualified to join. The blades on mine move very slowly but so smoothly that one could imagine some sort pneumatic damping is responsible......works fine via an adapter on my Z though. Bob Last edited by Bob L; 03-13-2018 at 12:47 AM.

03-12-2018, 06:16 PM	#5
sbjornda Junior Member Join Date: May 2011 Posts: 33	Originally posted by johnha Hi All, I've just acquired a 6x7 S-M-C-Tak 135/4 macro lens, although described as having a 'snappy' aperture, it isn't as snappy as my other lenses (possibly a couple of visible spots of wear/oil on the blades). I have no doubt it should be snappier (the blades can be seen moving - it's not instantaneous), but for the price I paid and considering the age of the lens I'm tempted to keep it (my second body only meters stopped-down anyway). So the question is, what problems might I expect? I can't seem to work out whether the camera holds the aperture open (letting the spring close it before exposure) or drives it closed (letting the spring open it after exposure)? Regards, John. I had one of those sluggish 135/4's as well. I had it CLAd but it didn't help - I suspect it was a weak spring, not oil on the blades. I finally sold it for pennies on the dollar and bought one in great condition. If the aperture blades are slow to close, you risk over-exposure: The shutter will fire before the correct aperture is reached. This problem usually is irrelevant if you switch the lens to MAN before you fire, as MysteryOnion says. As well, the MLU will close the aperture in advance. And if you're planning to shoot wide open it will be irrelevant. So there are several shooting situations where sluggish stop-down won't matter. But if you want increased depth of field and you don't want to take the time to switch to MAN or to trigger MLU, it's best to give up on this copy of the lens and to try another sample. Regards, Sterling

03-12-2018, 07:15 PM	#6
Theov39 Pentaxian Join Date: Nov 2015 Location: Sydney Posts: 594	I have a Pentax SMC AF 18-135 lens that seems to have sluggish aperture blades but it appears that the aperture level on the lens is getting stuck rather than the blades. It doesn't close all the way to the smallest aperture (eg f/22). Is this a problem or ONLY a problem if you want to shoot at the smallest aperture?

03-14-2018, 05:37 AM	#7
johnha Veteran Member Join Date: Apr 2012 Location: Lancashire, UK Photos: Albums Posts: 1,155 Original Poster	Thanks for the replies. I'll probably keep it (it wasn't expensive) and see how it goes. It is interesting to see so many examples of the 135/4 with similar problems. K mount note: My K mount M35/2.8 has a similar problem, this seems OK on film bodies but when using Green button metering on my K-5, it doesn't stop down fully before the meter reading is taken (using the DoF stop-down position around the release button helps though).