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06-14-2012, 03:32 AM   #1
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M85 f2+K-5 Overexposure Issue @ >f5

So here's the story and I'm hoping someone has a solution.

*** I've thoroughly read the guide on how to use stop-down metering with M-series lenses and relatively speaking, I've figured it out.***

Here's the issue- up to about f5, the cam slightly underexposes with the M85, but only -0.3, which I normally use anyhow, so it's no real issue. However, at roughly F5 (my aperture ring no longer has detents, so it's infinitely variable), there's an extremely razor-sharp line between a normal, usable exposure and several stops worth of over exposure. At roughly below F5, I'll have 1/4 shutter, as an example. A fraction of a degree more on the aperture dial smaller, it suddenly bumps to 0.4 and just continues. I just tried it under different conditions and it went from 1/250 to 1/40 in that tiny span. I've confirmed that the aperture blades aren't making a jump independent of the ring, thus messing up values.

Has anyone had experience with this and is this something I should just live with, or is there a technique to work around this?

Additionally, my understanding, and according to the instructions, is that the cam automatically goes into center spot metering when an M-lens is used, though, oddly, when I change the metering type, I come up with different values (which are overexposure values, too).

Overall, the lens is wonderful, but manual shooting on a pentax is not straight-forward. With my old Olympus, I would just observe the full-time displayed ev meter, set aperture and shutter accordingly, focus and shoot. Very easy.

06-14-2012, 03:59 AM   #2
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In many cases people shoot in AV mode with manual lenses - I only shoot them in Manual mode and use the green button to get me in the ball park for exposure. From there I adjust it - set it and forget it. If you are in AV mode, your cam doesn't know the aperture and assumes it is wide open.

In times like this its always helpful to

1) Post some pics with EXIF.
2) Its often what you are pointing it at that causes over/under exposures. Keep the scene in mind.
3) Chimp

A tip from another forum member suggests Set EV steps to 1/2 - the lens is in 1/2 stop adjustments.

I'm loving my recently acquired M85/2
06-14-2012, 06:17 AM   #3
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first of all, you need to understand that digital cameras are not perfect when it comes to metering on legacy lenses.

you may or may not be aware of this chart. I post it often, to show how ill mannered legacy lenses can be on digital cameras



your problem though, sounds worse, and may be more lens related than the camera.

the aperture setting should not impact exposure on the K5 as greatly as you desctribe, but if you look at the graph, faster than F4-5.6 will tendf to under expose and above this will over expose

the K5 should keep you always within a stop of correct exposure. The deffictive aperture ring, missing stops could be the issue, because you have no idea whether it moves or not either during exposure or during the stopped down metering process or both.

if the camera is consistent where you have solid aperture detents, it sounds as if the aperture ring is moving as you go, where there are no detents.

also, you are describing the shutter speed jumping for small adjustments, are you doing green button metering? that is how it is done for an M series lens. You should not see the shutter speed change AT ALL as you change the aperture ring, unless the lens has had the aperture activation lever removed and you are metering in AV mode.
06-14-2012, 08:10 AM   #4
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The shutter speed is not jumping on its own. It only jumps after changing the aperture setting, then hitting the green button, as instructed. The procedure is correct and brings up good results until that f5 point. Now, here's the oddity: The lens came with an old, Asahi filter on it. It's SMC coated and it's spherical. I've removed it since experimenting and it seems a bit of the exposure issue is gone and more manageable, though the bad behavior in some cases is there with this lens. Oh yeah, the ring is not drifting on its own. the only range where it has a slight drift is at f2 during the stop-down metering procedure. It drifts a minute amount, since I greased it and this movement actually seems inconsequential, as this range is not in the least bit problematic. If anything, the drift there might be f2 to 2.1, at most. Regardless, I'll keep pushing on, as I think this lens is in good shape, mechanically ok, despite the ring with no detents, but has quirks. So far, several shots from it are beautiful. I simply need to learn how this lens and cam combo behave together. Edit: more testing reveals that this filter might be the culprit and the gap has certainly narrowed to the usable and predictable range.. A shame, since it seems to be quite nice and solidly built, along with the spherical lens. Edit again, the filter helps little, actually. It seems highly dependent on conditions, but definitely, after f5, it overexposes. I'll chalk it up to the inherent characteristics of using a manual lens on these cameras. It is definitely not as easy as I hoped and experienced with Olympus and Konica lenses.


Last edited by snake; 06-14-2012 at 08:25 AM.
06-14-2012, 08:47 AM   #5
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Well, others seem to have better results using manual lenses, so your last statement definitely shows that it's a case of user error. Could you please post a video of the lens while you turn its aperture ring? I'd like to be sure that the aperture is actually closing linearly.
06-14-2012, 08:58 AM   #6
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QuoteOriginally posted by kcobain1992 Quote
Well, others seem to have better results using manual lenses, so your last statement definitely shows that it's a case of user error. Could you please post a video of the lens while you turn its aperture ring? I'd like to be sure that the aperture is actually closing linearly.
Never have I attributed it to anything but user error, mind you. If you look at my posts, I've done exactly the opposite and fairly explicitly. Even if the lens has quirks, it's a matter of me mastering it, which is why I'm here asking for tips and things I might have missed in the instructions or elsewhere. When I get a chance, I'll make a video and upload it.
06-14-2012, 09:06 AM   #7
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Yes, please do. And while you're at it, also try taking meter readings through live view, those should be 100% accurate. If the readings throught the viewfinder coincide with those through LV, it means it's the lens' fault for whatever happens past f/5. If not, I'd say it's a strange case of nonlinear metering with the K-5 focusing screen and this lens. By the way, if you're in Germany, you might check micro-tools, they have ball bearings so you can fix your detent-less M85
06-14-2012, 09:16 AM   #8
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QuoteOriginally posted by kcobain1992 Quote
Yes, please do. And while you're at it, also try taking meter readings through live view, those should be 100% accurate. If the readings throught the viewfinder coincide with those through LV, it means it's the lens' fault for whatever happens past f/5. If not, I'd say it's a strange case of nonlinear metering with the K-5 focusing screen and this lens. By the way, if you're in Germany, you might check micro-tools, they have ball bearings so you can fix your detent-less M85
That sounds like a good tip. As far as the ball bearing goes, I have the ball bearing. When I removed the ring, I saw it in its bore and it popped right out. There appears to have been no backing or anything, so it llooks much like the bore has worn out or whatever retaining system was there no longer is.

06-14-2012, 09:52 AM   #9
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If the lens is over exposing, beyond 1 stop below F5, you might have a sluggish aperture. The K5 should do better. Also what metering are you using spot or average, and what is the target you use to meter?
06-14-2012, 03:45 PM   #10
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For metering, I've used spot and center-weighted, although, according to the instruction manual, it will only spot (however, it could be chalked up to movement, but I thought I noticed settings changing when I flipped the switch). I am considering removal of that actuation lever for the aperture during stop-down metering. Then I can simply use aperture priority mode and ease one problem that way and use it similarly to how I used the Olympus: set an aperture, adjust the shutter according to the ev meter, set focus, shoot.
06-14-2012, 04:40 PM   #11
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QuoteOriginally posted by Lowell Goudge Quote
If the lens is over exposing, beyond 1 stop below F5, you might have a sluggish aperture. The K5 should do better. Also what metering are you using spot or average, and what is the target you use to meter?
+1, I'd be checking the iris. My 85/2 meters quite well.
06-15-2012, 08:57 AM   #12
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QuoteOriginally posted by Transit Quote
+1, I'd be checking the iris. My 85/2 meters quite well.
This is now looking like a strong possibility. It seems to have a slight delay. I'll open the mechanism up. clean it out, see if that helps speed things up. However, I'm really, really interested in simply removing the actuator lever, if possible, so that I can use Aperture Priority.at any aperture setting I wish. On further, invasive inspection of the mechanism, it appears that we do have a slow aperture here. Spring has been removed to feel the mechanism when manually actuating it and it's highly damped. It looks as if there was grease added to the wrong parts and it's too thick or old. Time for some cleaning. However, what is the opinion on removal of the actuation lever to enable A mode to work at any aperture? Edit again: I decided to remove the lever and see how it is. I also found out, after removing the focus ring, why the detent ball fell out. There's a little metal leaf that was crooked, so luckily I kept the ball. However, I will not reassemble it with the ball, as I like the ring the way it is.

Last edited by snake; 06-15-2012 at 09:41 AM.
06-15-2012, 10:49 AM   #13
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Put it all back together, with the lever. Didn't realize that the lever is necessary for everything to work properly. However, I might try to get another, cheap lens to gut and hope the levers are the same. In which case, I'll cut the top of the lever off. I want to keep mine just in case. However, the actuation mechanism appears to be gunked with grease that's too thick, but slightly. Regardless, I can still use the lens up until f5 with no issue. Comments on my idea to source another actuation lever? Then I can just run it in Aperture priority. Simple.
06-15-2012, 11:04 AM   #14
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QuoteOriginally posted by snake Quote
Put it all back together, with the lever. Didn't realize that the lever is necessary for everything to work properly. However, I might try to get another, cheap lens to gut and hope the levers are the same. In which case, I'll cut the top of the lever off. I want to keep mine just in case. However, the actuation mechanism appears to be gunked with grease that's too thick, but slightly. Regardless, I can still use the lens up until f5 with no issue. Comments on my idea to source another actuation lever? Then I can just run it in Aperture priority. Simple.
why not just clean the gunk out

all it requires is to pull the elements and flush the aperture with solvents, then blow dry with compressed air.

it is not as bad as it sounds, i have done a couple of kiron wide angles which are infamous for this issue
06-15-2012, 11:07 AM   #15
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QuoteOriginally posted by Lowell Goudge Quote
why not just clean the gunk out

all it requires is to pull the elements and flush the aperture with solvents, then blow dry with compressed air.

it is not as bad as it sounds, i have done a couple of kiron wide angles which are infamous for this issue
Because it does sound bad. I'll be clear- the aperture is fine, but one side of the linkage is not. In my case, it's very easy to swap that lever for one that I've cut down and I'd prefer to use aperture mode anyhow. The hard part is simply finding a donor lens that is cheap and has a lever that can fit this one. I thought about making one, but the spring attachment is a bit dicey.
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