[barchaetone]

Hello everyone,

I'm a veteran Pentax K-1000 user, but this is my first foray into late-1980s K-mount automatic stuff.

I was given a vintage Ricoh KR-30sp with a Tokina zoom lens (with Ricoh pin). I'm running a roll of film through it, and encountered a strange phenomenon. When I set the *lens* to auto-aperture (A) and the shutter dial to "P" for auto-program mode, the camera meters correctly. It chooses an aperture and shutter speed which are within about one stop of other cameras that I own. However, if I try any other mode, such as aperture priority (set the lens to desired F-stop, leave the shutter dial on P), or manual mode, the light meter is way off, as if it barely senses any light. I have to point the lens at a light a foot or two away at f/3.5 to get it to register about 1/2 sec for the shutter speed. It behaves accordingly. If I press the shutter, it's open for a half second (or 4 seconds, or whatever the meter is saying). Switch back to auto program mode, everything is peachy. The problem is that I prefer to shoot in aperture priority or manual. I hate program mode because I can't choose things like shooting wide open to blur the background, etc.

Has anyone encountered this before? Could it be the Tokina lens?

Thanks!

[stevebrot]

Welcome to the Pentax Forums!

Questions...

• When you have the aperture ring off the "A" position, does the lens stay wide open regardless of aperture ring position?
• What happens when attempting shutter priority?

If shutter priority works and the lens stays wide open at all settings (both are expected since P mode works), the problem might be the mechanical meter coupling between the lens and body (not the same as the aperture actuator.) If either of the members are missing or misaligned, the mechanism meters as if the lens were at minimum aperture. The result is that it takes a large amount of light to get any meter response.

Below is an image lifted from Dimitrov's excellent K-mount Web site. It shows the coupler on both body and lens sides of the mount (labeled "stop down coupler" and "stop down indicator" respectively):


Original location: Features and Operation of the Original K-Mount

Visually inspect both the "coupler" and the "indicator" for damage and alignment. If possible, compare both to a known good K-mount body and lens. Until physical damage has been ruled out, care should be taken to not mount the body with another lens. The same is true for the lens and another body. If the two do not properly engage, permanent damage may be done to another body or lens if mounted.

If neither shows obvious damage, the problem may be with the electrical connections between the "coupler" and the meter. You may be able to test this with lens off and the shutter speed dial at 1/125s (emulates manual mode). You should be able to move the "coupler" through its range with your finger nail. The meter indicator should respond to the movement of the couple.

I hope this helps.


Steve

[barchaetone]

Steve,

Thanks for the welcome and the wealth of information! It really does help. Your explanation makes a lot of sense.

To answer your questions, 1) the aperture stays wide open, 2) shutter-priority mode meters appropriately, both when selecting "SP" mode on the shutter dial (where 1/250 is the slowest shutter speed), and when also leaving the lens in "A" but manually adjusting the shutter speed. If I select 1/60, for example, that is the slowest shutter speed - and metering and auto-aperture selection work properly. The only thing that doesn't meter properly are aperture priority or fully manual modes.

I examined the lens and body. The stop down indicator and coupler are both undamaged and seem aligned. I don't have another body or lens immediately at hand to compare (my son has my old K-1000), but nothing seems amiss. The ring with the stop down coupler seems a tad loose (you can wiggle it a little horizontally within its plane, if that makes sense), but I'm not sure if that's within normal tolerances or not. Looking at the JES screws on the mount, it looks like someone used a Phillips head on one or two of the screws at some point, because they look slightly stripped, but I'm not 100% positive. Not sure where the problem might lie...

I took the lens off and slowly pulled the coupler down, and sure enough, the meter was sensing more light as if I was opening the aperture, just like you said.

Any ideas regarding anything else I can check? Much appreciated!

[pentaxus]

I would still guess that it is the coupler in the body being a little bent. If you move what is labelled as the stopdown coupler and the light meter indication changes in manual or aperture priority then that lever is probably slipping by what is labelled as the stop down indicator. It the meter indication doesn't change it means that your aperture VR in the body is bad.

[barchaetone]

pentaxus,

Thanks for the additional info. From what you say, I suspect the body. Maybe it has to do with the "wiggle room" that I mentioned with the coupler ring? If so, is there any way to fix that? The coupler doesn't look bent, but if it were to shift a little as the lens is being mounted, I could see that causing it to not catch.

If I can't fix, at least I can shoot it shutter priority mode (not SP mode but the one where you select the shutter speed while the lens is set on A). I'm used to doing that with a rangefinder. I adjust the shutter speed until I get the aperture I want.

However, ultimately, I'd like to get one or two sharp prime lenses--preferably Ricoh P to maintain the auto functions--to use with this camera. I don't care much for the optics or the weight of vintage Tokina zooms.

Thanks again!

[stevebrot]

that lever is probably slipping by what is labelled as the stop down indicator

...and it is that "slipping by" that is a hazard. If it slips by cleanly for both mount and dismount, everything is good. If the "stop down indicator" catches on the coupler on dismount, the lens could get stuck and/or both levers could get all bent up.


Steve

(...has a camera whose coupler was irreparably damaged by a defective lens...)

[barchaetone]

...and it is that "slipping by" that is a hazard. If it slips by cleanly for both mount and dismount, everything is good. If the "stop down indicator" catches on the coupler on dismount, the lens could get stuck and/or both levers could get all bent up.


Steve

(...has a camera whose coupler was irreparably damaged by a defective lens...)

Makes sense, thanks for the warning. Def good to know. When I mount the lens with the aperture less than wide open, as I turn it, and it clicks into place, the aperture opens up all the way. Is that the diaphragm pin (or whatever it's called) rather than the coupler that does that?

---------- Post added 07-06-16 at 10:21 PM ----------

Diaphragm actuator, I meant.

[stevebrot]

Is that the diaphragm pin (or whatever it's called) rather than the coupler that does that?

---------- Post added 07-06-16 at 10:21 PM ----------

Diaphragm actuator, I meant.

Yes, the actuator opens the aperture up as the lens is mounted.


Steve

[barchaetone]

I got the chance to test the body with a Pentax lens, and the meter worked fine in manual mode! So, that seems to suggest that the trouble is with the Tokina lens. I'll probably pick up a fast Ricoh prime, and I'll keep my fingers crossed that they place nice together.