Exposure problems with Irix 15mm lens

I would appreciate comments on the following problem encountered using an Irix blackstone 15mm f2.4.

Occasionally I get gross overexposure using this lens. I have tried it on a K1 and K3 with the same results
I have been testing it with Av and M exposure modes. - generally matrix metering. The lens is manual focus only .
When the over exposure happens , the metering values indicate a correct exposure. On most occasions, ( not sure if 100%) if I have checked the optical preview afterwards then the lens does not stop down. Operation of the preview lever has no effect for a while, then suddenly starts working.

That seems to indicate that there is an intermittent fault with the stop down mechanism. e.g if metered value is f8 @ 1/100 then shot is made at f2.4 @ 1/100.
the exif data would show f8 @1/100
I tried checking the stopdown lever in the camera lens mount but that does not operate on both cameras if there is no lens attached. - I assume that is normal .
( I remember on mechanical slr's that one could observe the lever moving by operating the stopdown lever on the body.)

I have checked the stopdown lever on the lens and that seems free and the aperture blades move very smoothly.

Has anyone experienced a similar problem?
Is my diagnosis correct or are there other things to check?
Maybe I have a faulty lens. It seems ok in all other aspects.

many thanks
Paul

Hi Paul, can't comment on that particular lens but have had similar experience before with a contact problem, f stop would suddenly disappear and show -- and aperture would be wide open. This would happen for a second only and was hard to spot.
I'd try cleaning the contacts as a starting point.

Does the irix have an aperture ring ?
If it does you could try setting aperture on lens and see if it's still happening.
Hope it's an easy fix.
Interesting lens that irix.

Derek

Thanks Derek,
I will try cleaning the contacts.

The irix does not have an aperture ring.
it seems a well made lens, nice feel to it and some clever design features. I hope it is a simple fix too!

Paul

Cleaning the contacts on the lens and the camera body, with a dry soft cloth, is the best place to start.

If there's a lens fault, then it's a new lens, so getting it replaced or fixed under warranty won't be a problem.

I reckon it's a dud lens Paul.
I've been using my 15mm Blackstone on my K1 very happily for some months. Focuses nicely to infinity, no decentering etc - very happy. I gave it quite a bit of use over the last three days and it was fine as usual. Tonight I took it out and the camera just showed the aperture as F--. I took the lens off, cleaned the contacts, took the battery out and replaced it - no difference. I then took several pictures - according to exif all were exposed wide open at f2.4. Since getting home, I've checked the aperture lever - moves smoothly by hand and aperture changes. Tried the Irix on a K5 - exactly the same response. Tried a different lens on both the K1 and K5 and everything was as it should be. Conclusion - I've got a dud lens, with virtually identical symptoms to yours. I'll be contacting IRIX - I bought mine direct from Europe.
Rod

Update on my IRIx 15 Blackstone aperture mechanism/registration failure.

I emailed the distributor in Poland who were happy to restore my lens under warranty. I then discovered it would cost about AU$100 to ship it to them from Australia. Another email from me resulted in redirection to Service IRIX in Korea. They in turn emailed me a DHL account number, so the lens will be collected from my home and shipped to Korea at IRIX's cost. Should get there within a week. Pretty good service I reckon

My IRIX 15mm Blackstone is back from warranty repair!

The fault was a poor internal electrical link within the lens mount. It took only 3 weeks and two days for my lens to be picked up at my home by DHL, shipped to Korea by Air Express, assessed and repaired, and air expressed back to me in Australia, with all costs borne by IRIX Service.

And yes, my lens again works the way it used to, with in-camera adjustment of aperture and correct registration of aperture in exif.

I reckon that service is hard to beat!

Thanks for the update and pleased you have got it sorted quickly. I have been away for a bit and will try my lens again. Very interesting that a fault was found.

Paul

I thought I should update this topic which I started in case it has put off prospective buyers!

The problem I reported appears to have disappeared. It has not reoccurred for months.
I contacted Cameraworld about the original tests and they said to return the lens to them for examination by Irix. I didn't do this as it was inconvenient at the time and then the problem seemed to stop.
In use I have found the lens to be excellent. I use it for landscapes so the manual focus is not a problem and in fact the focus lock is really useful.
I look forward to trying their new Edge Filter holder for 100mm filters when it becomes available. I emailed Irix recently but they could not give a date for purchasing.

Paul

Thanks for following up the original posts.