Macro 100mm WR overexposing

A bright sunny day with the macro 100mm on a K1, lens hood attached; in TAV and AV modes it is hopelessly overexposing with high ISO levels. Same in Manual using the green button. I tried different aperture reading settings but it made no difference. Switched to a different lens and that was fine. Any Ideas?

Check that the aperture lever is moving freely. If the aperture is slow then the lens won't be able to stop down quickly enough, overexposing the image.

Hi Rob,

Why high ISO on a bright day ? I used mine yesterday afternoon in the shade - K1 - ISO 3200 - 1/125 sec - F10

I just tried the lens on a different body (K50) and it was fine. Also tried another mechanically-linked lens on the K1 and that was fine too. It just seems the combination of the 100mm macro and K1 is giving the overexposure problem. HarisF1, the lever springs back but not snappily so you could be right, I have been flicking it for a bit but it hasn't got much quicker. Puzzling it should be ok on the K50 though.

Just found the same problem on another forum - oil from AF drive gears getting onto the aperture control ring. Get it cleaned off and should be fine but don't fancy doing it myself so I'll see if the local LCE can do it.

Before you do that, just look to see whether wide open images are overexposed too. They generally shouldn't be if the aperture mechanism is slow.

As a footnote, my 100mm WR is currently with Jps with exactly the same fault i.e. a 'sluggish' aperture mechanism. This the third occasion I have had to have this lens serviced to remedy this fault since I bought it new. It has now cost me over £200 in repairs
The lens will work fine for 9 - 12 months and then the problem re-occurs - heaven knows why. My two Sigma macros never cause any problems and they are much older.



Roger

Oh heck that's not good news. Does this happen with any other lenses?

Curiously, Auto setting exposes perfectly. Never used it before but you can set the ISO and in the menu are some priority options, I selected the one for sharpest images (it uses the lens ID for this); could have been depth of field or shutter speed. Here are a couple of cropped images from today with a Marumi close-up filter attached and with slight adjustment in Lightroom:



And one from last night with the Pentax ring flash set to -16, one side only, and the flash setting in the camera at -2. Manual setting.

Further experimentation has shown that I get the most consistent results with AV Hyper mode, I just taken the same subject with a series of exposures in that mode, changing ISO and aperture, and they all look virtually identical. It also allows you to change focus mode which Auto won't. No idea why this mode works when the TAV, AV and manual give mixed results but I shall keep experimenting and maybe hold off getting a repair as it sounds like the problem doesn't get fixed once and for all.

Some basic checks first, such as are you set on spot metering? If that was so and you were unaware of it, then wildly varying exposures could well result. I suggest centre weighted metering to avoid over exposure.

Have you checked the exposure compensation setting? A value of -0.3EV is always a good starting point as this usually avoids burnt out highlights.

In bright conditions high ISO values might mean we run out of shutter speeds, so even f/22 and 1/8000s might results in over exposure. If you are using the optimum aperture setting on the lens, be it f/8 or whatever the camera sets, then you will soon need faster speeds than 1/8000s to avoid over exposure as you increase the ISO.

If the aperture ring stops down and returns smartly when the lever is flicked, then the aperture mechanism is unlikely to be an issue.

Thanks John, yes I tried different metering and use centre-weighted metering as a default, except when spot metering is needed to avoid overcompensating for a dark background. The aperture lever doesn't click back sharply, it is as if it is damped so I suspect that is the issue. I have been further experimenting in P mode, changing between AV hyper, TV hyper, and the ISO setting, and weirdly everything comes out properly exposed and more consistently so than other settings. If oil leaking onto the aperture control is not uncommon then shouldn't Ricoh do something about it?

PS when I said overexposing I was getting ISOs of 10,000 and higher when they should have been in the hundreds, not something I could manage with exposure compensation.

I'm puzzled why you would need ISO values of 10,000 in bright light?

The aperture mechanism on Pentax lenses is very reliable, regardless of the age of the lens, so it's not a generalised problem. A slow aperture mechanism can be due to contamination on the blades - oil would certainly do the trick as it sticks the blades together. There shouldn't be any oil around the blades as it would stick them together. Surface tension....

In TAV mode for instance the ISO is the only variable the camera applies to get a well balanced exposure, the high values weren't my choice but what came when I pressed the button - hence the grossly overexposed images.

The oil isn't on the blades but the aperture control ring. I am struggling on my iPad to paste a link but the issue is in PentaxForums.com thread: Pentax DFA 100mm Macro WR sticky blades? A contributor dismantled the lens, saw the problem, cleaned off the oil and then it was ok.