I knew WD40 wasn't necessarily a wise move, but I had nothing to lose except a lens which was only reliable at maximum aperture in manual mode. ie not much use at all.

Andrew McP

In my case it was easy to see the problem was the lens, once I'd realised that might be the problem. I could see the aperture sticking when I had it off the camera, set it to "A" and moved the lever on the mount end around.

Andrew McP

I had this problem with my old Tamron 70-300, which had been on the shelf doing nothing for about seven years. It took me quite a while to work out what the problem was... but not very long to ruin the lens trying to fix it!

All I can say is don't bother partially dismantling it and carefully squirting a little WD40 onto the iris assembly. Surface tension just makes things worse, and several months later it's no better.

In the end I bought a very cheap replacement, but with two lenses to replace that's going to be more painful for you. Hopefully someone will have some better advice for you. But when I started peering around inside my lense I couldn't see anything obvious in the moving parts which was causing a problem, and I really didn't want to risk a complete dismantling, because I doubted my abilities to put it all back together again successfully. That led to the unsuccessful iris experiment.

Good luck.

Andrew McP

PS Even partial dismantling can be a little tricky! Well, it was for me.

I'll take your word for it. The only time I've ever been up in the air is when I fell off a swing when I was about six.

Maybe when I can afford to take a trip to Moscow and fly in an Su-27 I'll change my mind. Until then I'm quite happy down here getting neck ache, thanks.

Andrew McP

Oh come on now... you're messing with my head here! My heart says strike while the iron's hot... a 50-500 in the hand is worth two on a slow boat from China when I really need it next May/June.

My head says airshows are the only real use that this lens will get here (it's not a walk-around lens after all!), seven months is a long time in electronics (though not in lens & camera development) and there's a slim chance of both an HSM Sigma *and* a "K10-Super" being released in that time. Either of those might improve my chances of taking a decent shot in the heat of the moment.

Mmm...

Andrew McP

PS In my next life I want to be reincarnated as someone decisive. Or at least rich enough to buy two complete camera systems a year.

Oh dear, and I get paid on Friday.

Thanks for the link.

Andrew McP

Well, on a Pentax forum I feel slightly grubby, put it that way. I agree with you wholeheartedly though. However with a K100D and some Pentax glass on the shelf it'd be nice to stay in the Pentax fold.

I'm also, by nature, a contrarian. At airshows you often feel like you're in a Canon advert judging by the amount of Canon hardware you see bristling along the crowdline.

And of course another good reason to avoid Canon is the temptation of all those lovely big white IS lenses!

Andrew McP

I tried to buy one in June for this year's airshow season, but none seem to have made it to the UK since then (I do keep checking).

I'm going to buy a new camera after Xmas, hopefully a K10D. But if there are still no 50-500 Sigmas around by then I'll probably swallow my pride and buy a Canon 400D or something similar instead. It's not ideal, but the 50-500 is the only lens which offers the kind of quickly accessible range I want. I may get slightly faster focusing with the USM version of the 50-500 as well, which would help make up for losing IS.

I feel dirty even thinking about this though.

Andrew McP

That's a really nice shot.

I agree with you though that losing the foam would be an improvement. But nature generally gives with one hand and takes with the other, so on balance it's still a very satisfying shot to have taken.

Andrew McP

Ah, I think that's what they call a tactical error! Good luck purging your system of assorted unwelcome guests. A decent bout of food poisoning can be a real b*gger to get rid of.

Andrew McP