Oil on diaphragm - is it a problem ?

Hi,

I have a Takumar 1:2.5 135mm lens that seems to be in perfect optical condition. There is evidence of oil on the diaphragm however. I have seen mention of this before but I cannot decide if it is a real (as opposed to cosmetic) problem. I understand that if the oil reaches the glass, then there is a problem.

Your opinions and knowledge would be appreciated.

Regards, Pete Smith.

Hi,
Oil in a preset lens is not a major problem. It is a problem in an auto lens as it slows the stop down mech. If it bothers you, it is not generally diificult the remove the front group and clean the blades.

Regards
Kim

Hi!

Well, I don't have much experience, having only seen two lenses with oil on the diafragm blades. The first isn't mine, the second is a Tamron 24mm F2.4 that I bought recently... and it had oil.

To be honest, the blades didn't even move at first, because of the oil. Then, when I forced the mecanism to move, it shoed the oil. The problem was, as Kim put it, that it delayed the blade movement. But after a while of manualy moving the blades, the oil spread a bit and started to "disapear".

I don't really think it did disapear, it simply spread across a bigger surface and is less or invisible.

Today, the lens works nicely, even on my DS, stopping down positively and snappily. But I guess it depends on the lens/oil/diaphragm/etc....

Hi,
I have just re-read your original post. I thought you meant you had a Takumar lens. However, there isn't a 135/2.5 Tak but there is a 135/2.5 Super Tak and oil here will cause a problem. If you are sending the Super A to robin, you might want him to cleam the lens for you. It is a cracking lens when working properly.

Kim

Hi,

I've just checked my f2.5 135mm Super Tak (Which I agree is a beauty) and it has no oil. Nor do my other 5 Pentax lenses. However, my brother-in-law's Yashica 50mm does - a lot!

Where does the oil come from? Is it a symptom of the lens getting too hot, and barrel lubricant running onto the diaphram leaves?

Thank's

Hi,
The most common cause is from leaving the lens in a warm place such as the back shelf of a car. The older greases are oil based and the oil separates under heat and to a lesser extent age. Nowadays, if a lens is given a full CLA, it is usual the use a fully synthetic grease which reduces the problem.

Kim

Thanks, Kim.

Whew - I think I dodged a bullet with a Super Tak f1.4 50mm which had the usual rare earth yellowing. I cleared it in the sun this fall, but wrapped the barrel in aluminium foil to reduce the heat build-up. Glad I did - thank's to the folk here. I'm sure these old girls have the oil-based grease.

Cheers

The Super-A has gone off to Robin for a full service and seal change, together with an old SMCPKA 50mm 1:1.7 lens who's aperture ring refuses to move. I'll follow your advice and send the 135mm lens for cleaning in the new year. In the meantime I've just got hold of a SMCPKA 135mm 1:2.8 lens on eBay so I'll use that for a while.

Thanks for your help, once again.

Kim, what makes the lens a 'Super' Takumar. The lens I have makes no mention of 'Super'. It is engraved "TAKUMAR (BAYONET) 1:2.5 135mm serial no. ASAHI OPTICAL CO."

Aahh! Confusion reigns!!
You are talking Bayonet and I was thinking M42. The first Pentax lenses were Takumars with a preset diapraghm, when they added a "cocking" mechanism, they became Auto Takumars. The next generation had fully automatic diapraghm and were Super Takumars which became Super Multicoated Takumars and then SMC Takumars. With the advent of the K mount, Pentax dropped the name Takumar and the so called "K" series were actually named SMC Pentax. This then went through the A, the F etc suffix's. This pattern was followed for all the mainstream lenses. However, Pentax did introduce some budget 135 and 28 lenses. These had a slightly lower build quality and did not have the legendary coating that Pentax normally used. To differentiate these, they resurrected the name Takumar! I realise now that you must have one of these.

The oil probably will affect it. However, whether it is worth paying about £25-30 to have it cleaned bearing in mind the quality of the lens is another matter.

Kim