I've got a beautiful Asahi Prime, but it can't change aperture?

[Dubious Drewski]

Title says it all, really. I just received this beautiful vintage Asahi 50mm f/1.4 prime and I'm trying it out on my K10D. Nearly everything is working - I changed that setting that allows the camera to take pictures even when the aperture info can't be read from the lens. (This lens has ZERO electrical contacts - it's real oldschool)

But when it's mounted, the lens will only sit at wide-open aperture, I can't stop it down at all. Is this normal?

(Just a comment - holy cow this lens is fast! I'm so used to average-quality f/3.5 - f/5.6 lenses that it's odd to get such a response from a lens, even in the dark! This thing has so much character, from the ancient-smelling leather case it came with, to the way it kind of zooms in and out when you change focus. This is gonna be a conversation starter amongst my digital-only photography friends)

 

[Dubious Drewski]

Woah, I was browsing the internet for info on this lens and I came across this:

Good news:

The 7-element 50/1.4 design is a legitimate claimant to the title of sharpest normal lens ever made

Bad News:

unfortunately, (the lenses) have an internal element made of material known as "hot glass" which turns yellowish to brownish with age.

Uh oh!

The yellowing is curable by exposure to ultraviolet or sunlight

Well this lens is perfectly crystal clear, so I guess the previous owner shot outdoors alot.

This got my attention though:

The affected lens element contains thorium, a radioactive rare earth element. Several lens makers including
Pentax, Kodak, Leica, and Canon used this manufacturing technique in the
1940s to early 1960s to lower the index of refraction of specific lens elements.

Am I going to get eye cancer taking photos with this thing now?

Heh, I'm kidding, mostly. But am I?!

 

[KhronoS]

I don`t think that you gonna get eye cancer, because i guess it is used in very little quantities, and you don`t stay with the camera to the eye 24/24 for 10-15 years (just a wild guess)
Search a few more informations about this fact, but i don`t think you have to worry

 

[AlexParlett]

Tops of my head, the vintage Asahi's have a manual aperture ring?

 

[Steph]

Your lens should have an A/M switch on the barrel (A=automatic/M=Manual). Switch it to manual and set the aperture ring manually. Check the manual of the K10D to see which metering mode you should use to be able to use your lens.

As for the radioactive lens element it is only present in some M42 screwmount lenses. If yours is a K-mount (bayonet), it does not have a thorium element.

 

[Dubious Drewski]

Yes, it has a manual aperture ring and if the lens isn't mounted, I can see the blinds opening and closing as I twist the ring. But once I put it on the camera, it goes wide open and stays there. There's no A/M switch, turning the ring does nothing and it doesn't respond to the thumb dial on the camera.

My Ricoh 50mm prime behaves in the exact same way. (It also just has the focus and aperture ring)

So is this how these lenses are supposed to work on these cameras then? Or am I missing something huge?

 

[Helen B]

Pages 208 to 210 of the manual (which is available here: link) explain the various functions available with different lenses.

Best,
Helen

 

[DSLR noob]

put the camera on bulb mode and stop the ring down to 22 then take a picture and, while holding the button, look into the front of th elense to see if whatever is making the lens open up on the camera moves when the shutter is pressed (for metering wide open)

 

[Helen B]

You would also want to find out if the shutter speed changed as you adjusted the aperture ring, while the iris itself stayed open.

Best,
Helen

 

[Christie Photo]

I think there's a pin on the back of the lens. When the pin is pressed in, the lens should stop down. So..... When the meter is on, the lens should stop down, and again when you make an exposure.

Check to see if the pin is operating smoothly and be certain the meter is off when mounting the lens.

-Pete

OH.... wait a minute. I just realized you're trying to use this on a digital camera, so there's nothing mechanical to depress the pin during use. I'd bet there's a sliding switch on the lens that has A or M setting. You'll have to use it in the M position only.

Good luck!

 

[Christie Photo]

Is this your lens?

 

[Sandspur]

Is this a bayonet mount or the older screw mount? I'm assuming bayonet, because you'd need an adapter (which works quite well, BTW) if it were a screw mount. I have one of those. It was the only lens I shot with for years. Bought it in 1968 in Viet Nam, with an Asahi Pentax SV (pre-Spotmatic). Still have that camera, too.

Just pulled it out of my collectibles box and dusted it off.

Yeah, it's still one sweet lens.

Christie is right - whether it's the one he showed (that's mine) or the bayonet equivalent - there are simply no mechanisms that your modern digital body and that lens have in common. You can use it - only with the switch in Manual, of course. Just stop it down manually, do a test shot, and keep firing...
Enjoy it! I'm convinced that even the most expensive lenses around today can't hold a candle to some of those old Nikon and Pentax lenses.

Damn! I didn't know I owned the sharpest lens EVER! Cool ... especially for an old guy ... who'll be 65 tomorrow! Yes, you're all welcome to sing Happy Birthday, and then go away and leave the old fart alone ... I need a nap!)

 

[Dubious Drewski]

It's the bayonet mount. I can't find any pictures of my particular variation of this lens, so I shot it myself:

THAT is my lens.

put the camera on bulb mode and stop the ring down to 22 then take a picture and, while holding the button, look into the front of the lense...

Oh now I see! So the aperture snaps to position only exactly when I press the shutter release. So it was working the whole time, in full manual only. But because it stays wide open during metering, it can't work in any other mode except manual?

The aperture blades look very delicate - this lens is around 30 years old, I dunno if I like having the aperture jerked around so quickly! Heh. Sandspur, this lens looks and smells like it was just pulled out of the collectibles box and dusted off. And then put up on ebay...

It's a well-worn lens too, I love it. I wonder if any famous photos were taken with this lens. The mystery is exciting.

 

[Helen B]

..So it was working the whole time, it just didn't tell me that it has to be wide open to meter, is that it?...

It stays open so that you can see through it easily. The metering system needs to know what it will stop down to when the picture is taken, because it is metering at open aperture and not at the working aperture. That is why I suggested that you make sure that the shutter speed changes as you change the aperture. It's also worth reading the manual.

Good luck,
Helen

 

[Dubious Drewski]

Yeah, I'm sorry Helen. I have read the manual and I've even read that part prior to this, but I didn't catch any part that described a behaviour like this (The snapping aperture). But no, the shutter speed does not change while I change the aperture ring in aperture priority mode.