Apeture won't change....

Nygdan · Mar 15, 2005

I had bought two Chinar lenses on ebay. One is a 135mm. When i turn the apeture ring, nothing happens, I don't see the diaphram closing. Whats going on? Are 'long' lenses somewhat different than normal and wide lenses? This is the first long lens I've had. I suspect that they don't behave any differently, and that I should be able to see the apeture diaphram stopping down and opening up.

Here are two photos I took of the lens, the first is at f2.8, the next at f22. They're not different, and there is no movement inside the lens as I stop down. The photos are moderately large files, it was a rush job.

This is definitely a problem right?

f2.8

f22

Kent Frost · Mar 15, 2005

What camera mount does it fit to?

Nygdan · Mar 15, 2005

Its a K mount lens. THe rear lens cap says 'pk' but that doesn't seem to mean anything according to this page
http://kmp.bdimitrov.de/technology/summary/index.html

I think that the 'p' might be intended to refer to the lens being able to work in program mode.

Kent Frost · Mar 15, 2005

On the mount end of the lens, if you place the red dot at 12 o'clock, you'll see the lever at 3 o'clock. Set the aperture to 22 and lightly flick the lever to see if you can manipulate the opening. Feel for spring-loaded action, it should push against you. If it doesn't work, your lense is faulty.

Nygdan · Mar 15, 2005

Dang, I suspected as much.
I did what you suggested, moving the lever down has no effect on the diaphram in the lens. It seems like its a little springy, but, again, no change in the opening in the lens.

I think I am going to have to contact the seller. Thanks for the help.

Kent Frost · Mar 15, 2005

I'm willing to bet that some of the lubricant in the lens has seeped into the blades of the diaphragm, which is typical if it's been in a heated spot for too long, like a car or near a heating vent. However, if that's true, you should get some sort of reaction. Dunno, could easily just be a mechanical issue. But if it's a 135mm, you shouldn't have a hard time replacing it. Although if you're wanting the 2.8, you're probably looking near $50-70 for a good used one.
I assume that it's manual focus?

Mad_Gnome · Mar 15, 2005

This also happens sometimes when a lens ages, especially with lenses from the 80s. The helicoid grease breaks down, and one of the elements is oil, which contaminates the aperature blades. I have a Vivitar zoom lens with this problem, which I'll have to have srviced at some point. :grumpy:

Nygdan · Mar 15, 2005

Its manual, yes. I had gotten it and a 28mm f2.8 lens for aroudn 10$. But now this.

See, I have a pentax k100. It came with a 50mm lens. I bought a 28 mm lens a little while ago. When I saw this deal up, I figured, heck, its worth it just for the 135mm, and it might be interesting to have a somewhat longer lens to play around with. So I figured, what the heck.

I'm not trying to build some great glass collection or go overboard on anything, I just figured that it was worth trying out something different.

Now I have to deal with this issue. Usually E-bay itself is good with this, and will refund a buyer.

Kent Frost · Mar 15, 2005

Mad_Gnome said:
This also happens sometimes when a lens ages, especially with lenses from the 80s. The helicoid grease breaks down, and one of the elements is oil, which contaminates the aperature blades. I have a Vivitar zoom lens with this problem, which I'll have to have srviced at some point.

I agree, but that's only if it's been in that condition for some time. Most of the time when it happens, the diaphragm reacts very slowly. After time, like you said, it acts like more of a glue and just keeps the blades open all the time.

Kent Frost · Mar 15, 2005

Something to consider: The newer auto focus pentax cameras still use the K-Mount. You may consider getting a zoom lens. If you ever decide to upgrade to a new camera later on, an auto focus pentax would be an option since you'll have the lens for it.

Nygdan · Mar 15, 2005

I'm actually considering something like that now, getting a zoom that starts above 50. I guess it'll depend how this turns out tho!

Kent Frost · Mar 15, 2005

Actually, my girlfriend bought a 28-105 Promaster lens for her Pentax ME Super and she loves the thing. If you want to cover as much focal length as you can, a good setup to start with would be something like a 28-80mm and an 80-200mm. That's 2 lenses that will take you from 28-200 pretty economically, and they're super light weight.

Nygdan · Mar 16, 2005

Sounds intersting. I'll have to keep my eyes open for it.

Nygdan · Mar 16, 2005

wait, can zoom lenses even operate on non-powered cameras? You can zoom manually?

Kent Frost · Mar 16, 2005

Zoom is manual regardless of what camera you use, unless you're using one of Minolta's powered zooms lenses made for their auto focus camera bodies, which you don't have. You'll just have one more ring on the lens that you'll be turning for the zoom, making a total of 3 rings: focus ring, zoom ring, and aperture ring.
The focus, however, is what's automatic if you're using one of Pentax's auto focus bodies if you want it to be, you can go manual on that too. The only difference is that there's an auto focus (AF) coupler built in so that when you put an AF lense on an AF body, the sensor built into the body will recognize that it's on there, and the motor turns the coupler which turns the focus on the lense. But since the k-mount is the same, you can use AF lenses on non-AF bodies, and non-AF lenses on AF bodies, it goes both ways. It's just that you won't be able to focus automatically sometimes depending on the equipment you've got put together.