Question Regarding Aperture on Old Film Lenses

[utsuri]

So I was looking at and playing with my mom's old camera and unfortunately, I can't ask her this question, which will show up after I go through the background.
It's a 35 mm Minolta XG-1 with two lenses stored in the case: 50 and 135 mm primes. I was looking through the 135 and saw the physical aperture. Now, only having and currently using a compact P&S, I've never seen that before and thought, "Whoa! Way cool!" I moved the f-stop and saw the aperture narrow as the numbers got larger, which I knew would happen but it was so much fun to see.
But I noticed that sometimes after f-5 the aperture didn't move. It would open all the way up again, but to stop it down it was acting like it got stuck. On the 135 mm it has a lens hood, so I pulled it open, felt it shake, and then the aperture would narrow again to where it was supposed to be. Is this normal? I mean, these lenses are at least 25 years old and I have no idea how much my mom used her camera. I have a bunch of baby pictures I assume she took with it but I never remember seeing her use it. I think it just started costing too much for her budget at the time.
I've read somewhere on the forum about used lenses not holding focus; could that be what is occurring here? I had thought the focus was a different function on a lens. At any rate, I got curious about her camera because my first dslr should be arriving any day now and I realized how little I know about how a camera physically functions.
So, if anyone has an idea on what could be occurring and why, or where I might be able to find some answers, thank you in advance for helping me out. I figured asking a bunch of photographers is probably the best way to find some answers.

[Paul 92]

Great fun looking at these old cameras isn't it?? Really gives you a look into how a camera works and even though there's a computer in there now, as far as letting light into the body, they work the same way.
I have some old Nikon camera bodies that are basically for looks now, though they saw their share of use over the years.
Sounds like maybe a small mechanical glitch in the lens you're looking at. The aperture blades should open and close smoothly as you move the aperture ring. Sounds like maybe its getting stuck at f5, maybe a piece of dust or dirt in there or one of the blades could be bent slightly but enough to cause a hang up. If you feel like taking the lens apart further, may be a fun experiment!

[inkista]

Yeah, sounds like the mechanics aren't quite right. Most likely culprit, if you can see it on the blades, is old grease that's gone sticky/hard. Don't try to force anything. Apertures are delicate spring-loaded mechanisms.

If you are mechanically-minded, taking the lens apart (as long as you don't mind possibly destroying it) can be fun, but I'd also try and google around and see if there's any repair information on that specific lens. If you don't want to risk it, then you could look and see if there's a good repair guy in your neck of the woods.

The XG-1 had the old manual MD/MC mount, so those lenses can't really be adapted for a dSLR without mount modification. Only the mirrorless compact mounts (micro four-thirds, Samsung NX, Sony NEX) can use them with adapter rings.

[utsuri]

Thanks you guys! I did have a lot of fun just looking at it, feeling the weight of it with different lenses on. It's missing its battery cover and had no film in it, so I couldn't do too much, but it was fun. A nice trip into the past.
As much as I would like to take it apart, I'd hate not being able to put it back together, simply because it was my mom's. I found a camera shop to develop some of the 120 film I took with my grandfather's camera (his experiment to see what I could do with manual settings) so I figured I'd talk to them about the lenses and camera and see if they knew of someone around to fix something like that.
inkista, I had briefly hoped to be able to use the lenses on my new dSLR but I figured they wouldn't work. As it is, I'm not terribly disappointed they won't. They're different brands and different generations so I'll just take them as they are. It's just cool to have them, really.
Once again, thanks for the help. Right now, it's collecting dust in its old case again, but maybe I'll get them all fixed one day and play around with film some more.