Lost the aperture ball bearing, how to found out its size?

nainsurvolte · Joined: 20 Dec 2013 Posts: 17 Location: Canada

Yes I was not careful when re installing the back of my Vivitar 28mm f2 and loss the aperture steel ball. Embarassed

My question is, How can I know what size is that ball? I already know where I can get them given that the size can be purchased. I also already know also that 1 mm is not good. I purchased some and they get through the spring.

Now I did a non scientific measurement with small Hex screwdriver. The 1.5 mm seem to fit in the hole where the spring is while the 1.75 does not. Could that mean the 1.5 mm is the one Question

For reference, the one I own is the K11 listed on this page (or possibly the K13 looking at the serial number range)

http://photografica.robinparmar.com/vivitar28detail.html

Lloydy · Expire: 2022-01-01

I think your 'non scientific' method is actually very practical, and probably very accurate. But remember that the 1.5mm measurement of the hex driver will be across the flats and not the points. If you've got a caliper measure the across points measurement, or do the trignometary. Confused

nainsurvolte · Joined: 20 Dec 2013 Posts: 17 Location: Canada

Actually that is why I asked the question. Made me realize I had it all wrong... I assumed the dimension was point to point... Rolling Eyes

Thanks for correcting me.

It means that I need a 1.75mm steel ball.

Hexagon= 6 equilateral triangles. Doing some geometry by splitting the triangle in 2, you manage to have a triangle with a 90deg angle... and you find

R= .75/(cos(30)) = 1.73

Just a verification, the 1.75 Hex would give a 2mm. I never saw steel balls between 1.75 and 2mm. So up we go with the order.

Lloydy · Expire: 2022-01-01

I just measured a 1.5 hex wrench across the points and got 1.63mm. I'd be tempted to go with a 1.5mm ball.

philslizzy · Joined: 07 Aug 2012 Posts: 4749 Location: Cheshire, England

nainsurvolte · Joined: 20 Dec 2013 Posts: 17 Location: Canada

Guilty as charge, I am an engineer, Wink

But at the same time, taking a ball from another lens has been my first attempts. I can tell you the one from my Pentacon 50mm 1.8 is way too big and that there are no ball for the aperture in an old Nikkor 135 f2.8 pre-AI (also the reason why it is in pieces on my desk). For the rest of the lens I have, I don`t want to dismantle them. Micro tools via ebay can send 3-5 ball for 5$. Given the size of that ball I thought it was small as hell compare to the Pentacon and thus ordered 1mm ( I have a stock if people are looking for some Very Happy

)

@Lloydy,

Possible the 1.5 is a better choice, in these days, it was possibly easier to aim for 1.5mm ball +/- rather than 1.75 +/-... I may just play safe and order both and spare the S&H for 2 orders. If the 1.75 fits, it might make a tighter click than with the 1.5. Although the other Kiron lens I have are more of a subtle type of click. Rolling Eyes