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sourcing small springs for lens repair
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PostPosted: Thu Feb 11, 2010 8:04 pm    Post subject: sourcing small springs for lens repair Reply with quote

i have a sigma 400mm with weak aperture actuation. took it apart, blades are clean. i believe the culprit to be a small spring (possibly the pair of) just behind the mount. it uses the "clothes pin" style, maybe about 1cm on each side. anyone have ideas for a ready source??
(my other junk lenses don't use this type of spring~ and there are no small independent shops left in this area)

Thanks!


PostPosted: Thu Feb 11, 2010 8:08 pm    Post subject: Reply with quote

I don't know what you mean with clothes-pin style, but many a lens have been repaired with springs from cheap plastic ballpoint pens. Just an idea!


PostPosted: Thu Feb 11, 2010 8:28 pm    Post subject: Reply with quote

sorry I don't have a pic handy, but it's not a compression spring (like from a pen), it has two legs pivoting in the center like this one on the right:




sorry for the size, only pic i could find
basically I need a stiffer spring to close the aperture reliably.


PostPosted: Thu Feb 11, 2010 9:22 pm    Post subject: Reply with quote

Hi,

I have sourced some of these springs from old junk bodies, notably the old Exakta cameras ... Usually you can get them for free from a repairman bin, or you could try to build one by yourself using a piano chord and a Dremel ...


PostPosted: Sat Feb 13, 2010 6:21 pm    Post subject: Reply with quote

Hi,
"took it apart, blades are clean."
I'm wondering whether you cleaned the blade carrier & ring right into the corners - everything that moves has to be scrupulously clean and free-running.
You can easily re-tension the spring if it really needs it, just bend it a little against its operating direction - the only kind of spring that can't effectively be re-tensioned that I can think of offhand is the mainspring on Compur, Copal etc. leaf shutters. These are extremely brittle.


PostPosted: Sat Feb 13, 2010 7:01 pm    Post subject: Reply with quote

Oh yeah, forgot...
Check the mechanism between the mount & the diaphragm assembly for freedom of movement and alignment.
The length of the "prong" between the lens mount & the diaphragm on the 400 means that it has a lever effect on the ring at the mount end, trying to twist it.
Sometimes the ring will rotate freely until slight pressure is applied to the end of the prong, when it starts to drag.


PostPosted: Tue Feb 16, 2010 3:46 pm    Post subject: Reply with quote

These guys have some parts for repairing manual cameras as well as cleaning digital ones. I've ordered a filter-ring undenter from them and it works great!

http://www.micro-tools.com/store/home.aspx