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Quick look at the FOTGA autofocus macro tubes

Started Nov 13, 2013 | User reviews thread
lester11
lester11 Contributing Member • Posts: 596
Re: Quick look at the FOTGA autofocus macro tubes

hindesite wrote:

lester11 wrote:

I posted some information on the Fotga tubes a few months ago:

http://www.dpreview.com/forums/post/51450718

Six months later, I no longer use them, their aluminium mating surfaces have grown increasingly unhappy with the stainless steel surfaces of my lenses... One time (the last time!) I wasn't sure I was going to be able to take the tube off the lens without damage, about 3 minutes of slowly increasing panic! The tiniest drop of penetrating oil left for 20 seconds did the job.

Thanks, that is useful information - is it really aluminium? Does it just have poor anodising?

I'm not a metallurgist, though I do handle common metals from time to time.  It *looks* to me like it is aluminium, it seems it is that kind of "soft".  I don't think it has any anodising.  My guess is that it is plate, rolled to give a "reasonable" finished surface.  I'd also guess that it is a particular grade of harder aluminium alloy, perhaps a well-tempered aerospace 7068 or 7075.

I did think about leaving the tube on the lens rather than demounting it every time to minimise the chance of the surfaces seizing, but the problem there is that aluminium and stainless do interact electro-galvanically, there is some gap between them on the galvanic chart.

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Lester

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