Re: Sigma 400mm f5.6 APO
These lenses are notorious for fogging of the internal elements, so make sure you confirm the lens is truly clean before you buy. From what I've read on the web, it's the ones with 72mm filter threads that are prone (which may be all the manual focus ones for all I know). You obviously know to only get the APO version.
By coincidence, I've just been taking apart one of these with a CY mount that belongs to my uncle. Despite being in otherwise pristine condition, there was heavy fogging on the front lens group of the internal focusing group. This would appear to be an oily deposit from the lubricant used on the focusing helicoid. Having finally get to the dirty group, I've cleaned most of it off, but its a two element group and I need to separate them to clean between them. i don't have the correct tool for this at the moment.
I am not looking forward to putting it back together. It will be a major challenge not to get it full of dust since all the (large) front elements have to come out.
Once I've got it cleaned and reassembled, I will be testing it on my E3. It's a very compact lens for 400mm so I'm hoping it will work well.
E3 | E-M5 | EPL-1 |ZD9-18 | ZD12-60SWD | ZD14-54 Mk1 | ZD50-200SWD | ZD50-200 non-SWD | EC14 | ZD25 Pancake | ZD35 Macro | Panaleica 25mm |