Topic: sigma 400mm f5.6 apo - integrated lens hood - help/advice needed

[kentish cob]

I've mentioned elsewhere, the sticky zen finish on this particular lens.
Well I'm in the process of cleaning it with a view to selling it on as I haven't used it in years.

So, while the gummy barrel is fairly easy to clean down to the black metal with a craft knife blade and some "goo-gone", the integrated lens hood is almost stuck solid... either there's a bunch of gummy "shite" stuck up under it, or some form of o-ring has dislodged and is preventing smooth travel.

Anyone have any experience with this lens and this particular problem?
I can't see a way to remove the hood from the lens to give the whole thing a proper clean.

Thanks in advance.

[Pete_R]

You might be better asking over on MFlenses (http://forum.mflenses.com/). I did find a diagram of the element arrangement over there but nothing about removing the hood - but someone might know.

[jojonas~]

I thought looking up on how to repair a pentacon 135 2.8 as an example but with that one you basically need to take the whole thing apart starting from the back to get the hood off. I wonder if the sigma is the same...

[kentish cob]

Thanks for your suggestions gents.

To my mind, there's two possibilities...
Either: the front lip of the hood detaches (threaded..?) allowing the hood to "reverse" off of the body. The front lip appears to be moulded, but I may be wrong. I've tried to get a good grip to twist and see if it's a mated part but it's proving difficult (damned trapped nerve in my neck has left me distressingly weak in my right arm). Some friction method to increase the grip is probably required.

Or: the front element of the lens has a "step" on the back edge of its housing ring and is forming a "stop" which prevents the hood from being pulled off of the front of the lens (remove front element -> remove hood).  Problem here is there are no tooling grooves on the front element ring, so (again) some type of friction method is needed.

Does all this sound logical?
I can't imagine that factory assembly would be any more complex than either of the above?

[Pete_R]

It's more likely the front of the lens needs to come off rather than the front of the hood. The trim rings around the front of lenses rarely have any method of gripping them and a rubber tool  is usually the only way go. I sometimes use a latex glove stretched over a tin can or anything I can find that fits. Otherwise there are tools you can buy to do the job. e.g. http://www.ebay.co.uk/itm/9pcs-Camera-DSLR-Lens-Repair-Tool-Ring-Removal-Rubber-8-83mm-Accessories-/122395469104

On a few lenses, the whole front of the lens unscrews in one piece rather than just removing the trim ring. A close look at it will usually determine if it's all one piece or not.