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01-23-2014, 06:34 AM   #1
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Pentax-F SMC 35-70 - Dismantling Help?

I just received one of these bad boys, which is in good condition except for light fungus on the inside of the rear element. There are 2 plastic fingers opposite each other on the concentric holder of the rear optic - these look like an easy way to remove the rear optic with the right tool?
Anyone shed any light on this please?

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01-23-2014, 06:53 AM   #2
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In this particular model, the rear element is embedded into one of the two parts that form the black plastic baffle.

You should always use a proper tool (lens wrench) for jobs like this, but if you have a suitable tool like a calliper or long nose pliers, you can use that to unscrew (turn counter-clockwise) the centre portion of the baffle. It should not be too hard to turn, unless someone has glued it into place. Just be careful not to damage the lens!

Alternatively , you just need to unscrew 3 screws holding the baffle to the mounting flange. There are actually four screws, but one of the screws (of the two screws that are close together, the one on the right, looking at the lens with back-end pointing upwards) holds a square piece of metal, that acts as a stopper for the aperture actuating lever. Note that the lever is attached to the baffle as well.

Last edited by tom1803; 01-23-2014 at 07:29 AM.
01-23-2014, 07:21 AM   #3
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QuoteOriginally posted by tom1803 Quote
In this particular model, the rear element is part of the black plastic baffle.

You just need to unscrew 3 screws holding the baffle to the mounting flange. There are actually four screws, but one of the screws (of the two screws that are close together, the one on the right, looking at the lens with back-end pointing upwards) holds a square piece of metal, that acts as a stopper for the aperture actuating lever. Note that the lever is attached to the baffle as well.

You can remove the element completely if you wish, but you'll need to remove the actuating lever first, and then unscrew the tube that's holding the element to the baffle. Be careful to note the orientation of the element and not to reverse it when re-assembling.
Brilliant Tom - an answer at hyper speed!

On closer inspection someone else has opened it up, leaving the 4th screw head pristine! Actually the heads aren't too bad (he says optimistically). I'll undo the 3 screws with the mount facing down. If I understand correctly I should get cleaning access to the rear of the element but not be able to remove it (without removing the actuating lever first).

One thing I've noticed is that infinity doesn't seem to correspond to the furthest manual focus - could this have to do with the previous attempt? If so can I fix this?

01-23-2014, 07:40 AM   #4
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Actually, I just edited my message as I made a mistake.

The rear element cannot be removed. It's embedded into the housing.

Adjusting the infinity focus on a zoom lens is a bit tricky as you need to make sure the focus is correct at both the short end and the long end of the zoom. Unless there's a significant difference between the infinity mark and the actual AF infinity, I wouldn't worry too much. Some lenses will actually turn past the infinity marking.

01-23-2014, 07:55 AM   #5
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QuoteOriginally posted by tom1803 Quote
Actually, I just edited my message as I made a mistake.

The rear element cannot be removed. It's embedded into the housing.

Adjusting the infinity focus on a zoom lens is a bit tricky as you need to make sure the focus is correct at both the short end and the long end of the zoom. Unless there's a significant difference between the infinity mark and the actual AF infinity, I wouldn't worry too much. Some lenses will actually turn past the infinity marking.
It certainly looks as though it could be turned - just as well I didn't try!

I'll leave the infinity issue for now.

I'll let you know how I get on
01-23-2014, 02:08 PM   #6
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From my experiences with a number of infected optics I doubt that this amount of fungus causes any detectable image deterioration (tho' its hard to tell without taking identical pics with 2 lenses, one clean). I'd be inclined to ignore it. Too easy to do more harm than good. Ideally this was the reason you got the lens for a great price.....right?
01-24-2014, 09:54 AM   #7
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After some fun & games I'm pleased with the result - thanks Tom
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01-24-2014, 04:28 PM   #8
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You're welcome.

Looks VERY clean. Good work!

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