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Hoya 28mm Focus throw.
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PostPosted: Tue Dec 06, 2016 2:44 pm    Post subject: Hoya 28mm Focus throw. Reply with quote
As stated,I have a Hoya 28mm f2.8 that has strange Focus throw.At minimum it is and should be about one foot,fine.However it reaches Infinity at about 1.75 feet indicated,anything beyond that is totally out of focus.
Does anyone else experience this problem?

None of my other Manual kit does this I should add,if anything most of them struggle to reach infinity.

Camera used is a Olympus E-M10 with an adapter,same adapter used on other M42 Lenses in my kit.


PostPosted: Tue Dec 06, 2016 3:18 pm    Post subject: Reply with quote
It is likely that someone has incorrectly mounted the multi-thread focusing helicoid of the lens. By my calculations, the lens is 1.64mm shorter than it should.


PostPosted: Tue Dec 06, 2016 4:14 pm    Post subject: Reply with quote
My thoughts exactly Gerald,though not in a measurable sense. I have attempted reconstruction but cannot get any change I end up with the throw being too long and the retaining 'prongs' jumping out of register at extended focus (close up).The lens will not physically go amy shorter (wrong direction anyways!) The lip of the Filter ring is flush with the focus barrel at max. infinity setting,any attempt to adjust to get the barrel further out requires a full turn and as I said earlier results in retaining prongs disconnecting. So far I haven't messed with the actual helicoid screw part,that comes next Smile


PostPosted: Thu Dec 08, 2016 4:36 pm    Post subject: Reply with quote
This has now been rectified. I saw a post elsewhere on here regarding Fotga adapters and sure enough I have a Fotga adapter that is just under 1mm too short. But thats not the whole story.

While I was trying yet again to find out what was wrong I checked the lens elements,to make sure non were 'stuck' or not seated properly - and became suspicious of the 3rd element in the front assembly,to my way of thinking it was downside up,it is a double Convex (?) lens but the main 'curve was facing towards the rear.My understanding is that lenses in the front group generally face forward and in the rear group face towards the camera,except in compound cases.
I flipped the lens around and had an improvement in as much that infinity now came up at about 5 metres instead of just under 2 metres.

When I also then discovered my adapter was undersized I added a thin plastic shim to the connection between lens and adapter,bingo,Infinity just a smidgeon before the end stop.

Next,sort out a Takumar 28-80 focus ring Smile
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