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07-28-2011, 06:59 PM   #1
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Should I clean my A50/1.7 - or just call it a loss ?

I have an A50/1.7 - I like it a lot. But it has .... fungus I didn't care about it for the past year - but now looking at things, that side of the lens does appear a tad softer than the left side.. then again - I might just be imagining that. Best I can tell, its on the rear of the front group, front side of the element just in front of the aperture blades.

I've checked up on the net, read a fair few articles, have fashioned a Spanner Wrench set and now... Don't know if I'm being stupid and should just call it a loss and get a new one when it turns up for the $50-$80 locally on ebay...

What does anyone thats attacked an A50 through the front think ? I assumed going through the front would be easier, based on looking at how the rear is assembled (via Pentax SMC A5017 Lens Assembly ) - but am I wrong ?

I've not done a lens before - but I'm not entirely inept when it comes to mechanical construction.

What is the best thing to do ? and then whats the smartest ?

I know these aren't 'bank breakers' - but shipped to Australia they can be a little more than their initial price tag, and local supplies of the 50/1.7 aren't exactly large... same reason I'm not sure about using Eric for a CLA - as the round trip shipment would make it pretty uneconomical...

What are peoples thoughts ?

07-28-2011, 07:50 PM   #2
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It is doable, though not easy. Careful about a home made spanner, if it slips and scratches an element, you could be worse off. Real spanners are about $16 on ebay.
Spanner Wrench(1/32") Great Tool for Lens | eBay
If the fungus is on elements in the rear of the lens, then you must go though the rear, the diaphragm is in the middle and will block access. Same with the front. A rubber cane tip can be good to remove the ring around the front element, get one the right size. Then there should be a metal plate held with screws that holds the front group in place.
Pentax uses JIS standard for screws. You might want to get a set of JIS cross point screwdrivers. A set with #000, #00, #0 and #1 would be good.
Moody 4 Pc Extended Reach JIS Screwdriver Set/58-0405 | eBay
It is good to disassemble the lens over a shallow box or something to catch the tiny ball and other things that will fall out. Take many many pictures as you go! Figure out how you will keep the glass elements in the proper order and the proper orientation. If you install an element 'upside down' it can severely effect the IQ. Don't let pets or children near your work area. After you get the elements clean, wear rubber gloves to reassemble.
A thread for you to read:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/91560-pentax-m...-assembly.html

Last edited by gp1806; 07-28-2011 at 08:13 PM.
07-28-2011, 08:59 PM   #3
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If you can get the mount off, it'll look like the lens on the right:



Then it's probably easy to unscrew the rear lens group. It sticks out far enough to get a good grip on it. The potential problem is, the mount screws are going to be trouble without the JIS screwdrivers. If the fungus is not where you think it is, you'll need the spanner to get the rear group apart. You shouldn't need to worry about bearings as long as you don't slide the aperture ring off. It's held in by the mount. If you get down to individual elements, make sure you put them back facing the right way.

If it's a loss now and a professional repair is too costly, the worst case is, you buy a new lens anyway.
07-28-2011, 10:14 PM   #4
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If it's in the front side, you don't need to open up the rear end of the lens. Just unscrew the front rim (the one just outside the front glass) and you'd be able to take out the whole front group. It's easier than you thought

Good luck.

07-29-2011, 10:17 PM   #5
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thanks guys - I'll have a look for some spanner wrenches locally - I seem to find a lot of reports on MFLenses that the ebay spanners can be very hit-and-miss anyway ?
07-31-2011, 09:43 AM   #6
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Done! Details and Pictures in https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/153858-how-i-r...lots-pics.html

Thanks all for the tips/suggestions.
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