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08-10-2015, 06:55 AM   #1
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How to disassemble SMC Pentax-FA 100-300mm F4.7-5.8 front element?

Hi,

I recently picked up a SMC Pentax-FA 100-300mm F4.7-5.8 lens for a good price together with some other stuff, from someone who didn't know much about cameras. I figured I would have some fun with it on an upcoming trip, and then sell it on as I don't use long telephoto that much.

It works just fine, and seems sharp enough, but there's one annoying detail the seller didn't see before shipping it to me: it's got some minor fungus growing on the side of the glass right behind the front element. I bought it as is, and can't return it (nor do I want to).
It seems to be isolated to that element and is not that severe, but it seriously affects the value of the lens, the faith I have in it, and it's just plainly annoying.

Since it's isolated to the 2nd element alone, I was wondering if anyone if it would be easy to take off the front element of the lens. If I can get that one off, I'm pretty confident most the fungus will just come off with some wiping. Then I can resort to some days of UV-exposure and I think the lens will be fine.
Has anyone here ever done that?

I can see two small notches next to the front glass, and was wondering if that's how you get it out. If so, what tools should I use for this?
I don't have any pictures of the front side of the lens, but there is one in this for sale post. You can see the notches right next to the glass on the top and bottom of the 2nd picture.
The fungus on my lens is definitely before the glass element that is held in with the three visible screws. If it were any deeper in, I wouldn't try disassembling myself...

Any further tips are welcome.
Thanks in advance!

- Tom

08-10-2015, 07:15 AM   #2
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Yeah, you use a lens spanner wrench to unscrew with those notches.
08-10-2015, 08:36 AM   #3
TDN
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Cool, thanks! I had no idea what to look for.

Spanners are on their way
11-27-2015, 06:31 AM   #4
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Just a small follow-up on this:

I ended up disassembling the lens with only minor scratches to the paint of the filter ring. You really need to be careful with this one, even with lens spanners.
For future reference: you need to insert the sharp ends of the lens spanners into the two small holes next to the front lens element to screw the actual element a bit further down so the retainer ring is loosened. Then you need to use the flattened ends to carefully screw out the ring from the filter thread. The front element then simply screws out of the filter thread as well. You then have access to the screws to take the lens apart if needed. However, it turned out my fungus was limited to the back of the front element. After wiping it off with a lens cloth and reassembling, the lens performs beautifully!

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