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Flybye
Tinkerer
Username: Flybye
Post Number: 1
Registered: 01-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, January 29, 2010 - 07:05 am: | 
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The one picture that I have taken with the lens looked perfect. When I look straight through the lenses, it looks crystal clear. Then I decided to put a flashlight to it and I was like hmm. The element behind the front glass looks super hazy with streaks. As if someone opened it up, tried to clean it, did a bad job, and closed it back up. I put an LED flashlight at the back of the lenses and it looks super hazy. But again, just looking through it, it looks clear.
Is there an easy way to get to the element behind the front glass or is this a total tear down job? I'm also worried about the aligning issue that people talk about when putting them back together. Should I even be concerned if I can not see this haze without a light source directly on the lens? |
Gez
Tinkerer
Username: Gez
Post Number: 172
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, January 29, 2010 - 01:14 pm: |
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You're in luck! I did an AR 300mm/4.5 a few weeks ago. The haze is probably due to evaporated lubricant that has condensed on the back surface of the front optical cell and is not too serious as long as fungus hasn't started to eat the oil film. So you can leave it for a while until you have more experience/confidence.
Leave the name ring in place, it doesn't hold anything.
The 300mm is made along traditional lines. Pull the hood forward and you will see 3 grub screws at the rim just before the main barrel gets narrow. Slacken off those screws by a couple of turns. You should now be able to gently unscrew the whole protective shield exposing the front optical cell. Be very careful now as the large front glass is unprotected.
Extend the focusing grip to minimum focus, this will expose 3 more grub screws on the narrow part of the barrel, these hold the front cell. BEFORE slackening off these screws use a marking pen or similar to scribe the exact position of the front cell. This is important as you will need these scribe points later. Carefully unscrew the whole front cell, the thread should turn smoothly without much force being required.
A few gentle wipes of the glass with lighter fluid should remove the oily film, provided fungus hasn't got there! Screw the front cell back to the scribe points and tighten the grub screws. Do the same for the protective shield and you're done!
When you are happy things are OK apply some contact adhesive to the heads of the grub screws.
If the haze is between lens elements or in the back optical cell you are on your own. |
David_nebenzahl
Tinkerer
Username: David_nebenzahl
Post Number: 108
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, January 29, 2010 - 01:14 pm: |
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Sorry, can't help you with opening up this lens, but I can tell you that it's basically a matter of your comfort level. If you can live with the haze that you can see inside the lens, then you should just go ahead and use it; the haze probably doesn't make much difference in your photos.
If it really bothers you, though, then hopefully someone else here can give you advice on how to proceed. |
Flybye
Tinkerer
Username: Flybye
Post Number: 2
Registered: 01-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, January 30, 2010 - 05:00 pm: |
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Thanks Gez!
A few things:
When I pull the hood forward, I only see 1 hole, but it has no screw in it. Broken/missing screw or is there another trick to it?
When I focus to bring the lens forward, I only see 1 screw also. I'm sure there may have been a few variants to this. The screw on this barrel can easily be turned.
What about the screw hole on the barrel that I get access to from moving the hood forward? |
Flybye
Tinkerer
Username: Flybye
Post Number: 3
Registered: 01-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, January 30, 2010 - 07:21 pm: |
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Never mind. I got it! The screw under the hood was hardly there. I looked at it with a magnifying glass and it was partially there. I broke the rest off, tried to twist the front piece and it started turning!
Finally took it off, then I removed the front group. To my wonderful surprise, the haze was only on the outside of the rear lens. It immediately wiped clean, put everything back together, and it looks perfect! Only thing now is that I have no screw to hold down the front piece, and even if I did get a screw, I'd be too scared to try to tap that tiny hole myself.
But it does not look like it is going anywhere, so I'm sure I am good. Thank you so much again. I got these lenses at an amazing deal, and am super happy that the money I put was not in vain. |
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