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03-12-2017, 01:53 AM - 1 Like   #1
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It pays to regularly inspect your lenses...

... or how my DA* 60-250mm nearly made me cry...

Ok, so my weekend activities included hauling my new K-1 to a soccer based fitness-camp activity for kids, 60-250 attached, everything went great (not sure why there was all the fuss about the K-1s autofocus... it kept up pretty damn well for what clearly isn't a sports camera). Afterwards, mad dash back to the car and the rest of the weekends activities.

That evening, I get home and start putting my camera gear away, a quick check over to see if anything needs a clean, and... OH CRAP! One of the front elements of my 60-250 has a chip on the edge (technically a conchoidal fracture, apparently). What the... how did that happen? Oh god, is my precious lens ruined? Ok. Bit of panic. Turns out the retaining ring which kept the front elements had worked itself a little loose, loose enough for the elements to slip around a little, and enough that when sitting in my camera bag being jiggled about as I walk, enough to cause that precious, fragile glass to chip. Fingers on the front element, yep, clear movement. Really not cool.

Ok, so from my telescope hobby, I know that chips are not something to get super worried about, edges chip all the time if you are building your own 'scopes or needing to do an objective transplant. Normally these get covered by retaining rings or baffles, but the age old trick is to apply some matte black paint, prevent light hitting the reflective surfaces of the chip. No problem, except it isn't the front element with the chip, it is the one behind it. Great, surgery time on a 60-250... this is a little different from half-stuffed manual focus primes, but I carefully remove the front element group, dig up some india-ink and gently apply with a brush. Then I clean everything up, put it all back together and... tada! Looks not bad really. I did carefully position the blacked out chip to be at the 'bottom' of the lens, so that it would sit on short-edged dimension of the frame.

Now the big test, I put it on my K-1, and take some test shots at 250mm. Everything looks fine, no problems. I try to get some flare without the lens hood on... and just like before I have to really work on it to bring it out, everything looks as it was, no new visual nasties. Final test, white wall at f32.... not at all visible.
Everything is back the way it should be, minus the hit to the lens' value and my ego.

Big take away lesson, make sure nothing wobbles that shouldn't wobble. I might have avoided this if I had checked to make sure there was no movement in those front elements. I guess it ain't that bad in the end, but that small black mark will forever stand as a reminder.

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03-12-2017, 01:59 AM   #2
Ash
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Nice reminder.
Sorry for the accident. Incidents like these can never be reversed as much as we'd like to redeem ourselves for the oversight.
But if this lens is a keeper for you, then no significant loss.
Shoot on.
03-12-2017, 02:15 AM - 5 Likes   #3
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QuoteOriginally posted by GodsPetMonkey Quote
make sure nothing wobbles that shouldn't wobble
I gave up on my waist quite a while ago now.
03-12-2017, 02:34 AM   #4
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QuoteOriginally posted by Ash Quote
Sorry for the accident. Incidents like these can never be reversed as much as we'd like to redeem ourselves for the oversight.
But if this lens is a keeper for you, then no significant loss.
Thanks mate, and yeah, the lens is a keeper - if I was really upset about it I would look into getting it repaired, but I think I'll live with it for now. Might change my mind later, but I think that would come down to the aesthetics as I can't see any loss in performance.

QuoteOriginally posted by Kerrowdown Quote
I gave up on my waist quite a while ago now.
Haha, very different problem.

Though it gives me an idea - lens garters! Not sure what they would be good for, but hey, why not?

03-12-2017, 02:39 AM   #5
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QuoteOriginally posted by GodsPetMonkey Quote
Though it gives me an idea - lens garters!
Have to be from big fast aperture lenses, to get anywhere near me...
03-12-2017, 07:10 AM   #6
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nice repair job and good resourcefulness on how to execute. Got a new vocabulary word too, so double value from your post.
03-12-2017, 10:15 AM   #7
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QuoteOriginally posted by GodsPetMonkey Quote
snipped for brevity...I did carefully position the blacked out chip to be at the 'bottom' of the lens, so that it would sit on short-edged dimension of the frame....
Good success story. I thought it was risky to rotate elements with respect to each other, because minor defects in different elements might have previously been balancing each other out. I've usually heard that in the context of Schmidt Cassegrain telescope corrector plates but thought it applied to any multiple element optical system.
03-12-2017, 08:19 PM   #8
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QuoteOriginally posted by DeadJohn Quote
Good success story. I thought it was risky to rotate elements with respect to each other, because minor defects in different elements might have previously been balancing each other out. I've usually heard that in the context of Schmidt Cassegrain telescope corrector plates but thought it applied to any multiple element optical system.
Always a risk, but a pretty low one - these sorts of lenses are ultimately just refractors, a pretty simple design concept and the elements should be symmetrical across the x and y axis.

Any flaw in an individual element would need to be corrected in another by hand (painstaking process) and an asymmetry in the design would see some kind of alignment mark. Given the high precision of machining a major flaw is unlikely and anything that exists within manufacturing tolerance wouldn't be individually corrected for.

But I wouldn't go rotating things out of boredom

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