Lens dropped/knocked & not focusing

goinggreynow

goinggreynow

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Morning all.
Feel I should really know the answer to this but I dont!
An old manual lens has taken a hard knock/been dropped and now no longer focuses. The front element has cracked.
In simple terms, could anyone kindly explain to me what's probably gone on inside the lens and whether it's possible to repair?.
Is it most likley that one or more of the internal lenses is out of alignment or could it be more serious?
Could it be the cracked front lens even though it still seems to be seated correctly? May seem an obvious answer, but I've seen videos showing that even extensive damage to a front element can still result in half decent/in focus images.
the aperture mechanism still works fine if that's relevant.
Thanks
 
When you say that it no longer focuses - do you mean that the focus ring does not turn or that the focus ring turns and you cannot achieve focus? In the first case, the metal has bent and you need to throw the lens away. In the second case, the front element is cracked and therefore at least partially moved. Other elements will also have moved and you need to throw the lens away.

Repairing is difficult as you do not have a good front element. Also, various parts screw together and those screw threads can have multiple start points - you need to start the thread at the right start point. When you have finished repairing the lens, you will need to collimate the lens which is difficult without a collimator.
 
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What lens is it?
If it's not some rare-as-rocking-horse-poo ridiculously expensive one then chances are it's now bin-fodder.
As John says, with the front element cracked it's probably not worth trying to sort out the focus issue anyway.
 
technical term is focusitus im sure its a latin term
simply it means its F***ed
bin the old thing and buy a new one :LOL:
 
Wozzaaah said:
What lens is it?
If it's not some rare-as-rocking-horse-poo ridiculously expensive one then chances are it's now bin-fodder.
As John says, with the front element cracked it's probably not worth trying to sort out the focus issue anyway.
Click to expand...

holty said:
technical term is focusitus im sure its a latin term
simply it means its F***ed
bin the old thing and buy a new one :LOL:
Click to expand...
many thanks for all replies - much appreciated.
The focus ring turns OK, it's just that I cannot achieve focus.
I don't like the idea of binning the lens, but I appreciate the advice that it is probably the most sensible/cost effective/non time wasting solution that is open to me.
the lens is a Petri 28mm by the way.
Thanks again to all.
 
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john.margetts said:
When you say that it no longer focuses - do you mean that the focus ring does not turn or that the focus ring turns and you cannot achieve focus? In the first case, the metal has bent and you need to throw the lens away. In the second case, the front element is cracked and therefore at least partially moved. Other elements will also have moved and you need to throw the lens away.

Repairing is difficult as you do not have a good front element. Also, various parts screw together and those screw threads can have multiple start points - you need to start the thread at the right start point. When you have finished repairing the lens, you will need to collimate the lens which is difficult without a collimator.
Click to expand...
Thanks for these comments John.
Could I please ask a follow up. I've heard the term collimate before but admit I don't really understand the term. I note what you say about my broken lens but could I ask if the same (collimate) process is needed when taking a lens apart to clean it - e.g fungus removal. Or is it dependent on the lens and how it's constructed?
Thanks
Stuart
 
A collimated beam of light is one where all the rays are travelling parallel to each other which is what happens when light travels from an object infinite distance away. A collimator provides this parallel beam of light without having to be so far away. It allows you to set the infinity focus which you need to do every time you reassemble a lens. You could fudge it by focusing on something a long way away but you run the risk of not having critical infinity focus.
 
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goinggreynow said:
An old manual lens has taken a hard knock/been dropped and now no longer focuses. .... In simple terms, could anyone kindly explain to me what's probably gone on inside the lens and whether it's possible to repair?.
Click to expand...
OK. You probably know that lenses are focused by moving some optical elements forwards or backwards. But you do this by rotating the focusing ring. So obviously there has to be a mechanism to translate rotational movement into back-and forward movement. That mechanism is called a helicoidal focus mechanism and it looks like this:

helicoidandcollars.jpg

[Picture from LensRentals strip down of a Canon 35mm f/1.4 Mk II - link]

If you've dropped the lens, it's likely that something in that mechanism has become bent. Maybe the outer barrel of the helicoid had become jammed against the inner one and won't rotate. Maybe one of those spiral slots has become constricted and the pegs won't slide along them. Something like that. But this is completely independent of the front element being broken.

It's repairable, but it's going to be expensive. Not worth it for a cheap lens.
 
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I had a similar problem recently with a 17-40L. It wasn't knocked or dropped though (as far as I know, it was an MPB purchase) it just stopped focusing.

I dropped AJ Johnstone in Glasgow an e-mail with the symptoms ( they have a faciltiy for this on their website), to me the lens was worth repairing and they diagnosed a faulty focusing motor and calibration by e-mail. They were right, it was exactly that and my lens was repaired in just over a week, it cost just over £180, which for that lens, was worth it.

As has been said though, it might not be worth it on cheaper lenses, bearing in mind you have a damaged front element too.
 
Somebody kindly dropped my 16-35 F/2.8L I had lent them and returned with saying anything. Ended up pay £270 to get it repaired as it need a new USM and some rollers which took ages to arrive from Canon
 
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