So, you've just purchased your fancy new (to you) Auto Chinon 55mm F/1.4 and you anxiously await its arrival, it turns up and you see that the aperture doesn't close down, no matter how much you turn the ring or press the pin (Insert sad face here)
Well before you hastily rush off to put in a return request, I'm going to show you how to repair it step by step, bringing it back to its former glory.
To gain access to the internals of the lens, first focus to the minimum focus distance and unscrew the 3 small grub screws holding the filter rim in place.
Once these three screws are out, place them down somewhere that you're not going to loose them, (if you're not careful, you WILL lose them, they're tiny)
Once these are out, simply turn the filter rim counter clockwise until you can take it off
once the rim is off, you'll be greeted with a thin plastic retainer ring, this ring hold in the entire optical block. Using a lens spanner, turn this retainer ring counter clockwise until you're able to remove it.
Once removed, simply place it down somewhere and set it aside
Now it's a case of removing the optical block, This isn't as hard or as daunting as you might think. Once the retainer ring is removed, simply place your thumb on the rear element while holding the lens barrel and push upwards. This will remove the entire optical block from the housing in on piece.
With the optical block removed, you're going to want to remove the front element.
To do this, you're going to need a rubber suction tool or something similar that will fit inside of the front element threads, and just turn CC until you can take it out. (Sometimes this can be very tight, so you may need to use some heat to melt the adhesive)
Then flip the block upside down and remove the rear element. (You can do this one by hand)
Again, just twist CC until you can remove it.
Once both the front and rear element are removed, all you'll be left with is the housing for the aperture.
And this, is the root cause of your issues. This is what's preventing your blades from opening and closing, so let's fix it.
There's Three screws around the aperture housing, just go ahead and remove these.
Once these screws are removed, and placed somewhere that you're not going to loose them (DO NOT LOOSE THEM, OTHERWISE YOU WON'T GET IT BACK TOGETHER) you're going to want to remove the black ring pointed to here. The easiest way to do this is with a pair of tweezers, simply wedge underneath and pop up one side and then pop up the other side and lift out
once this is out, simply place it ton one side
Next simply use your tweezers to life out the Grey ring, this just lifts out.
Take note of where the notch shown in the image is. This notch has to go back in the gap in the housing when re-assembling. (You'll know where the notch is because there's only 1 and it's next to an aperture notch)
Once this ring is removed, just set this one to the side as well.
once the grey ring is removed, your blades will just simply fall out, ready for cleaning.
Once all of your blades and rings are removed, simply clean them. I use 99.9% Isopropyl alcohol in a jar and just place them all in this and let them sit for a few minutes
While your blades and rings are soaking, it's also a good idea to clean the inside of the aperture housing. I just have some Isopropyl alcohol in a small spray bottle. I just spray this generously inside of the housing and wipe off with a lint free cloth and give it a blow with some compressed air.
Once your blades and rings have sat for a few minutes, just remove them from the Isopropyl alcohol and dry them off with a lint free cloth, ensuring that any oil has been removed.
Once you're sure that everything is clean, it's time to reassemble your lens.
At the risk of sounding like a 90's Hayne's manual, putting everything back together, is just the opposite of taking it apart.
Flip your inner housing upside down (the black ring you removed before the grey one) and then place the grey ring on top of it. (Also upside down.)
You'll know that the grey ring is upside down because the small bumps on the grey ring will face towards you.
Make sure that the notch mentioned earlier on is above the gap of the inner housing ring.
Now it's time to put your blades back in place.
On your blades, you'll see two notches, you want these facing downwards, so that they'll fit into the holes.
To place your blades back in the housing, you're going to want to match up the notches on the blades with the holes on the housing rings. (Top blade notch matches with the U shaped hole, & bottom blade notch, matches with the O shaped hole)
You're going to want to go CC with your blades matching the notches to the holes until you have one blade left, Once your blades are in place, you'll notice that they overlap each other. (This is good, it means you're doing it correctly)
Once you get to the point where you have one remaining blade, this is where it gets a bit tricky, because you've got to place this blade underneath the first blade while still getting the notches in the holes like you have done for the rest of them. (The easiest way to do this is to very lightly lift the first blade from underneath and slide the last one underneath) you can then just slide it around gently until the notches fall into the holes. (HINT: THE BLADES ARE MAGNETIC, SO IT'S EASIER TO USE PLASTIC TWEEZERS)
If this is the first time you're performing an aperture repair, you WILL fail this part, drop all of the blades and have to re-do it multiple times before you get it right. Don't let this deter you, you'll get it eventually.
Once you've got all of your blades in place, you're then going to need to insert this back inside of the main housing.
The easiest way to do this is to place your blade assembly on top of an upside down film canister.
Slowly place your housing over your blade assembly. Ensure that when placing the housing over the blade assembly that it's level. Try your best to line the screw holes on the housing with the screw holes on the blade assembly base, this will make it much easier to make sure that everything is lined up correctly. Go slowly, otherwise you may knock the blades out of place and have to start again.
Once back in place, you can then re-insert your screws, from here it's plain sailing.
Screw your front and rear elements back into the aperture housing
Your aperture assembly / optical block then goes back inside of the lens barrel
Ensure when placing your block back into the lens barrel that the notch for your aperture blades goes over the pin inside of the lens barrel. This is easier if you set the lens to F/8 and auto.
once your block is back inside of the lens barrel and you're confident that the aperture is now working, simply re-insert your lens retaining ring and tighten it by turning it clockwise
Lastly replace the filter rim and screw it tight, then replace your small grub screws
Once all of the above steps are complete, you're all done and you SHOULD have a working aperture again. Now you can attach your new lens to your preferred camera and go enjoy it.
Please note, we take no responsibility if you're not able to get your lens back together or if you break something.
Although this guide is intended to be as simple to follow as possible, if you believe this repair to be beyond your technical abilities, you're welcome to send your lens to us and we'll do this for you for £50
If you'd like to send your Auto Chinon 55mm F/1.4 M42 Mount to us for an aperture repair, please contact us at: Service@gibsoncameras.com or call us on 01709278228
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