Fixing 20-35 mm f4. Left over bits.

**retneva** · 03-15-2018, 12:24 PM

I dropped my favorite lens.
Managed to fix the plastic zoom pin that was broken and reassembled everything, almost. I’m stumped by these little metal bits. When I disassembled they fell out from under aperature control plate.
What do they do? Where do they belong? How do i put them there?

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HarisF1 · 03-15-2018, 12:33 PM

These shims usually sit on the back of the helicoid and you'll find either the focus assembly or zoom assembly sit on these.

If you look at the back of lens as you dismantle it you will notice there's a point at which you need to remove four screws to get into the back of the focusing helicoid or aperture assembly. The two pairs of shims sit opposite each other, and the access to these screws shouldn't be blocked. The zoom ring or focus ring then goes on top of this.

That's the usual point at which they sit (on a DA* 16-50 at least), and I haven't opened up a 20-35 to see exactly where you'll find these.

Ontarian50 · 03-15-2018, 01:12 PM

Yes, these shims help calibrate focus. The assembler at the factory would have had a few thicknesses to choose from to get the lens correctly set up.

Without them, I think you'll find your lens focuses a bit past infinity. Also, some zooms have the focus adjustment on the front end, but the shims at the rear keep the whole lens unit ideally set up for best sharpness.

At least you have all three. Nothing more frustrating than finding you're one shim too short and can't figure out where it went to.

**retneva** · 03-16-2018, 02:51 AM

Thank you guys! That helped.
The second deeper set of 4 screws on top of the zoom helicoid and set in pairs. As far as I can tell all 4 of same thickness, but I don’t have a micrometer at hand to know for sure. Seems to work now and looks sharp.

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03-15-2018, 12:33 PM	#2
HarisF1 Veteran Member Join Date: Apr 2016 Posts: 543	These shims usually sit on the back of the helicoid and you'll find either the focus assembly or zoom assembly sit on these. If you look at the back of lens as you dismantle it you will notice there's a point at which you need to remove four screws to get into the back of the focusing helicoid or aperture assembly. The two pairs of shims sit opposite each other, and the access to these screws shouldn't be blocked. The zoom ring or focus ring then goes on top of this. That's the usual point at which they sit (on a DA* 16-50 at least), and I haven't opened up a 20-35 to see exactly where you'll find these.

03-15-2018, 01:12 PM	#3
Ontarian50 Veteran Member Join Date: Mar 2015 Posts: 530	Yes, these shims help calibrate focus. The assembler at the factory would have had a few thicknesses to choose from to get the lens correctly set up. Without them, I think you'll find your lens focuses a bit past infinity. Also, some zooms have the focus adjustment on the front end, but the shims at the rear keep the whole lens unit ideally set up for best sharpness. At least you have all three. Nothing more frustrating than finding you're one shim too short and can't figure out where it went to.

03-16-2018, 02:51 AM	#4
retneva Site Supporter Join Date: May 2013 Posts: 12 Original Poster	Thank you guys! That helped. The second deeper set of 4 screws on top of the zoom helicoid and set in pairs. As far as I can tell all 4 of same thickness, but I don’t have a micrometer at hand to know for sure. Seems to work now and looks sharp.