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[OM] Re: Lens groupings for a 4-element 2x teleconverter?

Subject: [OM] Re: Lens groupings for a 4-element 2x teleconverter?
From: Philip Pemberton <philpem@xxxxxxxxxxxxx>
Date: Tue, 25 Apr 2006 20:52:45 +0100
Never mind folks - I've figured it out.

Front element (1st):
  Flat side towards front

-- Spacer here

2nd element:
  Most curved side towards front. If you can't tell which side that is, put
  it against the convex side of the front element. One side will leave a gap.
  That's the side that should be facing the rear of the teleconverter.

3rd element:
  Most concave side to the front - this lens fits into a small black
  cylindrical frame that serves as a spacer.

-- Another spacer (like you didn't see that coming)

Rear element (4th):
  Concave side towards front, convex side towards back

Rear locking ring:
  There's a notch on the outer side of this ring. Use a VERY small
  screwdriver (be careful!) to turn it clockwise. It'll apply pressure to the
  rear element and hold the lens together. Stop turning when it gets to be
  adjacent to the notch in the side of the black mounting frame.
  
Disassembly isn't hard - put a bit of isopropyl on the back to loosen the
threadlock, then use the notch in the lock ring to move it anticlockwise
until it unlocks. If it's too stiff, push a screwdriver between the mounting
frame and the lock ring to break the threadlock and try again. If that still
fails, repeat but lever the ring out instead.

Reassembly is the reverse - push the lock ring into the mounting frame, then
move the notch in the lock ring back round until it's nice and tight. Get a
nice bright torch (flashlight) and shine it through the lens to make sure you
haven't left any fingerprints or dirt inside before you lock the lens back
together again, though (see below).

Total time taken to clean the teleconverter, including figuring out the lens
grouping: 2 hours.

Total time taken to pull the teleconverter apart and clean it again after
realising I'd left a thumbprint on an internal lens: Another 20 minutes.

Dusty teleconverter: Free
Bottle of 90% isopropyl: Found in the cupboard
Microfibre lens cloth: Found in a drawer
Jessops OM rear lens cap: £3.99
Repairing something that would otherwise have ended up in the bin: Priceless.

Apologies for the blatant ripoff of the Mastercard "Priceless" advert...

-- 
Phil.                         | Kitsune: Acorn RiscPC SA202 64M+6G ViewFinder
philpem@xxxxxxxxxxxxx         | Cheetah: Athlon64 3200+ A8VDeluxeV2 512M+100G
http://www.philpem.me.uk/     | Tiger: Toshiba SatPro4600 Celeron700 256M+40G

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