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Vivitar 28-90
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PostPosted: Thu Apr 26, 2018 2:26 pm    Post subject: Vivitar 28-90 Reply with quote

Hello all,

My name is Giovanni, I'm from Italy; I'm a long reader of the forum, and decided to register today because I need your help.
I'm the happy owner of a Sony A6000 machine; I've been bite by the "old manual" glass beast, so now my A6000 rarely sees its kit 18-55 lens, but instead I use it with a growing collection of old manual lens.
I actually own few Vivitar (S1 70-210 V3, 28-210), Pentax A (70-210), Olympus Zuiko (50mm), few russian prime lens (Mir-1B), etc.

I just got a Vivitar S1 28-90, whoch is a great lens, but it has, as usual, the iris blades covered in oil, and almost stuck.
Also the zoom barrel is really hard to move up and down, probably because the lubricant has moved onto the iris blades...

So, my question is: is there anybody that can help me in disassembling the 28-90 lens?
I'm a technician by job (and nature), so I should be able to dismantle and then mount it back again.
i already removed the front and middle lens groups, gaining access to the blades from the front; but this is not enough, because I really need to rempve the iris and clean it better.

I searched and searched, but I didn't found any useful information/manual on how to service the lens; can anybody help me?
A service manual would be very, very appreciated.
Even a step by step procedure would be welcome.

Thank you in advance!

Regards,
Giovanni


PostPosted: Fri Apr 27, 2018 7:13 pm    Post subject: Reply with quote

Welcome to the forum, croccodillo!

I have dismantled the Vivitar S1 28-90 a couple of times. It is a complex zoom, so many steps can be involved.

Since you have already removed the front and rear groups and you can access the iris blades, I recommend you try cleaning them in place. Get yourself some naphtha (aka lighter fluid), and several cotton swabs (known as Q-Tips here in the States) for this procedure.

Dunk a swab liberally in the naphtha and begin wiping down the blades. Exercise the iris so it opens and closes as you do this. But during this whole operation, be as gentle as possible with the cotton swab. Wipe down the blades repeatedly until no more sign of oil contamination exists. If you can access the blades' pivot points, be sure to soak these areas as well, because this is where much of the oil resides. Let the naphtha evaporate between cleanings, then close and open the blades to inspect the amount of trace oil that remains. Keep doing this until you can close and open the blades repeatedly with no sign of oil anymore. Obviously the blades should be "snappy" in behavior. Once the iris appears to be clean of all traces of oil, I would exercise the iris blades as many as 100 times to convince myself that no more oil will gravitate to the blades.

Now, as for the zoom function. You need to pull off the rubber grip from the zoom/focus collar. This will expose nylon bushings with screws in the center that run in curved slots. They control the focusing behavior as the zoom collar is pushed in and out. You have to be careful with these. If you attempt to move the collar back and forth too aggressively, you will strip out the bushing screws, and once you've done that, repair is not possible; the lens is ruined. So, remove all the bushings and screws and you should be able to slide off the collar (I think! It's been about six or seven years since the last time I dismantled a 28-90), exposing the zoom and focus mechanism and its lubrication. All of the old lube must be removed and replaced with a suitable lubricant. I've often seen lens lubricant offered on eBay, so that's one source. Others here may be able to suggest other sources for you.

Take plenty of pix with your digital camera as you dismantle the lens, so you'll know most easily how to put it back together again. When re-installing the collar bushings and their screws, be careful not to overtighten. It is not that difficult to strip out the threads, and once this happens, the zoom is toast. So, easy does it!


PostPosted: Fri Apr 27, 2018 9:24 pm    Post subject: Reply with quote

This is the helicoid grease I use.

https://www.ebay.co.uk/itm/HELIMAX-XP-Camera-Telescope-Optical-Instrument-Focusing-Helicoid-Grease-w-PTFE/271194713421?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649


PostPosted: Fri Apr 27, 2018 10:22 pm    Post subject: Reply with quote

Yep, that's the same stuff I see on US eBay.