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seanmckinney
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, January 17, 2006 - 10:39 am: | 
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Hello
I bought a 2nd hand sigma 80-200mm zoom for my minolta x700, its zoom was a bit grabby in places and the the lense reach its infinity stop slightly before what I would deem infinity. Since it was cheap I decided to have a go at adjusting it.
Mistake no 1)
should have stripped the lense in a lipped tray and not expected all 5 moubting plate screws to be involved in securing the mounting plate to the lense body, only 3 do that. Consequence the mount came away before I had time to not the mechanical connections between the apeture ring and the 'legs' inside the lense, I think I have it "sussed". Also the detent ball providing the click action of the apeture ring disappeared into the either, have you any idea how hard it is to find a 1.5mm ball bearing in carpet. I swept with an magnet and then hoovered and kept the dust, ye gads there was a lot. I swept the dust with a magnet but no ball so I a mates getting me one from Manchester, there are none in Belfast.
Mistake no 2) using cheap tacky jewellers screw drives cost me 1 screw that I will have to drill the head off, use good quality screw drivers for their size these screws were relatively tight. Anyway enough of the humour.
The questions, at the camera end of the lense where a set of thin washers that I guessed were/are shims. I thought these would be focus adjusters and I have been told that they are the adjustment for the wide angle end of the zoom range. The same person told me that the infinty adjustment was under the rubber of the grip. True enough under the grip was a tape joining a sleeve and sleeve around a lense holdet, the latter is on a multi start helical thread. and the sleeve and lense holder are connected by 'rollers' on the holder which fit in grooves on the sleeve. I assume I effectively just rotate the sleeve relative to the sleeve one way or the other until the lense's infinity matches mine then retape the 'seam'.
Am I correct in that thinking?
With the thread being a multi start does it matter if the threads are reengaged in the same relative positions? I dont think so but I may well be wrong.
Are the individual lenses likely to be mounted seperately or in something resembaling cartridges? I would like to clean the zoom action as it was a bit stiff in mid zoom although that may be down to cam like profiles in some of the roller guide ways I have seen. But I dont want to reach the stage of 'handling' individual lenses.
This is the view of the legs in the lense mount assembly that project into the lense "x" is on the apeture ring and is the one I am concerned about, "y" is on the actual mount and I think can only go 'one way'
http://i8.photobucket.com/albums/a9/seanmckinney/IMG_2729sigmalensebasecroppedthinne.jpg
I think "x" in the photo above 'wraps around' "x" in the following photo which is the view looking into the lense,
http://i8.photobucket.com/albums/a9/seanmckinney/P1170120croppedthinnedpainted.jpg the alternative would be to place the two "x"'s side by side which seems odd to me.
The following photo is of the partially 'exploded' lense \topurlhttp://i8.photobucket.com/albums/a9/seanmckinney/IMG_2726explodedsigmalensethinned.jpg
Sorry I cant seem to get the last two phots tpo act as links, you will have to copy and paste them.
Thanks Sean. |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, January 17, 2006 - 07:00 pm: |
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The cheaper Sigma lenses all use this split outer barrel held by tape. I have only worked on the EX types so cannot really help, but offer the following; Normally the infinity stop is secured to helical barrel and not the outer grip tube. If you are saying that it is just the scale that is out of position and the lens is otherwise correctly focused, then what you say may work. If focus is out, I would have thought that you would have to go deeper into the lens.
If you take out the optics you will be dealing with individual lenses or cemented pairs somewhere in the strip-down. Some of the groups may be held in a removable holder, depends on the inner construction.
I personally have never worked on a lens where the start position, of the multi start helix thread, was not critical.
If an operating lever has a U shaped end (X) it is usual for the lever on the other piece (lens or mount) to slide into the U shaped retainer.
Finally be careful what you lubricate these plastic bodied lenses with. The original lube is a product specific for plastics and metals. |
seanmckinney
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 18, 2006 - 02:42 pm: |
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Ta.
I found the missing ball today and surprise surprise I got in back in situ. With my X's coupled all seems well. It's so much easier once you have an idea where things go. I am about to start on the focus adjustment so we will see how things go there but the testing will have to wait for day light. I am tring not to lubricate anything as it all seems fairly smooth but I wont use Castrol LM or Duckhams finest wheel bearing grease. I do have some electrical/electronic grade silicon grease, would that be suitable?
Thanks once again.
Sean. |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 18, 2006 - 05:22 pm: |
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That electronic grade grease is better than nothing, if you just need the odd smear for assembly. |
seanmckinney
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 19, 2006 - 09:48 am: |
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Ta.
I think I have the focus sorted, it is a question of resetting how far down the helix the front lense is when the focus ring contacts its infinity stop. Seemingly quite a simple adjustment once you know how.
Some of the 'tape', notably that covering 'exposed' 'roller' slots under the rubber grip, was/is actually thin aluminium sheet with adhesive on one side, would you happen to know if this/these is/are a readily available item? Almost like an alumimium "post it note". |
Glenn middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 19, 2006 - 03:43 pm: |
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You can get aluminium shim but I cannot give you a lead on that. I just use a good industrial grade of double sided tape, the type used in car main dealers for general holding of interior door covers etc. A good substitute is the tape sold under the Harris label - decorating brushes etc in UK. If the aluminium is rigid enough, you can soak/rub the old adhesive off with Ronsonol (naphtha), otherwise just put tape over the old adhesive. If you need a complete replacement, some of the ali tape used on heating ducts can be substituted. All depends on thickness of original sheet used. If you need a fairly thick piece of metal, it may be worth looking in Craft Shops for the metal sheet that is used in making of those hideous embossed metal plaques. Although normally copper, I have seen 'silver' ones that were clearly polished aluminium, but you could use the copper material if that is all that is available |
seanmckinney
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, January 21, 2006 - 02:41 am: |
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Thanks |
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