lens repair

[devilgas]

[Ian]

Re: lens repair

How old is the lens?

You could try Luton Cameras, where others have had good service mainly in servicing and repairing cameras - I'm not sure how suitable they are for lenses.

To be honest I think Sigma would be the best choice in the end. I know Sigma quite well and their service reputation is first rate.

Ian

[Patrick]

Re: lens repair

Sigma are obviously the best qualified, so it sounds a reasonable price to me, I doubt independent repairers will do a much better price, may even be more expensive.
I have used Sigma's repair service and had no complaints.

Patrick

[devilgas]

Re: lens repair

thanks guys. sigma it is then.

ian, the lens is about 4-5 years old i guess. i bought it 2nd hand 3 years ago as the 200 was way too short for cricket and got too mushy with any kind of teleconverter on it.

[Ian]

Re: lens repair

OK - if it was only a little out of warranty I would bet that Sigma would have done the right thing and fixed it for free. If you have any issue with the same problem after it is fixed I am sure again Sigma will do the right thing.

Ian

[Graham_of_Rainham]

Re: lens repair

Have you tried "exercising" the lens.

In days of old when we had a "Sticky" lens, we gave them to the apprentice and told them to press the button on the lens and rotate the ring until it worked again Often this "exercising" fixed the problem.

Now of course you would have to use the DoF preview to snap the iris blades shut and open again. It may just do the trick.

[devilgas]

Re: lens repair

tried that (the DoF preview thing). the lens is opened right up for focus etc then stopped down when taking the photo, so each time i try to use it, it's doing this 'exercise' anyway. however with the lens not getting any wider than F20ish, the camera won't focus. if it was stuck wide open or say F6.3/7.1, then it'd be happy days as i only ever use that lens fully open or close to fully open.

now, i hear you ask...."if the lens is only used fully open, how'd it get stopped down?". we had the extreme sailing series in town a month ago and i wanted to use a slower shutter speed, so the camera got shifted from it's 'default' of big hole, the lens worked once, then got stuck.

the one thing i don't remember trying is altering the zoom. as the widest aperture changes across the zoom range. that said, with it being stuck with the blades mostly closed, i can't see it making much difference.

oh yeah, it's been tried on different camera bodies and the fault is with the lens

[Ian]

Re: lens repair

I don't think the aperture iris necessarily changes size through the zoom range, more that the limitations of the optical design makes a difference to the effective aperture through the zoom range.

Ian

[devilgas]

Re: lens repair

good point!!

[devilgas]

Re: lens repair

ok, tried a variation of the DoF preview and have got the lens semi working.

managed to get it to open the aperture right up (you'll see how in the stuff below), so my starting point for what's written below is a wide open aperture

if i dial in F10 then press the DoF preview button (PB from now on), then the aperture blades stop down to, I guess, F10. if i press the PB button again, they stop down further to about F20 and won't go any lower. i'm back to where i was when this thread was started.

however, if i hold the PB in and dial in a new aperture, the lens opens up, but not necessarily to the correct aperture for what is dialled in on the camera.

* if i do the above (hold the PB) and dial in the smallest aperture (F32 - F40 depending on zoom setting) then dial back out to F4.5 (@ 80mm) / F5.6 (@400mm), all while holding the PB, then the lens opens up - each 1/3 stop can be seen as the image gets progressively brighter in the viewfinder
* if i then release and re-press the PB on this new, lowest, aperture it stays open.
* dial in the next few lowest (F6.3 / F8 ) and it happily swaps between the 2 on pressing the PB.
* dial in F7.1 (@ 80mm) or F9 (@ 400mm) and i get back to the progressive sticking on each press of the PB.

the trick here was holding in the DoF PB whilst changing the aperture setting on the camera. this was what i *didn't* do at the sailing event. there, i just dialled in the aperture, pressed the PB and saw there was no effect under F20

whilst there is clearly a problem with the lens that needs fixing, i can at least workaround the problem. i think.

it's not been tested by taking photos yet, but it has least proven that the blades aren't stuck. the downside to the iris blades not being stuck means that the electronics are probably at fault (and yes, i have cleaned the electrical connection pads)

so thanks graham! not quite sure that what i've done is what you were describing but it's pretty close!

[devilgas]

Re: lens repair

Photo tests using the above technique worked fine, so I think I now need to decide if getting it repaired is worthwhile. As said before that particular lens has > 99% use wide open at cricket (the focus is too slow for rugby/football/rallying) so I'm tempted to leave it as it is.

[Ian]

Re: lens repair

I think your approach to this is impressively logical

Ian

[Graham_of_Rainham]

Re: lens repair

One more thought! I expect you have already cleaned all the contacts on the lens. However, over many years experience of copper edge connectors (pre gold plated) we again had the apprentice hard at work with, believe it or not, aluminium foil to rub on the surfaces of the connectors (very carefully of course) We were warned that the foil could short out the board (something about residual charge on capacitors) but never once destroyed a board or killed an apprentice

Seems that the very fine oxide layer on the foil was just abrasive enough to clean the contacts. One guy reckoned chewing gum wrappers worked best...

Good luck