Two problems with my new Tamron 17-50

[stavroshamster]

I've had my Tamron 17-50 for about a month and have only used it a few times but I have a couple of problems with it and would like some advice.

Firstly, I have noticed that the focus ring turns about 4-5mm past the infinity mark. I didn't notice this initially so am wondering whether it is a fault, although I have read on some forums that some lenses have this as a 'feature'. The problem is that my 300D doesn't seem to like it and it frequently focuses beyond infinity meaning the image is slightly out of focus (even though the focus indicator lights up). Do 17-50 owners also have lenses which focus beyond infinity?

Secondly, although I am extremely careful with keeping my equipment clean, there are several spots of dust and what looks like a hair (although it almost looks like a hairline crack - i am not 100%) trapped in the internal lens elements. No amount of blowing with the rocket blower will dislodge them. I don't really see how these have got in so easily, as I would assume that the internal elements should at least have some level of protection against dust/hair penetration?? I have had lenses for 10 years which have far less dust in them.

Obviously the lens is still under warranty - but where do you think I stand on both these issues? If the first issue is a feature rather than a fault, then are they likely to replace the lens because of the excessive dust??

Thanks...

[rox0r]

Dust gets inside zoom lenses as you extend them, the inrush of air into the seals drags tiny particles in with the air. The poorer the seals, the more dust gets in.

My Canon 17-55 is notorious for the same issue (thankfully mine hasn't suffered from it yet) but the solution is to take the front element off and give it a whizz over with the rocket blower.

I'm not sure about the Tamron but with the Canon you take off the 'sticker' on the front element that states the f number and wotnot and there are a couple of screws under there that release the element for access.

The easiest way to try and mitigate the amount of dust entering the lens is to chuck a UV filter on the front.

This is of course quite likely a warranty killer though if not done with care. Of course if the lens is still in warranty, which yours is, simply send it back and they'll sort it out and even re-calibrate it if necessary.

[Bobster]

and you've of course contacted intro 20 about your troubles?

[brammers]

Here's a link showing the effects of dust and dirt on lenses:

http://kurtmunger.com/dirty_lens_articleid35.html

Short answer - don't worry about it. It happens, if you're really fussed then send it in for servicing once every couple of years.

As to the lens focusing past infinity - they are meant to manually, but never in AF. Can we see some examples?

[stavroshamster]

and you've of course contacted intro 20 about your troubles?

Intro 20-20 are the importers of Tamron lenses yeah? I haven't had a chance to contact anyone yet as I have only just got back from holiday - but thought I would contact the place I bought it from first (Warehouse Express). The problem is that I was not sure whether what I have with the misfocusing and the excessive dust is a malfunction or not - and therefore how likely they will be to rectify the problem...

Here's a link showing the effects of dust and dirt on lenses:

http://kurtmunger.com/dirty_lens_articleid35.html

Short answer - don't worry about it. It happens, if you're really fussed then send it in for servicing once every couple of years.

As to the lens focusing past infinity - they are meant to manually, but never in AF. Can we see some examples?

Ordinarily I wouldn't worry about the dust and hair, but I have only had it a short time and it seems very excessive - and presumably it is only going to get worse. I haven't noticed any effects on my picture quality so far at the moment, but that could change I guess.

Here is an example of the infinity problem which I think shows the issue (images are cropped)...

Focus using manual focus on infinity line:



Attempt at AF by EOS 300D, the lens was about 3mm past the infinity marker here:



Although the camera doesn't always focus past infinity it is relatively common. What do you think?

Out of interest, how much would I expect to pay for someone to service/clean a lens?

[kalniel]

As the above - lens should not AF past infinity. The fact it mis-focuses at all on a good body should be enough to indicate a problem and needs returning or service.

Does it back-focus at closer distances too?

[stavroshamster]

As the above - lens should not AF past infinity. The fact it mis-focuses at all on a good body should be enough to indicate a problem and needs returning or service.

Does it back-focus at closer distances too?

I am not sure - what is the best way to check this out?

One thing I have noticed with a bit of experimentation this morning is that the problem is much worse at 17mm than it is at 50mm. In fact, it doesnt seem to be an issue at 50mm at all.

Is it definately a lens problem or could it be an issue with the AF system of the body?

[kalniel]

I am not sure - what is the best way to check this out?

http://focustestchart.com/chart.html

Is it definately a lens problem or could it be an issue with the AF system of the body?

Do you see this with other lenses? I think it's quite likely to be the lens, but simple enough to check if you have another lens that focuses properly.

[brammers]

Don't use 45º close distance focus test charts - camera AF systems just aren't designed to focus on stuff like that and you start introducing errors that you don't see in real life. Focus shift becomes a problem at such close distances, as does the fact that you don't actually know where the AF sensor is locking - they're bigger than the dots in the viewfinder and the viewfinder doesn't show DoF or focus accurately until about f5.6/8.

Instead, take a selection of objects (batteries work perfectly) and place them in the same frame but at different distances from the camera (preferably out of MFD) Focus on one and see which one is actually mostly in focus. Must be using spot focusing for this.

As I said though, it really shouldn't be focusing past infinity, so unless you've got consistant backfocus on all lenses, you probably want to send it back anyway. Focus issues can be down to the body or the lens, but a lens swap seems to fix a lot

[kalniel]

Good point, I forgot about that. Here's a longer distance one

http://www.northlight-images.co.uk/a...djustment.html

[tfboy]

The focus past infinity is possibly normal. Most lenses allow you to focus past infinity, it's to give some tolerance to temperature and pressure IIRC

[brammers]

It's perfectly normal to be able to do so manually tfboy. It's not at all normal that the AF continually settles past infinity.

[Bobster]

just looked at my 17-50 and it focuses 2-3mm past infinity (i can't test it on AF cos its broken and i need to send it away to be fixed)