70-200 F4 L lens

[davebell]

I recently purchased a 70-200F4 L lens for my 350D and it got

facntastic pictures with it. However, a few days after getting it I

noticed 2 small specs of dust on the glass element below the front/top

glass element (I am no expert....). Considering I paid GBP490 for this

baby, I thought that was not good enough and returned it for an

exchange. The second and third lenses had even more specs below the

top glass, albeit small and maybe I'm a nit-picker but that's loads of

money to pay for a lens if it has these imperfections. By the way, the

2nd/3rd lenses were clearly used/demo models as the one had a bit of

food stuck to it..... enough said. I got a refund but really want to

buy another one, am I being a pedantic nit-picker?

[aardvarko]

Dust in-lens doesn't make any difference unless it's thick enough to draw in with your finger. The dust COULD, given sufficient quantity (and I really do mean ludicrous amounts), reduce overall contrast. That's it. A lot of people seem to think dust or dirt will cause little black holes to appear in their images, and that's just a basic incomprehension of optics.

 

Look at it this way - whenever you zoom the lens, air whooshes around inside the lens, and with some lenses, INTO and OUT of the lens. Dust is inevitable.

[bens]

david, i'm an amateur and don't have this lens. i'm only writing cuz of the specks of dust issue. the food/demo issue would be unacceptable to me. but if i am getting great shots out of a lens, a couple of specs of dust would not cause me to return it. i in fact have bought a used lens at a 1/3 price break that has a lot more dust, and it takes excellent shots. glad i did. (canon 85/1.8, from keh.com)

[peter_white2]

Yes, you are picking nits. ;-)

 

Those specs of dust will have no effect on your images. All lenses get them, especially zooms. Buy another one, check it for food, and as long as there's no food, keep it. ;-)

 

I own quite a few lenses from Canon, Leica, Schneider, Rodenstock and Zeiss. All of them have some dust inside. And all make fine photographs.

 

If you really want to feel sick, hold any of your other lenses in one hand, take a flashlight and shine it through and look down the lens towards the flashlight. You'll be appalled at how much junk is inside. But it has no effect on your images.

[peter_phan]

A couple specks of dust are going to have absolutely no effect on image quality. If you look at the equipment of people who shoot for a living, you'd be surprised at just how dirty their equipment is, or just how dirty their equipment gets, with little or no impact on image quality. I've done plenty of shooting with excellent results, never even realizing how dirty my lens glass had gotten until I got home and took a good look at my lenses. There's a difference between unrealistic expectations and practical expectations. And most users know that a few specks of dust on the lens won't have any practical impact on image quality.

[davebell]

Thanks to all, my dust phobia has been exorcised and I will shortly purchase a replacement!

[robert_nancarrow]

All that has been said about dust is true, it doesn't make a difference in the pic or show up, in most cases, there is the one in a thousand case of it being in a area that does show up. Anyways, I don't think you're being nit picky, I would expect a new lens to have no visible dust inside and only the slightest little bit under very close inspection with a point source light while looking through. Bob.

[mick johnson]

My mate has just returned the same lens because it had 1, yes 1, speck of dust in it.

 

The second one had what looked like a bubble in one of the elements inside the lens.

 

He is just about to get his 3rd one and I've told him if it has any dust in it and he won't accept it to ring me and I will go get it for myself as I'm about to get this lens anyway.

 

I believe this lens is completely sealed and won't suck in dust as it does'nt change length when zoomed so it should be clean inside.

 

Mick.......

[mark u]

Think of dust this way.... Each point in your subject is emitting a cone of light which is captured by the front element and focussed by the lens onto the sensor. With the lens wide open, that cone has a diameter of about 15-50mm (depending on the focal length in use), whereas the dust spec is probably 0.1mm in diameter, so it blocks less than 1/22,500th of the light. Even stopped down to f/16 it's blocking less than 16/22,500ths of the light (assuming it's still in the optical path). However, at the rear element the light cone is becoming more focussed, and dust begins to be more of a problem. Of course, it's even more of a problem if it's on the filter that lies over the sensor - but even there, it usually only shows up when you use a narrow aperture that makes the focussed light cones more like a searchlight that can cast a shadow that shows up on the sensor.

[ky2]

My Nikkor 180/2.8 ED AIS, had a 2mm spec on its rear element. You could easily spot it, if you'd turn the lens upside down. It was my sharpest lens ever.

[PuppyDigs]

Shine a penlight down the barrel and look through the other side and you'll see a lot more

than 2 specs of dust. All lenses have some dust particles when new. That's just how it is.

Like others have said, the inner elements move during focus and zoom operations and

thereby displace air. The displacement of air will bring more dust. Some dust is

unavoidable. So, even if you returned the lens and got one without dust (extremely

unlikely), you'll soon suck in dust... So why waste your time peeping down the barrel of

you lens when you could be out shooting with it?

[oofoto]

David before you do:

http://www.7dayshop.com/catalog/product_info.php?cPath=777_4_409_40910&products_id=98411

[oofoto]

David before you do:

http://www.7dayshop.com/catalog/product_info.php?cPath=777_4_409_40910&products_id=98411

[davebell]

Thanks for that link Paul, I wioll check it out!