Dust in Canon L lens

[allan]

I am looking to sell a Canon 70-200L F4 lens and have noticed a light brown spec (about the size of a grain of salt) on the inside of the outer front element. I haven't taken any shots recently with the lens but irrespective of this , it would be something a buyer should notice buying this type of lens. I'm wondering if it is worth sending it to the canon service center to have the lens cleaned prior to selling. Any opinions?

Thanks in advance

[WRon]

Without actually taking a look at the lens, it's hard to give an informed opinion. However, I will say that, in general, small specks of dust don't deteriorate the image. The only true test is, of course, to take several shots with the lens at various focal lengths, f-stops, and lighting conditions, and see what the results are. Another good test is to shoot a clear blue sky and see if anything shows up on the image. Unless it's really bad, I don't think it would be worth sending it to Canon because it would be costly and it would take a long time to get it back.

[allan]

Thanks WRon
I guess the only thing that matters to me is what the buyer says when intending to purchase. I assume you are thinking it would cost more than $100 to have the lens cleaned?

[Yarddog]

Dust or specks or whatever on the objective lens has very little effect on the lens's sharpness. On the other hand just about anything on the opposite end makes a difference.

The same is true of binoculars. The objective lens can have a lot of scratches etc. and it doesn't seem to hurt the image at all. However even a speck of dust under the eyepiece will be immediately noticed.

Even tho the speck doesn't really do any harm optically, it really will reduce the value of the lens.

[suci]

Dust or specks or whatever on the objective lens has very little effect on the lens's sharpness. On the other hand just about anything on the opposite end makes a difference.

The same is true of binoculars. The objective lens can have a lot of scratches etc. and it doesn't seem to hurt the image at all. However even a speck of dust under the eyepiece will be immediately noticed.

Even tho the speck doesn't really do any harm optically, it really will reduce the value of the lens.

It depends on whether that is indeed dust and I can't imagine how it's got inside. Often small flaws appear in the glass of even the most expensive lenses. That fact is usually stated in the user's manual of the lens. It's not a fault, it's quite normal and will not affect image quality in the least.

[Yarddog]

At one time it was a sign of quality to have a few bubbles in the glass.

For some reason, it was impossible to make the very best optical glass without a few bubbles getting into it.

That has been a long time ago I guess as one no longer sees them.

[Mario Caputa]

Front element impurities are ok. There are no dust free lenses.