Protective front element

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10-02-2009, 08:55 PM
Sinh Nhut Nguyen

Protective front element

Hello everyone,

What is the protectivefrontelementon this lens? Is it just a regular white glass? Does it act like a filter? In the review of this lens, Bryan said that this front element can be replaced easily and inexpensively should something happened. I know technically any lens' front element can be replaced, but why are only supertelephos and the 300 f/4L IS have these protective front elements.By the way, today I tried to clean my 1-week old 500 f/4L IS' front element and found out that it was much tougher and stickier to do theusual circular mothion as though this front element is not made of smooth glass comparing to my other lenses.

Thanks for the replies.

Nate
10-02-2009, 11:15 PM
ShutterbugJohan

Re: Protective front element
Nate,

First of all, congrats on the lens. [:)]

As to your question, I believe it acts like a filter. I watched this link some time ago, and it shows the manufacturing process of the 500/4L. At one point in the assembly the worker screws what appears to be a large filter on the lens. I believe, but cannot prove, that that is the protective front element. Also, I know you don't use UV filters, but here are the reasons I believe that Canon likes UV filters:
- Canon sells them (but B+Ws are better)
- Canon makes lenses (i.e. 16-35) that require a filter to complete the sealing
- A Canon rep told me that he recommends using them
- If the paragraph above is correct, Canon uses a protective filter on the supertelephotos.
10-03-2009, 12:01 AM
wickerprints

Re: Protective front element

I should point out that the protective front element is not flat. It is slightly curved--a meniscus lens with no contribution to focus. The curvature is to prevent ghosting due to internal reflection, as described in Canon's EF Lens Work III.
10-03-2009, 12:19 AM
Fast Glass

Re: Protective front element

Quote:

Originally Posted by wickerprints

I should point out that the protective front element is not flat. It is slightly curved--a meniscus lens with no contribution to focus. The curvature is to prevent ghosting due to internal reflection, as described in Canon's EF Lens Work III.
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Interesting, I didn't know that.