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Author Topic: Lens coatings idea; why not coat the inside of the glass?  (Read 163 times)

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Offline balacau

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Lens coatings idea; why not coat the inside of the glass?
« on: March 07, 2010, 08:27:35 PM »
I was reading through the Sigma site today, looking (again) at the 4.5mm fisheye lens.  It mentions a rear mounted gelatin filter; but no "regular" filter size.

I have filters for most of my more expensive lenses, apart from the 10-20mm Sigma (probably going to get that sorted on Thursday), but the 4.5mm fisheye doesn't have that option. 

Would it not be possible for lens-makers to put this coating on the inside of the lens.  This would mean removing the coatings by trying to remove grit etc would be a thing of the past, at least in theory.  Or perhaps the technicalities/expensive of doing this would make it cost-prohibitive?

Just curious.

Best regards

Gavin
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Offline Goonybird

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Re: Lens coatings idea; why not coat the inside of the glass?
« Reply #1 on: March 07, 2010, 09:09:16 PM »
I would suspect that the front element of the lens protrudes too far to fit a front filter (due to the high curvature on wide angle lenses)
The gelatin filter would be interted at the rear probably as a neutral density filter?
The Anti-reflection coating on lens elements is on both surfaces by default to maximise light transmission through the lens and minimise internal reflections and ghosting.
With modern coatings there is a degree of scratch resistance, but as always take extreme care when cleaning.

Steffi UK
 
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