polishing out chip on front lens

wegi said:
A B+W 77mm 77 F-Pro Digital MRC UV Haze Filter £54.00
for some people not good to use one, but with this piece of glass in front, no chip in the lens....
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Anything that chips the front element will decimate a flimsy filter, as per my previous post. And will have likely caused more damage to the lens.

Regardless of what people's opinions are re image degradation of using pointless UV filters, or 'protection' filters, it's a 100% certainly they offer no protection against the type of direct impact that can cause damage such as a chip to a front element.

There's a video on YouTube that shows how little protection they offer, with a taught piece of **paper** offering better impact resistance!

In fact, here it is, watch it after 6 minutes;

View: https://youtu.be/P0CLPTd6Bds
 
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odd jim said:
Not really a fair or realistic comparison.
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Whilst it was made in jest, there is some truth in it. I'd never claim a filter makes no different at all to the resulting image but, in reality, the effects are generally far smaller than some would like you to believe.
 
jbw said:
A small scratch will just lower the contrast of the image slightly but will not result in marks or spots on the image. Just think nearly every astronomical telescope ( including the Hubble one) has a fairly large secondary mirror obscuring the middle of its optical path - the resulting images are fine, just a slight drop in contrast that is easily corrected in post processing.
My advice - leave the scratch alone and forget about it.
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Whilst rare now, mirror lenses used to be popular for still film cameras way back when, as they were far cheaper for a given focal length. They obviously worked fine, although bokeh would take on a "doughnut" type effect :)
 
Vertigo1 said:
Whilst it was made in jest, there is some truth in it. I'd never claim a filter makes no different at all to the resulting image but, in reality, the effects are generally far smaller than some would like you to believe.
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I understand what you mean, but I've seen plenty of images utterly ruined by the use of UV / protection filters (long lenses zoomed to max on safari, low light images with multiple street light refractions), and a smashed front element isn't intentional (re the comparison you made), sticking said UV filter on is, and people's intentions in doing so are misguided - there is very little protection offered by them.
 
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You will almost never see a spot in an image due to something on the front element; I'm half tempted to say "never," but then someone would prove me wrong. ;)

Every single point of a lens collects and transmits a complete image (as seen from it's position/FOV). You can block/eliminate large areas of the lens and the only thing it will do is reduce the brightness of the projected image/portion of.
Many do not realize this; when you increase the aperture size what you are actually doing is adding more areas of the objective lens to the projected image... it's effectively "stacking exposures." That's why the maximum aperture is limited by the diameter of the objective lens (typically), and it is why you can get vignetting at max aperture (because it is including the perimeter of the front element in the image).

If it is causing issues it's due to angular refraction of light and the *right answer* is to eliminate that area from the projected image by blacking it out. I highly doubt it's worth getting the front element replaced...
 
sk66 said:
but then someone would prove me wrong. ;)
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Extreme example using a Sigma 8mm fisheye at f/8 - the dark blobs around the edge were caused by droplets of water from the nearby Gulfoss waterfall freezing onto the front element. No such thing as a screw on filter for this lens so I stopped shooting and went back to the hotel to watch the spectacle from nearer warmth!

096096 by gpn63, on Flickr
 
graycbr said:
yep just got a quote back looking around £130 all in ...
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The only 'impact' you're going to have is resale value if the time ever comes. Whether the difference in used condition is worth £130 only you can decide. Personally I think I'd leave it & take the hit if/when sale time comes round.
 
Nod said:
Extreme example using a Sigma 8mm fisheye at f/8 - the dark blobs around the edge were caused by droplets of water from the nearby Gulfoss waterfall freezing onto the front element. No such thing as a screw on filter for this lens so I stopped shooting and went back to the hotel to watch the spectacle from nearer warmth!
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Good example.... I'm glad I knew better than to use absolutes.
It makes sense. On an extreme WA with a bulbous front element the large curvature prevents the edges from "seeing" the opposite side of the total FOV. So obstructions can't be "filled in" as effectively.
 
sk66 said:
You will almost never see a spot in an image due to something on the front element;
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You didn't use an absolute without qualification and mine is an extreme example! In normal use, with normal lenses, you're right, it's just that I'm not normal!!! :D
 
I bought a 90mm f2 lens for a song because it has a 2mm diameter chip in the centre of the front element. Chip area =
pi.gif
r² i.e. 3.14 x 1²= 3.14mm². Actual front element area = 3.14 x 23² = 1662mm² . As a % of the total area at full aperture, the chip occupies less than 0.2% of total surface area. At f11, (approx 50mm² surface area) chip occupies less than 6% of the surface area i.e. 6/100 of the surface area. When I used the lens in a contre jour lighting situation i.e. against the light - actually straight into a sunset - there was some visible flare - likely attributable to the chip. In normal light the chip had no effect on the image. I have since painted over the chip with a 2mm blob of matt black paint and have not encountered flare in contre jour lighting situations . Matt black paint is a well known remedy for countering lens flare caused by damaged lens elements - be they chips or cracks . The % surface area affected (as documented herein) is so small that it has no significant effect on the effective aperture. The cosmetic effect is noticeable but the performance effect is NIL once the chip is 'blacked out'. Neither the matt black paint, or the chip, shows up in the image … just as taking a photograph through a wire net fence will not show the netting in the final image.

dunk
 
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