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06-30-2008, 08:12 AM   #1
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Skylight v UV

Hi

Skylight or UV. Which is best to use to protect your lens and why?

Thanks, Paul

06-30-2008, 08:48 AM   #2
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A UV filter does mostly nothing. A skylight filter also induces colour casts.
06-30-2008, 09:15 AM   #3
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Hi ftpaddict

Re your sweeping generalisation:

QuoteQuote:
A UV filter does mostly nothing.
Not quite ! Try reading the following information:

QuoteQuote:
Digital sensors are infrared sensitive and most digital cameras have an infrared blocking filter built in.

Now there isn't usually a huge amount of UV around at sea level. There is some (that's what gives you a suntan or a sunburn) but most of it is scattered by the atmosphere. However as you gain altitude, for example by going up a mountain, the amount of UV increases. Under these conditions a UV filter can prevent a blue cast in photographs.

Since UV filters look clear and neutral to the naked eye, some people also use them as a protective filter which they leave on their lens at all times.
Best regards
Richard
06-30-2008, 11:25 AM   #4
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QuoteOriginally posted by Confused Quote
Hi ftpaddict

Not quite ! Try reading the following information:

It still does mostly nothing, unless you go to high altitudes.

A skylight or haze filter always does something, regardless of atmospheric conditions.

06-30-2008, 08:03 PM   #5
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I've tested Pentax SMC UV and SMC Skylight on my lenses, w/ or w/o filter, or w/ different filters, the results look pretty much the same. I don't see any color casting introduced by the skylight filter (slight pink color) at all.

I read somewhere that digital sensor isn't very sensitive to UV but very sensitive to IR (that's why an IR mask or block is used infront of all digital sensors). So a UV filter does pretty much nothing except protection. As to the extra pink or yellow cast introduced by a skylight filter, our cameras AWB will clear that out automatically unless you are using preset WB settings.

So to me, I'd use either one for protection purpose. But make sure it's at least a multi coated filter.
07-01-2008, 07:53 AM   #6
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1. Skylight filters are slightly red to prevent a blue colour cast on film, when shooting in the shadows or during midday. They are obsolete for digital. Their colour cast might be offset by the camera's White Balance

2. UV protection filters are colour less. They block UV light of app. 400nm and shorter. That is something the glass in the camera lens does anyway – mostly. There is some residual UV, which might get right through to the sensor. This is of almost no importance with modern ED lenses. It can be of importance with older glass (ED or non-ED), because the residual UV will not be focused properly (lenses are usually optimized for the yellow-green part of the spectrum), but introduce a unfocused blurry blue background (spherical aberration mostly) which can lead to reduced resolution of a lens (mostly fast lenses at fully open aperture). There was an interesting MTF test with the old Tamron 60B (300/2.8) at the fourthirds forum, where Poster "First_Light" measured MTF with and without a front filter. There was a significant increase in resolution, at 2.8 when the front filter was in place (roughly 10-20 % res. increase, compared to the measurements without filter) - but only at the max. aperture, because this is, where spherical aberration is most significant.

With modern lenses a UV-filter is usually not necessary, as it doesn't do anything good to the image. There are some shooting circumstances, where a high-quality filter (which does not degrade the image quality noticeably) will serve the purpose of protecting the front element of a lens:
– when shooting at the beach or anywhere near salt water, especially when windy
– when shooting at the beach or in deserts etc. where sand might ruin your front element
– when you shoot under conditions, where you have to clean the lens regularily (in snowdrift, rain etc.), because you will ultimately scratch the lens by wiping it dry...

Sometimes, when shooting under serious conditions (climbing springs to my mind) it might offer mechanical protection of the front element, especially when using large diameter lenses and no (or a retractable) lens hood. For me, in most cases a metal lens hood serves as a lens protection (apart from those shootings in the above mentioned conditions).

If you think, the use of a filter is necessary, only go for the best quality, as cheap filters will influence IQ negatively, So B+W MRC-coated filters or the Hoya/Kenko Pro Digital filter series or Heliopan SH-PMC filters.

Ben
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