What does a UV filter do?

Hi,

 

A dumb question, but what exactly does a UV filter do besides

protecting the lens? What should I be noticing with and without it?

 

I use a Hoya Super-HMC filter with Fuji Superia 100, Sensia 100 and

Provia 100F.

 

Thanks

Almost nothing at all. :) You may see a slight contrast improvement, but it will be almost negligible.

Somewhere on here is a comparison showing that several of the common UV filters just don't do much of anything.

 

The theory is that UV light can expose film, but isn't necessarily part of the visible image you see. And supposedly haze seen at long distances has more UV. So supposedly, using the UV filter should cut down on atmospheric haze and increase saturation, etc.

 

In reality, if you can't see the effect, then it's not doing much of anything. Try some shots side by side with and without it, and see if you can tell the difference.

Bassically it protects your lens.

They are also supposed to cut UV light. I believe that I saw a review of UV filters on this sight. The conclusion was that the Tiffen cut the most UV light and that the more expensive ones did not necessarly work better. Usually at lower altitudes it is not a big deal, but in the mountians it can become a problem with shadow areas having a bluish cast unless they are warmed up. Sometimes in the situation a UV isn't good enough and an 81A is required.

Nothing really, just a marketing ploy to get you to buy more equipment. Putting extra glass between the lens and the subject only increases the chance of trouble (flare, dust, finger prints, etc.) Unless you have a specific need for a filter (ie polarizer to darken sky, warming filter, etc) you shouldn't use one. A lens cap is cheaper and better at protecting your lens.

Optically speaking, they do nothing that the coatings on modern lenses don't already do.

I wouldn't want to purchase a used lens from someone who didn't use a filter.

A good UV filter should have a very slight yellowish tinge.

 

A good UV filter will cut haze and improve the contrast of clouds in the sky.

 

If you go up in altitude, UV increases and you will get bluer and bluer appearing pictures. EK made a set of 3 UV filters for increasing altitude. At the peak of some mountains, you will see an effect from the UV which a filter can help correct.

 

Modern lens coatings mainly address multiple reflections, and unequal focusing of light of different wavelengths, and etc.

 

Ron Mowrey

"Optically speaking, they do nothing that the coatings on modern lenses don't already do."

 

Not correct. Coating and UV filters work quite differently. A coating is applied to reduce reflections, also internal ones, which will cause flare and reduce contrast. An UV filter is designed to block the invisible part of the light spectrum which will cause some exposure to the film. UV light HAS visible effects on the film, even on color film. Many of the shots taken of the sea show a blueish surface of the sea, although in most cases it looks rather brownish to the human eye - the blue is caused by UV light reflected by the sea which hits the film.

 

However, I think that most commercially available UV filters don't have much effect. They don't cut off the spectrum very sharply, i.e. they still transmit a good portion of UV light. And also, many optical glasses used in lenses block UV just as good as the filter glass.

UV filters are typically sold as protective filters, rather than for any image-forming benefit.

 

Are UV filters a marketing ploy?

 

No more so than many other accessories. Working in a retail camera store, it is

certainly true that we like to add a UV filter to the purchase of every lens which will accept

one. As in any business, we like to make money. Filters add to the bottom line. But that

doesn't make them useless.

 

We have a large collection of filters we've taken off lenses, which have protected the lens

during a fall or other impact damage. I've removed a fair number of these from

customers' lenses. Often the filter ring is so badly dented that a strap wrench (on the lens

barrel) and pair of pliers (on the filter) are required to remove the dented filter. In many

cases, the lens was protected by the filter, and is still usable. In these more extreme

cases, the filter has paid for itself many times over.

 

More commonly, filters are valuable in mitigating lens coating damage and scratch

damage from grit, salt spray, and the like. Once a UV filter becomes too badly scratched,

smudged, or otherwise degraded, it can be removed and replaced at little expense. Try

doing that with the front element of your lens.

 

I realize I sound defensive, but I get rather annoyed when some on this site and others

assume that all stores are just trying to take advantage them, and don't have the

customer's best interests in mind. We're in business to make money, but we're not out to

screw people. We've stopped selling lead bags, because we think they're a waste of

money. They were an easy sell to travellers, and had a decent markup, but we don't think

they're very useful given modern airport security (using one seems more likely to get you

pulled aside for extra scrutiny). We try to make money selling products that people

actually need or have some use for.

If a UF filter has no beneficial effect on the exposure, by filtering out UV radiation, then the manufacturer has cheated the customer.

 

A properly made UV filter removes radiation in the 300 - 400 nanometer range of the spectrum. There are several varieties depending on the amount of UV removed. A properly made UV filter should have a slight yellow cast.

 

When you consider that film is sensitive to the UV radiation found in normal sunlight, and that UV can vary from place to place and depends on altitude as well, you will soon realize that it is useful.

 

As a protective lens, why not use a polarizer or less expensive, clear glass - safety type?

 

No, a UV filter is useful, you just have to make sure you use a good one. BTW, UV filters are essential in high altitude photography. There are 3 graded EK filters for just this purpose useful in about 30,000 ft increments.

 

Ron Mowrey

"As a protective lens, why not use a polarizer or less expensive, clear glass - safety type?"

 

A polarizer would make a lousy all-the-time protective lens, given that it will cause a

significant light loss, and some degree of color shift (global or local) in every picture

taken. It's a great filter for some circumstances, but not as a general protective lens.

 

What is a "less expensive, clear glass - safety type?" Is that any different from an $11.95

Hoya UV filter? (And yes, for the cognoscenti among us, I know that there are much better

grades of UV filters available. I'm just talking about cheap protective filters here. We can

have the argument about putting $12 glass on a $300 lens some other time.)

David;

 

Thanks, but that quote from me was intended as sarcasm. I believe in both protection of a lens and protection from UV.

 

I have a Nikon lens that 'lives' today due to a UV filter, and a zoom lens that 'survives' for the same reason.

 

Not having a spectrophotometer to 'read' the filters, I cannot tell which ones are better and which are worse. I have to rely on the mfgr for his integrity. If I cannot, then that is the fault of the mfgr. All of us do to some extent.

 

Ron Mowrey

Bob Atkins wrote an article for photo.net explaining this subject in some detail (a bit technical) - <a href="http://www.photo.net/equipment/filters/">Filters UV or not UV</a> (http://www.photo.net/equipment/filters/).

"A properly made UV filter should have a light yellow cast."

 

I'd rather think that such a filter is NOT a properly made one, since it will affect the tonality of the image. An UV filter is a filter which is made for filtering out UV rays - not anything in the visible range. If a filter has a yellow cast this means that the other (blue) end of the spectrum is cut off too much.

 

It is not easy to make a UV filter which starts cutting off just at the end of the visible spectrum and will block (i.e. absorb 90 per cent or so) of the UV rays. It IS possible to make such filters but not for a price a hobbyist would like to pay. At work we are using filters cutting off the red part of the spectrum very sharply. They cost around 25 USD for a bare filter with 12mm (1/2 inch) diameter, without mount. Look at the catalogue of Edmund Optics and you will find filters which will cut off UV rays very well. But don't look at the price...

 

It is obvious that a good UV filter can't be a cheap one.

Winfried;

 

If a UV filter is colorless it cuts out at the shorter wavelengths, or closer to 300 nm. The wavelengths of most concern are often closer to 350 nm, or in the middle of the range.

 

As you all know, dyes are not perfect, therefore there is a small amount of undwanted absorption. If a UV filter cuts properly at about 350 nm, there is a small tail into the region above 400 nm, giving the filter a slight yellow cast. The denser the UV absorption, the more the yellow cast.

 

High altitude filters used for UV are very dense, and very yellowish as a result.

 

Ron Mowrey

"Thanks, but that quote from me was intended as sarcasm."

 

My apologies. Rereading your post that is evident, in retrospect. Sorry for overreacting.