# New here



## gmazz (Mar 11, 2013)

Hello everyone, my name is Gabriel and I'm 15. I recently got into photography because I was given an old canon eos elan and lensess. About a month ago I bought a canon 350d body of craigslist to learn on. Since then I've really gotten into photography, I even decided to take photography class at my school.  I have a 28-80mm f/3.5-5.6 and a 100-300mm f/4.5-5.6. Both these lenses have filters on them, I never really paid attention to them until now. The 28-80 has a Tosiba A18 (81A), and the 100-300 has a Rolev m.c. SKY. What are the purposes of these filters and when should they be used?


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## Juga (Mar 11, 2013)

gmazz said:


> Hello everyone, my name is Gabriel and I'm 15. I recently got into photography because I was given an old canon eos elan and lensess. About a month ago I bought a canon 350d body of craigslist to learn on. Since then I've really gotten into photography, I even decided to take photography class at my school. I have a 28-80mm f/3.5-5.6 and a 100-300mm f/4.5-5.6. Both these lenses have filters on them, I never really paid attention to them until now. The 28-80 has a Tosiba A18 (81A), and the 100-300 has a Rolev m.c. SKY. What are the purposes of these filters and when should they be used?



From my non-expert opinion and my best friend, Google. It looks as if those filters are UV filters.


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## TCampbell (Mar 11, 2013)

Cameras benefit from filtering out wavelengths that are outside the visible spectrum.

When you pass light through a prism it splits into it's individual wavelengths and becomes a rainbow.  When you pass light through the edges of glass lenses, they do the same thing.  The lenses use extra elements that work as achromatic "doublets" to counter the effect, but it still happens... just to a much lesser degree.

That means that if you cut out the wavelengths of light beyond the spectrum that the human eye can see, you can technically get a sharper image.

Film cameras didn't have any built-in filters.  All digital cameras (at least every digital camera I've ever seen) _does_ have builtin UV and IR filters.

The UV (and IR) filters are no longer needed when the lenses are used on a digital camera ... because the camera already has the filters built-in (if you remove your lens, put the camera into manual sensor cleaning mode (so it opens the shutter), you can see the sensor, but the surface that you could "touch" (if you tried to touch it) is actually not the sensor itself... but a filter in front of the sensor (and usually there's two filters).

A UV filter and a SKY filter were very similar... the difference is that the "SKY" or "1A" filter offered a very very slight "warming" tone (a pinkish/reddish tone) designed to very slightly "warm" the look.  Basically that means the cutoff for UV was slightly into the visible blue range.  The effect was subtle.


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## Juga (Mar 11, 2013)

TCampbell said:


> Cameras benefit from filtering out wavelengths that are outside the visible spectrum.
> 
> When you pass light through a prism it splits into it's individual wavelengths and becomes a rainbow. When you pass light through the edges of glass lenses, they do the same thing. The lenses use extra elements that work as achromatic "doublets" to counter the effect, but it still happens... just to a much lesser degree.
> 
> ...



I knew I was right! haha jk . Thanks for the clarification for our new friend.


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## TCampbell (Mar 11, 2013)

BTW, the effect is called "chromatic aberration" but the nick-name is "fringing".  If you inspect an image at close detail you'll notice that subject near the edges or corners (far away from center) will have a "blueish" fringe on one edge and a "reddish" fringe on the opposite edge... caused by the lens not being able to focus all the wavelength at the same distance. 

Shorter wavelengths (blues) are more affected than longer wavelengths (reds) so blues have a closer focusing distance and reds have a longer focusing distance.  If you check a lens with a focus scale on it, you'll notice most have an extra mark showing you were to set the focus for IR photography.... because IR has an even longer focus distance than visible reds.


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## gmazz (Mar 12, 2013)

TCampbell said:


> Cameras benefit from filtering out wavelengths that are outside the visible spectrum.
> 
> When you pass light through a prism it splits into it's individual wavelengths and becomes a rainbow.  When you pass light through the edges of glass lenses, they do the same thing.  The lenses use extra elements that work as achromatic "doublets" to counter the effect, but it still happens... just to a much lesser degree.
> 
> ...



Thank you for the very thorough response, I think I'm going to shoot without the filters.


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