IR Cut filter

[Bobobird]

When I am away (like now) one of my stops are to my friend's camera shop.

While chatting about the new Canon big guns I asked to see some but could not as nobody would buy it open-boxed. He said I could go to the Canon centre and play around with them as much as I wanted.

Anyway he brought up an interesting point when I asked him about the filter holder in these lens. He said it did not actually have a filter but only a holder. If anyone wanted to add one they would need to get a replacement because the supplied one did not have screw threads.

He added that one filter that should definitely be put in was an IR Cut filter, supposedly it cuts out some light wavelengths and makes the pictures much sharper.

I thought all modern cameras already had IR filtering built-in.

Was he pulling my leg ??

[Manfred M]

I suspect your leg has gotten a bit longer. Modern CMOS sensors are sensitive to IR and UV wavelengths, so filters are installed by the camera makers as part of the package (along with the Bayer array and AA filter) . I seem to remember seeing ads from companies that would permanently remove the built-in filter for people who wanted to do IR photography.

The question is always about how "good" these filters are as the cutoff for near-IR and the beginning of the red wavelengths mean (around 700nm) tradeoffs have to be made. I had never heard of IR haze, but certainly in the old film days, near UV wavelengths did cause some haze, especially in shots taken at higher altitudes (or near large bodies of water), so UV filters would help here. People just left them on their camera lenses out of habit, and we continue to use UV (or possibly clear) filters to protect our front lens elements.

[dje]

I thought all modern cameras already had IR filtering built-in.

So did I Bobo, unless there's been some recent developments. My understanding is that the IR filter is often incorporated in the same assembly as the AA filter, and that this plate sits right in front of the sensor.

I suppose the colour mosaic filter on the front of the sensor will remove some IR but this probably provides insufficient reduction of IR by itself.

Dave

[jcuknz]

You can find out in a rough way as to if your camera has a built-in Infra-red filter by directing your IR TV [whatever] remote at it while watching in live view. If you see a bright light then you know that the built-in IR filter is not that strong. Another test is the exposure required when using an IR filter. A long one in bright sunlight of I think it was six seconds Kathy told us recently suggests to me that the camera has quite a strong filter built in. I am fortunate that one of my cameras, my wonderful Nikon 5700 which still is going strong eight/nine years down the track, only requires a one second exposure in a similar situation. Sadly for my IR endeavours the subsequent Panasonic cameras and my Oly Pen have proved to be strongly filtered. At one stage I did think of getting one of my FZ50s modified but there were problems with me in NZ etc. One thing I discovered that bridge/p&s can be better than DSLRs here with their live view systems. I always use AF which seems to work as well with IR light as visible light so I don't need a lens with its IR focus mark.
a couple of references from my favourites .....
http://www.kolarivision.com/tutorials.html
and perhaps better ..
http://www.lifepixel.com/

I use a 720mu type filter and get B&W results rather than deep red filters.