Having problems with IR photography

[nagoshua]

I just got an IR filter along with a cokin filter holder. When ever i use it i can see the reflections from the elements inside the lens on the picture. Im guessing this is because light is bouncing to and from the inside of the lens and the filter because i just held it to the front of another lens and i didnt seem to have this problem.
Im wondering if its just because the lens sucks, its a sigma 18-200mm and im looking to replace it very soon so it aint the end of the world if i have to wait a lil longer to do some IR photography but and ideas on stopping this problem would be a great help!!!

 

[Garbz]

Depends on what you mean by reflections? Lens flair is the fault of the lens. But if the reflections you mean are light hitting the area between the filter and the lens, then it's a fault of your setup. Post an example photo and if possible a photo of the filter in the cokin holder.

 

[ann]

did you use a lens hood as well?

that will help on flaring

 

[doenoe]

are you talking about the hotspot in the middle of the pic?
Thats because not all lenses are good to use for IR. When i started with IR, i used my kit-lens (18-55) and i got this hotspot. And the longer the exposure, the more you could see it. Using a higher f-number didnt help neither, since the spot would be smaller but also would be brighter. Now im using the 50mm 1.8 mkII for IR and it works like a charm.
I think there is a list somewhere on the web with the lenses that can be used for IR and which ones you cant use.

found something you might wanna read: http://heim.ifi.uio.no/~gisle/photo/ir.html