680nm IR filters?

[retinax]

Hello,
I'm thinking about trying IR with Aviphot 200/Rollei Retro 200. Beside the usual 720nm filters, on ebay I see these cheap IR filters that cut off at 680nm.

Has anyone used these? How are the results? Noticeably more speed? Of course the IR effect will be less, but how much less than a 720?

 

[Tim Gray]

Depends on the sensitivity of the film. If it’s more sensitive to red light than near IR, a filter like that (or a B+W 092) might end up like a deep red filter, as they let through a decent amount of deep red visible light. If the film is less sensitive to red than IR, you might be in luck.

 

[retinax]

The sensitivity curve is near flat from red to ~740 nm, where it drops off and hits 0 at 770. There's not much left with a 720 nm filter, but I've seen nice results online.

In practical terms, the question is how bright foliage will be rendered. As I've also seen examples of Aviphot 200 that show some wood effect already with a deep red filter, I believe it might be bright enough for me, I'm not looking to completely blow out the foliage in relation to other stuff. But I suppose it also depends on how much IR there is, maybe the results with such a filter will differ even more between very sunny and less sunny days?