The Efke is a true infrared film and rated at 100 asa without a filter I have used this film with a Hoya Ir720 filter and had to rate the film at 6 asa for best results.
This film has quite fine grain for a IR film
If you expose it with a Hoya R25 (red) filter and the infrared affect is not very noticeable.
Nice film I thought good IR effect.
This film can be loaded in subdued light without risk of fogging, the film has an anti halo base, you do not get the glow that you get with Kodak HIE due to this film having no anti halo base.
SFX is a near infrared film I have only ever used this film with my Leica III with a leitz deep red filter. It worked well but not as good as a true infrared film IMHO
If you can get the maco 400 Ir film that is well worth a try as it is much faster film and you can use it handheld if you wish.
I don't know much about IR film/photography, so...
Why would one/would one need an IR/red/whatever filter?
Without a red25 filter or an 87C("infrared filter"), the images will look almost the same as any b&w film.
So if I used this filter with the efke, what ISO would I shoot at? Would I be able to hand-hold it? (I have a VR lens, but no tripod.)
Edit: Oh, ISO 25. Is that hand-holdable? I'm using the 24-120 f/3.5-5.6 VR lens.
I would not use this filter. as the IR effect is hardly noticeable. you need a proper infrared filter like the hoya RM72 filter
This filter passes only infrared rays above 720nm
When I used this filter I had to expose the film at ISO 6 which is tripod time.
But I would be using IR film already...
On choice of film, I haven't used the Ilford because its spectral response doesn't look very promising. I've shot a fair amount of the Efke (and the old Maco 820c, which I believe was the same emulsion on a different base) and absolutely love it. 6 ASA seems about right, although I've been able to rate it higher and get some nice images at the limits of handholdability.
I haven't shot IR in 35mm in several years, but my recollection is that the meter on the camera (a Bessa-L) produced decent results if I set it at 100 ASA and metered through the filter.
Infrared is really fun. It's challenging to find ways to use it as something other than a special effect.
But I would be using IR film already... I'm confused.
I'm also kind of a newbie with infrared but I'll try a very basic explanation. Although you are using infrared film you need a filter that cuts out all visible light otherwise the infrared light will be overpowered by it and you won't get the proper infrared effect (just a normal lighting effect). That's why you need an opaque filter -- it will cut out the visible light and only let the infrared through (although how much depends on the filter and film used). With HIE you could use a red filter (25 or 29) and still get a good infrared look, but that is not the case with the remaining infrared films. The RM72 is a good choice because (I think) you can use it with all of the remaining infrared films.
I often use a red 29 filter with Efke and get a decent IR look. I found it doesn't work with the Rollei film though.