Hoya R72 with Canon EF16-35 F/4 - best focus?

TheAndyA

TheAndyA

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Andy
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Hi all,

Is there anyone out there using the same lens and IR filter combination as per the title?

Is there an ideal spot on the lens scale to use as a manual focus mark? At the moment (at 16mm) I'm lining up the red '16' mark with the line as shown in the attached photo, which is how I would normally manual focus for a standard landscape shot, this usually gives me the best results.
 

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I use the same lens on a couple of IR converted 5D2's using Liveview to focus. If you let me know the aperture that you tend to use then I can replicate your composition and see where it lands on the focus ring.

Bob
 
Okay Andy, I've looked at the difference between visible light focusing and IR (using Liveview) and it's very close. The IR "infinity" is half the marked line width past the visible light "infinity" at the long end and very slightly more (almost negligible) at the wide end.

The caveat to this is that my test may not replicate your usage. In my usage, the full spectrum is seen by the lens and it's only filtered at the sensor whilst your lens is only seeing the light passed by the filter.....ie, very little visible light.

Bob
 
I'm would guess that the difference between infrared focus point and the visible light focus point is negligible if you shoot at f8 and above ( because of the increased DoF). I suppose you are using manual focus in live view ? If so, and you are using a 720nm filter then it should be ok as that is not classed a true deep infrared filter anyway.
So first focus without the IR filter ( or focus with a visible light red filter fitted) , then fit the IR filter & dial in a reasonable f number and it should be ok. Try it and see - I think you will find I'm correct
James
 
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