ampguy
Veteran
without getting into specific lenses that have lens specific focus shift issues, are there any image quality issues when focusing at infinity where your lens is at infinity, vs say the hyperfocal distance or anywhere in between?
Another question is when using an IR (R72) filter with a camera that is focused on infinity, would the IQ be better if I focused a "few inches" in front of infinity, or more plausible, the hyperfocal distance plus some?
Picked up a Bower 46-52 step up adapter from one of those camera/electronics places on powell in union square, and am thinking of taking some IR photos with the M6 and Zeiss biogon 28/2.8, and the hexar AF both which have 46 filter sizes (and my R72 filter is 52).
I realize from past use with this that I need to add about 4-5 stops and that the focus issue is mainly up close (infinity focus worked fine beyond 100 feet with old Pentax *ist DL).
Another question is when using an IR (R72) filter with a camera that is focused on infinity, would the IQ be better if I focused a "few inches" in front of infinity, or more plausible, the hyperfocal distance plus some?
Picked up a Bower 46-52 step up adapter from one of those camera/electronics places on powell in union square, and am thinking of taking some IR photos with the M6 and Zeiss biogon 28/2.8, and the hexar AF both which have 46 filter sizes (and my R72 filter is 52).
I realize from past use with this that I need to add about 4-5 stops and that the focus issue is mainly up close (infinity focus worked fine beyond 100 feet with old Pentax *ist DL).
charjohncarter
Veteran
IR: different filters different corrections, different films, in the old days when there was more than one film, required different corrections, different focal length lenses require different corrections. But don't freak, most users don't bother to correct (if they do they over correct) and try to shoot with small apertures. DOF will take care of any focus issues, if there are any. These corrections are very small (average .5 to 1%) and are mostly useful in scientific work.
Efke R820 is all that is left. ISO 25 with no filter, with R72 (720 nm cutoff), ISO 1, Yes one. At least for me, that is what I use.
Efke R820 is all that is left. ISO 25 with no filter, with R72 (720 nm cutoff), ISO 1, Yes one. At least for me, that is what I use.
Most lenses have an IR focussing index that give a good indication of the difference. F8 usually covers the error on most lenses. I have lenses that the IR mark is within the F2 DOF, and others that are closer to F8. On most lenses, 100ft works well as infinity for IR work.
ampguy
Veteran
Thanks all, I guess a more general question would be to ignore the IR portion of the question and ask if there is an object at 5km, is there image quality difference if you focus at infinity, or near infinity at say f16 on a 50mm lens?
For those not aware, infinity in lens design is a number, a large one, but still a finite #, it's in the Leica M book for one or more lenses, but I don't recall the #.
For those not aware, infinity in lens design is a number, a large one, but still a finite #, it's in the Leica M book for one or more lenses, but I don't recall the #.