Vivek Iyer Posted January 16, 2007 Share #1 Â Posted January 16, 2007 Advertisement (gone after registration) Now that the IR contamination issue is drummed up everywhere and folks are using IR cut filters, I would like to ask if anyone has noticed focus shift (incorrect focus) when an IR cut filter is being used. Users of the IR cut filters on fast lenses, perhaps could comment on this? TIA Â While trying IR cut filters on lenses (fast and wide) to take care of IR problems on an Epson R-D1s, I notice significant shifts. Â (Interesting that there were no/few complaints about the purple fabrics from the Epson R-D1/s!! This is a very sweet camera with very high sensitivity for UV and IR. Naturally, it creates problems with normal visible light, especially when it comes to color fidelity). Link to post Share on other sites More sharing options...
Advertisement Posted January 16, 2007 Posted January 16, 2007 Hi Vivek Iyer, Take a look here Anyone experienced focus shift with IR cut filters?. I'm sure you'll find what you were looking for!
jaapv Posted January 16, 2007 Share #2 Â Posted January 16, 2007 1.4/75 without IR cut: spot-on. With IR cut: spot-on. I must confess I fail to see how this focus shift could be explained theoretically. Link to post Share on other sites More sharing options...
Guest guy_mancuso Posted January 16, 2007 Share #3 Â Posted January 16, 2007 I have yet to notice anything there on focus shift. pretty much dead on all the time and if off it is me Link to post Share on other sites More sharing options...
Mark_Rinella Posted January 16, 2007 Share #4 Â Posted January 16, 2007 No shift here. My M8 went back to Leica in NJ when I first received it for rangefinder alignment. The focus was spot on when I got it back and has remained that way with the 486 filters. Link to post Share on other sites More sharing options...
sean_reid Posted January 16, 2007 Share #5 Â Posted January 16, 2007 I've seen no focus shift at all. Link to post Share on other sites More sharing options...
pascal_meheut Posted January 16, 2007 Share #6 Â Posted January 16, 2007 Same for me: no focus shift and I tried it because I ajusted my rangefinder myself. Link to post Share on other sites More sharing options...
rondeb Posted January 16, 2007 Share #7 Â Posted January 16, 2007 Advertisement (gone after registration) No shift here. My M8 went back to Leica in NJ when I first received it for rangefinder alignment. The focus was spot on when I got it back and has remained that way with the 486 filters. Â Hi Mark. I'm shipping mine off to NJ today for an adjustment as well. How long did it take to fix yours up? Thanks, Ron Link to post Share on other sites More sharing options...
Mark_Rinella Posted January 16, 2007 Share #8 Â Posted January 16, 2007 They turned mine around in one day. I did call and speak with Brenda Olesin beforehand. Link to post Share on other sites More sharing options...
steve_l Posted January 16, 2007 Share #9 Â Posted January 16, 2007 If anything, the focus would be off *without* the IR filter, because the IR component focuses at a different place than the visible light component (e.g., the fuzzy bright foliage issue) Link to post Share on other sites More sharing options...
willemvelthoven Posted January 16, 2007 Share #10 Â Posted January 16, 2007 i use a heliopan ir/uv cutoff on my noct. no focus shift whatsoever. i did some experiments with a 28mm size IR cut off behind my CV12 and 15mm lenses. that was useless because of severe focus shift. i'm sorry about that because the cyan vignetting was almost nonexistent. the 12 mm is not usable with a ir cutoff in front of the lens. just too much vignetting. Â i have no tech explanation for the focus shift but is was considerable. the focus plane moved almost 0,3 mm. (that's a lot for a wide angle lens) Link to post Share on other sites More sharing options...
jaapv Posted January 16, 2007 Share #11 Â Posted January 16, 2007 " behind" your CV ......lenses" I don't quite get that. Would you care to elaborate? Link to post Share on other sites More sharing options...
scott kirkpatrick Posted January 17, 2007 Share #12 Â Posted January 17, 2007 Putting a filter behind a lens would increase the optical path length because of the extra glass that the light goes through, and the resulting image would not lie on the original image plane. 0.3 mm sounds like a plausible shift. So this was simply a bad idea in the first place. Â scott Link to post Share on other sites More sharing options...
Vivek Iyer Posted January 17, 2007 Author Share #13 Â Posted January 17, 2007 Folks, Thanks a bunch for all the replies. Â Jaap, You raised a good question (the first post). In principle, any glass put in the optical path alters the focus. Most of the time it isn't significant. Â I should clarify my post regarding the filters on wides (can't help comment on this- the Dutch ingenuity is showing in this thread!): Â My careful experiments on wides were with rear filters on super-wides as Willem posted! There is little or not significant shift on the Superwide Heliar 15mm f/4.5 lens, in my tests. Â There are significant shifts while using a 25mm f/3.5 Canon or 2.5cm f/4 W-Nikkor-C lenses. These could be exceptional due to their simple optical designs (4 elements in 3 groups- topogon variant- Canon and 4/4 Topogon clone- Nikkor). Â Thanks again folks! Link to post Share on other sites More sharing options...
jaapv Posted January 17, 2007 Share #14 Â Posted January 17, 2007 Vivek- interesting. That would mean there is a relationship to the distance the light has to travel, making the focus shift for a filter in front of the lens disappear into the tolerances, but relevant for the much shorter distance between lens and sensor. And it would be for any filter - not just IR. Making the insitence of Leica for using a filter -any filter at all times on lenses with rear-mounted filters understandable, as the focus shift will be angle of incidence related it would introduce spherical aberration. Link to post Share on other sites More sharing options...
Riley Posted January 17, 2007 Share #15 Â Posted January 17, 2007 were there not originaly in 35mm film cameras separate focus marks for daylight and IR light ? Link to post Share on other sites More sharing options...
jaapv Posted January 17, 2007 Share #16 Â Posted January 17, 2007 were there not originaly in 35mm film camerasseparate focus marks for daylight and IR light ? Â Yes -but that is something different. I indicates the difference in focal plane for visible and IR light. Link to post Share on other sites More sharing options...
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