IkarusJohn Posted October 10, 2012 Share #1 Posted October 10, 2012 Advertisement (gone after registration) Lloyd Chambers has this comment on his website: As I prove unequivocally with a range of colored filters using the Leica M Monochrom in Filters and Focus Error / Sharpness, there is a shift in focus starting with a faint shift for a yellow filter, and very substantial and disheartening shift with a dark red filter, so much so that ƒ/11 is not adequate to compensate. This is a very serious quality issue that a Leica MM shooter must mitigate when using color filters, or suffer a severe loss of image sharpness. Now, I imagine focussing a Noctilux at f11 at a metre, this might be conceivable - the depth of field is about 250 mm, but at 3 metres, the depth of field is 11 metres, and from 10 metres it is just over 4 metres out to infinity (okay, beyond 20 metres - let's not split hairs). For the Summilux 21 ASPH, at 700 mm at f11, the dof is almost a metre, and at 5 metres everything from a metre to infinity is theoretically in focus. Yet good old Lloyd says that with a red filter, even the APO lenses can't focus accurately. I'm not really bothered enough to subscribe to Digilloyd, particularly as he seems to have a rangefinder blind spot, which nears psychosis when it comes to the Monochrom. My question is - has anyone noticed focus shift using red filters in practice (I understand the theoretical issue), and have they been able to deal with the issue by stopping down? I can't really imagine wanting to use a red filter for a close object wide open (it's possible, I guess), primarily because I tend to use a red filter for big skies - that usually means wide angle and stopped down. Cheers John Quote Link to post Share on other sites More sharing options...
Advertisement Posted October 10, 2012 Posted October 10, 2012 Hi IkarusJohn, Take a look here Focussing Monochrom with filters. I'm sure you'll find what you were looking for!
Lindolfi Posted October 10, 2012 Share #2 Posted October 10, 2012 Thanks John. The defect of focus from a focus shift due to longitudinal aberration and the use of colour filters is independent of focus distance. So it is not true that the defect is more problematic for a focus distance of 1 meter compared to a focus distance of infinity. 1 Quote Link to post Share on other sites More sharing options...
giordano Posted October 10, 2012 Share #3 Posted October 10, 2012 How can this be a problem on the Monochrom but not on the M9? Quote Link to post Share on other sites More sharing options...
IkarusJohn Posted October 10, 2012 Author Share #4 Posted October 10, 2012 Thanks John. The defect of focus from a focus shift due to longitudinal aberration and the use of colour filters is independent of focus distance. So it is not true that the defect is more problematic for a focus distance of 1 meter compared to a focus distance of infinity. Thanks Bert. Would you mind expanding on this? Does this mean that stopped down, depth of field has no impact on longitudinal aberration? and if so, does it follow that focus bracketing will not solve the problem? I used red, orange and yellow filters on my Hasselblad and in all honesty didn't notice focus shift at all - I'm nervous about going back to those photos now ... Quote Link to post Share on other sites More sharing options...
tele_player Posted October 10, 2012 Share #5 Posted October 10, 2012 Color filters are rarely (never?) used on an M9. -robert How can this be a problem on the Monochrom but not on the M9? Quote Link to post Share on other sites More sharing options...
Lindolfi Posted October 10, 2012 Share #6 Posted October 10, 2012 John, the unsharpness in the image from focus shift of different colors comes from the fact that the focal point for red for instance is behind the film plane and for blue in front, while green is just on the film plane. The distance between the red and green focal point creates the unsharpness. And that does not depend on focus distance nor DOF. As an example: if the focal length for red is 0.1 mm longer of a 50mm lens than for green, the distance between the red and green focal points is 0.11 mm for a focus distance of 1 meter, while it is 0.1 mm for infinity. And so, although the DOF obviously is much more shallow at 1 meter than at infinity, the unsharpness effect is about the same. To give an example: if you photograph the moon with a not perfectly corrected lens with green or red filter, the unsharpness effect will be about the same when photographing a photograph of the moon at a distance of 1 meter with those filters. Hope this makes clear what I wrote earlier, John. 3 Quote Link to post Share on other sites More sharing options...
Guest borge Posted October 10, 2012 Share #7 Posted October 10, 2012 Advertisement (gone after registration) Is this a joke? Will this shift in reality be very noticeable in normal day-to-day shooting? Quote Link to post Share on other sites More sharing options...
pop Posted October 10, 2012 Share #8 Posted October 10, 2012 Is this a joke? Will this shift in reality be very noticeable in normal day-to-day shooting? That's why Bert wrote "with a not perfectly corrected lens" and it explains in part the price for a good lens. Good lenses are corrected such that they keep this error very small. Quote Link to post Share on other sites More sharing options...
IkarusJohn Posted October 10, 2012 Author Share #9 Posted October 10, 2012 It seems for sharpest focus (which is not really a depth of field issue), if you're using a red filter, you should bump the focus slightly, as with the old IR mark on previous lenses. Can't help but think this is another storm in a teacup, with Mr Chambers wanting to make his point. Quote Link to post Share on other sites More sharing options...
algrove Posted October 11, 2012 Share #10 Posted October 11, 2012 Guess I'm stupid, but just took 500 images with colored filter on my MM and I do not see focus shift, but then I only shoot with one eye. 2 Quote Link to post Share on other sites More sharing options...
pico Posted October 11, 2012 Share #11 Posted October 11, 2012 (edited) Thanks John. The defect of focus from a focus shift due to longitudinal aberration and the use of colour filters is independent of focus distance. So it is not true that the defect is more problematic for a focus distance of 1 meter compared to a focus distance of infinity. Although only to a very minor degree, as one focuses closer the focal length of the lens increases, therefore depth-of-focus increases to an advantage. Do NOT confuse with depth-of-field. Ah, so be it with 35mm format which uses such terribly short focal lengths of which large format people worry not. Just being pedantic here. Really, nothing has change vis-a-vis digital vs film. . Edited October 11, 2012 by pico 1 Quote Link to post Share on other sites More sharing options...
Hosermage Posted October 11, 2012 Share #12 Posted October 11, 2012 John, the unsharpness in the image from focus shift of different colors comes from the fact that the focal point for red for instance is behind the film plane and for blue in front, while green is just on the film plane. The distance between the red and green focal point creates the unsharpness. And that does not depend on focus distance nor DOF. Hi, thanks for the explanation. However, I thought this is what APO lenses are for? It uses elements to bring the 3 lights of different frequencies to a common focus point. Also, isn't this usually only problematic for a longer focal length? That's why you see APO for 90mm, 75mm. As I read somewhere, the 50'Lux ASPH is also APO by design but it wasn't marked as such because there isn't a non-APO ASPH design before it, so the new 50'Cron is marked APO to distinguish it from the previous ASPH version. Anyway, I don't understand why Lloyd would say that MM will still mis-focus for APO lenses. Quote Link to post Share on other sites More sharing options...
Guest borge Posted October 11, 2012 Share #13 Posted October 11, 2012 Hi, thanks for the explanation. However, I thought this is what APO lenses are for? It uses elements to bring the 3 lights of different frequencies to a common focus point. Also, isn't this usually only problematic for a longer focal length? That's why you see APO for 90mm, 75mm. As I read somewhere, the 50'Lux ASPH is also APO by design but it wasn't marked as such because there isn't a non-APO ASPH design before it, so the new 50'Cron is marked APO to distinguish it from the previous ASPH version. Anyway, I don't understand why Lloyd would say that MM will still mis-focus for APO lenses. So with a 50 Lux the focus should be pretty spot on even if you use colored filters? If not I might as well cancel my order of a bunch of B+W MRC 46mm color filters! Not that I will ever receive them anway... "Out of stock" everywhere! Quote Link to post Share on other sites More sharing options...
Sawboneslf Posted October 11, 2012 Share #14 Posted October 11, 2012 I originally posted this question to Lloyd Chambers. He had not yet tested the APO 50/2. His opinion was that ALL lenses by all manufacturers have this issue except for the Coastal 60/4 lens. There is no way to overcome this problem with a rangefinder other than focus bracketing. In my view, either a truly apochromatic lens, live view, or an EVF on a future Monochom M camera would correct this problem. Perhaps this is why the summacron 50/2 is being produced? Quote Link to post Share on other sites More sharing options...
Guest borge Posted October 11, 2012 Share #15 Posted October 11, 2012 (edited) I originally posted this question to Lloyd Chambers. He had not yet tested the APO 50/2. His opinion was that ALL lenses by all manufacturers have this issue except for the Coastal 60/4 lens. There is no way to overcome this problem with a rangefinder other than focus bracketing.In my view, either a truly apochromatic lens, live view, or an EVF on a future Monochom M camera would correct this problem. Perhaps this is why the summacron 50/2 is being produced? I guess someone should contact Leica regarding this and get an official reply. It would be nice to get an official statement especially in regards to which lenses are affected or not for example. Anyway, I'll do some tests with my mm + 50 lux and the b+w mrc filters i've ordered a few weeks back from Adorama.. If and when they are shipped and delivered Edited October 11, 2012 by borge Quote Link to post Share on other sites More sharing options...
Sawboneslf Posted October 11, 2012 Share #16 Posted October 11, 2012 I did not want my post to become a debate on the merits of a paid subscription. Thie portion of Diglloyd's blog that this question appeared on is free. Longitudinal aberration is a physical fact, as noted in the above responses. I agree that Leica should address these concerns as I also am on the waiting list for the monochrome camera. Quote Link to post Share on other sites More sharing options...
Lindolfi Posted October 11, 2012 Share #17 Posted October 11, 2012 Pico is right in that with closer focussing the difference in focus of different colours becomes slightly bigger as I have shown with the 50 mm lens at 1 meter or infinity (0.11 mm instead of 0.1 mm), but that is peanuts compared to the change in DOF, so there is no relation. ( Focal length does not change when focussing nearby, but image distance of best focus does.) David was right in pointing out that an APO lens should not have the issue. Strictly speaking it still is not correct for all wavelengths (colours), but it is the best correction we have at 3 given wavelengths. Only in the far red, we can have some shift in focus when using a filter on an APO lens, as the error-wavelength curves steeply climb just at the edge of the visual spectrum. The reference by John to the infrared mark on the focus barrel of some lenses is spot on. But in the infra red the curves are really climbing and it makes sense to correct focus for it. Does anybody have the sensitivity spectrum of the Leica MM? 2 Quote Link to post Share on other sites More sharing options...
wattsy Posted October 11, 2012 Share #18 Posted October 11, 2012 I'm not really bothered enough to subscribe to Digilloyd, particularly as he seems to have a rangefinder blind spot, which nears psychosis when it comes to the Monochrom. I think you are right. If there is one thing I've had to learn when using a Leica (especially when I migrated from film to digital bodies) is that you have to accept that the RF doesn't provide precision in all circumstances. You have to learn to make a few allowances here and there for a bit of focus shift, when focussing and recomposing etc. Learning to nudge the focus when using a strong red filter (if that's what is necessary) is hardly a big problem. 2 Quote Link to post Share on other sites More sharing options...
Guest borge Posted October 11, 2012 Share #19 Posted October 11, 2012 David was right in pointing out that an APO lens should not have the issue. Strictly speaking it still is not correct for all wavelengths (colours), but it is the best correction we have at 3 given wavelengths. I guess the question then is: What lenses has an APO design? Only the APO branded one's or does this include the 50 and 35 Summilux ASPH's as well for example? Since there are many people that say that they in fact are APO designs and constructions. There are details on the MM's spectrum sensitivity range here: http://www.l-camera-forum.com/leica-forum/leica-m9-forum/238912-m9m-spectral-sensitivity-5.html Quote Link to post Share on other sites More sharing options...
Jager Posted October 11, 2012 Share #20 Posted October 11, 2012 I've had my MM for about six weeks now. I've taken something on the order of 2400 shots with it. Of those, probably 50-60% used a medium-yellow filter, a smaller number used a yellow-orange filter, and a smaller number yet used a red filter. Lenses have included the Noctilux (no colored filters used), 35 Summilux ASPH (a non-APO lens), 50 Summicron (a non-APO lens), and a 50 Summilux ASPH (a purported APO lens). Empirically - I do photography, not camera-focus or lens-resolution tests - I've noticed no focus issues when using color filters. My focus hit rate has remained the same whether I'm using filters or not. It also approximates what I have long gotten when using my M9 - a camera for which I've never used a color filter. So for me, I can see no practical difference. I'm not disputing the theoretical issue. Quite the contrary, the optical phenomenon that Lloyd alludes to has been known for decades. And yet I don't recollect there was all that much angst around the use of color filters back in the day when we all carried film cameras. It's also possible that if I shot lots with red filters I might start to notice the issue more. But as has already been mentioned, a red filter creates fairly dramatic and sometimes surreal effects - something most of us aren't inclined to use in an everyday, all-the-time fashion. Yellow filters, historically those most used in black and white photography, have little-to-no theoretical focus shift. Certainly not any on a pragmatic basis. Based upon what I'm seeing, focus shift worries when using colored filters on the MM is a bit overblown. 11 Quote Link to post Share on other sites More sharing options...
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