glenerrolrd Posted October 11, 2012 Share #21 Posted October 11, 2012 Advertisement (gone after registration) DL s point and the implied impact on using the MONO is quite different that traditional "focus shift" . Start with a given that almost all lenses have some small differences in the focus points of the RGB components . Only a truly APO lens like the Coastal Optics creates consistent focus of RGB . The Leica lenses are of course superb and well corrected ..many approximating an APO result . However when you add a strong colored filter ....you alter the focus points of each of the RGB ..so RED maybe nearer and GREEN maybe farther . If you can cover this with DOF ..it may not be an issue ....this seems to be the case with a light yellow filter . But when using a dark red filter ..he could see the effects even at F11. Depending on the image content (and color ) you may never see it or be bothered by it . However you can t work around this by adjusting focus (unless you can determine you focus point by evaluating the RGB distribution in the scene ). My take away was that I might be disappointed if I was using RED filters on my 21/3.4asph but would have no issues if using a yellow filter on the 75 APO . This would bother me if shooting the big clouds in the everglades but not at all in street shooting. It is certainly a "Fine Point" as are many of DL observations . Happy to be corrected if I didn t understand this . Link to post Share on other sites More sharing options...
Advertisement Posted October 11, 2012 Posted October 11, 2012 Hi glenerrolrd, Take a look here Focussing Monochrom with filters. I'm sure you'll find what you were looking for!
jaapv Posted October 11, 2012 Share #22 Posted October 11, 2012 I am reading this discussion with increasing amazement. A red filter does not magically change the light falling onto your sensor. It merely blocks non-red light. That means that if you now find your image out of focus, the red part of you unfiltered image was out of focus to begin with. That is called chromatic aberration, to which all non APO lenses are prone to to varying degrees. So yes, you are seeing chromatic aberration. What is new ? Link to post Share on other sites More sharing options...
mjh Posted October 11, 2012 Share #23 Posted October 11, 2012 What is new ? Nothing. Autofocus systems use a colour temperature sensor to adjust the focus depending on the dominant wavelengths; otherwise the AF would be slightly off under tungsten lighting if it was calibrated for daylight (or vice versa). It’s the same phenomenon. Link to post Share on other sites More sharing options...
jaapv Posted October 11, 2012 Share #24 Posted October 11, 2012 So why is Lloyd making such an issue out of it? Link to post Share on other sites More sharing options...
luigi bertolotti Posted October 11, 2012 Share #25 Posted October 11, 2012 Is an issue based on nothing.... ; or, better to say, on nothing specifically related to MM.... you could find the same on a BW film with red filter... I even seem to remember that for very critical film cameras (Large Formats) there used to be some facilities to fine/tune focus with filters on (but I can be wrong or confused by something similar) Link to post Share on other sites More sharing options...
luigi bertolotti Posted October 11, 2012 Share #26 Posted October 11, 2012 Nothing. Autofocus systems use a colour temperature sensor to adjust the focus depending on the dominant wavelengths; otherwise the AF would be slightly off under tungsten lighting if it was calibrated for daylight (or vice versa). It’s the same phenomenon. Thanks : I confess I didn't know at all of this detail about AF systems... Link to post Share on other sites More sharing options...
Rick Posted October 11, 2012 Share #27 Posted October 11, 2012 Advertisement (gone after registration) How much of his issues with his red filter focusing tests has to do with the problem he has with keeping his lenses from back focusing? I would think that he needs to sort that out first. Something in his picture on the above referenced site is way off on the red filter side. Every distance is blurry on the red filter side of that spit image example. http://diglloyd.com/blog/2012/20121010_2-LeicaMM-filters-reader-query.html Link to post Share on other sites More sharing options...
glenerrolrd Posted October 11, 2012 Share #28 Posted October 11, 2012 I am reading this discussion with increasing amazement.A red filter does not magically change the light falling onto your sensor. It merely blocks non-red light. That means that if you now find your image out of focus, the red part of you unfiltered image was out of focus to begin with. That is called chromatic aberration, to which all non APO lenses are prone to to varying degrees. So yes, you are seeing chromatic aberration. What is new ? Did you read Lloyd s blog post ? What I posted I believe is an accurate restatement of his point of view ...and it is quite different than your statement. You appear to saying his point and the discussion that follows is nonsense ? Not having the desire or ability to test myself..I generally try to understand first before discounting the opinions of others . I know from discussion with LLoyd and with the lens designer at Costal Optics ..that they fully understand the meaning of APO and things that can affect it . He goes on to support his tests with examples on his paid site . Would lead me to believe his findings . The question should not be ...does he know what he is talking about ..he does .. but rather are his findings relevant for the type of photography you might do. The example I gave was using a RED filter on a non APO wide angle ..where it might make a difference (depends on the RGB pattern in the image ) verse using a yellow filter on a APO lens ..where it would seem to be immaterial . Or did I misunderstand your POV which seems to be that a RED filter does not alter the focus point of the RGB light . If I misunderstood your point my apology . Link to post Share on other sites More sharing options...
pico Posted October 11, 2012 Share #29 Posted October 11, 2012 Is an issue based on nothing.... ; or, better to say, on nothing specifically related to MM.... you could find the same on a BW film with red filter... I even seem to remember that for very critical film cameras (Large Formats) there used to be some facilities to fine/tune focus with filters on (but I can be wrong or confused by something similar) Generally, we LF people rarely fuss about focus shift because we can refocus after stopping down. We also do not obsess about diffraction due to small (numerically high) apertures because diffraction is related to absolute aperture diameter and our F/22 is still large. Color shift is generally covered in depth of focus because our lenses are very much longer than 35mm equivalents...and for real worriers we have precision vacuum film holders. Link to post Share on other sites More sharing options...
AlanG Posted October 11, 2012 Share #30 Posted October 11, 2012 I haven't seen his tests but it seems odd to me that the shift could be so great with good lenses. I haven't heard of photographers having problems like this in the past and in many years of using filters the only time I worried about focus shift was using glass filters on the back of view camera lenses. So out of curiosity I ran a test. Not having an MM I used a 5DIII with 45mm TSE lens (not tilted) at f2.8. The focus point was on the word "Robert" and the books are 10 feet away. On magnified live view I couldn't see any change by using a red filter. Nor did I see a problem at 100% I also split the color channels of a shot that had no filter and all channels seem to be focused on the same spot. So I'm not sure what I'd have to do to see the problem. My guess is that his filter may have a magnification factor. He could try again with gel filters to eliminate that possibility. Other than that I am not sure why the lenses he is testing would focus color that differently than my 45mm lens and still be able to make a good image. Here are the 100% crops. (Sorry about the noise but I spot lit the books and then didn't bother to adjust exposure or anything in the raw processing and b/w conversion.) Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/189868-focussing-monochrom-with-filters/?do=findComment&comment=2139317'>More sharing options...
swamiji Posted October 12, 2012 Share #31 Posted October 12, 2012 Did you read Lloyd s blog post ? What I posted I believe is an accurate restatement of his point of view ...and it is quite different than your statement. You appear to saying his point and the discussion that follows is nonsense ? Not having the desire or ability to test myself..I generally try to understand first before discounting the opinions of others . I know from discussion with LLoyd and with the lens designer at Costal Optics ..that they fully understand the meaning of APO and things that can affect it . He goes on to support his tests with examples on his paid site . Would lead me to believe his findings . The question should not be ...does he know what he is talking about ..he does .. but rather are his findings relevant for the type of photography you might do. The example I gave was using a RED filter on a non APO wide angle ..where it might make a difference (depends on the RGB pattern in the image ) verse using a yellow filter on a APO lens ..where it would seem to be immaterial . Or did I misunderstand your POV which seems to be that a RED filter does not alter the focus point of the RGB light . If I misunderstood your point my apology . Having a POV does not change the laws of physics. Having a paid site does not make one an expert. The physics of light is well know to many here. It has not changed because of new technology. If Lloyd proposes something that appears to violate the physics of light, we should understand why first, before we discuss how to correct. I believe the other forum members have stated the case against clearly. Link to post Share on other sites More sharing options...
Guest borge Posted October 12, 2012 Share #32 Posted October 12, 2012 I wonder how many subscribers Lloyd gets on his site due to these "must read" articles on the MM. Considering the amount of people on the waiting lists I guess there could potientially be quite a few people interested in paying up to read this. Taking a small thing and blowing it out of proportions is therefore a good business idea. Link to post Share on other sites More sharing options...
luigi bertolotti Posted October 12, 2012 Share #33 Posted October 12, 2012 Just to make an effort to give credit to his assertions... I wonder if there could be a significant factor to account for, due to the ABSENCE of the Bayer filter... : after all, in a normal "color" sensor the value of a certain pixel derives from INTERPOLATION of values of adiacent pixels, which in turn do receive color-filtered wavelengths... could be that some serious computation is worth to be made about... but of course one would need the details on the in camera algorithms used for the RGB interpolation... Basically : pixels from std. Bayer filtered sensor are a "computed mix", from a no Bayer-filtered sensor (but, with a red filter in front of the lens) are all a "red biased" matrix... how MUCH this has an appreciable effect is a challenging math exercise (if someone likes to afford it... welcome) Link to post Share on other sites More sharing options...
IkarusJohn Posted October 12, 2012 Author Share #34 Posted October 12, 2012 The logical solution would be to include a correction into the red filter. Link to post Share on other sites More sharing options...
swamiji Posted October 12, 2012 Share #35 Posted October 12, 2012 But the relationship of focus point of each frequency to the sensor remains unchanged regardless of sensor or nothing would be in focus. Given that the filter is perfect. The best solution would be to go shooting. If you want to deal with deep red filters, buy an M8... Link to post Share on other sites More sharing options...
pgk Posted October 12, 2012 Share #36 Posted October 12, 2012 I haven't seen his tests but it seems odd to me that the shift could be so great with good lenses. Agreed especially at f/ll - that's a substantial shift. On magnified live view I couldn't see any change by using a red filter. So if it was simply the red light then I too would have thought that a focus shift would be clearly visible. He could try again with gel filters to eliminate that possibility I wondered about this but to be blunt, if filter thickness was the problem then surely using any filter should create some visible degradation? No doubt something is wrong with the tests but I very much doubt that the conclusions are correct. Link to post Share on other sites More sharing options...
Kittyphoto Posted October 12, 2012 Share #37 Posted October 12, 2012 So I'm not sure what I'd have to do to see the problem. My guess is that his filter may have a magnification factor. He could try again with gel filters to eliminate that possibility. Other than that I am not sure why the lenses he is testing would focus color that differently than my 45mm lens and still be able to make a good image. +1 Anyone with MM could verify this? Link to post Share on other sites More sharing options...
Guest borge Posted October 12, 2012 Share #38 Posted October 12, 2012 +1 Anyone with MM could verify this? I would love to, If the colored filters were available anywhere. They are out-of-stock everywhere I have checked - both locally and internationally, and I have purchased B+W MRC yellow, yellow/orange and red filters (all 46mm) from Adorama but they haven't shipped in 3 weeks now... I am also on the "in-stock" notification list at B&H and other sites! So maybe some time next year when I hopefully have received the filters. Link to post Share on other sites More sharing options...
brianv Posted October 12, 2012 Share #39 Posted October 12, 2012 Another fun test for my incoming Monochrome. I need to convert the 85mm F4.5 Ultra-Achromat to M-Mount. Corrected all the way out to near Infrared. Calcium Fluorite. Adjusted for inflation, same cost as the Summicron APO. Link to post Share on other sites More sharing options...
pgk Posted October 12, 2012 Share #40 Posted October 12, 2012 I often shoot above water with a camera in a housing fitted with a thick ~5mm flat glass port in front of the lens. Other than a minute amount of chroma in the corners there is no effect from shooting through the thick glass - with lenses down to 35mm focal length. (Below that I haven't tried because its usual to use a domed port). But I'd be very surprised indeed if a thin optical filter would do much, and I'm pretty sure that adverse effect would have been seen before if the filter thickness was the issue. Link to post Share on other sites More sharing options...
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