Guest d.sge Posted March 7, 2016 Share #1  Posted March 7, 2016 Advertisement (gone after registration) What about coma wide open makes a photograph better that you'd be willing to pay anything for it? Link to post Share on other sites More sharing options...
Advertisement Posted March 7, 2016 Posted March 7, 2016 Hi Guest d.sge, Take a look here Coma. I'm sure you'll find what you were looking for!
wizard Posted March 7, 2016 Share #2 Â Posted March 7, 2016 You mean more coma or less coma? Usually, less coma is preferred, as coma is an optical deficiency resulting in less contrast and sharpness, so I would definitively NOT pay for MORE coma. Link to post Share on other sites More sharing options...
david strachan Posted March 7, 2016 Share #3  Posted March 7, 2016 Yes, one doesn't want coma. One of the real bugbears in lens design. Easy enough to get rid of CA in PP, but coma is a curse. I can't stand it in star photographs....the ultimate test! Link to post Share on other sites More sharing options...
Guest d.sge Posted March 7, 2016 Share #4 Â Posted March 7, 2016 I'm with you, Wizard. Â The presence of coma wide open leads me to believe that such an offending lens (think the Voigtlander Noktons) was created by a manufacturer thinking that lens would be used on an APS-C camera. Why will people spend money on that? Show yourselves. I'd like to feel less like an ass after seeing examples of when those spirally corners benefit a photograph. I really don't get it. Link to post Share on other sites More sharing options...
david strachan Posted March 7, 2016 Share #5 Â Posted March 7, 2016 Hehehe..that's why I stick to APS-H and APS-C size...M8's sensor with full size lenses... coma is radically reduced. As are so many aberrations. Link to post Share on other sites More sharing options...
david strachan Posted March 7, 2016 Share #6  Posted March 7, 2016 You mean more coma or less coma? Usually, less coma is preferred, as coma is an optical deficiency resulting in less contrast and sharpness, so I would definitively NOT pay for MORE coma. Coma is a defect showing "comet" shaped tails to point light sources, from which the name originated. They also look like "butterflies". I'm not aware of it defined problem of "contrast and sharpness". Link to post Share on other sites More sharing options...
jaapv Posted March 7, 2016 Share #7  Posted March 7, 2016 Advertisement (gone after registration) What about coma wide open makes a photograph better that you'd be willing to pay anything for it? Nothing. it is an optical aberration, the better the lens, the less coma. Link to post Share on other sites More sharing options...
Guest d.sge Posted March 7, 2016 Share #8  Posted March 7, 2016 Coma is a defect showing "comet" shaped tails to point light sources, from which the name originated. They also look like "butterflies". I'm not aware of it defined problem of "contrast and sharpness".  Are the corners of (missing link) something other than coma (beyond being a definitive example of someone paying $1100 for a Coke bottle, of course) then?  Edit: Not sure why the link ...c1.staticflickr.com/9/8668/15852291792_6e1fa8d995.jpg isn't appearing. Link to post Share on other sites More sharing options...
david strachan Posted March 7, 2016 Share #9 Â Posted March 7, 2016 Yes, looks like extreme coma to me. I'm sure it'll have other defects too, but the size is a bit too small to see. Like all lens aberrations, it depends on your subject, as to how noticeable they are. Link to post Share on other sites More sharing options...
wizard Posted March 8, 2016 Share #10  Posted March 8, 2016 Coma is a defect showing "comet" shaped tails to point light sources, from which the name originated. They also look like "butterflies". I'm not aware of it defined problem of "contrast and sharpness".  David, your definition is correct. However, every optical fault or misbehaviour that I am aware of (with the possible exception of vignetting, which in my view is not an optical fault anyway) will inevitably lead to a reduced definition in those areas of a picture where that optical fault is active, and will in turn lead to reduced contrast and/or sharpness. As far as coma is concerned, if points (coma is not limited to point light sources, that is just where you can best see the effect) are reproduced with comet shaped tails, you bet that there is a problem with lack of contrast and sharpness resulting therefrom!  Cheers,  Andy Link to post Share on other sites More sharing options...
jaapv Posted March 8, 2016 Share #11  Posted March 8, 2016 Are the corners of (missing link) something other than coma (beyond being a definitive example of someone paying $1100 for a Coke bottle, of course) then?  Edit: Not sure why the link ...c1.staticflickr.com/9/8668/15852291792_6e1fa8d995.jpg isn't appearing. Click on the "link" icon and copy-paste. Alternately upload the image here. Link to post Share on other sites More sharing options...
Guest d.sge Posted March 11, 2016 Share #12 Â Posted March 11, 2016 Yes, looks like extreme coma to me. I'm sure it'll have other defects too, but the size is a bit too small to see. Like all lens aberrations, it depends on your subject, as to how noticeable they are. That's someone else's photograph from the Zeiss 35/2.0 Biogon, a highly corrected lens. Take a step up at the same speed and one has the 35/2.0 Summicron ("bokeh king," ASPH, it doesn't matter). After over 50 years of lens designs we're all still relegated to various optical deficiencies. I don't get it. I've got forty or so years to go, but by then, at this rate, I'll still have to settle for swirly corners and/or some degree of field curvature." What corrected optical failures might I not have to pay for in the future? It doesn't look like Adobe will be able to fix those $3000 failures any time soon. Link to post Share on other sites More sharing options...
pico Posted March 11, 2016 Share #13 Â Posted March 11, 2016 Coma tells us that the lens design is defective. On the other hand, in large format some people think it is desirable and lenses with coma. None in 35mm that I know of. . Link to post Share on other sites More sharing options...
Guest d.sge Posted March 12, 2016 Share #14  Posted March 12, 2016 Pico, do you have any references to that LF remark? The presence of examples of "successful" prints would be great, but I can't think of any renown photographers (Gursky (LF), Shulman (LF), Eggleston (120 and 135), Cartier-Bresson (135), not sure of Shore's format of choice, etc.) whose prints have have been universally admired that have had swirly corners or obvious field curvature. Heck, if anyone can point to a renown print with even a minute degree of field curvature obvious with your face smushed in it, even an 8x10", please reference it here. Link to post Share on other sites More sharing options...
michaelwj Posted March 12, 2016 Share #15 Â Posted March 12, 2016 Coma tells us that the lens design is defective. On the other hand, in large format some people think it is desirable and lenses with coma. None in 35mm that I know of. . The pre-asph 35 summilux comes to mind as a very popular lens sold for ~40 years loaded with coma. Â In general, all errors can be accounted for, at a cost - $ and/or size. Think of the new Zeiss Otus line. Â Cheers, Michael Link to post Share on other sites More sharing options...
lct Posted March 12, 2016 Share #16  Posted March 12, 2016 All wides show some more or less coma at full aperture folks. Go shoot some street lamps tonight if you don't bellieve me Otherwise, the latest Zeiss Loxia 35/2 would be "defective" as well. See https://fstoppers.com/originals/fstoppers-reviews-beautifully-crafted-zeiss-loxia-35mm-f2-lens-67394. It just has more coma than, say, a Summicron 35/2 asph but their price is not the same obviously. Link to post Share on other sites More sharing options...
Guest d.sge Posted March 13, 2016 Share #17 Â Posted March 13, 2016 I'm more concerned about concrete in the foreground being rendered evenly across the frame at around 2 -3 meters. Link to post Share on other sites More sharing options...
lct Posted March 13, 2016 Share #18 Â Posted March 13, 2016 I'm more concerned about concrete in the foreground being rendered evenly across the frame at around 2 -3 meters. Â I don't understand sorry. Would you mind to elaborate? Link to post Share on other sites More sharing options...
Guest d.sge Posted March 14, 2016 Share #19 Â Posted March 14, 2016 I'd say not a problem, LCT, but uploading an image to this thread is going to take more time than me typing all of these words. Maybe tomorrow. Link to post Share on other sites More sharing options...
michaelwj Posted March 14, 2016 Share #20 Â Posted March 14, 2016 Coma tells us that the lens design is defective. . I keep coming back to this point in my mind. Coma doesn't mean the lens design is defective, it just means coma correction was not a priority. I can think of a huge list of things I don't want in a lens, but that doesn't mean the design is defective. For example, I really don't like distortion in a lens, but it doesn't mean a lens with distortion is defective, maybe even illumination was a higher priority for the designers. Likewise with finder blockage, that is a hugely defective design, you can't even see what's in the picture! Yet some people live with it as they have other priorities. Personally, if a lens has coma wide open, I can live with it, provided it fits in with MY priorities. Â On the other hand, for an astrophotography lens, coma would mean a defective design! Â Michael Link to post Share on other sites More sharing options...
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