michaelwj Posted May 10, 2016 Share #81 Â Posted May 10, 2016 Advertisement (gone after registration) Do you lose coupling below 70cm with the SA? I guess it doesn't matter too much with a 21 but just wondering. Yes. No dent to let you know either. Link to post Share on other sites More sharing options...
lct Posted May 10, 2016 Share #82 Â Posted May 10, 2016 [...] What was this thread originally about? Something about 21mm lenses? :-) Sure but... 6. Differences in optical distortion are minimal between symmetrical and asymmetrical designs nowadays so differences in stretching are minimal as well, right? Link to post Share on other sites More sharing options...
T*Sonnar Posted May 10, 2016 Share #83  Posted May 10, 2016 Not everything is possible, you will lose something by trying to one lens look like the other, resolution, width, shape - it is not just a simple transform.  I don't follow your stitching comment? A 50mm shot does not stretch the corners, two of them do not stretch their respective corners, so it is only how they are taken and stitched that stretched corners can arise. So it is all about stitching. But we digress.  Michael  ps. It's nice to have near real time discussions.  Well i wasn't suggesting you'd actually do it.  I'm saying that it's the projection that is the 'problem'. Not how you get there. By stitching, or by using a wide lens in there first place. There is no difference to using a 21mm, or stitching a few 50mm frames together to achieve the same angle of view. The result is the same, when the projections are the same. Link to post Share on other sites More sharing options...
michaelwj Posted May 10, 2016 Share #84 Â Posted May 10, 2016 Sure but... 6. Differences in optical distortion are minimal between symmetrical and asymmetrical designs nowadays so differences in stretching are minimal as well, right? Depends how hard you look! There is also 50 years of lens design in the meantime which surely can't be a bad thing :-) Â And lct, this is the Leica forum, small differences are what we discuss all the time! Link to post Share on other sites More sharing options...
michaelwj Posted May 10, 2016 Share #85 Â Posted May 10, 2016 Well i wasn't suggesting you'd actually do it. Â I'm saying that it's the projection that is the 'problem'. Not how you get there. By stitching, or by using a wide lens in there first place. There is no difference to using a 21mm, or stitching a few 50mm frames together to achieve the same angle of view. The result is the same, when the projections are the same. But the projections are not the same. One is a 21mm and the other is a bunch of 50mm's. Link to post Share on other sites More sharing options...
T*Sonnar Posted May 10, 2016 Share #86  Posted May 10, 2016 But the projections are not the same. One is a 21mm and the other is a bunch of 50mm's.  Until you stitch them.  You are completely free to do that rectilinear, or spherical, or cylindrical or .. It's your choice. Just like it's Leica's choice to offer an optically corrected lens or not.  Here's a little more about projections: http://www.kolor.com/wiki-en/action/view/Understanding_Projecting_Modes  There is no way that one can tell with which focal length it was taken, or how many pictures it took, by looking at the end result. Link to post Share on other sites More sharing options...
lct Posted May 10, 2016 Share #87  Posted May 10, 2016 Advertisement (gone after registration) [...] And lct, this is the Leica forum, small differences are what we discuss all the time!  Samall differences AND camera bags  Link to post Share on other sites More sharing options...
the warrior Posted May 10, 2016 Share #88 Â Posted May 10, 2016 Well folks, I can only bring small photographs with f4 today have given me the SA F4 for testing, I find something interesting here to see the two lenses in the same situation.I find differences between the two lenses in f4, differences in light collection, half a step f4 collects more light.I also find differences between the two lenses at the corners the SA f3,4 open to f4 lets in light that flame, the SA f4 no. I see more than sharpnes in the SA f4, but in the F3,4 (open to f4) is less sharpnes. My opinion on sharpnes in general is very similar in both lenses. Honestly I am inclined to the SA f4, I will buy this lens. Â I do not appreciate too much difference in the vignette corners.The policy of any company is its new products are better than the others, is normal, if not to tell this would not sell new products, some say that Leica does not tell the whole truth and that some of its older products are better than modern, I think it is possible. Â SA f4 in f4 Â Â Sa f3,4 in f4 Â Â SA f4 in f4 Â Â Sa f3,4 in f4 Â Â Â Â And more photos of SA F4 Â Â Â Link to post Share on other sites More sharing options...
the warrior Posted May 10, 2016 Share #89 Â Posted May 10, 2016 These photographs do not have any further treatment. Link to post Share on other sites More sharing options...
Peter Branch Posted May 10, 2016 Share #90  Posted May 10, 2016 One of the ways of minimising the visual effect of perspective distortion, the so called "Egg Head" effect, when using very wide angle lenses is to deliberately introduce negative, i.e. barrel, distortion.  This is easily demonstrated using the manual transform function in ACR.  If a lens has a natural degree of negative distortion then the visual effect on this type of distortion can be quite obvious and it will make a lens seem less prone to the "Egg Head" effect. Perhaps ironically it is lenses with this form of distortion that can give the more pleasing result.  It cannot be too strongly emphasises that with very wide angle lenses a change in view point of only a few millimetres can have a significant effect, Similarly a small degree of negative distortion can also be significant.  Comparisons between lenses for this effect need to be made under virtual laboratory conditions to be meaningful. Link to post Share on other sites More sharing options...
michaelwj Posted May 10, 2016 Share #91 Â Posted May 10, 2016 But surely when you apply a barrel distortion in ACR you are reducing the field of view (by unstretching) and reducing the resolution (by interpolation of pixels). There is no free lunch, you need to choose your weapon and deal with it Link to post Share on other sites More sharing options...
michaelwj Posted May 10, 2016 Share #92 Â Posted May 10, 2016 These photographs do not have any further treatment. Very interesting. I've not seen many direct comparisons between these two lenses. Thank you. Michael Link to post Share on other sites More sharing options...
michaelwj Posted May 10, 2016 Share #93  Posted May 10, 2016 If a lens has a natural degree of negative distortion then the visual effect on this type of distortion can be quite obvious and it will make a lens seem less prone to the "Egg Head" effect. Perhaps ironically it is lenses with this form of distortion that can give the more pleasing result.  The way I see it, the more symmetrical a wide angle lens it, the more the lens it projecting a spherical image onto a plane. This accounts for the reduced resolution at the edges (they are starting to get out of focus) and the loss of illumination (inverse square law). The light at the edges has further to travel and hits the film at a very high angle - in particular the SA(3.4) projects far more image onto the film (there is less space between the negatives) and has very bad coloured edges on digital. On the other hand, an asymmetrical design allows for the light to be more parallel as it hits the film, it is projecting far less curvature onto the plane. The result is a more even illumination and resolution, but we have now had to distort our sphere to be be flat. This is never noticed unless a circle or head is placed near the edge of the frame, and in landscape shots can add to the feeling of falling into the scene, which I think works very well.  We all really need one of each .  You're negative distortion description is a very easy way to visualize what is happening.  Michael Link to post Share on other sites More sharing options...
the warrior Posted May 11, 2016 Share #94  Posted May 11, 2016 The light at the edges has further to travel and hits the film at a very high angle - in particular the SA(3.4) projects far more image onto the film (there is less space between the negatives) and has very bad coloured edges on digital. Michael  It's true, I shot two spools of TriX 400 with the SA F3,4 and the distance between negative is minimal, I have come to the same conclusion.  Tomorrow I will shoot two reels with the SA F4 .... see.  It is also true that there is serious evidence to go to a lab, but I do not buy my glasses for that, I go out into the street, that's my laboratory.  Pictures do not lie, the SA F3,4 is fainter at the edges and in the center, the SA F4 collects more light, perhaps almost a step.  I like the SA F4 for several reasons.  I hope I have helped solve some doubts.  Another day will put more photos.  Still very attentive to his words. Link to post Share on other sites More sharing options...
michaelwj Posted May 11, 2016 Share #95 Â Posted May 11, 2016 I hope I have helped solve some doubts. Â Â Â Â I think you are a long way to solving your own! Link to post Share on other sites More sharing options...
lct Posted May 11, 2016 Share #96 Â Posted May 11, 2016 Hehe yes and minor distortions are easy to adjust in PP. This way the poor man of the Warrior's last pic could have his toothache cured hopefully . Just kidding . Link to post Share on other sites More sharing options...
the warrior Posted May 11, 2016 Share #97 Â Posted May 11, 2016 I see no distortion .. !!You should not listen to me, I just do pictures with the lenses. Â To day wiith Leica Monochrom and "the beast", the SA F4 in f4. Â Link to post Share on other sites More sharing options...
lct Posted May 11, 2016 Share #98  Posted May 11, 2016 Nice pic but lenses with zero distortion do not exist as you know. Would you shoot your mother in law in the corner of a 21mm image? Just kidding again sorry but i would not do that sort of gift to anybody in my family. Just for sake of illustration:  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/259440-real-world-21mm-lens-comparisons/?do=findComment&comment=3042926'>More sharing options...
kenf Posted May 14, 2016 Share #99  Posted May 14, 2016 A very interesting discussion!  I've never gone this wide on a RF, but now that I have an M-P I'm considering it.  Question - I don't think my budget would stretch to a 21/3.8 so I'm considering a 21/2.8 ASPH.  Would performance on the M-P's sensor be good, or should I hold out for the f/3.8 lens?  It will be joining my 35/2 ASPH and 75/2, would the "look" be complementary? Link to post Share on other sites More sharing options...
kenf Posted May 14, 2016 Share #100  Posted May 14, 2016 I'm getting all twisted up - it's the most current 21 I'm comparing the 21/2.8 to - the f/3.4, not the f/3.8. Link to post Share on other sites More sharing options...
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