Original or updated lens design?

<p>I am putting the Loxia 50mm f2 for Sony E mount through some tests this week. It is an age old Planar double Gauss design with no modern aspherical lenses, yet it has been produced specifically for a digital full frame camera, which for short back focus RF type otics normally requires a modified lens design to allow the corner or edge pixels to properly record the well off centre imaging rays. My field use to date has been positive and it is a marvellous traditional operation type of lens (full control on the lens of aperture, DOF, focussing) for a digital camera, a smooth beauty in use. My question, if anyone is informed of the answer, is this older Planar design modified or updated, and to what extent?</p>

<p>Planar lenses have many variations. The Loxia Planar is optimized* for use with the thick (2 mm) cover glass on A7 cameras. Variances like vignetting and distortion can be automatically corrected (menu option) in firmware, effective for both RAW and JPEG files. Zeiss lets these issues slip a little, concentrating on low CA, resolution, and flat field (considering the cover glass). Even uncorrected, the Loxia 50/2 and 35/2 have less than 1% distortion.</p>

<p>Sean Reid finds that the corner sharpness improves the closer you focus, because the lens is further from the focal plane. In the real world, everything but the subject of a closeup is nearer or further away and out of focus anyway, so it's not something to worry about.</p>

<p>As you can see in the example below, the corners exhibit none of the smearing, even wide open, you find with legacy lenses like the Leica Summicron 50/2. The panels are cropped from a full-sized 24 MP image, reproduced pixel = pixel in your browser. For the overview, click on (http://d6d2h4gfvy8t8.cloudfront.net/18045161-md.jpg)</p>

<p><img src="http://d6d2h4gfvy8t8.cloudfront.net/18045162-lg.jpg" alt="" width="1500" height="675" /></p>

<p>* Optimized: As the angle of incidence increases at the sensor, the distance light travels through the glass increases with the tangent of the angle. In order to focus on the sensor itself, some negative field curvature is used in the lens design. I would not expect the Loxia to do well if adapted to a different camera, much as Leica and other rangefinder lenses don't do well on the Sony A7. The Leica M9 has a 0.8 mm cover glass, which works well (enough) with legacy lenses, but tends to admit more infrared than desirable. At 0.5 mm, the M8 needed to use an hot mirror IR blocking filter.</p>

 

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<p>I would not expect the Loxia to do well if adapted to a different camera</p>

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<p>Quite so - the cover glass thickness of the A7 Series cameras has been included in the optical design of the Loxia.</p>

 

 

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<p>Quite so - the cover glass thickness of the A7 Series cameras has been included in the optical design of the Loxia.</p>

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<p>This was evidenced in tests of another Sony lens, the new 24-70 f/2.8 G-Master. Roger Cicala (LensRentals) found it necessary to insert a 2 mm glass flat when measuring MTF for this lens. for what it's worth, the 24-70/2.8 is on its way to displacing the Loxia lenses from my backpack. It's that good, and I'm out of space after adding a flash unit to the kit.</p>

<p>https://www.lensrentals.com/blog/2016/04/sony-goes-world-class-the-24-70mm-f2-8-gm-mtf-and-variance-tests/</p>

<p>Thanks for the field lens resolution examples, Edward. I will be doing the same with my example. I like the Sony 16-35mm zoom, but regret the lack of DOF and manual aperture, so I imagine I would have the same feeling with the 24/70, not to mention the slower speed, weight and encombrance, and especially if I would use it mainly at or around 50mm. I will just use my feet a bit more with the Loxia.</p>

<p>I did the same test using a Leica Summicron 50/2 (v2, 1964) and a Nikon 50/1.4 AIS. While the Loxia was clearly the top dog, the Nikon edged out the Summicron, particularly in the corners. Nikon and Leica lenses of this era tended to have high resolution and low contrast, which I think the examples illustrate. You can find them in my portfolio.</p>

<p>http://www.photo.net/photodb/folder?folder_id=1081662</p>

<p>The only justification I see for a manual aperture ring is for video. Even then, the thumb wheel is not that hard to use without upsetting the camera. On the other hand, a manual ring can be made stepless, standard on a professional video camera.</p>

<p>With the electronic finder of an A7, you get a continual DOF preview*. The real value of DOF is the way the background (or foreground) appears in relation to the actual plane of focus. Actual numbers in a scale are based on someone's assumptions. None of the manual aperture rings for the Sony have DOF scales, and I have never actually used the scale on a Batis lens beyond figuring out how to set it up for display.</p>

<p>Even with a zoom lens, I use my feet to establish the relationship between foreground and background, then zoom to crop in the viewfinder. Numerically, 24-70 doesn't seem much, but there is a huge difference in field of view between very-wide and medium tele. Despite the size and weight, the balance point is at the edge where the lens reaches full diameter, about 3/4" in front of the flange. That's right where the knuckle of the third finger of my left hand supports the camera, with my thumb and middle finger on the zoom (or focus) ring.</p>

<p>* Viewfinder effects = ON, the "soft" aperture goes to the preset value immediately. If OFF, the aperture goes to preset once focus lock is achieved. Manual is always manual (duh). The new 24-70 GM is always preset. The new 85/1.4 has a manual aperture ring, but it is aperture-by-wire. GO FIGURE!</p>

<p>Thanks Edward. I take your points related to my view of the pros and cons of primes and zooms, in reference to the little Loxia MF lens. Of course I use the eyepiece or monitor for judging the OOF effects, but I have been weaned on DOF and using one f stop down from the normal circle of confusion value that they use on preparing the DOF scales is usually my starting point when pre-visualising the shot.</p>

<p>I did some quick tests tripod mounted A7rII with Loxia at about 12 feet and twice or three times that distance. Here are two images of the end wall at my place at f2, the first a corner image at about 33 inch wide image, the second of the overall image. These are just extra fine jpegs at 42 MP as I have not yet processed the RAW data. The corner performance improves quite a bit by f2.8 and is optimum around f5.6 or f8. At all f-stops the edges seem as sharp as the centre, and certainly by f2.8. I did the check to decide whether I would keep the lens or not (10 day return privilege).</p>

<p>Not sure how to create a link, but the reduced size images (that can be clicked on to enlarge) are in the Loxia folder of <br /> Thanks Edward. I take your points related to my view of the pros and cons of primes and zooms, in reference to the little Loxia MF lens. Of course I use the eyepiece or monitor for judging the OOF effects, but I have been weaned on DOF and using one f stop down from the normal circle of confusion value that they use on preparing the DOF scales is usually my starting point when pre-visualising the shot.</p>

<p>I did some quick tests tripod mounted A7rII with Loxia at about 12 feet and twice or three times that distance. Here are two images of the end wall at my place at f2, the first a corner image at about 33 inch wide image, the second of the overall image. These are just extra fine jpegs at 42 MP as I have not yet processed the RAW data. The corner performance improves quite a bit by f2.8 and is optimum around f5.6 or f8. At all f-stops the edges seem as sharp as the centre, and certainly by f2.8. I did the check to decide whether I would keep the lens or not (10 day return privilege).</p>

<p>Not sure how to create a link, but the reduced size images (that can be clicked on to enlarge) are in the Loxia folder of http://www.photo.net/photos/aplumpton.</p>

<p>Happily, the softness at widest apertures in the corners is really just that, a very small area. The photos I uploaded have none of the sharpness of the originals, due to the image siuze reduction for PNet uploading. I think I will be quite happy with this lens.</p>

<p>Apologies for the last post which is a jumble. Here is the intended text:</p>

<p>Thanks Edward. I take your points related to my view of the pros and cons of primes and zooms, in reference to the little Loxia MF lens. Of course I use the eyepiece or monitor for judging the OOF effects, but I have been weaned on DOF and using one f stop down from the normal circle of confusion value that they use on preparing the DOF scales is usually my starting point when pre-visualising the shot.<br>

I did some quick tests tripod mounted A7rII with Loxia at about 12 feet and twice or three times that distance. Here are two images of the end wall at my place at f2, the first a corner image at about 33 inch wide image, the second of the overall image. These are just extra fine jpegs at 42 MP as I have not yet processed the RAW data. The corner performance improves quite a bit by f2.8 and is optimum around f5.6 or f8. At all f-stops the edges seem as sharp as the centre, and certainly by f2.8. I did the check to decide whether I would keep the lens or not (10 day return privilege).<br>

Not sure how to create a link, but the reduced size images (that can be clicked on to enlarge) are in the Loxia folder of <a href="/photos/aplumpton" rel="nofollow">http://www.photo.net/photos/aplumpton</a>.<br>

Happily, the softness at widest apertures in the corners is really just that, a very small area. The photos I uploaded have none of the sharpness of the originals, due to the image siuze reduction for PNet uploading. I think I will be quite happy with this lens.</p>

<p>To post an image, it must be located in a website PNET recognizes, like Flikr or your PNET portfolio. Dropbox will work, but only if someone clicks on the link. The image must be JPEG, not exceeding 700 pixels in width, nor above a certain size in MB (see the posting rules). You then click on the little green monitor in the tool bar above the response box, and copy the address of that image to the dialogue box. In Portfolio, you can right click on an image and select "copy image address" for the link.</p>

<p>Some hosting sites (e.g., Flikr) will automatically size the proxy image to fit the screen. If you click on the proxy image, it will open up in a much larger size on your screen, up to the full resolution at which it is saved.</p>

<p>That about exhausts my knowledge of the posting process. Others can chime in if you have further questions.</p>

<p>Edward, I don't use Flickr and my mouse doesn't have a right click (Mac). What I did was to blow up the image (100% or 33 inches wide), select only the edge area and reproduce the image in jpeg at an acceptable size for my PNet portfolio.</p>

<p>The purpose of course was to get an idea of the Zeiss designed (Cosina produced?) lens and its capabilities. This I did get and was surprised at the not unreasonable f2 performance (f5.6 and f8 are of course near perfect) and would recommend others to check out its capabilities if the flexibility of a manual prime is of interest to them.</p>

<p>There are other ways to use a crippled mouse to do the same thing ;)</p>

<p>What you did was just fine, and it's pretty much all I do (not a FlickR user either). Now that you have the Zeiss (Cosina) Loxia, work on overcoming your aversion to using f/2. That's a habit carried over from SLR days, where wide apertures were meant to sell lenses, not to be actually used, and manual focusing was <em>passé</em>. Sony and Zeiss team up a little better. (I encountered a photographer using a Nikon 400 mm lens at f/16 "to get a better depth of field," in a theater no less.)</p>

<p>Please replace "your aversion" with "any aversion." This was not meant to be personal. What I'm trying to say is that fast prime lenses for the Sony (Leica, et. al.) lend themselves to use wide open. While the DOF is shallow, the Loxia is very sharp across the entire frame, to the corners. In the "aperture race" of the 60's, fast lenses were almost unuseable wide open. The shallow DOF makes focusing somewhat unreliable on a DSLR, even auto focus. Focusing is touch and go with a rangefinder too, due to it's inherent limitations. Between peaking and auto-magnification, the Sony is ideal for fast primes.</p>

<p>You are right, while I never had much problem with focusing a 50mm at f2 using my former Summicron on a film M, the Sony is great with its peaking and auto mag capacities. The late 1970s early 1980s Mandler designed 50 mm was no slouch wide open at the edges either, but it was probably an exceptional optic for its day (and it is still made and sold today, which speaks for its quality). The corner problem at f2 is very slight on the Planar. I need on occasion high corner resolution mainly with my architectural and landscape shots, which are in any case normally made at smaller apertures. When shooting close subjects (say 5 to 20 feet) the edges are usually outside the plane of intended sharp focus, so any corner deterioration is insignificant and wrapped in blur.</p>

<p>In blowing up the Loxia images I am happily surprised at its high resolution and neutral tonality. I have no connections to Sony or Cosina, but this lens, or at least my production copy of it, is a jewel. The bokeh may not be the smoothest I've seen, but it is very good and has no readily visible double line effects.</p>