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#1




swing lens cameras and focussing distance
I would have posted this in the original thread but it has got long
now and fragmented as to topic. I posted some detailed calculations in the thread with the subject line "The opposite of a closeup lens?" on April 6th 2004 two times and April 7th 2004 once and in addition on April 14th 2004 showing an important link for people interested in swing lens cameras, namely http://www.funsci.com/fun3_en/panoram2/pan2_en.htm I have posted a lot of technical stuff and maths backing it up. I use swing lens cameras for maybe 10% of all my photography so maybe that is a high proportion. I have a college degree (BSc) in Physics for what it is worth and of course I studied Optics as part of that. I am not claiming to be an expert on Optics, especially since I have earned my living developing software for many years, but at least I can claim to have some sort of awareness of the subject and a rudimentary grounding. These cameras are important to me so I thought that anybody who followed my calculations might be interested in what I have to say next. Here goes... Now this is theorising and speculation but I personally do not believe that anybody can make a lens with an accurate focal length. I assume a 0.5% error at least. So taking the Noblex 150, assumed fixedfocussed at 10.4m, then this has a 50.93 millimeter drum radius according to the film width and angle specs and there won't be much variation in the examples they make. Fair enough! They say their lens is a 50.75mm focal lens lens. You what?!? It could be anything from 51mm to 50.5mm. There is nothing they can do to stop that unless they adjust the gap between the front converging lens and the diverging lens behind it to correct it. Do they do that? Do they do any adjustment at all? I suspect that the manufacturers of these cameras do make some adjustment but the most important adjustment, if you have followed my calculations, is to make sure the secondary principal point of the lens is exactly on the axis so that the magnification is correct and so that as the lens swings round then parts of an image will always stay on the same place on the film surface. Now I challenge anybody here to find out from manufacturerpublished specifications where the lens is fixedfocussed to on any swing lens camera except the Noblex range. I doubt you wil find it. And why? It could be that the only adjustment they are making to the camera is to make sure the secondary principal point is on the axis so that the image doesn't move on the film as the lens swings round. But then the focussing distance will be thrown out when they adjust this. So they will not be able to publish any figures. So you don't know what distance your camera is fixedfocussed to and you have got to take pot luck in getting one that focusses at the distance you have a preference for. In my case I will not pick bones and will say outright that I want my swing lens camera to be focussed at infinity because I use it most at that distance. But secondary principal point on the axis is the most important thing otherwise you lose horizontal resolution in a big way. The two are opposites. For me, at least, anybody claiming a distance focussed to is setting the lens to focus at that distance rather than doing the far more important thing of getting the secondary principal point sited exactly on the axis. If Noblex are claiming figures for focussing distance then they will be adjusting the lens to achieve that figure and not adjusting the lens to make sure the secondary principal point lies exactly on the axis which I feel they should be doing instead. It is possible to have the best of both worlds but it takes a lot of adjustment. If you want a lens in a swing lens camera fixedfocussed at infinity then you have got to make sure that the secondary principal point stays on the axis at all time but you can adjust the gap between the converging lens and the diverging lens behind it (for as Tessar design) to focus it. This will shift the secondary principal point again off the axis but by a process of adjusting them both you will finally arrive at the optimum setting. But it seems to me that the emphasis for the Noblex focussing models has shifted entirely away from the position of the secondary principal point being on the axis which to me (with calculations to back it up) is the most important thing. 
#2




swing lens cameras and focussing distance
Hi Roland, Sorry, but the Horizon 202 cameras are not focused at infinity, as I have shown in a related posting, citing the Noblex 135 series (same format) models, but more like focused at a middistance of 7m or so. The noblex 135 models are focused at an even farther middistance point (7.5m), as shown by the comparison of focusing tables for the two cameras in my posting. For both the horizon 202 and Noblex 135 (and 150 series) cameras, infinity is on one edge of the hyperfocal setting, rather than at the precise focusing point. So any calculations assuming an infinity focus are simply in error, yes? Second, the critical value is not focal length variations of the lens etc. but whether the (curved) plane of focus is placed on the (curved) emulsion. See critical focusing at http://medfmt.8k.com/mf/critical.html regards bobm  ************************************************** ********************* * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* 
#4




swing lens cameras and focussing distance

#5




swing lens cameras and focussing distance
the evidence that the horizon 202 is focused at 7 meters is very simple; it is virtually identical to the noblex 135 series in format/coverage, which we know per mfger's specs is focused at 7.5 meters. If you compare the noblex 135 DOF for various f/stops against matching horizon 202 DOF, you get nearly identical values  if anything, the horizon is slightly closer, meaning its focusing point is less than 7.5m at same stops etc. so if the noblex 135 is focused at 7.5m, the horizon 202 has to be focused at about 7.5m as well, given similar DOF values, lenses, and film formats. Again, you can't use the fixed lens DOF calculator with the fixed 28mm lens and apply it to the swing lens case with a different film format and much wider coverage on the larger film format etc., even if you do modify CoC. That's why your answer for fixed 28mm lens doesn't match case of noblex 135, which has similar specs, swinging lens, and format and coverage. It is just a happy coincidence (or more russian copying?) that the horizon 202 matches the Noblex 135 so closely... in short, the horizon 202 is nearly identical to the Noblex 135 in DOF vs. f/stop charts, format, swing lens type, etc., so it must be focused at the same point, viz., 7.5 meters or so, not infinity. bobm  ************************************************** ********************* * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* 
#6




swing lens cameras and focussing distance

#7




swing lens cameras and focussing distance
Bob Monaghan wrote:
It is just a happy coincidence (or more russian copying?) that the horizon 202 matches the Noblex 135 so closely... Are you suggesting the Russians had a time machine? From Marco Pauck's excellent web site:  The Horizon 202 is in production since ca. 1989. It is a successor of  the Horizont (note the 't') which was produced from ca. 19671973. The first Noblex, the model 150 medium format camera, was made in 1992, the first 35 mm model appeared in 1994. Ralf  Ralf R. Radermacher  DL9KCG  Köln/Cologne, Germany private homepage: http://www.fotoralf.de manual cameras and photo galleries  updated April 29, 2004 Contarex  Kiev 60  Horizon 202  P6 mount lenses 
#8




swing lens cameras and focussing distance
no, but good points dates; however, there are lots of models of both noblex 135/150, some of which are adjustable focus, others fixed focus, and as others have pointed out in this thread, they evidently come in various focusing distance flavors ;) Ditto, there are models of the Horizon 202 series, such as my horizon 202S, which were aimed at the postsoviet market, vs. the military Horizon/Horizont/Horizon series. Certainly, a lot of changes have been made by various parties in some postsoviet camera models (cf. Kiev88CB/CM series) to appeal to the world market more, adapted other back styles (e.g., hasselblad compatible backs) and so on. Moving the focusing distance between two models is simple in comparison ;) grins bobm  ************************************************** ********************* * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* 
#9




swing lens cameras and focussing distance
Your calculations say the horizon is focused at 280 meters, while the specs of the similar lens/format noblex 135 swing lens camera are 7.5m, yet the DOF between the two are remarkably similar ;), viz.: horizon 202 noblex 135 5.6 2.9m to inf 2.3m to inf 8 2 m to inf 1.8m to inf DOF DOF deals with image size and image magnification to allowable printing sizes for a given quality level (viz., CoC). There is no underlying physics, it is purely a darkroom print quality range based on assumptions of film format and enlargement factors. why swing lens is not same as fixed lens The swing lens camera produces an image that is equivalent in coverage and magnification to one which would be produced by a much wider lens on a much larger format (e.g., 18mm on a 6x6cm which would be cropped to 24x56 or 24x65mm yielding 110 degrees horizontal coverage, as with the Horizon 202s etc.). You aren't enlarging the image produced by the 28 or 29mm lens on a 24x36mm film slice, you are enlarging the equivalent of an 18mm lens used with a cropped MF negative size of 24x56mm etc. This is why using a DOF calculator designed for fixed lenses doesn't do justice to the swing lens case. They happen to be close, if you fiddle with them and vary CoC etc., because the 28mm lens is close to its hyperfocal distance at any distance past 3.3m (at f/8 on 35mm format per http://medfmt.8k.com/brondof.html). In short, DOF is about image magnification, and the limits for a cropped image covering 110 degrees on 24x56mm (equiv. to 18mm on a cropped 6x6cm format) from a Horizon 202 is going to be different than a fixed 28mm lens on some lesser format. The close convergence between the two DOF for similar swing lens cameras suggests to me that they must have similar fixed focusing distances, viz., circa 7.5m per Noblex camera specifications. Suggesting that one must have a fixed focus distance of 7.5m and the other 280m (!), and that in the process the mfgers have gotten their own camera specifications wrong, isn't convincing to me. sorry, but we just have to agree to disagree on this issue ;) As I've noted, I do agree with you on other issues/posts, just don't find this convincing, rather, an artifact of hyperfocal convergence in calculator ;) bobm  ************************************************** ********************* * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* 
#10




swing lens cameras and focussing distance
(Bob Monaghan) wrote in message ...
Your calculations say the horizon is focused at 280 meters, while the specs of the similar lens/format noblex 135 swing lens camera are 7.5m, yet the DOF between the two are remarkably similar ;), viz.: horizon 202 noblex 135 5.6 2.9m to inf 2.3m to inf 8 2 m to inf 1.8m to inf Let's look at the "bigger picture" and avoid maths this time. Horizon 202 Noblex 135U f2.8 5.5m  inf f4 3.9m  inf f5.6 2.9m  inf 2.3m  inf f8 2.0m  inf 1.8m  inf f11 1.5m  inf 1.4m  inf f16 1.0m  inf 1.0m  inf You can see from the above figures that the Horizon 202 must be focussed at a further distance than the Noblex 135U. As the stop opens up then the values diverge more. At f5.6, for example, the closest infocus object is 2.9m for the Horizon and 2.3m for the Noblex. That is obvious. And yet why, at f16, do they both have objects 1.0 in focus? The answer must be that the Horizon is assuming a greater CoC size than the Noblex. So if the Horizon were using the smaller CoC size that the Noblex is using then all those minimum distances for the Horizon would be higher, right? I could produce the figures, but as I said, I am skipping the maths this time. It is there in another post of mine if anybody is interested. DOF DOF deals with image size and image magnification to allowable printing sizes for a given quality level (viz., CoC). There is no underlying physics, it is purely a darkroom print quality range based on assumptions of film format and enlargement factors. why swing lens is not same as fixed lens The swing lens camera produces an image that is equivalent in coverage and magnification to one which would be produced by a much wider lens on a much larger format (e.g., 18mm on a 6x6cm which would be cropped to 24x56 or 24x65mm yielding 110 degrees horizontal coverage, as with the Horizon 202s etc.). You aren't enlarging the image produced by the 28 or 29mm lens on a 24x36mm film slice, you are enlarging the equivalent of an 18mm lens used with a cropped MF negative size of 24x56mm etc. This is why using a DOF calculator designed for fixed lenses doesn't do justice to the swing lens case. The Horizon 202 has a 28mm lens and is exposing film through a slit at the back. That is the simple physics of the situation. It effectively takes lots of these shots during a single operation of the camera so you get lots of slits worth of photograph all joined together. It is a 28mm lens with a frame size of 24mmxslit width which varies. The depth of field calculators still apply. The only adjustment you have to make between a 35mm fixed lens camera and the Horizon 202 is to allow a larger CoC because the photograph has a wider horizontal size and so is unlikely to be enlarged by the same extent as would a 24x36mm shot. If the CoC is 0.03mm for the 24x36m frame then it will higher for the wider frame of the swing lens frame. They happen to be close, if you fiddle with them and vary CoC etc., because the 28mm lens is close to its hyperfocal distance at any distance past 3.3m (at f/8 on 35mm format per http://medfmt.8k.com/brondof.html). Then please go ahead and fiddle with these figures and vary the CoC size and show us what you come up with. Note that as the stop opens then the figures between the two cameras diverge. In short, DOF is about image magnification, and the limits for a cropped image covering 110 degrees on 24x56mm (equiv. to 18mm on a cropped 6x6cm format) from a Horizon 202 is going to be different than a fixed 28mm lens on some lesser format. The close convergence between the two DOF for similar swing lens cameras The figures show a divergence as the aperture opens up. suggests to me that they must have similar fixed focusing distances, viz., circa 7.5m per Noblex camera specifications. Suggesting that one must have a fixed focus distance of 7.5m and the other 280m (!), and that in the process the mfgers have gotten their own camera specifications wrong, isn't convincing to me. What I am saying is that although one manufacturer may aim for a focussing distance of 7.5 meters, they may actually end up with one focussed to 7m if they are forced to adjust the position of the lens to make sure the secondary principal point sits bang on the axis, as it should. In the case of the Noblex then I just do not trust their figures in any case. If they make focussing models that move the secondary principal point off the axis then they aren't much better than a bunch of monkeys so I mistrust all their figures. sorry, but we just have to agree to disagree on this issue ;) As I've I can agree with that, at least. ) noted, I do agree with you on other issues/posts, just don't find this That we agree or disagree on certain things does not matter. Obviously you have one view and I have mine. If people all held the same views then the world would be a boring place and we wouldn't want that (or would we?). ) convincing, rather, an artifact of hyperfocal convergence in calculator ;) For far distant scenes, give me a Horizon 202 over a Noblex 135U any time. I would recommend the Horizon 202 for that purpose warmly, so long as you don't mind the camera dropping to bits in your hands. 
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