I can't really offer any better advise than has already been given, but the first thing I thought of when I read your question was the Kodak book mentioned by rbultman. It was tremendously helpful to me in understanding movements.
I can't really offer any better advise than has already been given, but the first thing I thought of when I read your question was the Kodak book mentioned by rbultman. It was tremendously helpful to me in understanding movements.
From Ed Bray:
I am pretty sure that only the Camera Back needs to be vertical to ensure that buildings remain with the correct perspective,
From Struan Gray:
True. I was going to add
Well, this good ol' rule is valid only for quasi-symmetric lens formulae. I mean: any of our beloved LF lenses except telephotos. But usually nobody will tilt & shift a telephoto lens to capture a tall building anywhere in the world
The strange effect was discovered a few years ago by a friend on the French LF forum http://www.galerie-photo.info, who was doing architecture shots with a digital SLR camera and one of those wide-angle retrofocus tilt+shit lenses available for small format cameras. He discovered that even if the sensor = the back of the camera is kept perfectly parallel to the vertical lines you want to see vertically projected in the images (e.g. the rectangular windows and edges of a rectangular building), you might get into some kind of trapezoid distorsion when you tilt the lens axis up.
In this situation the image is not sharp since it does not comply with Scheimpflug's rule, the "lens panel" not being parallel to the building and sensor plane.
The reason is extremely subtle and directly related to the fact that for those retrofocus lenses, the pupils are not located in the nodal planes (= principal planes). The effect hardly ever showed-up before, simply because there are no retrofocus lenses available for the large format (with the exception of an improbable LF Flektogon aus Jena, an absolute rarity once mentioned here).
The effect will exist even in a distorsion-free optical system, for example a perfect lens element like the "theoretical thin aplanatic lens element" available in the Oslo lens design software. Simply add a diaphragm in front of the element and look for a spot-diagram of a grid-shaped extended object. Keep the object and image planes parallel with respect to each other, but tilt the "lens plane": the image will be of course blurred but also strangely distorted. The effect naturally vanishes if the diaphragm is located just at the centre of the perfect thin lens element. This also applies for all quasi-symmetrical lenses like all wide-angle and standard LF lenses for which the pupils are located very close to the nodal points.
I have made a short summary (in French) of this effect in this article
http://www.galerie-photo.com/decentr...en-format.html
Simply look at figures 15 and 16, at the end or the article, appendix #1, showing Oslo-edu simulations of the image of a square grid through a theoretical 'perfect thin aplanatic lens element'.
To perform the simulation yourself, you can dowload the Oslo command files from here
file "retrofoc-simul-oslo.zip" to be downloaded from here http://cjoint.com/?CJbjVn1ZbET
Once loaded, plot the optical system itself (lens->drawing->system) and use from the main menu the "Source" feature and select "pixelated object" choose a grid and click OK.
With command file retrofoc5.len available from the zip collection juste pointed above, you'll see the distorsion in the image although both object planes and image planes are parallel.
The only difference between figure 15 and figure 16 are that in figure 16, the diaphragm is located at some distance ahead of the lens. In both figures the object plane and the image plane are perfectly parallel. According to the good ol' rule of LF photography, in both cases no distorsion should occur. Yes of course in figure 16 the image is blurred since the set-up does not obey Scheimpflug's rule. But in fact distorsion appears on figure 16, where the diaphragm is not located at the nodal point of the thin lens element: therefore we get an optical system which is like a retrofocus or a telephoto; the entrance pupil simply being the diaphragm itself, is not located at the nodal point. This simulates what happens in a thick compound lens like a wide-angle retrofocus lens. We already knew that panoramic stitching requires to rotate around the entrance pupil and nowhere else, this is another manifestation of special effects in perspective and projection for defocused images that happen in a lens for which the pupils are not located in the principal or nodal planes.
As a conclusion, yes Ed and Struan you are right...
... since here we do not use retrofocus wide angle lenses (Vade Retro, Satanas), and that all 35 mm photography, be it film or digital, is strictly banned here!
Thank goodness for that.Originally Posted by Emmanuel BIGLER
As a conclusion, yes Ed and Struan you are right
Part of me is groping for a vaguely-remembered exercise in optics design in which the aperture is moved from behind a single meniscus to in-front. In this case, the lens itself is asymmetric, and the movement of the aperture trades various aberrations such as field curvature and distortion for others like coma and astigmatism. I can't help wondering is something similar is going on here.
In any case, one of the joys of movements on LF cameras with normal LF lenses is that you can separate the effects of rise and tilt. When I'm taking a picture I tend to work through three stages to get the image on the ground glass how I want it. First framing, then geometry, then plane of focus. There is some feedback and adjustment between the three aspects, for example, adjusting the geometry through movements can make for small changes to the framing, but I find it useful to treat them pseudo-individually in series.
I stumbled across this video this morning which explains movements.
https://www.youtube.com/watch?v=0JU-eHpk97Y
The video is short. It explains each movement and then the effect of each movement in the ground glass.
He also mentions a PDF that describes camera movements but you have to send him an email in order to get it.
Regards,
Rob
My flickr stream
From Struan:
In this case, the lens itself is asymmetric, and the movement of the aperture trades various aberrations such as ... I can't help wondering is something similar is going on here.
Well, the strange distorsion that you can simulate with Oslo exists even when computed with a theoretical perfect thin aplanatic lens, something which is only a mathematical entity that takes bunches of rays on input in a simulation and dispatches them on output without any aberrations.
Of course in a real lens, the exact location of the iris has a strong influence on several aberrations. The Wollaston meniscus will exhibit its best image quality only of the iris is located at the proper distance in front of the lens element. Something totally counter-intuitive.
And if we go back to the end of the XIXst century, the Old Masters have recognised very early the advantages of quasi-symmetric designs that we still use today with the view camera ; types of lenses but that cannot be used with reflex cameras for short focal lengths.
In such a quasi-symmetrical design, the iris is located very close to the centre of symmetry of the glass assembly; the pupils are located very close to the nodal points; hence fans of rays entering throught the entrance pupil will on exit exhibit a fan of rays with the same angles (property of nodal points); and the whole lens will be free from the very special effect mentioned above: you just need to keep your film plane parallel to the building and you are allowed a somewhat loose tolerance on tilting the lens itself.
So let's enjoy our symmetrical designs, and let retrofocus lenses live with their "built-in" distorsion when used to make an image between parallel planes but with an optical axis slanted and a blurred image
I apologise for this digression that could appear as complex and very confusing, but as soon as we accept what happens in our quasi-symmetical lenses, as far as perspective rendition is concerned, we can forget about the glass and consider only what happens in a pinhole camera, i.e. central perspective like discovered in Renaissance times.
We just have to consider the entrance pupil of our lens, this is our equivalent pinhole defining alignments in object space, and imagine that exit rays come out of the exit pupil like if we had the rear part of a pinhole camera with its pinhole located at the centre of the exit pupil. So in a sense our view camera, as far as the geometry of the image projection is concerned, is like a pinhole camera, for which the entrance and the exit would be separated by some distance that has no influence on what is projected, i;e. exactly what the artists have been drawing since the XV-st century.
So basically
- setting the lens position in object space and setting the film back defines the kind of projection we would have in a pinhole camera, therefore commands perspective rendition but does not guarantee any sharpness;
- setting the lens plane in position and tilt commands image sharpness, has a very weak influence on the projected geometry if the lesn is quasi-symmetrical.
Sharpness is something that we do not care for in pinhole photography.
The problem is that different view camera controls inter-mix the 2 effects at the same time.
For example Saint Ansel's tilting of the back to take a picture of the Mittens in Monument Valley solves the problem of image sharpness for the foreground, but brings-in some trapezoid distorsion. This is hard to notice in the image; nobody cares.
In order to keep the film plane vertical you would have to tilt the lens panel in order to get the foreground sharp (according to Scheimpflug) and eventually you would get short of image circle ...
In architecture shots you can proceed in a very counter-intuitive way. Instead of framing the composition like with a small hand-held camera, and afterwards tilting to get vertical lines projected parallel on the ground glass, you could first set the camera horizontal and the back vertical, and only after that, define your image frame by moving the front standard or the rear standard vertically. This might not be practical if you are too close to very tall building.
Then one should remember that what the camera sees is defined by the position of its entrance pupil: if the image is not good in terms of perspective rendition, may be you have to move the camera and experiment another view point ... but for a 100-story building, carrying a ladder and climbing on it is not be very helpful to get a better perspective. And tilting the camera in all directions will not change the position of the entrance pupil beyond some very minor adjustments.
Thanks Emmanuel.
dikaiosune01: in case this has you worried and confused, here are my three main ways of proceeding:
1) in Scotland, where I am often taking landscapes where everything is far away. I just point the camera at the scene, focus, and shoot.
2) mostly in Scotland, if I'm taking pictures of vegetation patterns on the ground in front of me: I just point the camera, focus roughly, lean the lensboard forward to lay the plane of focus along the ground, and shoot.
3) in my local woodland: I keep the camera horizontal. Frame with shift and rise/fall. Focus roughly. Place the plane of focus with tilt and swing. Shoot.
The last case corresponds to what an architectural photographer would do: it leads to a photograph which looks more like a classical painting or architectural drawing, in which the perspective follows academic rules. I find it works well for woodland and tree photographs too.
Thanks, Struan for this useful and efficient summary. I totally agree with you.
Yes, we do not need to take all our LF pictures like if we wanted to properly record the frontage of a classical building in compliance with classical rules.
Like Eugène Atget did in his famous views of the old Paris : he preferred to be short of image circle, but would never allow any slanted verticals.
http://www.gingkopress.com/i/atget-paris_i3.jpg
Regarding Struan's point #2, the advantage of tilting the lens panel if you have axis tilts, is that once focused this tilt (when applied subsequently) only slightly defocus the image.
But for a landscape where you do not care for perfectly corrected projection, you can also tilt the rear standard back and refocus.
In old Europe, sometimes, even the most scrupulous LF photographer (who would always insist on perfectly levelling the camera and would feel dishonoured to let any kid of trapezoid distorsion in his images), will have hard times to decide for the proper camera movements and precise corrections to apply.
For example in Champagne, France, the old city of Troyes with its magnificent half-timbered houses has some challenging subjects to offer
And in Alsace, in Strasbourg, the Saint Guillaume Church with its slanted frontage wall is waiting to challenge your skills!
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