Natural shots with wide angle lenses ?

[thomas]

Focus is performed manually and thru the lens with a technical camera. If it's sharp on the ground glass, it's okay (admitting the back is well aligned with the ground glass).
So I don't really understand how a lens should be calibrated for a technical camera ?

True. Looking at the entire scene posted above the subject (the tree) is not at infinity it's just a few meters distance.
But as to the calibration in general you have to see if the lens really is set to infinity. Mine was exactly calibrated to the default Contax mount - Cambo in the Netherlands is just a 2 hours drive from my home town so I visited the factory for adjustment and in their calibrator it was accurate. But it was not accurate to my back - it focussed wider than infinity. So we made a quick fix at Cambo but at home I adjusted it by myself again. As far as I know this is not uncommon... the contrary, as with the digibacks the tolerances are far smaller.
Regards, Thomas

 

[archivue]

If you are using a 40mm lens, and stitch to cover an image of 51,3x68,3mm you will have an image similar to a 28mm lense... no matter the way you have produced the image, it will looks similar in therm of "wide angle effect" !
The effect depends on the focal lenght / "film format"... not only the lens !

A 120 mm with a 4x5 will gives you exactly the same angle of view and perspective rendering as a 240 with a 8x10 camera... as a 47 with a 37x49 sensor.

When you are using a wide angle, if you still want to have a "natural" view you must :

Keeping the camera levelled
Using shift but not too much
Avoid object in the foreground
Using a lens that have minimal distortion

With a 22mp back, i've found that a 45 lens is a nice compromise... but sometimes you have to go larger...

 

[carstenw]

The way superwides handle corners is different from lens to lens, though. Some have the kind of stretching, which only looks right if you position yourself in front of the print in a similar position to where the camera was. As far as I know, this is actually realistic. Other lenses "compress" the corners more toward the centre, which, printed, looks more natural from a distance, but is actually less realistic. You can kinda get a feeling for the difference if you look at before-after shots w/ the Hasselblad 28mm:

http://diglloyd.com/diglloyd/free/HasselbladH3D/index.html#LensCorrections

Move your mouse over the image to see before and after. There is a lot going on in those corrections, but you will see that before, the corners are a little tighter, and after, a little more stretched.

Maybe this stretching has something to do with what you mean?

 

[Jack]

Rectilinear wideangles will render straight lines correctly, but they dimensionally distort regular geometric shapes like squares and circles or cubes and spheres. This is due to presenting what is in actuality a spherical, 3-D capture and rendering it in a flat, 2-D display. (Think about the views on a 'map' of the earth versus a 'globe'.) By contrast, lenses with barrel distortion will curve straight lines about the optical center, but the curvature tends to render dimensional geometric shapes more like how we see them in real life, so we tend to accept them better. Thus when using a rectilinear super-wideangle lens, it is incumbent on the photographer to position the subject carefully to avoid all obvious dimensional distortions.

In almost all cases, a super-wide lens with a bit of barrel distortion renders a typical scene with a variety of irregular geometric shapes more pleasantly than a true rectilinear lens. The primary exception being larger subjects with a series of recognizable parallel lines, such as architecture. So it's best to choose which you use based on what your primary subject is.

 

[anGy]

Maybe this stretching has something to do with what you mean?

Not really.
Barrel distortion or corner stretches of the HC 28mm are well corrected in Phocus. I have not the knowledge to understand if this lens is an hybrid lens, having some equal angular slices lens - and some equal planar distances lens caracteristics. Depending on the shot I sometimes see more barrel distortion and sometimes more corner stretch as if te 28mm was a rectilinear lens. But it's certainly just my eyes getting wrong.

Anyway this is not what I was talking about when saying that wideangle lens shots are less natural. I will try to better illustrate what I have in mind - if the pooring Belgian weather permits...
Thanks fo your posts guys.

 

[ddk]

Rectilinear wideangles will render straight lines correctly, but they dimensionally distort regular geometric shapes like squares and circles or cubes and spheres. This is due to presenting what is in actuality a spherical, 3-D capture and rendering it in a flat, 2-D display. (Think about the views on a 'map' of the earth versus a 'globe'.) By contrast, lenses with barrel distortion will curve straight lines about the optical center, but the curvature tends to render dimensional geometric shapes more like how we see them in real life, so we tend to accept them better. Thus when using a rectilinear super-wideangle lens, it is incumbent on the photographer to position the subject carefully to avoid all obvious dimensional distortions.

In almost all cases, a super-wide lens with a bit of barrel distortion renders a typical scene with a variety of irregular geometric shapes more pleasantly than a true rectilinear lens. The primary exception being larger subjects with a series of recognizable parallel lines, such as architecture. So it's best to choose which you use based on what your primary subject is.

Thanks for the education Jack, now I understand why I so like and prefer my none rectilinear lenses. :salute:

 

[archivue]

rectilinear or not, it depends on subject... but i can't see no interest in "moustache distorsion" !