Stitching vs wideangles

[thomas]

Here's an example with Digitar 47XL (@ f11) and P45 on Cambo WRS at 20mm shift.

The movements the WRS is capable of:

Scene.
Red frame is the film plane of the P45. Right side is 20mm shift:

Crop center (lens wise):

And here's an 100% crop. On the top of the image I indicated the amount of shift in mm.
JPEG quality 80% but I think it's good enough.
Should also be viewed in print size (@ 300dpi).
http://forum.getdpi.com/gallery/showimage.php?i=5177&original=1&c=newimages&cutoffdate=1

A plane motif would have been better to show sharpness fall off but as an exapmle this should be fine.

 

[carstenw]

I don't completely understand the math of shifting yet. What is the effective focal length of the 47mm shifted and stitched to its limits?

 

[thomas]

I don't completely understand the math of shifting yet. What is the effective focal length of the 47mm shifted and stitched to its limits?

Carsten,

the film plane of the P45 is 49.1 x 36.8mm.
If you stitch to the limits lateral you add 20mm on each side so the film plane is 89.1 mm wide.
If you go for a 3:4 format it's 89.1 x 66.8mm and the diagonal is 111.4mm.
So the coefficient is 0.55. The 47mm will be like a 26mm.
If you go for 2:3; 47mm ~ 27mm.
If you go for the full film plane with shift to the limits lateral and vertical the film plane is 89.1 x 76.8mm; 47mm ~ 24.5mm.

edit:
but of course you have to consider sharpness fall off (that's what my test shot is about).
I feel totally safe within +/- 12mm [so the film plane is 49.1mm + 12mm(left) + 12mm(right) = 63.1mm wide here].
+/- 17mm is still good enough for the most purposes.
+/- 20mm is a bit too soft but usable for some purposes (depends very much on the motif as well).
The vertical -25mm is only usable if there is sky in the respective area of the image... (sky is very forgiving if it is not sharp...)

 

[carstenw]

Interesting! Thanks for working through this. It seems that for someone shooting static subjects, the 47 might even be preferable, as long as I am not adverse to extra work.

 

[thomas]

Interesting! Thanks for working through this.

you're welcome!

It seems that for someone shooting static subjects, the 47 might even be preferable, as long as I am not adverse to extra work.

it is extra work of course! But don't forget that at the same time you add a remarkable increase of resolution as well!
When you did it a few times and have a sophiticated workflow you get used to it and actually if you appreciate the quality of each of your images it's worth the effort.
Exposure is tricky. I expose for the shifted capture, not for the center shot. If you push the shifted shots in post to correct light fall off you basically end up with ISO 150 (or what) at the edges (light fall of at full shift is 1.7EV at the edges) - not good with the P45! On the other hand highlight recovery in Cature One works so brilliant that some overexoposed highlights in the center shot are mostly not a problem. Best is to shoot exposure variants but it's not always possible to merge them afterwards.... you have to decide it during the shot. Or just do exposure variants all the time and look what works best in post.
Oh, yes, I have a center filter as well but the color cast is sheer maddening - the center filter adds lens cast to the sensor cast and you just can't get it right therefore.

 

[jotloob]

a 3 x 3 shifting stitch is pretty easy with the Horseman and it's click stops every 5cm. doing a 3 x 3 pano is not so simple unless you have a two axis rig with a degree scale on each axis...i suppose the cube owners can chuckle here.

Here a 3x3 stitched image .
Camera is ARCA SWISS 6x9 + APO-SIRONAR DIGITAL 4,5/35mm.
Shift is done in 10mm steps both axis .
The first image shows the "base image" , shot from center position , and is what you would get , when you would not use the stitching technique .

View attachment 19045

View attachment 19046

Jürgen

What I do not understand yet , is the cyan cast in the left part of the sky and the deep dark blue in the right part .

 

[thomas]

What I do not understand yet , is the cyan cast in the left part of the sky and the deep dark blue in the right part .

Magenta cast center/right hand as well.
The colour cast calibration is off here I think.
Or did you use a center filter?

 

[jotloob]

Thomas

Color Cast Calibration ? ? ? Please give more details .
NO centerfilter was used .

Jürgen

 

[thomas]

Color Cast Calibration ? ? ? Please give more details .

Jürgen,

"lens cast calibration" or "white shading" or "white reference" or however named in your raw software.
Mostly you shoot a white opal plate for every position of the lens/back.
Don't you?
Here's the workflow for Phase backs in Capture One - http://www.phaseone.com/upload/4_simple_steps_to_calibrate_on_fixed_lenses_windows.pdf - there must be something similar in your software as the procedure is basically the same with all tech cameras/LF lenses.

 

[jotloob]

Thomas

Thank you for pointing out "Lens Cast Calibration" .
I did not know anything about that topic , because up to now , I did not do any stitching with super wide angle lenses .
That on the other side means , learning again and find the process for PHOCUS , the HASSELBLAD software .
I will then come back , with a hopefully better result .

Jürgen

 

[thomas]

Thank you for pointing out "Lens Cast Calibration" .
I did not know anything about that topic, because up to now , I did not do any stitching with super wide angle lenses.

you'll see that even without movements there is colour cast... not that obvious but still.

 

[jotloob]

Now , for a better understanding .
Assume , I want to do a 3x3 (3x2 , 3x1) stitched image using a particular lens .
It is brilliant sunshine .
My understanding so far is , that I take a custom white shot and a real shot of every stitching position . Then I process these with PHOCUS and I keep the custom white shots for future use with the same lens for similar light situations .
(their positions noted down , of course) .

Do I have to follow that procedure for an image I will take when it is cloudy or any other light condition ? ? ?

What is the information from that custom white shot to be "combined" with the real shot in the raw converter . In my case PHOCUS .

And yes , I do agree , there is a color cast , even when shooting just out of a center position with a SWC , for example .

Jürgen

 

[carstenw]

Unless you take a purely neutral white shading file, I am not sure that you will be able to reuse it. If you get a neutral one done, then it would correct the general tendency for the lens at that shift position, but any casts in the scene would be uncorrected.

 

[jotloob]

Carsten

You express what I thought it would be .
To be correct , for any image you want to shoot , using stitching techniques , you will have to take a custom white shot for every shift position .
And if you want to shoot an other image next day , you will have to do the same again .
Is that what you mean ? ? ?
It would make sense to me as the light conditions vary a lot .
Daylight is not daylight . There might be slight differences .
I found this by using my SEKONIC C-500 prodigi color meter .

Jürgen

 

[Don Libby]

There's certainly different schools of thought about taking LCCs. One school says you have to take one for every exposure while the other describes having a "library" of the various movements.

I subscribe to the library method. The first thing I do with a new lens is shoot a complete library of movements beginning at zero-zero and working my way in 5mm increments. When finished I load them in C1 and go from there.

The only time I bother shooting a LCC is is I do something out of the ordinary like tilting the camera (level on the horizontal but tilted upwards or down).

The library has worked well for me.


Don

I also normally take detailed noted on what I shoot with each image using a voice recorder. Frame #, f/stop and movements.

 

[thomas]

"Colour cast" we are talking about here is actually "sensor cast". Therefore a library of LCCs should work. However I find the correction is more accurate if I do the LCCs for each capture in the particular light situation.
Too, I rarely shoot with the film plane shifted to maximum. Mostly I do two shots with the back turned 90° in portrait mode and shift left/right 17mm... but rise and/or fall varies with the motif. In addition it's handy to have the LCC shots right within the session as I process them as well as TIFs to use them for correction of vignetting afterwards in Photoshop (could take them from a library as well of course... but this way it's a bit faster).
So I'm on the "every exposure" side...

 

[jlm]

a four shot pano, rollei 110, also a test of a 1200pix wide attachment

 

[woodyspedden]

Beautifully done John, as always

Must be nice to walk out the door of your workplace for lunch and have these images to work for. Love it LOL

Best

Woody

 

[jlm]

i see those cranes every morning when i go to work and have tried to shoot them many times. tough with all the background, plus they are huge and move around. i need to keep at those buggers

thanks woody

 

[jlm]

test load of a 1200h by 2300w jpg