Equipment & Techniques > Cameras, Lenses and Shooting gear
Gigapixel Lens A7r
David Mills:
I didn't really know how to title this topic. The question is - If one is attempting to produce super sharp huge prints (6X18 feet) through the process of a multi-row stitched (landscape) panorama and HDR, what lens would you recommend for the A7r to accomplish this? I'm not talking GigaPan. GigaPan is not an option. Thanks.
Bart_van_der_Wolf:
--- Quote from: BAPP on August 02, 2015, 11:41:03 pm ---I didn't really know how to title this topic. The question is - If one is attempting to produce super sharp huge prints (6X18 feet) through the process of a multi-row stitched (landscape) panorama and HDR, what lens would you recommend for the A7r to accomplish this? I'm not talking GigaPan. GigaPan is not an option. Thanks.
--- End quote ---
Hi,
In general, one needs a lens that has very good center performance, because some of the edge/corner detail of each tile can be cropped/blended out by using a larger overlap between the tiles (which will of course require to take more images). But more important is to use an appropriately longer focal length that produces a larger on-sensor magnification (= resolution) while at the same time balancing with the diffraction effects of the narrower aperture required to maintain a certain Depth of Field. Maybe even focusstacking needs to be used for some of the tiles..
So basically you need to calculate backwards from the required number of pixels for the intended output size and viewing distance, to the required number of pixels in the stitched image. Then divide that number of pixels by the number of tiles (with overlap) that is required, and build in a margin for resampling losses (so rather down-sample than up-sample). Angle of view and possible use of different projections also plays a role.
The scene content may also add a few limitations that may need to be factored in, like DOF, subject movement, changing light, etc., but starting with the technical calculation will present the physical shooting requirements which may need to be relaxed a bit if the practical shooting conditions require it.
Cheers,
Bart
NancyP:
Figure out what your total angle of view will be, horizontal and vertical. You want a good 1/3 overlap on each side. You might also want a little "extra" on the edges of the image. So:
3 x Total Angle of View
__________________ = # shots per row (or column)
Lens Angle of View
So if you wanted a total horizontal angle of view of 120 degrees, and had a good 85mm lens on hand plus your FF camera (lens vertical AOV 16 degrees, assuming you shoot in portrait mode), you would need 23 shots per row.
If you then wanted a total vertical angle of view of 40 degrees, with the same 85 mm lens and FF camera (lens horizontal AOV 24 degrees), you would need 5 shots per column. That's 115 shots total for entire image. There's generous cropping room at the edges.
This explains the appeal of the Gigapan automated system and of the indexed rotators for these gigapixel images. Even shooting one row manually/by eye takes some time.
David Mills:
Thanks. All great information on the "how to". Any specific suggestions on a lens for the A7r. I do some extreme backcountry locations that require multi-day backpacks so the GigaPan is not a practical option for this application unless I pack it in via horseback. Thanks and thanks again.
Bart_van_der_Wolf:
--- Quote from: BAPP on August 03, 2015, 12:47:43 pm ---Thanks. All great information on the "how to". Any specific suggestions on a lens for the A7r. I do some extreme backcountry locations that require multi-day backpacks so the GigaPan is not a practical option for this application unless I pack it in via horseback. Thanks and thanks again.
--- End quote ---
Hi,
The required focal length depends on the required file resolution for output. The required output resolution is determined by the viewing distance of the print.
Example, an 18 feet wide print would probably be viewed from some 6 to 18 feet distance. If it must retain high resolution with shorter viewing distances, everything scales proportionally. Let's assume 10 feet viewing distance, easy to calculate with, then for someone with 20/20 visual acuity, the output must be printed from a 29 PPI source image (which would be upsampled to 360 PPI for printing with good output sharpening).
The 29 PPI image means that the print file before upsampling to native printer resolution would be 29 PPI x 216 inches = 6264 pixels wide. That's easy enough with most lenses that offer enough Field Of View for your scene, 2 or 3 stitched images would already allow to that. Those 2 or 3 images would need to cover the angle of view you want to shoot. If the angle of view is extreme enough to compromise the available lens quality, a longer focal length and more stitched images will be required.
However, if you need the same viewing quality at 1 foot (1/10 of the example) viewing distance, then you'd perhaps need 10x as many pixels, or something like 15-16 images with 30% overlap taken with a much longer focal length, per required Row (maybe 5 rows will suffice). If cylindrical projecton is acceptable, then not much (if any) additional resolution is required. For Rectilinear projection it would depend on the actual angle of view to cover.
So you need to determine the print viewing conditions, and the scene angle of view to cover, the rest can be calculated. Maybe a good 24mm, or 35mm, or perhaps a lightweight 50mm lens is all you need, but to determine that more info is needed.
As far as traveling lightweight, I can still recommend a click-stop indexer if you indeed need to stitch many images for the field of view you have in mind, and you could even use that instead of a ballhead or other head if you need to shave of as much weight as possible. But then a very lightweight (but with significant load capacity) Easy Leveler II will allow to do the final leveling and composing, to finish what you started with the tripod legs. I use one mounted directly on the tripod base plate, and a Manfrotto click-stop indexer on top of that with an Arca Swiss clamp on top of that for my No Parallax Point (NPP) bar (a RRS MPR-CL II) . Multi-Row setups may require more components.
Cheers,
Bart
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