Two-shot panoramic rehabilitation?

In short:

Besides being the least number of required multiple shooting, the 2 fisheye stitching capability is unique: It's the only way of assembling two fisheye images without fear from parallax error.

The flip side of the coin is that a lens that fully fits all the requirements to get the (hoped) highest Image Quality on a modern DSLR is yet to be available on the market at the time of writing.

Requirements for a product that would fulfill the needs of the two-shot (aka Double Shot) panographer are stated in a last paragraph.


Why is two-shot unique?

Which prerequisite for highest possible output panographic quality from two-shot?

Why is two-shot so different from three-shot?

Can there be situations when two-shot capability is mandatory?

Can two-shot panorama rival the quality from "more than' two shots ?

Are there fisheye lenses for DSLR camera on the market potentially suitable for two-shot panoramic (a.k.a. Double Shot)?

Can the new 5.6-mm Superfisheye from Sunex be used for Double Shooting?

Can the new 4.5-mm fisheye lens from Sigma be used for Double Shooting?

Can't the huge FOV of the shaved Tokina@10-mm or Nikkor10.5-mm be used for pseudo-Double Shooting?

What are then the drawbacks that make two-shot not so popular?

The ideal lens that the two-shooter eagerly expects


Why is two-shot unique?

Because the NPP location along the optical axis depends on incidence angle in the object space.
Assuming the (sole and continuous) seam to be really stitched at the 180-deg mark, all the pixels of this circular border between the two hemispherical images are equidistant from the center of both images. Translated into angle measured from the aiming axis during shooting the two photographs, this implies that the NPP (here Non-Parallax-Point for 90-deg incidence angle) is consequently sole, fixed and pre-determined. This is unlike all other cases where fisheye lens is involved.


Which prerequisite for highest possible output panographic quality from two-shot

Until the availability of an "ideal" lens on the market (see § ):

But then the stitching software has left to it only to blend the (preset) identically warped pair of images images one panorama after the others. For ever and all shooting situations.

Fundamental consequence: when these prerequisites are respected and unlike any other fisheye cases, the distance from the lens of all the (fixed) objects in the scene shall never be problematic.

Note: It is assumed that photographic craft is properly handled and including adequate exposure setting, D.O.F and focus setting.


Why is two-shot so different from three-shot?

Only one additional shot should not make such a difference, shouldn't it?
Paradoxically, going from the "ideal" situation of two shots -described above- to three shots shall puts the panographer into the worst case as parallax errors impact is concerned!

The greatest possible change of the root-cause for parallax errors along the seams is to be feared: the incidence angle goes from 90 deg (at Nadir and Zenith) to 60 deg (on the Horizon) and the 30-deg difference means the largest possible shift of the NPP along the axis. A compromise has consequently to be adopted for the NPP location and stitching perfection cannot be hoped for if objects are located too close to the lens.

Even the tiles on the floor may well be a nightmare to stitch correctly while being one meter away or so, if one wants the closest objects on the horizontal plane to fit correctly without the least parallax error, as it is generally preferred Two-shot allows both to happen simultaneously.

Additionally, while three-shot shall considerably improve the Image Quality of the panorama on the horizontal part by avoiding the use of the softer part of the source image, it may degrade the quality at both Nadir and Zenith by compounding parallax error to residual uncorrected distortion errors and to softness (blur).


Can there be situations when two-shot capability is mandatory?

Yes. They are not the majority, but there are some challenging cases where (or when) the 2 fisheye stitching capability is mandatory.

A very recent illustrated example:

The panorama inside my dishwasher could probably haven't been done without: the distance of the closest objects was about two centimeters from the front glass of the lens in most directions in all the shots:

I had to cheat a little since there is still no compact fisheye lens on the market that makes a full circular image on a digital sensor together with a wide enough Angle of View that would insure decent sharpness and contrast near the seam. I dared to expose that worst possible seam on the most obvious visible position, i.e. on the horizon of the panorama:

I have consequently and fortunately used a "shaved" Tokina zoom and made two pseudo (i.e. crossed) composite circular images. The "shaved" Nikkor 10.5-mm could have been an excellent substitute though. Both have ~195-deg useful from an overall effective 200+ angle of view, while this was remarkably not claimed in their specification and neither in their patent data!

The "how-to" is here .


Can two-shot panorama rival the quality from "more than' two shots ?

When the same level of skill and care is involved the quality of the panorama shall be better with higher number of shots and of course also if the focal length is chosen accordingly (and vice-versa). The native resolution being greater, the Image Quality shall always be better if the harware is adequate (lens, camera, etc.). The best part of the source images shall be viewed in the output panorama. Two shot ultimate cannot beat that.

In both case automated operation workflow can be used to increased batchable and high quality throughput: highly accurate panohead and rotator, calibration of the lens/camera/panohead assy, use of template for stitching, etc.

BUT, once again there is an indisputable advantage for the double shot way: NO parallax error. When this shall happen inevitably on some occasion with more than two shots and thus requiring some post-editing of the panorama output, it cannot happen with two shot if the prerequisites (read above) are respected.

This is why specific foolproof photographic gears are made for two shot panoramic: the camera or the lens cannot be placed another way that the unique ideal position (the whole assembly may even be locked in place) and minimal training is required to get repeatable adequate images. IPIX TM branded HW is a typical example.


Are there fisheye lenses for DSLR camera on the market potentially suitable for two-shot panoramic (a.k.a. Double Shot)?

Yes (but only partly).


Can the new 5.6-mm Superfisheye from Sunex be used for Double Shooting?

Yes, the designer has claimed this possible as it is advertised on the Sunex web site.

But this opinion has been challenged by others. Controversy arose recently on panography fora such as Panoguide.com when sample photographs were provided by Sunex and showing in fact the extreme sensitivity to the accuracy of alignment during shooting: to avoid "dark seam" in the output panorama seem really to be a challenge.

I was however able to produce some panorama devoid of the dreaded dark shadow line along the seam with some other samples pairs of source images I was kindly provided with. The panorama. The PTGui project script.

The skill and experience of the photographer might well be the key to success and that may be problematic. The question remains open...


Can the new 4.5-mm fisheye lens from Sigma be used for Double Shooting?

Yes. That was not the intention of Sigma but the Angle of View is in fact about the same as the Sunex but with a smaller diameter. Hence the output resolution shall be lower.

As the lens can be fully coupled with the camera and stopped from f/2.8 down to f/22, the vignetting along the edge of the image circle can be somewhat attenuated (this cannot be done with the Superfisheye) and the sharpness improved.

I was able to produce some panoramas with this lens.

The skill and experience of the photographer might well be the key to success and that may be problematic. The question remains open...


Can't the huge FOV of the shaved Tokina@10-mm or Nikkor10.5-mm be used for pseudo-Double Shooting?

Yes, I think so.

Shooting in landscape mode yields two opposite images of more than 194-deg of useful HFOV. The VFOV is restricted to 120-deg but this allows to produce high quality panographies from two shots only per panorama only.

For instance, I can imagine Google's Street View panoramas of much better quality than those that I have viewed until now and that could be simply made with a pair of opposite FF DSLR cameras.


What are then the drawbacks that make two-shot not so popular?

1) As the input image must be fully circular the dimension of the diameter is limited to less than the width of the DSLR sensor i.e. about 14.5-mm to cover the low end smaller EOS Canon or 23.8-mm for the FF DSLR. In addition, the Angle of View must be at least 185-deg.

The direct consequence of these two requirements leads to a reduced resolution when compared to multiple shots (at least three) with other fisheye lenses of higher focal length.

2) As the effective Angle of View of the circular fisheye lenses that were more or less intentionally dedicated to two shot panoramics is generally about only 185-deg, the outer part of the image near the edge is compressed, blurred, affected by residual uncorrectable Chromatic Aberration and by vignetting. The output stitched panorama shall have a weaker meridian annular part than shall be evident upon viewing.

There is no real true substitute to the popular PScamera/Fisheye adapters that are still widely used in the Real Estate low end panographic (aka "IPIX style") craft.


The ideal lens that the two-shooter eagerly expects

To put it shortly: give us a lens having the control, the compactness, the angle of view and the optical qualities of the Nikkor 10.5-mm or the Tokina 10-17 (@10-mm) without their quirks (i.e. useless focus setting scale or no aperture control ring) but with a scaled-down focal length while keeping a back focal length still compatible with a FF DSLR!

Designers, please go back to the drawing board...