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Author Topic: Perspective Control Options: Tilt-shift Lens Vs. Stitching  (Read 3119 times)
Nick S.
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« on: April 02, 2014, 11:06:26 AM »
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I'm interested in learning about ways to combat the keystone effect while capturing landscape/architectural images. Acquiring a tilt-shift lens seems the best solution, but would require me to lug heavy, bulky and expensive gear (such as the Canon TS-E 45mm f/2.8 on a 6D). As an alternative, it seems that image stitching would allow similar results with more compact equipment. I'd rather not rely on software to correct distortions after the images are captured, so I'm looking for ways to make corrections in the field. I'll be starting from scratch with an new digital camera and lens, and possibly some sort of panorama rig (perhaps the Really Right Stuff Pano Elements Package). I'd appreciate any thoughts or advice forums members would like to offer.

Thanks,
Nick
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BartvanderWolf
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« Reply #1 on: April 02, 2014, 11:49:49 AM »
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I'm interested in learning about ways to combat the keystone effect while capturing landscape/architectural images. Acquiring a tilt-shift lens seems the best solution, but would require me to lug heavy, bulky and expensive gear (such as the Canon TS-E 45mm f/2.8 on a 6D).


Hi Nick,

In-camera solutions for perspective correction require a shift-able lens or a significant crop of a wide angle shot after the shot. Obviously, cropping will cost image quality, but when the required output is smallish, it might work. Getting the perspective correction perfect in camera is not easy, so you might need to still correct a bit in post-processing.

Software solutions vary in quality, but Pano-stitching software (PTGUI Pro is the most uses dedicated allpication) usually offers superior resampling algorithms compared to e.g. Photoshop. In fact, stitching software offers much more control and accurate projection methods, and it can combine the corrections for keystoning or squaring with corrections for residual lens distortions in one go, thus preserving quality with a single resampling pass instead of two. Stitching software also allows to shoot with longer focal lengths, thus increasing resolution, while making up for the angle of view by stitching multiple tiles. It usually also offers possibilities for removing people/traffic ghosts when multiple/overlapping images are taken of the same area in the scene.

The RRS kit allows to expand the possibilities from single row to multiple row shoots over time. You don't need to invest for the most flexible solution at once, you can do it as the need presents itself (and budget becomes available) over time.

Cheers,
Bart
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D Fosse
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« Reply #2 on: April 02, 2014, 12:01:10 PM »
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As for lens distortion, that's determined by the total angle of view. Put several 85 mm shots together in a pano, and the net result is the same as a single 20 mm shot (except you get more pixels). Stitching relies on distortion to work, because you need all exposures to be taken from the same optical point. Shifting the camera won't work; you'll get parallax error and the frames won't join properly.
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Nick S.
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« Reply #3 on: April 02, 2014, 12:32:59 PM »
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Thanks Bart and D Fosse for your replies. To explain further, I'm a painter interested in reference photos to supplement oil sketches produced in the field. My goal is to produce photos with as little distortion as possible so that they resemble my "plein air" paintings and my memory of the location as closely as possible when I return to the studio. The photos are very helpful when creating larger studio versions of the field sketches. In the past, I've made due with photos taken with a Nikon FM (film camera) and Nikkor F 50mm f/1.8 lens (both purchased in 1980). Often my subjects include trees or buildings that require me to tilt the camera upwards to get the entire scene in the frame. Naturally, this results in perspective distortions that I'm forced to ignore while using the images as reference material when painting. I'm ready to upgrade my equipment and want to get a digital camera, lens and tripod combo that will make my reference photos more useful. A normal focal length (roughly 43 mm) would be ideal, and the ability to shift the lens upward after leveling the camera would help reduce the perspective errors. I was thinking that taking two photos, (the second shifted up while keeping the camera level on some sort of pano rig) and stitching them together into a single image might have the same effect as a single image taken with a tilt-shift lens. Your responses make me think that my idea is unsound.

Nick
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Manoli
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« Reply #4 on: April 02, 2014, 07:09:52 PM »
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Often my subjects include trees or buildings that require me to tilt the camera upwards to get the entire scene in the frame. Naturally, this results in perspective distortions that I'm forced to ignore while using the images as reference material when painting.

Nick,
I'm not sure I've understood your requirements fully, but if the basic requirement is, as you say above, to capture the entire scene, why don't you simply buy a suitable wide(r) angle lens, and use something like DxO Viewpoint to correct the perspective distortion. 

http://www.dxo.com/intl/photography/dxo-viewpoint/wide-angle-lens-software
http://www.dxo.com/intl/correcting-distortion-dxo-viewpoint-2
http://www.dxo.com/intl/node/3352
http://www.dxo.com/intl/node/2347

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Nick S.
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« Reply #5 on: April 02, 2014, 07:40:03 PM »
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Thanks for the links, Manoli. It seems perspective correction software is a lot more sophisticated than I had imagined. I guess in-camera corrections aren't really necessary with the availability of software like DxO Viewpoint. I'll download the trial version and work through the tutorials. This is good news, as I'll be able to shop for a more compact camera and lens combination. A 28mm lens on an APS-C body or perhaps a normal zoom on a M4/3 will lighten my load and give me the focal length I'm looking for.

Nick
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Ellis Vener
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« Reply #6 on: April 07, 2014, 11:33:18 AM »
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The attached photograph was shot with a Canon 17mm f/4 TSE lens on a Canon EOS-1Ds Mark III.  The gray frame delineates the angle of view captured by a single frame with this lens in's unshifted position. I set the camera to manual exposure mode and shot the central frame and then moved the lens to extreme shift position and rotated it, shooting a frame at each click stop. The stitching was done in PTGui and output asa layered TIFF for cleanup work in Photoshop . Clean up work consisted of removing people and some slight corrections to  near/far parallax errors that  PTGui on its own did not resolve to my satisfaction. In the end I decided I could not easily resolve the two errors at the very bottom of the final image where the rail was only a few inches from the lens.

A more ideal solution which would have eliminated all parallax errors when shooting would have been for the lens to remain stationary and shift the camera body's position instead. 
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Ellis Vener
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Creating photographs for advertising, corporate and industrial clients since 1984.
Jim Kasson
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« Reply #7 on: April 07, 2014, 01:24:21 PM »
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Thanks for the links, Manoli. It seems perspective correction software is a lot more sophisticated than I had imagined. I guess in-camera corrections aren't really necessary with the availability of software like DxO Viewpoint.

Or you could use what you may have already installed. The Lightroom 5 perspective control tool is really pretty good, and free if you're already a user. It even has an automatic, or "I'm feeling lucky" mode.

Jim
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SZRitter
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« Reply #8 on: April 08, 2014, 09:58:48 AM »
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A Pano rig would be as much, if not heavier than a TS/E lens. And add a level of complication.

Shift, as mentioned is obviously your best option for ultimate quality, where as software is the lightest alternative. If your end goal is not a high-end print or commercial clients, then software should be more than adequate.

Since you are starting from scratch, you have a couple of options. You can maximize portability/quality and go M43. Although no native shift, there are plenty of adapters that allow you to shift legacy lenses from other systems. I am assuming you don't want to be hauling a massive rig in addition to your painting supplies. But that is just my opinion. The best camera is always the one that you enjoy using the most.
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Nick S.
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« Reply #9 on: April 08, 2014, 06:03:13 PM »
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Thanks, Ellis, Jim and SZ for your input. This is great information that will give me a lot to think about.

Nick
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Lightsmith
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« Reply #10 on: April 17, 2014, 01:18:53 AM »
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Big and bulky to me is a 4x5 view camera on a sturdy tripod and not a DSLR with a single lens. Stitching is a way to make panoramas or higher resolution composite images but it is a poor way to correct perspective for architectural photography. If you want quick and dirty use a P&S camera with a wide angle lens and then adjust the image in Photoshop. It may be good enough for you.

The tilt shift lenses in addition to adjusting for perspective will change the plane of focus so you get foreground, middle ground, and background in sharp focus. They can also be shifted to create a 3 image panorama set very quickly. They require a more technical approach but produce results that cannot be obtained in any other manner without taking hundreds of images and spending hours making a composite in post processing.
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OldRoy
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« Reply #11 on: April 18, 2014, 07:01:32 AM »
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Sledge hammer, nut, cracking, anyone?
Dear me, what a complicated set of considerations in order to make a reference snap to assist with a later painting! Tilt-shift lenses, PTGui stitching, pano-rigs...

Given the image quality now available from even small cameras, plus the range of wa/normal primes (you might well even get away with a decent zoom) you can just de-keystone in software as suggested. Any consequent image degradation would surely be insignificant considering the intended use as an aide-memoir.

Or maybe I didn't understand the requirement?

Roy
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BartvanderWolf
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« Reply #12 on: April 18, 2014, 07:10:54 AM »
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Sledge hammer, nut, cracking, anyone?
Dear me, what a complicated set of considerations in order to make a reference snap to assist with a later painting! Tilt-shift lenses, PTGui stitching, pano-rigs...

Hi Roy,

The purpose was not that clear from the onset, so it frankly seems a bit cheap to comment after the requirements were more clearly specified. Indeed, if only required as a reference for painting, a simpler solution may suffice.

Cheers,
Bart
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OldRoy
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« Reply #13 on: April 18, 2014, 08:03:47 AM »
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I read the second relevant post too. And I still don't understand why such a simple requirement calls for such top-heavy solutions!
But it doesn't matter!
Roy
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Lightsmith
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« Reply #14 on: April 20, 2014, 08:00:04 PM »
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Re-read the OP. Nothing about taking a snap shot to put into a scrap book. That is your perspective but not that of the OP.
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