Monday, February 28, 2011

Tilt-Shift vs Software Geometry Correction

The Canon TS-E 17mm F/4L.
Complex design allows for several configurations
in multiple directions, and orientations.
In today's comparison I pit a Tilt-Shift Canon TS-E 17mm F4L lens against the Samyang 14mm F/2.8 prime with DxO Optics 6.5.4 geometry correction function in a quest to see just what advantages a $2500 lens has over a much simpler budget solution.

Big fat front element and
2 lbs of lens. One heavy
Lens!
The first question to address is what is a tilt-shift lens really good for? Essentially the key to a tilt-shift lens is to bring much of the advantages of a large format view camera to the compact 135 format SLR. The primary advantages are to correct for perspective distortion and to increase the depth of field although one of the more popular uses for Tilt-Shift lenses is to create selective depth of field which wedding photographers utilize in their tool kit of effects. Some of this can be created with a far more affordable Lensbaby, but the image quality is certainly no where near a proper tilt-sgift lens by any stretch of the imagination. Also some of this can be done by software programs like Adobe Photoshop. A popular website does a reasonably good job of simulating the effect at http://tiltshiftmaker.com/

One of the main things I shoot in photography is interiors, and many of my clients like to have perspective correction in their images. To do this, you can either use a tilt-shift lens, or to use software solutions found in software like DxO Optics or Adobe Photoshop/Lightroom. I was curious for some time, just how much of a benefit using a tilt-shift over software solutions. Aside from the major learning curve in using a tilt-shift lens properly, it does produces some spectacular results. If you want to learn a little more about how tilt-shift lenses work, this link and this other link to learn about controlling the depth of field.
Parallel perpendicular lines with the Canon TS-E 17mm 

So why compare the 14mm against the 17mm tilt-shift? Well simply put, with 11 degrees of range of adjustment, is precisely the amount of difference between the angle of view between a 14mm and a 17mm (104° vs 93°). In theory, from the same shooting location the shot should look similar to each other when correction has been applied.

Samyang 14mm with no correction
The Samyang 14mm certainly captures more of the image than the 17mm at the same shooting location, and when working with the idea of correcting later, you do need to be conscious of the fact that your subject must be well isolated from the borders. A simple 1/8th of the narrowest part of the frame is the amount of room you need to give your subjects from the border.

Correction is best done in something like DxO Optic as it gives some of the best geometric correction simulations, comparable to the Tilt-Shifts. I found that Lightroom and Photoshop's attempts at geometric correction is too linear, and in most cases, those images are unusable.


Between the standard options to set-up perspective correction, there are additional tools that help simplify and speed up the process by giving control points you draw to determine how to correct the perspective–much like morphing software in animation programs of the past. A quick adjust with the UP/Down function corrects like the shift function on the tilt-shift.
Samyang 14mm with Up/Down correction
Although the scale is smaller on the Samyang (The 11 degrees affects both directions on the tilt-shift), the differences between the tilt-shift and the software version are very subtle. One might even argue that the software correction is closer to accurate and what my eye had seen, but even the stock 14mm image represents the subject much truer, even though the perspective was pretty extreme.

Samyang 14mm with Up/Down and X/Y Ratio Correction
By using the X/Y Ratio, we can now correct the image further. This brings it more in line what I would expect to see (essentially compressing the perspective to only being two point perspective rather than 3 point perspective).

So what does the tilt shift do that can't be done with software? The biggest benefit is the tilt-function of the lens. This increases the depth of field so close and far objects are more in focus with a larger aperture. This is extremely handy when doing product photography when you want all of your object in focus, rather than doing focus stacking. Frankly even in my field tests, I found that my Samyang 14mm was still easier to use both to correct for shift functions and to compensate for depth of field by stopping down. I didn't particularly find the TS-E friendly to use (mostly due to the fact that in a viewfinder it's too small to see anything, and scanning all over hell's acre in liveview to nail everything right). In fact, I found large format view cameras much easier to do tilt-shift work because of the very large ground glass to compose with. It almost seems that this lens combination needs a tethered laptop to really be helpful.

Where the Tilt-shift lens really shines is in deep depth of field landscape shooting.
You need patience and need to check all corners of your image to ensure perfect focus.
In conclusion, do I think a TS-E lens is worth it? Honestly for my kind of work, I'd say no. I can control my image far better through software, than trying to fiddle with the knobs and dials on a TS-E. Even many experts on tilt-shift lenses say it's a bit of a guessing game to getting it right, and sometimes it can take years to master. I'm not really all that interested in investing that much time when I can frankly make most of my adjustments during processing.

EDIT (March 7th, 2011):
Just wanted to add an additional point. The TS-E is very sharp, but very difficult to master. My opinion on getting one or not is strictly based on the concept of using this specifically for maximum DoF. This is more specific to the 135 format 5D and up bodies where you can use apertures of F/11 or more with marginal consequences. On a crop format, you can technically get deeper depth of field on a lower aperture because of the crop factor, however, diffractive limits do keep you from going too high at the cost of image quality. Of course crop cameras cannot shoot as wide as these shots with the same lens. The TS-E is sharper than the Samyang with software correction, but and there is a but. In the time it takes me to get the TS-E perfect, I can set-up my Samyang, shoot and move off to maybe half a dozen other shots before the TS-E is right. You have to be patient with it, and I do like the results of it, but the limitations of not seeing your entire image as you make corrections through-out is very annoying when I know that I can set my Samyang at even F/5.6 and everything will be in focus.


MC TS-PC Harblei 45mm Super Rotator (requires an adapter)
This is a very patient specialists lens, and needs to be treated as such. There are a multitude of other options to pick from and this lens is difficult to fit well in a person's bag. I certainly see it difficult to find it a convenient lens to bring on a trip somewhere unless you know your vantage points well. It's not practical and you'd be better suited for something a little less wide like a 24mm F/1.4 that has autofocus and metering that works with you. Even the TS-E 24 would be a far more practical choice than this ultra wide beast. However if you are looking for the effect of a view camera in a small compact body that is digital, this is about the only option out there for under $6000. After that, I'd recommend the Pentax 645D with something like a Hartblei lens.

4 comments:

  1. Many thanks for the informative post. I am just getting into architecture/real estate photography and will try to find a 14-24/2.8 and struggle along with Lightroom for the time being.

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  2. I totally agree! I was thinking about getting the 17mm TS-E. However, it is $2400-$2500 USD currently. It seems to me that I can get the same effect from a 14mm Canon lens.
    Thanks for sharing!

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  3. Very interesting comparison! I'm trying to decide as well. For me it's coming down to either the Samyang 24mm f/3.5 TS which will be available in May or a conventional wide angle lens like 20/2.8, 18/3.5 or 18/2.8.

    I would mainly use it to correct the shift, the increased dof is not so useful for me.

    My question is, if you correct the picture later in post, how much of the picture do you loose? If you start with a 12mp picture, how much would the corrected picture have? (still having a ratio of 2:3)

    -Peter

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    Replies
    1. Hi Peter, sorry for the delay in responding.

      a 14mm lens after maximum geometry correction is equivalent to a 17mm T-SE. That should give you a pretty good idea of how much loss.

      I always as a rule of thumb leave about 1/8 of the edge of my subject free from the frame edge when using a 14mm wide angle.

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