Considering a TS lens

Started Nov 9, 2012 | Discussions thread
J Perry New Member • Posts: 4
Re: Considering a TS lens - TILT CALCULATOR


New this forum so please excuse me if this post seems inappropriate. I too am considering a T/S, probably 24 mm. Usage would be small product photography where controlling plane of focus is important, even with 24mm. I believe the image quality difference of contolling plane of focus vs using a lens stopped down is significant but have no proof!

Anyway, I truly miss the control I had with my long-gone 4x5 monorail view camera. Of all the things DSLRs can do, they simply can't control plane of focus without a T/S lens.

Before I make the jump to an expesnive T/S, I want to determine how hard it is to properly set the tilt angle on one of these lenses. My 4x5 used scales and lines on the ground glass to make the tilt calc.

Given my usage, fairly close,  small subjects, say laying on a table, is anyone interested in spending an hour for me testing an algorithm I came up with that calculates tilt angle? I haven't found anything like this on the web and Canon's manuals offer little help.

I created an Excel spreadsheet that asks for the following info:

1) Lens focal length (so you can use with any T/S lens).

2) The height of the center of the sensor above (and at right angle to) the plane of focus.

3) The angle between the plane of focus and the plane of the sensor

The angle can be determined quickly using a cell phone with the free bubble level app.

Anyway, by entering those three values, my spreadsheet calcs the tilt angle that needs to be dialed into the lens. Dial it in, re-focus the lens and, if my theories are correct, the plane of focus should be very close if not perfect. Simply refocus the lens ... anywhere in the frame then select your f-stop depending on hieght of objects above or below the subject focal plane.

If this works, it eliminates the need for checking focus at near subject then far subject and readjusting tilt and doing it all over again. The object here is to eliminate setup time.

Tools needed: T/S lens, computer with Microsoft Excel, tape measure or ruler, something to measure angles (e.g. smartphone with free level app), and my spreadsheet.

My spreadsheet contains a drawing showing the theory and giving instructions. It also explains the relationship of a tilted lens and the effect of f-stop. A yard stick might make the perfect subject since it is flat, defines the desired object focal plane and can be magnified in Photoshop to determine the quality (accuracy of the plane).

A yardstick would allow some quantitive measurements .... photo using tilt with lens wide open ... and then photo with tilt angle 0 and stop down, looking for quality differences. If I'm right, an f2.8 properly tilted lens will outperform an f-stop only shot ... but I don't want to spend $2K to find out.

If my theories are correct and I didn't mess up the math, the spreadsheet should be good for any tilt lens as well as any subject matter.

What I'm really after is determining if my algorithm works and, if so, does it reduce the time and improve accuracy in getting the correct subject focal plane.

If interested in helping, please let me know. Thanks - John

 J Perry's gear list:J Perry's gear list
Canon EF 14mm f/2.8L II USM
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