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Thread started 11 Oct 2013 (Friday) 15:48
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Anyone doing math on shift photography? Scheimpflug lines placement questions

 
uOpt
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Oct 11, 2013 15:48 |  #1

Anyone into this? I wonder about two things.

1) Say I am standing on the east wall of Mdina, Malta, 30 meters above ground, and I intend to put the focus plane on the ground 30000mm below me, with a 24mm shift lens. The shift angle I would need is 0.04583 degrees to put the Scheimpflug line on the ground. How the oink am I supposed to set that? Even if I had that kind of precision the lens has a notch at zero and snaps right into it.

2) given this very low angle required and that nothing perfect mechanically and I bet every lens on the planet has a very small shift angle even if it doesn't want to - how comes we don't have every lens on the planet with a focus plane parallel to an imaginary ground 100m below us? (with focus at infinity) Obviously the focus plane has snapped to vertical.


My imagine composition sucks. I need a heavier lens.

  
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Oct 11, 2013 19:28 |  #2

uOpt wrote in post #16363719 (external link)
Anyone into this? I wonder about two things.

1) Say I am standing on the east wall of Mdina, Malta, 30 meters above ground, and I intend to put the focus plane on the ground 30000mm below me, with a 24mm shift lens. The shift angle I would need is 0.04583 degrees to put the Scheimpflug line on the ground. How the oink am I supposed to set that? Even if I had that kind of precision the lens has a notch at zero and snaps right into it.

2) given this very low angle required and that nothing perfect mechanically and I bet every lens on the planet has a very small shift angle even if it doesn't want to - how comes we don't have every lens on the planet with a focus plane parallel to an imaginary ground 100m below us? (with focus at infinity) Obviously the focus plane has snapped to vertical.

I never used a TS lens but as far as my logical understanding is, i think it really depends on the angle you have the camera - with lens - pointed to. I dont know where you got the 0.04.. degrees from, but if the camera is regularly on a tripod which looks straight, i.e. 90 degrees when its pointed horizontal, it would be around another 90 degrees to bring the focus plane to the ground.


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uOpt
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Oct 11, 2013 20:21 |  #3

The camera is horizontal in this example, I should have mentioned that. The 0.04 degrees are correct, it is what a 24mm focal length lens needs to (at infinity focus) have the focus plane horizontal 30m below you. I'm just trying to clean up some misunderstandings I might have, namely how the heck I am supposed to set that, or maybe I don't need infinity focus at those distances from the Scheimplug line anymore?


My imagine composition sucks. I need a heavier lens.

  
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Mike ­ K
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Oct 11, 2013 22:42 |  #4

uOpt wrote in post #16363719 (external link)
Say I am standing 30 meters above ground with a 24mm shift lens. The shift angle I would need is 0.04583 degrees to put the Scheimpflug line on the ground. .

You are correct. When the focal plane (usually ground plane) is far from a wide angle camera lens, the amount of tilt angle (not shift angle) is negligible. If you take all of your landscapes at a high vantage points, there is no need of a tilt lens. However, as the camera nears the focal plane and the focus length of the lens increases, the tilt angle starts to increase in a very non linear fashion. This table lists the tilt angle as a function of lens focal length and distance of the focal plane from the lens center.

http://www.fototime.co​m/C3AAFA55AF0E6FD/xlar​ge.jpg (external link)

Note that using a Canon 17 TSE lens, very little tilt angle is needed until you get to about a lens height of about 2 feet (1.6 degrees). However, at 2 feet you have already exceeded the maximum tilt angle capability required for a Canon 90 TSE (8 degrees). Even with wide angle tilt shift lenses, as you get closer than 6-12 inches the amount of tilt required really climbs. At high tilt angle, fine adjusting lens focus and tilt angle can be very difficult, as these two variables interact. A good tripod permitting low angle camera positions, and careful adjustment of magnified Live View are essential. A very general rule of thumb is to use a near field object to fine adjust the tilt and a subject at infinity for focus. several iterations of focus and tilt angle adjustment are often required.

Here is an article with these calculations formatted in a lens specific fashion. The author suggests for a WA lens, standing height, that a tilt angle estimate via the table is sufficient. Don't bother with more tilt angle adjustments, simply focus and shoot. However as one kneels and gets lower, more care is needed in setting tilt angle.

http://www.luminous-landscape.com/tutorial​s/focusing-ts.shtml (external link)

If the low angle shot is not your compositional cup of tea, then perhaps you will only use shift, not tilt.
Mike K


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uOpt
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Oct 11, 2013 23:05 |  #5

Thanks. I read those articles and have my own program based on the formulas.

I just still can't understand why the floor, then -say- 100m below me, would be in the focus plane with infinity focus and practically no shift, although it is parallel to where the camera is aiming. I suppose that is because objects at 100m are sharp when the camera is at infinity no matter where they are relative to the camera?


My imagine composition sucks. I need a heavier lens.

  
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Oct 11, 2013 23:17 |  #6

uOpt wrote in post #16364477 (external link)
Thanks. I read those articles and have my own program based on the formulas.

I just still can't understand why the floor, then -say- 100m below me, would be in the focus plane with infinity focus and practically no shift, although it is parallel to where the camera is aiming. I suppose that is because objects at 100m are sharp when the camera is at infinity no matter where they are relative to the camera?

As you reduce tilt you also increase the angle between the near DOF and far DOF. So imagine you did get 0.04 deg of tilt, you would effectively have the same DOF in front of you as with zero tilt.


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Canon ­ Bob
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Oct 12, 2013 14:39 |  #7

uOpt wrote in post #16364477 (external link)
I just still can't understand why the floor, then -say- 100m below me, would be in the focus plane with infinity focus and practically no shift, although it is parallel to where the camera is aiming.....

Does your mental picture of the geometry take into account that, unlike a more conventional lens, the TS lenses don't have a flat field of focus?

Bob


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Oct 12, 2013 15:08 |  #8

Canon Bob wrote in post #16365713 (external link)
Does your mental picture of the geometry take into account that, unlike a more conventional lens, the TS lenses don't have a flat field of focus?

Bob


Damm Bob you got a lot of L lens.

I am a new owner of the TSE 24mk 1 and a TSE 17mm.
Can explain the field of focus on a tse lens please.

tse 17mm

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Canon ­ Bob
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Oct 12, 2013 16:04 as a reply to  @ farmer1957's post |  #9

David Summerhayes gives a detailed explanation in his Tilt-Shift tome here (external link) and it's far better than any drivvle I could come up with.
Bob

A quote from the relative passage
A final word about the Canon TS-E 24mm tilt shift lens
I have read in many reviews from owners of these lenses complaining about the edges not
being sharp at wide apertures. This is true and although not desirable it is necessary and
can be quite simply explained. This lens is not of a flat field design! A good example of a
flat field designed lens could be an enlarger lens or macro lens. These lenses are designed
to focus on a flat field plane where the focus holds true as well at the centre of the field as
it is at the edges. Many wide angle lenses are corrected for this but then again they do not
have to operate at such extremes as the tilt/shift designs.
Imagine if you will the difference in distance from the camera to the centre of the focus
plane verses the distance from the camera to the edge of the focus plane. When using a
24mm lens with its 84° angle of view, if the centre of the field is 3.5 metres away from the
camera, the edges of the field will be 5 metres away. At 18 metres the edges of the field
will be 25 metres away and so on. When using this lens at the widest aperture and at
moderate distances, the focus plane could be imagined as radiating out from the camera
rather than a flat plane as previously described. The moral of the story is to always stop
down to get the most out of this lens design and retain corner sharpness.
It is necessary for the lens not to be a flat field design to accommodate ‘shift’.
Imagine what would happen to your focus when you shifted left or right if the edges of the
lens focused further away than the centre! When shifted the centre focus would jump
forward, magnification would change ever so slightly making stitching difficult.
What people are actually seeing when they focus on lens charts or a flat field object is not
so much ‘soft focus’ as in lens aberration but more just plain ‘out of focus’. Perhaps if the
lens chart was curved to be equidistant from the lens the result would be different.
It should be carefully noted that for the same reasons, the edges of the frame may appear
out of focus when this very wide angle lens is tilted, even when the correct angle of tilt has
been calculated. Here it might be wise to think of the ‘flat’ plane of focus as being
slightly bow shaped. Once the angle of tilt has been calculated I would suggest not
focusing right in the centre of the lens but instead to find an object about a third of the way
into the composition to average out this annoying quality of the lens design. Again it is
always best to close down a few stops to achieve the best results.


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uOpt
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Oct 12, 2013 17:03 |  #10

ejenner wrote in post #16364499 (external link)
As you reduce tilt you also increase the angle between the near DOF and far DOF. So imagine you did get 0.04 deg of tilt, you would effectively have the same DOF in front of you as with zero tilt.

Right. So what happens with that other plane in the DOF that's below me parallel to the direction of the camera? Does it suddenly disappear when you go 0.004 to 0.000? But you can't get 0.0000000 since manufacturing isn't perfect.


My imagine composition sucks. I need a heavier lens.

  
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uOpt
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Oct 12, 2013 17:09 |  #11

farmer1957 wrote in post #16365757 (external link)
Damm Bob you got a lot of L lens.

I am a new owner of the TSE 24mk 1 and a TSE 17mm.
Can explain the field of focus on a tse lens please.

tse 17mm
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IMAGE LINK: http://s1110.photobuck​et.com …ed-1_zpsa89a6175.jpg.html  (external link)

farmer

That's an easier case since the focus plane is pretty close to the camera.

You place the whole focus plane on the stick. You do that as follows:

  • place the scheimpflug line (which is always in the same plane as the camera, e.g. right below) at the right distance, which you do by selecting the right shift angle. You get this out of one of the tables or you do the math yourself. If you are 0.5meter from the start of the object and your focal length is 17mm then the shift angle is 2 degrees
  • now use focus to rotate the focus plane around the scheimpflug line so that it is right on the stick. Start with infinity, work down
  • Fine-tune both
  • Snap


This assumes the beginning of the stick is intersecting with your camera plane. If it does not you make focusing easier by moving or extending it so that it does, because that enables the above easy path of finding both focusing parameters.


ETA: this is the shift focusing article I like best. However, it doesn't have the math to do your own calculations or write your own programs:
http://www.waldonell.c​om …al-and-tilt-swing-lenses/ (external link)

Example pic, but you need to read the above link to understand:
IMAGE: http://www.waldonell.com/workspace/uploads/lens_focus_planes4.png

My imagine composition sucks. I need a heavier lens.

  
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rent
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Oct 13, 2013 15:08 |  #12

If you are 30 meters above ground, and you want the focal plane be on the ground, you don't really need any tilt at all, as your calculation proves it (0.046º is practically nothing). The tilt will come into play when you want to do this at maybe 0.5 meter above ground.

Put it another way, you can do this with a non-TS 24mm lens and pretty much get the same effect. Maybe stopping down an extra stop for good measure. :p

-alex

uOpt wrote in post #16363719 (external link)
Anyone into this? I wonder about two things.

1) Say I am standing on the east wall of Mdina, Malta, 30 meters above ground, and I intend to put the focus plane on the ground 30000mm below me, with a 24mm shift lens. The shift angle I would need is 0.04583 degrees to put the Scheimpflug line on the ground. How the oink am I supposed to set that? Even if I had that kind of precision the lens has a notch at zero and snaps right into it.

2) given this very low angle required and that nothing perfect mechanically and I bet every lens on the planet has a very small shift angle even if it doesn't want to - how comes we don't have every lens on the planet with a focus plane parallel to an imaginary ground 100m below us? (with focus at infinity) Obviously the focus plane has snapped to vertical.


http://portfolio.alexj​iang.com (external link)

  
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Oct 13, 2013 16:31 as a reply to  @ uOpt's post |  #13

I would like to thank uOpt and Canon Bob for your efforts into educating me on how to use a tilt shift lens.

Ok I have been focusing my lens the wrong way and haven't been using my f stops to help me get a sharper image.

I do have a glare problem and my shutter speeds are over 2 seconds, I cannot use live view because its so dark. And when I switch to live view it changes my shutter speed and I get glare. or I have to change ISO and f stops to be able to see enough to focus with live view. And glare washes out my pool cues.

Farmer




  
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Oct 13, 2013 17:13 |  #14

Try switching to bulb and adjust your SS such that you can see better in LV.


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Oct 13, 2013 17:33 |  #15

rent wrote in post #16368000 (external link)
If you are 30 meters above ground, and you want the focal plane be on the ground, you don't really need any tilt at all, as your calculation proves it (0.046º is practically nothing). The tilt will come into play when you want to do this at maybe 0.5 meter above ground.

Put it another way, you can do this with a non-TS 24mm lens and pretty much get the same effect. Maybe stopping down an extra stop for good measure. :p

-alex

So the answer to my original question is that anything 30+ meters below me (and visible in the frame for a given focal length) is in focus anyway (with focus at infinity). I think that sums it up.


My imagine composition sucks. I need a heavier lens.

  
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Anyone doing math on shift photography? Scheimpflug lines placement questions
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