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Author Topic: Shooting square to a flat plane (surface)  (Read 8805 times)
marcmccalmont
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« Reply #20 on: July 19, 2012, 05:21:57 AM »
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Like Marc, I'm thinking of some of the following RRS or similar components.

Stuff that can be used for horizontal alignment/squaring:
  • 1. MPR-73: 73mm Multi-purpose rail (with 1/4" camera screw), for mounting under the Leica Disto. It has an anti-twist flange that can be mounted to square the rear of the Disto. I had a Wimberley P30 lens plate laying around which functions just as well, maybe it's cheaper.
  • 2. B2-FAB/mAS Mini-Clamp Package, for mounting the MPR-73 on a horizontal bar at a right angle.
  • 3. A horizontal (CB-18 and/or CB-28) Bar, for sliding the miniclamp package with Disto along to check for identical distance at both ends (or average along the width of the bar if the wall is not even). For increased accuracy, the bar itself can also slide in the clamp that holds the bar, so you can achieve a measuring base of allmost twice the bar length.


Then you replace the bar by your camera with camera plate.

Following this horizontal parallel bar/wall calibration, you can calibrate the vertical parallel by minimizing the measured distance when you vary the pitch angle. It helps to use a geared head or a geared leveling plate for such precision alignment.

BTW, using a bar parallel to the surface automatically compensates for any minute non-square mounting of the Disto to the bar. Whatever slight angle there may be, the distance is measured at that same angle in the left and right measuring position.

They also sell a slightly cheaper package which combines the dual clamps with a bar (items 2 and 3 of the above list), in case you have don't have one or the other yet and would have to purchase both.

Cheers,
Bart
Smart! with this set up you could slide the disto to the center (over the head) measure this distance then slide the disto out to one end and just set the same distance, done!
Marc
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Marc McCalmont
BartvanderWolf
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« Reply #21 on: July 19, 2012, 06:53:09 AM »
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Smart! with this set up you could slide the disto to the center (over the head) measure this distance then slide the disto out to one end and just set the same distance, done!

Indeed. In practice I think the fastest way will be:
1. Center the Disto over the center of the ballhead or geared head.
2. Rotate to find the shortest distance. You can do both yaw and pitch at this time, but the pitch requires calibrating the pitch rotation axis, like in a pano head, if the highest accuracy is required. At a large distance a slight off pitch rotation axis wil become less important.
3. Slide the Disto to the left on the bar, and shift the bar to the left in the head's clamp, and look for differences in the distance. Rotate the yaw angle to compensate, and check by shifting the Disto to the centered head position again (now at the right of the bar).
4. For additional verification, shift the Disto to the right of the bar, and the bar to the right in the head's clamp. This will double the measuring base offered by the bar's length.
5. Hope that nobody bumps into the tripod ...

Cheers,
Bart
« Last Edit: July 19, 2012, 07:13:20 AM by BartvanderWolf » Logged
dwdallam
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« Reply #22 on: July 28, 2012, 04:32:33 PM »
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Ok set your tripod up one leg forward 2 legs back, if the distance from the rear legs to the wall is equal the tripod is parallel to the wall. I have a A/S cube so it is easy to look down on the head and square it with the tripod but a straight edge against the rear display should be good enough to look down and square it off. Or one could with some help put a yardstick against the rear screen and make sure both ends are the same distance to the wall.
Marc

This won't work, on second thought, because the lens still needs to be squared to the wall HORIZONTALLY.
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dwdallam
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« Reply #23 on: July 28, 2012, 04:42:21 PM »
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OK so you take two measurements? Why not just one? Move the disto left to right until the shortest distance is achieved? It's more accurate to take two measurements I assume?

Like Marc, I'm thinking of some of the following RRS or similar components.

Stuff that can be used for horizontal alignment/squaring:
  • 1. MPR-73: 73mm Multi-purpose rail (with 1/4" camera screw), for mounting under the Leica Disto. It has an anti-twist flange that can be mounted to square the rear of the Disto. I had a Wimberley P30 lens plate laying around which functions just as well, maybe it's cheaper.
  • 2. B2-FAB/mAS Mini-Clamp Package, for mounting the MPR-73 on a horizontal bar at a right angle.
  • 3. A horizontal (CB-18 and/or CB-28) Bar, for sliding the miniclamp package with Disto along to check for identical distance at both ends (or average along the width of the bar if the wall is not even). For increased accuracy, the bar itself can also slide in the clamp that holds the bar, so you can achieve a measuring base of allmost twice the bar length.

Then you replace the bar by your camera with camera plate.

Following this horizontal parallel bar/wall calibration, you can calibrate the vertical parallel by minimizing the measured distance when you vary the pitch angle. It helps to use a geared head or a geared leveling plate for such precision alignment.

BTW, using a bar parallel to the surface automatically compensates for any minute non-square mounting of the Disto to the bar. Whatever slight angle there may be, the distance is measured at that same angle in the left and right measuring position.

To give an idea of the accuracy. A 1 mm difference over a 800 mm measuring base (like with a single CB-18) represents 0.072 degrees, and a 1 mm difference over a 1300 mm measuring base (like with a single CB-28) represents 0.044 degrees of accuracy.

'RRS' also sell a slightly cheaper package which combines the dual clamps with a bar (items 2 and 3 of the above list), in case you have don't have one or the other yet and would have to purchase both.

Cheers,
Bart
« Last Edit: July 28, 2012, 04:44:30 PM by dwdallam » Logged

dwdallam
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« Reply #24 on: July 28, 2012, 05:13:40 PM »
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Indeed. In practice I think the fastest way will be:
1. Center the Disto over the center of the ballhead or geared head.
2. Rotate to find the shortest distance. You can do both yaw and pitch at this time, but the pitch requires calibrating the pitch rotation axis, like in a pano head, if the highest accuracy is required. At a large distance a slight off pitch rotation axis wil become less important.
3. Slide the Disto to the left on the bar, and shift the bar to the left in the head's clamp, and look for differences in the distance. Rotate the yaw angle to compensate, and check by shifting the Disto to the centered head position again (now at the right of the bar).
4. For additional verification, shift the Disto to the right of the bar, and the bar to the right in the head's clamp. This will double the measuring base offered by the bar's length.
5. Hope that nobody bumps into the tripod ...

Cheers,
Bart

OK so exactly what should I buy to do this as cheaply as possible?
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BartvanderWolf
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« Reply #25 on: July 28, 2012, 07:07:59 PM »
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OK so you take two measurements? Why not just one? Move the disto left to right until the shortest distance is achieved? It's more accurate to take two measurements I assume?

Hi,

When you shift the Disto along a straight bar, the bar is only parallel to the wall surface if the distance is the same left/right and in between. When the bar is parallel to the surface, the camera will be perpendicular to the surface.

Cheers,
Bart
« Last Edit: July 28, 2012, 07:31:56 PM by BartvanderWolf » Logged
BartvanderWolf
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« Reply #26 on: July 28, 2012, 07:30:13 PM »
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OK so exactly what should I buy to do this as cheaply as possible?

Hi,

You suggested that you already have an RRS ballhead (I assume with clamp), and a camera with an RRS camera (L-)bracket.

In that case you need a Disto (relatively expensive compared to some home improvement alternatives, but with enough power and accuracy to also work with outdoor light levels on bright surfaces) to begin with, and assuming you don't already have any of the RRS components mentioned, you'd need the components mentioned in post #19.

If the amount of money involved is an issue, you could try and find some cheaper clones of some of the mentioned items on eBay or similar, but I have no suggestions beyond the specific ones I mentioned which have proven to be compatible.

Cheers,
Bart
« Last Edit: July 28, 2012, 07:33:40 PM by BartvanderWolf » Logged
dwdallam
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« Reply #27 on: July 28, 2012, 09:46:25 PM »
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Hi,

When you shift the Disto along a straight bar, the bar is only parallel to the wall surface if the distance is the same left/right and in between. When the bar is parallel to the surface, the camera will be perpendicular to the surface.

Cheers,
Bart

Yes I see what you're saying, but if it is measured accurately from any point on the bar (given the bar is true), then it will be equidistant from any point on the bar.  I'm assuming that the measuring device isn't accurate enough to take one measurement. In any event, I see what you mean.
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dwdallam
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« Reply #28 on: July 28, 2012, 09:48:25 PM »
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Hi,

You suggested that you already have an RRS ballhead (I assume with clamp), and a camera with an RRS camera (L-)bracket.

In that case you need a Disto (relatively expensive compared to some home improvement alternatives, but with enough power and accuracy to also work with outdoor light levels on bright surfaces) to begin with, and assuming you don't already have any of the RRS components mentioned, you'd need the components mentioned in post #19.

If the amount of money involved is an issue, you could try and find some cheaper clones of some of the mentioned items on eBay or similar, but I have no suggestions beyond the specific ones I mentioned which have proven to be compatible.

Cheers,
Bart

Ok thanks. You said that there is a mount that allows mounting the Disto right on the ball head?
« Last Edit: July 28, 2012, 09:55:34 PM by dwdallam » Logged

BartvanderWolf
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« Reply #29 on: July 29, 2012, 04:56:54 AM »
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Ok thanks. You said that there is a mount that allows mounting the Disto right on the ball head?

Hi,

Yes, that's the MPR-73 multi purpose rail or similar with a 1/4" camera screw, which mounts under the Disto. I already had a similar item from Wimberley (a P30 lens plate + optional SW-100). I think a P10 or P20 lens plate plus the SW-100 camera screw would work the same for this purpose, they all three have the anti-twist nubs, and save you a US$ 3 and a few grams of weight.

You can check the prices with dealers who have this stuff in their assortment (e.g. http://www.tripodhead.com/products/lens-plates-specs.cfm). There may be clones available on the internet but AFAIK only Wimberley and RRS make very accurate Arca-Swiss style dovetail accessories to match the lever versions of the Ballhead clamp.

Cheers,
Bart
« Last Edit: July 29, 2012, 05:20:51 AM by BartvanderWolf » Logged
dwdallam
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« Reply #30 on: July 29, 2012, 05:35:45 PM »
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Bart,

What model is that Disto? I simply cannot find one on the Leica site that has the rail on the bottom, or anything like it.

Hi,

Yes, that's the MPR-73 multi purpose rail or similar with a 1/4" camera screw, which mounts under the Disto. I already had a similar item from Wimberley (a P30 lens plate + optional SW-100). I think a P10 or P20 lens plate plus the SW-100 camera screw would work the same for this purpose, they all three have the anti-twist nubs, and save you a US$ 3 and a few grams of weight.

You can check the prices with dealers who have this stuff in their assortment (e.g. http://www.tripodhead.com/products/lens-plates-specs.cfm). There may be clones available on the internet but AFAIK only Wimberley and RRS make very accurate Arca-Swiss style dovetail accessories to match the lever versions of the Ballhead clamp.

Cheers,
Bart
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BartvanderWolf
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« Reply #31 on: July 29, 2012, 07:59:35 PM »
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Bart,

What model is that Disto? I simply cannot find one on the Leica site that has the rail on the bottom, or anything like it.

Hi,

They don't have a built-in rail, but 1/4th inch camera screw threads. That's where the MPR-73 rail or Wimberley foot is attached. Looking at the pictures of the current Disto D3 models (I have an older D3 model) and up, they are still fitted with those screw threads, near the bottom rear end of the instrument. You may want to verify that before buying.

Cheers,
Bart
« Last Edit: July 30, 2012, 03:16:40 AM by BartvanderWolf » Logged
elf
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« Reply #32 on: July 30, 2012, 02:39:34 AM »
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Won't chimping work?
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AFairley
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« Reply #33 on: July 30, 2012, 11:40:48 AM »
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Won't chimping work?

I think there is some merit to this suggestion.  I have tried to align the camera using the mirror technique, measuring, etc., but always when I checked live view, I could see that I was not exactly centered and perpendicular because of convergence of the edge of the artwork and the edge of the LCD on one or more sides..  If you tweak the setup so that the edge of your LCD and the edge of the artwork is parallel for each side of the artwork, you know you are correctly aligned.  For square pieces, you might want to make a jig to extend the sides out match the aspect ratio of the LCD; it's easy to make a precisely cut spacer unless the artwork is tiny.
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Ellis Vener
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« Reply #34 on: July 30, 2012, 01:28:44 PM »
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 My set up for squaring up a camera to art work that is being copied is little complicated. On the tripod head I have a Really Right Stuff PCL-1 clamp an mounted in that, a  RRS CB-18 camera bar. On the bar I have A RRS two way FAS clamp and mounted in that is a large Manfrotto leveling base and on that is  a second PCL-1. The camera mounts on the second PCL-1.

The tripod head (I use a very heavy duty Foba ASMIA) and first PCL-1 let me get the camera more or less square to the plane I'm photographing and then I slide the FAS along the CB-18 to get the camera perfectly centered on the subject. The leveling base and second PCL-1 are to really and exactly fine tune the camera position.
I check this all with a Zig-align set up: http://www.zig-align.com/zig-align/zig-align_Home_page.html
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Ellis Vener
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elf
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« Reply #35 on: July 31, 2012, 02:38:57 AM »
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I think there is some merit to this suggestion.  I have tried to align the camera using the mirror technique, measuring, etc., but always when I checked live view, I could see that I was not exactly centered and perpendicular because of convergence of the edge of the artwork and the edge of the LCD on one or more sides..  If you tweak the setup so that the edge of your LCD and the edge of the artwork is parallel for each side of the artwork, you know you are correctly aligned.  For square pieces, you might want to make a jig to extend the sides out match the aspect ratio of the LCD; it's easy to make a precisely cut spacer unless the artwork is tiny.

If you have a lens that has a field of view (on the sensor) of 40 degrees and a sensor that is 4000 pixels wide, each pixel will represent .01 degrees which is less than one arc minute.  I suspect that this will be more accurate than any other measuring device.  If the subject has precise horizontal and vertical lines, then it should be relatively easy to align. If not, just pick a set of horizontal and vertical points (that can be resolved by the lens) that you want to be aligned.  If you're using a wide angle lens and the resolution isn't good enough, switch to a telephoto lens for the alignment.

Here's an ASCII representation:
      .   .   .
      .   .   .
      .   .   .

It would probably be more precise to use Photoshop to determine the alignment, than to use the camera LCD.


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BartvanderWolf
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« Reply #36 on: July 31, 2012, 04:25:44 AM »
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If the subject has precise horizontal and vertical lines, then it should be relatively easy to align.

This will unfortunately not be available all the time. Then what?

Quote
If not, just pick a set of horizontal and vertical points (that can be resolved by the lens) that you want to be aligned.

Where/how would one pick those points? An automatic leveling Laser cross beam may work indoors, but it is rarely powerful enough at larger distances or outdoors.

Quote
If you're using a wide angle lens and the resolution isn't good enough, switch to a telephoto lens for the alignment.

And by reducing the angle of view your measurement base is reduced and thus accuracy. In actual practice, it is quite hard to get perfect alignment, and most subjects do not have exactly square edges either. And then there is lens distortion, and decentering.

Quote
It would probably be more precise to use Photoshop to determine the alignment, than to use the camera LCD.

Shooting tethered is always useful, it may however not be that practical outdoors (try shooting with the sun in your back). It's best to have a few more alternatives in one's bag of tricks.

Cheers,
Bart
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PDobson
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« Reply #37 on: September 21, 2012, 11:38:49 AM »
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I restored a Lotus 7 many years ago when setting up the suspension I manually set the ride height, caster, camber and toe in. All I used was 2 people, a tape measure and an angle gauge with a bubble level. Several years later I was curious so I took it to a professional with all the automated equipment. It was spot on no adjustments to make. It's amazing how accurate your eye and a tape measure can be!
Marc

Some friends of mine did a head to head test comparing a modern Disto-X to  old-fashioned compass/clinometer/tape for the purpose of cave surveying. They were getting consistently better closure with the old-fashioned methods than with the theoretically superior EDM. Our best guess as to the reason, is that skilled operators naturally correct for their errors while the electronic methods leave no room for adjustment.

When given the choice, I greatly prefer using the Disto. It's fast and I don't have to get into a crazy positions trying to get my eye behind the instrument. Surveying underground is not a comfortable activity.

I guess the point of this anecdote is that you shouldn't underestimate manual measurements. It's slower and takes more skill, but the results can be very good.

Phillip
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