# Thread: How to align camera and flat object ?

1. ## How to align camera and flat object ?

'There were some suggestions of using an animation stand, but I would think they are too small for testing LF lenses.'........................................................no way, the biggest of these were humongous tanks, that could hold motion picture cameras in perfect register.

2. ## How to align camera and flat object ?

Any of them 12 feet long or larger?
Most lens testing is at 10x enlargements.. so a normal lens on an 8x10 is 12 inches.. x 10 is 12 feet.

3. ## How to align camera and flat object ?

Who said it had to be? Not the guy who started this thread, you're the only one who's brought up 12 feet, or that 'most' testing is at 10x enlargements, which wasn't part of the original question, and he didn't say what kind of lens he was testing either, ...................................................here's the original question,............................... 'For the purposes of lens testing, I need to photograph a flat target so that the film plane and the target are strictly parallel. I have found that for critical MTF measurements, even small deviations affect the results.'

And that's exactly what you do with an animation stand, photograph a flat target registered on a 'cell', with the film plane and 'flat art' paralell to each other, if it's a matter of what you said later on, after he asked the original question, instead of what he said, then it's a different proposition,

4. ## How to align camera and flat object ?

Henry,

In response to your question "Would you do some math on the resolution of the numbers of the triangle for finding center and perpendicularity?", I'm afraid I don't quite understand what you are doing. Perhaps I'm missing something, but I can't visualize how you can arrange two opposite diagonals which are lined up precisely enough so the line between their endpoints can be bisected to obtain the center point. I can calculate angular errors, but I have to have a fairly precise specification. For example, if you know two sides of a triangle are precisely equal, and you know the altitude and base reasonably well, I can tell you how far off from perpendicular a line to a presumed midpoint would be depending on the relative error in the placement of the midpoint. Suppose the altitutde is about 20 feet, and the base is about 10 feet, then the presumed right angle from the presumed midpoint would be off by about one half the error in the placement of the midpoint relative to the base. The anglular error here would be in radians. So if the base were 10 feet, and the midpoint off by 1/16th of an inch, the relative error would be (1/16)/120 = .000520833. Half of that would be .000260417 radians or about .015 degrees, which is a little less than one minute of arc. View camera standards and tripods certainly can't be set to that degree of accuracy, so this error would be small compared to those arising from the setup of the camera. Also, even if you assume the camera were set up absolutely perfectly and that the subject plane departed from perpendicularity by such an angle, then the departure of the subject plane from the exact focus plane some tens of feet from the center of the field would be a small fraction of an inch. Since the relative error in the position of the image plane is the magnification times the relative error in the image plane, this is much smaller than the invevitable focusing/film placement errors.

As I noted previously, instead of trying to be more precise than the equipment allows for, one should use repeated measurements each done after stanrting from scratch, and then average. The hope is that the setup errors, which are beyond our ability to measure effectively, are random and will pretty much cancel out in the average.

5. ## How to align camera and flat object ?

This animation stand suggestion isn't very pratical. For one thing they're generally fairly large. You'd need a truck to move one. They're not cheap, unless you find one being sold for scrap by a company that's changing it's business model. And if you did get one, you still have to mount the camera correctly on the head! The cameras used have pins in them to insure that they don't twist and the film plane is parallel to the art work/table.

BTW, Snow White was shot on a custom built stand that Disney fabricated. You can see it in the lobby of the building where the library is on the Disney Burbank campus. It's about 12' tall and has about a dozen trays that can move for more realistic portrayal of fantasy land.

QT, why don't you just take the lens to an existing MTF machine and do your tests?

MW

6. ## How to align camera and flat object ?

BTW, Snow White was shot on a custom built stand that Disney fabricated............................That's not quite correct, Disney collaborated together with Acme to produce the multi-plane animation stand that Snow White was shot on, which premiered Dec 21,1937.

7. ## How to align camera and flat object ?

In fact in 1924, Adolf Furer bought the Acme tool and manufactuing, a tool and die shop on San Fernando RD. In 1928, Walt and Roy Disney contracted w/Acme to modify a Bell & Howell for stop motion, in 1936 they collaborate on the above multi-plane animation stand.

8. ## How to align camera and flat object ?

Hmmm, that's very interesting. All this time, I thought only Wiley Coyote bought from Acme. ;-)

9. ## How to align camera and flat object ?

Good morning,

"Any of them 12 feet long or larger? Most lens testing is at 10x enlargements.. so a normal lens on an 8x10 is 12 inches.. x 10 is 12 feet."

--darinwc , do you work for Microsoft ;-) That would be 10 feet, OOPs.

"One point though, with a view camera, if the lens is not perpendicular to the gg then all bets are off. So before lining up the resolution target align your lens / gg accurately. I'd be interested to hear how this can be done simply. "

--rob, place 1 mirror at the film plane that has been scribed thru with any pattern and light it from behind thru the gg. Place another mirror flat to the lens with a center hole scribed thru the mirror plating to the plain glass. Now look thru from the lens, it will look like sighting down a pipe or a 'Slinky' until it's dead-on. It's easier to do than describe.

"The mirror method seems the simplest and most practical, but there is one potential problem. Your pointer towards the lens, no matter how it is arranged has to be exactly flat on the subject plane. That means it should have a large base of contact. Otherise slight errors could be magnified. "

--Leonard Evens, by back-lighting thru the gg. the light is diffused, no pointer to worry about. Standing at the camera you can see when everything is exactly aligned in the target mirror. When the pattern is aligned, it really lights up. By removing the lens board you can align the film back and lock it down (watch it move). Then install the lens and align and focus the lens the same way and lock that down (watch it move). Move the focus adjustments and watch it move all over the place, which is why you align it when it's focused.

None of this is hard, it's exactly the same as aligning an enlarger

10. ## How to align camera and flat object ?

Sorry Leonard, I knew exactly what I meant! <grin>

Maybe this will explain:

Start with a camera position facing a large, flat (we hope) wall. From the camera pull a tape from the center of the lens to a point on the wall well to the left, mark the wall with a pencil and then pull the same tape distance off to the right of the camera to the wall to obtain an equal distance measurement to the first. Measure between the two marks on the wall and mark the middle of that distance. That mark is the center line and when extended out to the camera is perpendicular to the wall.

Here is the triangle:
Corner A is the camera position, B is the left mark on the wall, C is the right mark on the wall, D (where the test target is located) is the midpoint between B&C.
Lets say: AB=25 feet, BC=25 feet, CA= 25 feet.

If I mismeasured by 1/16 of and inch between AB and CA, how much angular error is there in terms of the camera film plane and the test target? Or perhaps another question is: If the target is 2 feet square how much error will show up at one or both edges?

I hope this makes sense.
I can probably do this myself but I think you will have additional insight that will add value to the thread.

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