How can I ensure that a lens is pointing absolutely vertically downwards?

Question

My uncle makes models of all sorts of things. To help him, he uses his camera(s) as scanners by photographing his various bits, and then performing further CAD on the resultant images. These models will not fit onto a conventional flatbed scanner as they're 3D.

To eliminate parallax and perspective errors, he rests the item on the floor and tries to align the camera lens vertically and centrally over it. Therein lies the problem. To get the best accuracy, the lens needs to be as vertical as possible.

He's tried using a spirit level against the lens(es), but that's error prone with the lens(es) being various diameters. Similarly against the back of the camera bodies. He's also tried a plumb bob on a string held somewhere in the centre of the view. If the lens is looking along the string, it's kinda vertical. This is tricky too (especially in storms).

Is there any other way to ensure that a camera lens is pointing absolutely vertically downwards?

Answer 1

A good way is to set a mirror flat on the floor, and check the reflection of the lens in the viewfinder. It should be exactly centered:

• This actually ensures that the lens axis is perpendicular to the plane of the shots, so it also works to shoot something vertical or at an angle (but you have to find some way/person to hold the mirror)
• The hardest part is finding a suitable mirror which is not encumbered by a frame that could add an angle. Edit: signal mirrors as found in survival kits could be good candidates, the hole in the center makes it easy to position them (or mark their position).

Answer 2

A cheap/easy way is to get a length of clear acrylic pipe and paint the rim (cut edge) of both end openings. Something like this would work.

When centered on the photography platform (floor), and with the camera sensor parallel, the entrance and exit rings created by the painted edges will form concentric circles (an alignment bullseye). You need to use paint that contrasts with the platform/floor, or place a piece of white paper down first.

You will need to make sure at least the bottom end is cut perpendicular; but that is easy to check with a square, and easy to fine tune with basic tools/sandpaper (the upper end is less critical). And it may be necessary to get/cut a shorter tube so that there is enough depth of field to see both rings reasonably clearly; but the shorter the tube is the less parallax there is to show any misalignment (stopped down focus with a manual aperture lens, or DOF preview can help).

In theory any cylinder can work, but using clear acrylic eliminates/minimizes a lot of issues with lighting/shadows.

This DIY is similar; fussier to make but accurate to .01˚.

And this is one I made from a clear acrylic box. I painted the inside of the lid white, the outside of the lid red, and the bottom of the box black. Then I used a mill/cutter to drill through the bottom and remove the white paint from the lid. When everything is aligned you get a perfect white circle with a red center.

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Edit: I just looked down and realized my coffee cup makes a functional parallax bullseye if the surface it's on is level. Certainly less precise, but also a lot easier/cheaper.

Answer 3

Using a cube or cylinder made of clear acrylic or glass, place a dot of black paint dead center, both ends. Best if the two dots are well spaced, perhaps 50mm or better (2 inches). Instead of dots, you can scribe a crosshair.

Place this alignment tool on a flat surface directly under the lens. The camera will be square if the two dots appear superposed in the viewfinder.

Answer 4

I place a circular bubble level on my LCD display when the camera is pointed at the floor. This assumes that the LCD display is parallel to the sensor plane. This has served me well for the camera bodies I use for product photography.

There are bubble levels for camera hot shoes (where you attach an external flash unit). This assumes that the hot shoe is perpendicular to the sensor plane.

Newer cameras have level sensors built in, however, they don't have enough resolution for critical leveling.

Helpful for aligning your camera are geared tripod heads. Many have bubble levels built in and angle indicators. This assumes the base of the camera is perpendicular to the sensor plane.

Image taken from Home Depot - Johnson Circular Bull's Eye Level.

Image taken from B&H Photo - Vello Three-Axis Hot-Shoe Bubble Level

Answer 5

Quick, Easy, Portable, Repeatable, and (most of all) Accurate plumb reflector.

The easiest and only truly accurate way to retro-reflect an image is by using a liquid whose optical surface is flat by definition (notwithstanding the Earth's curvature).

Any other method relies on mechanical precision which is limited by your tools and skill, neither of which is limitless. The true beauty of this technique is that it always shows a plumb (perpendicular) line even if the surface under the container is tipped or irregular.

Here's How: Place any non-viscous (light) liquid in a container that will enhance the reflection in the centre of the field; and, use the reflected image of the camera lens, centred. Tip: Black coffee in a dark cup or bowl will work well. Use a surface large enough to avoid the edges of the liquid which are meniscus curves.

That's it, Well Done.

Good luck.

Answer 6

Since it appears your uncle will need this on a continuing basis, he may want to invest in a good copy stand. Then, he can simply mount his camera on the copy stand and be reasonably assured that it is plumb and level.

Cheap copy stands are cheap and somewhat inaccurate. Good copy stands tend to be pricey. Since your uncle sounds handy, he may be interested in crafting his own.

There are plans around the Internet for cobbling something together from scratch, but old film enlargers are dirt cheap these days, and can easily be re-purposed as copy stands.

Here is one crafted out of a Besseler 23C II, a classic, well-built enlarger. I picked it up at a camera swap meet. I had talked to the seller a few times during the day, but didn't bite at $10. At the end of the day, every one was packing up, and he ran up to me and said I could have it for free, if I also took another old enlarger for free that he hadn't been able to sell! How could I pass that up! (I attached the lights and polarizers when I got it home.)

It's worth looking for a stand (or enlarger) with a tilted column. This means your uncle can work on models of various sizes, without the base of the stand getting in the way on larger models.

Fast forward through an emergency medical move in which I had to leave that behind — I find myself with an 18" cube of my father's photos to scan and deliver to my siblings, after his passing. So, I went onto CraigsList, and found a Besseler 23C II again!

It is quite easy to modify, requiring only removal of a "C" ring to get the enlarging head off of a 1 cm (3/8") rod. Rather than fabricate the odd-angled aluminum box shown in the photo of my earlier stand, I plan to make a simple wooden platform, attached to the original head-mounting rod, then use a simple screw as a plumb adjustment. This is the way the original enlarger head was adjusted, so be sure to understand that before taking it apart.

With that in place, one can then use the "mirror" technique outlined above to align it… once! Then, your uncle can quickly and accurately shoot models as fast as he can put them under the copy stand, with no further adjustments needed.

That will deal with the "plumb" part; what about the level?

If you go to this much trouble, I'd rather permanently affix a quick-release on the copy stand, so you won't have to futz with the unpredictable "roll" alignment problem of attaching the camera via the typical 1/4" tripod screw. Then, your uncle is truly ready for "snap in and shoot" experience.

I use the Manfrotto 394 quick release system used on their 310 Mini-Gear Head. It is sturdy and stable, and rated for 10kg (22 pounds). It has multiple holes — if you mount it with two screws, the "roll" alignment problem goes away. Newer versions than that pictured actually have tiny bubble levels built in. But almost anything of reasonable quality will do, like the very popular Arca-Swiss system.