Basics and calibration

Heads up

Before we can actually shoot a 360 degree image, there are some basics to be covered here. I will assume you have some basic knowledge about DSLR cameras, and know your way with manual settings and the affect the changes in aperture and exposure time have on the resulting image. If you have never shot in manual mode, I will strongly suggest starting out experimenting with these manual settings before getting into shooting panoramas, especially in HDR. In this basics section I will stick to normal LDR photos, we will get into HDR soon enough… just to keep things simple.

 

Parallax?

Basically the shooting comes down to swinging your camera with wide-angle or fisheye lens around whilst taking overlapping pictures, and then stitching these to a single image containing the whole environment seen from one point. But when we just swing our cam around on our standard tripod head, and stitch the images, it will contain parallax errors. Parallax is the shifting of the background against foreground objects when rotating your camera on the wrong pivot. This can be experienced yourself with a simple trick: just stick up your thumb on eye-level. When you turn your head side to side whilst looking at your thumb, you will notice the background shifts in relation to your thumb. Imagine taking two pictures in the left and right position, if the garden shack in both pictures would be aligned over each other, the foreground will not match because it shifted, this is a stitching nightmare! (red insert)

 

No parallax!

Now do the thumb-trick again, only this time try to rotate your head around your eye. When done correctly you will see no shifting in the background in relation to your thumb, this is exactly what we need for stitching. You will realize now, that your standard tripod head is not going to work if you want to shoot a panorama, if its 360 or not. When you want to overlap images, parallax is not-done.

 

Panoramic heads


To overcome this problem, we have to use a special panoramic tripod head. This tool allows us to put the camera in the right position to rotate it, without getting parallax errors. Some heads allow only horizontal shooting, and some can be rotated vertically too. Examples of these are the NodalNinja, PanoMaxx, Kaidan Panohead, Panosaurus and ReallyRightStuff. They all have a rotatable, horizontal bottom arm, on the end a vertical arm is fixed, extended upwards. This arm can slide over the horizontal rail for parallax adjustment. At the top of this slide-able vertical arm, another vertical arm is connected with a pivot, so it can rotate around vertically. On this arm the camera will be fitted on a slide block which again can slide in the vertical rotating arm.. This way we can adjust and rotate the camera in every direction we want to, 360 degrees vertical and horizontal.



So just for clarity, I will call these three arms the horizontal rotating, vertical fixed, and vertical rotating arm.
 

 

Finding the no-parallax-point

I’ve already told you how to find the no-parallax point with your eye and thumb, but how to find it with the camera? It’s a job that needs to be done quite carefully to reach the least amount of deviation for the best stitching result. Because we rotate the camera in 2 directions: horizontally and vertically, we will need to adjust both directions separately. First we will adjust the vertical slider, and then the horizontal. This is because the horizontal rotation needs both sliders to be adjusted. With the vertical rotation, the horzizontal slider position doesn't matter. Fix the camera on your tripod with pano-head. You can roughly assume the correct horizontal position by centering the lens over the pivot of your panohead. Place the camera just outside the center, so you know witch way to slide your camera to make the parallax lesser. The vertical position will be somewhere near the end of your lens when using fisheyes (The nikon 10.5  i use has it exactly on the golden ring at the end of the lens).



 


Adjusting the vertical slider

First we need 2 objects which can act as alignment targets. Keep in mind it all has to be in-focus, so you might close your aperture to increase your field of depth. Something like a window frame and the top of a chair, or a piece of sticky-tape on a window and another object like a house outside. You will be sure they won't shift. a chair could always be moved accidentally. Align the two targets in the middle of your viewfinder, and then take three pictures with the targets in the upper, middle and lower section of the picture. Put them on the PC screen for close observation. adjust the slider on the rotating vertical arm either further away or closer to the vertical rotating arm pivot (depending wich side you shifted to after the rough alignment). Take another two pictures and compare the parallax error to the previous two images on your computer screen. When the parallax error (background shift) decreases, you are going the right way. If it increases, you have gone too far, so just make small adjustments to the slider, like a millimeter or so. This way you know when you start to come close to the no-parallax point. Repeat these steps until you find that your alignment targets don't shift anymore when you swing your camera up and down. vertical slider is adjusted!

 

Adjusting the horizontal slider

Adjusting the horizontal slider goes pretty much the same as the vertical, just in another direction. For the horizontal rotation we need 2 vertical lines, like a door, window frame or wall, or the same taped window trick. Now put your camera in a position that the camera and the 2 alignment objects are in-line, so the foreground and background objects touch each other when viewing straight at them. Now take three pictures again, one with the alignment targets on the left side, the middle and on the right side of the picture. put the images on your computer for closer reference again.
Now slide the fixed vertical arm of your panohead either closer to, or further from the panoheads horizontal pivot (your tripod center) depending on the side you shifted to during rough alignment. Now take another two pictures and compare the images to the previous two. So when you reach your no-parallax point here, you have calibrated your pano-head! Don’t forget to mount the markers for the sliding positions so you can disassemble and assemble your head without having to calibrate again!

 

you could also visit this link to get an impression of where to start your calibration, these values are very close to, or straight up perfect.

 

 

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