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A Note on the No-Parallax Point (Not Nodal Point)

Often, people will say that you need to rotate your camera around “the nodal point” of your lens to eliminate parallax when taking panoramas. Unfortunately, this is not correct for several reasons.

Firstly, there is not a single nodal point for a lens, in fact there are 2 (front and rear). Secondly, neither of these 2 nodal points is the point around which you need to rotate the lens to avoid parallax [1]. One should rotate the lens around the entrance pupil (the apparent position of the aperture stop) to avoid parallax. This position is also called the No-Parallax Point (NPP for short).

There are complications of course. The entrance pupil position can change depending on the angle at which the light rays enters the lens. This is especially noticeable in fisheye lenses where the entrance pupil can move significantly at extreme angles off-axis.

Peleng 8mm Fisheye Entrance Pupil Shift. (Left) The entrance pupil (the bright spot in the middle) when looking near the optical axis appears to be about a cm of two back from the front bezel of the lens. (Right) At nearly 90 degrees from the optical axis, the entrance pupil is at the same plane as the front bezel.

This shift in entrance pupil can occur in “normal” lenses as well but usually to a smaller degree. A more detailed examination of where the entrance pupil is located and can be shifted can be found here (pay attention to p.10 in particular). So the next time some says “nodal point”, gently guide them to use the term “entrance pupil” or “no-parallax point” instead.

Notes

[1] From Wikipedia: “The nodal points are widely misunderstood in photography, where it is commonly asserted that the light rays “intersect” at “the nodal point”, that the iris diaphragm of the lens is located there, and that this is the correct pivot point for panoramic photography, so as to avoid parallax error. These claims generally arise from confusion about the optics of camera lenses, as well as confusion between the nodal points and the other cardinal points of the system. (A better choice of the point about which to pivot a camera for panoramic photography can be shown to be the centre of the system’s entrance pupil.”

Customer Service

DSC08736I recently had some problems with a lens, the autofocus stopped working in cold (but not freezing) conditions. The lens exhibited very similar issues, but on a more permanent basis, when I first got the lens just over a year ago. At that time, I had to send the lens twice for repair before it would start working properly. They replaced an internal part the second time and it seemed to work when I got it back in February 2012. I used the lens happily during the Spring and Summer in warm climates but when it got cold in late Autumn, the AF started acting up again.

After a bit of testing, I was quite certain the problem was with the temperature of the lens and wasn’t due to the camera (tried it on different bodies with the same result). The critical temperature seemed to be around 5 degrees C below which the lens would stop focussing properly. It seemed as if the clutch connecting the focus ring to the lens wasn’t releasing properly preventing the lens from autofocussing. It could have been due to an electronic part or mechanical interference due to differential thermal contraction. In any case, the lens had to be sent back. Of course, the warranty period had just expired so I wasn’t terribly hopeful that I could get the lens fixed for free.

After a few weeks, I got a message saying my lens was being sent back. I was pleasantly surprised that I wasn’t going to be charged for the repair. The box I received looked a bit bigger than the one I sent. Opening it up, I saw that instead of repairing the old lens, they’d sent me a brand new replacement. So I have to give a big thumb’s up to Sony for this customer service interaction. It makes up for the lens faults in the first place.

NEX-7 Tips and Tweaks

Some tips for optimising the NEX-7.

  • NEX-7 EVF Contrast. A common criticism is that the EVF is too contrasty and that shadows are blocked up. This is in the default settings but it is easy to rectify by using different Creative Styles. I use the Portrait Style with contrast set to -3. This gives a much flatter image with lots more shadow detail. It won’t affect the RAW file but give a more comprehensive preview of the scene tonality. I also find setting the style to Black and White helps when doing street photography as it cuts out distracting colour and focuses the eye on shape and form.
  • The dreaded iISO hotshoe. Often described as “proprietary”. Funny that we don’t usually hear of “proprietary Nikon lens mount” or “proprietary Canon vertical grip”. Read Herb Keppler’s article on a bit of history of the ISO shoe (origins date from before 1913) and the need for an improved design. Historical contingency has led to the tyranny of the masses (locked into a mechanically deficient design) so it’s just something we have to live with. The fact is that a cheap and simple adapter is all that is needed to use conventional ISO hot shoe accessories. I have no problems using normal radio triggers on the NEX-7.
  • Video button. Download and install the latest v1.01 firmware now! Having the ability to lock out the video button is worth the firmware update alone. I no longer take random clips of my feet.

 

A new year and a new website

It’s 2012 already so it’s time to begin things afresh. The old website was becoming a bit unwieldy to update so I thought it was time to move over to WordPress for content management and for putting a pretty face to it all. What really matters are the photos and I will set up dedicated galleries for showcasing my work and also for allowing clients to view their commissions. I will also amalgamate some of the blog posts I have been making at my other site so to bring things all into one place.