Here is my tips on how I set the nodal point 100% correctly on the Sigma 8mm on a Agnos MrotatorTCPS panohead.
From early 2005:
I have a method that works quite well it entails some thought but works 100% everytime.
Now this is my method worked out by me and is suited to the MrotatorT series rotators using a Sigma 8mm fisheye.
See if you can follow me as I haven't as yet built the web page or taken any photo's of this method.
- Turn your MrotatorT upside down and using a scribe or sharp blade run around the plate (with the bubble level) and mark it so when you remove the bubble level plate from the actual rotator base (3 hex/Allen screws) when upside down you will see a complete perfect circle.
- Now what I did was find the centre of this circle with some vernier callipers and two X scribe marks. "Dead centre of the circle"
- Using a centre punch being extremely careful mark for accurate hole drilling. then drill a small hole (about the size or smaller then the three hex bolt holes).
- Now, put it all back together we now know "exactly" where centre really is! This is the centre line of the tripod and where the nodal point "must" line up too in both X and Y coordinates.
- Still with me? Easy... OK now I used a length of 20lb 0.45mm fishing line and made a nice circle loop around the Sigma 8mm Fisheye lens with only "minimum" amount of slack (bugger all). When you fit the fishing line to the lens you will be amazed to see that the "Gold Ring" (the commonly know position of the nodal point) has a slight "detent" and the fishing line fits "beautifully" within the detent groove.
- Now we need a "Plumb Bob" I used a 150gram steel bugger. Now your getting the picture aren't you? BUT WAIT! You need to attach it in a special way to your fishing line loop you made earlier. It "MUST" be attached with it's "own" loop of fishing line. These "TWO" separate loops are very important as they operate independent of each other and must have minimum friction.
- Now that done, you set the tripod up on "perfectly level" flooring and make your adjustments to the X and Y of the camera fitted to the MrotatorT until the "Plumb Bob" points exactly to the centre of the hole you drilled in the MrotatorT bubble level plate. Once you have achieved this I will tell you that you are as close as possible to the nodal point as you will ever get using a Sigma 8mm Fisheye Lens. Remembering that the nodal point is "NOT" in a fixed location inside a fisheye lens when being rotated. But the nodal movement is minimal.
I have since thought of some improvements to this system I worked out but I will save them for the day I publish my web page. The reason I have not added these improvements to my own set up is because once I set mine I have been happily shooting panoramas and didn't see the point in upsetting a perfectly good nodal point position only to help others and cause myself the extra work.
I don't offer a 100% guarantee. But for me it has been the "Most" successful, least "Painful" nodal point set up I have ever done! No need for numbers or taking a thousand photo's and stitching and checking etc.