Of Parallax and Nodal Points
For a while now my good buddy David Orr and I have been discussing ways to get higher resolution. Yes, MORE MEGA-PIXELS! Now I know right off you are thinking “Dude the mega –pixel war is just pure bullshit”…well, Maybe. For the majority of people that do nothing more than snap and share. You are completely right. For that one only needs a 2mp camera and with that I am being generous because I know people crop. Even your average photographer that is an advanced hobbyist, a 16 – 20mp camera is more than sufficient. Even I, if I only printed as large as my Canon Pro-100 will go – 12” x 18”, The 20mp from my Canon 6D is just perfect to do that print at Fine Art Quality.
But the thing is for me, I sell a lot of prints and more and more people want LARGE wall filling prints. The majority of my prints are 24” x 36” up to about 40” x 60” and even larger. In fact, I’ve done two prints that were wall filling metal prints at 10’ and 12’ wide. That takes a LOT of Mega-Pixels. While I can use some tricks like using ON1 Perfect Resize I can get away with my relatively small number of pixels. As long as I can maintain 100 ppi. It WILL print. But the truth is you need 240 – 300 ppi for the size print you make in fine art quality. And people spend a lot of money, I want them to have the best even though with the long viewing distance of a large print you can get away with less. I want to please even the pixel peeping photographers out there.
The reality is, I need about 50mp. Second reality, I’m a professional photographer and in this new world, well we don’t make much money and we can’t afford the equipment that is out there. The good stuff usually goes to people that have a “real job” and can afford the nest as a hobby. So, David and I wanted to explore how we could do this on a budget using mostly what we had. The first solution that came to mind and the subject of this piece is Stitched Multi-Exposure Panos (Panoramas) except we are not so concerned with the “Panorama” aspect of it. as we are shooting multiple images and combining them for a higher Mega-Pixel count. 50, 75 even 100mp+
If we were going to do this well we needed the right equipment t. While you can do panos even hand held. It’s best on a tripod and one that has a Pano Head or a rotating head outside of the ball head. But there still is a problem even with that. The problem of Parallax. Now I’ll let you Google that cuz Its complex and even sometimes I have a hard time wrapping my head around it. But do this; Close one eye and line your thumbs up in straight line going out from you. Now close that eye and open the other. See how the thumbs are no longer lined up? That’s Parallax Error and what this means is that objects that are relatively close to each other, and those to the background subject will line up differently from frame to frame as you swing your camera to make the panorama. This error confuses the Panorama Software and leads to smearing, bloating, distortions, loss of sharpness or even worse, two of the same object in the image cuz it was that far off.
We needed a way to get past that. Problem is, that’s expensive too. What you would need is a Panoramic Gimbal Head set-up. Companies like Really Right Stuff and Nodal Ninja make them but in the right configuration they can set you back $700 and that not counting a Leveling head – which I found out later may be more important than the pano-head – Can set you back another $300. That’s a $1,000+, Heck I’d really like another lens for that. So, was there a way we could do it on the cheap and still get MOST of the way there?
So, what we thought was; Could we take just one piece of the set-up, the Nodal Slide and make that work? That is what I tried and the actual subject of this article. (I’m not really going to go into how to shoot Multi – Row Panoramas. People that have been doing it a lot longer than I have get articles and videos on it, Let Google be your friend)
The equipment I started out with was an Oben CT-2381 Tripod and an Arca Swiss Monoball Z1 sp (Single Pan) Ballhead. This Ballhead in the SP edition allows for Pano rotating without the need to loosen the ball itself. So, it, by itself, could be used for Panos and is one of the reason I bought it years ago, besides being a great ballhead.
For the trial, I bought a Really Right Stuff MPR-192 Nodal Slide & Mini-Clamps Package for $180. My intentions are I want to shoot with my Canon 70-200 L 4.0 at either 70 or 100mm and try to get the same Field of View as a 24 or 35mm image but with multiple images to get 50+ MP.
Setting it all up
So, I mounted my Canon 6D with 70-200 L 4.0 using the lens collar onto the clamp of the Nodal slide. Now you need to find the Nodal Point or more correctly the Non – Parallax point or Focusing Center of the lens and have that rotate directly over the center point of the tripod. After watching a few videos, it didn’t seem that hard. I just needed two objects in line with each other and be able to swing the camera, that was also in line with those two objects. left to right and see right in the VF or Live View when the two objects stayed inline, no matter how you swung the camera. When it was, cool and that should be it. OK well not so fast. I first tried two support posts for my carport. Nope, couldn’t see anything. OK Maybe I need to be farther away. Tried two palm trees. nope even worse. So then copying what I saw on one of the videos I got out two light stands (flash) and placed them in line and I got REAL close to the front one. THAT worked perfectly and I could see Parallax movement. Even with the longer focal length which don’t show as much as using wider angle lenses. But I needed the long lenses because I wanted More Frames, more frames, more total Mega-Pixels….allowing for some loss due to overlap that is necessary for Pano software to work.
So, I was able to get the nodal point for the desired focal lengths (it’s different for every focal length) I made marks with a silver marker on the slide for 70 and 100 MM and then I also did one using the 40mm Pancake Lens I have, as there may be times I want to use that lens too. What I found was the 70-200 really needs to be far back on the slide, like almost awkwardly TOO far back and I’m kind of glad you have to have the tripod level to do this since the whole works would be almost at the tipping point. So, it shows how forward the Focal Center is on that lens. What was even more surprising (not really cuz I knew this) was that the focal center of 40mm pancake lens was at or actually a little in front of the front of the lens. It’s a clear way to see how pancake lenses work in that; how do you have a 40mm Focal length on a lens that isn’t 40mm deep?! The answer is, the focal center is out in front of the lens.
Equipment set, now on to the testing
Well, doing my tests on a few Pano/Hi Rez images made just using a Nodal Slide worked just fine. I did images that were shot at 100mm in the vertical position and 3 x 6 (3 rows, 6 frames each). I overlapped approximately 30% side to side and 50% top to bottom This yielded a 14400 x 9600 48 x 32@ 300ppi, 138mp image. Next, I did a set at 70mm 3 x 4. This yielded a 10800 x 6200, 36 x 24 @300ppi 72mp Image. My hope was to duplicate the Angle of view of a 24mm lens but at higher resolution, I didn’t quite achieve that and instead had the angle of view of about 35-40mm which was still fine for the subject. I then went back and shot at 50mm a 2 x 4 which yielded a 54mp image but more closely approximated 24mm FOV
To Download Full Size File Click Here
Now I knew that if I was doing single row panos just using the nodal slide would be fine, in fact it could easily be done just with a Pano Head and no Nodal slide. But would a Nodal Slide be enough to A: not have any parallax and B: have any worsening of Keystone distortions because the camera was rotating up and down at the ballhead and not centered over the ballhead as would happen when using a Gimbal + Nodal Slide setup. The gimbal would/should keep the Film/sensor plane over center, without it the film plane would move slightly forward or back depending if the camera was shooting down or up.
As it turned out, because I was shooting with such relatively long focal lengths, neither was much of a problem. I did not have any problems with parallax in the foreground where it should have been noticeable and because the focal lengths were so long the lens did not really get angled up or down that much. The images stitched easily and quickly in Lightroom.
What really turned out to be more of a problem was while I initially got the tripod very level the soft sand shifted and the more I shot the less level the panos became. This was FAR more of a problem than Parallax or Geometric distortions. As can be seen in this un-cropped image. This would a reason why you may want to add a Leveling Base below the Balldead and slide. Just to make that adjustment easier. BUT it comes at a $300 Price tag, so I think I could just keep a better eye on my tripod level
A few days later I repeated the tests out in Joshua Tree National Park and even stepped up the game. Shooting 3 x 7 100mm sequences to try to better duplicate 24mm (it did perfectly and yielded 118mp with overlap – It’s less MP than the 3 x 6 because I overlapped at about 50%). The images contain Cholla Cactus about 20’ forward of the camera so that really would be a good test. Again, there was zero problems with Parallax or Distortions. So, it proved good enough to me that I don’t really need the entire Gimbal Swivel setup.
Here’s that image, Excuse any spots or smears in the sky, they are the product of a botched sensor cleaning.
To download The Full Size Watermarked Pano Click Here
To download the Standard 24mm Single image Click Here
However, this produced a new dilemma. One of Depth of Field. Now I want the mountain in the background to be super sharp for a High Rez, something sometimes lacking in a single image. But of course, I also want the foreground to be in the Field of Acceptable focus. Using a normal 24 Mm Lens and focusing at infinity at f/16, the hyperfocal distance would have been 4’. So, everything from 4’ to infinity would have been in the acceptable filed of focus. If I focused at Hyperlocal than ½ the distance (2’) to infinity would now be in focus. Looking at this scene the closest object was about 20’ away. So, it would not have been a problem.
But now we switch to a 100mm lens, focused at infinity the hyperfocal distance is 68’ So only things that are from 68’ to infinity are in acceptable focus. OK so you say I could have focused at Hyperfocal, ½ that distance would mean now 34” to infinity is in focus but that still yields my 20’ foreground cactus outside the field of focus. OK, so how about doing the bottom row of exposures focus on the foreground subject distance. And I did try this. So, here’s the next problem; A 100 mm lens focused at 20’ has a TOTAL DOF of only 12’ so that mean 8’ behind my subject the focus falls off so there still will be this transition zone between, the foreground and the Infinity Focused other two rows of images. It’s something to work out but the answer may be to shoot at 70mm cuz the numbers may work out better. Still a work in progress.
Finally, back home again, I tried out using 40 MM pancake lens to make a simple 24mm FOV with just 2 x 4 shooting and yielding 58mp image. Again, no parallax errors but because of the short focal length you can see this is where a Gimbal would make a difference. NOT enough to make me buy one. But you can see how the keystoning of the up and down images splay out more and I believe are exaggerated by no longer being over the ball center. So, as you rotate more to each side, the lower corners droop down more. In the end, it still was not a problem because the software set to Perspective and Not Spherical ironed it all out
Just buying a Nodal Slide and doing long focal length Pano/High Rez images works out just fine. Except for maybe the most demanding people that pixel peep to the enth. It’s enough. In fact I would go so far as to say you could even do it without the Nodal Slide but I think it is worth the $180 investment…for me. I do think if you want to shoot at wide angles, 50mm and less, then a Gimbal /Nodal Slide / Leveling Head, would probably be what you want. But for myself I have to question; At $1,000+ for that setup…. would I just rather put that towards a 50mp camera? The answer for me is: Yes. Pano/Hi Rez is fun and it’s challenging. It’s neat because you don’t exactly know what you will get till you get home…almost a film like experience. But do I really want that “all the time” ? My answer is no. For the most part, I want to spend the majority of my time just “seeing” and this process can get in the way. And it just doesn’t fit every subject. Shooting at the ocean with a moving surf is just ridiculous to align. Doing long exposures, just would be pure luck. So no. Will, I do it for now when circumstances warrant? Heck yeah. Nothing like zooming in and seeing a rock at 300 meters away clear as can be. And being able to print a 40 x 60” at full 300 ppi resolution. That’s pretty darn cool.
So, in the end, I’m glad I spent the $180, I think that investment was worth it and I know I will use it like I do all my other tools of Filters and lenses to bring my vision to fruition.