Not sure if this is the right thread, but I'd like to chime in that whatever you guys come up with, I'd LOVE for it to do 11x14. Not being able to scan 11x14 easily in my house is probably the #1 reason I have not gotten into it yet. My wallet will thank you if you ignore the request I just wrote.
Hi John,
There's no reason, other than available space, that this type of system couldn't work with 11x14. You probably wouldn't need to work at 1:1. You could save space by having the camera move instead of the negative, but that would be more complicated to do.
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
On the note of distortion, simply imaging a very detailed slide and allowing software like PTGui to optimize for lens distortion parameters, and keeping tabs on the outliers, control point errors to be culled, and re-optimizing the stitch until you have a control point error of 1 or even less will characterize a lens more than well enough for ultra accurate stitching. Those parameters can then be saved and reused, obviating the need for any future lens distortion optimization. What's left is simply to align and blend. It seems prudent to let the software take care of distortion and not give it much more thought.
You're right. I'll use a fisheye lens and let the software do the work.Originally Posted by Daniel Moore
Of course, that's an example of reductio ad absurdum, but the point is that the less distortion there is to begin with, the fewer the pixels that have to be moved (stretched, smeared, averaged, interpolated, etc.) by software.
I've completed my assembly (no light source yet), and have been measuring it with a machinist's square (ground to <16 microns accuracy over 6"), and with a bit of adjustment, I believe my system is square and parallel within one or two thousandths of an inch. It required buying the right sort of stuff, but beyond that it wasn't that hard. I put a clear ruler in place of the negative and moved it throughout its range--no change in focus, no wandering off line, etc.
Rick "film at 11, probably in the first thread" Denney
Note to rdenny: *while stitching with fisheye lens captures is possible, it isnot advised. I should have been more thorough in my response, my apologies.
And that's an example of a strawman argument, as Daniel was not suggesting otherwise. His suggestion wasn't very different from your suggestion of correcting distortion in raw software. We all agree that we should work at minimizing problems through good hardware design, while making whatever improvements are practical through software.
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
Hey, I said it was reductio ad absurdum.
So far, we've had a train of people saying something that sounds like, don't worry about the mechanics, you can fix it in software--you'll never see the effects.
But there is obviously a point at which the effects will be visible, as the reductio ad absurdum is intended to illustrate. (That is NOT a strawman--it is a completely legitimate form of argumentation.) Do we know where that limit is? I rather doubt it. But I certainly don't want to find it by accident, negating all my expense and construction effort and having to begin again with a different precision requirement. When pixels have to be moved, there is loss. Less loss is better.
I feel a bit like you feel, Peter, when people question whether this project is worth doing. This is now the third or fourth time I've felt the need to defend mechanical and optical precision so that we can minimize software-based corrections.
Rick "especially since mechanical and optical precision just isn't that hard to achieve" Denney
Rick, you'll use the best lens you can. You'll then have to correct it's distortion. No defense of measures of precision is necessary. It's inescapable that you'll need some lens correction and this is the one thing that weighs the least in this project since the software is that good, so that parts really 'done' in my opinion. Bigger fish to grill.
A further note, as it occurs to me, which it doesn't immediately, that obscuration of detail in blending at the seams could be a substitute for lens correction. Let the seams go and slap some paint on 'em is another alternative, but hardly a substitute for single or smaller pixel accurate seams.
Daniel, you are right, of course. I did not connect your post to my statements two pages back, but I see that connection now.
I have actually followed your process using not PTGui but Panavue, which allows the placement of control points. I did iterate on lens correction until I could make my control points align perfectly for a panorama that was based on a Canon 20-35 zoom, which suffers from fairly significant barrel distortion on the wide end. Those nine images were a lot of work! Of course, for that one, I was also bending it into a cylindrical projection, and it was not helped by the fact that I did not rotate the camera on its nodal axis--a troublesome error. I thought it was worth the effort.
Nisqually Valley from Mount Ranier, linked only because it is not large format.
I have also attempted simple positional stitches by scanning both ends of a 6x12 film in my Nikon scanner's glass holder. I never got a clean stitch, simply because I had to turn the film around and one image was always slightly rotated from the other one. The small rotational correction, when the software could find it (I was using Photomerge which doesn't have control points--my version of Panavue is obsolete on my current machine), always took the edge off parts of the image. I went back to the glassless carrier which allows the two scans to be made without repositioning the negative, and the machine precision was sufficient to support a pixel-perfect stitch with no blending. That seems a bit more like what we are hoping for here, except, as you say, lens distortion is the one major difference. That is part of what is driving me to attempt high levels of mechanical precision, though.
Rick "who's done just enough stitching to know how hard it is to do well" Denney
Hi Denny, I've been using stitching for years for studio product work and interiors. Using a 4x5 camera and a stitching adapter plate I get a 4-up matrix of images that overlap by 6mm. I focus on the groundglass of my 4x5 and it's simple and repeatable. The 4x5 camera eliminates the distortion as the camera remains fixed and the capture unit (DSLR or digital back) is what moves. The images ALWAYS line up. Working with a Canon 5D (MK1) in the studio I churn out 43MP files from a "chip" that is 42 X 66mm in size.
I work in PTGUI (pro version) and have it set up to "remember" my stitch pattern, helping with areas of soft focus or low detail. I recently had a project photographing some 30x40 watercolors for use on billboards, essentially the camera was used as a "scanner" and the results were exceptional. I shot a 9-up pattern with a 33MP digital back that covered almost the entire 4x5 glass. The finals "shots" after stitching were over 250 MP and the client called to ask how I did it.
MultiStitch
Large format digital capture
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