3 TECH Q's

1. Does the nodal point change on PC lenses as perspective adjustments are made, making the lenses impractical to use for single row (stitching) panorama image making?

2. Has any reliable testing been done on Focus Stacking software to learn it's effect on image sharpness, dynamic range or whatever? Does camera "noise" present in each file build up as multiple files are stacked resulting in a more noisy final image?

3. Concerning the vibration caused loss of image sharpness in all 36mp cameras at low shutter speeds: If what causes the sharpness loss is the shutter first curtin and mirror movements in camera, why is it that the problem dissapears at higher shutter speeds given that what causes the problem is equally present at all shutter speeds?

I needs to knows before the money flows.
TIA

1. Possibly a little bit but not enough for it to really matter IMHO but I have not tested this.
2. Not sure about testing but I wouldn't think it would change noise since it utilizes different parts of different images. Not something you probably need to worry about.
3. Shutter vibration is more pronounced at shutter speeds that aren't fast enough to freeze the motion or are so long that the effect of the shutter movement is an insignificant part of the exposure. In general speeds of 1/40 to 1/4 seconds are most susceptible and it tails off from there. A camera with an electronic first curtain capability like the D810 completely eliminates this. So it is not ALL 36 mp cameras. My review of the D810 covers this in some detail including how to set up the camera to completely eliminate all internal movement in the camera at the time of the exposure. It starts on page 6: http://www.ejphoto.com/Quack%20PDF/Quac ... 202014.pdf

Noise should be lower than the alternative of cropping from a single exposure as you are gathering more light in total (more photons) and at a given final image size you have more pixels on the subject. Without a PC lens you have to have the horizon mid frame and take extra frames to allow you to crop to final composition

For focus stacking sharpness should be higher as you shoot at optimum aperture and take only the best of the pixels to add together, there is probably some blending or averaging in the overlap so directionally this should reduce noise but I suspect it would take detailed analysis to find the difference.

In both cases (panorama stitching and focus stacking) what is the alternative? For panoramas you could crop from a single frame, but the quality will suffer from up sampling to get to the final image. Or you could take a whole lot of extra frames to allow you to crop to your desired composition.

For focus stacking, you can stop down but you lose sharpness due to diffraction or potentially you can't stop down low enough to get the full DOF coverage that can be achieved with stacking. So the issue is moot in my view as even if it does suffer a little due to what the software does, it is better than the alternative or can't otherwise be achieved.

STEVENMAJOR wrote:1. Does the nodal point change on PC lenses as perspective adjustments are made, making the lenses impractical to use for single row (stitching) panorama image making?

2. Has any reliable testing been done on Focus Stacking software to learn it's effect on image sharpness, dynamic range or whatever? Does camera "noise" present in each file build up as multiple files are stacked resulting in a more noisy final image?

3. Concerning the vibration caused loss of image sharpness in all 36mp cameras at low shutter speeds: If what causes the sharpness loss is the shutter first curtin and mirror movements in camera, why is it that the problem dissapears at higher shutter speeds given that what causes the problem is equally present at all shutter speeds?

I needs to knows before the money flows.
TIA

Hi Steve,

I'll give my opinion,

1) PC lenses will work fine as long as they are not running windows 8.  The lens should be running Mac OSX or Linux.  Oops, sorry--not that PC.
It will depend on the lens design.  With a tilt-shift lens, and a strong tilt, the back focal distance changes from one side of the tilt to the other.  Thus the parallax could be variable.

I come from a 4x5 view camera background and did a lot of tilts, rises and swings, including mosaicking scanned 4x5 together.  Nodal point was never a problem.  (examples in my mosaics gallery).

2) ALL resampling loses sharpness due to statistics of sampling and also increases noise.  Interpolations/extrapolations must be done, and just like downsize resampling, one may need to sharpen after the resampling.  I do not worry about sharpness or noise in my mosaics, or the degradation from noise.  Usually, there are so many pixels, it is simply not an issue.

3) The reason why vibration does not affect image quality at all shutter speed is due to momentum.  Given an impulse with a shutter opening, it takes some time for to move the massive camera.  The shutter speeds where image degradation is most pronounced will depend on the mass of the camera and the impulse it is given.

Reading between the lines of what I think you may want to do, here is what I do.  I have pretty much replaced my 4x5 with digital mosaics.  I have a home built pan head that keeps the DSLR in landscape orientation.  I do all mosaics in landscape orientation.  That way the near to far distance in the typical landscape frame is the short side of the frame.  Then I let focus shift from frame to frame using standard lenses, no tilt-shift needed.  I also don't worry about the horizon: any curvature I fix in post processing.  I use ptgui pro.  I fix perspective distortion in photoshop (in palce of rises at the lens).  Sometime I also do different exposures on different rows, e.g. land versus sky and pgtui handles it amazing well.

Examples:
http://www.clarkvision.com/articles/large_mosaics/

http://www.clarkvision.com/galleries/gallery.mosaic/

Roger

1.  Don't know

2.  Don't know

3.  Seems to me…..the image softness you refer to is caused by the vibration resulting from the mirror slapping (or slamming) into the frame (shutter box?) at the end of its upward travel.  

Seems to me that this slamming is violent enough that there is remnant vibration as the shutter(s) is(are) still traveling across the front of the focal plane.   

Of course, if the camera is of small enough mass, then even the shutter/mirror momentum might very well cause some image softness.  And this is one reason why I greatly enjoy a massive DSLR….over a DSLR of lesser mass    

In my mind, an extremely fast shutter speed can eliminate (or virtually eliminate) any of that image softness that occurred when the mirror slammed into the frame or shutter box.  And BTW, wouldn't this image blur from vibration occur even in lesser MPX DSLR's?  We just would not normally see it except in the highest MPX files.    

While shooting last Summer it appeared to me that that threshold (the one needed to stop that image blur) was reached at 1/3200 second (when shot with my D610/battery grip filled with batteries).   

Greatly slowing everything or dissecting the camera…..one might get a perspective of what is happening:          

https://www.youtube.com/watch?v=0dVmGVa3Rbw

https://www.youtube.com/watch?v=fyqbIuTzRVI

Robert King

Thanks all for the help and suggestions and for disposing my concerns. The links provided understanding to the concepts expressed for this seeing is believing fellow.
Great