Flip Images Sharper/Better?

[Peter Moretti]

I have heard anecdotally that flip modules actually improve image quality. Is this the case and if so, how/why?

I'm not talking about eliminating any degredation that comes from flipping the image in post, rather an actual better image coming right off the adapter.

THANKS.

[Bob Hart]

Peter.


With most erecting or flip paths, the prisms, or mirrors or hybrid of both folds the path back on itself or sideways then straight again as it rotates the image in four reflective stages.

For the 35mm sized image to be covered without vignetting, prisms or mirrors can only be so small before vignetting occurs. The physical size of these component require the path in most instances to be at least 125mm from groundglass to the first camcorder optic.

I managed to get the flip enclosure even shorter by implementing a porro-prism layout, offsetting the image to the side as well as upward and placing the reclining rear-facing prism over the top of and in a forward position overhanging the groundglass disk.

This layout is not an option for orbiting or elliptiod groundglass motion systems.

The collateral benefit of the longer path is that the camera is set furthur back from the groundglass in an optical sense but remains physically close.

Any tendency for the corners of the flat surface of the groundglass image to be softer is minimised because the distances from camcorder to all parts of the groundglass surface vary less than if the camcorder lens is closer, which is a common non-flip setup. A non-flip adaptor which used the same non-folded direct path length would be too long to be of convenient useability. The image quality would be slightly better without four extra reflections gpoing on.

[Dennis Wood]

Peter, this is not necessarily true although if you compare Brevis flipped vs non-flipped footage, there is a noticeable difference. There are a few reasons for this, the largest being the design of our flip achromat. It is purpose designed to reduce both spherical and chromatic aberration given the parameters of it's intended use. The system was a year in the works, and it was worth it. FreshDV has explored the Cinevate flip sharpness issue quite thoroughly.

We'll be posting all 8 of the Brevis "Video University" segments for public viewing (starting this week) as well as an extensive testing series featuring the HV20, XH-A1, and HPX500. The DSC labs rear illuminated Ambi system, with a set of 72db (12 stop), resolution, and chroma OSGs will be used.

One of the fascinating things we've found already is that the bare XH-A1 has more chromatic aberration (a lot actually) then the same camera shooting through the flipped Brevis + 50mm f1.4 fd. This clip demonstates also why the Brevis can be 4 stops more efficient than anything else out there, when the 35mm lens is stopped down to f5.6.

[Bob Hart]

I should have qualified in my previous post that it is possibly easier for a mug home-builder like me to get better results with a long-setback arrangement with store-bought components than the close-setback arrangement.

Bout time I sat back and kept quiet methinks instead of offering blind alleys to readers.

[Dennis Wood]

You're advice is better then you think Bob. We had some very good results with a 58mm very weak achromat whilst using an 18" lead tube :-) The form factor leaves much to be desired..but for an off the shelf experiment, it worked quite well.