Originally Posted by jaychatbonneau
Thank you for your nice reply.
While 2.35 and 2.40 are often used interchangeably, they are not the same thing. For example, using a 2.40 lens with a video processor that is stretching for 2.35 would introduce sone unsightly distortion. That is why there are 2.40 lenses, 2.37 lenses, 2.35 lenses, and video processors that let you stretch by different percentages. Also, the Sony 500ES has a native aspect ratio of 1.89 not 1.78.
I really have three questions:
1. Will I need a separate video processor to use a 500es with a 2.40 lens? Can the internal video processor be adjusted to do the appropriate stretch? I know it can for 2.35 lenses.
2. If the 500es can't do stretch for 2.40 on its own, how much stretch do I need to program the external video processor for? Remember the native aspect ration on the 500es is 1.89.
3. How precisely can aspect ratios be entered into video processors? Limited to two digits after the decimal?
Thanks for your help!
Anamorphic lenses for home theater projection stretch the image horizontally by 33% or (compress it vertically by 25%). What you end up with is a 2.37:1 aspect ratio when extrapolated from a 16:9 display (1.78 x 133% = 2.37). AFAIK, no HT lens manufacturer differentiates between a "2.35:1 lens" and a "2.40:1" lens (or even a 2.37:1 lens), at least in terms of manufacturing two different options. I believe some of the Prismasonic lenses allowed for variable stretch, but I am not familiar enough with their product to know how this is implemented.
Just about any video processor used for electronically stretching the image does so by the same 33%. Lumagen processors do allow for variation lesser or greater than 33%, I believe. If you want to stretch material to compensate for the rare film that falls outside of the 2.35:1 / 2.40:1 ratio "family," a Lumagen would be a good investment. Otherwise, you are left with the same 33% stretch that just about every projector manufacturer has built in. Normally this is not an issue, since it works with just about any consumer anamorphic lens available.
To add further confusion, aspect ratio is also influenced by throw ratio. If you are in the lens "sweet spot" (typically around 3 - 3.5X screen height back) you will end up with around a 2.37:1 aspect ratio from the lens itself. If one were to pair this lens with a 2.35:1 screen, you would have an image that slightly bleeds into the left and right screen surround for both 2.35:1 or 2.40:1 material, and barely perceptible letterbox bars for 2.40:1 material. If you choose a 2.40:1 screen, you end up with the opposite - slight bleed top and bottom.
But all of this is also dependent on throw ratio, like I originally stated. If you have an extremely long throw (say, 4 or 5X screen height), the projector / lens combo will create an aspect ratio of less than 2.35:1 (perhaps, 2.25:1). Conversely, if you have an extremely short throw ratio, you will end up with the opposite problem (a ratio of greater than 2.40:1). This is true of any anamorphic lens, regardless of manufacturer. Fortunately, the cast majority of installs fall into the sweet spot and this is not an issue.
RE: the Sony projector. The Sony has a 1.33X stretch built in for consumer anamorphic lenses, and a 1.25X stretch built in if you want to use a "professional" anamorphic lens (one used in commercial cinemas). I don;t know of anyone using the latter solution.
That said, it is important to note that the Sony will not vertically stretch native 4K content! The above applies to 1080 and lower resolution content only. If you want to scale native 4K you will *probably* need a Lumagen (I say probably because we have not confirmed compatibility with Lumagen regarding Sony 4K content yet).
As for the difference between scaling 2.35:1 or 2.40:1, it is really so negligible as to not be worth worrying about. It is amazing how much you need to mangle geometry before it becomes noticeable.
Kelvin might jump in and comment on his ISCO 1.25X lens.