Sony has two quality levels of optics. The standard lens is impressive, especially when compared to the optics found on many lower cost 4K DLP projectors (selling for 1/10th of Sony's price).
The ARC-F (All Range Crisp Focus) lens is Sony's premium projector lens and it is used in Sony's more expensive models like the VW1025ES, VW5000ES and the GTZ380. The main reason why the VW1025ES is $20,000 more than the VW915ES is that ultra-high-quality optics are very expensive, and you're going to enjoy a sharper image for your greater investment.
The ARC-F features an 18 element all-glass large-aperture lens that includes six Extra Low-Dispersion (ELD) elements) that ensures outstanding focus across the entire screen and significantly reduces chromatic aberration (color fringing). If you are projecting onto a massive screen, it is worth the premium to be able to extract every ounce of detail from the 4K SXRD panels.
The ARC-F also lets more of the laser light source’s brightness reach the screen increasing the VW1025ES rated brightness by 300 lumens compared to the VW915ES.
For maximum flexibility Sony offers an optional short throw version of the ARC-F lens which can also be utilized with the VW1025ES.
So while upgrading to an ARC-F lens equipped projector is an expensive proposition, it may be worth it to those who want to extract every bit of detail from Sony’s native 4K SXRD panels.