The problem with this notion is that no population of creatures with flat eyespots shows any sort of intra-population range like this were even a small portion of the population has dimpled eyespots to any selectable degree.This is a common assertion, but it just isn't true.
Now, if these 1,829 gradations really evolutionary steps that are in fact small enough to cross in fairly short order (a few generations each under selective conditions), it seems quite likely that such ranges in morphologic expression would be seen within a single gene pool of a single species. Species that have simple flat light-sensitive eyespots only have flat light-sensitive eyespots.
No individual within that species shows any sort of dimpled eye that would have any selective advantage with regard to increased visual acuity.
(The exact size that is "perfect" depends on the brightness of the lighting in a particular environment.) An example of a narrow aperture lensless eye is found in the chambered nautilus. To get a lens, a ball-shaped mass of clear cells with a slight increase in the refractive index is needed.
Once this mass is formed, it can be refined with very slight increases in the refractive index to produce greater and greater visual acuity.
The ratio of the proteins can be different in different places, so the lens material is not optically uniform.