Which is better? Assuming they are using the best glass.
1) ED triplet objective lens + ED singlet lens field flattener
or
2) ED doublet objective lens + ED doublet lens field flattener
Look forward to your replies!
Which quad APO config is better?
Option (1) though having the advantage of a simple construction, nominally requires the FF mounted close to the imaging plane (minimizing colour aberrations). This leads to the augmentation of the effects of small surface irregularities (such as scratches) and any dust particles would be visible as shadows on the imaging plane. Usually such a resulting FF will also be a source of internal ghosting reflections and will require it to have good antireflection coating properties.
Option (2) will not need to have the FF mounted close to the imaging plane, and causes fewer focusing and mounting problems. But this in effect will require the FF to be achromatized to suppress colour aberrations (hence double), and each FF element would be of a different glass type (one crown, one flint, etc).
Option (2) will not need to have the FF mounted close to the imaging plane, and causes fewer focusing and mounting problems. But this in effect will require the FF to be achromatized to suppress colour aberrations (hence double), and each FF element would be of a different glass type (one crown, one flint, etc).