UYOk has The Petzval design - which is what this is - dates from 1840.
https://en.wikipedia.org/wiki/Petzval_lens
Singlet lens - no attempt to correct for dispersion (chromatic aberrations)
Doublet lens - better: corrected for two wavelengths
Petzval - better than a doublet and cheaper to make than a full triplet APO.
Triplet - corrected for three wavelengths
Refrlector - corrected for ALL wavelengths.
For refractors there is a trade-off: colour correction vs cost and durability. Recent glass types have tipped the balance in favour of triplets in the range 80-130mm aperture though IMHO beyond that catadioptics are good for 120 - 250mm, beyond that reflectors reign.