I notice that these lenses have hugely different element counts and very different amounts of special glas. Nevertheless, higher element count and more lavish use of special glas does not necessarily lead to better performance, or does it?
What are the reasons?
Sigma 90/2.8: 11 elements, 10 groups. 5 SLD elements, one aspherical element
Voigtländer 90/2.8: 7 elements. 5 APD elements.
Loxia 90/2.4: 7 elements. 3 APD elements.
What is it, that higher lens count does not appear to lead to better resolution, or does it?
And higher APD/SLD count: Does it lead to better correction of LOCA and lateral chromatic correction?
In which way does lens perfection and perfect spacing (Zeiss quality) compensate for higher lens counts that other lenses may need to achieve similar performance?
Is close up performance a differentiator between these lenses and a reason higher lens counts are needed?
There are just so many things I do not understand here.
Is that an apples to apples comparison? If the design goals were the same, then maybe, but Sigma's need for the more complex lens may have been determined by the relatively tiny size of the lens.
Knut. wrote:
What is it, that higher lens count does not appear to lead to better resolution, or does it?
And higher APD/SLD count: Does it lead to better correction of LOCA and lateral chromatic correction?
I am not a lens designer, but I have researched this recently due to curiocity. Think of the optical elements or exotic glass as inputs into an optical formula. More inputs = more possibilities. And a lens designer deals with a huge number of possible trade-offs across several conflicting dimensions:
- resolution
- focusing method
- minimal focus distance
- optimal focus distance
- field curvature
- manufacturing tolerances
- several types of aberrations
- target sensor stack
- distortions
... and probably many more I'm not even remembering. Basically, each formula is a set of trade-offs. For example, the Voigtlander is a unit-focus lens which is a choice not available for AF lenses.
