hkv wrote: ↑Wed Aug 12, 2020 12:05 pm
I want to understand more how the OLPF affect image quality and resolution. I was assuming that at high magnification, e.g. 20X+ the Abbes diffraction limit would be more limiting than the OLPF. I may be wrong, but I made an excel trying to calculate the resolution needed of the sensor at different magnifications. At low magnification, I would need a sensor resolution closr to the A9 (which has 24 megapixels), but at higher magnification, it drops dramatically. At 60X and the N.A 1.2 (water immersion), the sensor pixel density must be only 5,25 megapixels to capture all the details. I would assume the OLPF then makes little difference. Here is my list at different magnifications and assuming a Nyquist theorem factor of 3 (2 is normally enough, so figures should be even lower).
4X - 20,99 MP
10X - 20,99 MP
20X - 18,44 MP
40X -7,40 MP
60X (Oil) - 6,64 MP
60X (water) - 5,25 MP
100X (Oil) - 2,57 MP
So my question is how the OLPF really can limit the sharpness and resolution using e.g. a 60X objective when a sensor resolution of 6 MP should be enough and it is being captured using 24 MP? Help me to understand this! If I can improve resolution and sharpness I will for sure remove the OLPF on my A9!
Interesting thought, I think you're on the right track. I need to consult someone with more knowledge.
What I know is, the OLPF is a net negative to our stuff no matter which way it is sliced. That said, we are usually more limited by the objective's power, especially with Mitutoyo lenses that most use for reflected light.
It's hard to say which matters more. Nikon's entire sensor stack for the Z-mount is only 0.7mm. Sony's presumably older models has thick sensor coverglass, which is detrimental to UWA lenses. Examples can be seen here:
https://www.youtube.com/watch?v=NJBGAbcZc7s
https://www.youtube.com/watch?v=PMfshUJGZow
(Unfortunately the author seems to deny the existence of this problem, despite it being well known)
Here's why:
https://www.lensrentals.com/blog/2014/0 ... it-matter/
Leica engineers seems to be fully aware of this problem, same as the ones that engineered the Z-mount cameras, as the sensor glass is very thin. For Nikon, it's a requirement as many of us would like to adapt the 14-24mm.
As for your MP calculations, would you mind sharing the formula? They all seem off to me, by a huge margin actually.
Assumptions: 550nm, monochrome
60x water, NA 1.2: 18.1529MP
100x oil, NA 1.25: 7.091MP
Since we are using colour sensors, the results should be multiplied by a liberal amount to account for debayering errors and other "esoteric" stuff. I usually toss in a factor of 2. This means an Oly 20x Sapo would work incredibly well with a 65MP monochrome fullframe sensor, which translates to above 100MP in colour as losses are accounted for. Assuming your 10x is the UPlanFL with an NA of 0.3, it gives ~41MP, so easily suitable for 60MP FF sensors.
Here's the formula I use:
https://www.microscopyu.com/tutorials/m ... resolution