MTF of new announced 600/6.3 PF Z-lens

[MEPER]

Such MTF's looks promissing?
I know you can't judge image quality by looking at MFT.

[Birna Rørslett]

MTF is an indicators for image quality, but not necessarily the only one to pay attention to. The lens should deliver images with high contrast  -- and sharpness of detail --  but are they pleasant to the eye as well? MTF cannot tell that.

By the way, long lenses tend to have "better" MTF curves than their shorter siblings. and given the lens is f/6.3 wide open, one likely will expect MTF figures in this ballpark anyway for a modern design.

[Frank Fremerey]

Tempting, much more than the 400 f/4.5S for me. Current price in Germany is 4.719€ ... gosh ...

[Øivind Tøien]

Nothing special compared to 500mm f/5.6 PF, but both so excellent that there is no need to be concerned about performance resolution wise. The quality of these long prime lenses is high enough that they are diffraction limited (not talking about the PF effect) near wide open aperture, with front pupil size important for determining maximum resolving power. In planetary astrophotography, it is well established that it is the diameter of high quality optics that determines the optimal maximum magnification to be matched to a specific sensor pixel size.

[pluton]

Almost all well-designed lenses at about 100mm and longer (for 24x36) show very flat MTF curves, especially when compared to my beloved wide-angle lenses.  I suppose that compressing the MTF lines for the different line-pair frequencies represents ongoing progress. If these MTF charts are accurate.

[ColinM]

In case you didn't know, at least two NG members are already shooting with this lens.

Look for Grebe images by Anthony on this page
https://nikongear.net/revival/index.php?topic=1938.1425

And Elsid here
https://nikongear.net/revival/index.php?topic=1938.msg199545#msg199545

You'll also see their comments on the practical considerations of using the lens out in the real world in comments on this page
https://nikongear.net/revival/index.php?topic=1938.1470

[Akira]

The MTF charts published by the manufactures are geometrical one and not the diffraction one.  The resolution is limited by the f-number, but the geometrical one doesn't include this effect.  The MTF in reality is shown by the diffraction MTF.

Here is a screen capture of the explanation on the relationship between the f-number and the diffraction MTF of 30 line/mm.

[Akira]

The meridional (green broken) line in the MTF chart decreases towards the corner because of the vignetting caused by the lens barrel.  That works like stopping down the in the meridional direction which lowers the MTF limit into the peripheral of the image circle.

[Øivind Tøien]

Thanks Akira, interesting and in line with what I stated about planetary astro application of high optics quality optics.
What is the source for those charts?

[Akira]

Thanks Akira, interesting and in line with what I stated about planetary astro application of high optics optics.
What is the source for those charts?

Glad to be of any help, Øivind.  This is a screen capture from the introduction of the new SIGMA 500/5.6 lens on YouTube (starting at around 14:15 by quoting the equation of Rayleigh Limit):

https://www.youtube.com/watch?v=a3h7HmO0Pbo

The presenter, Mr. Ohsone, is optical engineer and current product manager of SIGMA.  He explains that the diffraction MTF performance of the modern telephoto lenses have reached the theoretical limit.  He also says that if you require higher performance than the new 500/5.6 offers, you have to go for faster lenses like 500/4.0.

[Øivind Tøien]

Glad to be of any help, Øivind.  This is a screen capture from the introduction of the new SIGMA 500/5.6 lens on YouTube (starting at around 14:15 by quoting the equation of Rayleigh Limit):

https://www.youtube.com/watch?v=a3h7HmO0Pbo

The presenter, Mr. Ohsone, is optical engineer and current product manager of SIGMA.  He explains that the diffraction MTF performance of the modern telephoto lenses have reached the theoretical limit.  He also says that if you require higher performance than the new 500/5.6 offers, you have to go for faster lenses like 500/4.0.

Thanks, that makes a lot of sense. (So it seems Sigma is presenting quite different MTF curves for their lenses that cannot be directly compared to Nikon's  etc.)

In planetary imaging for visible wavelengths we are employing the 5x rule, that is - multiply pixel pitch with 5x to obtain the matched aperture. So with a  2um pixel pitch one would with a 300mm f/4 lens apply teleconverters to ideally obtain about f/10 aperture for maximum magnification that is best matched to the sensor, so 820mm with stacked 1.4x + 2.0 converter gives that approximation of f/11. With a 500mm f.5.6 lens only a 2x converter (1000mm f/11) should be used to reach the same limit. The stacked 1.4x + 2.x converters would apply more magnification than optimal for that combination, but would be appropriate for a 500mm f/4 lens (1400mm f/11). The stacking of a large number of frames helps bringing out the low contrast details that can be sharpened without being overwhelmed by noise in addition to the lucky imaging aspect that only use the best of the frames. Obviously we are more picky with our camera bodies that have a much larger pixel pitch and are looking for an image that looks sharp to begin with, but the same principle applies.

[ColinM]

And in case any of you haven't seen examples of what Øivind is mentioning, have a look here

MTF charts are (sort of) interesting, but the end results of using the lenses get my attention much faster

https://nikongear.net/revival/index.php?topic=1867.1110;topicseen