Toothwalker wrote:
Au contraire. It's aberrations (plus flare and diffraction) that shape the MTF curves. At f/1.4, you can be sure that the departure of the MTF curves from ideal is mostly due to aberrations. The difficulty is to tell the aberrations apart, and I don't think there is anybody who can do that from a single MTF slice in object space.
Of course, there is always room for educated guesses. If the tangential MTF falls well below the sagital MTF towards the image corners at mid apertures, and if the lens design is asymmetrical, lateral chromatic aberration is the prime suspect.
Is this what tends to happen with Sonnar designs. I have noticed that in zeiss MTF charts pretty much all the Sonnars show strong divergence of tang and sagital MTF when stopped down and less divergence wide open. Here are some examples
edit: for some reason when I pasted the links it broke them. You will have to cut and paste the whole link to view the graphs
Should one expect all these lenses to have much lower lateral CA in the corners wide open than at smaller apertures? I have always thought that Zeiss lenses would be top drawer for landscapes stopped down, but what you are suggesting is that these sonnars may struggle a bit with CA in the corners when stopped down. I have noticed that the symmetrical planars don't show this same pattern at least not nearly as much and perhaps would be a better choice if one is worried about CA in the corners in such situations.
Ok, fair enough. I usually don't think of shifted focus as an aberration, but rather as a distortion but I guess you are right - aberration is a more general concept that includes distortion.
Specularist wrote:
If we have a series of MTF graphs for two or more f-stops, I believe we can take the educated guessing a bit further, since we know that lateral colour is the only aberration that isn't reduced by stopping down (except for distortion, which doesn't influence the MTF). If all aberrations except lateral CA are reduced by stopping down, but the tangential curves in the field don't improve or improve only slightly upon stopping down, then it's reasonable to assume that lateral chromatic aberration is the culprit.
That is correct.
It is even possible that the tangential curves in the field deteriorate slightly upon stopping down.
Steve Spencer wrote:
Is this what tends to happen with Sonnar designs. I have noticed that in zeiss MTF charts pretty much all the Sonnars show strong divergence of tang and sagital MTF when stopped down and less divergence wide open. Here are some examples
[snip]
Yes, that is what happens with Sonnar designs. I have experience with only three of them (2.8/85, 2.8/135, 2.8/180), where the last one is my least favorite Zeiss lens just because of abundant chromatic aberrations. I would still wholeheartedly recommend the 2.8/85 though. Its CA is insignificant in practice.
Should one expect all these lenses to have much lower lateral CA in the corners wide open than at smaller apertures?
Yes and no. Lateral CA is independent of the f-number and equally strong at all apertures. However, its manifestation in the form of conspicuous color fringes may indeed become more clear at smaller apertures as other aberrations are cured upon stopping down. The sagittal curve goes up and the tangential curve stays behind.
I have always thought that Zeiss lenses would be top drawer for landscapes stopped down, but what you are suggesting is that these sonnars may struggle a bit with CA in the corners when stopped down. I have noticed that the symmetrical planars don't show this same pattern at least not nearly as much and perhaps would be a better choice if one is worried about CA in the corners in such situations.
Sonnars, like Distagons and Tele-Tessars for example, may struggle a bit or a lot with lateral color. I will not say that Sonnars are unsuitable for landscapes. These designs and their MTF charts have been around for decades and their suitability for a specific type of photography does not change because of a particular interpretation of their spec sheet today.
"I will not say that Sonnars are unsuitable for landscapes."
A judicious restraint, as the Sonnars I use are all brilliant for landscape photography at typical working apertures (f5.6-f11); the two noted below have their own threads here, full of images that support this view.
"..pretty much all the Sonnars show strong divergence of tang and sagital MTF when stopped down and less divergence wide open."
Not these two, over the optimal portion of their FL ranges, and the gains with small apertures are very significant:
..which is one reason people use them. You might also note the values at frame edge/corners: 18-21mm, and the general flatness of the 40 lp/mm curves, which is consistent with excellent contour shaping according to CZ.
The Contax 1.4/85 Planar returns poorer centre performance at the same optimal aperture as the Contax 2.8/85mm Sonnar - for fine detail rendition - a key measure for landscape lenses shot at ideal apertures. The Planar would struggle to match the Sonnar for landscape work even by f2.8, going by its positively anemic performance at f1.4, relative to the Sonnar wide open. More than twice the weight too - so not a wise choice for this admittedly niche use.
Yes they are. They are measured at multiple distances that includes infinity. The ZF 100/2 MP is measured at 1:2 and 1:10 reproduction ratios and at infinity.
Lotusm50 wrote:
Not to be picky here and i don't mean to single you out, but the issue needs airing, IMHO. How do you know what was "necessary"? How would you determine what weight was necessary?Would you have traded-off performance for weight? How much?
CZ obviously thought the weight was necessary or it would not be designed the way it was.
This is type of trade-off issue for uses where Zeiss appears damned if they do, and damned if they don't. If they give the lens the performance that people expect and desire, then people complain that it is too heavy, too big or too expensive. But if they would trade-off performance for weight, size and cost issues, then people would complain that it's not any good and not worth bothering with. This is similar to the discussion around the ZF 25/2.8. Zeiss designed the lens with what appears to be an optimal set of trade-offs, providing excellent performance in a relatively compact, reasonably priced lens. Yes, people complain that it doesn't perform exactly like it's bigger more expensive brother, the 21/2.8. Never mind that it is nearly half the price of the 21/2.8. Quite frankly (and Zeiss has learned this from their market response over the past 3 or 4 years), if Zeiss went down the route of the 25/2.8 with the new 35/1.4 people would complain about its performance all day long. So Zeiss gives us the a 35/1.4 with fewer compromises in the name of size and cost. The market spoke and Zeiss listened and responded appropriately with the 35/1.4. If size and weight is more important to the buyer than (wide open) performance then they can buy the excellent and very reasonably priced ZF35/2.0.
Sven Jeppesen wrote:
You can't compare those lenses. And this lens is also rather big
Why not? Both are 35 mm f/1.4 SLR lenses, both can be used with for instance Canon systems. I would in fact say that it's one of the lenses one must compare the new Zeiss with.
I was rererring to the new lenses, not some adaptable stuff which cost more than the new ZE 35/1.4 and which is not easily recoverable with another when something happens to it.
