[Leica] 180 mm report. part 3

[Erwin Puts <imxputs@knoware.nl>]

Flare and unsharpness gradient.

The general idea of flare in fact consists of three  distinct phenomena.
Stray light or veiling glare, that is unwanted light that is 
distributed over the whole image area and reduces contrast and 
lightens up the deeper shadows.
Then we have secondary or ghost images that are caused by small 
lightsources, that are reflected by lens surfaces. And then we have 
halos around point sources as when we take night pictures of 
lampposts that are surrounded by a strong halo. Secular highlights 
also are affected by this as highlight details are washed out.
Of course these phenomena are not unrelated, but have different manifestations.
The 2.8/180 does not exhibit any stray light, blacks are deep dark 
and lightsources are very tightly delineated. Specular highlights 
show finely graded shades of white and secondary reflections are only 
observable under very unfavorable and seldomly encountered 
circumstances.
The 2/180 again does not have any stray light and for such a lens it 
is amazingly well behaved here. Halos are also very well suppressed 
although a shade less than the 2.8/180. Secondary images can be seen 
when shooting straight into the sun or another strong light source. 
When the light source is just outside the image area, and very 
oblique, then we may see in certain but not all situations, a veiling 
glare that can be distractive. The excellent suppression of stray 
light shows in the details that hold contrast and gradation.
This topic should be approached with some care. It is always possible 
to force a lens in a situation where flare of whatever character will 
be visible. Both 180 lenses are extremely well shielded from flare, 
and one really needs to some optical aerobics to induce flare, and 
then only in the area of ghost images and  bright spots of some 
extension.
In 99% of situations both these lenses can be used without any 
consideration for glare.

The sharpness/unsharpness gradient is obviously related to depth of 
field. It is not well known that the DoF extension (distance before 
and after the sharpness plane) only depends on the reproduction 
factor. That is, when  two  objects are photographed such they they 
are of equal magnification, irrespective of the focal length, the DoF 
is identical.   In practical terms, an object taken with a 35 mm at 
3,5 meter and the same object taken with a 180mm at 18 meter will 
have identical DoF. So if we wish to compare the unsharpness 
impression of two different lenses, or make any general statements. 
we should take care to compare pictures taken at equal magnifications.

Finer points of difference between the 2.8 and 2 version is the 
somewhat smoother gradient of the 2.0 lens. At the same reproduction 
factor and same distance before/behind the subject, the detail 
rendition of the 2.8 is slightly harsh, that is outlines of detail 
are quite crisp. maybe a bit over-crisp. The 2.0  produces a bit more 
washed out patches of color. The wider aperture is responsible for a 
big part of course here. When stopping down to 2.8 the Summicron 
approaches the Elmarit, but stays on the soft/fuzzy side of detail 
outlines. Whatever you prefer, you need to do some careful comparison 
here to make up your mind. There is a character difference here, base 
partly on the correctional choices. The Summicron might reproduce the 
background unsharpness a bit less pronounced and so help focus on the 
main subject.

I am doing a major research project on these topics, so please see 
these notes as preliminary and not definitive.

As general conclusion I may note that the 2.8/180 is by a small notch 
the best, closely followed by the 2/180 which has a slightly 
different character of rendition and by some distance the 180 
position of the 70-180 vario lens. The 180 is a premium focal length 
and Zeiss with a 2/200, Canon with a 1.8/200 show what their 
designers can do when reigns are loosened.
Within the R line these two lenses would be enough to convince anyone 
to try the Leica R for optical prowess.


Erwin

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