p.2 #1 · Testing the ZM C Sonnar 50 1.5 & 3 other lenses
This is, of course, the beauty of being able to magnify focus. Non need to worry about overshoot. That said, I am extremely surprised that the C-Sonnar focuses past infinity as it is a RF lens and you can't (or I can't) pin down infinity focus with a rangefinder so have to assume that the infinity stop is accurate.
BrianVS wrote:
The focus shift is the problem. Most people stop down for infinity- and on the C-Sonnar, that pushes the focus past infinity. When stopped down, I focus slightly closer than infinity and let the shift bring things into focus.
With a Jupiter-3, the focal length is longer. Wide-Open/Close-up and F4/Infinity is typical.
p.2 #2 · Testing the ZM C Sonnar 50 1.5 & 3 other lenses
At infinity, the lens is closer to the sensor- this could be a problem for the Sony. The Leica uses offset microlenses to accommodate light coming in at steep angles. Getting used to focus shift is easy with a rangefinder, you learn to leave the overlaid images slightly offset rather than bringing into full coincidence.
p.2 #4 · Testing the ZM C Sonnar 50 1.5 & 3 other lenses
Personally I have never used the C-Sonnar at infinity although I was surprised to read BrianVS's comment about its infinity stop being long of infinity. I agree with briantho's observation that as a close range lens for portraits and indoor events (intimate concerts, etc) it is wonderful. And it can be switched from Nex7 to A7 according to subject. However, it would not occur to me to use it as a landscape lens - that's not what it is for, which is why Zeiss offers two fast 50 ZMs. They have different purposes. That said I was still interested to see the comparison with other 50s, including the 55ZA, but not for across the frame sharpness, where the C-Sonnar is never going to be a competitor.
p.2 #5 · Testing the ZM C Sonnar 50 1.5 & 3 other lenses
briantho wrote:
My tests were done focusing stopped down, such as most people do with mirrorless cameras like A7R, so focus shift can be ruled out.
I'm thinking the problem with a full-frame mirrorless camera with the Sonnar at infinity is the steeper angle of incidence. The Leica sensor is designed to work well with light at steep angles. The angles are steepest at infinity.
p.2 #9 · Testing the ZM C Sonnar 50 1.5 & 3 other lenses
I've taken quite a few lenses there- I should compile some comparisons. What I've noticed: the field curvature of the Sonnars kills the corner sharpness at infinity. The actual focus curves towards the camera at the corners. I modified one J-3 to reduce field curvature by moving the rear triplet, but it was unusable when i got it.
p.2 #12 · Testing the ZM C Sonnar 50 1.5 & 3 other lenses
"I had to look at the 100% crop"...
The wires to the right hand corner, starting to push intensity aliasing of the M Monochrom. Also gives an idea of "Pixel Peeping DOF". The 50/1.1 Sonnetar includes a mechanism for the rear element to fine-tune the lens. I was thinking of making a mechanism for the J-3 to do the same. I have a lot of parts.
Apologies to the OP for taking the thread off into a tangent. Sonnar formula lenses "fascinate me"- basically an optical design that did not work out for SLR's for focal lengths less than 100mm. Optimized to transmit the maximum amount of light possible, before lens coatings were applied.
