edwardkaraa wrote:
I'm sorry but that sounds like you just want to be contrarian. The glass cover thickness is calculated into the lens design, and a thinner cover glass will result in image degradation.
no. i seriously doubt they are including the cover glass in the lens design calculation, it seems unnecessarily limiting for their own future sensor designs. from a design perspective it seems much easier to just try to just set ray angle limit on lens designs than to design lenses with built in aberrations that are counteracted by the specific refractive properties of the cover glass (which could easily change in future models due to sourcing issues or newer tech). also, if they were designing lenses with built in astigmatism that would be removed by the cover glass i would imagine they might be able to build smaller lenses since ray angle issues would be used in the design rather than avoided.
sebboh wrote:
no, native lenses just have to be designed to reach a certain level of performance for the worst sensor. i sincerely doubt they are designing the lenses so that they would perform worse with thinner cover glass. PDAF issues don't come into play in the design of native lenses since they all use on sensor focusing methods.
I believe that the glass thickness affects the ray travel distance to the sensor, and thus thinner glass would affect the focusing distance, possibly in a non-correctable way for floating element lenses.
carstenw wrote:
I believe that the glass thickness affects the ray travel distance to the sensor, and thus thinner glass would affect the focusing distance, possibly in a non-correctable way for floating element lenses.
i doubt it given the extra range that is designed into AF lenses.
sebboh wrote:
no. i seriously doubt they are including the cover glass in the lens design calculation
carstenw wrote:
Zeiss has gone on record saying so, and I believe that Leica also discussed it when they released their digital Ms.
my understanding of those statements was that they were designing lenses with less acute ray angles (obvious from looking at the designs) for use in digital sensors rather than film. the statements were ambiguous to me, but it would be very foolish for leica or zeiss to do that with their rangefinder lenses since leica has used different thicknesses of cover glass in different m-camera models (as has sony in NEX cameras according to people who've attempted to remove it).
Extra range doesn't help you when there is a floating element, since everything is designed to be at exact distances and relations to each other for perfect focus. Moving the whole package back and forth at non-infinity would degrade performance.
Is Leica known to have different cover glass thicknesses? If that is the case, they must have moved the sensor as well, since light travelling through glass converges faster than through air.
Thinking further about this, it would mean that the flange distance is some kind of effective distance to some calculated point in the sensor package, and not the hard distance from lens mount to the pixels themselves.
We really need some of the experts to come and chime in here. I think we are all just going on what we have read here, and not on first-hand knowledge.
Leica specifically had to use a very thin sensor cover, in fact so thin that there is not enough IR absorption, causing IR contamination in synthetic fabrics. The M8, M9 and M240 all suffer from this to varying degrees. However, it was the lesser evil, as for Leica, corner smearing is totally unacceptable for their super expensive lenses, and a thin cover was the only solution to make the lenses work.
Also center focus plane is not affected by the cover thickness, but the thicker the cover the more shift in the focus plane in the image periphery and corners. This does not include astigmatism that causes plain and simple smearing. I am talking here about field curvature caused by the sensor cover. My ZM 25 which has one of the flattest field of any RF wide as used on the M9, suffers from acute field curvature on the A7. The curvature is in a U shape, and for example, a subject focused in the center at 1 meter will get me sharp borders at around 2-3 meters behind the focus plane. I would imagine if Sony designs wides with a reversed U shape field curvature this problem should be resolved?
I've been trying to keep up with this and other threads and have even read Tim Ashley's informative reviews on the 35ZE and the limited number of M lenses he has, but I still feel pretty uninformed on how many M lenses perform.
Has anyone done any systematic testing on the Leica M 35/2 asph or M 35/1.4 asph (not the FLE)? Or even the zeiss zm 35/2? Plenty of people own these erstwhile treasures, but few people seem to be reporting on their experiences with them on the A7r?
p.137 #10 · A7/A7r - performance with WA RF lenses
carstenw wrote:
Thinking further about this, it would mean that the flange distance is some kind of effective distance to some calculated point in the sensor package, and not the hard distance from lens mount to the pixels themselves.
yup.
i believe leica documented the changes in IR filters from m8 to m240, but i've only seen other people quoting them.
p.137 #11 · A7/A7r - performance with WA RF lenses
edwardkaraa wrote:
This does not include astigmatism that causes plain and simple smearing. I am talking here about field curvature caused by the sensor cover. My ZM 25 which has one of the flattest field of any RF wide as used on the M9, suffers from acute field curvature on the A7. The curvature is in a U shape, and for example, a subject focused in the center at 1 meter will get me sharp borders at around 2-3 meters behind the focus plane. I would imagine if Sony designs wides with a reversed U shape field curvature this problem should be resolved? ...Show more →
the field curvature is not separate from the smearing, they are interrelated aberrations and they are both caused by the interactions between the lens design and refraction through the cover glass.
i would think it would be possible for sony or zeiss to design a lens with reversed aberrations to cancel out the effects of the cover glass, but i doubt they will because it would be incredibly shortsighted. what we actually see instead in the lenses designed for short flange distance AF cameras is lenses with rear elements designed to straighten out the angle at which light hits the sensor.
p.137 #12 · A7/A7r - performance with WA RF lenses
sebboh wrote:
the field curvature is not separate from the smearing, they are interrelated aberrations
Is field curvature always an aberration, or is it a design choice to either compensate for or ignore the difference in distance to a given portion of the frame for varying planes in the scene?
p.137 #13 · A7/A7r - performance with WA RF lenses
RustyBug wrote:
Is field curvature always an aberration, or is it a design choice to either compensate for or ignore the difference in distance to a given portion of the frame for varying planes in the scene?
nearly all aberrations are design choices and tradeoffs (flare probably less of a design choice).
p.137 #15 · A7/A7r - performance with WA RF lenses
A7R with CV15 f/4.5 at f/8 Cross post from A7R images.
This is a test of the APS-C Size Capture set to On for manual lens. So the 15mm functions like a 22mm lens with a fairly clean result easy to tweak in LR5. I am pretty happy with the result and I think this will work for me until I see a some new wide angle lenses designed for this camera.
