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Optics Theory - This forum is aimed towards the TECHNICAL side of photographic OPTICS THEORY. There will be some overlap by camera/manufacturer, but this forum is for the heavy duty tech discussions. This is NOT the place to discuss a specific lens or lens line, do that in the appropriate forum. This is the forum to discuss optics or lenses in general, to learn about the tech behind the lenses and images. IF you have a question about a specific lens, post it in the forum about that type of camera, NOT HERE.

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Old 05-01-2012   #41
JHutchins
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Originally Posted by Scheelings View Post
Ok, but if I focus on something at 1.5, take a shot, then step down to say 2.8, does refocussing correct it - or is this lens always out of focus - even if it appears in focus in the viewfinder - from F2~4?
What camera are you using? If you're using something that allows you to look through the lens at the selected aperture (e.g. an electronic viewfinder interchangeable lens camera, or an SLR with the depth of field preview engaged) then something that appears to have the center of focus on a particular point at f2.8 actually has the center of focus on that point at f2.8 (barring user error).

If you're using a rangefinder or an SLR that holds the aperture open while you focus and stops down only for the exposure, then something that appears to be have the center of focus on a particular point at f2.8 may actually have teh center of focus on a different point.
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Old 05-01-2012   #42
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Originally Posted by JHutchins View Post
What camera are you using? If you're using something that allows you to look through the lens at the selected aperture (e.g. an electronic viewfinder interchangeable lens camera, or an SLR with the depth of field preview engaged) then something that appears to have the center of focus on a particular point at f2.8 actually has the center of focus on that point at f2.8 (barring user error).

If you're using a rangefinder or an SLR that holds the aperture open while you focus and stops down only for the exposure, then something that appears to be have the center of focus on a particular point at f2.8 may actually have teh center of focus on a different point.
I'm using a Leica M8. So Actually I was weighing up whether to get the 1.5 Sonnar or the 2.0 Planar. Half a stop doesn't sound like much to give up if more of my shots are going to be as tack sharp as I would expect from Zeiss....

Maybe I need to research some planar vs sonnar threads.

Is there much difference with Bokeh?
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Old 05-02-2012   #43
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Originally Posted by Scheelings View Post
I'm using a Leica M8. So Actually I was weighing up whether to get the 1.5 Sonnar or the 2.0 Planar. Half a stop doesn't sound like much to give up if more of my shots are going to be as tack sharp as I would expect from Zeiss....

Maybe I need to research some planar vs sonnar threads.

Is there much difference with Bokeh?
So with a Sonnar on an M8 the center of sharp focus can and will be different from what your rangefinder tells you it is. This can be dealt with -- it's just a matter of having an idea of how your lens behaves at various apertures and distances.

But these are very different lenses and if you're considering the Sonnar just for the extra half stop then probably you'd be happier with the Planar. It is a sharper lens, it vignettes less, it is more neutral. The Sonnar imparts a color of its own, yes, the bokeh is significantly different from the Planar, also contrast, field illumination &c. Apologies for the obvious advice, but if you're on the fence you really should do a tag search on flickr for both lenses because the best reason to get a Sonnar is that you like the Sonnar look and to understand it you should see it.
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Old 05-02-2012   #44
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What JHutchins said and to add that the Zeiss "C" designation lenses are a throw back to old and loved lens designs with warts and all. They are meant to be like that for good reason. If you want clinical looking images then the Planar is probably for you.
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Old 05-27-2013   #45
semilog
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What JHutchins said and to add that the Zeiss "C" designation lenses are a throw back to old and loved lens designs with warts and all.
The C-Biogons 35/2.8 and 21/4.5 do not have many warts.

Due to their relatively symmetrical designs they have some vignetting and don't do well in the corners on digital sensors. On film they are darned close to flawless.
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Old 05-29-2013   #46
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Originally Posted by f16sunshine View Post
Focus shift is caused by the internet.

...as are many other photographically related afflictions.

EDIT (6-2-13)

I did a bit of poking around and found a couple of fairly good articles on focus shift:
http://photographylife.com/what-is-focus-shift
and http://diglloyd.com/articles/Focus/FocusShift.html

Hope these will help...
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