Focus shift tests of Zeiss C Sonnar apparently optimized for 1.5

[richard_g]

<p>Here is a set up I used for testing the focus shift of my C Sonnar on the M9 where I din't have to make innumerable notes and wait for film development, where the 100% crop facility of Lightroom was helpful instead of just inspecting negatives or prints, and where the focus target was less equivocal than previous set ups I have tried, such as book spines, model soldiers or chess pieces. I used a WhiBal white balance card radiate graphic and pushed the tabletop tripod in and out with the lens set to minimum focus (0.9m) determining the point at which the radiate graphic was most vivid, with the edge of the card immediately beneath the 20cm mark.</p>

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[richard_g]

<p>Here is the 100% crop at f1.5. Not as sharp and contrasty as f2 which follows, and with some front focussing evident, about 1.5cm with the sharpest point probably at the 18.5cm mark.</p><div></div>

[richard_g]

<p>Here is f2 and it is sharper overall and with some front focus of about 1cm, the sharpest point being at 19cm.</p><div></div>

[richard_g]

<p>Here is f2.8, sharp from the 20 to the 22cm marks, slightly back focussed.</p><div></div>

[richard_g]

<p>Finally f4 where it is sharp from the 20 to the 24cm mark, back focussed again. There are some who claim there Sonnar seems to be optimized for f4. My conclusion is that this is optimized for around f 2.4 or so, which I think others have also found. Look at the building and it puts all of this into some perspective. The corner nearest the ruler is at the 20cm mark.</p><div></div>

[baisao]

<p>Great test, Richard! Thank you</p>

[rgerraty]

Comparing my ZM C Sonnar 1.5 optimized lens tests with the tests of Marek Fogiel with his 1.5 optimized lens suggests

that my copy is quite different and useable across all of the wider apertures in the way that his seemed clearly not to be.

See his results at f4. How much variation there is copy to copy is unknown.

 

http://www.rangefinderforum.com/forums/showthread.php?t=51742&highlight=mfogiel+zeiss+sonnar

[rgerraty]

All the distances here are of course an overstatement considering the angle of the ruler to the lens axis.

[philip_wilson]

Thanks Richard- I ended up buying one (although I almost went with the Cron- the Zeiss Bokah was the deciding factor). I

will have to charachterize mine

[richard_g]

I do hope you like it. It was a great impetus for improvement in my photography. Even at f5.6 I love this lens and

recognize my shots with it. And the colours are beautiful. I've dropped mine three times and wrecked a filter and a hood

but the lens is still perfect.

[kivis]

<p>Good test. I has similar results with mine.</p>