The infinity mark on Zeiss Superachromat

[wieslaw1]

<p>Does anybody know how to focus the Zeiss Sonnar Superachromat at infinity.<br>

This is a special lens and the infinity mark on the lens barrel can be overdriven. How to set it correctly?</p>

 

[q.g._de_bakker]

<p>Visually.<br>

That's what focussing screens are for.</p>

[leighb]

<p>For once Q.G. and I agree. ;-)</p>

<p>Quoting from the Zeiss datasheet for the Sonnar 250mm Superachromat:<br>

"As the distance setting ring has no ∞-stop position, focusing for long-range work must be made on the groundglass of the camera."</p>

<p>Long telephotos sometimes have a physical stop beyond the nominal infinity focus point to accommodate dimensional changes caused by temperature extremes.</p>

<p>- Leigh</p>

 

[ondebanks]

<p>My experience with the Mamiya 200/2.8 APO (easily the optical equivalent of the Superachromat, and more focus sensitive since it is 2 stops faster) is that true infinity focus varies noticeably with temperature - I mean the temperature swing from day to night, not a degree or two change during the day. Shooting this lens wide open, or with a 2x TC, I nail focus much more consistently with my 645 AFD (focus confirmation) and digital back (zoom-in chimping) than I did with visual focus on my M645 1000s and WLF.</p>

<p>In the pre-digital-feedback days, some astrophotographers like Chuck Vaughn calibrated their APO tele lenses for infinity at different temperatures, and stuck a label beside the focus pointer to mark these infinity points. They trusted this method above judging infinity on the focusing screen. These were predominantly 35mm cameras, however, with inevitably pokier viewfinders.</p>

[q.g._de_bakker]

<p>If you would make it a habit to agree with me, Leigh, you would not be wrong so often...<br>

;-)</p>

[wieslaw1]

<p>Thanks.<br>

Indeed, I focus rutinely on the ground glass of my Linhof, but with a hand held cameras I often go for the calibrated scale.<br>

It is intriguing how the T change (and focus shift) translates into the barrel extension.<br>

Lens rotation from infinity mark to the end, some 1.2cm, extends the lens by about 4 mm. A quite large extension.<br>

Another question:<br>

In addition to the shutter speed scale engraved in white on the lens ring there is also a mirror speed scale in green (from B up to 1/125) which is not accessible. What is this for?</p>

[marek_fogiel]

<p>It is in seconds, for long exposures in B mode.</p>

[q.g._de_bakker]

<p>Indeed.<br>

You can't set those speeds, but they will tell you how long to keep the shutter open on B for any of the aperture values appearing next to the exposure times.</p>

[wolf_rainer_schmalfuss]

<p>The ZEISS Superachromat 5,6/250mm has no MC coating and must always be focused with the focusing screen. But even of its age, it is the best lens ever being built for special fine photography.</p>

[wieslaw1]

<p>But there is some kind of coating, the lens appears blue. What kind of filter would you recommend for color and for b&w photography. I would need at least a polarizer for both and although at present I might not need the optimal resolution of 250 lines/mm, sometimes in the future i might.</p>

[q.g._de_bakker]

<p>The SA does have a coating, but, as Wolf Rainer said, not the regular T* multicoating.<br>

Coating doesn't work well over such a wide range of wavelengths the SA uses to form an image. Layers designed to improve transmission of some wavelengths will lower transmission of wavelengths at the other end of the spectrum.</p>

<p>The fluorite element in the lens is coated also to protect it against humidity, which would erode it over not too long a period.</p>

<p>You should use any filter you would use on any other lens to do what you would use that filter on any other lens for. No difference.</p>

 

[wolf_rainer_schmalfuss]

<p>Hello Wieslaw, a polarizer fillter is the only one you need, together with an lens hood. I recommend, to use only the best polarizer filter brands available! I guess, you will never being able to overstep the full capacity of this excellent lens, regardless with film or digital! For anything else, Photoshop is your best friend.</p>