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To infinity and beyond (specs for infinite focus)

dslr micro four thirds lens spec focal distacne

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#1 James Wallace

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Posted 14 April 2016 - 10:27 AM

Hey there.

 

In my day job I regularly shoot from gimbal stabilizers and aerial rigs using dslr and mirrorless cameras and lenses.  Given that I do not often have access to a wireless follow focus,  I have to improvise and work with hyperfocal distances and such.  

 

The one piece of information that would be really usefull to me when planning shoots where we will be hiring in this sort of gear never seems to be available in any review or spec sheet.  That is the distance beyond which the lens has infinite focus.  I can usually take a rough guess with fixed primes, but with compact zooms it's a completely mixed bag.  I often resort to google image searches and taking a guess based on the lens markings, but some newer lenses have no focus markings at all.

 

For instance on an upcoming shoot using a Sony a7rii we are considering using a Ziess Vario-Tessar T* FE 24-70mm F4 ZA.  The lens has no focus markings and I can find no spec sheet anywhere that tells me even approximately at what distance this lens achieves infinite focus.  This information would be really useful to me.

 

I know that by using hyperfocal distances I am to some extent negating this issue and always achieving the maximum possible field of sharp focus in any given situation, but it seems like this info should be available as a matter of principle.

 

Does anybody know where this spec might be available for modern lenses?

 

Thanks 


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#2 Jean-Louis Seguin

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Posted 14 April 2016 - 11:34 AM

I read somewhere that the rule of thumb is infinity is 600x the focal length.

Ex: 50mm x 600 = 30000mm = 30 meters.


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#3 Dom Jaeger

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Posted 14 April 2016 - 12:26 PM

I'm not sure how what you're asking about ("the distance beyond which the lens has infinite focus") is different from the hyperfocal distance?

Most Depth of Field Calculators should tell you the hyperfocal distance given a focal length and f stop. It will also depend on the size of the format or a chosen Circle of Confusion figure, since depth of field - or more accurately what you might choose to describe as "in focus" - is a somewhat arbitrary decision.

So for example 24mm at f/4 using a CoC of 0.02mm gives you a hyperfocal distance of about 24ft, with everything from about 12ft to infinity "in focus". (A more relaxed CoC of 0.03mm is often used by DoF calculators for full frame 35mm cameras, which would alter the 24mm f/4 hyperfocal distance to around 16ft, with everything sharp beyond 8ft. Zeiss themselves would probably argue for a tighter circle of confusion, so I'll stick with 0.02.)

50mm at f/4 has a hyperfocal distance of about 100ft with everything sharp from about 50ft to infinity. But if you stop down to f/8 the hyperfocal shifts to 51ft with everything beyond 26ft sharp.

At 70mm f/4 the hyperfocal distance is about 200ft.
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#4 David Hessel

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Posted 15 April 2016 - 11:45 AM

I am not sure if you are aware of this or not but that FE lens doesn't have markings because it has a focus by wire electronic focus. It is non-linear so a half rotation done quickly could go through the entire range of focus while a slow half turn rotation might only shift focus a foot. It makes repeatable focus near impossible and I really don't like it at all. It would probably be more difficult to set the lens to the hyperfocal distance than to figure out what that distance is.


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#5 Simon Wyss

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Posted 15 April 2016 - 12:32 PM

You can’t have your cake and eat it.

 

It’s either a lens made for film motion-picture cameras or something in the electronic realm. The electronic people think forward, they are part of the future, they change everything.

 

In reverse they pass over the solid things, they are not part of the present, and they don’t think backwards, to the existing. Zeiss has gone plastic* like many other companies. No more the old brass Tessar but a Sony Zeiss Vario-Tessar, what a guff.

_________________

 

*Plastic and electronics are about the same to me.

 

Am doing an overhaul of a 1955 Paillard-Bolex H-16 plus a Kern Pizar 26mm f/1.9, a Kern Switar 50mm f/1.4, and a Kern Yvar 150mm f/3.3. More than $1000 are asked for an Yvar 150 today although they consist of only three lenses. Switar 10mm f/1.6 have ten lenses and are sold way cheaper. What a guff.


Edited by Simon Wyss, 15 April 2016 - 12:33 PM.

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