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Arri SRIII and Alura Zoom - Will it work?


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#1 Aidan Gault

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Posted 13 October 2015 - 12:28 PM

Hey guys,

 

Was wondering would anyone have any insightful theories as to why glass like an Alura Zoom 18-80mm would not work when shooting super16 film on an Arri SRIII. I know about the effects of the crop factor, but was wondering is there any special coatings on newer "digital" glass that could effect an emulsion in a certain way?

 

Any thoughts or experience in this area?

 

Ta,

Aidan


Edited by Aidan Gault, 13 October 2015 - 12:33 PM.

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#2 Kenny N Suleimanagich

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Posted 13 October 2015 - 12:58 PM

Why wouldn't it work? No reason it shouldn't assuming both camera and lens are PL mount.
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#3 Satsuki Murashige

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Posted 13 October 2015 - 01:33 PM

It's usually just an issue of clearance. Some PL lenses like the Angenieux Optimo DP zooms are designed only to work on non-mirror reflex cameras because they have a long protruding rear element which would hit the mirror. Also some wide lenses get very close to the mirror, so you should check just to make sure. No idea about the Aluras specifically though, sorry.
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#4 Dom Jaeger

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Posted 14 October 2015 - 04:44 AM

There's no reason Alura zooms shouldn't work on an SR3, in fact the Arri website specifically mentions that "while optimized for digital cameras, they are compatible with film cameras".

 

"Optimised for digital" I would assume means the lens has a large enough image circle to cover current cinema camera sensors, and is also PR speak for "really sharp", though in truth they are no sharper than the last generation of zooms designed for film cameras like the Angenieux Optimos. There are no specific coatings that are only compatible with digital cameras. Some lenses designed for specific digital stills cameras may have a small amount of spherical aberration built in to them to optically correct the effects of that particular camera's OLPF stack, but as far as I'm aware this is not the case with digital cinema lenses. As Satsuki said, with occasional PL lenses there can be issues with clearing the mirror on a film camera, but the Aluras are OK.

 

The main thing to watch out for when using 35mm format lenses on 16mm cameras is shiny surfaces inside the mirror cavity around the gate, since the lens image circle is much larger than the camera gate aperture, and the excess light can bounce off a surface and potentially flash or fog the film. 


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#5 James Martin

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Posted 05 November 2015 - 12:50 PM

I am pretty sure the Alura zooms would work. The SR3 has clearance issues with the viewfinder and some lenses, but the Aluras should be OK.


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#6 Satsuki Murashige

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Posted 05 November 2015 - 01:27 PM

Actually, I bet 'optimized for digital' is probably code speak for telecentric lens design, which means that the light rays exiting the rear pupil are parallel and 90 degrees to the focal plane. Digital sensors can display more vignetting with a non-telecentric lens due to the individual photosites not collecting photons entering at extreme angles. Film doesn't have this issue, all photons that strike the film get recorded.
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#7 James Martin

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Posted 05 November 2015 - 01:30 PM

Yes i always took that to be the meaning of the phrase. Panavision introduced their new "Primo V" lenses with similarly vague marketing.


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#8 Dom Jaeger

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Posted 08 November 2015 - 08:39 PM

Actually, I bet 'optimized for digital' is probably code speak for telecentric lens design..


Yes, of course you're right Satsuki, that would be the main design change needed for lenses used with digital sensors. Can't believe I forgot that!

We've rented a lot of vintage or just pre-digital era lenses out with Alexas and other digital cams and it usually isn't a problem, but occasionally - usually wide angles and zooms - you get more corner darkening and colour fringing than the lens exhibits on projection (or on film) which would be the effect of non-telecentric light hitting the sensor.
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#9 Kenny N Suleimanagich

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Posted 09 November 2015 - 09:28 PM

Is there somewhere I can read more about telecentric lens design, that you guys would recommend?
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#10 Satsuki Murashige

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Posted 10 November 2015 - 01:06 AM

Here are a few good reads:

http://ilovehatephot...s-nomenclature/

http://www.reduser.n...anar-what-is-it

Several years ago, some folks over on Reduser were having vignetting issues with their Leica M rangefinder lenses which have a very short flange depth and lack of telecentricity turned out to be the culprit. Turns out that photosites on CMOS sensors have a sort of 'Kino Flo style' egg crate on their front face which blocks light coming in at stray angles. So lenses which produce parallel rays are more efficient.
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#11 Kenny N Suleimanagich

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Posted 10 November 2015 - 10:26 AM

Thanks! That is so interesting. Does telecentricity also mean better MTF then? 


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#12 Satsuki Murashige

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Posted 10 November 2015 - 01:18 PM

No idea, sorry. Basically, in order for a wide lens to be more telecentric you have to increase the distance of the rear pupil from the image plane which means adding a retrofocal element (reverse telephoto) to the back. So there are trade-offs there between adding extra glass and thus aberrations versus having better telecentricity. Lots of other factors as well. For real answers, you'd have to ask a lens engineer!
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#13 Dom Jaeger

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Posted 12 November 2015 - 08:42 AM

Is there somewhere I can read more about telecentric lens design, that you guys would recommend?

 

Telecentric lenses have been around for a while, but a lot of applications use 'object space' telecentrics, which are telecentric in front of the lens. Handy for things like microscope optics or lenses used in industrial metrology to accurately measure objects, since there is no distortion or magnification changes at different object distances. Not much use for cinematography though, since the front element basically needs to be the same size as the object being filmed! Most online information relates to these kinds of industrial 'object space' telecentric lenses.

What we're talking about are 'image space' telecentric lenses, which are telecentric behind the lens. Without investing in books on digital photography technology, there's not a whole lot of online information, but here's a few pages I've come across that are informative:

https://books.google...rensics&f=false

http://photo.stackex...-in-lens-design

 

You can physically check how telecentric a lens is by looking through the back of the lens at the exit pupil, which is the image of the aperture as seen through the rear optics. The deeper the aperture seems the more telecentric the lens. Lenses with a combination of shallow exit pupil and rear elements much smaller than the format size, like certain Zeiss Standard Speeds or Cooke Speed Panchros, will be far from telecentric.

 

 

Does telecentricity also mean better MTF then?

 

 

 

Not necessarily, better MTF is a function of the whole lens design and build quality, I'm sure you could find a crappy lens that is also telecentric. 

It just means that on digital cameras you will minimise the chances of introducing uneven illumination and colour fringing. 

 

A big advantage to telecentric lenses is that they don't breathe (change magnification as you rack focus), not something measured by MTF. But there are definite disadvantages, too. The rear element needs to be at least as large as the format size, and by limiting one design parameter other compromises might be forced on the lens design. So telecentric lenses are often larger and contain more corrective elements. Usually you'll find modern cinematography lenses described as "near-telecentric", because making them perfectly telecentric was too much of a design compromise, and being nearly telecentric is good enough.

 

Certain cameras, like Alexas, that have fairly large photosites are generally pretty tolerant of non-telecentric lenses. Maybe it's accepted as part of the "vintage look", but nobody seems to complain about Zeiss Standards or Cooke Speed Panchros vignetting on Alexas. Different camera sensors no doubt react differently.


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#14 Kenny N Suleimanagich

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Posted 12 November 2015 - 09:54 AM

Thanks Dom! Something I knew very very little about previously
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#15 Drew Bienemann

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Posted 18 November 2015 - 10:49 PM

Ive mounted the lightweight Aluras on an SR3. Worked out perfectly.


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#16 Philipp Kunzli

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Posted 10 December 2015 - 01:17 PM

It alway depends what you're going for.

It works fine. The only issue is the your "widest" focal length is the 15.5mm from the aura... 

That on a S16mm... hmmm... but as I said, it depends what your going for...


Edited by Philipp Kunzli, 10 December 2015 - 01:18 PM.

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#17 Freya Black

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Posted 10 December 2015 - 02:01 PM

It alway depends what you're going for.

It works fine. The only issue is the your "widest" focal length is the 15.5mm from the aura... 

That on a S16mm... hmmm... but as I said, it depends what your going for...

 

 

On an 18-80mm zoom the "widest" focal length will be... ...18mm

 

Freya


Edited by Freya Black, 10 December 2015 - 02:02 PM.

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#18 Freya Black

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Posted 10 December 2015 - 02:15 PM

 

Was wondering would anyone have any insightful theories as to why glass like an Alura Zoom 18-80mm would not work when shooting super16 film on an Arri SRIII. I know about the effects of the crop factor, but was wondering is there any special coatings on newer "digital" glass that could effect an emulsion in a certain way?

 

The "crop factor" isn't really anything to do with the lens but more to do with the size of the gate.

As a result a 35mm format 18-80mm zoom on a super 16mm camera will give the same focal lengths as a 18-80mm super16 zoom on a Super 16mm camera. This is because the focal lengths of the two zooms are the same.

 

As has already been implied however, it might be easier to find Super16 zooms with wider focal lengths, but there is no "crop factor" hidden in the glass. Of course if you go the other way and put a Super 16 zoom on a 35mm movie camera then you are likely to get vignetting on the wider end of the zoom at least.

 

Freya


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#19 Brian Drysdale

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Posted 10 December 2015 - 02:36 PM

Of course, some older 16mm zoom lenses were only 17mm at the wide end.


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#20 Philipp Kunzli

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Posted 17 December 2015 - 09:48 AM

 

 

On an 18-80mm zoom the "widest" focal length will be... ...18mm

 

Freya

Sorry... Thought he was talking about the 15.5 - 45 LWZ Alura... My bet... :-)


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