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Differences between zooms and variable primes?


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#1 James Steven Beverly

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Posted 17 August 2010 - 11:26 PM

What are the differences between zooms and variable primes? It seems the only real deference is that variable primes have a much smaller over all focal length, which begs the question, why buy a set of expensive variable primes when a good quality zoom works so well at a fraction of the price? B)
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#2 Rob Vogt

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Posted 17 August 2010 - 11:50 PM

What are the differences between zooms and variable primes? It seems the only real deference is that variable primes have a much smaller over all focal length, which begs the question, why buy a set of expensive variable primes when a good quality zoom works so well at a fraction of the price? B)



Which zoom are you referring to? The Optimo 25-290 is about 40-60k if I'm not mistaken and the variable primes can be had for about 10k each if not less. The variable primes, b/c they have a smaller zoom range also are typically faster than most zooms, they're a T2.2. The Variable primes are meant to give you a fast alternative to primes which would take an 8 lens set down to 3. They intercut almost identically with spherical primos as an Angenieux would with a set of Cookes (although most people would probably go with a PV 11:1 than a set of VPs).
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#3 Dom Jaeger

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Posted 18 August 2010 - 12:43 AM

The term variable prime as I understand it also refers to the fact that it does not necessarily keep focus when you change the focal length.

Freed of that rather stringent requirement, and with a generally shorter focal range, they can be made lighter and faster, as Rob said.

Proper cinematography zoom lenses like the Angenieux 24-290 mentioned have a very tight tolerance on their defocusing curve, something like plus or minus 0.01 mm of equivalent back-focus. Practically speaking, that means they should resolve 200 line pairs/mm throughout their zoom range without needing to alter the focus ring.
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#4 Stephen Williams

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Posted 18 August 2010 - 03:46 AM

The term variable prime as I understand it also refers to the fact that it does not necessarily keep focus when you change the focal length.

Freed of that rather stringent requirement, and with a generally shorter focal range, they can be made lighter and faster, as Rob said.

Proper cinematography zoom lenses like the Angenieux 24-290 mentioned have a very tight tolerance on their defocusing curve, something like plus or minus 0.01 mm of equivalent back-focus. Practically speaking, that means they should resolve 200 line pairs/mm throughout their zoom range without needing to alter the focus ring.


Hi,

ANY cine VP will focus throughout it's range, the term is being incorrectly being used on Reduser by people with still zoom lenses, that don't hold focus throughout their range.
Variable Primes have the QUALITY of image primes, zooms historically were a compromise, less so today.

To my knowledge only Cooke & Zeiss have ever made any lenses called Variable Primes. FWIW any cine prime that has zero breathing is actually a VP!
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#5 Dom Jaeger

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Posted 18 August 2010 - 09:52 AM

Hi,

ANY cine VP will focus throughout it's range, the term is being incorrectly being used on Reduser by people with still zoom lenses, that don't hold focus throughout their range.
Variable Primes have the QUALITY of image primes, zooms historically were a compromise, less so today.

To my knowledge only Cooke & Zeiss have ever made any lenses called Variable Primes. FWIW any cine prime that has zero breathing is actually a VP!


But I get all my information from Reduser, never let me down yet... :lol:

Actually what I said was they don't necessarily keep focus through a change in focal length.

I haven't had a chance to project Zeiss VPs to see how well they keep focus, I'm sure it would be pretty good, but they are, by definition, not designed for in-shot zooming. They are designed to be set to a focal length and then used as a prime. Or perhaps Zeiss/Arri are just using a marketing trick, and they're actually short zooms.

At any rate the term variable prime is usually used to describe a lens with variable focal length range but less precision zoom mechanics and elements in order to have the image quality and speed of a prime. Otherwise why not call it a short zoom?

Schneider for example make variable prime lenses for projection, allowing a small focal length change to adjust the projected picture image size. They are not designed to zoom, which primarily means they do not hold focus.
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#6 Stephen Williams

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Posted 18 August 2010 - 10:08 AM

At any rate the term variable prime is usually used to describe a lens with variable focal length range but less precision zoom mechanics and elements in order to have the image quality and speed of a prime. Otherwise why not call it a short zoom?


I disagree, I understand a Variable Prime to be an exceedingly high quality & expensive no compromise short zoom lens. The vast majority of zooms do not have the quality of primes so are not worthy of the title variable prime.

Schnieder make some Vario Focal 'Variogon' lenses, I do not concider those to be Variable Primes, just short zooms that dont hold focus.
http://www.schneider.../variogon_e.htm
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#7 Rob Vogt

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Posted 18 August 2010 - 10:13 AM

The term variable prime as I understand it also refers to the fact that it does not necessarily keep focus when you change the focal length.

Freed of that rather stringent requirement, and with a generally shorter focal range, they can be made lighter and faster, as Rob said.

Proper cinematography zoom lenses like the Angenieux 24-290 mentioned have a very tight tolerance on their defocusing curve, something like plus or minus 0.01 mm of equivalent back-focus. Practically speaking, that means they should resolve 200 line pairs/mm throughout their zoom range without needing to alter the focus ring.


I wouldn't consider them lighter by any means... They're not as big as the 24-290, but they have weight to them. The only set I've ever been on them with we didn't do any zooming in shot so I can't comment about that otherwise.
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#8 Stephen Williams

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Posted 18 August 2010 - 10:55 AM

I wouldn't consider them lighter by any means... They're not as big as the 24-290, but they have weight to them. The only set I've ever been on them with we didn't do any zooming in shot so I can't comment about that otherwise.


You will find they focus 100% throughout the range & they have to because people focus by distance marks, it has to be spot on. The Arri VP's are extreamly heavy which is the main reason they have never been very sucessful, however what a bargain second hand @ $10,000 each.
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#9 Dom Jaeger

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Posted 18 August 2010 - 11:26 AM

I think maybe there's some confusion here between the term variable prime and the Zeiss/Arri range of lenses called Variable Primes.

As I said earlier, the Zeiss lenses are probably more like short zooms, albeit with the ability to lock off various focal lengths, so yeah, they're heavy.

But the term variable prime is also used to describe other lenses, like the projection lenses I mentioned. They use less elements because they don't need to be a zoom lens, so they are faster and have better optical properties.

Here's the blurb from Schneider:


Variable Prime

Variable Prime lenses are cinema projection lenses with a variable focal length of 7%, designed to allow precise control of picture size while maintaining the highest image quality standards of our prime lenses.
To continue to address the needs of today's multiplex designers, Schneider has developed the first series of Variable Prime projection lenses. The Variable Prime VP-CINELUX series consists of 13 lenses that have the unique property of adjustable focal length. With their 7% range of picture size adjustment, the image they project can be precisely sized to fit the screen. These lenses are correctly called Variable Prime lenses. They are not zoom lenses, so they don't have the performance compromises and light-loss associated with zooms. They are all fast F/2 lenses, projecting large quantities of light and producing bright, uniformly illuminated, high-resolution images even on the largest of screens.


But I realize the original post was probably referring to the Zeiss lenses, rather than the generic term, so I shall apologise and bow out.
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#10 Stephen Williams

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Posted 18 August 2010 - 12:54 PM

I think maybe there's some confusion here between the term variable prime and the Zeiss/Arri range of lenses called Variable Primes.

As I said earlier, the Zeiss lenses are probably more like short zooms, albeit with the ability to lock off various focal lengths, so yeah, they're heavy.


But I realize the original post was probably referring to the Zeiss lenses, rather than the generic term, so I shall apologise and bow out.


Hi,

Were talking about cine lenses here, Cooke also produced the Variokinital (1975) & Variopancro (1981) Their primes were called Kinital 16mm & Pancro 35mm at the time.
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