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Lens tests


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#1 dbledwn11

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Posted 24 November 2005 - 09:07 PM

i'm going to be shooting some tests soon and i was wondering about the lenses i'm using. i want to be getting the sharpest images possible for the real thing so i thought it would be a good idea to know in advance what f-stop the lenses need to be set at to get optimum results.

now i've read that f4 tends to be the optimum aperture, but surely this changes from lens to lens.

so is it necessary to specifically test for that kind of thing or not?

if so is there a particular method for doing so?

just so you know these are the lenses:

Angenieux Paris F.12 -120 1:2.2 Zoom Lens
Carl Zeiss F1.4/35mm Distagon Lens
Carl Zeiss F1.4/50mm Planer Lens
Carl Zeiss F1.4/85mm Planer Lens
Carl Zeiss F.2\135mm Planer Lens

fitted for an Aaton7.

are these lenses any good?

thanks.
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#2 Laurent Andrieux

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Posted 25 November 2005 - 07:20 AM

Try not to work the Angenieux under 3.5 (4-1/2) The zeiss should be good until 2.8. But when you really need to open more, you usually can't avoid doing so... The best is to work at around 4 - 5.6
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#3 dbledwn11

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Posted 25 November 2005 - 01:45 PM

so you're saying not to worry about testing the lenses?

sorry.
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#4 lluis

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Posted 25 November 2005 - 01:46 PM

The Zeiss lenses that you have come from Contax SLR 35mm still cameras and will perform much better that your Angenieux zoom at any stop. I have used it full open with great results. Of course 2.8/5.6 will perform better...
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#5 Laurent Andrieux

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Posted 25 November 2005 - 04:57 PM

so you're saying not to worry about testing the lenses?


Do you have an FTM lab ? Is it realy worth testing since you know it would be better around T 4 ?
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#6 dbledwn11

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Posted 25 November 2005 - 07:30 PM

Do you have an FTM lab ? Is it realy worth testing since you know it would be better around T 4 ?


if i knew what an FTM lab was i could answer that one, as it is i'll just go for the f4 mark

thanks for the help.
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#7 Laurent Andrieux

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Posted 26 November 2005 - 07:13 AM

It's a good and easy way to determine not only the definition but also the dynamic range of an optic in different situations (different T stops esp.).

Edited by laurent.a, 26 November 2005 - 02:50 PM.

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#8 BritLoader

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Posted 26 November 2005 - 01:16 PM

I have often heard that lenses are at their optimum performance at t4, however I have really never been given a full explaination of what this means.

Obvoiusly there are noticable differences in DOF that come with different t stops, past this what is the effect of the different aperture on the image taken.

Am I right in thinking that there is an effect in terms of contrast and saturation?

Also I had kind of picked up the idea that t4 - 5.6 gives the most desirable DOF for shooting the human face, enough leway to have the eyes nose and ears to be sharp, whilst still allowing the background to be soft enough to leave our attention with the face. Of course this is a variable with the focal lense of the lense. Is this factor part of the idea of an optimum stop, or a seperate question altogether.? <_<
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#9 Leo Anthony Vale

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Posted 26 November 2005 - 01:30 PM

I have often heard that lenses are at their optimum performance at t4, however I have really never been given a full explaination of what this means.


---The optimum stop is usually about one& a half to two stops below wide open.

At the widest stops, abberations from the edges of the lens reduce sharpness.
As the iris is closed, the edges are covered eliminating those abberations.
As the stops get very small, diffraction effects kick in. The edges of the aperture blades bend the light rays, thus smearing the image a bit. Yeah, depth of field increases but sharpness goes down.

---LV
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#10 BritLoader

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Posted 26 November 2005 - 01:55 PM

thanks leo,

so is there no difference in terms of contrast, saturation etc, only in 'sharpness' (as apossed to DOF)?

also, is the two and a half stop rule similar on zoom lenses and primes?
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#11 Laurent Andrieux

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Posted 26 November 2005 - 02:48 PM

When a lens has aberrations, it's not only definition that is affected, but also contrast, chromatic aberrations etc.

Usually a lens is at its best in the middle of the avaible apertures.

Considering that 2 stops closer than the widest aperture is also a good basis, since the widest aperture is a matter of commercial considerations.
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