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Zeiss Sonnar T* 135mm f/1.8 questions
#1
Hi all,

 

I read the excellent review on the

Zeiss Sonnar T* 135mm f/1.8 lens

at

http://www.opticallimits.com/sony-alpha-..._za_135_18

 

There were a couple of things that I wanted to ask, hopeing that perhaps

someone would know the answer. Partial answers are also welcome!

 

-------

 

1. "The front element does not rotate thanks to an IF (internal focusing) design."

Sure. But does ANY lens element rotate (inside), or the internal focus translates a

lens in the vertical direction without rotation?

 

-------

 

2. "Unfortunately there're no seals against dust and humidity".

 

What sealing does this refer to?

Sealing at the rim of the front lens along the edge?

Or sealing of the focuser ring (how?).

Or there are "cracks"/discontinuities at various locations on this lens?

 

-------

 

3. "In manual focusing mode it operates very smooth but there is a little

play when changing the focus direction - this is typical for non-SSM

Sony lenses."

 

How big is this backlash? ("play")? Is it consistent between lenses?

 

--------

4. "the lens shows a little vignetting at f/1.8 (~0.55EV)"

This is at the bottom/top or right/left side, or the corners?

 

--------

5. Regarding the "screw-driven AF" mechanism on the bottom: I assume that by turning

this around an internal component moves, but the manual focus ring does not turn around.

Could someone try this?

 

---------

6. Finally, a bonus question. Would manual focusing work by turning the manual focus ring

WITHOUT a camera body attached (i.e. no power); just projecting the light on a piece of

paper?

 

Best regards,

Sapkas

#2
Quote:Hi all,

 

I read the excellent review on the

Zeiss Sonnar T* 135mm f/1.8 lens

at

http://www.opticallimits.com/sony-alpha-..._za_135_18

 

There were a couple of things that I wanted to ask, hopeing that perhaps

someone would know the answer. Partial answers are also welcome!

 

-------

 

1. "The front element does not rotate thanks to an IF (internal focusing) design."

Sure. But does ANY lens element rotate (inside), or the internal focus translates a

lens in the vertical direction without rotation?
Why is this important to know? Can not think of any valid reason.... That the front element does not rotate is important.

Quote:-------

 

2. "Unfortunately there're no seals against dust and humidity".

 

What sealing does this refer to?

Sealing at the rim of the front lens along the edge?

Or sealing of the focuser ring (how?).

Or there are "cracks"/discontinuities at various locations on this lens?
Sealing of everything. If you do not shoot in heavy rain or during sandstorms, it is not of that much importance.

Quote:-------

 

3. "In manual focusing mode it operates very smooth but there is a little

play when changing the focus direction - this is typical for non-SSM

Sony lenses."

 

How big is this backlash? ("play")? Is it consistent between lenses?

 

--------

4. "the lens shows a little vignetting at f/1.8 (~0.55EV)"

This is at the bottom/top or right/left side, or the corners?
A lens is round, the image rectangular. Evident how the vignetting would be...

Quote:--------

5. Regarding the "screw-driven AF" mechanism on the bottom: I assume that by turning

this around an internal component moves, but the manual focus ring does not turn around.

Could someone try this?

 

---------

6. Finally, a bonus question. Would manual focusing work by turning the manual focus ring

WITHOUT a camera body attached (i.e. no power); just projecting the light on a piece of

paper?
Of course. But WHY???

Quote:Best regards,

Sapkas
#3
Quote:Hi all,

 

I read the excellent review on the

Zeiss Sonnar T* 135mm f/1.8 lens

at

http://www.opticallimits.com/sony-alpha-..._za_135_18

 

There were a couple of things that I wanted to ask, hopeing that perhaps

someone would know the answer. Partial answers are also welcome!

 

-------

 

1. "The front element does not rotate thanks to an IF (internal focusing) design."

Sure. But does ANY lens element rotate (inside), or the internal focus translates a

lens in the vertical direction without rotation?
 

I'm not sure about the relevance of this one ?

 

Quote:-------

 

2. "Unfortunately there're no seals against dust and humidity".

 

What sealing does this refer to?

Sealing at the rim of the front lens along the edge?

Or sealing of the focuser ring (how?).

Or there are "cracks"/discontinuities at various locations on this lens?
 

In theory water/dust could/creep into the lens body via the unsealed focus ring, yes. I would take a while though.

 

Quote:-------

 

3. "In manual focusing mode it operates very smooth but there is a little

play when changing the focus direction - this is typical for non-SSM

Sony lenses."

 

How big is this backlash? ("play")? Is it consistent between lenses?
 

Make it 1mm. 

Whether it is consistent - hard to tell. It is about the same on the ZA 16-80 (which I still own).

 

Quote:--------

4. "the lens shows a little vignetting at f/1.8 (~0.55EV)"

This is at the bottom/top or right/left side, or the corners?
 

Vignetting is a radial effect. The gradient depends on the focal length and format.

 

Quote:--------

5. Regarding the "screw-driven AF" mechanism on the bottom: I assume that by turning

this around an internal component moves, but the manual focus ring does not turn around.

Could someone try this?
 

The focus ring is decoupled from the AF gear so it does not rotate in AF mode.

 

Quote:---------

6. Finally, a bonus question. Would manual focusing work by turning the manual focus ring

WITHOUT a camera body attached (i.e. no power); just projecting the light on a piece of

paper?
 

It does.
#4
Thanks for the responses. Answering them one-by-one.

 

Quote:Why is this important to know? Can not think of any valid reason.... That the front element does not rotate is important.
 

There are valid reasons (even if you can't think of themSmile

I am planning a scientific use of this lens.

A rotating inner lens with tiny dust grains changes the flatfield and stray light pattern on the images.

Best if the inner lens does not rotate, but only translates. This is my best bet.

 

Quote:Sealing of everything. If you do not shoot in heavy rain or during sandstorms, it is not of that much importance.
 

And if you have this lens sitting outside in a desert for years in an enclosure that opens up during the night?

The lack of sealing may not be critical, if it is about as good as a Nikon or Canon lens.

If the comment meant that sealing is poor in comparison with typical Nikon or Canon lenses then thay might concern me.

 

Quote:A lens is round, the image rectangular. Evident how the vignetting would be...
 

The vignetting has cylindric symmetry with respect to the optical axis. This is trivial.

The image is rectangular (but not a box).

 

But which point on the chip does 0.55EV vignetting refer to? Vignetting will be different

on the horizonal edges, vertical edges and the corner. I just want to figure out where the 0.55EV

was measured at (my guess: corner).

 

Quote:Of course. But WHY???
 

 

There is no "of course". I have a lens (Canon 200 f/1.8 AF), where focusing does not work

even in MF mode, unless the lens (and its CPU) is powered up by a camera body.

I admit this was a surprise, and reverse engineering was quite an effort.

Glad to hear it would work on this lens.

 

Note: I am not attaching a DSRL to this lens, but mating it with a CCD.

 

Thanks again!

Sapkas

#5
Quote:I'm not sure about the relevance of this one ?

 

 

In theory water/dust could/creep into the lens body via the unsealed focus ring, yes. I would take a while though.

 

 

Make it 1mm. 
 

That is huge!

OK, I will measure this on a rented lens in about a week, and will report.

 

Quote:Whether it is consistent - hard to tell. It is about the same on the ZA 16-80 (which I still own).
 

That is very useful info.

 

Quote:Vignetting is a radial effect. The gradient depends on the focal length and format.
 

I am curious about the f/1.8 setup, and 28mm from the optical axis.

 

Quote:The focus ring is decoupled from the AF gear so it does not rotate in AF mode.
 

That is good news (and expected). Thanks for confirming.

 

 

Quote:It does.
 

Also good news.

 

Cheers

Sapkas
#6
So you want to use this lens in a manual focus fashion only. Maybe the Zeiss 135mm f2 ZE/ZF is a better idea? It won't show the MF ring play when changing direction, it most probably will not rotate any lenses, due to the way MF lenses usually focus, it is optically superior (very low LoCA in comparison to the Sony/Zeiss lens). And you only "lose" 1/3rd of a stop.

#7
If memory serves me right, the vignetting value is for the corner, but it is for a camera default adjusted image, not the lens' own performance.

Anyway, the application sounds to me a lot like astrophotography, where pixel peeping is justified. LoCA isn't so critical unless imaging is OSC. It's effects are diminished in LRGB and negligible in narrowband. What you mostly want is a point source remaining a point regardless where it is in the frame. Accurate focusing is a pain hence the question on the degree of backlash.

I use the Canon 135L in such a fashion. It is unusable wide open for OSC as the red channel focus is miles away from green/blue. But used for narrowband you focus for a single wavelength and all is well. Almost, my sensor isn't exactly perpendicular to the optical axis giving a noticeable defocus effect (like tilting a lens). We're talking in the magnitude of 10s of microns here and I don't fancy adjusting that out!

Oh, will the focusing be automated? It will likely shift too much with temperature.

The ZF version of the lens would be quite interesting for a different reason. As it has a user controlled aperture, that would allow the ease of trading speed for reduction of size of point sources. A trick I heard of is to use a front aperture mask, but I suspect that would throw off the design of complicated photographic lenses as opposed to much simpler astrographs. Might need to check if it has rounded aperture blades though, unless you like the diffraction spike look.

Anyway, sounds like Sapkas is renting the Sony to see how it works, and that's the best way to find out as terrestrial photographers don't tend to look at things in the same way.
<a class="bbc_url" href="http://snowporing.deviantart.com/">dA</a> Canon 7D2, 7D, 5D2, 600D, 450D, 300D IR modified, 1D, EF-S 10-18, 15-85, EF 35/2, 85/1.8, 135/2, 70-300L, 100-400L, MP-E65, Zeiss 2/50, Sigma 150 macro, 120-300/2.8, Samyang 8mm fisheye, Olympus E-P1, Panasonic 20/1.7, Sony HX9V, Fuji X100.
#8
Quote:So you want to use this lens in a manual focus fashion only. Maybe the Zeiss 135mm f2 ZE/ZF is a better idea? It won't show the MF ring play when changing direction, it most probably will not rotate any lenses, due to the way MF lenses usually focus, it is optically superior (very low LoCA in comparison to the Sony/Zeiss lens). And you only "lose" 1/3rd of a stop.
 

Indeed, I will use this in MF fashion only. Thanks for the suggestion on the 135mm f/2 ZE/ZF lens. I will check it out.

 

Regarding the ring play, now that I have such a lens, I confirm that it is indeed about 1mm.

The same backlash is present when driving the focus through the slotted screw on the flange.

 

I also looked inside the lens while focusing, and identified the group of lenses (or single lens) moving, and

it seems to me, from the barrel that is holding this moving component, that it is not rotating, but simply sliding.

 

Regarding LoCa, I don't know how serious it is for the Zeiss 135/1.8 lens. I fancy this lens because of the large aperture,

and even the difference f/1.8 to f/2.0 matters (f/1.8 takes in 23% more light when compared to f/2).

 

Quote:If memory serves me right, the vignetting value is for the corner, but it is for a camera default adjusted image, not the lens' own performance.
 


I will measure it.

 

> Anyway, the application sounds to me a lot like astrophotography, where pixel peeping is justified. LoCA isn't so critical unless imaging is OSC. It's effects are diminished in LRGB and negligible in narrowband. What you mostly want is a point source remaining a point regardless where it is in the frame. Accurate focusing is a pain hence the question on the degree of backlash.

 

What is OSC?

 

 

Quote:I use the Canon 135L in such a fashion. It is unusable wide open for OSC as the red channel focus is miles away from green/blue. But used for narrowband you focus for a single wavelength and all is well. Almost, my sensor isn't exactly perpendicular to the optical axis giving a noticeable defocus effect (like tilting a lens). We're talking in the magnitude of 10s of microns here and I don't fancy adjusting that out!


Oh, will the focusing be automated? It will likely shift too much with temperature.
 

Yes, I plan to have automated focusing through the focuser ring, or perhaps using the slotted screw.

 

Quote:The ZF version of the lens would be quite interesting for a different reason. As it has a user controlled aperture, that would allow the ease of trading speed for reduction of size of point sources. A trick I heard of is to use a front aperture mask, but I suspect that would throw off the design of complicated photographic lenses as opposed to much simpler astrographs. Might need to check if it has rounded aperture blades though, unless you like the diffraction spike look.
 

I can't stop down the aperture to f/2. I need the light.

 

Quote:Anyway, sounds like Sapkas is renting the Sony to see how it works, and that's the best way to find out as terrestrial photographers don't tend to look at things in the same way.
 

Will send feedback later, when I had a chance to try it. Thanks for the wise words.

 

Sapkas
#9
Quote:What is OSC?
OSC = one shot colour. Generally speaking, using a bayer pattern colour filtered sensor like that of most colour cameras. That way you need to have all wavelengths in good focus at the same time otherwise different colours will be blurred due to different focus points of each wavelength.

Colour astrophotography is also done by using a mono sensor and then using separate RGB filters in turn. Thus you only have to focus for each wavelength area at a time and don't have to worry about others. Of course this only really works if the subject doesn't change for long periods so you can align and recombine the image.
<a class="bbc_url" href="http://snowporing.deviantart.com/">dA</a> Canon 7D2, 7D, 5D2, 600D, 450D, 300D IR modified, 1D, EF-S 10-18, 15-85, EF 35/2, 85/1.8, 135/2, 70-300L, 100-400L, MP-E65, Zeiss 2/50, Sigma 150 macro, 120-300/2.8, Samyang 8mm fisheye, Olympus E-P1, Panasonic 20/1.7, Sony HX9V, Fuji X100.
#10
I measured the vignetting of the Zeiss 1.8 lens. For a 24 x 36mm format sensor, 52% of the light is received at the edges

along the long side, and 39% is received in the corners (that is, 48% of the light is lost at the edges, and 61% in the corners).

 

I did the measurements with a 39mm x 39mm sensor, and vignetting on this larger format chip is: 51% at the edges (center line),

and 19% in the corners.
  


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