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bokeh
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Post new topic   Reply to topic    conurus Forum Index -> Contax N to Canon EF Mount Conversion
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Joseph Wang



Joined: 06 Jun 2008
Posts: 15

PostPosted: Sat Jun 07, 2008 3:47 am    Post subject: bokeh Reply with quote

I understand at the moment the conversions for Contax N to Canon EOS are sold out. I have a Contax N 100mm f2.8 waiting to be converted. How long do I wait if I wish to get it converted to EOS mount ? Can I make my order now ?
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conurus
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Joined: 15 Aug 2006
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Location: Vancouver, Canada

PostPosted: Sat Jun 07, 2008 1:52 pm    Post subject: Reply with quote

We apologize for the disruption. We are making a new batch of mounts from scratch and it is well under way now. However, we do not have a scheduled date at this point. Thank you for your patience in the meantime.
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frank



Joined: 05 Feb 2008
Posts: 17
Location: Boston, USA

PostPosted: Sat Jun 07, 2008 3:06 pm    Post subject: Reply with quote

Is this the same to the 24-85 & 70-200mm conversions, too?
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lam



Joined: 27 Apr 2008
Posts: 127
Location: Bangkok Thailand

PostPosted: Sat Jun 07, 2008 4:06 pm    Post subject: Reply with quote

me too.

my list
N50
N85
N100
N24-85

my wish list
N17-35
N400
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Joseph Wang



Joined: 06 Jun 2008
Posts: 15

PostPosted: Sun Jun 08, 2008 12:34 pm    Post subject: Reply with quote

Some lenses are more important for the conversion but some are less. This is my list, the first being the most important.

N 100 2.8
N 400 F4

I would believe N100 is the most important. I do lots of hand held makro work, focusing at 1:1 or 1:2 magnification is not easy, it makes it more complicated with a manual aperture. Yes, I have C-Y 100 Makro-Planar and Zeiss Nikon 100 Makro-Planar, but manual focusing these lenses with manual apertures are not easy. This is why I believe N100 is the most important to be converted.

N 400 is BIG. Handling it is not easy, it would make the job easier with a automatic aperture.

I find converting other N lenses less important. There are many better alternatives.

N 85 1.4 This is a very old design of Zeiss normal lens and suffers from astigmatism. I find the new Zeiss Nikon mount lenses are better alternatives. I would prefer using ZF 85 1.4 than ZN 85 1.4. Again, the images from the former is prettier than the latter one with a very much improved bokeh. 85 1.4 is those lenses when you use it at large aperture most of the time, automatic aperture is less important.

N 50 1.4 I find ZF 50 1.4 or ZF 50 f2 Makro-Planar are better alternatives. Both N85 and N50 suffers from astigmatism whereas the newer generation of Zeiss lenses has been very much improved in this respect.

What do you think ?
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crazeazn



Joined: 24 Sep 2007
Posts: 10
Location: Houston, Texas

PostPosted: Mon Jun 09, 2008 4:57 pm    Post subject: Reply with quote

whats lense astigmatism? isnt that for the eye? Confused Question
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conurus
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PostPosted: Tue Jun 10, 2008 2:54 am    Post subject: Reply with quote

Our goal is to convert all 9 lenses in the N series. We intended to serve photographers who bought into the Contax N system and wanted to move to the latest digital camera bodies. We need to be able to convert all the N-mount lenses they have already purchased in order to ease the transition.

Astigmatism is the inability to focus both on the sagittal (think of lines radiating from the center, as in the spokes of a bicyle wheel) and the tangential (think of the tire of the wheel) at the same time, even if they are both at the same distance from you. We are the experts in mount electronics but not optics, but at the risk of oversimplication you can review the MTF curves published by Zeiss and if the solid curve (sagittal) and dotted curve (tangential) are far apart from each other, then there is astigmatism.

Zeiss made a good number of 85/1.4 (Y/C, Rollei, Sony Alpha, ZF, N) and the N Planar is the most complex design of them all, with a total of 10 elements in 9 groups. In terms of sharpness it is no match for the Makro-Sonnar 100/2.8, but I suppose that is not the point. As a portrait lens the N Planar 85/1.4 can't be beat, and I speculate that the lens is optimized for portraiture and that may have been one of the reasons for the complexity of the lens design compared to other 85/1.4's.

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Joseph Wang



Joined: 06 Jun 2008
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PostPosted: Tue Jun 10, 2008 6:40 am    Post subject: Reply with quote

Astigmatism can exist both in the eyes and camera lenses.

It exists in the N-lenses. In the history of the development of Zeiss lenses, N lenses are the first series in 35mm photography that Zeiss has to consider autofocus in the design. As a result, some lenses are made more complex than the manual counterparts. N100 f2.8 has 12 elements whereas ZF 100 f2 has only 9. As a result of this complex design, it tends to make the lens more astigmatic. Not surprisingly, N 100 is more astigmatic than ZF 100.

The same is true for N 85 1.4 when compared with ZF 85 1.4 and N 50 1.4 with ZF 50 1.4.

The same is true for N 17-35. Since it is a zoom and is able to autofocus, it has a complex design. It is certainly more astigmatic than the three ZF primes, ZF35, ZF28 and ZF25.

In general, the N lenses are more astigmatic than the ZF counterparts.
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Joseph Wang



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PostPosted: Tue Jun 10, 2008 6:46 am    Post subject: Reply with quote

Since N 85 1.4 suffers from astigmatism, I would prefer ZF 85 1.4 for portraits. Another even better example is C-Y Zeiss Contax 85 f 1.2.

Astigmatism tends to produce bad bokeh. If you wish to avoid bad bokeh, avoid N lenses, choose the Makros and use the ZFs.
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Joseph Wang



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PostPosted: Tue Jun 10, 2008 6:50 am    Post subject: Reply with quote

It is actually the G lenses when Zeiss first design with autofocus in 35mm photography, sorry my mistake.
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John Black



Joined: 24 Jun 2007
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Location: Dallas, TX

PostPosted: Tue Jun 10, 2008 7:49 am    Post subject: Reply with quote

I'd recommend the C/Y 100/2 Planar over the new Zeiss 100/2 ZF. I'd also put the 100/2 ahead of the 85/1.4N.

http://www.pebbleplacephotography.com/Offload/PDFs/Planar_2_100mm_e.pdf

An example the 100/2's "3D" abilities -



And a portrait -



And shooting into the sun -



I know it's easy to pull the best pictures across a wide range of time; those were all the same day.

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conurus
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PostPosted: Tue Jun 10, 2008 3:08 pm    Post subject: Reply with quote

Joseph Wang wrote:
Since N 85 1.4 suffers from astigmatism, I would prefer ZF 85 1.4 for portraits. Another even better example is C-Y Zeiss Contax 85 f 1.2.

Astigmatism tends to produce bad bokeh. If you wish to avoid bad bokeh, avoid N lenses, choose the Makros and use the ZFs.


Bad bokeh may for example arise from over-correction of spherical abberation in a lens design. Astigmatism lowers the sharpness of a lens but I am not sure if it affects bokeh as well.

Being a portrait lens, bokeh is a high design priority for the N-Planar 85/1.4, and my use of it over the last couple of years extensively for shooting people has confirmed that.

Before you purchase a lens, MTF curves published by Zeiss are a useful data point, but there is always the danger of reading too much into tea leaves. For instance, other than the macro lenses, the curves are all measured at infinity, which tells you little about its performance at portrait distances. To infer that a lens has bad bokeh and unsuitable for portraiture by only reading MTF curves measured at infinity, with all due respect, is a bit far-stretched, in my humble opinion.

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Joseph Wang



Joined: 06 Jun 2008
Posts: 15

PostPosted: Tue Jun 10, 2008 4:30 pm    Post subject: Reply with quote

I would agree with Conurus that I might be extrapolating too much. Why Zeiss only show the MTF at infinity for most lenses ? Indeed, Zeiss does show MTF at different distances, but this is only for the Makro lenses. For non-makro lenses, MTF infinity is a good enough representation of the performance. For makro lenses, there are big difference in MTFs at difference distances.

I had good time with my C-Y 100mm f2 and I have no doubt that it is a very good lens ( one of those not having astigmatism). However, I have ZF 100mm f2 as well. I can tell you that this one is even better. Try it, you will believe me. ZF 100 f2 performs better at f2 than C-Y 100 f2 at f2. ZF 100 f2 at f4 is better than C-Y 100 f2 at f 5.6, so it is at least one stop better.

Well corrected lenses tends to have beautiful circular bokeh. On the other hand, astigmatic lenses do not have diffuse circular bokeh, they have uneven looking bokeh with ugly edges. The pattern of bokeh is very much related to whether a lens is astigmatic or not.
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John Black



Joined: 24 Jun 2007
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Location: Dallas, TX

PostPosted: Wed Jun 11, 2008 3:16 am    Post subject: Reply with quote

I'm sure the new ZF is a fine lens optically; however, I prefer C/Y ergonomics - it's smaller and its aperture ring design is superior. They are two different lenses - the ZF being a macro and the C/Y being a telephoto. For macro use I'd opt for the 100/2.8 N - its bokeh has some very unique traits. When Bo-ming has mounts in stock again, I'll probably do another 100N. And when the 50 is finally available, I'll be standing in line too Smile
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conurus
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PostPosted: Wed Jun 11, 2008 3:20 am    Post subject: Reply with quote

Hi Joseph,

I did some googling on this topic and found this:

http://ogiroux.blogspot.com/2008/04/lens-connoisseurship.html

Quote:

Finally, if the radial and tangential lines of the edge contrast pair are separated by a wide margin, then the lens is astigmatic at that distance from the center, and the bokeh will not be Neutral (but could be either Good or Bad).


So, according to this author, astigmatism does not necessarily imply bad bokeh.

Anyway I am posting this picture from the N-Planar at f/1.4. This kind of bokeh is classified as "neutral".



bbq.jpg
 Description:
 Filesize:  431.95 KB
 Viewed:  16979 Time(s)

bbq.jpg

EXIF Information  Details
Camera make  Canon Camera model  Canon EOS-1DS
ISO  100 Focal length  86mm
Shutter speed  1/5000 seconds Aperture  f/1.4

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