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bokeh
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Joseph Wang



Joined: 06 Jun 2008
Posts: 15

PostPosted: Mon Jun 16, 2008 3:27 pm    Post subject: Reply with quote

Here is one example I mean by bad bokeh. You could look at the hair and see that it has BOTH blurr and sharp margins on one single strand of hair. For good bokeh, you need even blurring at all margins. This type of blurring with area of sharpness is due to the presence of astigmatism. The problem of having sharp margins is that it attracts attention to the wrong place . Ideal bokeh should have soft even margins. Astigmatism always give you a bad bokeh because it gives areas with different degrees of blurring.


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conurus
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Joined: 15 Aug 2006
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Location: Vancouver, Canada

PostPosted: Mon Jun 16, 2008 5:33 pm    Post subject: Reply with quote

Thank you for sharing with us pictures from the Y/C mount manual focus Contax 85/1.4. I would like to point out that the N-mount autofocus 85/1.4 is a completely different optical design with different design objectives.

Let's look at the ZF 85/1.4 photozone review, in particular the sample pictures at the end of the review. You could take a look at the sample with a lot of green foliage at the top right hand corner.

http://www.photozone.de/Reviews/46-nikon--nikkor-aps-c/256-zeiss-planar-zf-t-85mm-f14-review--test-report?start=2

Let's focus on the circular blurred patches in the background. The circles have sharp rings around, with the circumference brighter than the center of the circle, which is what is classified as "bad" bokeh and indicates over-corrected spherical aberration. The problem is less serious as the Y/C 85/1.4, but it is there.

Looking at my pictures from the N-mount 85/1.4, the circular patches are very even throughout, and the bokeh is neither "good" nor "bad". The bokeh is neutral.

The way I understand it, you are trying to select a portrait lens and bokeh is your primary selection criteria, and you are considering the ZF. Many factors affect bokeh, the most important of which is spherical aberration, and with all due respect I do not get your fixation on astigmatism and the conclusions you drew from astigmatism alone, even when real photos proved otherwise. Most of the lenses we discuss in this thread are reviewed in photozone. To make an informed decision you simply need to look at their sample pictures and pay attention to the circular patches and see if they look like doughnuts (bad bokeh), even (neutral bokeh) or bright in the center and fades towards the edge (good bokeh), and try to find if there are any double lines (bad bokeh). N 85/1.4 is neutral and ZF 85/1.4 is slightly on the "bad" side, although I am sure that great portraiture has come from either of the two lenses (and the Y/C mount too, even though its bokeh is even worse).

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Joseph Wang



Joined: 06 Jun 2008
Posts: 15

PostPosted: Tue Jun 17, 2008 3:50 am    Post subject: Reply with quote

Do you have a site to show me the photos from N 85 1.4 ?
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Joseph Wang



Joined: 06 Jun 2008
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PostPosted: Tue Jun 17, 2008 3:58 pm    Post subject: Reply with quote

Well, sometimes N 85 f1.4 does give circles with sharp rings around. Here is an example.

http://www.dpgallery.com/resource/contax/n/n_85_gallery_012.asp

I believe that ZF 85 1.4 and N 85 1.4 sometimes give circles with sharp rings.

There are lenses rarely give circles with sharp rings, they are C-Y 100 f2, C-Y 60 f2.8 and C-Y 85 f 1.2. They also render the face and skin better than the others, partly because they are not astigmatic.

This photo is produced by C-Y 100 f2 at f 2.8 Kodak 200 HD made to A4 prints. This image is produced by scanning the print. I love the skin tone.



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jjlphoto



Joined: 17 Jan 2007
Posts: 102

PostPosted: Tue Jun 17, 2008 4:32 pm    Post subject: Reply with quote

Here's a great site with informative info on this stuff:
http://www.vanwalree.com/optics.html
A nice third party source that is fairly objective. I'd hate to see a hissing match get started here. Crying or Very sad
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conurus
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Joined: 15 Aug 2006
Posts: 795
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PostPosted: Tue Jun 17, 2008 6:22 pm    Post subject: Reply with quote

Joseph Wang wrote:
Well, sometimes N 85 f1.4 does give circles with sharp rings around. Here is an example.

http://www.dpgallery.com/resource/contax/n/n_85_gallery_012.asp

I believe that ZF 85 1.4 and N 85 1.4 sometimes give circles with sharp rings.

There are lenses rarely give circles with sharp rings, they are C-Y 100 f2, C-Y 60 f2.8 and C-Y 85 f 1.2. They also render the face and skin better than the others, partly because they are not astigmatic.

This photo is produced by C-Y 100 f2 at f 2.8 Kodak 200 HD made to A4 prints. This image is produced by scanning the print. I love the skin tone.


Neutral bokeh renders an out of focus point as an even circle. An even circle may still have a well-defined edge.

Bad bokeh renders an out of focus point as a circle with an edge which is brighter than the center. The circle is rendered as a ring and looks like a doughnut.

Good bokeh renders an out of focus point as a gradually fading disc, with no well-defined edge at all.

Notice also that when you have good bokeh in the background you tend to have bad bokeh in the out of focus foreground areas, and vice versa. Since the background is more important than the foreground, we call the bokeh good if the background is good.

Judging from the N85 link you provided, I'll grant that there is a slight ring around the blurred patches. I suppose you will never have 100% neutral all the time since it would amount to perfectly correcting spherical aberration under all conditions. So even neutral lenses will sometimes err on the good side or on the bad side. You can make a lens which always err on the good side for the background but then it will be under-corrected for spherical aberration and you will have bad bokeh for the foreground.

Judging from the 100/2 Y/C shot that you posted, it also has neutral bokeh, you can still discern out of focus points as circles. For a lens with good bokeh you can't tell any edges in the discs at all, since the blurred discs would have no defined edges.

I hope you will find what you like. You seem to be happy with the Y/C 100/2 so far.
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MomoInu



Joined: 15 Aug 2006
Posts: 68
Location: Santa Fe, NM

PostPosted: Tue Jul 08, 2008 7:04 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.



You've got an error in your statement somewhere.

As Bo-Ming pointed out, bokeh is more a result of the degree of correction of spherical aberrations. I find the bokeh of the 100mm Makro-Sonnar to be quite nice and smooth, further the 85/1.4 N Planar has about the most wondrous and creamy bokeh I've seen. Further the 24-85 has a fine and unobtrusive bokeh that I don't think you can call "bad" in any way. I haven't used the 70-300 in a long time, but from memory, it wasn't bad at all either. And in spite of it's obvious astigmatism, the 17-35 N doesn't produce bad bokeh (at least in my use of it). In fact, if any of the lenses has a questionable bokeh is "might" be the 50mm N -- where it is a matter of taste and/or circumstances. That said, I do agree that the ZF's (at least for the 4 ZF lenses I have) have excellent bokeh. The ZF Makro's have excellent bokeh and perhaps are a bit nice in this area than the N's Makro-Sonnar. And while the ZF 85mm is pretty good, I still think the bokeh of the 85mm N-Planar is better -- especially for portraiture where the lens truly shines.
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Joseph Wang



Joined: 06 Jun 2008
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PostPosted: Mon Jul 28, 2008 10:09 am    Post subject: Reply with quote

Hello MomoInu,

I used to believe bad bokeh is related to astigmatism. There are two different schools in the web I found and one school say is due to astigmatism but others may say it is related to aberration. Well, one has to go deeper into optics to discover the truth. What I feel certain now is bad bokeh is related to the divergence of the line pairs in the MTF graph.

N 85 f1.4 has divergence of the line pairs. Most people in this site would say it has a good bokeh. Bokeh is best judged in the head only shots. It would be nice if someone would show me a photo with a nice bokeh taken by N 85 1.4. Bo-Ming showed me one, but it would be nice if I could see more.
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doc



Joined: 23 Feb 2008
Posts: 26

PostPosted: Tue Jul 29, 2008 5:07 pm    Post subject: Reply with quote

85N@1.4


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MomoInu



Joined: 15 Aug 2006
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Location: Santa Fe, NM

PostPosted: Tue Jul 29, 2008 10:00 pm    Post subject: Reply with quote

Joseph Wang wrote:

N 85 f1.4 has divergence of the line pairs. Most people in this site would say it has a good bokeh. Bokeh is best judged in the head only shots. It would be nice if someone would show me a photo with a nice bokeh taken by N 85 1.4. Bo-Ming showed me one, but it would be nice if I could see more.



I think the harshness of the example you showed at the top of this page is due primarily to the very harsh back lighting and blown-out highlights. I think you would see something quite different if the image was captured in the same lighting conditions as your example with the c/y 100/2.0

The example posted by Doc, immediately above this post, is much more representative, and consistent with what I've seen from this lens. (note to self: make sure you send your N 85 lens in for conversion, as soon as Bo-Ming has his supplies suitably replenished.)
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conurus
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PostPosted: Wed Jul 30, 2008 2:50 am    Post subject: Reply with quote

Hi Joseph,

Read MTF curves of the following two lenses. They have almost no divergence in the sagittal and tangential MTF curves.

1, Planar 50/1.4 (N or Y/C).
2, Makro-Sonnar 100/2.8, especially at 1:10, which is tight head portraiture distance. The two MTF curves hardly diverges at all.

Do you think they will have the best bokeh on earth? Because the solid line and the dotted line are so close to each other?

(MomoInu already said no to this one, from his experience with the N 50/1.4. Not that N50/1.4's bokeh is bad, but it does not rank among the greatest, contrary to what your theory would have predicted. I will add that Makro-Sonnar 100/2.8, while having great bokeh for a macro lens, especially in macro range, is no compare to N 85/1.4 in that department.)

Can we predict bokeh by reading MTF curves? I don't think it is that easy, and I don't think anyone has successfully predicted bokeh with MTF curves alone.

Also, as requested, I digged up a tight portrait which I have model release for, from the N Planar 85/1.4.



CRW_4341.jpg
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ISO  100 Focal length  86mm
Shutter speed  0.004957 seconds Aperture  f/1.4

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Joseph Wang



Joined: 06 Jun 2008
Posts: 15

PostPosted: Fri Aug 01, 2008 4:21 pm    Post subject: Reply with quote

Thank you for showing me all these photos.

Although I know my opinion is different from others in this site, I really believe that the divergence of the line pair is related to bad bokeh.

I brought my Canon 5D and Contax N 100 2.8 a few months ago. The latter is waiting to be converted. After a while of using the Canon digital, I came to one conclusion. No matter how I do the colour balance in the Photoshop, In the end, the colours from the Canon are never as good as film. In particular, the skin colour from the Canon is never as good as the Velvia from the scanner.
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Joseph Wang



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PostPosted: Fri Aug 01, 2008 4:31 pm    Post subject: Reply with quote

I would like to say further on the MTF of N85 1.4. When k=1.4, the line pairs stay quite close to each other. The graph does not tell how the lens behave at f2-4. These are the important f nos for portraits. The graph showed bad divergence at f=5.6. People care less on this because they rarely shoot at f5.6 except in the studio. I think the graph tells very little on the true behaviour of the lens.
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Joseph Wang



Joined: 06 Jun 2008
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PostPosted: Tue Sep 02, 2008 5:58 am    Post subject: Reply with quote

I received my conversion of Contax N 100mm f2.8 and got my "new" lens two weeks ago. It is an excellent conversion. It makes me able to manual focus ALL the time. I can manual focus with or without the autofocus working. Thank you, Bo Ming.

Another question, since N85 f1.4 can be converted now, there must be someone here who has tried both N 85 f1.4 and Canon EOS 85mm f1.2. How do they compare to each other ? Which has better bokeh ?
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doc



Joined: 23 Feb 2008
Posts: 26

PostPosted: Wed Sep 03, 2008 11:48 am    Post subject: Reply with quote

Not a great picture, just for comparison...
Same exposure (hand-handle), same develop in DPP.



dpp b85N-14.jpg
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Camera make  Canon Camera model  Canon EOS-1Ds Mark II
ISO  100 Focal length  86mm
Shutter speed  1/400 seconds Aperture  f/1.4

dpp b85L-14.jpg
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canon @1.4
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dpp b85L-14.jpg

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Camera make  Canon Camera model  Canon EOS-1Ds Mark II
ISO  100 Focal length  85mm
Shutter speed  1/400 seconds Aperture  f/1.4
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