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Archive 2011 · Does the 5N 'exaggerate' field curvature?
  
 
Sosua
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p.6 #1 · p.6 #1 · Does the 5N 'exaggerate' field curvature?


OK, back to my original field curvature issue...

Here is an example of the neighbors house (about 25 meters away) with my 35mm F2.8 Summaron at F5.6 (The widest aperture where I can get everything pretty much in focus via focusing a little deeper). It is however quite a fine margin of error to do so and everything should be in focus from about 10 metres in a perfect 'hyperfocal world':


Summaron-5.6-full-scene by Sam Waldron, on Flickr

Now edge crops - sharp enough (trees behind the edge of the house are about 100 metres further away):


Summaron-5.6-Edge-crops by Sam Waldron, on Flickr

However, to do this at 5.6, I need to sacrifice focus on the house as shown below due to the deeper focus:


Summaron-5.6-centre-crops-OOF by Sam Waldron, on Flickr

Its workable with the Summaron and easier at F8 of course, but would a Biogon 35mm let me do this at F4 or less??



Dec 13, 2011 at 07:56 AM
Sosua
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p.6 #2 · p.6 #2 · Does the 5N 'exaggerate' field curvature?


I also was reading the other day, Denoir was saying its the 35mm F2 Biogon that has the flattest field? And the Biogon-C had issues?


Dec 14, 2011 at 04:48 AM
douglasf13
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p.6 #3 · p.6 #3 · Does the 5N 'exaggerate' field curvature?


Sosua wrote:
I also was reading the other day, Denoir was saying its the 35mm F2 Biogon that has the flattest field? And the Biogon-C had issues?


Both the ZM 35/2 and 35/2.8 have some issue at the corners on NEX, but are better on the 5N than the 5.



Dec 14, 2011 at 04:49 AM
rscheffler
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p.6 #4 · p.6 #4 · Does the 5N 'exaggerate' field curvature?


Was the comment by Luka based on use with an M9? From my experience with the ZM35C on the M9, it does exhibit some slight field curvature characteristics into the corners. And the ZM35 f/2 likely has that flat field at infinity.

Unfortunately my one 5N forest test scene doesn't lend itself very well to this aspect. But if you look at the upper corners, the ZM35C image seems to show more focus there than compared to the CV35 f/1.2 II. What I find interesting, and is corroborated by Doug above, is the much more disturbing blur into the corners exhibited by the ZM35C. For example at f/5.6 the Zeiss looks quite nervous while the CV is very smooth. Naturally at f/4 it's even more nervous looking. This is perhaps a less extreme example of the astigmatism issues of the Biogon design exhibited in my ZM21/2.8 samples of the same scene. So I would guess that for your desired use, the ZM35C probably wouldn't give you pleasing edges/corners at f/4. I no longer have the 5N at my disposal, so perhaps Doug can confirm this if he still has the lens?

The CV lens, based on the block diagram on the Cosina site, seems to be that of a more telecentric design than the 35C. And it looks very normal into the corners of my 5N images compared to the 35C.




Dec 14, 2011 at 05:42 AM
Sosua
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p.6 #5 · p.6 #5 · Does the 5N 'exaggerate' field curvature?


Thanks Ron - Luka was talking about on the M9, so possible it would not translate to the 5N.

Will check out your links - thanks - my Summaron is doing well to be honest at 5.6, looks like however to get sharp corners on planar subjects at wider apertures I have to spend quite a few more $$ and size though.

I guess this is what we get for using lenses on a sensor not designed for them - trial and error



Dec 14, 2011 at 06:01 AM
 

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rscheffler
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p.6 #6 · p.6 #6 · Does the 5N 'exaggerate' field curvature?


Sam, I noticed you recently added a CV40 f/1.4 (based on another post), and perhaps it's just a rental to try with the GXR, but I'm curious what you find from it in terms of field curvature.

I just received a used one today and have been playing with it on my M9. It's my first time using this lens and was surprised to find that it appears to have huge field curvature readily apparent with distant, relatively planar subjects (like a house across the street). For example, at f/5.6, if the house across the street is in focus, say about 25m away, then objects only about 5-10m away are in focus along the edges of the image. And it seems like the central 'sweet spot' for good focus is quite small on FF, maybe half the frame at most.

Let me know if you also notice field curvature on the GXR/NEX.

Ron



Dec 16, 2011 at 08:04 PM
douglasf13
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p.6 #7 · p.6 #7 · Does the 5N 'exaggerate' field curvature?


rscheffler wrote:
Sam, I noticed you recently added a CV40 f/1.4 (based on another post), and perhaps it's just a rental to try with the GXR, but I'm curious what you find from it in terms of field curvature.

I just received a used one today and have been playing with it on my M9. It's my first time using this lens and was surprised to find that it appears to have huge field curvature readily apparent with distant, relatively planar subjects (like a house across the street). For example, at f/5.6, if the house across the street is in focus, say about
...Show more

My CV 35/1.4 is like that on NEX. In order to sharpen up the corners at infinity at medium apertures, I have to focus the center past infinity, which only works on some adapters.



Dec 16, 2011 at 08:18 PM
rscheffler
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p.6 #8 · p.6 #8 · Does the 5N 'exaggerate' field curvature?


Thanks Doug. I found a couple other references to this behavior referring to the 35/1.4, but not really anything concrete about the 40/1.4... sounds like they're related in this behavior. Not a problem though since my intent with this lens is more or less wide open near distance work of mostly non-planar objects. Other lenses that I have, like the ZM50 f/2 seem to be much better for field flatness stopped down.


Dec 16, 2011 at 11:22 PM
Sosua
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p.6 #9 · p.6 #9 · Does the 5N 'exaggerate' field curvature?


Yeah Ron, unfortunately its still an issue for landscape type work on the 5N / GXR M (although F8 will overcome it) at middle apertures. I'll test if its slightly better on the GXR, although it seems to still be evident.

I was hoping to have a 'dual purpose' lens as the speed and interesting rendering is fun wide open, but usually i'm shooting landscapes or images where I want a more technical IQ...



Dec 17, 2011 at 12:35 AM
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