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Archive 2011 · Does the 5N 'exaggerate' field curvature?
  
 
Sosua
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p.2 #1 · p.2 #1 · Does the 5N 'exaggerate' field curvature?


Thanks guys - lots of interesting information here.

I guess the good thing is at the apertures I would expect / want everything to be in focus (which is where I tend to shoot), performance is great edge to edge and I can get my subject sharp with a separated background at bigger apertures.

I don't really shoot flat objects at wider apertures so real world it isn't a problem for me - Just seemed to be a little more pronounced than what I expected (using FF glass on a crop sensor) is all.




Dec 07, 2011 at 03:52 AM
Specularist
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p.2 #2 · p.2 #2 · Does the 5N 'exaggerate' field curvature?


denoir wrote:
Actually he speaks of astigmatism and not of field curvature. They're related but not the same. Field curvature affects the whole image space while astigmatism only one directional component.


Okay. More accurately then, the filter introduces curvature of the tangential focal surface. The result is similar to overall field curvature, in that refocusing can often improve the sharpness of structures at the edge of the field (e.g. a horizon, the side of a building, etc. anything with predominantly tangential orientation, which of course depends on how the photographer frames the image).



Dec 07, 2011 at 03:11 PM
philip_pj
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p.2 #3 · p.2 #3 · Does the 5N 'exaggerate' field curvature?


Good of Dr Nasse to weigh in on the wide angle issue on the NEX series. His main point is that symmetrical wide angles need to be designed with the camera in mind as a key design criterion.

The serious loss of tangential performance got me looking at the NEX image thread - it's not insiginificant in Nasse's comparison charts, and this at f5.6.

Note also that the performance heads south just a few millimetres off image centre, about 3mm image height in fact! Hardly just the 'edge of the field'.

You can picture the image deteriorating like ripples from a stone dropped in the centre of a circular pool of water, with each ripple becoming increasingly less distinct laterally as it moves outwards from the centre.

Fine detail contrast, one key reason for using such lenses in the first place, deteriorates the most.

It would be interesting to know how thick the Sony NEX filter is relative to the digital Leicas. And if the NEX 5n differs from the NEX7, and what Sony are doing about it. If anything. It may be that trade-offs are involved in any design move in the direction taken by Leica WRT microlenses and minimal filter thickness, and the hypothetical effect on performance using lenses designed specifically for NEX.

45 degrees of beam tilt, it always seemed too good to be true to get top performance from the small symmetrical wide angles with such extreme inclination.

His view on the matter is quite unequivocal, and disadvantages also include aperture sensitivity and diminution of field illumination.



Dec 08, 2011 at 12:02 AM
pdmphoto
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p.2 #4 · p.2 #4 · Does the 5N 'exaggerate' field curvature?


I wonder if Sony are well aware of the situation and making changes as we speak? The flood makes a good excuse for the delay Right after the flood they announced that it would not affect the initial USA delivery date, but now it looks like Feb-March of next year Considering its very poor performance with wide angle lenses, it might be a prudent move on their part.


Dec 08, 2011 at 12:14 AM
Sosua
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p.2 #5 · p.2 #5 · Does the 5N 'exaggerate' field curvature?


Hmmm... i'm still struggling with this a little to be honest - If I take a shot even at F8 and don't nail the focus, I am still getting irregular results.

for example, when I say 'nail focus':

At 35-40mm and F8 - If I focus just a little deeper than my central subject at distance everything looks awesome (this is to account for the inward curvature, leaving the middle acceptably in focus, while ensuring the edges are still within the curved plane) . However, if I focus too deep, I retain sharp borders, but lose centre detail and similalry if I focus 'correctly' on the centre subject the borders drop well out of focus.

The margin of error just seems very small, even at F8.

I will post some samples when I get home - perhaps its being aggravated by my 'test scene' not being flat, but focussing at 35mm, F5.6-8 and 25 plus metres away, it should be a complete non-issue (hyper focal would be 7-10 metres)



Dec 08, 2011 at 12:18 AM
douglasf13
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p.2 #6 · p.2 #6 · Does the 5N 'exaggerate' field curvature?


I have the same, or probably worse, field curvature issues with the Nokton 35/1.4. Even when stopping down, getting the corners to be sharp requires focusing past infinity in the center, which some of my adapters accommodate. The odd thing is that the Nokton has essentially no color shift and very little vignetting compared to all of the other 35mm rangefinder lenses that I've used.

I wonder if both of these Noktons have a zone B dip that makes the corners of the aps-c sensor look bad? The Minolta/Sony 35/1.4 has this issue, so it actually looks better in the corners on FF rather than aps-c.



Dec 08, 2011 at 12:25 AM
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p.2 #7 · p.2 #7 · Does the 5N 'exaggerate' field curvature?


pdmphoto wrote:
I wonder if Sony are well aware of the situation and making changes as we speak?


Sony are aware that thick filters cause astigmatism, of course. It's doubtful they care about it though, beyond making their cameras work well with their own lenses.

It's not news that thick glass filters in front of the sensor introduce significant astigmatism for lenses with steep angles of incidence. The Rodenstock HR Digaron lenses were designed precisely to counteract that astigmatism, by incorporating the 2 mm filter glass into the optical calculation of the lens, i.e. giving the lens the appropriate amount of opposite astigmatism by design. Rodenstock built an entire sales pitch around this idea years ago!

It's also the main reason Leica use such a thin IR filter on their rangefinder cameras, and why the M8 and M9 lack an anti-aliasing filter altogether.



Dec 08, 2011 at 10:53 AM
denoir
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p.2 #8 · p.2 #8 · Does the 5N 'exaggerate' field curvature?


Well, the lack of an AA filter is a different thing - there is AFIK no reason why a beam splitter would cause astigmatism. Leica hasn't used AA filters in other cameras as well that don't use rangefinder lenses - the DMR and the X1 to take two examples.


Dec 08, 2011 at 11:03 AM
uhoh7
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p.2 #9 · p.2 #9 · Does the 5N 'exaggerate' field curvature?


@sousa

I am also struggling within irregular results, and the problem is most obvious at longer infinity shots where you can really look at the edges for small details.

Factors:

1)me
2) me
3) adapter assisted focus issues
4) ?

sebboh wrote:
why should it be best at f/2?

(re leica 28/2 M)
I'll have to look up the review, but it supposedly is sharpest everywhere at f/2--this would be on a M7 or M6. That's where all the money is going, said the review.

Maybe that;s not even possible at f/2, but my nikkor 180 AIS ED is widely described as sharpest at 2.8--everywhere.

I did test last night and it had seemingly perfect corners f/2 1 meter---i focused at the corner.




Dec 08, 2011 at 02:34 PM
JimBuchanan
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p.2 #10 · p.2 #10 · Does the 5N 'exaggerate' field curvature?


I agree that a lot of the dollars for Leica lenses gets one enhanced image quality at wider apertures versus other brands, but the optimum IQ still requires a one or 2 stopdown even for Leica.

uhoh7 wrote:
(re leica 28/2 M)

I did test last night and it had seemingly perfect corners f/2 1 meter---i focused at the corner.


Did the 28/2 show the field curvature as described above?



Dec 08, 2011 at 03:47 PM
 

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sebboh
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p.2 #11 · p.2 #11 · Does the 5N 'exaggerate' field curvature?


uhoh7 wrote:
(re leica 28/2 M)
I'll have to look up the review, but it supposedly is sharpest everywhere at f/2--this would be on a M7 or M6. That's where all the money is going, said the review.

Maybe that;s not even possible at f/2, but my nikkor 180 AIS ED is widely described as sharpest at 2.8--everywhere.

I did test last night and it had seemingly perfect corners f/2 1 meter---i focused at the corner.


that sounds like the reviewer doesn't know what they're talking about or is just into hyperbole. lots of people said that about the original noctilux too. that's not how optics work though. the lens may be so good at f/2 that there isn't much noticeable improvement on stopping down, but it will improve till diffraction starts to play a role (around f/5.6). you can see that it improves on stopping down just by looking at its mtf charts where the cron clearly performs better at f/2.8 and better still at f/5.6.



Dec 08, 2011 at 03:48 PM
uhoh7
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p.2 #12 · p.2 #12 · Does the 5N 'exaggerate' field curvature?


sebboh wrote:
that sounds like the reviewer doesn't know what they're talking about or is just into hyperbole. lots of people said that about the original noctilux too. that's not how optics work though. the lens may be so good at f/2 that there isn't much noticeable improvement on stopping down, but it will improve till diffraction starts to play a role (around f/5.6). you can see that it improves on stopping down just by looking at its mtf charts where the cron clearly performs better at f/2.8 and better still at f/5.6.


Well, I'm glad I brought it up

Might even have been Rock Huffwell in one of his guises.

Wait here it is:

"Leica, in recent decades, has developed a fine line of high speed lenses, most of them with aspherical elements. Many photographers agree that the high speed Leica lenses seem to be optimized for shooting at or near maximum aperture, with little or no advantage in stopping down, except to control depth of field."

From photo.net review by Charles Barcellona

http://photo.net/equipment/leica/28/



Jim, I have not peeped hard enough with proper shots to really answer that yet.



Dec 08, 2011 at 03:55 PM
denoir
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p.2 #13 · p.2 #13 · Does the 5N 'exaggerate' field curvature?


sebboh wrote:
that sounds like the reviewer doesn't know what they're talking about or is just into hyperbole. lots of people said that about the original noctilux too. that's not how optics work though. the lens may be so good at f/2 that there isn't much noticeable improvement on stopping down, but it will improve till diffraction starts to play a role (around f/5.6). you can see that it improves on stopping down just by looking at its mtf charts where the cron clearly performs better at f/2.8 and better still at f/5.6.


Indeed. There are very few lenses that are better wide open than they are stopped down - and it's always very slow lenses (f/4 and slower). The 28 Cron is better at f/2.8 and much better at f/5.6 in terms of raw optical performance. It's very good at f/2 but not anywhere near class leading.

The 28 Cron is the last lens I'd recommend for a 5N. It's a character lens, not an ultimate performance lens. For its character to come through you need FF as most of the interesting stuff happens at the edges. On a cropper it's just mediocre and IMO a complete waste of money. You don't get an interesting look, you don't get high performance, bokeh is often dodgy etc There are a lot of better choices to spend $4,000 on...





Dec 08, 2011 at 04:08 PM
sebboh
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p.2 #14 · p.2 #14 · Does the 5N 'exaggerate' field curvature?


uhoh7 wrote:
"Leica, in recent decades, has developed a fine line of high speed lenses, most of them with aspherical elements. Many photographers agree that the high speed Leica lenses seem to be optimized for shooting at or near maximum aperture, with little or no advantage in stopping down, except to control depth of field."

From photo.net review by Charles Barcellona


this just means that in designing the lens leica chose to focus on wide open performance more than performance at optimum aperture, not that wide open is the best aperture. e.g. the 35mm lux asph is extremely good wide open (and that was a key design goal) and it improves on stopping down, but it doesn't get as sharp on stopping down as some other lenses that are optimized for stopped down shooting at the expense of wide open shooting (e.g. the zm 35/2).



Dec 08, 2011 at 04:11 PM
sebboh
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p.2 #15 · p.2 #15 · Does the 5N 'exaggerate' field curvature?


denoir wrote:
The 28 Cron is the last lens I'd recommend for a 5N. It's a character lens, not an ultimate performance lens. For its character to come through you need FF as most of the interesting stuff happens at the edges. On a cropper it's just mediocre and IMO a complete waste of money. You don't get an interesting look, you don't get high performance, bokeh is often dodgy etc There are a lot of better choices to spend $4,000 on...


mmm, priorities come into play here. i've not seen a better performing 28mm lens at f/2 (or probably f/2.8), it has the best bokeh of any 28mm lens i've ever seen (most are much dodgier), at f/5.6 i doubt anything will beat it in a noticeable way on the NEX, and finally the color character should still come through on the NEX. if you want a 28mm for the NEX and have the cash i don't see anything else that compares.



Dec 08, 2011 at 04:16 PM
denoir
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p.2 #16 · p.2 #16 · Does the 5N 'exaggerate' field curvature?


I don't know specifically about 28 mm, but for instance the Zeiss 25/2.8 Biogon blows it away at all apertures.

From an old test:







Center:






Mid:







--








Center:






Corner:







As for bokeh:









































--

Finally regarding colors - mostly it comes from the vignetting which you lose on a cropper.




Dec 08, 2011 at 04:23 PM
sebboh
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p.2 #17 · p.2 #17 · Does the 5N 'exaggerate' field curvature?


denoir wrote:
I don't know specifically about 28 mm, but for instance the Zeiss 25/2.8 Biogon blows it away at all apertures.


but it is f/2.8 and bigger(?).

that is outstanding bokeh for a 28mm.

here is what the bokeh looks like from another 28/2 that still has better bokeh than most fast 28s:







Dec 08, 2011 at 04:27 PM
kosmoskatten
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p.2 #18 · p.2 #18 · Does the 5N 'exaggerate' field curvature?


I definitely think the 28 Summicron is a little lost on APS-C. It is a sweet lens on full frame for sure. I don't think there are too many 28's that make the transit into APS-C nicely. The ZM 25 that I have is a stunning lens on full frame, it replaced the 28/2 Summicron for me. I still think the 28/2 is the bees knees on full frame - I just preferred the ZM 25/2.8.

On APS-C the ZM25 falls a bit flat. Sharp, contrasty, distortion free - and a bit flat. I need to offload the ZM25 on someone shooting full frame or keep it until a full frame solution to my taste is shipping. I can't see why I would ever actively pursue a Leica 28/2 for APS-C myself. Perhaps if I were using it on full frame and had a side kick, but other than that, no.

Edited on Dec 08, 2011 at 04:48 PM · View previous versions



Dec 08, 2011 at 04:35 PM
denoir
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p.2 #19 · p.2 #19 · Does the 5N 'exaggerate' field curvature?


sebboh wrote:
but it is f/2.8 and bigger(?).


Yes, slightly bigger, but at a third or a quarter of the price.


kosmoskatten wrote:
On APS-C the ZM25 falls a bit flat. Sharp, contrasty, distortion free - and a bit flat. I need to offload the ZM25 on someone shooting full frame or keep it until a full frame solution to my taste is shipping.


That's the general curse of crop formats - you lose the interesting stuff going on at the edges. You get a more uniform rendering from a good lens but also more flat and boring. Once you get used to a set of lenses on FF it's very difficult to use them on a cropper. My first serious camera was a 7D and I liked it very much.. until I got a 5DII. I simply couldn't go back to the 7D after that - the output looked so flat and boring. The same thing with the M9 & NEX. It's terrible what a crop sensor does to those lovely M lenses. I'd love to use a NEX for tripod based shooting (where the M9 sucks), but I get disgusted each time I see the mutilated output from my favorite lenses.

At the same time I have a Leica X1 that is a cropper as well, but I've never had any issues there. The lens was designed for ASP-C and the rendering isn't nearly as flat as when you use a FF lens on a crop camera.

I'm guessing the same would occur if you used a medium format camera lens on a 135 FF camera...



Dec 08, 2011 at 04:48 PM
sebboh
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p.2 #20 · p.2 #20 · Does the 5N 'exaggerate' field curvature?


kosmoskatten wrote:
I definitely think the 28 Summicron is a little lost on APS-C. It is a sweet lens on full frame for sure. I don't think there are too many 28's that make the transit into APS-C nicely. The ZM 25 that I have is a stunning lens on full frame, it replaced the 28/2 Summicron for me. I still think the 28/2 is the bees knees on full frame - I just preferred the ZM 25/2.8.

On APS-C the ZM25 falls a bit flat. Sharp, contrasty, distortion free - and a bit flat. I need to offload the ZM25 on
...Show more

it looks like it is still a great lens on aps-c, just not as special. what makes it special for the NEX is there is nothing else around 42mm and f/2 (or faster).



Dec 08, 2011 at 04:57 PM
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