View Full Version : Lenses with bad/strong Coma?
The more I research the more I think I am slowly starting to understand all the terminology having to do with OOF rendering.
Specifically, I bellieve that Coma is somethhing that appears to create a feeling of circular bokeh if I am not mistaken.
I actually really dig images that have this feeling. Having shot digital for the last 5 years where the lenses are cropped seems to decrease if not eliminate the chances of coma happening.
This was one of many motivations for me to buy a RF, so as to get some of that nuance effect from different lenses and different film/processing.
All of that being said, I am still not that sure which lenses are known to have strong coma. Everyone generally is pursuing "creamy" bokeh which by all means is very usefull and desirable in many instances, however, I think it can also be boring at times when 50% of your image is OOF, alll depending on the subject.
So, getting to the point, does anyone have any recommendations for lenses in LTM that are known to produce some odd bokeg, specifically strong coma?
Thanks!
keithwms
12-18-2007, 09:01
You might look and see what a wide open noctilux does for you, but that's a pretty high price to pay for what you want. I seem to recall some vivitar slr lenses give bubbly bokeh. My nikon 50/1.2 also gives bubbles wide open, but again it's an slr lens.
Roger Hicks
12-18-2007, 09:20
35/1.4 Summilux pre-aspheric
Cheers,
R.
nikonhswebmaster
12-18-2007, 09:30
Comatic aberration is of course present in all lenses, but is really only present at the edges (off axis light) where points of light get a "coma" effect, which is wedge shaped toward the edges.
It does not appear in on-axis parts of the image.
But all aberration would seem to contribute to the term amateurs have applied to the out of focus areas in their photographs, bokeh.
yeah, would love to have the Noctilux, but out of my range and considering I am new to RFers, would make me a poser. ;)
How much does the 35/1.4 Summilux pre-aspheric go for in user condition?
In M/LTM, the lenses that come immediately to mind are Noctilux, Summitar and Summarit.
Non-Leitz, most prominent in my mind: Canon 35/2 (very bad), Canon 50/1.4 LTM,
CV 40/1.4. Other CV lenses are less sensitive. The Canon 50/1.2 and 35/1.8 are
pretty good.
All Sonnar variants (Zeiss LTM and C-Sonnar, Nikkor 50/1.4, Canon 50/1.5)
are pretty robust in terms of comatic aberation, but instead loose
resolution towards the edges, wide open. Summicrons for f >= 50mm are
pretty stable too, the 35/2 ("Bokeh king") shows it a little bit.
Roland.
yeah, would love to have the Noctilux, but out of my range and considering I am new to RFers, would make me a poser. ;)
How much does the 35/1.4 Summilux pre-aspheric go for in user condition?
From $600:) to $1200:mad:
Wow, looking online I cannot even find them for sale anyways...
From $600:) to $1200:mad:
Roger Hicks
12-18-2007, 15:36
As a matter of idle interest, when did the term 'comatic aberration' (7 syllables) begin to replace plain old 'coma' (2 syllables)? And what do the extra 5 syllables add?
Cheers,
R.
Strange as it might seem, not all of us think in English.
Brian Sweeney
12-18-2007, 16:12
According to "Optics and Optical Instruments" by B.K. Johnson, 1960, coma is effected by the position of the lens' diaphrapgm. I made a "monocle" lens out of an I61 mount with the aperture well in front of the 50mm single-element optic. It is RF coupled. Did just what the book claims it should do. Lots of Coma.
Coma! You want Coma! How about "Deep Coma".
http://www.rangefinderforum.com/forums/attachment.php?attachmentid=53437&stc=1&d=1198023558
Roger Hicks
12-18-2007, 16:29
Strange as it might seem, not all of us think in English.
Fair enough. In which languages is the term 'comatic aberration' preferred to 'coma'? German is probably a strong candidate...
This is a genuine enquiry, not a wind-up.
(Translation for Americans and other whose native language is not English: a 'wind up' is a deliberate attempt to play on someone's gullibility or prejudices).
(Second note to Americans, etc: the bit about mother tongues IS a wind up)
Cheers,
R.
Fair enough. In which languages is the term 'comatic aberration' preferred to 'coma'? German is probably a strong candidate....
Yup. All the best,
Roland.
Brian Sweeney
12-18-2007, 16:38
This article on monocle lenses:
http://kiev4.narod.ru/tutorial/kiev4_02_e.html
Posted by a new RFF member has several examples of images with strong coma, but not "deep Coma".
foto_fool
12-18-2007, 20:21
Brian - thanks for the very demonstrative image, and for the experiment that produced it. Knowing that all design is compromise, this would lead me to suppose that aperture placement in a particular lens design is a compromise. In lenses that exhibit strong coma - perhaps due to less than optimal aperture placement? - what is GAINED in the compromise?
And what's up with lenses that render coma at full aperture?
- John
BTW - the Kiev site shows some interesting images - at monitor resolution the images almost look like IR shots, but with blue sky. Very painterly.
nikonhswebmaster
12-18-2007, 20:33
Wish I'd thought of that.
Smart-ass!
(That's a compliment, by the way).
Cheers,
R.
Coma is produced by the comatic aberration in a lens.
It is usually not annoying to photographers, but is a real pain to astronomers since it makes stars move out of place, and look like comets because of the coma.
Freakscene
12-18-2007, 21:22
The aberration that we refer to as 'coma' is oblique spherical aberration. The term comatic aberration, strictly speaking is incorrect in English but is creeping into common use (which means it will soon become correct usage, in all likelihood), probably from German.
LTM lenses with strong coma include the Summarit 50/1.5 and Summitar. Coma occurs when rays from an off-axis point of light in the object plane create a trailing "comet-like" blur directed away from the optic axis. This creates the 'circular-swirly' look in the outer field.
The shot above with 'deep coma' actually doesn't display the effect that well - the trees aren't swirling much. There is also a good amount of field curvature and on-axis spherical aberration complicating matters.
These classic coma shots from the Nocti come from FlickR's tremendously prolific Tommy Oshima:
http://flickr.com/photos/tommyoshima/271435187/
http://flickr.com/photos/tommyoshima/281078121/in/set-72157594292218784/
I have a Noctilux but try to avoid this look.
Marty
Here's a side crop from a photo taken in a lit entryway. Noctilux. Guh.
http://www.rangefinderforum.com/forums/attachment.php?attachmentid=53461&d=1198042886
Actually, ironic as it may sound, I find Tommy's work inspirational. In fact, the second photo you posted is one I have posted in other forums previously as an example of the types of bokeh I find pleasing.
Obviously not the only type, but in that instance, with those colors and contrast, it really seems magical to me.
This are another couple with a Graphlex Speed Graphics:
http://www.flickr.com/photos/tommyoshima/445174821/in/set-72157594583422733/
http://www.flickr.com/photos/tommyoshima/445174813/in/set-72157594583422733/
His stuff in general is really great.
I will have to check out the Summitar. Thanks for the info everyone who has responded.
Freakscene
12-18-2007, 22:34
I have a lot of respect for Tommy too; please don't take anything I wrote above as anything except admiring - personal styles differ. I don't try to emulate him, but I like what he does and even when i don't like it, I tend to appreciate what he's trying to show.
Marty
Yeah I understood you. :)
And I agree, emulation is counter-productive. For me though, I definitely am interested in producing some dreamy and somewhat abstract OOF effects.
The search for the right lense continues... Simply cannot afford most of these recommended. I just want to start using my new Bessa... ;)
I have a lot of respect for Tommy too; please don't take anything I wrote above as anything except admiring - personal styles differ. I don't try to emulate him, but I like what he does and even when i don't like it, I tend to appreciate what he's trying to show.
Marty
Brian Sweeney
12-19-2007, 02:47
The term "comatic aberration" is not found in any of the formal books on optics that I've got. The term used is "coma", and it is listed as a lens aberration.
I suppose it, like the work "Bokeh", will be found in every-day forum language from now on. It is descriptive of the optical property, as is Bokeh.
Astigmatism is also responsible for the football-shaped "swirlies" in lenses, including the Summarit.
The term comatic aberration, strictly speaking is incorrect in English but is creeping into common use (which means it will soon become correct usage, in all likelihood), probably from German.
I don't think so, coma in German is Koma while the other aberrations are called aberrations. On Google you find very few hits (http://www.google.de/search?q=komatische-aberration+OR+komatische-abweichung) for "comatic aberration" in German (about 5) and a number in the thousands (http://www.google.de/search?q=comatic-aberration) for English.
Philipp
Brian Sweeney
12-19-2007, 09:21
The term "comatic aberration", from a quick google search, appears to be used in formal papers and patent applications going back decades. It is more exact than "coma" which has meaning outside of optical design. In books on optical design, "coma" is within context and is the term used. In patents, I can see the expanded term used as definitions must be exact in scope. I've gone through the patent process within the field of optical communications, and the exact meaning of words is "very binding". Never use a two-cent word when a fifty cent word will do.
nikonhswebmaster
12-19-2007, 10:01
Comatic aberrations are similar to spherical aberrations, but they are mainly encountered with off-axis light.
Brian you use the word Coma to describe the photograph, and aberrations to describe the lens. These are very common terms in lens test articles. But you are right they are not likely to appear in a user article, because the photographer is going to be more interested in the image's description, not the glass.
It is not however a 50 cent word, it is just the only one used to describe a lens. Bokeh is not yet acceptable in tests or design, since it cannot be measured or formulated in lens design.
Brian Sweeney
12-20-2007, 04:04
Okay, so Roger got me spun-up. I'm not used to seeing the term "Comatic Aberration" in text books on optics and optical design. I went through a couple here at work. "Coma" appears to be the much more used term in engineering books. "Principles of Optics", Max Born and Emil Wolf, 1959 uses "Coma" but "Comatic Aberration" does not appear. "Optics" by Hecht and Zajac, 1979, uses "Coma" in the index. The text uses "Coma, or Comatic Aberration," ...
So this is one instance where the Physicists and Engineers chose the simpler term for technical writing, rather than a much more exact term. That is fairly rare. The term "Bokeh" does not appear in any of these text books...
This article on monocle lenses:
http://kiev4.narod.ru/tutorial/kiev4_02_e.html
Posted by a new RFF member has several examples of images with strong coma, but not "deep Coma".
Very interesting to me what are "strong coma" and "deep coma"? :) As for me I see on your example photos not only coma but great curvature of field. And on my examples the curvature of field is not so great. That's the only difference, I think. Maybe I'm mistaken.
Brian Sweeney
12-20-2007, 13:21
Deep Coma is what I feel like at the end of the work-day! Kind of like that photo...
principe azul
12-20-2007, 13:28
On coma and comatic aberration, my guess is that it's down to confusion - in popuar usage - with *chromatic* aberration, which seems to have become a big talking point once people started using lenses designed for film cameras on digital cameras.
Deep Coma is what I feel like at the end of the work-day! Kind of like that photo...
:) Good joke. So do I.
As far as your image is concerned it seems to me that the effect is not produced by coma. You can easily check this by moving the diaphram here and there. If it is coma - the images blurring at the edges will be different. But I think this is curvature of field (I do not know if this is correct translation of the term from Russian). I can explain what I mean. The meniscus concentrates rays not in focal plane but in a "curved surface" like plain with bended corners or like sphere. This results in images like your example because the film sirface is flat and farther from the center of the picture - more discrepansy between the film surface and the "focal surface". This effect does not depend on the diaphragm position, it depends of aperture.
i love the summarit --- grat lens --- i also love my canon 50/1.2
Brian Sweeney
12-21-2007, 15:06
> But I think this is curvature of field (I do not know if this is correct translation of the term from Russian).
Your translation, and English, is excellent. My thinking on curvature of field: I would have expected "something" in the image to be in focus as a function of distance from the center. As you look at the image from edge to edge, everything goes out of focus quickly. If "only" curvature of field was involved, something should have been in focus, either closer or farther from the main focus at the center. This lens seems to capture all of the aberrations at once.
Cale Arthur
12-21-2007, 15:46
On coma and comatic aberration, my guess is that it's down to confusion - in popuar usage - with *chromatic* aberration, which seems to have become a big talking point once people started using lenses designed for film cameras on digital cameras.
I thought chromatic abberations only occured at open-mic nights and guitar stores? :) ..sorry, couldn't resist.
--c--
This lens seems to capture all of the aberrations at once.
I agree with you: both coma and curvature. And my observations shown that the more lens diameter - the more curvature of field. My 42mm monocle with 20 mm lins diameter has less curvature than 135mm one with 40 mm lens diameter. And the coma is minimized for both of them,
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