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Old June 14th, 2009, 05:29 PM   #1
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chromatic abrasion

for some reason with my HD-200ub im noticing alot of Chromatic abrasion with the stock lens. Anyone know what the cause could be?
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Old June 14th, 2009, 05:43 PM   #2
 
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I think you mean chromatic aberration?
The 16x fujinon lens normally displays CA it hi zoom ratios and hi-contrast scenes.
Try stopping the lens to f/4, back off the zoom a bit and don't overexpose the scene.
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Old June 14th, 2009, 05:46 PM   #3
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Ah good to know. The scene that it displayed in it was fully open 1.4 zoomed in all the way. So that would make sense!
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Old June 14th, 2009, 07:35 PM   #4
 
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Also, take great care to focus properly. Chromatic aberration increases as you move out of the plane of focus.
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Old June 22nd, 2009, 01:29 PM   #5
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Are there any images someone could post here that illustrate the CA issues? Are there internal settings that can be made to reduce it (gamma settings, etc)? Roughly how bad are the issues at f1.4, moderate zoom?
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Old June 22nd, 2009, 01:38 PM   #6
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Are there any images someone could post here that illustrate the CA issues? Are there internal settings that can be made to reduce it (gamma settings, etc)? Roughly how bad are the issues at f1.4, moderate zoom?
It's a fact of life with virtually all HD lenses, even the Canon HJ40 has it bad!
Not much in terms of camera settings you can do, but you can get rid of it to a large extent in post - not my area but I believe you'll just pick an area of CA and choose that as a colour and then de-saturate that colour, works pretty well.
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Old June 22nd, 2009, 03:16 PM   #7
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Why would CA be more prevalent in HD video lenses as compared to lenses utilized on DSLRs? The sensor resolution on DSLRs is much higher than the 1920 x 1080 HD we are dealing with. Optics are optics - are they not? Or am I simply not understanding something basic?
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Old June 22nd, 2009, 03:25 PM   #8
 
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I can take a stab at an answer, here. CA is the result of the optical error that comes from the difficulty in focusing light of varying wavelengths at the same focal plane. Modern HD(v) cameras have photo-receptors arranged on 3 different planes, for each channel R,G, and B. So, ideally, this would call for a lens that can focus the R, G and B components of the image at 3 different planes...a difficult, if not impossible, task.
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Old June 22nd, 2009, 05:05 PM   #9
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Bill - I take it that the design you outlined is different from whatever is used on dslrs?
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Old June 22nd, 2009, 05:17 PM   #10
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I can take a stab at an answer, here. CA is the result of the optical error that comes from the difficulty in focusing light of varying wavelengths at the same focal plane. Modern HD(v) cameras have photo-receptors arranged on 3 different planes, for each channel R,G, and B. So, ideally, this would call for a lens that can focus the R, G and B components of the image at 3 different planes...a difficult, if not impossible, task.
Why don't I see this type of CA in the 'prosumer' fixed lenses such as the XH-A1 or something?
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Old June 22nd, 2009, 11:27 PM   #11
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I'm not up on how dslr cameras get the R G B colors filtered to the sensor - but my Canon L glass delivers great images w/o CA that I can see - even at magnification. ED glass or fluorite elements are used to eliminate most all CA - very common in high end astronomical telescopes (TeleVue, Takahashi, etc.).

My point is that good optical design exists for solving this.

Any updates from anyone on the Canon 14x for the 700???
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Old June 23rd, 2009, 01:54 AM   #12
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Why would CA be more prevalent in HD video lenses as compared to lenses utilized on DSLRs? The sensor resolution on DSLRs is much higher than the 1920 x 1080 HD we are dealing with. Optics are optics - are they not? Or am I simply not understanding something basic?
It is there in DSLR lenses, more so in some lenses than others. It's certainly there in prosumer fixed lenses too.
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Old June 23rd, 2009, 07:26 AM   #13
 
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I beleive most DSLR sensors use a single matrix of photoreceptors. Unlike videocam 3-chip sensors they are all located on the same focal plane.

IMHO, most of the CA is the result of inadequate optics design. I say this because my stock 16x and 17x Fujinons, as used on the JVC HD110 show very high CA, especially at extreme zoom. I am also using several different Nikon 35mm zoom lenses, couple with an MTF adapter for telephoto shots on my HD110. CA, is virtually un-noticeable with the 35 mm lenses. Why this is the observable case, I can only assume that it is the higher quality of the 35mm glass. Another possibility: high zoom ratio lenses are harder to optimize than low zoom ratio lenses. Video zooms like the 16 and 17x cover much more of a zoom range than the 35mm equivalents, which are more like 8x. As I said earlier, the appearance of CA is highly related to out of focus areas of the image. 35mm lenses have a much larger circle of confusion, so, the apparent CA is not as noticeable. The shallow DOF of 1/3 inch lenses tends to amplify the occurence of CA.

edit: On second thought, this is a bogus ratonale because my 35mm lenses maintain their CA-free performance, even when used on a 1/3 inch sensor.
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Old June 23rd, 2009, 07:57 AM   #14
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As I said earlier, the appearance of CA is highly related to out of focus areas of the image. 35mm lenses have a much larger circle of confusion, so, the apparent CA is not as noticeable. The shallow DOF of 1/3 inch lenses tends to amplify the occurence of CA.
.
There is a contrary line of thought that the wider the aperture the worse the CA looks due to the fact that the fringed borders cover a wider area due to being out of focus. This makes sense.
I think you're right in your evaluation fo why it's there - video lenses stretch optical design to - and it seems beyond - the limits of what's possible, while your DSLR lenses are much simpler by comparison. Also the HD lenses need to be designed to resolve much finer detail due to the smaller pixels on the sensors of 2/3" and espcially 1/3" cameras.
I'm no scientist, just my thoughts and observations.
Steve
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Old June 23rd, 2009, 09:22 AM   #15
 
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35mm lenses have a much larger circle of confusion, so, the apparent CA is not as noticeable. The shallow DOF of 1/3 inch lenses tends to amplify the occurence of CA.
Thanx steve....this whole statement is wrong. I got it backwards. I.E. 35mm lenses have a shallower DOF(smaller circle of confusion) than 1/3 inch lenses, but, it's all irrelevant, anyway, when using a 35mm lens on a 1/3 inch format.
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