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04/24/2006 01:18:47 PM · #1 |
Latley ive had this obsession for lenses mainly teleconverters for my canon S2. Ive bought a few newer converters and some older ones. Since ivee been buying these and trying them out im starting to see the difference in the glass, or the the quality or somthing. When i look at other random pictures online or on tv im starting to see video and stuff with this same poor quality or cheap glass or somthing that i see on some of the lenses that dont seem to work on my camera.
Its like im training my eye to see whats good, and whats not. There is a weird blue shaddow or a blue rainbow or somthing that bad glass or the wrong glass has and you can also see how in the center it seems to be more aligned or sharper or somthing its kinda hard to explain but i can see it and its more common then i thought.
I seem to see it more with like mobile cameras, like on the news when they are out in the field or at some event |
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04/24/2006 01:25:35 PM · #2 |
Cheap lenses will always show some degree of chromatic aberrations, or purple fringing (the blue/purple lines you mentioned). Even very high quality lenses sometimes have that, in certain conditions.
Teleconverters are usually sharper in the center, where the light rays do not have to bend so much, as compared to the edges, where light bends a lot. These are the reasons why good quality glass is so expensive, especially longer focal lenghts. The more you try to minimise these defects, the costlier the lens becomes. It is just something we all have to live with, as light is not that easy to control ;-)
Message edited by author 2006-04-24 13:26:57. |
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04/25/2006 02:29:36 AM · #3 |
I dont notice it all the time though, its like they use different cameras at different times and some are better then others, or have longer focus or somthing.
I always thought it was the cheap tv.
Why is the outline blue? It reminds me of 3D without wearing 3D glasses. |
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04/25/2006 05:11:04 AM · #4 |
| It's caused by chromatic aberration The lens cannot focus all the frequencies of light at the same point, so the red or blue components appear offset. |
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04/25/2006 01:31:02 PM · #5 |
| Is there a filter you can get to help correct that problem? |
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04/30/2006 11:30:37 AM · #6 |
| Why is it always blue? i dont seem to notice anything but a blue shadow. |
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04/30/2006 11:58:51 AM · #7 |
There's even more to it than that. Sometimes when you are watching stuff on TV, they are using a zoom lens that is zoomed to a better part of the range for a particular scene. Similarly, the lens may be stopped down in some pictures which will also help these issues.
Sometimes films look good because of the camera man, not the equipment alone...
Interesting question as to why it's always blue. I have some guesses, but I'd like to see someone else's take on this. |
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04/30/2006 01:08:04 PM · #8 |
Originally posted by BowerR64:
Why is it always blue? i dont seem to notice anything but a blue shadow. |
If you look closely, the fringing is actually more purple than blue, although of course overall color-balancing of the image either in-camera or through PP will effect how you see it. Blue/violet is the shortest of the light waves in the visible spectrum, and in the nature of how the lens is displacing the unequal-length light waves it is projected outwards rather than inwards (of a given shape) and thus is most visible where a dark shape occludes a light BG.
R.
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04/30/2006 01:55:10 PM · #9 |
The chromatic abberrations of lenses can be mitigated to some extent in post processing. If you have Adobe Photoshop, use the 'Hue and Saturation' control. Choose the 'blue' or whatever color is closest to the offending one (dropdown window at the top of the control window), and decrease the saturation of that color, reducing to gray. If the abberrations are too large then this does not help much, but for smaller ones it works well.
It is possible to get high quality teleconverters but they are very expensive. The ones priced less than $100 (USD) are cheap galilean optics consisting of two elements; a positive front element and a negative rear element. Adequate color correction with just two elements is possible but the manufacturers of these are more into cheap than high quality. The galilean arrangement was chosen because: A - it is cheap, and B - the assembly is very short compared to other lens combinations. |
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