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Old November 26th, 2002, 09:58 PM   #1
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Optical question...

I don't know where to post this so here goes...

I have a Sony TRV25 miniDV camcorder. I noticed that the image quality is rather poor at the long end of the zoom range. I don't know what this phenomenon is but it consists in getting sort of phased out color rings around the contours of objects, especially those that are out of focus. I can see redish and greenish fuzzy lines around contours of branches in the background as I was filming a Woodpecker. When I used to do a lot of photography, I would get this when doing macro work with really cheap lenses. I can send a sample still by e-mail (since I don't have a web site) and would like to know what this is called and if it is due to my camcorder having a cheap lens. Even though this camcorder is not a pro machine by any standards, Sony does boast the fact that it has a "Carl Zeiss" lens so I expected the quality to be better. Just wondering how up the scale I would have to go (price and equipment wize) not to get this effect.

Thanks for any info.

Marc Potvin.
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Old November 26th, 2002, 10:31 PM   #2
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Some new articles recently posted on the DV Info Network cover lens defects http://www.dvinfo.net/articles/optics/lensdefects.php If you look at defect 4 and 5 (Chromatic Aberrations) that should explain the defect your encountering. A camera like the GL2 with 20X lens (longest telephoto in that type camera) and Canons rare earth, fluorite glass would handle your color issues (and get you closer to the birds) very well.

Jeff
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Old November 27th, 2002, 10:54 AM   #3
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What is the medium through which you see these artifacts? Hopefully not yr camera LCD. Your TV? Keep in mind that colored contours are most often the result of misconvergenced CRT displays. Also to remember is that single CCD camera's are more prone to generate those fringes.
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Old November 27th, 2002, 04:34 PM   #4
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Are you digitally inhancing the zoom ability of the camera or useing the X10 only ?It is much better to add a tele lens than use the in camera multiplyer
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Old November 28th, 2002, 10:32 AM   #5
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Thanks for the info on optics. Just wondering if there would be a big difference with the optics in cameras such as the PD150 or the XL1 as compared to those in my TRV25?

Marc.
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Old November 29th, 2002, 07:30 AM   #6
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Big visible difference...I don't think so... In general. optics for photografic applications (even the consumer ones) are much more demanding. On the resolution part (optical resolving power), DV doesn't need more than 360lp for the whole screenwidth (needs even to be limited in order to avoid optical aliasing) This means for 1/4" CCD about 75 lp/mm. This is not a big deal as compared to what is needed for photographic lenses. In addition to that, from F4 on, resolution is being diffraction limited for those small devices, which makes that even the most sophisticated optics will not resolve any better. "Contrast" of the optics as referred to distributed glare (coatings, dispersion..) is not a big isssue either. The dynamic range of DV video is far below that needed for photographic applications. Of course image forming internal reflection(ghost images) need to be avoided, but single layer coatings are cheap and reduce this effect for 80% and are applied for all consumer lenses these days. What makes (pro lenses expensive is their mechanical robustness, their better coatings, and not to forget, their "wide" zooms not available on consumer versions. Lens correction gets expensive at wide angles
Correcting (off axis) chromatic aberations, field curvatures, geometric distortions, eat $$$ at wide versions.
Although correction for chromatic aberations are, thanks to the modern "good" (dispersion, birefrengence...) glasses existing in a wide variety of refractive indexes, not a big deal anymore, the 3CCD versions even don't need that kind of correction because of the separate colorpaths (like in 3 lightvalve video projectors)
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Old November 29th, 2002, 06:09 PM   #7
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The fringing effect was seen on every medium I used, the camera LCD, my TFT laptop computer screen and on TV. I did use the digital zoom but only to 20X (from the optical 10X). I guess I should have tried the same shot with the digital zoom off to see the difference. I like to avoid the digital zoom as much as possible but since I like to shoot wild animals and birds... I end up using it a bit too much. But since I am a perfectionnist, I'll probably end up turning off the digital zoom and getting a better image if a bit smaller animal in my picture.


I know this is mostly a pro forum but would anyone (less professional) have tried the Sony Tele-converters for the consumer cameras??

Marc P.
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Old November 29th, 2002, 06:21 PM   #8
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Re: +_+ "I know this is mostly a pro forum but would anyone (less professional) have tried the Sony tele-converters for the consumer cameras??"

That's me! I'm the non pro, pro handycam man. I have seen footage shot with the VX2000 and the Kenko wide and tele adaptors. Kenko makes great adaptors!

Regarding Sony consumer adaptors, don't bother. For the last 4 years I've only come across unhappy stories about them.
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Old November 30th, 2002, 04:41 AM   #9
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Marc, If you see the fringing on all those displays, like Ken already supposed, the digital zoon will be the problem. The problem is that in this case yr cam's pixel processor has to extract still 720x480(576) pixels out of a (too) reduced number of effective CCD pixels, thus creating color where there isn't.
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Old November 30th, 2002, 05:35 AM   #10
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Comparativly the tele extender will give you a better quality than using the digital enhancement. I agree with Frank that Kenko (for the price) is a good way to go and you can get a X3 or even a X5 as you like to shoot critters. I use them for the same type shots and gave up on digital enhancement awhile back due to the extra's you get in your shots with that method .
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Old November 30th, 2002, 01:21 PM   #11
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I'm in Ottawa, Canada and have trouble finding Kenko dealers. I prefer not to order from the States if possible. Anyway, I've just gone out today and shot a few birds in photo mode. I've posted a good example of the fringing effect I'm getting on my Yahoo photo album. It is at maximum "optical" zoom. I guess the strong backlight doesn't help with the fringing.

You can see the picutre at:

http://photos.yahoo.com/marcpotvin

Click on "Test" and you will see the thumnail of the Downy Woodpecker I shot this morning. If you view the largest version of the photo, you'll see clearly the fringing effect along the left side of the wooden bird feeder.

I'll try to see if I can get in touch with a Kenko dealer around here or at least a mail order dealer in Canada.

Thanks for all the info.

Marc P.
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Old November 30th, 2002, 01:38 PM   #12
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Marc,

I've gone to your link and it says your album is empty.

Jeff
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Old December 1st, 2002, 07:32 PM   #13
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Hi again,

I've solved the problem with my album. I had no problem accessing it but I didn't know I had to change the settings so that other people could access it also. The settings are now fixed and anyone can access it.

http://photos.yahoo.com/marcpotvin

Marc P.
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Old December 1st, 2002, 07:43 PM   #14
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Do you have a filter on the lens and if so what brand?

Jeff
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Old December 2nd, 2002, 06:00 AM   #15
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From what I see, I think Jeff's first feeling about chromatic aberations was right...but what we get here goes beyond what is known in the general geometric optics as chromatic aberations where "in focus" CA is generally being discussed. Lens design relates to a bunch of compromises (and cost factors!). One of the difficult (and expensive) things to keep within limits is the "out of focus" CA, and that's what happens to your picture,Marc. (yes Jeff DOF and COC often gets "colored" in color images...). The basic problem, which can easely be verified by raytracing, is that the optical paths for different wavelenghts in CA corrected optics originate not allways from the same optical exit pupil diameter. They converge at the focal plane, but spread out outside this plane...
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