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Old February 9th, 2008, 12:14 PM   #1
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Can you spot the Chromatic Aberration?

No, this isn't a gameshow (though it sounds like a good one for us geeky types).

I've attached a picture that I posted on a local filmmaking site taken with my XH-A1 and the Letus Extreme. (Forgive the expression -- this always happens when I get in front of a camera.)

One of the more knowledgeable folks there said he saw Chromatic Aberrations, but only having experienced my Canon XH-A1's own unique CA, I cannot see them. I was wondering if anyone here could identify them for me so I can know what to look for -- not seeing any green or purple color fringing. Does CA have other looks?

Thanks for your time.
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Can you spot the Chromatic Aberration?-crazy35mmbrandon.jpg  
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Last edited by Brandon Freeman; February 9th, 2008 at 12:22 PM. Reason: typo
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Old February 9th, 2008, 01:32 PM   #2
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Quote:
Originally Posted by Brandon Freeman View Post
Chromatic Aberrations...I was wondering if anyone here could identify them for me
The green fringe on the right side of the banner with "e n" on it and purple fringe on the black letters ("e n") and white spot in the bottom right. It's certainly not enough to bother most viewers; I've seen much worse in broadcast television.

Quote:
Does CA have other looks?
Yes. A variety of colors (including red) in high-contrast areas. C.A. also includes the overall color cast of the lens (and sensor), many are slightly yellow and red, but that may be corrected in-camera or with post-processing.
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Old February 9th, 2008, 02:08 PM   #3
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Brandon,

CA can also come in yellow and blue aside from green and magenta.

In your sample, as it is, its not distracting. But to clearly know what your looking for i boosted saturation. Tho you wouldnt be pushing it this way its just to show you where it is.

its usually found around the sides and usually appears in areas of high contrast. like black and white.

Ive attached the image showing you where they are.

I hope this helps you.

Ted
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Can you spot the Chromatic Aberration?-crazy35mmbrandon.jpg  
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Old February 9th, 2008, 04:43 PM   #4
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Brandon, I've seen much worse CA from other adapters and stock attached lenses - I think the image is completely satisfactory. The quality of the image is there, and it'd be subjective at this point - the average person, even he or she had the concept of CA described to them, probably wouldn't spot it here. Cheers!
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Old February 9th, 2008, 05:52 PM   #5
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Gotcha. Thank you very much!

I really had no concept of CA until my Canon XH-A1, which sadly is its one flaw. The CA I get from the Canon stock lens (at the wide angle) is WAY worse than this, so that's why when it was pointed out, I go, "Huh?"

I did buy very cheap Canon FD lenses, so I'm sure if I got a higher quality selection, it'd be flawless.

But, sadly, that means more money that I don't have, so... A little bit o' CA never hurt an independent filmmaker. :)
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Last edited by Brandon Freeman; February 9th, 2008 at 05:53 PM. Reason: added a parenthetical
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Old February 9th, 2008, 05:54 PM   #6
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And, sadly, I don't naturally have any color or tan in my face. The over-saturated look just once again reminds me that I am Data's cousin. :(

;)
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Old February 9th, 2008, 06:08 PM   #7
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The CA appears to be not a circular pattern but uniformly apparent from top to bottom of the image. This would suggest it may be a normal camcorder imager artifact. It is not lens related.
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Old February 9th, 2008, 08:01 PM   #8
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The CA appears to be not a circular pattern but uniformly apparent from top to bottom of the image. This would suggest it may be a normal camcorder imager artifact. It is not lens related.
Ah. Then the A1 CA issues continue to haunt me. At least it's not nearly as bad as shooting wide with the stock lens.
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Old February 10th, 2008, 06:11 AM   #9
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Brandon.

One experiment you might try - if your Letus35 is actually screwed into the filter mount on front of your camera and not supported on rods or other brackets.

Set your cam up on a good strong steady tripod. Turn it on and observe the image. Gently rotate the Letus clockwise in the filter thread one turn only.

The line which runs through the sign to left of you in your posted image may be apparent in the viewfinder if you look hard for it. If it is there and it rotates clockwise around the LCD screen, or other lines swing up and around through the left side of frame there are two possibilities.

The reason why I suggest you do this is that the line to me looks like an internal refllection within the Letus flip path which would normally lie outside of the camcorder image area. All flips including the benchmark Mini35 will show something if you zoom back far enough. You alone will know if there was a real line or seam through the text on that sign.

You may be zoomed too far back, scanning too large an area of the GG and picking up an edge of the flip path.

Your camcorder sensor image center and the Letus35 optical center axis might not be coincident, which could be mirror or prism misalignment within the Letus, skewed optical centre axis or an offset within the camera itself. The original early Letus flips were pretty ordinary as far as centering was concerned due to movement on any or all of three joints in the casework due to compliance in the adhesives, or the screwholes in the plastic.

Regardless of this, most appliances yielded a satisfactory image if you zoomed in to the recommended position which took you inside the edges of the mirror path as the mirror areas were fairly generous.

I am led to understand that the Letus Extreme has been more carefully engineered and joint compliance as existed with the plastic flip model is gone because the casework is all metal.

If the vertical line down the left side remains evident and is also there when the Letus35 is not attached to the camera, your camera itself may be faulty.

To test for in-camera optical center offset relative to image sensor centre, pick a small target on the wall with the camcorder zoomed right in and sitting on a locked off tripod. Adjust the tpripod until the target is dead centre in your image.

Zoom back without bumping the camera and see if the target is still deadcenter in the viewfinder or LCD screen. Chances are it may have drifted off to the right and may be a bit high.

Dennis Woods of the Brevis adaptors has reported some difficulties with some small camcorders which I won't name in relation to offset images. This is not a new phenonmen, evidently found also in several older cameras and across brands.

There is no a lot can be done about it except to zoom in closer to get inside the edge of the flip path. You may need to move from the fullsize Letus35 to the Letus Mini.

Don't take my word on this as I am very much in lucky guess territory here.

Consult with Quyen or Hien Le about your difficulties and also look back through posts by Dennis Woods concerning your camera which may be the same one you refer to.

Last edited by Bob Hart; February 10th, 2008 at 06:33 AM. Reason: added text
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Old February 10th, 2008, 02:44 PM   #10
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Thanks, Bob. I don't have the issue outside of the Letus, and actually, I've determined that it is in fact the alignment being a little off. Basically, I've found that I can still nudge the Letus around a bit with the rod system, so I pushed, pulled, rotated and whined at it until I was able to get the picture centered. If the left side does still act up, I just push it a little farther left, but usually, it's fine.

Odd thing is my 2.8 28mm prime vignetts quite a bit more than my 3.5 35mm-105mm zoom. In fact, the zoom is nearly clear on the edges. I did pay more for the zoom, though.
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