CurtPalme.com Home Theater Forum

[lyd]

I just realized something totally wild is happening when I converge my 8500. When I look through the corner of my eye, like look straight at the right side of the screen and then shift just my eyes to the left side of the screen, the grid looks radically different! This is most noticeable when looking at red + blue. Looking at it in the way I describe above, the blue lines appear entirely off of the red lines. When I look straight at them they are fine. When I look at them from any angle with my glasses off they are fine.

What the heck is going on? It has to have something to do with different wavelengths refracting differently through the medium of the lenses of my glasses, or something crazy like that. It sure freaked me out, in any case. All this time I have been chasing blue convergence issues that didn't exist. Bizarro.

Anyone else experienced this?

lyd

[ncc1701d]

Yes i have experienced it for very long time.

I use contacts and have astigmatic errors on both my eyes, but have used regular lenses for years.
I was seeing blue shadows over all text on movies and was irritated because it looks just like convergence errors on blue.

When sitting in my sofa there were blue shadows, but if i walked up to the screen they vanished. My optitian? or what it's called said it was my astig-error's fault.

2 months ago i decided to get new tubes for my pj, and thought of replacing my contacts at the same time,
so i went for contacts that correct my astig errors, and WOW.. the image got so much clearer and better. Completely got rid of the blue "shadows" + i see everything much clearer and sharper.

(actually i got the lenses before the tubes so i could see the difference clearly before swapping tubes)

Now i have new lenses AND new tubes WOW

[chillman]

Actually I think this is what's called chromatical abberation (or something like that don't know the exact english term) Look at a white strip trough the side of the glasses and you will see a red seem on the one side and a blue on the other. So I guess it's better to wear contacts when adjusting convergence

[ecrabb]

Yep, it's chromatic aberration - which is basically is a refraction effect. You need a multi-element lens to prevent it - which doesn't work too hot stuck on your face.

This is why I can't stand ever wearing my glasses. My contacts go in when I get up in the morning, and they come out when go to bed. I hate glasses.

It's funny - this very topic came up in the other forum just a few days ago:
Don't do convergence while wearing glasses.

SC

[WanMan]

You just noticed this? Wow, I see this out in the wild. For instance, and solid color sign at night if tracked will have a color-shifted halo on one side. Heck, I can sit back at the sweet spot and stair at any line on the screen and while keeping my eye on that line move my head and prescription eyewear around and see this aberration. Not worn glasses for long?

In fact, sitting in front of this 22" monitor (1600x1200) I can look at the vertical line that defines the web browser window. I can keep an eye on it while moving my head to the left and right. The line presents a red halo on the left when looking left, and a blue halo on the right when looking right.

[lyd]

[garyfritz]

[ecrabb]

Gary, the billboards are LED, which emit a pretty pure wavelength of light. Compared to other display technologies, the primaries on an LED billboard would be much more 'discrete' (I can't think of a better term.) Given that, I'd expect the chromatic aberration to be more pronounced compared with other technologies - which would exhibit much softer transitions between primaries.

We only have one of those big LED boards here in town that I know of. I NEVER wear my glasses outside the house (I really HATE glasses), or I'd driver over and see what you mean. If were just a programmer or something and didn't rely so heavily on perfectly corrected eyesight (video, photography, HD, design, etc.), I'd get surgery. But, every opthalmologist and O.D. I talk to says the corrective procedures just don't have the success rate and outcomes that I'd likely be happy with - and it's non-reversible - so I'm stuck with contacts for the foreseeable future.

SC

[garyfritz]

Yeah, I suspected something like that. It really is strange how pronounced it is on that type of sign.

I've been sorely tempted to do LASIK or similar for decades, but I'm with you -- the results are variable and can be scary. Even people who don't have severe vision problems afterward often have bad problems with dry eyes &etc. Since I live in a near-desert, that could be a serious problem for me.

[lyd]

Well, I might eat my words somewhat here.

I did convergence again last night, with this issue in mind, and while awareness of the problem did allow me to converge more accurately than I think I have in the past, it was a serious pain in the butt. I was jumping around like a flea on a hot-plate trying to look at each zone straight-on.

Then it occurred to me that maybe this wasn't even the best approach. Perhaps I should be converging while sitting in the viewing position and staring at the center of the screen, compensating for the chromatic aberration of my glasses with the convergence itself. I didn't do that, though, and it did look good. Apparent sharpness at the screen edges was better than it had been, the way I was doing it before.

I also converged using a pattern off the DVE HD disk rather than the internal one this time. Not sure if that accounted for any of the perceived improvement or not.

lyd

[Mark_A_W]

Well, I can't stand contacts, they make my eyes water constantly, and are a PITA.

But I've never noticed this affect at all wearing glasses. It depends on your glasses/prescription.

[WTS]

HI,

THere a similar thread going on at AVS. I can't see any differences when I wear my glasses and turn my head sideways. I guess thats why I bought Carl Zeis lenses so I wouldn't have vision problems.

[lyd]

My frames broke the other day, so since I'm shopping for some new specs I figured I'd look into this a little more. It seems to all just come down to the material, as far as chromatic aberration is concerned. Your Zeiss lenses may be superior in other ways, but if you don't have noticeable issues with this problem then it looks like it is just because they are made of crown glass or hard plastic resin rather than one of the other lens materials.

The "Abbe number" indicates a material's variation of refractive index with wavelength, the higher the number the better. Polycarbonate lenses like I have are at the absolute bottom of the list, with an Abbe number of 30. Crown glass and hard resin are 59 and 58, respectively.

So it looks like I need two pairs, one with a set of poly lenses for normal wear, and one with plastic lenses for movie watching and projector fiddling. Contacts would solve the problem entirely, of course, but I really prefer glasses.

lyd

[voodoo7869]

the problem is caused by high correction factor in the lens. this is normally associated with plastic lenses I think the optometrist called it achromatic diffraction. it is more common in rectangular lenses less in round or oval. He said it occurs when they grind the lens the fingers that hold the lens have pressure which slightly warps the lens I mean slightly. that slight miscorrection causes color separation. if you have a low power factor or a round lens that warping is greatly reduced to almost nill. he says to completely avoid it glass lenses are the best but no guarantee. contacts should not have this problem at all due to being on the eye.

just my 2 cents

or rather the optometrist's

[lyd]

[BGSPCS]

I have glasses and i too I experience that problem. When i was trying to converge my CRT, every time i moved my head everything changed. I have the problem with LED signboards, and with my LED rope light. If i move my head in circles the lights appear to move.

It gets very annoying.

[garyfritz]

voodoo, what you're describing sounds like a mechanical warping of the lens causing distortion. I'd call that a flaw in manufacturing.

Chromatic aberration is an inherent property of the lens plastic. Different plastics have different levels of CA. The Abbe number that lyd mentioned is the technical way to measure CA. Eyeglass vendors tend to push high-index plastic, because the high refractive index results in thinner lighter lenses and a more attractive look. But the higher index plastics also have higher amounts of CA. They work fine if you have a low-power prescription, but the more intense your prescription, the more the high-index plastic will cause CA.

I can't stand the high-index plastics they usually recommend. I get color fringing all over the place. I go with the old-fashioned plastic with a refractive index around 1.58 or so, vs. 1.65 or 1.67 for the high-index. (I dunno what the Abbe numbers are for these plastics.)

[voodoo7869]

that makes more sense. I just asked himabout it and he said what i stated above. Maybe he was trying to make it simple for us stupid folk or better yet maybe he did not know the real reason

[paw]

[lyd]

Wow, paw. I'm glad you're happy with the outcome, but your recommendation is enough to talk me out of it.

My room-mate had it about 4 or 5 years ago, and he seems to be one of the cases you read about on the brochures. No negative effects whatsoever, just clear vision.

I'm still too wary of all the possible gotchas to try it myself.

Plus, aside from a short-lived experiment with soft contacts in high school, I've been wearing glasses for over 30 years. I just can't get used to the way I look without them, anymore.

lyd