CurtPalme.com Home Theater Forum

[David_Web]

I did a little experiment today when I found a perfect target.
It's a small glass plate with what appears to be silver oxide as the marking.

So why not rig up some sort of light source and project it with a HD8 rev2 left from my marquee (now fitted with HD145)

I used my 60mm macro on my D80 to take the pictures as close as I could get.

The lens was set to OK focus and then I moved the screen (a white box) to get as good focus as I could get.
The distance was approx 1.5m as I don't have a bigger place to test atm.
Will do later though. When it get darker in the other rooms.

The big markings with the "1" are 1mm apart with 1/10th mm markings in between.

The bad part is that I can't see if it flares and adjust focus to avoid that.
Hmm, maybe I could make a target for that.

[Nashou66]

Interesting now you need to try that with the Blue HD144 lens. See how much better it can reproduce the "target" .

Athanasios

PS repost this in the all about lens thread too!

[1031]

That sounds quite good method because tube itself has nothing to do with that kind of test
Hey if you "test rig" is on hand´s test how much picture is sharper if you use same hd-8 and block it´s aperature smaller (easiest to put some black cardboard that has smaller hole than lens diameter is in front of lens)
You should see improvement in sharpnes.

[ecrabb]

Hmmm... Very interesting. The only problem I see is without a scaled wedge, any comparisons between lenses will still be fairly subjective, ala "this looks sharper than that". You still wouldn't know how much sharper - quantitatively speaking.

If we had a scaled wedge, we could objectively say at what point you reach the resolution limit of any given lens. This particular target is also pretty low-resolution, relatively speaking.

If somebody had a decent physical setup and several different lenses to test, I could make up a resolution wedge test pattern on a piece of clear film at 4000ppi that should clearly show the limits of even the very best 9" lenses. I could even make it "CRT sized" and put wedges in the corners to test sharpness in both the center and the edges of the lens. That would be fascinating... To me, at least... Because I'm a geek.

SC

[perisoft]

[David_Web]

I did some quick testing by poking a tiny hole in alu foil. And at it's best sharpness it had some flaring.
I have to see if this will be corrected by the foremost focus knob, which I guess as the flare comes from the edge.

A full sized target sounds like a good idea. Although I don't see an easy way to do it.
Mechanical setup sounds like a pita.

[ecrabb]

The target itself would be the easy part. I'd build a vector file with a line wedge, and index in line pairs/mm. Then image to film at 4,000 ppi, which should cleanly represent ~75 black/white line pairs/mm by my calculations - no more. Still, that should be about double what any CRT lens is capable of... I think. Aren't the good 9" lenses in the 20-30 lp/mm ballpark?

Yes, the physical/mechanical setup would indeed be a pita.

SC

[Tom.W]

The GT-17.

HD120 are the most desirable lens for the 9" liquid coupled projectors, they are optimized for image widths from 2 to 3 meters and have 12 line per mm resolution.

Where is Zeiss when you really need them ?

I understand achase is using Zeiss lenses but they do not come cheap ! And it's not quite a CRT projector but close...

[ecrabb]

Thanks, Tom. So, if the GT-17's are good to 12 lines/mm, a target that approaches 150 lines/mm should be adequate for evaluation, then.

SC

[Tom.W]

[quote="ecrabb"]Thanks, Tom. So, if the GT-17's are good to 12 lines/mm, a target that approaches 150 lines/mm should be adequate for evaluation, then.

SC[/quote

With what lens ?

[tse]