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Just got my French Prisms - Page 6

post #151 of 303
5/27/08 at 8:39am
These prisms seem to perform as well as any 2 prism based lens in most respects (and actually better than most in terms of focus).

But, the problem I'm noting is bad ghosting. This is easily seen with white text on a black background. For instance, the credits (like the "Hasbro" one) at the beginning of Transformers. This is the only aspect of these where their performance seems less than other two prisms systems.

Ghosting is caused by internal reflections and the angles of the prisms not great enough to move the ghosting off screen. It is true that these prisms operate at a much smaller angle than other two prism systems (which is why they can be so small).

I'm assuming this ghosting cannot be eliminated because it is a product of the angle of the prisms, but has anyone figured out anything I may have overlooked?

Thanks.
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post #152 of 303
5/29/08 at 8:35am
can anyone tell me what material is the corrective element made of? how thick should it be? and can one be made and put in a typical DIY 2 prism based anamorphic lens? or is it some special material that is too expensive to have for a DIY lens?
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post #153 of 303
5/29/08 at 9:16am
Quote:
Originally Posted by speedtriplex View Post

can anyone tell me what material is the corrective element made of? how thick should it be? and can one be made and put in a typical DIY 2 prism based anamorphic lens? or is it some special material that is too expensive to have for a DIY lens?

I'm assuming you are talking about the astigmatism correction element? If so, I've never seen anyone use one in DIY.

To me, the biggest issue with DIY is the CA. For that, you'll most likely need an achromatic prism pair. The common approach for this is crown and flint glass, but I've not seen anyone find a source for prisms of this nature. If we could this would be the "killer app" for DIY anamorphic.
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post #154 of 303
5/29/08 at 10:21am
Person99,

Thanks for your answer :-)

Yes you're right about the astigmatism correction element. CAVX is putting one in his upcoming Aussiemorphic III, so I figured why can't anyone put it too if one knows how to go about it :-)

I already have a BK7 prism pair for the lens, only want a corrective element now :-)
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post #155 of 303
5/29/08 at 9:00pm
Quote:
Originally Posted by Person99 View Post

I'm assuming you are talking about the astigmatism correction element? If so, I've never seen anyone use one in DIY.

To me, the biggest issue with DIY is the CA. For that, you'll most likely need an achromatic prism pair. The common approach for this is crown and flint glass, but I've not seen anyone find a source for prisms of this nature. If we could this would be the "killer app" for DIY anamorphic.


As these too small ?

http://www.escoproducts.com/products...ses.php?show=1
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post #156 of 303
5/30/08 at 8:48am
Quote:
Originally Posted by HDGTX View Post

As these too small ?

http://www.escoproducts.com/products...ses.php?show=1

Those are lenses. They cannot be used to create the optical stretch.
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post #157 of 303
10/17/08 at 7:37am
Thread Starter 
Well nothing ever came about with a metal enclosure, so now that my screen is ready I will be rebuilding my enclosure for my prisms. I already have some 1x6 lumber that I will be using this time around vs. 3/8th stuff I used before. The enclosure before was stable and all but driving the screws in to the side side panels and very close to the edges of the top and bottom pieces was causing cracking.

I will be using a similar design, but I just thought of a possible modification which will make for easy adjustment of the prisms if need be.
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post #158 of 303
10/20/08 at 1:32pm
It seems that these French prisms are quite popular so I also ordered one pair. Still not arrived but I am trying to do an article about building it to the local magazine. I am trying to make it work in short throwing distance. I can report what is the working range with panasonic ax200 if anybody is interested. I have seen the great article about the other available trophies but not with this one. Let´s see how it goes.
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post #159 of 303
10/20/08 at 1:35pm
Quote:
Originally Posted by myky View Post

It seems that these French prisms are quite popular so I also ordered one pair. Still not arrived but I am trying to do an article about building it to the local magazine. I am trying to make it work in short throwing distance. I can report what is the working range with panasonic ax200 if anybody is interested. I have seen the great article about the other available trophies but not with this one. Let´s see how it goes.

These are not bad--no image shift, very good on preserving focus, etc. They have one fatal flaw though. The angles used means that the reflected ghost image is on the screen and it is pretty bad with these.
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post #160 of 303
10/20/08 at 7:15pm
Quote:
Originally Posted by Person99 View Post

These are not bad--no image shift, very good on preserving focus, etc. They have one fatal flaw though. The angles used means that the reflected ghost image is on the screen and it is pretty bad with these.

I was under the impression that these had an anti reflecting coating...

Mark
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post #161 of 303
10/21/08 at 6:53am
Thread Starter 
They do, I have not any reflection issues, nada, zip. Even putting the coated side of the prism directly into the projector's beam produced nothing but a shadow.

I just noted what you said about the lettering reflections Person99 in your earlier posts from May. We saw Indiana Jones this past weekend with the lens in place, and their were a couple fo scenes with lettering at the bottom of the screen at the beginning, neither my family members (my toughest critics) or I noted ghosting letters. Also we've watched some baseball and football and no problem with the tickers or score boxes. Tonight I wanna try and get some screen shots hopefully so I will try and look for that, even though I may not want to perhaps in closing credits.

In any event I made some progress on my updated enclosure. As I noted earlier an idea quickly came to me of how to easily access the lens to make quick adjustment and clean the lens' if need be. In the pics to follow you'll see how I'm doing this. I did re-use the corkboard from my last case as it is a good way to hold the lens' in place. I might still change that out for this padding you put in your kitchen drawers to hold holds things in place, but we'll see.

Here is a pic of all the material it is composed of

As you can see I already hinged the top cover

Then with everything put together

Open-says-me

Profile view


Latches attached, lens' in place for test closing

Success


For size reference I put a PS3 game next to it




In front of projector




It was at this point that I discovered because of the thickness the wood the prisms were being raised just a little bit to much so I had to cut it down. I basically sliced the bottom panel in half. It was a pain but I got it done, late though so that's why no screenie pics yet, hopefully tonight.



Need to sand that bottom panel a little more to smooth out the rough cut, lightly sand the hardware and spray the whole thing black for a finished look. I really like the hinged approach as it made it simple to be able to re-positon the prisms and then lock it down. This way I could also get quick access if need be to dust off the lens' from time to time.
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post #162 of 303
10/21/08 at 7:17am
Hi Oman321,

as i see, you use the same epson projector like me, which has no possibilty for vertical stretch. So my question, how do you stretch the image? HTPC? Or external video processor?
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post #163 of 303
10/21/08 at 7:27am
Quote:
Originally Posted by oman321 View Post

They do, I have not any reflection issues, nada, zip. Even putting the coated side of the prism directly into the projector's beam produced nothing but a shadow.

I just noted what you said about the lettering reflections Person99 in your earlier posts from May.

Even coated prisms will have some reflections (look inside the case and see the reflected image).

Couple of observations. If you have an LCD projector which has a poor panel CR, you might not see the ghost image that bad because either the black is too gray, or the white text is too dim. I see them on a PJ with a calibrated (tested) ANSI CR average of 650:1 and a peak ANSI CR of 900:1 with about 400 ANSI lumens. A dimmer projector or one with worse ANSI CR may not reveal the issue.

Secondly, after looking at your pictures, I can say that I've tested with the prisms much closer together (almost touching like Mark and others set up their lenses) whereas you have them spread out much more so the reflection may hit the inside of the case instead of bounce back out. I will try increasing the distance between the prisms to see if this eliminates the on screen reflection. I'll report back after some testing.
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post #164 of 303
10/21/08 at 9:35am
Thread Starter 
Widlarizer,

I got the discontinued Key-Digital 4x1HDMI available at Digital Connection. I was able to get it at a slightly better price over what they are advertising it now for. Price has gone down, up, down, up recently so maybe wait a while if you decide you want it. It's great for a 720P projector and forum user ebr uses it with 1080P projector. The only down side is that it doesn't accept a 1080P signal(though it does output one) and it doesn't do 24fps.

Person99,

That would be cool if you could test that out. I have the Epson HC400 not calibrated and the manufacturer's specs say 5000:1 CR, 1500 ANSI Lumens. I know this is spec sheet ratings and not real world tested, calibrated, and properly setup numbers, it's just to let you know what I have and what the spec sheet says. Link

As far as the positioning of the prims, I was testing out my screen on friday and threw my old enclosure back together to align things. I first started with a print out of the schematic that I posted early on in the thread where the lens' do touch. I then needed to move the lens' in order to properly stretch the image to fill the screen. I then traced the result on the cork board that I was using for easy reference, that's just how they ended up being positioned. Maybe it resulted in an unrealized benefit, we'll see. Thanks for the feedback.
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post #165 of 303
10/21/08 at 9:55am
Quote:
Originally Posted by oman321 View Post

Person99,

That would be cool if you could test that out. I have the Epson HC400 not calibrated and the manufacturer's specs say 5000:1 CR, 1500 ANSI Lumens. I know this is spec sheet ratings and not real world tested, calibrated, and properly setup numbers

OK, if using it in one of the theater modes it is around 400 Lumens--so about what I've got. But, it has pretty elevated black levels, so you might not be able to see the ghosted image because your black level is so high (i.e. the "gray" or black is actually brighter than the ghosted image).

I'll see if the ghosted image is bright enough to snap a picture of.

Quote:
Originally Posted by oman321 View Post

As far as the positioning of the prisms, I was testing out my screen on friday and threw my old enclosure back together to align things. I first started with a print out of the schematic that I posted early on in the thread where the lens' do touch. I then needed to move the lens' in order to properly stretch the image to fill the screen. I then traced the result on the cork board that I was using for easy reference, that's just how they ended up being positioned. Maybe it resulted in an unrealized benefit, we'll see. Thanks for the feedback.

What gives the stretch is the angle between the prisms. You can get the same amount of stretch either with the prisms touching or if the prisms are 1" apart.
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post #166 of 303
10/21/08 at 10:07am
Quote:
Originally Posted by oman321 View Post


I got the discontinued Key-Digital 4x1HDMI available at Digital Connection. I was able to get it at a slightly better price over what they are advertising it now for. Price has gone down, up, down, up recently so maybe wait a while if you decide you want it. It's great for a 720P projector and forum user ebr uses it with 1080P projector. The only down side is that it doesn't accept a 1080P signal(though it does output one) and it doesn't do 24fps.

If you are using it with a 720p projector (or any projector with a vert resolution up to 800), a used Lumagen DVI is a great processor. They can be had used for about $350.

In addition to the vertical stretch you'll get 11 point gamma adjustment, 4 calibration memories per input, the ability to input 1080p/24, the ability to output rates other than 50/60 Hz (if you have a PJ that accepts 48 or 72 as I do, this is great).

The biggest limitations of the DVI are no output above 800 vertical lines and no true film mode deinterlacing of 1080i (although I find 1080i film via it digital input seems to do pretty darn good most of the time with the component input being a bit weaker--but with 1080p/24 input you don't need a 1080i mode for blu ray).

For 1080p output or true film mode deinterlacing of 1080i or slightly better SD scaling, you need to step up to the Lumagen HDP which is going for around $750 used or $1000 new.
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post #167 of 303
10/21/08 at 11:05am
@oman321:
Thanks for your quick answer
I think, that it may be cheaper for me, to purchase a new projector including the vertical stretch, instead of searching for a key digital 4x1 video scaler here in germany
But you're right, beside that, the Epson EMP TW 700 is a great home cinema projector
Do you have any test images of your DIY anamorphic lens?

@Person99:
Thanks for your advice I'll have a look where i could purchase an used Lumagen DVI here in europe...
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post #168 of 303
10/21/08 at 11:39am
Thread Starter 
I'll have to try the different modes tonight and see if I see anything.

Widlarizer, If I were shopping around I probably would certainly get a projector with the V-stretch built in. At the time when I bought mine it wasn't a prevalent feature for HD signals. I know the Panasonic AX100 featured it but I didn't like all the problems that projector was plagued with. Also the Key Digital does feature a horizontal squeeze mode which allows me to leave the lens in place and get a regular 16:9 image, although 16:9 stretched over a 2:35 hasn't seemed that bad either.

I don't have screen shots yet, I will hopefully be trying to capture some tonight.
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post #169 of 303
10/21/08 at 12:35pm
Yeah, i already purchased the new Sanyo PLV Z700 which offers a built-in v-stretch.
But i still wanted to use my TW700 in the bedroom
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post #170 of 303
10/22/08 at 6:49am
Thread Starter 
So I managed to get some screen shots yesterday. Word of warning, I don't have a tripod and I cannot set the white balance on my camera. I have a basic Nikon 4MP camera on which I turned off the flash and set the timer to take the picture. I tried propping the camera up on the back of my HT seats but it wasn't working out, so I had to hold the camera while sitting in the back row very still with both hands. Some came out better than others, some more crooked than others . As I'm sure most of you realize the images in real life look way better. Also reflection of the soffit area above the screen is also not an issue real life.

Indiana Jones: Spoiler alert if you haven't seen the movie






Star Wars III Revenge of the Sith
Lots of great scenes in this one, hard to choose so I gave them all to you













Over the Hedge, good movie.





This has got to be my favorite



Person99, I was looking for the letter ghosting in different areas to no avail, including the Star Wars pics above. Then my wife and I decided to watch the most recent episode of Terminator:Sarah Connor Chronicles. After the show one of the logos that popped up on the screen was a black background with white lettering across and arched up in about 3/4's of the screen and what da you know, I saw some of the letter ghosting on the far right about 1/4 of the screen "curses". Anyhow I paused the image and started to investigate, what I discovered was that by placing my hand on the inside left side of my enclosure I was able to eliminate about 80% of the ghosting. I think by lining the inside of the case with velvet it will help to eliminate most if not all of the reflection issue. In any event the prisms are still a keeper for me, as this is still not an issue with subtitles with me.

The trophy prisms, HTB, and even the CAVX lens (no offense Mark) introduced reflection issues. I know of one person who picked up a CAVX lens second hand and was getting reflections shot back into and through out the room. Most issues were addressed by covering up the rear exposed section of the lens. For the money I am still quite pleased. I'll report back when I line the case and see if it thoroughly addresses the issues. Might be a couple of weeks though as I need to get back to work and finish the rest of my basement. Still looking foward to your results, perhaps the prism separation is taking care of some of the ghosting which is why I only got it in the far right.
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post #171 of 303
10/22/08 at 11:14am
Nice pics oman321
Which throw ratio do you have in your home theater. I'm asking because i would like to know how much pincushion do you get with these prisms?
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post #172 of 303
10/22/08 at 12:49pm
Thread Starter 
My projector is about 14' away from the screen so 168". If I understand it correctly I'm supposed to calculate the width of my 16:9 screen which would normally be 82.5". So 168/82.5 = 2.03 throw ratio?

My screen goes in about 3" from the edges. I got an excel calculation sheet from Aussie Bob which helped to figure how much curve I needed. Without the lens in place you can see that the edges of the image (about 6" in) don't quite make it down to the screen bottom. with lens in Place the edges make it all the way down.
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post #173 of 303
10/22/08 at 1:30pm
Ok, 2.03 throw ratio sounds good and i've forgotten, that you have a curved screen
Well...nice setup. I wish i could build a curved screen for my homecinema...but it seems quite difficult for me
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post #174 of 303
10/23/08 at 6:25am
Thread Starter 
Not as tough as you may think, I was a little nervous about it at first, but now that I've done it, it was quite easy. It kind'of depends if you are putting a curved screen on a false wall which is also curved like me or if you are putting a curved screen on a flat wall like tr6 (someone else who built a curved screen like me), his screen build . You can check pics of my screen build in my construction thread linked below in my signature line.
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post #175 of 303
10/24/08 at 2:14am
About the enclosure. I founded out that the felt stickers for furniture legs are quite good to "eat" the light (black and brown ones). You can find these in your superstores quite easily. They will sell those small circle ones (which are useless) and also A4 size. Many have just painted the inside but it still reflects the light (not much but still a little). It will also covers your prism if you want to move those (pass through and stretch options).
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post #176 of 303
10/24/08 at 6:17am
Thread Starter 
Thanks for the tip myky I will keep that in mind. Right now I plan to use some left over velvet that I have from my screen border. It does a great job at sucking up light. The lens I plan to leave in place all the time in wide mode. My scaler does provide a horizontal squeeze mode for 16:9, but I gotta say my 16:9 doesn't seem bad at all stretched to 2:35. Until I get some sort of masking in place I may just view it that way.
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post #177 of 303
10/28/08 at 6:01am
Thread Starter 
I have my new enclosure all spray painted and looking good in black. I also lined the inside with my left over velvet, to cut down the letter reflections which also makes it look very nice.

I went to snap off some pics to show it here and my batteries are dead... I'll try to post some pics soon.

BTW, I tried to observe if the letter ghosting would still be an issue and they appear to be about 98% or more taken care of. That's good enough for me.
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post #178 of 303
10/28/08 at 10:31am
Quote:
Originally Posted by oman321 View Post


Person99, I was looking for the letter ghosting in different areas to no avail, including the Star Wars pics above. Then my wife and I decided to watch the most recent episode of Terminator:Sarah Connor Chronicles. After the show one of the logos that popped up on the screen was a black background with white lettering across and arched up in about 3/4's of the screen and what da you know, I saw some of the letter ghosting on the far right about 1/4 of the screen "curses".

Yep. That is where it is. I did some testing this weekend and could not eliminate the ghost images in any way with these prisms. It is on the same side of the screen as the front prisms "thick" end.

Quote:
Originally Posted by oman321 View Post

Anyhow I paused the image and started to investigate, what I discovered was that by placing my hand on the inside left side of my enclosure I was able to eliminate about 80% of the ghosting. I think by lining the inside of the case with velvet it will help to eliminate most if not all of the reflection issue.

This may help, but I've tried triple black velvet in the case and to ensure that it was a case problem I tried them without a case (so there is an almost infinite case). In all cases (no pun intended) there was a ghost image--i.e. nothing eliminated it.

Quote:
Originally Posted by oman321 View Post

The trophy prisms, HTB, and even the CAVX lens (no offense Mark) introduced reflection issues. I know of one person who picked up a CAVX lens second hand and was getting reflections shot back into and through out the room. Most issues were addressed by covering up the rear exposed section of the lens.

As an FYI I also have an Aussiemorphic Mk II and the current HTB lens at my house that I've also tested. You are correct that all of the low cost prism based lenses have reflection issues. Most can be treated as you noted or left unchecked (a reflection on the back wall does not disturb the movie at all).

But, here is the CRITICAL point. Neither the Aussiemorphic nor the HTB introduce reflections that are on the screen. In other words, though they may have reflections, they don't make ghost images on the screen. I'll take a mini-screen image on the back wall over a ghosted image anytime.


Quote:
Originally Posted by oman321 View Post

Still looking foward to your results, perhaps the prism separation is taking care of some of the ghosting which is why I only got it in the far right.

Nope. The results are above. Ghosting is always on the side with the thick edge of the front prism. Honestly, given the intensity of the ghosted image, I think you are not seeing it as much because of your PJs elevated black levels (no offense intended). I have some neighbors with PJs that have elevated black levels like yours, so I may try to test on theirs to see if my theory holds true. I think that black on your PJ is gray enough that it is actually brighter than the ghosted image most of the time. If this is true, then these prism are probably fine with projectors that have high black levels such as LCD projectors, pre-DC3 DLPs, and the old (1400x788) JVC LCoS machines. I think on projectors with a calibrated on off contrast ratio of under 1500:1 (so a rated on/off of about 3000:1 or less) these will work, on higher CR projectors they will not.

Just as an FYI, all my testing thus far has been done with a PJ that measures (not specced) as follows:
Average ANSI CR: 647:1
Peak ANSI CR: 890:1
On/Off CR: ~2800:1
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post #179 of 303
10/28/08 at 1:07pm
Thread Starter 
Person99,

Thanks for the feedback and taking the time to do some more testing. As it stands now it seems to me that the velvet has helped with most of my issues, although I only had a chance to quickly check it and it would be worthwhile for me to continue and try to observe if the ghosting problem is persistent. I can also try putting the projector in different modes i.e. theater mode, theater 1 or 2 and see if this makes a difference with black levels and makes the ghosting more apparent.

Let me ask, since you have an MkII and a HTB lens, you wanna give me one, jk. Actual question, they basically use trophy prisms correct? The MkII might uses special ordered Bk7 lens' but I'm not sure. So with these no ghosting problems, but on the versions that you have are they coated on the sides and top and bottom if they were standing up? If I get some trophy prisms am I gonna have issues on screen because of the lack of AR coating? I suppose they could be lined with something to eliminate the issue.

If I were to do this I would probably go with the small ones as I would need to get the lens to fit inside a projector shelf/soffit. Seeing how these are so small I would hope the small trophy prisms would be ok also. In any event for the time being I'll hopefully be ok, if the ghosting does become an issue the trophy prisms would be worth investigating for my needs, as they are the alternative that would best fit my budget.

Also a small picture reflected back wouldn't be a big deal for me as the projector will eventually be enclosed, with only a port for the image to shine thru.
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post #180 of 303
10/29/08 at 12:19am
Do not worry about the ghost image. All trophies that people are using for anamorphic lenses will have ghost image. So do not jump from one ghost image to another

Please read the great article about the DIY anamorphic lens (award plaques). Read specially the section "Reflections".

It just happens if you do not have good anti reflection coating. I believe that the French prisms are only coated from the sides, but how about the actual "lens" part? Anyway you will not get rid of the ghost image unless you will order your prisms from optic company or something (which will make the real AR coating and that means a special layer(s) to the surface of the lens where the light hits).

If you really want to see your trophies or normal prisms performance watch one of the James Bond beginnings and voila! You will see it.

If you do not see it, please tell us how did you get rid off it
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