DIY anamorphic lens

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#1,241
You have to expect light losses and reflections if the prisms are just sitting on a board out front. Try taping the ends first and then see if that helps. The more edges you block (IE make a case too), the better it gets. I have a number for a supplier of these J series, so might have to give them a go soon...

Once you build a case, you can then tilt the lens to correct some of the edges errors. But it is looking very good none the less. That "leia" shot is great as the stormtroopers look focused right across the screen 🙂

Bud - 4 prisms? OUCH!!!
Mark
 
#1,243
Mark Techer said:
You have to expect light losses and reflections if the prisms are just sitting on a board out front. Try taping the ends first and then see if that helps. The more edges you block (IE make a case too), the better it gets. I have a number for a supplier of these J series, so might have to give them a go soon...

Once you build a case, you can then tilt the lens to correct some of the edges errors. But it is looking very good none the less. That "leia" shot is great as the stormtroopers look focused right across the screen 🙂

Bud - 4 prisms? OUCH!!!
Mark
Click to expand...

Oh, I know there will be reflections. I was just being very specific giving my critical impression of the actual test I did, not the whole DIY Prism adventure. But yes, I do still dislike all these light losses from reflections. If the light is reflecting from the faces of these prisms, I must stop the face reflections without losing that light. Not likely to happen without a fancy coating. The way I see it, when light hits glass, it is either reflected or absorbed to some extent by the surface, but I am not optical glass expert.

Bud and Mark,

Thanx for the feedback. I have my projector aimed practically dead centre on the screen with almost zero lens shift. One of the reasons that the screen is wider at the bottom is actually because the whole contraption is pointing down (the weight of the prisms!). Since the thing is pointing down, the lower part of the prisms is farther away, and so the projected image there is travelling farther and has more space to refract, so it is visibley wider at the bottom.

It would seem to me that a 4 prism setup is simply trying to replicate larger angled prisms and that 4 prisms may actually cause more light loss as evident in the trouble-some reflections. By putting two prisms together, you bend more light in the glass, and compared to the two prism lens, it refracts less on its trip between prisms. The trouble is though that unlike two larger individual prisms, 4 small prisms have more reflective faces. If we had larger anti-reflective prisms, we'd be laughing 🙂

My goals right now are:

1) Mask/sand/paint or otherwise block the reflections from the 4 non-face sides of the prisms, the top and sides.

2) Align the projector such that is is aimed totally dead centre at the screen AND level and with its projected image perpendicular to the screen (not aimed slightly left or right, but 90 degrees to the screen).

3) Align the prisms as straight as possible in whatever masked or case enclosed form I can manage.

I will post further photo's as I go.
 
#1,245
I think I know what it is now. It was late last night, so I forgot. During dark scenes, sometimes with contrasting bright and dark areas, or somewhat more overal dark scenes, there were reflections on the screen obscurring the already otherwise dark parts of the scene. Sometimes it was obvious, but other times perhaps the scene was dark and mashed up with reflections and it just obscurred the dark areas. I think the reflections on the screen during the darker contrasty scenes must have made it look bad. I still noticed some light loss, but perhaps it is not as bad as I first thought. I'll do the work on the prisms sides and aligning it all and try again.

I have total light control, but the walls are not black. I have some masking on the ceiling, but there are some white ceiling tiles. The only light source is the projector and the lcds/leds on my AV equipment.
 
#1,247
Mark Techer said:
I am gonna say that yes there is a small light loss as the prisms sitting in the light path and even the most transparent glass is not 100% clear. But when I remove my lens, the difference is not that visible to the naked eye, so I am going to say no more than 5%, but closer to 2% loss...

Mark
Click to expand...


Is there an easy way to measure the light loss? Such as with a light meter on a camera, or something you can place on or near the screen to measure the intensity of an image with and without the lens? (There would have to be some sort of optical zooming, because the lens will change the amount of light hitting the screen because of its stretch capability.

Anyway, Morkys, with respect to CA, you show similar results to what I saw--I could only really see the CA on the sides--specifically, the right side of the screen. Slight masking to create a bit of overscan would sharpen those edges out quite nicely.

I also noticed that the prisms aren't completely uniform internally. If I paused a scene on the screen, and then tilted the prism back and forth, I could see a bit of waviness in the image as the prisms moved, but it isn't anything that I ever noticed in a moving image with the prism stationary, such as during a pan.
 
#1,248
I found an affordable light meter at JAYCAR Electronics. It comes with a "photo" sensor that sits either in the light path or might be able to measure the amount of reflected light off the screen - which I think is better as that is what we see... I'm guessing that if there is a difference, the meter's reading will show it. The meter reads in LUX. Is there an easy conversion from LUX to ANSI - LUMEMS or is not worth the math for this excercise. The meter only costs around the $50 mark, so I will get one soon...

CA
When your prisms are aligned correctly, the small amount of CA should be equal on both sides, not just one. Initially I had it one side too, but noticed that my geometry was not 100% either, so adjusted the prisms once again. This latest adjustment also caused me to mod the case but seems to be working very well now...

I pick up the new case in the morning - laminated black MDF fully edged...

Mark
 
#1,249
Lumens vs. Lux--taken from Wikipedia:

Lux versus lumen
The difference between the lux and the lumen is that the lux takes into account the area over which the luminous flux is spread. 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux.

=======

So it appears that Lux is simply Lumens/square meter. If you wanted to convert from lux to lumens, simply multiply lux by the area of the image.

But in either case, it shouldn't matter if you are only interested in a percent difference, whether you use lux or lumens, the percent difference would be the same.

Interesting about the CA--I had really observed it on the one side the worst, but I can see by Morkys' pictures above that he has it on both sides. Regardless, CA is a part of these lenses, for better or for worse. Slight overscan of the image over masking should solve that problem...


Oh--and do show pictures of your new case!
 
#1,250
morkys: Thanks for posting the nice pictures! You are at the exact same state that I am. I'm also using a board in front of my projector 🙂 I just wish I had a better camera to take pictures with.

You will see a *huge* difference if you just mask the ends of the prisms. Seriously, I was amazed by the difference. And I'm just using black electrical tape. I'm not sure if it's worth trying to roughen the edges or not, but masking will really help with your contrast and reflection issues.

I didn't have any time to play with reflections over the weekend. Yeah, silly holiday stuff 🙂 Hopefully I'll have my enclosure built within the next two weeks.

Oh, about the tilt...even if you have a zero-offset projector you will probably need to tilt the lens assembly. It needs to be perpendicular to the light path. Even though the top of your image might be at zero-degrees, the bottom of the image is at a greater angle. I don't know how long your throw is, but maybe it's long enough that this isn't a problem for you. I know that with my 7205 I'll still need to tilt the lenses down and plan to built a ceiling mount that can do that.
 
#1,251
I will check out the geometry again and do the masking. My projector has zero offset when no lens shift is used and that is how I try to use it. I can use it this way, so why introduce any distortion, blurry image or focus issues un-necessarily. I realize I am lucky that I can do this and not everybody is able to use zero offset. I wonder if other projectors I have my eye on like the Mitsubishi HC5000 BL or the JVC DLA-RS1 are like this. Anyhow, this is fun. I have to sell my old screen so I motivate myself to get this going faster. I am going to make a platform to sit the projector on such that I can tell that the projector is totally level and totally perpendicular to the screen and totally centred. Then I need to work on the geometry of the prisms in front and I should make some progress. I lost sight of another Panamorph 752 sale, somebody else bought it, so maybe this destiny? I wish I could have afforded a Primasonic H1000 but I guess I am saving money and being more creative this way.

thanx again for the help in this fun adventure.

Wish me luck and I will tripod my next photo's for you folks 🙂
 
#1,257
Greetings, everyone! I've been a (*very*) long time lurker in this thread. I've been planning a CIH setup for ages and specifically chose my projector (an Optoma HD72) for its CIH-friendly features.

I thought it would be a while before I could afford an anamorphic lens - or even have the time to tackle it as a DIY project. But that changed the last time I checked back in on this thread and saw the new development with the crystal trophy wedges!

Now I'm kinda stuck between a rock & a hard place... I'm starting construction tomorrow on a living room (dual purpose theater room) remodel. The projector, screen and all speakers are going to be enclosed in soffits along 3 of the 4 walls. My original plans called for the soffits to be just deep enough to accomodate the projector, but now I'm thinking I should allow some extra depth for when I get the lens built. How much extra depth should I allow for a lens assembly made from 2 of the crystal trophy prisms?

One other question - since the HD72 doesn't have a recessed lens, does that mean I should be able to go with the 4x6 prisms?
Does anyone know the depth difference between a lens assembly made from 5x7 prisms vs. one made from 4x6 prisms?

Thanks in advance for the help!
 
#1,258
dracul said:
mark, your blogspot email is bouncing back to me. you got a valid email ?

vlad
Click to expand...

When did you try to email me?

I have had some major problems with the service provider who made me change the email yet again 🙁 so it is now cavx01@bigpond.com A real PITA but at least it good to know there is always a way to get in contact with me through this site 🙂

Hopefully it will not change again...

DonnyBahama said:
Greetings, everyone! I've been a (*very*) long time lurker in this thread. I've been planning a CIH setup for ages and specifically chose my projector (an Optoma HD72) for its CIH-friendly features.

I thought it would be a while before I could afford an anamorphic lens - or even have the time to tackle it as a DIY project. But that changed the last time I checked back in on this thread and saw the new development with the crystal trophy wedges!

Now I'm kinda stuck between a rock & a hard place... I'm starting construction tomorrow on a living room (dual purpose theater room) remodel. The projector, screen and all speakers are going to be enclosed in soffits along 3 of the 4 walls. My original plans called for the soffits to be just deep enough to accomodate the projector, but now I'm thinking I should allow some extra depth for when I get the lens built. How much extra depth should I allow for a lens assembly made from 2 of the crystal trophy prisms?

One other question - since the HD72 doesn't have a recessed lens, does that mean I should be able to go with the 4x6 prisms?
Does anyone know the depth difference between a lens assembly made from 5x7 prisms vs. one made from 4x6 prisms?

Thanks in advance for the help!
Click to expand...

Hi Donny,

It will depend on the actual prisms you go with. I am using large prisms 7.5 x 5.5 and therefore the case is 8" deep in order to get the correct amount of stretch.

Then you have add a little extra for the tilt factor as well.

Also if making it all fit into a sofit, make sure that your "hole" is the same sixe as the lens (at least horizontally)...

Mark
 
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