Hello 🙂 You have no idea how long it to me to find the "Have You Searched" button. I was about to stab someone 
With that out of the way...
I am working on a super short throw projector concept, I have been ransacking the various DIY projector sites/forums for a few days now but I'm still not 100% on the details.
Anyway, i wish to project a high quality image in the 30-40" range at the shortest distance possible. This is to be incorperated into a multitouch table and im trying desperately not to build a 1.8m high monster like i keep finding on the net
The shortest focal length triplet i have found so far is the 180mm from here: http://diyprojectorkits.com/store/index.php?main_page=product_info&cPath=6_10&products_id=29
I can project an image of the size i want from with around 500mm from the lens to the screen, which is brilliant.
Thats one piece of hardware out the way, but now i need an LCD and some fresnels.
I need to have as high a res a possible, in a wide screen (16:9 or 16:10) format. A 19" widescreen LCD monitor would be perfect at 1440x800 pixels however i would need big (410mmx255mm) fresnels to catch all of that.
Option two is to run two 15" panels side by side and line up the projected images, i can get away with smaller fresnels but i would need to double up on all my hardware.
From my reading it appears that one should use a fresnel with a focal length the same or similar to that of your projecting lens. I am not 100% on this but i guess that is to maximise the utilisation of the lens. If your fresnel is short focal length then you wont be able to project your whole image, if the fresnel is long focal length then you will be using a smaller portion of the lens and will exagerate any defects in the lens.
The fresnels from the Short Throw kit here: http://diyprojectorkits.com/store/index.php?main_page=product_info&products_id=33 (1) 220mm FL 400 x 320 x 2mm (1) 330mm FL 400 x 320 x 2mm are reported to work ok with the super short focal length projector lens, however they are slightly too small for my 19" LCD. Also, will i encounter any problems from trying to use the whole width of the fresnel? How much 'margin' should I allow for around the edge?
This company: http://www.bhlens.com/fresnel_lens.aspx manufactures and sells fresnel lenses in big sizes. This lens interests me:
Product:BHPA520-4
Size: 420*260mm
Thickness: 4mm
Material: PMMA
Groove pitch: 0.3mm
Focal length: 520mm
It is wide enough to fit my entire 19" screen into but has a very long focal length. The long focal length could cause problems with my short throw projector lens as well as increasing the total length of my projector. Also i havent heard of anyone using these lenses before so i have no idea on the quality.
Right. Comments anyone 😀
Main things i want to know:
Is there anything obviously wrong with my plan so far?
Are my thoughts right on the need for fresnel focal lengths that match your projection lens?
Can i use the entire width of a fresnel or do i need to leave a margin round the edge?
Can i use the 520mm focal length fresnel with a 180mm focal length projection lens?
Are there other products from other sources i should know about?
With that out of the way...
I am working on a super short throw projector concept, I have been ransacking the various DIY projector sites/forums for a few days now but I'm still not 100% on the details.
Anyway, i wish to project a high quality image in the 30-40" range at the shortest distance possible. This is to be incorperated into a multitouch table and im trying desperately not to build a 1.8m high monster like i keep finding on the net
The shortest focal length triplet i have found so far is the 180mm from here: http://diyprojectorkits.com/store/index.php?main_page=product_info&cPath=6_10&products_id=29
I can project an image of the size i want from with around 500mm from the lens to the screen, which is brilliant.
Thats one piece of hardware out the way, but now i need an LCD and some fresnels.
I need to have as high a res a possible, in a wide screen (16:9 or 16:10) format. A 19" widescreen LCD monitor would be perfect at 1440x800 pixels however i would need big (410mmx255mm) fresnels to catch all of that.
Option two is to run two 15" panels side by side and line up the projected images, i can get away with smaller fresnels but i would need to double up on all my hardware.
From my reading it appears that one should use a fresnel with a focal length the same or similar to that of your projecting lens. I am not 100% on this but i guess that is to maximise the utilisation of the lens. If your fresnel is short focal length then you wont be able to project your whole image, if the fresnel is long focal length then you will be using a smaller portion of the lens and will exagerate any defects in the lens.
The fresnels from the Short Throw kit here: http://diyprojectorkits.com/store/index.php?main_page=product_info&products_id=33 (1) 220mm FL 400 x 320 x 2mm (1) 330mm FL 400 x 320 x 2mm are reported to work ok with the super short focal length projector lens, however they are slightly too small for my 19" LCD. Also, will i encounter any problems from trying to use the whole width of the fresnel? How much 'margin' should I allow for around the edge?
This company: http://www.bhlens.com/fresnel_lens.aspx manufactures and sells fresnel lenses in big sizes. This lens interests me:
Product:BHPA520-4
Size: 420*260mm
Thickness: 4mm
Material: PMMA
Groove pitch: 0.3mm
Focal length: 520mm
It is wide enough to fit my entire 19" screen into but has a very long focal length. The long focal length could cause problems with my short throw projector lens as well as increasing the total length of my projector. Also i havent heard of anyone using these lenses before so i have no idea on the quality.
Right. Comments anyone 😀
Main things i want to know:
Is there anything obviously wrong with my plan so far?
Are my thoughts right on the need for fresnel focal lengths that match your projection lens?
Can i use the entire width of a fresnel or do i need to leave a margin round the edge?
Can i use the 520mm focal length fresnel with a 180mm focal length projection lens?
Are there other products from other sources i should know about?
the first problem I can see you will have is a monster of a projector and all you want to do is project a mere 40" picture. You might want to reconsider. Also I think the shorter you can get your FL of fresnals, the more compact you should be able to get the projector.
Someone quote me if I'm wrong.
Also why would you want to run two LCD panels side by side and line them up. I don't think you can double the output like that. It's like shining 2 torches at the same spot. It don't get much brighter.
Someone quote me if I'm wrong.
Also why would you want to run two LCD panels side by side and line them up. I don't think you can double the output like that. It's like shining 2 torches at the same spot. It don't get much brighter.
Line them up side by side. Not too concerned with brightnes, but i need resolution. It would be like having a 1024 + 1024 x 768 sized display.
As for only getting a 40" picture, the main goal of the project is a multitouch interface, its not a 'tv' though i plan on trying to arrange it so i can project out the side as well and it can double as a conventional projector (though a very short throw one unless i swap the optics around). Think of it more as a computer monitor, lots and lots of tiny pixels for viewing text and CAD models in high res.
I would very much prefer to be able to use the single 19" display option, although if i can arrange a cheap dual light source then the 15's could be a possibility after all. The triplet lenses arent hugely expensive and the fresnels are cheap as 🙂
As for only getting a 40" picture, the main goal of the project is a multitouch interface, its not a 'tv' though i plan on trying to arrange it so i can project out the side as well and it can double as a conventional projector (though a very short throw one unless i swap the optics around). Think of it more as a computer monitor, lots and lots of tiny pixels for viewing text and CAD models in high res.
I would very much prefer to be able to use the single 19" display option, although if i can arrange a cheap dual light source then the 15's could be a possibility after all. The triplet lenses arent hugely expensive and the fresnels are cheap as 🙂
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