I have been reading this forum for about a month or so and have been truly amazed by what all of you have been able to accomplish. I have been thinking about possibly starting my own project, but due to limited space can only have the triplet about 3-4+ ft. from the screen. I'm not looking for anything more then either 60" to 72" diagonal. I have been playing with the "Focal Calc II" and have included a screen shot below, with the figures that may work. I have found and puchased the 254mm triplet (it was only $18.95 S/H, so I thought what the heck), though I am aware that for a 17" LCD it will be pushing it a bit. I have seen a 15.4 wide-screen at a local Walmart for $138.99, but by the time I get to purshasing, it will probably be gone. The monitor will probably be the last thing I buy so I can find the best output for my money. Please take a look at them and let me know if it's doable and what problems I may expect.

Thanks,

Darin

Click to view attachment

Here's also another, more riskier one! Also thanks again for any help you can give

Darin

Click to view attachment

I may have missed it (perhaps you meant to say more after "I have found and purchased"), but do you have access to a 254mm FL triplet lens? Because according to the calculator, that's whats required for those specs.

Sorry for the confusion. I just edited it and hopefully it should be a lot clearer.

Thanks for the correction!

Darin

I just realized (sorry it takes me a minute), but the "Focal Calc II" doesn't tell me what the "focal length" of the rear fresnel is. So what I am also wondering is what should that be, other then something that is large enought for the 17in. LCD. Does the focal length of the rear fresnel matter?

Thanks,

Darin

Can you give us more info on the triplet you have?

The focal length of the rear fresnel determines how far from the rear fresnel you'll place your lamp. Closer (shorter) is better (brighter) - in general. Common rear fresnel focal lengths are 220 and 330 millimeters.

The focal length of the rear fresnel doesn't enter into the focalcalc stuff.

I got the lens @ American Science & Surplus. The link is: 254mm/10in. Triplet Lens

I'm not 100% it will work, but it was only $18.45 with S/H, so it was cheap enought to take the risk.

Thanks Durachko for your help and you too sensibull,

Darin

Pretty sure that lens will produce dim corners with a 17" LCD. The standard triplet is pushing it with a 17, and the lens you bought has a smaller field of view (FOV) because of its length. It doesn't look like a bad lens, though, and might work with a 15". Can't tell you for sure -- you'll just have to experiment.

Thanks sensibull for the FYI about the FOV, but this brings me to another question. How does one determine the FOV of a lens so they can determine if the lens will be good enought for the size of their LCD?

Darin

FOV Test.

Sensibull thanks again for all you help. I know I will have a lot to learn, but my build is still a few months away, just gathering data for right now. Now about the "deem corners" you mentioned if I used the 254mm triplet. I was wondering if I would notice them on the 17in, if I ran it in either 1280x720 for 16:9 and 1024x768 regularly since a lot of these LCD usually black board when you use a lower resolution than native. At least the ones I've seen at work.

Correction: The LCD monitors at work (IBM ThinkVision and HP 1755) don't automatically put a black boarder, but one can be done if needed. I'm just getting old and remember a few laptop monitors doing that, so I remembered it wrong. Anyway, I should be able to put a black boarder at the top and bottom of the screen for 16:9 and then all around for 1024x768 in 4:3. I know I would loose some resolution, but it's hard finding 1280x720-800 15 inches and probably be even harder/expensive in a few months.

Thanks again,

Darin

Maybe. Maybe not.

In all seriousness, I can't really say for sure. I've never built a 17". Nor have I read about anyone using that particular triplet. Certainly running 16:9 or a "screen within a screen" would reduce overall size and help you fit your projection within that triplet. Whether it will work perfectly I don't know.

Either way Sensibull, I thank you for your patience and answers to my rather "newbie" questions. I know I have a lot more studying up and researching before I start my build, but I am certain with all the useful information in this forum and the help of all of you, it will be a successfull one.

Thanks again for everyone's help and insight,

Darin

My projector is making a 75"+ (@16:9) from about 5 feet. Dunno what your triplet is like, but the LL standard triplet will just get the job done - if you are very accurate with the fine tuning.

Ozstang65 your plog was one of the most detailed and encouraging ones I've read. I have really enjoyed most of the ones of read so far. I am still reading them and will probably be still reading them for the next few months. The more data the better. The reason I bought the "10in./254mm triplet" was because of my distance restrictions and that is the number that the "Focal Calc II" came up with for the type of "triplet" I needed. I have been playing around with the app for several weeks now trying to come up with something that would work with a 3-4+ foot throw with a 17in. monitor, that gives a 60" to 72" projection. Trust me, I wasn't looking around for a cheaper triplet, but the "focal length" that the app described. I wish it had given me some idea as to it's FOV so I would have a better idea as to what to expect. Oh well, if the 254mm doesn't work, I'll try something else, at $18.45, its probably the least expensive thing I'll be buying.

I am also looking for a valid alternative light source then the 400W MH due to it's heat and complicated installation. I am still reviewing previous experiments to see what is available. Anyway. Any help, advice, guidance will be greatly appreicated.

Darin

Sensibull or anyone else who can answer this quick question! I just received my 10in./254mm FL Lens and after reading the information about the "FOV Test", I tried a little experiment. I turned off all the lights in my office (I don't have a 17" LCD at home) and focused the lens in front of the LCD in one hand and then in the other held up a piece of paper. I moved both hands until I could clearly see the screen on the sheet of paper. The corners were pretty clear and I could make their edges out fairly well. What I am wondering is would this experiment be accurate enough to determine whether or not the lens will work with a 17" LCD?

I will probably go ahead try the "FOV Test" anyway, but I just wanted to see if the above is OK too. Well either way please let me know and again thanks to everyone for all the help so far.

Edit: Sorry, but another quick question: I read in a few topics that the frensels needs to be equal to or less then the triplet. Is this true. If so I know 3DLens.com carries 220mms frensels that should work with a 17" and if not then I can always by the "Pro Frensels" from LL.

Darin

Actually, it's the opposite. The focal length of the front fresnel (or one closest to the triplet) should be equal to or longer than the FL of the triplet. The rear fresnel is typically shorter, though it can be equal to the front fresnel.

Sorry, I'm not the right guy to answer your FOV question with any degree of accuracy.

I'm just getting my feet wet & actually looking to go as cheap as possible just to make sure this is something I want to do.

I am looking to use an old 47" RPTV screen & cabinet so I want a shorter throw.
This Lens will give me a 3.5ft unsplit throw & a 3 1/4 ft split throw.
I plan on using a 15" sceen & putting the TV in the corner of my soon to be rec-room so if it sticks out the back it won't be a deal breaker.

I also found a triplet with an 82 mm focal point & that will according to the calculator about 1 ft 2 inches & that just sounds to me like it just wouldn't work though.