Does anyone have expierence with this (or a similar) SurplusShed Lens?
http://www.surplusshed.com/pages/item/l3926.html

From what I understand it is a doublet, and therefore might have lower image quality than the Pro lens triplet that LL sells.
Are there any other disadvantages to using this lens?

I am planning on building my first projector based on the X2Gen MW15a 15.4" (1280x800) monitor.

The 600mm lens would be a big advantage to me because it would allow me to move the projector far enough back to properly do keystone correction via the front fresnel. This lens is also less than half the cost of the Pro Lens (and is in stock). By the way I am planning on using either the 650mm Pro Fresnel, or the 550mm 3dLens fresnel. Any recommendation on which one would work better with the 600mm FL?

Telescope lenses often do not have an appropriate FOV, since they're generally optimised for a small visual field.

For the fresnels, it's best if the FL of the collector fresnel is somewhat greater than the FL of the objective lens. For that reason, the 650mm pro fresnels would be a better bet. The reason that you want the collector fresnel to be of greater FL is because the objective lens MUST be further from the LCD than it's focal length in order to acheive focus.

With a doublet, you may experience some chromatic distortion in your projected image, but I really think that the biggest issue that you may experience is spherical abberation due to the lens' designed FOV. It could be that you'll get lucky and it won't be bad.

Thanks for your response.

I thought the FOV was related to the diameter of the lens? So a larger diameter lens would produce a larger field of view. If I understand you correctly, however, apparently it is more complicated than that?

It if was just based off of the diameter (and the focal length), then wouldn't this lens actually provide a better FOV, since it has a slightly larger diameter (and a longer focal length)?

Are there any good resources on FOV that you could point me too?

FOV is actually something that's part of the criteria for designing a multiple lens element. The point of the multiple lenses is to correct problems with spherical abberation and chromatic distortion inherent in any real-world lens. The stronger the lens, the greater these factors are.

Spherical distortion happens because of the curvature of the lens itself, which results in pronounced differences in the angle of incidence vs the exit angle at different meridians. This has a tendancy to "squish" the image.

Chromatic distortion happens because lenses don't affect all colours of light equally. Blue light has higer energy but is more susceptible to being bent than red light.

The multiple lens elements in a triplet (or indeed a doublet) are intended to correct for these factors, but they can only correct for them within a limited scope. Sorry, but there's no "quick guide to calculating FOV" out there -- at least none that I know of.

Thanks for the info SupraGuy.

Is it safe to assume that the 22" or 24" Beseler is a better option than the above telescope objective lens then?

I would really like something near 600mm EFL if possible, as it will be easier to keystone properly.

The Beseler are a triplet and the 18" fl can be had for about the same price as the SS lens but the longer 22" and 24" Beseler triplets are hard to find most of the time and sell for more money.

I would guess that the FOV of the SS would be wide enough for a 15.4 but there is only one way to know for sure.

The SS doublet will not be as sharp and you should be able to see a slight differences so if you want the sharpest picture go with the pro lens.

It would be nice to see how the SS lens worked. If it worked OK on the 12" or 15" LCD's it would be a nice low cost lens.