why are most fresnel lenses i can find double sided with different focal length on both sides and would i have to pry those apart to use them with a standard monitor ?
and does anybody know where to buy one in germany ?
I use a cheapo fresnel lens with my setup and it really is a fantastic way of allowing a higher FOV setting and greater immersion.
after reading some of these links, I'm seriously thinking about getting a couple of those 'high res' F550's and using my old monitor for a dual monitor setup..
Anybody successfully had a radeon 9800pro (or any radeon, I s'pose) running LFS across 2 monitors, or is it only Nvidia cards that can be used this way?
I haven't personally done it since I use a Parhelia, but other people have said that ATI cards will work if you use the Hydravision drivers. LFS needs to see one single surface to work properly and apparently the hydravision stuff allows this.
Catalyst Control center does the job with one big surface spanned across 2 monitors, but I tried it, and it wasn't very cool without the fresnel lenses due to the turning. The perspective doesn't feel right like that. Kegetys managed to find a solution, but that was kinda slow.
There was a thread at RSC, I think, with photos showing a rig with two fresnel lenses arranged in a way so that the middle bar wasn#t visible anymore.
big fresnel lenses are sometimes sold as TV magnifiers (TV LUPE in german) for old ppl in specialized shops, prices i have seen were like 40-60 Eur depending on the size.
In that thread the guy sits quite far from the screen, like 70-80 cm.
To have a proper perception of speed in a game, the FOV of the screen in your eyes must be the same as the in-game FOV. We have the in-game FOV bigger than the angle at which we see our screens, that's the sourse of the problem.
If we calculate the real screen's FOV and set this value to the in-game FOV, it would look like a narrow window. It would look a bit like the image that we see in a window of an aircraft sitting in the middle or on the other side. I have 17" and my eyes are in 1 meter from the screen, thus I'd need to set in-game FOV to 18.18°! (=2*arctg0.16)
To have in-game FOV 90° and percept it properly, we'd need to place the monitor in 1/2 of it's width from our eyes . For example, 17" screen has 32 cm useful width => the eyes should be in 16 cm from the screen.
So, what I'd like to have, look at the picture. The same 17" screen, but with such a lens, that would make it look like 1m from the eyes (and the eyes would focus on 1m, not on terrible 16 cm), and consequently it would be like 2m screen. Real 90°FOV.
Though, with such distances the distance between the eyes affects the view.
[edit] Who is good at physics? What's the dependence between the focal length, the distance between the lens, the eye and the observed object?
They also sell different focal lenght lens for the same sizes, that maybe a consideration also.. keep us posted on what they say as I'm on the edge of ordering one myself - sounds worthwhile
According to my calculations, it's possible to get big FOVs with lens that has shoter f. In terms of FOV the big F550 (400 mm) can give only 50-55 FOV comfortable for eyes (about 500 mm distance between the eyes and the virtual picture), while 310x310 lens with f220 can make up to 90° (about 600 mm between the eyes and the virtual picture).The only question is if the distance between the eyes affects the image, because in this case you need to look from only 155 mm. I've asked them about this too.
This is the result. The is just a sales manager who knows absolutely nothing in optics and doesn't even read my message carefully. It was the second reply, in the first he said "i don't know how to use it with a sim", in the second question to him I wrote "gust tell me what angular size can i obtain". I think he saw the word "angular" for the first time in his life.
Okay, I've managed to figure out everything by myself. Just googled to restore my school knowledge of optics, refigured the formulas and the geometrical method.
I'll write the results later. [edit: nope, the short f isn't good.]
P.S.: "magnifying factor for simulation purpose"... I didn't expect it to be of different kinds. You learn somehing new every day.
It's simple, short F means MORE magnification, long F means LESS magnification. infinite F means plain transparent glass.
So you can increase the effect by having shorter F (can use bigger FOV etc), while paying with more distortions probably due to practical reasons (imperfections of the lense, distance between the eyes is not zero, for most ppl etc)
as the detailed article says, he found that focal length of 11" = ~ 26cm is the best compromise for him.
Eh, eh, the F550 is not the best one. You don't need a very large screen, neither a very long f. As Avih has written, it is closer to a simple glass. I took more time to consider what I select.
As I've calculated, with f550 you can get about 50° FOV. I think, 80° is obtainable with lens with shorter f. It works fine for just enlarging your screen, but to get an effect described by the aviasimmer, you need different lens.
I did some more calcs, and see that the main thing to consider is the relationship of the f and the width of your screen (if it is only one, with 2 screens no problem to make 90° real FOV). To get 90°, actually you need f to be 1/2 of your screen width or shorter.
thisnameistaken: I think, it's better to analyse the options with geometry, not notionally. I'll make schemes in an hour.
I haven't looked through one of those for ages too (since a friend of mine had one which he put infront of the TV where a spectrum was connected ). I wasn't too impressed back then btw, but it might be due to so many factors.
So, I don't have any practical experience, which I think is what counts most.
Theoreticaly speaking though, I'd say that the distance of the lense from the subject (i.e. screen) changes the angular size of the image, which in practice allows us to see more details (bigger image), while the distance of the lense from the eye doesn't change the angular size but does changed the preceived distance of the image. This is just intuition though, and regarding a magnifying glass, without trying to calculate it theoretically as others have done here before.
A fresnel lense might be a bit different from "normal" magnifying glass though since it has one flat side and one curved side, while magnifying glass has 2 curved sides. They might have exactly the same effect though, up to the focal length as a function of the curvness of the lense. Again, I didn't try any calculations.
But again, I do think that practical experience is very important here beyond the theoretical aspect. Eventhough it CAN be calculated, I'm sure that there are practical aspects that aren't calculated usually in ideal cases, such as the fact that the eyes have some distance between them, some common distortions of such lenses (maybe towards the outer sides), etc.
So I'd love to hear some comments when you get and play with it a bit
edit- on that MSFS page someone wrote him that he uses the F55 and he's pretty satisfied with it. I'd say it should be a good buy to start experimenting.
Here are my calculations. The original values are for the lens given in the Rick Lee's article. Measurement unit is mm. I think it's not a problem to input the 2 F550 dimensions - size and focal length.
According to my calculations, 220 mm focal distance is the best for this purpose for 19", 17" and smaller monitors.
Check, if they are right. (note: I had to re-learn this stiff 6 years after I learned it a little bit at school, that time I prefered the geometrical method )
If the main purpose is FOV (with some restrictions), you may even play with MS Excel solver to optimise it.
[edit: here is the geometry. The advantage of the small focal length is larger FOV. Though, hasn't a single meaning and there are other discussable aspects. For example, a disadvantage of a very short focal length is that you have either little depth or big magnification. The best solution is a larger screen. ]
[edit2] So, I think I'm going to order 2x#401B and 2x#A310b. If I don't need some, I'll tell other simmers how cool they are and resell, or will make birthday presents to some friends.
[edit 3] Okay, the very last detail to these things. Actually, there are few things that differ. Without taking the size into consideration, there is only a trade-off between the depth and the FOV. Focal length is a decisive parameter here, the longer f.l. is the more depth and the less FOV is. Wider screen allows improving of both values.
Because doing that would cause the universe to implode.
(it's because, that equation is essentially: 1 / (1/a - 1/b) ... so if "a" and "b" are equal, you end up trying to solve 1 / 0, which is undefined, hence the implosion of the universe)
illepall
