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View Full Version : Fresnel Lens users...a few questions



Numanoid101
11-06-2006, 01:08 PM
Hi all, after a lot of reading here and elsewhere I have ordered a fresnel lens from 3dlens.com (the f550) and have a question.

Based on my reading it looks like the best clarity occurs at the focal length of the lens (21 inches for the 550) and the best tradeoff for depth/clarity is about 30% less than the focal point...15-16 inches. I'm seeing most users are putting them 7-10 inches from their monitor which is much less than the recommended distance. The question is why? The followup question is have any of you tried placing it out more to about 15 inches? Any difference?

I've got a 19" flat panel and 15 inches should be OK, but I'm wondering if anyone has tried it.

Thanks!

Numanoid101
11-06-2006, 01:08 PM
Hi all, after a lot of reading here and elsewhere I have ordered a fresnel lens from 3dlens.com (the f550) and have a question.

Based on my reading it looks like the best clarity occurs at the focal length of the lens (21 inches for the 550) and the best tradeoff for depth/clarity is about 30% less than the focal point...15-16 inches. I'm seeing most users are putting them 7-10 inches from their monitor which is much less than the recommended distance. The question is why? The followup question is have any of you tried placing it out more to about 15 inches? Any difference?

I've got a 19" flat panel and 15 inches should be OK, but I'm wondering if anyone has tried it.

Thanks!

Lurch1962
11-22-2006, 05:08 PM
Numanoid,

I use a smaller fresnel of size 7X10 inches and focal length 12 inches. It's flexible and can be bent quite sharply. I've found that its off-axis performance improved rather markedly when I bent it in the horizontal axis so that the radius of curvature was equal to the focal length, i.e., 12 inches. Note, the smooth side faces you and the grooved side faces the monitor. And the optimum distance for comfortable viewing proved to be a spacing of 8-9 inches between the screen (a flat 19-inch CRT) and the closest part of the curved fresnel.

As you can imagine, the 7X10 inch size means that one's eyes must be pretty close to the fresnel in order to see the full screen, but man, is it impressive. It's like watching an IMAX film.

Most folks set their monitors at a distance so that the screen subtends an apparent angle of about 30 degrees horizontally. With my fresnel setup the apparent field of view is now about 100 degrees (!), which means that my retinas are filled by approximately 10 times more area.

The IL2 series offers a 90 degree field of view as the widest. This is very close to the 100 degrees I see, and therefore there is basically a 1-to-1 size correspondence between the simulated world and how it would really appear.

Another advantage of a short focal length fresnel: it at least partially corrects for the inherent distortion in wide fields of view. In any flight sim I've ever flown, the world view is always rendered using a gnomonic projection, which at large angles causes noticeable radial stretching. In such a view, the ideal view point is from a distance such that the percieved angle of the view equals the rendered angle (assuming the screen is truly flat.) So for example, at a 90 degree FOV and a screen horizontal width of 18 inches, your eyes should be only 9 inches from the screen in order to see the view as undistorted.

I run at 1600X1200, which allows a not-too-pixellated view even with the rather great effective magnification of my CRT screen. Moreover, the imperfect resolution of a fresnel actually smoothes the view a bit, too. But with moving imagery absolute sharpness can be sacrificed to some extent anyway.

I must say that the impact of such a large view size is astounding. Flying at low level over a large city while in the cockpit-off Wonder Woman view is a stomach-churning thrill ride!

TSmoke
11-23-2006, 08:00 PM
This has fascinated me for some time.

For anyone who uses a fresnel lens would it be possible to see a before and after picture of what you are seeing on your screen?

I just may accidentally break the overhead projector at work and scam its lens LOL.

cmirko
11-24-2006, 12:37 AM
well im a new user for fresnel lense http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif also F550

and i must say its a gret thing, it does get some time to set it up in the first place, and some more time to get used to "washed" out look (colours are not that bright anymore) but the magnification effect is niceeeeee (22" compaq looks like 34" at least in various head/lens positions) and the "3d" effect is a great thing - low level flying has never been more fun http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif


also, for track-ir users there is a "mode" in which you can put the lens real far from the screen and put your face about 15-20 cm from lens - that way you only see the screen and nothing else http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif and not even the whole screen http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif but it feels like being totally in the game - because you have to really turn your head to see things and you cant see any surroundings of your computer room/desk http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif wow ! have to experiment a bit more http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif but it's a keeper http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif


@tsmoke - cameras don't do it justice http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif, its too perfect so you see a lot of things human eye doesn't, subjectively - fresnel (at least for me) lens givesa 10% washing of all colours (easily fixable if that is the "problem") and magnification is a thing which every user has to balance with image clarity - in my experiments i can read whole instrument table with max zoom out view now just at a glance http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

this is just magnification effect - its not possible to photograph 3d effect of lens http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif
http://forum.racesimcentral.com/attachment.php?attachme...=395491&d=1160531453 (http://forum.racesimcentral.com/attachment.php?attachmentid=395491&d=1160531453)
http://forum.racesimcentral.com/attachment.php?attachme...=395490&d=1160531453 (http://forum.racesimcentral.com/attachment.php?attachmentid=395490&d=1160531453)

Doug97
11-24-2006, 01:00 PM
Wow, are you using the Triplehead2Go as well?

cmirko
11-27-2006, 12:14 AM
oh m8 http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif i wish i was http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif those are not my cockpit pics alas http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

cmirko
11-29-2006, 03:04 AM
these are the pics of my home made - "quickfold" (tm) http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif pit

http://s44.photobucket.com/albums/f19/cmirko/?action=vi...rrent=Picture043.jpg (http://s44.photobucket.com/albums/f19/cmirko/?action=view&current=Picture043.jpg)
http://s44.photobucket.com/albums/f19/cmirko/?action=vi...ent=Picture039-1.jpg (http://s44.photobucket.com/albums/f19/cmirko/?action=view&current=Picture039-1.jpg)

and also some fresnel lens pics

http://s44.photobucket.com/albums/f19/cmirko/?action=view&current=IMG_0875.jpg
http://s44.photobucket.com/albums/f19/cmirko/?action=view&current=IMG_0874.jpg

magnification effect - same distance eyes to monitor -

http://s44.photobucket.com/albums/f19/cmirko/?action=view&current=IMG_0885.jpg
http://s44.photobucket.com/albums/f19/cmirko/?action=view&current=IMG_0886.jpg

the lens - monitor distance is 10.5", this gives (for me) best 3d depth/magnification/clarity of viewed image and my eyes to lens is something like 15" (didn't measure), but if i want to feel totally in the game i can put my head "into" the game by closing eye-lens distance to 5-6" and do not see the outer world at all (that is possible because lens is focusing image into infinity so you always see it "far" away - that is the 3d part which is hard to explain and impossible to photograph http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif)