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The reticle diameter in the Spit is measured in mils, 150 I believe. In the Tempest it is 100.
Edit... Sorry Lurch. I didn't see your post. I was not sure if the Spit's reticle size was 150 mils or not. I do know that the Tempest has a smaller reticle size than the Spit...that IS historic. Intel QX6700 Quad Core @3.22 EVGA nForce 680i SLI MoBo / 2 Gigs RAM 2x 8800 GTX SLI / SB X-Fi CH Controls with Franken Potato |
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Yah he's measuring the ring against the reflector glass and ruler. The ring stays constant in his eye while the glass and ruler appear smaller, it is a perspective difference. I know how many degrees the ring is when I know range and wingspan to fill the ring. It's twice the arc-tangent of half the wingspan divided by the range, at over 50 yards it's well within a degree accurate. There's no reason to measure your screen or pixels as 3D renders like sims don't measuer by the pixel, which has been pointed out here years ago. Let the GAME and 3D engine provide the scales. It's easier and more direct. "My views are solely my own and do not reflect the views of my Squad or its members" |
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I have not added to this thread for a while, but I have done a little more research on the subject...
I have taken a series of screen shots of a P-40M through the gun sight of a KI-84...Interestingly enough the P-40M does seem to fill the larger ring of the gun sight at 100m and the smaller ring at 200m. The wingspan of the P-40M is 11.35 meters...The Mustang P-51D comes in close at 11.28...Allowing for the games display variable of 3.28 feet (1 meter) this (should) place the P-51, F4F, and Spitfire within the same rings at 100/200 meters...I have to test this theory with screen shots when I have the time, but if it is true then it would mean that the "gun sights" built to this scale can be used for judging a fighters distance (fighters with a wingspan of 11 to 12 meters). I will explain everything in detail if my theory "pans-out"...   This message has been edited. Last edited by: zardozid, I'm just a Rock 'n' Roll footnote... |
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One thing the game does not represent correctly for most gun sights is the diameter of the collimating lens as compared to the projected reticle size. Given that the collimator is close to the reflector plate, differences in distance along the optical axis are small enough to largely ignore.
In brief, the maximum dimension of the reticle pattern (that includes any line segments extending beyond the outer circles) can be no larger than the diameter of the collimator. Take the Ki-84 image in the previous post. A careful comparison will reveal that the reticle diameter is a bit larger than the graphical representation of the bulging collimating lens immediately below the reflector plate. And in-game, as the pilot's head "shakes", the reticle can wander some distance across the reflector and still be seen in its entirety, implying an even larger "window" of visibility. For some other gun sights this is even more obvious. But this cannot be. The viewing geometry dictates that the clear aperture of the collimating lens imposes a limit on the maximum angular extent of a projected image. Let's imagine the following... If the apparent angular diameter of the collimator is 5.7 degrees as seen from a particular viewing position, then a 100 mil (5.7 degree diameter) reticle will *just barely* fit into the view. The slightest offset from the optical axis will cause part of the reticle to become invisible. In order to see the full reticle even while the eye's position wanders due to head shake, the pilot must move closer to the sight. Let's say he moves in to half the former distance; the collimator will now appear to be about 11.4 degrees in diameter (twice the former 5.7 degrees), which will very comfortably fit the reticle (still 5.7 degrees across) and allow some offset of the eye in the L/R and up/down plane. Of course, all this is really trivial, because the graphical discrepancy has no impact on the otherwise realistic behavior of the reticle. I only point it out so that one can further understand a gun sight's workings. |
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 That's also why K-14 gunsight is wrongly modelled. It actually has two collimators, side by side under a common reflecting glass, one for air to air and one for air to ground fire. Pilot should only be able to see the air to air reticle above half of the reflecting glass and should shift his head a little bit to the side in order to do that, like in german planes with shift-F1. "In short, the Spitfire MkIX was the best fighting machine of its day. Its great tactical advantage was that, apart from its longer nose and more numerous exhaust stacks, it looked exactly like the inferior Spitfire MkV, and in the air the Germans would not know the difference - until we hit them." ~ Wg Cdr J E 'Johnnie' Johnson |
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Sorry if it's OT
I notice the plane icon only shows color and range, where is the setting for that? in dif. setting only on/off plane icon. is it conf.ini? thanks. |
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I'm not at home right now so I can't refer to the game for the exact name of the setting, but once you open the "hardware/input" option panel in "IL2 1946" their is an function that you can assign a joystick button (or keyboard button) to, its called "toggle icon type" (or something like that)...once you assign a button to this function you can cycle through a few different icon types while playing the game...I think it goes 1) color and distance, 2) color, distance and type, 3) color, distance, type and call sign, (ect)...the last option is icons off. I hope this helps... I'm just a Rock 'n' Roll footnote... |
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 It works...thanks. |
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thx for confirming that this is correct in real life, but the part i dont understand is, there is another way you can look at this same example of our pilot looking at the distant enemy aircraft in his gunsight, ... a) - if i sit on a chair and look through a glass window at a me109 aircraft 200 meters away parked on the tarmac (ie like is the case if i am seated in my aircraft cockpit), and i then lean forward or backwards, varying my distance from the glass by about 50 cm, then then the 109 i look at does not look larger/smaller. in other words that 109 still occupies the same degrees of my eyesight (ie mill's). but if it is normal for this reflector gunsight reticle that is projected onto my gunsight viewing glass to change in size while i lean forward/backwards by about 50 cm, then the size ratio between the luminated circle of the reflector gunsight and the viewed distant object (our 109) does appear to change. b) - and that is exactly what happens when in il2 you use the pilot lean-forwards/backward function, when leaning forward the gunsight itself is larger (we are now closer to it and it occupies a larger part of our FoV), but if you measure the luminated gunsight reticle on your monitor it has stayed exactly the same ! so when our experimenter placed his ruler onto his gunsight glass and observer if that luminated circle changed size when he leaned forward/backwards it really should have stayed the same (since his measurement of that distant 109 would have stayed the same to) if you add A and B above together, then you could look at the luminated reticle representing a fixed value of degrees, and it being the equivalent of looking through an infinitely long hollow tube at a distant object, and if the viewer moves forwards/backwards by a few meters closer to that distant object, then the diameter of the "viewing tube" remains the exact same. thats essentially where my confusion lies, because the 2 views of looking at this produce totally different results, hope you can "shed some light" on where i am going wrong 
i suspect you are talking about the illustration of the optical path lines that are traced between the viewers eye and the angled glass plate being incorrect ? at least thats what i was wondering about, and with the A and B examples i gave above, would those lines have to be illustrated as being parallel instead ? ie, that the distant 109 is seen as an object of a certain number of degrees (mill's) from our own aircrafts viewing point (ie the optical lines diverge), but that for the pilot inside our own aircraft the small movement of 50 cm forwards/backwards it would seem that those "optical path ray's being traced" should in fact be running in parallel (instead of diverging/converging) (minor edit for spelling correction) This message has been edited. Last edited by: grifter2u, |
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zardozid,
you might find this webpage interesting, it is about all the different gunsights used in different aircraft in WB's http://www.errthum.com/troy/warbirds/gunsites/history.html the ones in il2 will be slightly different, but it gives you at least a basic reference to go by to compare what we have in il2. |
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Wow! I remember this site...I have not visited this web site in a few years, and I'm kind of surprised it's still around. I used to play "WarBirds" all the time (back in the good old days), did you ever fly the "friendly sky's"? Their was a short period of time when I didn't have a computer strong enough to run IL2 (when was that? 2002-3?) and then I still played it for some time as I could shoot things down, and sucked at IL2 _LOL... I'm just a Rock 'n' Roll footnote... |
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Grifter,
Sorry for the brevity, but I'm about to take off for dinner with friends, so I'll get back probably tomorrow with more. But in the meantime, you seem to have fully grasped the picture. Indeed, the reticle is simply a virtual image projected effectively infinity. Even 50m might as well be infinity, considering the small off-axis eye placement allowed before the reticle becomes invisible (insufficient parallax to discern reticle pattern shift with respect to a *very* distant backdrop.) |
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An optometrist will tell you 20 feet to infinity.
"My views are solely my own and do not reflect the views of my Squad or its members" |
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Grifter,
The best thing you can do now is make your own functioning gun sight. Yes, it's simple and easy! Here's what you need: 1) Any simple magnifier, at least 2 inches in diameter. This is the collimator. 2) a piece of window glass from, say, a 4X6 picture frame. This is the reflector plate. 3) A flashlight, preferably one with a parabolic reflector. The "old fashioned" kind with halogen or other tungsten filament bulb might be best. 4) A reticle pattern you will make from card stock or thin plastic sheet. (You will not need the small folding mirror as shown in the diagram above. That's the one angled at 45 degrees and which redirects the light after passing through the reticle, before reaching the collimator. Your sight will have the flashlight directing the light straight up, not horizontally. Simpler, and works in exactly the same way.) #1 to #3 are off-the-shelf items. Your reticle can very simple, and must use an opaque material which will block all light except that passing through the reticle cut-outs. I recommend a small hole no more than 1-2mm in diameter, and 4 straight lines in a cross pattern, with the hole in the center. Try to make the lines as narrow as posible. Leave a space of a few millimeters between the hole and the inner end of each line. The full pattern size could be 1-2 inches across, but this will depend on the size/focal length of the magnifier. Or you could go with convenience and make it the same size as the flashlight opening at the front.) Use the gun sight diagram as your guide, with the main difference being that your light will shine upward toward the collimator. The critical part is the spacing between the reticle and collimator. In order that the emergent image be collimated, the reticle must lie at the focal position of the lens. This is easy to determine... To find the focal length of a lens, measure the distance between the lens edge and the image brought to sharpest focus. The sun is good for this, as it's bright and small enough to act as a point source. But don't burn your "screen"! You could refine the collimator-to-reticle spacing after assembly in this way... Place a piece of white paper on the reticle, and point the lens toward a distant streetlight at night. Adjust until sharpest focus is achieved, then remove the paper. It's best to make the flashlight/collimator assembly first, then attach the reflector plate afterward. You will likely find that you don't get even illumination across the reticle pattern. That's most likely because the flashlight's parabolic reflector is not optimized for this kind of application. But real WW2 sights often suffered from this to a certain extent, mainly because of filament/lamp misalignment. Finally, you may observe that when you move your eye's sight line so that you're seeing the reticle through the lens edge, the pattern will be somewhat distorted and perhaps move with respect to the target. This is an unfortunate "defect" of simple lenses. To avoid this, aspheric lenses of a particular shape are used in real sights. But all of this notwithstanding, from the simplest and ready to hand materials you can fashion a real, functioning optical sight that will teach you much. |
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hiya lurch,
i have recently been looking at prices for ww2 gunsights online, one day i might buy one. i dont think building one wouldnt give me the answer i am looking for, because it requires the reticle to be of the correct authentic mill size exactly like the original gunsight had. if we know from our previous discussion that the luminated reticle of the gunsight does not change size when the pilot leans forward/backward, then how large exactly is this gunsight reticle on a 100 mill gunsight in a real cockpit ? can you give me a formula to calculate this ? whatever gunsight a pilot was using in one of these fighters (like a 109, spitfire, hurricane etc), the gunsight was within an arms reach of him (between 60 and 100 cm roughly)so in a real aircraft he could have placed a ruler against the glass of his gunsight and directly measured it from where he is sitting. the method to measure this is what i am after. the formula needs to be one that applies to the real world (not our pc monitor or in-game screen in il2). i would presume that since we know the mill size (being 100 or 110 mill for ex), and we know the 100 or 60 cm distance the pilot sits from his gunsight, then this should be enough data to work from and come up with a direct physical measurement of what size this luminated reticle would be (since it is circular, i presume it will be a radius numerical value). i am aware this luminated reticle is projected into infinity, but to the pilot's viewpoint it is project onto (or through) the glass plate of his gunsight, so in real life he could measure it directly by simply stretching his arm out and placing a ruler on the glass. |
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Grifter,
My "recipe" for making a gun sight was simplified, but was still quite valid for understanding the principles of parallax reduction via collimation. So the crude reticle pattern was suggested so as to get you started with minimum fuss. The reticle's physical size has nothing whatsoever to do with the pilot's viewing distance from the sight. It depends *only* on the collimating lens's focal length (for a given mil size.) Here's the formula, for a 100 mil reticle: 100 mil diameter = lens focal length / 10 Mils are milliradians, or thousandths of radians. 100 milliradians = 1/10 radian, which is 5.73 degrees. So if your lens focal length is 145mm, a 100 mil reticle circle should be 1/10 this, or 14.5mm in diameter. |
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thanks lurch, that means we need to know the specific focal length for a real historical gunsight, like for ex the Reflector MkII which was used in the early hurricanes and spitfires, or a revi sight used in an me109. i have done some googling in the last few hrs to see if i can locate this info, no luck so far (i presume the 145 mm you stated was an hypothetical example). i did however find from another post in this forum that ..."Collimating lens - placed at a distance from the reticle equal to the lens's focal length, so as to collimate, or make parallel, the light emerging through it. This makes the reticle pattern appear to be at infinity." i think this means we could simply measure the exact dimensions of one of these historical gunsights, and deduce the focal length of the lens. other than taking one of these units apart and trying to figure out the focal length of the lens it is using, that might possibly be an alternative method if what that poster said is correct. i presume that the distance measurement on the gunsight is done from the center point of the glass lens thickness rather then its surface (by the looks of it those lenses are about 1 to 2 cm thick so the measuring point matters), and then measuring the distance from that point to the reticle. lurch, how come the formula doesnt include a viewer distance variable, ie the default distance the measurer should look at the luminated reticle when measuring it. i would have presumed that would have been from 1m distance (even if we know the optical lines are parallel, and not diverging or converging) |
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i never tried warbirds, but i kept a copy of that webpage because it gave a good list of all the various types in different historical planes. i started with il2 when the demo was originally released, and was hooked. prior to that it was earlier versions of ms flightsim, some EAW and falcon4. |
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Grifter,
The quoted definition of the collimator was by myself, back in the days (2003-4?) when I used the nick "Clouds". As you suspected, the focal length of 145mm I gave was just plucked out of the blue as an example. It doesn't matter what the collimator's focal length is. You could use a small or huge lens, as long as the reticle's diameter is 1/10 the lens's focal length (for a 100 mil angular diameter.) Again, the pilot's viewing distance has absolutely no bearing on the reticle's apparent diameter in the sight. His eyeball could practically be pressed up against the reflector, or he could be sitting in the rear gunner's seat. In either case the reticle will appear to be 100 mils across. (Of course, the rear gunner's view would have only a tiny portion of the reticle visible at an one time due to the now small apparent size of the sight itself, but if it could be seen in its entirety, it would be a 100 mil reticle.) That's the beauty of collimation! ================= A surplus gun sight once sold by Edmund Scientific (and looking very much like the cross sectional diagram posted earlier) had an achromatic collimator 50mm in diameter with a focal length of 150mm, iirc, which would be a focal ratio of f/3 (150 / 50 = 3). By achromatic, I mean a cemented doublet, just like a binocular objective lens. The reticle it contained was a 1/10 radian (100 mil) circle which was broken, or segmented, with possibly a central dot, but I can't recall exactly. From the preceding paragraph, you've deduced that a binocular objective lens could serve as your collimator. Most bino objectives have focal ratios of between f/3.5 and f/4.5, with something like f/3.75 being most common. You can get really cheap surplus 80mm (3.1 inch) diameter bino objectives. Try this... http://www.surplusshed.com/pages/category/achromats_1.html ...and look through the numerous pages. ========================== Here's the real deal Navy Mark8 reticle for $5!! http://www.surplusshed.com/pages/item/m2598.html Just accurately measure the circle's diameter, and find a lens with a focal length 10 times that, and having a focal ratio no greater than about f/4. Easy peasy! So, if the reticle's circle is 12.5mm across, you need a 125mm focal length lens having a diameter *at least* 125 / 4 = 30mm. But that's a rather small effective window--50mm is certainly better, which is a f/ratio of 125 / 50 = f/2.5. If you make your own reticle based on a specific lens you obtain, the focal length of the lens is best determined as follows... Your parts list: - the lens, of course! - a mirror - white (or a light toned) piece of card or thin plastic - a flashlight - a needle - 1) Place the lens close to or against the mirror. Ideally, the lens's front surface should face the mirror. 2) With the needle, poke two very small holes through the card or plastic "screen", about 1 inch apart. 3) Place the flashlight against the "screen" so that it shines through the two holes. Tape them together. 4) Aim the flashlight/"screen" toward the lens, and adjust the spacing/position until the reflected-back image of the holes is adjacent to the holes themselves and of *exactly equal* spacing. Here you're using the lens as an autocollimator. The light is passing through the lens twice, the second time after reflecting off the mirror. When the target (the two holes) and its image are of identical size, the lens is directing truly collimated light toward the mirror, which then comes back through the lens. So the lens "sees" parallel light rays as though from an infinitely distant source, from which the focal length can then be reliably measured. The focal length is the distance from the *middle* of the lens to the projected image n the "screen". By middle, I mean *both* the center of the aperture and the midpoint between the two surfaces. Note that the midpoint between lens surfaces applies to lenses having more-or-less similar degrees of curvature on both surfaces. (Relatively small differences are OK.) But meniscus type lenses, i.e., those having one surface convex and the other concave, are more problematical. But you shouldn't have to worry about this. ==================== EDIT: Looked at the Mk8 reticle more closely. If the physical diameter is 12.5mm, a measurement on-screen from a close-up photo indicates the 100 mil circle is about 7.8mm. If so, a 78mm f.l. lens should be used. Here's a close possibility, for 12$... http://www.surplusshed.com/pages/item/pl1082.html It's a single element, and therefore is not achromatic. It will exhibit some chromatic aberration, but it may not be too bad. The lens shape should be OK for this application, it having one side flat. Another possibility. A 2-element copy-type lens which might perform better, although it's $38... http://www.surplusshed.com/pages/item/pm1101.html --Lurch-- |
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