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Setting up the zoom correctly in FSIM

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Joined: 03 Feb 2016
Posts: 106
Location: Buckinghamshire, UK

PostPosted: Mon Aug 28, 2017 3:18 pm    Post subject: Setting up the zoom correctly in FSIM Reply with quote

Hi, I thought I would share this with the forum, credit goes to almost aviation on youtube, I am just sharing my experience to make life easier. Flying with a higher zoom takes a little getting used to at first but there is no going back for me now.

original work here on this channel https://www.youtube.com/watch?v=ikwToOzX_UA&t=300s

I am a PPL pilot and have quite a few hours on the BA 777 simulators when they were at Cranebank some years back. The perspective of my sim view compared to RW and sim experience always bothered me but I didnt really know how to properly solve this, I knew that simobjects sometimes looked too small and that the perspective didnt feel right, but I am not one for guessing what looks right, it has to be correct!

I have a Jetmax 777 setup, I use 3 42" 1080p HD TVs for my outside view which runs on a seperate PC with a GTX1080TI powering the graphics. Using NVsurround I have always been bothered by the perspective distortion the default zoom level produces on the left and right displays when trying to project the FOV accross 3 flat screens arranged around my Jetmax. This equation does not fix the fisheye but it does reduce it because you will be correcting the "simulator window or the letterbox that we view the fsim world through" by setting up a proper ratio zoom level so that your monitor displays accurate sized/scaled scenery for your display.

assumption = WideViewAspect=TRUE is enabled

My screen is 52cm high and my seated position when adjusted positions my head (or my camera!) 130cm away from the middle screen. For my outside window (my TVs) to render scaled accurate simobjects at a sim vertical FOV of 34degrees, my viewing position needs to be postioned exactly at the correct distance from the screen which is 77cm, but I sit further back than this and cannot get any closer neither do i want to!

use this calculator to figure out the optimum distance https://www.pagetutor.com/trigcalc/trig.html

Enter A as 1/2 your screen height and X as 17 (half of the full 34degrees vertical sim distance). The optimum distance your head should be positioned at is the answer for side B, thanks trigonometry!

ball park formula to calculate correct viewing distance for default zoom 1.0 is roughly full screen height in my case 52cm divide by 0.67 = approx 77cm (0.67 is the rounded TAN of 17)

My actual viewing distance is 130cm from the screen giving me a physical FOV (what my HDTVs provide) of about 22 degrees, this means at zoom 1.0 I am seeing a 52cm viewing window (my TVs) displaying a sim view of 34 degrees, fsim is rendering too much of the world within this narrower view, so out of scale than my actual viewing angle should allow. So I am zoomed out too much, I am seeing too much of the world because I am sat too far back to preserve the default desktop trigonometry. This is confirmed by the left and right views which are displaying objects which are really almost 90degrees to my left/right in the sim but physically at around 60degrees on my monitors.

How to calculate your zoom based on your actual head position.

Screen height is 52cm actual (not including bezels)

I am sat (my eyepoint) 130cm from the screen? I need to zoom in to preserve the scaling within fsim so my viewing window displays the right amount of fsim world in proportion to my screen and viewing distance , but how much is mathematically correct?

The field of view is inversely proportional to the zoom factor, ie as the physical FOV decreases the zoom level increases and vice versa

to calculate the zoom (Z), you use (h=screen height, d is distance from your screen)

Z= 34/ 2 arctan (h/2d)

this breaks down in my case to;

Z= 34/ 2 arctan (52/2x130)

34/ 2 arctan (52/260) 52/260= 0.2

34/ 2 arctan (0.2)

arctan of 0.2 = 11.31

2 x 11.31 = 22.62

34/22.62= 1.50 zoom level required for my viewing distance of 130cm to render objects in scale.

example 2, to calculate a zoom level if you sit 85cm away from a 70 cm screen

1) divide your sceen height by your actual viewing distance x 2 eg 70/170 = 0.411

2) find the arctan of 0.411 which is 22.380

3) multiply by 2 which gives 44.760

4) divide 34 by 44.760 gives a zoom level of 0.75

you need to zoom out becasue you are not seeing enough of the fsim world through your displays, on this occasion so the preference would be to move your viewing position back to match the zoom level 1

To set the default zoom level, you can navigate to the camera.cfg located in the sims app data folder (same place as the fsx/p3d.cfg) and alter the default zoom to match your calculated zoom for each camera you use.

I find that the higher zoom means I have lost some of the view in front of the aircraft, therefore I have compensated by pitching the camera down a little by adjusting the pbh value in the camera.cfg also

InitialPbh XYZ-90 to 90.0 (pitch)-180 to 180.0 (bank and heading)
Defaults: 0.0 Camera pitch, bank and heading orientation offset from the default in degrees. Note that positive pitches give a downward view. Positive headings are to the right.

Now for the final spanner! I actually dont like zoom 1.50! so I am using 1.30 which looks better because the depth of field is lost the more you zoom in so a compromise was needed!

Hope this helps, have fun

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Joined: 06 Jan 2015
Posts: 472
Location: Sydney - Australia

PostPosted: Mon Aug 28, 2017 5:26 pm    Post subject: Reply with quote

Thanks Keith

Very informative.

JetMax 737, SA 737 v1.7
P3D 4.1 FSUIPC 5.122
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Joined: 06 Jan 2015
Posts: 472
Location: Sydney - Australia

PostPosted: Sun Oct 29, 2017 3:55 pm    Post subject: Reply with quote

Hello Keith

How is the Zoom Factor going?
I have been playing around with the display setup my self.
Recently I have updated to 55" screens (from 42")
I have two screens on a SSTD JatMax one is to the left hand side and the other out in front so the forward motion line is somewhere near the middle of the front (RHS) screen. This situation brings up a whole new set of problems which most are solvable but the BIGGEST problem is that when you ZOOM or look away from the Default Front Centre you get DISTORTION
and that problem I'm not able to solve.


JetMax 737, SA 737 v1.7
P3D 4.1 FSUIPC 5.122
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