Since Fallout 3 doesn't take as kindly to monitor rotation as Oblivion did, making big images like that isn't easy. It requires a bit of Photoshopping (or GIMPing) and GECKery to do.
It's something I picked up from a screenshooter on FO3Nexus; he called it "Megastitching".
Here's the process I devised:
First off, you need to gain control of the Eye Adapt Speed in the weathers' imagespace modifier through GECK (FO3Edit can't do it last I checked, IMODs are too complex and are just listed as hex data). For instance, I have the default weather systems, but I have my own personal tweek to it (basically, all weather/IMOD entry overrides, nothing new).
You need to find out what weather system and time of day (sunrise, sunset, night, day) you are currently subject to in-game, and then locate that in the Fallout3.esm or any subordinate module you have loaded. You then need to isolate what Imagespace Modifier is associated with the weather/ToD you are currently under. Once in there, change the Eye Adapt Speed to 1 in the Additive field. This sets it so the simulation of brightness adaptation of the eye in the HDR system is static and doesn't work (unless via console... I'll get to that). It's probably most prudent and safest to just simply set ALL imagespace mods in that weather system to have eye adapt of 1, as transitional interpolation between two imagespace mods with different times of day may screw it up. You may use FO3Edit to ESMify ESPs so you don't have to directly alter any of your weather mods' modules.
If you fail to control the eye adapt speed, you will notice a distinct difference in brightness of the screens.
Next, fire up the game and find a place you want to screenshoot at. Set up your face/body pose. I recommend Groovatron (which is what I used in "This Rose Has Thorns"). Using the distance blur also helps.
If you don't like the HDR level, there is a way to control it via the console, through a command ClearAdaptiveLighting (or "cal" for console shorthand). Look at the ground and enter the command to make the HDR brightest, look into the sun and CAL it to make it dimmest.
Next up is camera setup. To mimimize perspective effects from borking up alignment, you'll basically be taking the image via a narrow-angle lens. TFC 1 out of your char once your pose is set up, and back away. Set the FOV to 15 degrees (console command "FOV 15"). Re-set up your camera positioning to account for the change in FOV.
Now comes the reeeeally tricky part, as it requires a very steady mouse hand.
First off, this may seem counter-intuitive, but make sure your mouse's in-game setting isn't at minimum sensitivity. It may seem that you want to, but higher sensitivity levels actually make the view move in visibly discrete units of angle, making it easier to detect when you've veered off. If you're lucky to have a Logitech MX-518 or other mouse where you can adjust on-mouse sensitivities on the fly, put it at minimum, as that'll make it easier to control.
Now comes the actual screenshooting. Leave the HUD on, as the crosshair will help with alignment. Aim at your char's face and pick out some facial detail and focus on it as a positional reference (for my above screenie, I used two eyelashes on the right eye). As soon as you have it perfect, KEEP YOUR HAND ON THE MOUSE and keep it absolutely still. With your other hand, open the console, and enter the command "TM", or ToggleMenus, which will hide the HUD. Before exiting the console, take your hand off the mouse. As you're still in Console mode, moving the mouse at all won't bork up your camera position.
Once out of console, take your screenshot.
Re-enable the console, and TM again to get the crosshair back. And again, before exiting the console, put your hand back on the mouse.
Now for the truly tricky part (honest this time!):
Move your mouse downward slowly, observing for ANY horizontal movement. If you notice any, re-align. Go all the way back up to your positional reference if you must. Make sure you have a bit of the view from the previous screenshot overlapping. TM the HUD out of the way as described above, and take your second screenshot, and then re-enable the HUD. Make sure you're changing your handle on the mouse while in console.
Repeat again until you have all the screenshots you want in your view.
Exit the game, and let your mouse hand rest for a bit, as it's likely on the verge of cramping.
Open up Photoshop, or equivalent and open up your first screenshot. Copy it, and paste it into a new document, with a larger height than your screen res; to be safe, multiply your vertical res by how many screenshots you took. Paste all the others in too, on different layers. Line them all up as best you can in the overlap regions.
You will inevitably have some misalignment Add layer masks to the layers in question and blot them out with a minimal hardness brush in the mask.
Merge the layers all together, crop out the empty space at the bottom (or top), or just copy-paste the merged layer into a new doc, save, and presto, you have a supersized image.
» Tue Dec 14, 2010 8:08 am 
