I'm running bundler on a set of photos with no focal length information. I first ran into a problem because the image resolution was too high (5312x3984 pixels) for sift to handle, so I downscaled them all to half their size. Incidentally, if someone has a link to the sift source code, please share it: I want to rebuild it with this limitation lifted, and also make a 64bit version of it.

Anyway, according to FAQ item 1, I first ran the bundler.py script with the --extract-focal parameter to obtain the list.txt file, and there I extended each line with " 0 3187". This is probably not the real focal length, just a quick estimate (I've read that a reasonable estimation for the focal length is max(width, height) * 1.2). Then I ran the bundler.py script again (with no options), so that it could compute the matches, and then I ran bundler list.txt --options_file options.txt and got this:

[OnInit] Running program bundler
Loading images from file 'list.txt'
[BundlerApp::OnInit] Processing options...
[BundlerApp::OnInit] Loading frame...
[BundlerApp::OnInit] Loading images...
[ReadGeometricConstraints] Reading 0 tracks
[ReadGeometricConstraints] Reading tracks took 0.000s
[ReadTrackPairs] Read 0 track pairs
  Avg. proj error [0 projections] = -nan
[BundleAdjust] Error: no good camera pairs found!
[BundleAdjust] Trying a backup approach...
[BundleAdjust] Error: no good camera pairs found!
[BundleAdjust] Picking first two cameras...
[BundleAdjust] Adjusting cameras 0 and 1 (score = 0.000)
[GetJPEGDimensions] File ./image20170205_134820745.jpg: ( 2656 , 1992 )
[GetJPEGDimensions] File ./image20170205_134551277.jpg: ( 2656 , 1992 )
[BaseApp::SetTracks] Setting tracks for image 0...
[BaseApp::SetTracks] Finished in 0.000s
[BaseApp::SetTracks] Setting tracks for image 1...
[BaseApp::SetTracks] Finished in 0.000s
bundler: BaseApp.h:271: std::vector<KeypointMatch>& MatchTable::GetMatchList(MatchIndex): Assertion `p.first != p.second' failed.
Aborted (core dumped)

Could it be because my focal length estimation was way off, or is there some other problem here?
Also, when downscaling the photos, should the focal length be downscaled proportionally, or should itbe left untouched?