Fantastic first pursuit camera images for a DIY hand-wave smartphone pursuit camera!
You chose the right camera estting, 4K 60fps video (at 1/60sec frame exposure) is a good setting to use for 240Hz pursuit camera via hand-wave iPhone. It produces literally 60 photograph-quality freezeframes per second -- the brute force sample rate increases your likelihood that an imperfect handwave created a near-perfect pursuit photo. (More samples compensating for lack of a camera rail).
They could be better but they are pretty decent attempts.
teo wrote: ↑18 Nov 2021, 19:58
I understand that I’m looking for full vertical alignment of the sync track. After taking a few screen grabs, I’m realizing that none of “aligned” images are aligned across the entirety of the screen.
Sometimes the tilt of the camera can cause effects that create inconsistencies on the sync track, since not all pixels refresh at the same time (on the display panel, and on the camera sensor). Getting consistency on both is sometimes challenging but what you did is good.
If you switch to a video app, it becomes easier to pre-focus (manual focus) -- iPhone apps like DSLRCamera or ProCam lets you configure manual focus and exposure-per-video-frame.
If you handwave,
- Try holding your phone in portrait mode
- Left hand holding left edge of phone
- Right hand holding right edge of phone
- Start video
- Do not move your arms or shoulders
- Spin your computer chair to follow the UFOs
- Spin back and repeat a few times, about 3 to 5 passes per video clip.
- Jog through the video with your smartphone player's slider and screenshot the clearest frame
(Better to use a player app that can save full-resolution freezeframes, or transfer the video file to the PC and frame-step through it).
Ideally, most of the time, camera lens should be same as human viewing distance (arm's length from lens to screen). However, due to smartphone limitations, and wide-angle issues, you may want to use optical zoom (if you have optical zoom), or move closer to the screen (not recommended for viewing angle sensitive screens like TN).
Some reviewers zoom on just one UFO, while others use an entire column. If you use a portrait smartphone, zoom your camera (or get closer) until top sync track is almost top edge, and bottom sync track is near bottom edge. If you use a landscape smartphone, you may want to zoom into just one row at a time (middle row is the most common). Keep sync tracks visible, they are essentially your certificate of camera tracking accuracy. I can tell you a LOT just by looking at your sync track.
Right now, you need the sync track lines to be perpendicular to the horizontal lines. You're parallelogramming a little bit with vertically straight sync track lines but tilted horizontal lines. So if you're getting best freezeframes from a tilted camera, make suer your sync track lines are perpendicular to the horizontal lines. You can rerorate the whole image in an image viewer if need be, but not essential.
Refer to this images for reference:
So in this case, if you've parallelogrammed the sync track (lines in sync track not 90-degree perpendicular to the horizontal lines), your motion blur error margin is your deviation from the perpenducular red lines. The line disjoint is at the very top/bottom of sync track, so it's harder to see than a mid-line disjoint (e.g. between 2nd and 3rd tickmarks of 4 vertical tickmarks). Your error margin (~25%-ish) is not significant in the case of 240Hz sample-and-hold but becomes a major error margin for strobed pursuit camera photography which can reduce motion blur by about 60% to 90% (depending on selected PureXP level), or up to 99% (on best custom PureXP setting).
Also, if you keep having too much error margin, try reducing camera exposure to only 2 or 3 refresh cycles. You will have gaps in your sync track, but it can then be easier for strobed pursuit camera photography from hand-wave. Multiple refresh cycles are recommended to emulate human vision integration time period for more accurate motion-blur capture. However, for strobed pursuit camera photography, this is far less critical and you can make do with just 2 refresh cycles (1/120sec exposure at 4K 60fps for 240Hz strobe, or 1/60sec exposure at 4K 60fps for 120Hz strobe). Refer to this diagram for error margin of less-than-4-refresh-cycle pursuit camera capture:
In your case, refer to "Missing Mark" for camera exposures shorter than 4 refresh cycles. Technically, the human vision integration time has been in the ballpark (order of magnitude of 1/30sec) originally designed back in the 120Hz days. But getting WYSIWYG photographs of display motion blur remains very accurate for displays at any Hz at pursuit camera capture of 4 refresh cycles (even for temporally dithered displays such as DLP).
So in the event of difficulty doing hand-wave pursuit camera, it's acceptable to shorten camera exposure down to 3 refresh cycles or sometimes even 2, at least when it comes to non-temporally-dithered displays (LCD/OLED). (More refresh cycles per pursuit camera photograph is more important when the display is doing temporals to generate color, so that film can more emulate human vision averaging behaviors).
Quick Tips
- Test out a 3rd party app that lets you control camera exposure per frame (as well as more easily do fixed-focus). Preconfig the camera and start recording before you pursuit a few times per video clip
- Try holding phone with both hands, with a fully stiff body (just spin computer chair to pursuit)
- Use optical zoom where possible instead of coming too close to monitor. You want to simulate eye-to-panel viewing distance, but you can use optical zoom to blow up the UFOs bigger into the resulting photo. However, getting closer to the screen is acceptable if no
- If difficulties persist, please post a cloud link to your video file (GDrive/Dropbox link) or upload to YouTube (so I can single-framestep via "." and "," keys). I will inspect your technique and pull out the best freezeframe, in case it's a freezeframe-selection technique issue rather than a hand-shakiness issue.
Hope this helps!
Once we've selected good pursuit camera attempts, we can crosspost them back to the main XG2431 thread (if you wish)