by MarkBour » Mon Jul 04, 2022 4:07 am
alter-ego wrote: ↑Mon Jul 04, 2022 2:08 am
johnnydeep wrote: ↑Sun Jul 03, 2022 1:52 pm
alter-ego wrote: ↑Sun Jul 03, 2022 1:13 am
I missed answering this part. As the description states, the dashed lines are extended exposure times so that the sun trails instead of just forming a dot. The intermittent dark regions within trails are clouds blocking the sun.
Thanks for this and your prior response, but I still don't get it. Were the long exposure times
necessary to take the pin hole camera shots? I'd think not since it's the bright sun being imaged and not a dim nighttime star. Why couldn't the result just be the three full analemmas shown in the middle?
→ For the sun trails (to the left and right of the full analemmas), the exposure times were somewhere between 15min and 20min long. They were that long only to create the trails, not for improving light collection.
→ I estimate individual sun exposures to be 10's of seconds. This exposure time is longer than needed to image the sun on a cloudless day but seems quick to me for solargraphy and the paper that's used. Only the sun can be recorded during a single image having these exposure times. The landscape, however, benefits from cumulative exposures over the year.
→ Not sure what you're asking. The result is what was wanted. If no sun-trails were made, the result would be just the 3 full analemmas. To capture this image, the camera shutter opened thousands of times over the year. Personally, I like the half-analemmas on each side. The composition of tilted full and half analemmas on each side of the central, due south analemma is a new and artful representation the seasonal sun.
@johnnydeep, maybe not your nemesis, I think you understand them well enough to ask intelligent questions!
So, as June 21 is the summer solstice and "peak" day, let's look at a few sample daily exposures. If by some chance I have this figured out correctly.
On June 20, like many days leading up to the solstice, you'd:
- Leave the shutter closed up until 13:15,
- except for a very brief exposure at 11:00, 12:00, and 13:00.
- Then open from 13:15-13:30, closed from 13:30-13:45,
- open from 13:45-14:00, closed from 14:00-14:15,
- open from 14:15-14:30, closed from 14:30-14:45,
- open from 14:45-15:00, closed from 15:00 for the rest of the day.
The result, for June 20 et al, you'd get 3 dots near the middle, and 4 line segments on the right half of the sky.
June 21:
This day is special. You take more exposures:
- You first open the shutter from 9:00-9:15, close the shutter from 9:15-9:30,
- open from 9:30-9:45, close from 9:45-10:00,
- open from 10:00-10:15, close from 10:15-10:30,
- open from 10:30-10:45, close from 10:45 to 13:15,
- except for a very brief exposure at 11:00, 12:00, and 13:00.
- open from 13:15-13:30, closed from 13:30-13:45,
- open from 13:45-14:00, closed from 14:00-14:15,
- open from 14:15-14:30, closed from 14:30-14:45,
- open from 14:45-15:00, closed from 15:00 for the rest of the day.
The result, for June 21, you'd get 4 bright line segments on the left half, 3 dots near the middle, and 4 line segments on the right half.
after June 21, drop the right half captures and keep the left half captures.
So, on June 22 and for many days thereafter:
- For the day, you first open the shutter from 9:00-9:15, close the shutter from 9:15-9:30,
- open from 9:30-9:45, close from 9:45-10:00,
- open from 10:00-10:15, close from 10:15-10:30,
- open from 10:30-10:45, close from 10:45 for the rest of the day,
- except for a very brief exposure at 11:00, 12:00, and 13:00.
The result, for June 22 and on, you'd get 4 bright line segments on the left half and 3 dots near the middle.
If that much makes sense, then we can go back to @alter-ego 's fine diagram for the more complete picture of the year. Really, they were capturing more than 4 line segments on each half, it looks like maybe about 7, but the idea is an easy extension of my description to more 15-minute segments earlier in the morning and later in the afternoon. You do the 11:00, 12:00 and 13:00 exposures year-round, so you get the 3 central full analemmas, which I realize you already understood. But you capture these morning segments only from June 21 to August 30 and December 21 to April 13, and you capture the afternoon segments from April 13 to June 21 and from August 30 to December 21. Those are thus drawing smeared-out half-analemmas.
Maybe I have this right. And maybe that helps it make more sense.
[quote=alter-ego post_id=323909 time=1656900516 user_id=125299]
[quote=johnnydeep post_id=323897 time=1656856361 user_id=132061]
[quote=alter-ego post_id=323887 time=1656810807 user_id=125299]
I missed answering this part. As the description states, the dashed lines are extended exposure times so that the sun trails instead of just forming a dot. The intermittent dark regions within trails are clouds blocking the sun.
[/quote]
Thanks for this and your prior response, but I still don't get it. Were the long exposure times [b][i]necessary[/i][/b] to take the pin hole camera shots? I'd think not since it's the bright sun being imaged and not a dim nighttime star. Why couldn't the result just be the three full analemmas shown in the middle?
[/quote]
→ For the sun trails (to the left and right of the full analemmas), the exposure times were somewhere between 15min and 20min long. They were that long only to create the trails, not for improving light collection.
→ I estimate individual sun exposures to be 10's of seconds. This exposure time is longer than needed to image the sun on a cloudless day but seems quick to me for solargraphy and the paper that's used. Only the sun can be recorded during a single image having these exposure times. The landscape, however, benefits from cumulative exposures over the year.
→ Not sure what you're asking. The result is what was wanted. If no sun-trails were made, the result would be just the 3 full analemmas. To capture this image, the camera shutter opened thousands of times over the year. Personally, I like the half-analemmas on each side. The composition of tilted full and half analemmas on each side of the central, due south analemma is a new and artful representation the seasonal sun.
[/quote]
@johnnydeep, maybe not your nemesis, I think you understand them well enough to ask intelligent questions!
So, as June 21 is the summer solstice and "peak" day, let's look at a few sample daily exposures. If by some chance I have this figured out correctly.
On June 20, like many days leading up to the solstice, you'd:
[list][*]Leave the shutter closed up until 13:15,[*] except for a very brief exposure at 11:00, 12:00, and 13:00.[*] Then open from 13:15-13:30, closed from 13:30-13:45,[*]open from 13:45-14:00, closed from 14:00-14:15,[*]open from 14:15-14:30, closed from 14:30-14:45,[*]open from 14:45-15:00, closed from 15:00 for the rest of the day.
[/list]
The result, for June 20 et al, you'd get 3 dots near the middle, and 4 line segments on the right half of the sky.
June 21:
This day is special. You take more exposures:
[list][*]You first open the shutter from 9:00-9:15, close the shutter from 9:15-9:30,[*]open from 9:30-9:45, close from 9:45-10:00,[*]open from 10:00-10:15, close from 10:15-10:30,[*]open from 10:30-10:45, close from 10:45 to 13:15,[*] except for a very brief exposure at 11:00, 12:00, and 13:00.[*]open from 13:15-13:30, closed from 13:30-13:45,[*]open from 13:45-14:00, closed from 14:00-14:15,[*]open from 14:15-14:30, closed from 14:30-14:45,[*]open from 14:45-15:00, closed from 15:00 for the rest of the day.
[/list]
The result, for June 21, you'd get 4 bright line segments on the left half, 3 dots near the middle, and 4 line segments on the right half.
after June 21, drop the right half captures and keep the left half captures.
So, on June 22 and for many days thereafter:
[list][*]For the day, you first open the shutter from 9:00-9:15, close the shutter from 9:15-9:30,[*]open from 9:30-9:45, close from 9:45-10:00,[*]open from 10:00-10:15, close from 10:15-10:30,[*]open from 10:30-10:45, close from 10:45 for the rest of the day,[*]except for a very brief exposure at 11:00, 12:00, and 13:00.[/list]
The result, for June 22 and on, you'd get 4 bright line segments on the left half and 3 dots near the middle.
If that much makes sense, then we can go back to @alter-ego 's fine diagram for the more complete picture of the year. Really, they were capturing more than 4 line segments on each half, it looks like maybe about 7, but the idea is an easy extension of my description to more 15-minute segments earlier in the morning and later in the afternoon. You do the 11:00, 12:00 and 13:00 exposures year-round, so you get the 3 central full analemmas, which I realize you already understood. But you capture these morning segments only from June 21 to August 30 and December 21 to April 13, and you capture the afternoon segments from April 13 to June 21 and from August 30 to December 21. Those are thus drawing smeared-out half-analemmas.
Maybe I have this right. And maybe that helps it make more sense.