Eclipse of moon on Oct. 27

Prometheus wrote:
In article , Alan Browne
writes

William Graham wrote:

Unless you've got a flash with a guide number of 250 thousand
miles........


That would require an f/1 lens for ISO 100. If the lens is f/4 then a
GN of 1,000,000 miles would be required...


Don't forget the flash would have to fire about 2.69s before the shutter
is fully open.

And don't use times shorter than 1/60, or you won't capture the light
returning from the edges. (That might look interesting, though...)

-- Lassi

Lassi Hippeläinen wrote:

And don't use times shorter than 1/60, or you won't capture the light
returning from the edges. (That might look interesting, though...)

More interesting if a bit late to open ... get a doughnut image.

The diameter of the moon is ca. 3.48E6 meters. For the edges you would need 1/2
of that. C is about 3E8 m/s, giving an image return of about 5.8ms. so a
shutter speed up to 1/172 of a second would work if rear curtain began falling
1/172 of a second after leading edge of light returned. (Call it 1/160 then).

In any case, much easier to expose as 'bulb'. Fire flash, wait 2 seconds, wait
for moon to flare up with the light, let go.


Cheers,
Alan.


--
-- rec.photo.equipment.35mm user resource:
-- http://www.aliasimages.com/rpe35mmur.htm
-- e-meil: there's no such thing as a FreeLunch.--

Lassi Hippeläinen wrote:

And don't use times shorter than 1/60, or you won't capture the light
returning from the edges. (That might look interesting, though...)

More interesting if a bit late to open ... get a doughnut image.

The diameter of the moon is ca. 3.48E6 meters. For the edges you would need 1/2
of that. C is about 3E8 m/s, giving an image return of about 5.8ms. so a
shutter speed up to 1/172 of a second would work if rear curtain began falling
1/172 of a second after leading edge of light returned. (Call it 1/160 then).

In any case, much easier to expose as 'bulb'. Fire flash, wait 2 seconds, wait
for moon to flare up with the light, let go.


Cheers,
Alan.


--
-- rec.photo.equipment.35mm user resource:
-- http://www.aliasimages.com/rpe35mmur.htm
-- e-meil: there's no such thing as a FreeLunch.--

Lassi Hippeläinen wrote:

And don't use times shorter than 1/60, or you won't capture the light
returning from the edges. (That might look interesting, though...)

More interesting if a bit late to open ... get a doughnut image.

The diameter of the moon is ca. 3.48E6 meters. For the edges you would need 1/2
of that. C is about 3E8 m/s, giving an image return of about 5.8ms. so a
shutter speed up to 1/172 of a second would work if rear curtain began falling
1/172 of a second after leading edge of light returned. (Call it 1/160 then).

In any case, much easier to expose as 'bulb'. Fire flash, wait 2 seconds, wait
for moon to flare up with the light, let go.


Cheers,
Alan.


--
-- rec.photo.equipment.35mm user resource:
-- http://www.aliasimages.com/rpe35mmur.htm
-- e-meil: there's no such thing as a FreeLunch.--

In article , Lassi Hippeläinen
writes
Prometheus wrote:
In article , Alan Browne
writes

William Graham wrote:

Unless you've got a flash with a guide number of 250 thousand
miles........


That would require an f/1 lens for ISO 100. If the lens is f/4 then
a GN of 1,000,000 miles would be required...
Don't forget the flash would have to fire about 2.69s before the
shutter is fully open.

And don't use times shorter than 1/60, or you won't capture the light
returning from the edges. (That might look interesting, though...)

Now that leads to an interesting idea, use a shorter shutter time with
the flash to shutter delay adjusted so that you do not capture the
centre. I wonder if there are any nuclear bomb pumped lasers left over
from the star wars project.
--
Ian G8ILZ

In article , Lassi Hippeläinen
writes
Prometheus wrote:
In article , Alan Browne
writes

William Graham wrote:

Unless you've got a flash with a guide number of 250 thousand
miles........


That would require an f/1 lens for ISO 100. If the lens is f/4 then
a GN of 1,000,000 miles would be required...
Don't forget the flash would have to fire about 2.69s before the
shutter is fully open.

And don't use times shorter than 1/60, or you won't capture the light
returning from the edges. (That might look interesting, though...)

Now that leads to an interesting idea, use a shorter shutter time with
the flash to shutter delay adjusted so that you do not capture the
centre. I wonder if there are any nuclear bomb pumped lasers left over
from the star wars project.
--
Ian G8ILZ

Alan Browne wrote:
Lassi Hippeläinen wrote:

And don't use times shorter than 1/60, or you won't capture the light
returning from the edges. (That might look interesting, though...)


More interesting if a bit late to open ... get a doughnut image.

The diameter of the moon is ca. 3.48E6 meters. For the edges you would
need 1/2 of that. C is about 3E8 m/s, giving an image return of about
5.8ms. so a shutter speed up to 1/172 of a second would work if rear
curtain began falling 1/172 of a second after leading edge of light
returned. (Call it 1/160 then).

But this is radar business. The light has to travel there and back
again, so the total delay is twice the difference in distance, or 1/86.
1/60 leaves some room for inaccuracies.

-- Lassi

Alan Browne wrote:
Lassi Hippeläinen wrote:

And don't use times shorter than 1/60, or you won't capture the light
returning from the edges. (That might look interesting, though...)


More interesting if a bit late to open ... get a doughnut image.

The diameter of the moon is ca. 3.48E6 meters. For the edges you would
need 1/2 of that. C is about 3E8 m/s, giving an image return of about
5.8ms. so a shutter speed up to 1/172 of a second would work if rear
curtain began falling 1/172 of a second after leading edge of light
returned. (Call it 1/160 then).

But this is radar business. The light has to travel there and back
again, so the total delay is twice the difference in distance, or 1/86.
1/60 leaves some room for inaccuracies.

-- Lassi

That would require an f/1 lens for ISO 100. If the lens is f/4 then a GN
of 1,000,000 miles would be required...

I'll check the rating on my old 285...

Uhh... nope.

That would require an f/1 lens for ISO 100. If the lens is f/4 then a GN
of 1,000,000 miles would be required...

I'll check the rating on my old 285...

Uhh... nope.