Focal lengh to capture the moon

[Cunha]

Hi,

I need to photograph the moon in a way that occupies most of my 35mm FF frame without crop. Or bigger than the frame. I need a clear full moon with craters (no problem).

The image will be in portrait mode.

My test using a Canon EF 100mm macro L lens resulted in a very small image for my needs (image attached).

What lens do you suggest to produce a big image of the full moon?

Thank you very much.

[Waddizzle]

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@kvbarkley wrote:

Luckily the moon is a brightly sunlit object so the sunny 16 rule comes pretty close.

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I was using the "Looney 11" rule.  But, since it was only half a moon, I doubled the ISO.  I took some shots at f/8 and ISO 100, too.  I cropped the photos a little bit, too.  I understand the Moon to be a brightly lit, dark rock, nearly the color of asphalt.

What about motion blur of the Moon, though?

[kvbarkley]

I think the moon is bright enough to not have to worry. I did some quick googling amd the moon moves about 1 degree every two hours. (depending on....) Assuming you have 4000 pixels per degree, that means it moves 4000 pixels in 2 hours or 4000 pixels per 7200 seconds. So it would move 1 pixel in 0.5 seconds, which says that shutter speed should not be an issue for the moon, if I have my math right.

[Waddizzle]

"So it would move 1 pixel in 0.5 seconds, which says that shutter speed should not be an issue for the moon, if I have my math right." 

Your math may be correct, but the Moon can still waltz completely of the screen in about a minute at nearly 1000mm, which just seems faster than 1 degree every two hours.  My 150-600mm has a rated AOV of 16.4 - 4.1 degrees. 

The crop sensor [x1.6] is probably cutting that long end down to 3 degress, if not less.  The Moon is moving out of the frame, from center to off the frame in a couple of minutes, at most.  I really need to time it, though.

[ebiggs1]

Or perhaps the Looney 11 Rule.

[Waddizzle]

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@ebiggs1 wrote:

Or perhaps the Looney 11 Rule.

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Yeah, I tried to modify that some.  Rather, I experimented with varying the parameters of it some.  I assume that the rule applies to a full moon.  I was shooting at roughly a half moon, and my shots were coming out a bit dark, by what I estimated to be about 1 EV.

So, I began tweaking different legs of the exposure triangle, to see what the effects would be.  When I dropped the shutter speed to 1/50, that's when I realized motion blur could be an issue, or maybe not.  I simply didn't know.

What else was I supposed to do, sitting around on a bench an hour before dawn, waiting for some ducks to show up, while staring at the half full moon?

[RobertTheFat]

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@Waddizzle wrote:

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@ebiggs1 wrote:

Or perhaps the Looney 11 Rule.

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Yeah, I tried to modify that some.  Rather, I experimented with varying the parameters of it some.  I assume that the rule applies to a full moon.  I was shooting at roughly a half moon, and my shots were coming out a bit dark, by what I estimated to be about 1 EV.

So, I began tweaking different legs of the exposure triangle, to see what the effects would be.  When I dropped the shutter speed to 1/50, that's when I realized motion blur could be an issue, or maybe not.  I simply didn't know.

What else was I supposed to do, sitting around on a bench an hour before dawn, waiting for some ducks to show up, while staring at the half full moon?

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The thing about a half moon is that the reflected light comes off at a much less favorable angle, as compared to a full moon. I believe I've read that the difference in brightness between a half moon and a full moon is about a factor of five, not two. And of course you can't trust your lying eyes, which will adjust their aperture and sensitivity without telling you.

[Waddizzle]

"The thing about a half moon is that the reflected light comes off at a much less favorable angle, as compared to a full moon. I believe I've read that the difference in brightness between a half moon and a full moon is about a factor of five, not two. And of course you can't trust your lying eyes, which will adjust their aperture and sensitivity without telling you."  

Yeah, I think you're right.  I'm reviewing the EXIF data, and I compensated 2 stops to get it back into the center of the historgram.

[TCampbell]

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@Waddizzle wrote:

I always wonder about shutter speed when photographing the Moon.  Is 1/100 sec fast enough to freeze the motion of the Moon with almost1000mm [600mm x 1.6 = 960mm] of lens staring at it? 

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The Earth spins at an angular rate of about 15 arc-seconds per second.

A 600mm lens on an APS-C sensor has an angular dimension of 2.1º x 1.4º (that's the size of the area of sky visible in on the sensor.)  That translates into 7560" (arc-seconds) x 5040".

The sensor dimensions on a Canon APS-C camera with an 18MP sensor (e.g. using your T5 for example) are 5184 x 3456 pixels.  

That works out to 1.46 arc-seconds per pixel (at 600mm on a Canon APS-C camera with an 18 MP sensor).

You're only shoot 1/100th of a second.  That means the angular motion is only .15 arc-seconds.  That works out to about 1/10th of a pixel worth of movement in the 1/100th second exposure.

Also... the 15 arc-seconds per second of angular movement (diurnal motion) aused by the rotation of the Earth only applies if an object is over the equator.  (near delcination 0º).  If the object is not directly above the equator then you multiple the 15 arc-seconds by the cosine of the declination of the object.  In other words, 15 arc-seconds per second is a "worst case" scenario.  Most objects move at an angular rate which is even slower.

Bottom line:  No need to worry about excessive movement causing blur when shooting the moon.

[Waddizzle]

"A 600mm lens on an APS-C sensor has an angular dimension of 2.1º x 1.4º (that's the size of the area of sky visible in on the sensor.  ...  ...  Bottom line:  No need to worry about excessive movement causing blur when shooting the moon."  

Ooh.  Ooh.  Numbers!  Thanks for the info, Tim. 

My crude estimate that got me thinking [guilty, I think too much] was this.  I had realized that it was the Earth's rotation that I was seeing on the LCD, not the Moon's orbit.  If the Earth rotates 360 degress in 24 hours, or 1440 minutes, then the Moon could be moving as much as 0.25 degrees per minute, which would easily explain why it walks out of the frame in a couple of minutes, or so.

I never thought about counting pixels across the sensor's surface.  Thanks, again.