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Old 25-07-2018, 10:07 PM
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BarneyMaroon (Tony)
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Keeping Moon and Horizon in focus

Hi all, I wanted to have a crack at taking a photo of the eclipsed moon against foreground.

I have an Olympus EM5 attached (prime focus) to an SW ED80. How many metres from an object do I have to be for it to be in the same "depth of field" as the moon.

100m
200m
1000m?
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Old 26-07-2018, 08:13 AM
JA
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Hello x + C (),

157.9m I'd say .

At the very least - to put an upper limit on it, definetly ~5km (& less), as that is the distance to the observable horizon, at which, by eye, we also see the moon in crisp view, (depending on your height).

As to the lower (near) limit, try it and see before Saturday's eclipse, if that's what you had in mind to set up for. Aperture / f/number) controls the depth of field, so if you have insufficient depth of field with your setup, for the image you'd like to capture, you can use a mask over your scope to reduce aperture and increase your depth of field. A simple circle cut out of dark paper smaller than your existing aperture. Every 1.4x less in diameter is 2x less light, or one f-stop.

Have fun,

Best
JA

Last edited by JA; 26-07-2018 at 08:23 AM.
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Old 26-07-2018, 09:51 AM
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troypiggo (Troy)
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I've never tried it on astro images, but maybe look into hyperfocal distance focusing. Normally the range of acceptable focus is limited by focal length, aperture size, and circle of confusion (sensor).

Hyperfocal distance is an optical property where you can set the focus to a particular distance (H) and everything will be in focus from H/2 to infinity.

More here: https://www.photopills.com/calculators/hyperfocal-table

And here is a calculator for you to figure it out for your particular gear: https://www.photopills.com/calculators/dof

Looks like for your camera and ED80 the distance to focus would be around 3-3.5km. Might take some trial exposures to nail it.
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Old 27-07-2018, 11:00 AM
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BarneyMaroon (Tony)
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Thanks for pointers

Yes, will try and do some test runs tonight. Yes I was thinking about tomorrow morning. The western horizen is damn hard in inner Brisbane. A sunset eclipse would be just magic from top of Mt Coot-tha, but dawn in the West is harder.

Or I might sleep.

Cheers.
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Old 27-07-2018, 11:03 AM
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BarneyMaroon (Tony)
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Aperture

Love the idea of stopping down with a paper cover. Nice!
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Old 27-07-2018, 11:06 AM
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BarneyMaroon (Tony)
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I'm slow today

Finally got the smart joke JA.

Cheers,
x+C

or

V

If x in R^n and on a finite domain.
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Old 27-07-2018, 11:11 AM
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This image was taken with a full frame camera (5DmkII) through an ED80 with a 2x barlow and, as you can see, the moon and the FG are both in focus. The building was probably about 500m away.
Good luck with the eclipse
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Old 27-07-2018, 08:13 PM
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BarneyMaroon (Tony)
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Nice

Quote:
Originally Posted by pluto View Post
This image was taken with a full frame camera (5DmkII) through an ED80 with a 2x barlow and, as you can see, the moon and the FG are both in focus. The building was probably about 500m away.
Good luck with the eclipse
Nice pic! 500m is good! I am really stuck for a location at the moment.
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