fivemack: (iguana)
[personal profile] fivemack
The partially- and totally-eclipsed moons do not in any useful respect resemble a duck. Which is a pity, since I know that I have the kit to take quite good pictures of ducks.



The correct exposure for the sunlit moon is about 1/50 f/8 at ISO 400.

partial

The correct exposure for the copper-coloured eclipsed moon is about 2 seconds f/8 at ISO 400.

total

So if you want an image of the moon showing how the sunlit crescent blends into the sunset-lit eclipsed part, you'd have to take two shots at exposures 100x apart and merge in Photoshop afterwards. Fine, that's the kind of thing Photoshop is for.

There is a horrible technical problem, which is that the camera (particularly if running at f/13) won't auto-focus on something as faint as the eclipsed Moon. And it won't run long enough exposures in live-view mode to be able to see whether you're in focus; for the partial phase I could focus accurately on the illuminated part, but at totality everything's quite fuzzy. There must be an accepted solution to this - I suppose I should have pointed at a bright star and live-view-focussed there, but it was 3:30am and the Moon in a region of the sky without really obvious bright star.

Then we run into the fundamental problem. With the long lens and teleconverter, the moon comes out 2000 pixels across, so one pixel is half an arc-second near enough. Unfortunately, the moon moves across the sky at a rate of about 1.3 million arc-seconds per day (that is, all the way round the sky in one day), or fifteen arc-seconds per second, so in a two-second exposure the best you can hope for is sixty pixels of blur. I took a thirty-second exposure to demonstrate this:

motion-of-moon

That's if the tripod doesn't wobble. And with the very bright uneclipsed-moon in the frame you will see every wobble ... this one is the least-wobbly partial-phase picture I managed.

inadequate-pink

An actual telescope mount would be solid enough to hold everything still, and would have a little motor to rotate it to follow the motion of the moon; on the other hand it would cost more than the already-quite-extravagent birding lens, I would use it no more than six times a year, and it would take half an hour to set up at 0230 with sleep-befuddled brain. So with what I've got the right answer is probably to give up on filling the frame and go for something artier instead:

DSC_0068
From:
Anonymous( )Anonymous This account has disabled anonymous posting.
OpenID( )OpenID You can comment on this post while signed in with an account from many other sites, once you have confirmed your email address. Sign in using OpenID.
User
Account name:
Password:
If you don't have an account you can create one now.
Subject:
HTML doesn't work in the subject.

Message:

 
Notice: This account is set to log the IP addresses of everyone who comments.
Links will be displayed as unclickable URLs to help prevent spam.

July 2017

S M T W T F S
      1
2345678
9101112131415
161718 19202122
23242526272829
3031     

Most Popular Tags

Style Credit

Expand Cut Tags

No cut tags
Page generated Jul. 24th, 2017 08:41 pm
Powered by Dreamwidth Studios