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Wednesday, November 13, 2013

Size matters

Some calculations will seem very intimidating at first. They won't bite.

Telescope


Diameter of mirror, D1=150mm
Focal length of mirror, f1=750mm
Focal length of eyepiece, f2=28mm
Resulting magnificationf1f2=7502827
f-number, N=f1D1=150750=5


Next up is a concept I don't fully understand. Macimum theoretical resolution of a telescope. Capability to see small details. This is apparently a function of telescope diameter and light wavelength. At least in theory. Stuff like aberrations and seeing come in the way, but there is a maximum theoretical resolution. For visual light we get

α=140D1=1401500.93 arcseconds


So, I won't be able to distinguish details smaller than about 1 arcsecond. For reference, the moon is about 30 arcminutes.

Camera

The telescope is interesting in itself. Let's see what happens if we attach a camera to the telescope. First we figure out the plate scale measured in arc seconds per mm.

Width 3888 px;22,2mm
Heigth 2592 px;14,8mm


Plate scale =206265f1=206265750275 arc seconds per mm


Sooo... images I take with my camera will be roughly 1,7 by 1,1 arch degrees.  The moons diameter is roughly half an arch degree. This seems to be in line with my first experimental photos. Waiting for the moon to come up so veryify this. Moon, where are you?

What about resolution?

1,7 arc degree divided by 3888 pixels gives roughly 2292 pixels per arch degree
or 0,63 pixels per arch second

Seems the camera resolution is comparable to the telescopes theoretical maximum resolution. Cool.

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