Equipment for Astronomical Imaging

7/29/2019 Equipment for Astronomical Imaging

1/28

Equipment for Astronomical

Imaging

Lecture given at Bangalore Astronomical SocietyAstrophotography Workshop 27th April 2013

M.Sathyakumar Sharma


2/28

Topics to be covered

PART I

A little flashback.

Telescope, a brief idea of how light can be worked with.

Telescope, a study of types and sub types.

Requirements for the Amateur Astronomer. Basic to Advanced. Q&A

PART II

A Note on Stability.

Mounting Systems: History, Types and Present Technology. Requirements for the Amateur Astronomer. Basic to Advanced.

PART III

Cameras, Types of Imaging. Types of Cameras.

Application in astronomical

Requirements for the Amateur Astronomer. Basic to Advanced.


3/28

Flashback of Ye Olde Teleskope

Hans Lippershey or Pirates of the Caribbean?

Galileo Galilei and Johannes Kepler

Sir Isaac Newton


4/28

Working with Light

Bending of Light

Prisms: Used to disperse light to its constituents.

Lenses: Used to converge or diverge rays of light.

Refractive Index of Glass.

Types of Lenses used on Astronomical Systems.

Glasses used in Astronomical Instruments.

Mirrors and their surface finishing.


5/28

Working with Light II

Refractive Index of Glass:

In optics the refractive index or index of refraction n of a substance (optical medium, aka

glass etc) is a dimensionless number that describes how light, or any other radiation,

propagates through that medium. It is defined as;

n = c/v

Where n is the refractive index, c is the velocity of light in vacuum and v is the velocity of

light in the medium through which it is passing at that point of time.

Refractive index of materials varies with the wavelength. This is called dispersion; it causes

the splitting of white light in prisms and rainbows, and chromatic aberration in lenses.

In opaque media, the refractive index is a complex number: while the real part describes

refraction, the imaginary part accounts for absorption.


6/28

Working with Light III

Types of Lenses used in Astronomical Telescopes.

Singlet Lens:

Achromatic:

Doublet Apochromat:

Triplet Apochromat:

Glasses used in Telescope lenses: ED and Fluorite.

Note on Field Curvature.

Not all rays of light focus at the same

point if a flat imaging sensor is used.


7/28

Working with Light IV

MirrorsA Concave mirror of the radius of curvaturesame as a convex lens can converge light the

same distance.

Since the mirror requires only one surface

to be precision finished, it is cheaper to make

and in large sizes there is no option anyway.

Types of Surface finishes.

a) Optical Flat: One surface is flat to a

fraction of a measured wavelength of

light.

b) Spherical: Surface is part of a sphere of

a given radius.

c) Parabolic and Hyperbolic: Part of a

parabola or hyperbola of given foci.


8/28

Telescopes

Types and Sub types

Types

1)Refractor: Lens, or combination of multiple

lens systems.

2)Reflector: Mirror for converging rays.

3)Catadioptric: Combination of Lens and

Mirror(s)


9/28

RefractorMade up of;

a) Singlet lens: Commonly found in toy telescopes and imitation

antiques and genuine antiques.

b) Achromatic Doublet: Typical Department Store Telescopes,

Budget refractors for Visual Observers. Not satisfactory at

short focal lengths.

c) Apochromatic Doublet: Typical mid priced telescopes, very

good colour correction, suitable for visual observing and

imaging. Good at short focal lengths.

d) Apochromatic Triplet Telescope: Typical mid to high pricedtelescopes, price varies of type of glass, coatings and

branding.

e) Quadruplet/ Petzval: Crme de la Crme of Refractors:

Typical High end scopes commonly used by

astrophotographers requiring a portable setup.


10/28

Reflector

Components:

Primary Mirror: Converges light rays from Infinity to a single point, parabolic

surface finish typical, spherical in cheaper instruments.

Note: .

Secondary Mirror: An mirror used to deviate light perpendicular to

the optical axis. This is simply used so that the observers head does not come in

the way.

Focuser: Holds the eyepiece or camera and contains a rack and pinion system or

a friction drive system like the Crayford type focuser, rotational motion of a knobtranslates to linear motion of the eyepiece holder called the drawtube to bring

objects to a focus.

Eyepiece: A combination of lenses in a calculated order to magnify the image.

Magnification = Fo /Fe.


11/28

CatadioptricCommon Name: Cassegrain telescope

Common Components:

Primary mirror

Secondary Mirror

Tertiary Mirror

Optional Corrector plate/lens.

Types:

a)Classical : Parabolic Primary, Hyperbolic

secondary

a) Schmidt: Spherical Primary, Parabolic

secondary, Corrector plate.

b) Maksutov-Gregorian: Corrector lens,

Spherical Primary, parabolic secondary

c) Ritchey Chretien: Hyperbolic primary and

secondary only.


12/28

Requirements for the Amateur AstronomerRefractor: Min- 80mm F/6 to F/10

Reflector: Min- 130mm F/5 to F/8

Catadioptric: Min-127mm F/12

Bits and Bobs:

Lunar Imaging: Mobile phone with camera, point and

shoot digital cam, computer webcam with webcam

adapter to fit telescope focuser.

Planetary imaging: Webcam with adapter as above.

Solar Imaging: A Solar filter for white light or a H-alphasolar telescope for H-alpha imaging, along with webcam

and adapter

Deep Sky Objects: Film/Digital SLR, T-Ring, Nosepiece,

filters etc etc....


13/28

Q & A for Part I


14/28

Stability

Every system intended for recording events requires some

form of support structure to protect it from basic interruptions

like vibrations and wind.


15/28

Mounting systems

The 49 Foot telescope of William Herschel

EQ6 and HEQ5 Mounts from Sky-Watcher

Joseph Von Fraunhofer


16/28

Types of Telescope mounts

Alt-Azimuth:

Basic motion is in the horizontal and vertical planes

giving two axis of rotation.

Variants: Photographic Tripod and Dobsonian mount.

Equatorial:

Two axis of rotation with one parallel to earths axis

called Polar Axis or Right Ascension and the other axis

orthogonal to the Polar axis called Declination.

Variants: German, English, Yoke, Fork etc.


17/28


18/28

Requirements for the Amateur Astronomer

Note: German Equatorial Mount or GEM is the most

common type of equatorial mount mass produced

for the Amateur Astronomer.

Basic: EQ1 or EQ2 Equatorial mount. Payload 3kgmax.

Semi-Mid Level: GOTO computerised HEQ5 or EQ6.

Payload capacity 18 to 25kg.

Advanced: Paramount ME, Takahashi Temma 200,Astrophysics Mach 1, Losmandy etc.

Payload capacity 40 to 50kg +


19/28

Astrophysics Mach1

Takahashi Temma 200

Losmandy G11


20/28

Bits and Bobs-IPolar Scope

GOTO Kit for EQ3-EQ5

mounts

Basic tracking motor for EQ1-

EQ2 mounts


21/28

Bits and Bobs-II


22/28

Cameras

DSLR

Dedicated

AstronomicalCCD Camera


23/28

Sensor Types

CCD : Charge Coupled Device ~ Photo sensitive diodes.

Very sensitive to light

Available in monochrome or Colour

Monochrome more sensitive than colour Bayer MatrixHigh QE Quantum Efficiency.

Requires auxiliary electronics for image processing and transfer.

CMOS: Complimentary Metal Oxide Semiconductor ~ Photo sensitive

capacitors.

Good sensitivity to light.Available mass produced only in colour.

Low QE.

Electronics built into the sensor.

The quantum efficiency (QE), or incident photon to converted electron (IPCE) ratio,of

a photosensitive device or a charge-coupled device (CCD) is the percentage of

photons hitting the device's photoreactive surface that produce charge carriers.

T f C


24/28

Types of Cameras

for

Astronomical ImagingCMOS BasedMobile phone.

Webcam.

Planetary/Lunar/Solar cam.

Point and Shoot.Digital SLR.

Companies manufacturing CCD Based cameras.

SBIG Santa Barbara Instrument Group

Apogee

QSI Quantum Scientific ImagingQHY

FLI

Opticstar Ltd.

Atik.

CCD Based cameras

Webcam/Planetary/Lunar/Solar cams

Monochrome and Colour cooled astronomical

cameras.

Cooled CCD cameras


25/28

Requirements for the Amateur Astronomer

Lunar Imaging: Min- Mobile phone with camera.

Better images with Phillips SPC900 webcam

Expensive option : cameras with Sony ICX618 chip.

Solar Imaging : Solar filter must with the cameras above.

Planetary imaging:

Min: Phillips SPC900 webcam or Celestron Neximage.

Better images with dedicated planetary imagers like Opticstar PL-131C, PL-131M,

QHY5, QHY5-II, SBIG STi., Imaging Source DMK21AU618, DSLR with video option

etc.

Deep Sky: Min- DSLR by Canon preferred.

Mid level Atik 314L, 314L+, Opticstar DS-145 ICE.

Expensive option: SBIGST8300 Mono or Colour, QHY 8, 9, 10.


26/28

Mandatory Accessories


27/28

Optional AccessoriesFilters : Glass substrate with specialized coatings

Eg: Planetary filters, Ha, Hb, OIII, SII, UHC, Moon filter.

Common sizes: 2 and 1.25

Filter Wheels: To hold the filters in a Carousel for ease of

use.

Manual and USB

Guide cameras: For long exposure imaging to compensate

for human errors, mount mechanical errors.


28/28

Q & A for Part II and III

Equipment for Astronomical Imaging

Documents