Is a DSLR right for you

All of this assumes that a DSLR is the best astrocamera for your purposes. Maybe it isn't. Before taking the plunge, consider how DSLRs compare to other kinds of astronomical cameras (Table 1.4, Figure 1.4). Notice that the DSLR provides

Figure 1.4. Left to right: a film SLR, a DSLR, a webcam modified for astronomy, and an astronomical CCD camera.
Table 1.1 Types of astronomical cameras and their relative advantages, as of2007

Non-SLR Webcam or

Astronomical Astronomical

Film

Digital

digital

astronomical

CCD camera CCD camera

SLR

SLR

camera

video camera (smaller format) (larger format)

Typical cost

$200 + film and processing

$800

$200

$150

$2000 $8000

Megapixels

Equiv. to

6-12

3-8

0.3

0.3-3 4-12

(image size)

6-12

Ease of use

++

++

+++

+

++

(for astro-

photography)

Also usable

Yes

Yes

Yes

No

No No

for daytime

photography?

Suitability for:

Moon

++

++

+++

-

- ++

(full face,

eclipses)

Moon and

+

+

++

++++

+++ +++

planets

(fine detail)

Star fields

++

+++

-

-

+ ++++

and galaxies

(wide-field)

Star clusters

++

+++

-

-

++++ ++++

and galaxies

(through

telescope)

Emission

+++

++

-

-

+ ++++

nebulae

if suitable

(++++ if

(wide-field)

film is available

modified)

Emission

++

++

-

-

++++ ++++

nebulae

if suitable

(+++ if

(through

film is

modified)

telescope)

available

Key: - Unsatisfactory + Usable ++ Satisfactory +++ Very satisfactory ++++ State of the art a great combination of high performance and low price - but it's not ideal for everything.

A few years ago, film SLRs were almost all we had. Their striking advantages were interchangeable lenses, through-the-lens focusing, and the availability of many kinds of film, some of them specially made for scientific use.

Most astrophotographers back then didn't fully appreciate the film SLR's real weakness, which was shutter vibration. Even with the mirror locked up to keep it from moving, the shutter always vibrated the camera enough to blur pictures of the Moon and the planets. For deep-sky work, this was not so much of a problem because the vibration didn't last long enough to spoil an exposure of several minutes.

Digital SLRs have the same vibration problem since the shutter works the same way. For that reason, DSLRs are not ideal for lunar and planetary work. Non-SLR digital cameras, with their tiny, vibration-free leaf shutters, work much better, though they aren't suitable for any kind of deep-sky work because of their tiny, noisy sensors.

For detailed lunar and planetary work, webcams and other video devices work better yet. They are totally vibration-free, and they output video images consisting of thousands of still pictures in succession. Software such as Reg-iStax can select the sharpest frames, align and stack them, and bring out detail in the picture. Despite its low cost, this is the gold standard for planetary imaging.

For deep-sky work and professional astronomical research, the gold standard is the thermoelectrically cooled astronomical CCD camera. These cameras are appreciably harder to use; they work only with a computer connected. They are also substantially more expensive, but the image quality is second to none. Because the sensor in such a camera is cooled, it has much less noise than the sensor in a DSLR.

Until recently, astronomical CCDs were 1-megapixel or smaller devices designed for use through the telescope. Now the gap between DSLRs and astronomical CCDs, in both performance and price, is narrowing because both are benefiting from the same sensor technology. If you are considering a high-end DSLR, you should also consider a larger-format astronomical CCD that can accept camera lenses to photograph wide fields.

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