Corrections and Updates
Last revised 2011 August 30
This page will be revised as the need arises. Note however that it is not possible
to track every change in the digital camera industry, and you should always use the World Wide Web
and other current sources of information to help you make decisions.
New technology:
Recommended software: DeepSkyStacker is exceptionally
easy to use and well-documented. I strongly recommend it for processing DSLR images (as an alternative
to the software mentioned in the book).
Live focusing: Many newer DSLRs, especially Canons, provide live focusing so you can confirm
the focus by viewing the sensor image, highly magnified, in real time. I consider this a must-have feature.
Right now the Canon XS is one of the lowest-priced DSLRs that work well for astrophotography;
I strongly recommend it.
Vibrationless imaging: Many Canons provide a mode called "silent shooting" where the shutter
is already open and the exposure starts electronically with a minimum of vibration.
Click here for more about this.
Red sensitivity: I have reliable reports that the Pentax K-r and K-x have considerably
more deep-red sensitivity than competing Canon and Nikon DSLRs. I have not yet evaluated them for
astrophotography in detail.
Known misprints in the first printing:
The pictures on pages 176, 179,
186, and 189 were printed with insufficient contrast.
Page 186 is the worst afflicted. To see these pictures properly
on your computer screen, view the
sample pages.
[p. 212]
| Change: |
|
DSLR Focus 95, 95 |
| To: |
|
DSLR Focus, 95 |
Other clarifications for the second printing:
[p. 6, footnote]
| Change: |
|
On the Web at http://web.canon.jp/Imaging/astro/index-e.html. |
| To: |
|
Formerly on the Web at http://web.canon.jp/Imaging/astro/index-e.html. |
Canon took this web site down in early 2008, apparently feeling that it was no longer up to date.
[p. 50]
| Change: |
|
Recently, Meade Instruments introduced
a design they call Ritchey-Chrétien...
|
| To: |
|
In 2005, Meade Instruments introduced
a design they called Advanced Ritchey-Chrétien...
|
| |
| Change: |
|
However, the decision to call it
Ritchey-Chrétien is controversial, and the name may not stick.
|
| To: |
|
The decision to call it Ritchey-Chrétien
was controversial, and in 2008 Meade agreed to stop using that name.
|
In fact, the change came in response to a lawsuit. For now, the illustration at the top of p. 50 is
not being changed because these telescopes are already in users' hands and were bought as a type of
Ritchey-Chrétien. Meade's optical system is a good one; it just isn't a Ritchey-Chrétien.
[p. 78, caption]
| Change: |
|
decentered element |
| To: |
|
decentered element or misaligned T-ring |
If the lens is attached with a T-ring (as some older lenses are), misalignment
(non-perpendicularity to the sensor plane) can arise there.
To fix a misaligned T-ring, loosen and retighten the screws that
hold the inner part of the T-ring in place
relative to the outer part.
[p. 95]
| Change: |
|
best known and most elaborate is |
| To: |
|
first to achieve wide use was |
| Change: |
|
which has gradually evolved |
| To: |
|
which gradually evolved |
Updates to DSLR Focus seem to have stopped in 2006,
but I have seen no actual announcement of discontinuation.
Other focusing software is being updated regularly to support newer cameras.
[p. 171]
| Change: |
|
because 0.51/2.2 = 0.73 |
| To: |
|
because 0.5 = 0.732.2
|
in order to more closely match the preceding formula.
The text is correct, but the original example caused some confusion.
[p. 179, figure caption]
| Change: |
|
Left: ... Right: |
| To: |
|
Top: ... Bottom: |
[p. 187]
The illustration on p. 187 does not make clear why the boxcar filter is used.
Here's a revised version with a better explanation:
Click here to download EPS version
Other notes
On the subject of calibration:
-
It is somewhat unclear whether bias frames are needed with a DSLR. In theory, yes; in practice,
especially with Canons, some kind of bias subtraction is already done in the camera.
I suspect that Nikons in Mode 3 give a more "truly raw" image and are more likely to benefit from bias frame
subtraction. A bias frame is a dark frame with the shortest possible exposure (1/1000 second
or less), taken with the same ISO setting and camera temperature as the astrophotos and
dark frames.
- Be sure to use many calibration frames — numerous darks and flats — for the same
reason that you take numerous exposures of the celestial object: to keep down the grain.
It makes no sense to take 10 exposures of a celestial object (to avoid grain) and then
do the calibration with just one dark or flat frame (thereby reintroducing a lot of grain).
|
