Telescope Reviews: Uncle Rod, I Want to Take Pictures

Hello all;
As always, that is a very well researched and written article. There are, however, a couple of minor points that I'd like to address.

The advantages of using a CCD sensor as oppsed to using a CMOS one for digital image capturing are lessening significantly with every new dSLR generation. This is due in no small part to the ever incresing ISO (formerly known as ASA)levels.

Simply put, ISO determines the sensors' (or films') sensitivity to light. With the current crop of entry level dSLR cameras routinely advertising ISO 1600 and higher levels, dSLR cameras are quickly becoming THE way to capture celestial images.

All newer generation dSLR cameras have a filter over the image capturing sensor which is called the Bayer array. Again, simply put, the Bayer array divides the sensors' level of sensitivity into the separate RGB spectrum. In other words, one photosite with use a red filter, the site next to it will have a green filter and then a red filter, etc. alternating between red and green. The next row of photosites will star off with a blue filter, followed by a blue filter, then green, alternating back and forth between blue and green.

Now, based on this alternating pattern, there will be twice as many green photosites as there are red or blues sites. This is because the human eye distinguishes green twice as easily as it does either red or blue. This translates into green becoming the predominate color in any given photo, with a camera settings being set to factory levels and no postprocessing being done.

This SEEMS like a severe disadvantage to using a dSLR camera in relation to using a dedicated astrophotography CCD camera, however, in reality it can become a HUGE advantage.

How? By adjusting the dSLR cameras' level of sensitivity to any one of the three primary colors, red, green or blue, we can now take photos which are predominately red satuarated, or green or blue on any combination of the three primary colors. The beautiful thing about this advantage is that it can done in-camera before the photograph has been captured or it can be accomplished just as easily and accurately in postprocessing, ie on a computer.

One of the reasons why dSLR cameras were not widely used in the past for astrophotography is because of the lack of live view. All dSLR cameras behave in the same manner as their 35mm film grandfathers, that is, the operator sees the image directly through the cameras' lens and in reality the operator is seeing the image exactly as the cameras' capturing device will record it.

It was very difficult to piggyback a camera because the user had no easy method of being able to view the image before capturing, therefore afocal photography became the method of choice, which subjected the camera to longer exposure times and far less accurate focusing.

Again, with more and more entry level dSLR cameras having live view incorporated into their designs, piggybacking is becoming more popular as the camera user is able to see the image on the cameras LCD screen before the image is captured in exactly the same manner as a digital point and shoot. Personally, for general usage I don't like live view, however it does have some very nice applications as in astrophotography and microphotography.

In fact, astrophotographyusing a dSLR camera is one of the reasons why I became a member of this forum. I've been an amateur astronomer since my early teens (more of a dedicated stargazer, actually) with photography being my main diversional pursuit, and it's only because my son has an increasing interest in astronomy that I have now ordered my first telescope, a Celestron Nexstar 8".

If a person takes between 20,000 and 40,000 photographs per year, such as I do, then a dSLR coupled to a telescope is a very natural evolution.

Awesomely good article, Uncle Rod! keep up the great writing.
Mark