Long-term Planning: CCD or DSLR?
Posted 12 January 2013 - 07:32 AM
OK, I'm trying to do some long-range planning (and saving), and would one day like to get into Astrophotography, but only for bright things -- don't think I have the patience for those awesome nebulous photos. In fact, if I could image the planets in the Solar System, that would probably be enough for me...maybe some star clusters too (M37, you were impressive last night! And Jupiter, I wanted to have a photo to look at this morning!)
We currently only own 2 fairly cheap cameras (meaning, not good for AP, and only for basic photography). My debate is, would it be better to get a real good camera that is DSLR (for its overall usefulness as well as at-scope), or would it be better to go with something like Celestron's NexStar CCD imager? What would be a good overall (AP *and* photos in general) digital camera, and what would be a good CCD imager, to compare?
This is all somewhat more long-term; I'm thinking in one or two Christmas's -- I want to learn the basics first. But, I am curious as to the thoughts if a DSLR may be too heavy for the single-fork-arm, or if the CCD imager has problems?
Posted 12 January 2013 - 09:55 AM
A DSLR has both advantages and disadvantages.
- Quality CCD chip
- Large pixel count (eg 15Mpx and up)
- LCD Viewfinder
- Live View (on most modern DSLRs)
- Movie Mode (on most modern DSLRs)
- Storage to SD card (or similar)
- Output sockets to connect pc (for both control purposes and viewing images on laptop)
- Ability to produce RAW files (no image processing)
- Versatile (can be used as ordinary "family" camera)
- Expensive (compared to general webcams that is)
- Heavy (affecting telescope balance)
- Generally used only for single frame captures
- Prospect of fouling mount base (so not being able to image near zenith)
- Difficult to focus (as viewfinder is designed for bright, daylight, use)
Don't be lured by the large pixel ount of a DSLR - eg 18Mpx - as some quite stunning images have been obtained using humble webcams with a 640x480 resolution (= 0.3 Mpx!). The larger the megapixel count, the larger the image files are and the more processing power and time it takes.
The Celestron NexImage and Meade LPI are (in the UK at least) around the £80-120 mark and produce decent images. The cheapest DSLR that I'd recommend - Canon 1100D - is at least twice to three times that price. The NexImage has the same CCD chip as the highly-regarded Philips SPC900 (see below).
Recently, a company called Morgan Computers here in the UK had bought all of Philips old stock of SPC880 webcams (hardware identical to the much revered SPC900 and flash-upgradeable to SPC900 spec) and initially was charging £5.00 (yes FIVE) rather than the £90 that the SPC900 was selling for a few months before.
Sadly, they are now out of stock and being that this was an "end-of-line" item, it won't be coming back into stock.
It is interesting to see that whitebox SPC880's (even the unflashed versions) are selling at around the £50 and upwards mark on fleabay.
Most images that you see on Cloudy Nights and, indeed in the NexStar forum, have been produced with webcams of various kinds and then subesquently stacked and processed (using software such as Photoshop Elements) and are the result of hundreds of images produced as a video (.avi) file with the best frames "grabbed" by a program such as Registax, rotated if necessary and then stacked to improve the S/N ratio.
Webcams are fitted via a suitable adapter (often called a "nosepiece") into the telescope in place of an eyepiece. Viewing and focusing has to be done via the pc/laptop screen.
The only way that I'd advise getting a DSLR for AP work is if you were going to buy one anyway for general day-to-day use. To fit a DSLR to a telescope, you would need a suitable T-ring and T-adapter and the camera is then used in place of an eyepiece. This is called "Prime Focus" imaging.
You can also buy brackets to place your camera in a suitable place to "look" through the eyepiece - just as you wouls do. This is afocal imaging. The camera needs to be held rock-steady to avoid blurry pictures - hence the mention of a bracket.
Finally, a DSLR can also be mounted atop the telescope tube - again using a suitable bracket - in "piggyback" style where the telescope's optics are not used for imaging as the camera has its normal lens in place. This can be used for widefield shots of the night sky.
There is a great piece of software available for controlling Canon cameras (not sure if there is anything for Nikon/Sony/Pentax/Olympus DSLRs) called "Backyard EOS" and here is a LINK. Software is around $30 and you get a 30-day, full-feature "try before you buy".
For deep-sky (read long exposure) work, modified webcams or specilised AP imagers (such as those from Starlight Instruments or Atik) need to be used as thermal noise from the electronics (eg "amp-glow") needs to be controlled. Most of these modified webcams of specialised imagers are also activey cooled. That's when the prices start at £300 and just head on upwards.
If you can't find a Philips SPC880/900 webcam on fleabay then the Celestron NexImage has been getting some good reviews. Astronomics (sponsor of Cloudy Nights) has the NexImage 5 for $199 (they are currently out of stock) - here's a LINK. If you buy from Astronomics - mention that you are a member of CN to get a discount (unspecified).
Hope this helps.
Posted 12 January 2013 - 11:27 AM
There's really 3 classes of cameras. There's DSLRs, CCD imagers, and webcams. Note that all 3 really have a CCD in them, so when I say CCD imager here, I'm referring to those designed specifically for long exposure astrophotography.
For planetary and lunar imaging, you want to take movies and stack the individual frames. A simple, cheap webcam will work really well here. Since most modern DSLRs have a movie mode, they can be used as well.
For good quality DSO imaging, a DSLR or a CCD image will work. The only disadvantage of the DSLR is that it has an infrared filter in it so it will not pick up some of the data on the red end that a CCD imager will. Of course, the DSLR has the advantage of being used for many other purposes as well.
If you opt for a serious CCD imager, you then have to decide between one-shot (captures all colors at once) or B&W, which requires taking a series of images through various filters to assemble into a color image. The advantage of the one-shot is, of course, simplicity. However, the B&W sensors have greater sensitivity and lower noise, and you can choose what spectral lines you want to image by selecting your filters. Also, since the B&W imager with a filter will be looking at a narrow band of the spectrum, this method of imaging does better in light polluted areas.
I personally like the DSLR as a choice for those starting out, or those who don't want to get too serious about AP. It is a very versatile solution that lets you do daytime imaging and take family movies, as well as use it for lunar/planetary movie-imaging and long exposure DSO images. There are many AP-ers who use them to create stunning images. The infrared filter is only a minor impediment, and if you really want to, you can have the camera "modded" to remove the filter.
If you get a DSLR, be sure to get a Canon. There's tons of software out there to control DSLRs for AP, and they all support Canon at a minimum. You also want to be sure to get one with Live View which helps with focusing, and with movie mode for planetary imaging. The articulating rear screen on some of the newer models is VERY handy when the back of the camera is pointing at the ground - which is common.
One option to consider, albeit an expensive one, is the Canon D60A. The "A" is for astronomy and it is designed with astronomers in mind. It has a filter that allows much more of the infrared through, and is supplied with many astro-friendly accessories such as an intervalomoter and an AC adapter. This camera sells for a lot more than the similar T3i, but is ready to go for astronomy.