On Thu, 28 Apr 2005, Gary McKenzie wrote:
I have tinkered with my -DS a bit taking some star photos. Nothing more than 5 minutes so far. A few things I've discovered:Hi, I'm thinking of buying a Pentax *ist DS Digital SLR specifically for astronomical imaging and would appreciate some info on the camera.
Specifically, what chip is used as the ccd sensor - I have been told that it is the same ccd as in the Nikon D70? Is this so?
Also, is the IR filter removable (this is to increase red sensitivity for Hydrogen Alpha images) - on a Nikon D70 it is removable relatively easily, and on Canon cameras is a royal pain to remove.
Is the "raw " mode truly raw?
What are the noise levels like on long exposures- several minutes plus....
Thanks in anticipation,
- Noise reduction works pretty well, but halves the available photo time (since the noise reduction shot takes the same amount of time as the exposure). I have not tried taking a single black frame and subtracting it in post-processing. Ideally, that should be done in RAW anyway (before the bayer interpolation), and I've yet to find a tool to do that.
- Raw mode is more RAW than is desirable, actually. It's a bastardized TIFF file format with 12-bit uncompressed (but packed at least) raw sensor data. There are also at least three low-quality JPEGs embedded in it... one of them full size so it tends to be about 10-15% of the filesize for normal photos.
- You will need the AC adapter for any long-time exposures. I posted awhile back on the voltage/current of the power adapter and someone responded with 6.5V, 3.0A. Since I'm a cheap bastard, I have modified a 6V 1A wall-wart power supply to provide 6.5V. Yes, the 0.5V difference is important... the camera will shut off on long exposures thinking the battery is dead with 6.0V. I measured the current requirements under various conditions as follows (6.5V lab power supply)
0.073A On (standby, light meter inactive) 0.172A On (meter active) 0.253A Meter and LCD active 0.608A Bulb, shutter open 0.450A Noise reduction frame in progress (after Bulb shot) 0.120A SD card write 0.3-1.5A Internal flash recharging.
Someone else mentioned which sensor it uses... Sony ICX413AQ. I managed to find a datasheet for it awhile back, but it didn't have a whole lot of useful useful data on it (unless you were going to build your own camera). The sensitivity plot on http://www.deep-sky.co.uk/dslr/dslr.htm was lifted from it. I do not know how easy the IR filter is to remove... if you find out, let me know... :)
-Cory
************************************************************************* * Cory Papenfuss * * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * *************************************************************************
