Taina Because the budget is limited I did not want to buy two cameras, one for DS and one for planets.
Stefan, a camera that can stretch from planetary to DSO will be too compromised, IMHO.
For planetary, dark current noise is of no importance since the noise for short exposures will be dominated by the read noise (for each pixel, dark current noise is given in photoelectrons per second, while read noise is given in photoelectrons per pixel -- a constant number, no matter the length of exposure). Amp glow is also of no importance -- you won't expose for long enough to see amp glow. In the meantime, you want good sensitivity, so you can keep very short exposures to freeze atmospheric turbulence. Dynamic range is not really important because you will be stacking hundreds to thousands of frames; the stack will improve dynamic range. Size of sensor is rarely a limitation with planets. In fact, most of the time you will be using a only small region of interest from even small sensors. Downloading time is supremely important to get fast frame rates. Fast FPS is king.
On the other hand, for DSO, you will need very low dark current -- and that is where a cooled sensor helps. The length of time to read the data is of no importance (as long as there is fast readout to a on-camera buffer to keep the amp glow low). It is good to have low read noise (that way, you can use relatively short exposure times), but it is not mandatory -- if you have dark skies, you can use longer exposures to minimize the effect of read noise. Dynamic range is quite important for certain types of deep sky object -- to reduce the galactic center from saturation while getting sufficient exposure for galactic arm -- but even there, you can stack images with different exposures to achieve high dynamic range. Amp glow is somewhat important, but the problem can be minimized by taking calibration frames. Size of frame is important for nebulas, although less important for most galaxies (M31 is of course an exception, but there is only one M31 in the sky). Downloading time is of no importance -- taking 3 seconds to download an image with 300 seconds exposure is negligible.
So you can see that for almost every aspect, what is important for one type of imaging is the opposite of what is needed for the other type of imaging.
If you can only afford one camera, you would have to decide which aspect of imaging you want to do first. Because you don't need large sensors, a planetary camera will be cheaper, and you don't need expensive filters (a single Radian Quad filter cost more than a planetary camera). However, you need to weight the opportunities when a planet is favorable, versus when nebulas are available since there is so many more of the latter -- a DSO camera may actually give you more enjoyment per dollar per hour.
Speaking of building your own refractor, I ground my first 5" mirror in high school back in the mid-1960s :-).
Chen