CCD vs CMOS

[Struders]

Just a quick question, again. I have been doing some research into using webcams for taking pics.

Now I keep seeing that ccd chips are more desirable than cmos, why?

...And I'm also reading that ccd's work better when there cooled again, why?

[riklaunim]

CCD noise reduces better then temperature drops down. Design feature. So you don't see astronomy DS long exposure cameras with CMOS sensors.

As for webcams. Cheap CMOS cams will be bad, however top-brand models will work as good as SCP880NC/900NC or even better (the "HD" webcams with bigger modern sensors and USB 2.0).

[jgs001]

Something to consider... the Canon dSLR cameras that most of us use, have CMOS based sensors. I don't know Nikon. Comparing the CMOS in my QHY5v to my CCD based SPC900, the 5v is better, but that might be the mono and USB2.

[themos]

The way it's been explained to me is that CMOS chips waste a bit of real-estate on the chip for support electronics instead of photon-sensitive material. But recently, "microlensing" has enabled CMOS chips to catch up as they nudge the otherwise wasted photons into the right area of the chip.

[brianb]

But recently, "microlensing" has enabled CMOS chips to catch up as they nudge the otherwise wasted photons into the right area of the chip.

But CMOS still has more variattion in photosite sensitivity than CCD ... because each pixel has its own amplifier and they don't all have the same gain. This translates to image noise. They also run hotter, again increasing image noise. The upside of CMOS is the faster readout which is possible.

[themos]

good points, brian.

[malc-c]

Does anyone know if the Celestron NexImage (which I understand is a re-housed spc 900) can be made to capture DSO by cooling it down using a dry ice cube for example, or does it require the use of the CMOS 40xx chip switching mod ??

[Struders]

Interesting reading so does cooling the chips help reduce the noise?

I have 2 small peltier thermal elements doing nothing and a load of old pc heatsinks... I can a little project coming together here!

[riklaunim]

Does anyone know if the Celestron NexImage (which I understand is a re-housed spc 900) can be made to capture DSO by cooling it down using a dry ice cube for example, or does it require the use of the CMOS 40xx chip switching mod ??

NexImage is just a webcam like SPC900NC, but with custom firmware. It has no long exposures so it won't work for DS imaging. First thing sorted by price that can do DS imaging are QHY5 cameras - http://astrofotky.cz/~rick/ and http://thx8411.over-blog.com/pages/Cooling_the_QHY5_imagerautoguider_step_1-3170312.html

Using dry ice isn't a good idea. Strong cooling of open camera can cause water vapour to condensate or freeze inside the camera potentialy destroying the electronics or fogging the sensor window.

Peltier cooling can be use with propper housing of the camera. You can do a cold finger or a cold box (with desiccant) design to use the peltier cooling of the sensor with limited risk of water condensation.

[malc-c]

So where I was steered towards the NexImage, I would of been better off paying the extra £50 for an QHY5 QHY5 Guider & Imaging Camera | Telescope Accessories | Rother Valley Optics

[brianb]

Thermal noise in silicon based sensors roughly halves with each 7C decrease in temperature, but thermal noise isn't the only sort that's involved. Cooling sensors does help, but in the case of webcams, you also need the electrical mod to enable long exposures to be done at all.

Condensation onto the sensor surface is a very real issue if sensors are cooled. Staring with a Neximage, you'd need to replace the whole casing - in fact you'd need to replace the casing to get a Peltier cooler anywhere near the chip ....

.... More trouble than it's worth, IMHO.

[Digz]

Something to consider... the Canon dSLR cameras that most of us use, have CMOS based sensors. I don't know Nikon. Comparing the CMOS in my QHY5v to my CCD based SPC900, the 5v is better, but that might be the mono and USB2.

For completeness, older Nikons have CCD (D70, D200 etc) however some of newer models (D7000, D300, D700 etc ) have CMOS.

[Struders]

After all the comments and research I present to you my brickcam! from a few parts I had laying arround I've managed to put together this...

...its the best thing I've ever made!!!

Dont know how good this is going to be at imaging, should be able to get the moon though I think. I tested it today with a seagull sitting on the roof quite far away and got some pretty good results so far.