CCD camera

[EmanuelC]

Hey guys, how`s going?
Emanuel here, from Portugal, nice to join your forum.
Need some help, im trying to purchase a ccd camera, but im a completly rookie on this field.
I own a Williams Optics apochromatic refractor, a 132mm FLT, mounted on a Celestron Cgem Go-To mount;
For imaging, im using a normal, not modified, Nikon D3100, but i would like to do the next step, a dedicated CCD camera.
The thing is, i dont know what to choose; to be honest, i dont want to spend 3000 pounds or euros on it, but what really makes me confuse, its to understand the correct camera, pixel size, etc, suitable for this refractor, that is a F/7.
Any thoughts on this?
Thanks,
Emanuel

[NickK]

The first thing is work out what you want to image.

Next work out the field of view etc and then go from there - an example field of view calculator would be 12 string's ccd calc: http://www.12dstring.me.uk/fov.htm where you input the scope, camera and the looks at a variety of targets. The page will give a good feeling for the FoV.

The 383L is a good camera, although I think the 4xx series now eclipses this in my own opinion. However for bright targets (planets and solar) you'll want a fast exposure to reduce smearing caused by atmospheric churn. A fast frame rate is good to reduce the differences between the frames.

For DSO the frame rate and exposure time are really second to having low noise in my view.

I would suggest also thinking about using a mono and filters. One Shot Colour (OSC) is a nice feature but most astrophotographers switch to mono+filters as it allows narrow band etc.

[EmanuelC]

Hey Nick, thanks for answering.
DSO`s are my target; planets i do it with my oldtimer Phillips webcam SPC 900 NC.
Didn´t know that FOV calculator, very nice.
Most of the guys talk about mono over color, but, having a very dark sky, like i have, and being myself a newcomer to deep astrophotography, wouldn´t be better the color ccd for me?
Cheers

[NickK]

Hi,

The CCD sensor for all OSC cameras (including your DSLR) has a colour 'bayer' matrix that covers the mono sensor underneath. The upside is that you get a colour image for every sub-image you take however there the downsides are:
* the matrix reduces the actual image resolution - this is because each pixel is either R, G or B only. The values are averaged out in a process called debayering. This means you don't get a full image resolution for each R,G,B but an interpolated image.
* because the RGB filter is part of the sensor itself, using narrow band filters may be difficult or slower. This is because the more filters, there is a reduced amount of light at the desired wavelengths making the chip less efficient.
* it is not possible to adjust the exposure time for each channel. So it's possible for one colour to saturate but leave the others unsaturated.


For me. personally, I'm a detail/unusual object junkie rather than getting things perfectly beautiful which means I'll often use the mono by itself to see targets in more detail than I would before.

[EmanuelC]

Hi,

Humm, i see what you mean.
You know, thats the kind of information extremely valid, that i didn`t knew.
So, in this case, honestly, how difficult it is to to do an image?
Im just asking, not because im lazy, wich i am , but because, usually, i have one night to do astrophotography, and the next night will be....i dont know when... you know what i mean?
Is it perfectly normal to do a full object in one night, with all the subs, luminances, reds, blues and greens?

[chrisjbaileyuk]

Hi Emanuel

As someone who images with colour and mono CCD's I would say the time savings of colour over mono are not as great as you first think. A colour CCD works well enough on a fast scope but at f7 (which I believe your FLT132 is) you need long colour exposures to work well. Yes you do need to take R G & B and possibly L frames but you could well be taking shorter exposures so the net result is closer. With mono you also get a chance to do Ha imaging (yes you can do it with colour but why would you). With the FLT I would look very closely at the mono 490 which has enough pixels to bin colour frames and overlay unbinned L. With the extra sensitivity of the binned colour frames you would probably even out the colour vs mono argument completely.

Chris

[EmanuelC]

Hello Chris,
Yeah, im so use to do it in color, with the Nikon, that is taking me a while to jump to mono.
Overall, everyone is saying the same, the superior quality of the mono, by all the mentioned qualities, and yes, with the F/7 focal of the 132mm, i need long exposures, and most probably the color will not be uniform with OSC cameras.
Perhaps if i use focal reducer things can be better, but... this is something i really need to think over...