Help me choose a camera

[JohnC]

Advice please chaps.

Budget is £500 or there abouts.

I want the best colour camera i can get, for use with Lx2oo with 6.3 field reducer.

Main contenders are Atik and DMK.

I am also purchasing a Watec 120n for visual astronomy for outreach sessions at local schools.

Any comments from users would be appreciated.

Hope to add ED80 to the rig soon.

Many thanks in advance.

John

[RobH]

Hello John,

It depends what you want to image.

For the moon and planets, the DMK.

Deep sky, The Atik.

Cheers

Rob

[JohnC]

Thanks, main interest are galaxies and nebulae.

[RobH]

The Atik then, the DMK is a fast frame rate camera ideal for shooting several thousand short duration frames which are then stacked using a program like Registax, where the good quality frames are selected and then combined into the final image. Because of the short duration of the frames, you can take advantage of the moments of good seeing and to a great extent neutralise any atmospheric distortions.

The Atik is a differnt type of camera, which has a very sensitive CCD chip and is used for taking much longer exposures in order to capture faint detail.

You can get either monochrome cameras, or One Shot Colour (OSC) cameras. With the mono cams, to produce a colourimage, you will need to shoot separate red, green and blue images through coloured filters, and then combine these into a colour image later.

OSC cams have a red, green and blue matrix on the chip and will give a colour image without the use of filters.

Mono cams have greater resolution and sensitivity though.

Hope this helps

Cheers

Rob

[JohnC]

Thanks, sorry to bombard you with questions!

What model due you recomend?

New or secondhand.

I think that i would be satisfied with a single shot colour for sometime as i have only limited time.

Is the loss in resolution great between monochrome and colour?

[RobH]

Hello John,

In practice you won't find a huge loss in reslolution between a mono cam and a OSC.

The difference is that in the mono cam, every pixel is used.

In a OSC, each pixel has either a red, green or blue dye on it, so, red, for example, will be recorded on 1/3 of the amount of pixels as if you used a red filter with a mono cam. The matrix of coloured dots is called a Bayer matrix.

What you will notice, on very faint objects, is a lack of sensitivity compared to a mono cam. However, there are loads of deep space objects that will come out great with a OSC, and only if you're trying for really tough objects will you notice a problem.

Check this out....a great camera

http://www.firstlightoptics.com/proddetail.php?prod=atik_16ics

Have a word with Steve at FLO....he may have something along the same lines or better secondhand.

Cheers

Rob

[JohnC]

Thanks Rob

I was getting a bit bogged down in all the various cameras.

Do you have an opinion on the DSI III?

I had a play last year with the DSI I and their drizzle software. I thought that it was good for a beginner but they do seem to get knocked.

I wonder if that is justified?

Many thanks for taking the time to answer my questions.

John

[RobH]

Hello John.

Ask away....no problem

The DSI 3 has a great chip, but is an uncooled camera, as are all the DSI range. This means that you have to be really thorough with dark frame aquisition, making sure that your darks are taken at pretty well the same temperature as your light frames (your actual images).

The reason for this is that in an uncooled camera, there will be a lot of thermal noise, the amount of which changes rapidly with temperature (higher temp=more noise), and this noise is removed by subtracting a matching (temperature an exposure time) dark frame. Also, the longer the exposure, the more noise.

All of this can be a right pain, as you have to shoot darks during your imaging session, or spend ages shooting a library of them for different temperatures by putting the camera in a fridge and changing the temperature.

The Atik is a cooled camera, and as such has far less thermal noise. While it's still a good idea to take darks, it's by no means as crucial, and there are various stacking algorithms that will remove the small amount of noise that you will get.

I started with a DSI pro 1, and, while it was good to learn the discipline of temperature matching darks etc, it soon became rather tiresome, and even a 2 degree change in temperature during an imaging session can wreck an image if not correctly dark subtracted in an uncooled camera with long exposures.