Imaging in Colour - Where do the filters go

[johnb]

Hi

I’m sure the answer is obvious, however. Currently I connect my dslr to a scope take a number of images and then stak and process – now for colour I believe I need to follow a similar but different process looking at various posts people do things like

L = 55 @ 5 min's

Ha = 10 @ 10 min's

RGB = 20 @ 5 min's each bin x 1

I’m assuming that we need filters for L Ha and RGB

Where do the filters fit, on the end of the scope ?, if the DSLR is attached to the scope no option there so even though it may be obvious to some its not to me ?

Thanks in advance

John B

[arad85]

If you have a DSLR, it has inbuilt filtering - it will have an RGB matrix on the sensor that will give you RGB out of the back of the camera. Trying to put another RGB filter in front of the camera will only increase exposure lengths.

Filter sets are generally applied using a filter wheel that sits between the camera and the 'scope.

Perhaps psychobilly (or others can help out on the pros and cons of using a H alpha filter and DSLR

[Whippy]

RGB filters are used with mono cameras. DSLR's and one shot colour (OSC) cameras as arad has already said, shoot in colour anyway so there's no need for colour filters. Ha filters only let through the hydrogen alpha light (Ha) emitted by various objects (mainly nebulae) which can either be used on it's own as a mono image or part of a colour image (false or otherwise).

Not sure about using Ha filters with colour cameras as I've never used one, but I think there's something about losing sensitivity or pixels involved. Someone who knows might be able to shed some light on this .

Tony..

[Psychobilly]

What DSLR is it...

Ha filters can be used on DSLR's to produce either mono images

or combined with the RGB data to produce HaRGB images...

Ideally the DSLR (easy if its a Canon) Should be modified to improve its Sensitivity to Ha...

Narrowband data can be captured on night where Luna would otherwise make things more difficult and also are largley "immune" to LP...

Peter....

[Merlin66]

You can use different filters to get different results.

For extreme narrowband OIII, SII and Halpha you really need a mono CCD preferably cooled!! This is serious stuff!!

A DSLR with it's original factory fitted in-built filter is designed 90% of the time for home shots of mum and the kids. The colour balance is achieved by using a UV-IR filter which cuts out the extremes.

The CCD chip in a DSLR has a peak efficiency around the green at 550nm and quckly drops off to 15% at the Halpha. This can be increased by pulling out the filter and replacing it with a special UV-IR filter (like the Baader) which will increase the efficiency at H alpha to around 35-40%.

So for DSO's etc and a DSLR the prefered solution is no filters , well other than maybe a Light Pollution filter if your skies are bad, and replacing the original filter - "Modding" the camera.