Filters or Filters?

[scotty365]

Im confused which set to buy, LRGB or the H-alpha, OIII, SII. Can anyone tell me the differences, I intend on imaging various nebulea. I intend to get a I/R-U/V filter, however Ive read that these filters already remove the unwanted I/R?

Confused,

Scotty

[bern]

Hi Scotty,

The L filter in the LRGB set is an IR/UV block filter. The other filters don't need additional filtering as long as you buy good quality imaging filters from a reliable source.

LRGB is for creating true colour images with a mono camera, the Ha, OIII and SII filters enable you to create pseudo or false colour images which can reveal intricate features in emission objects. They're also useable in full moonlight.

bern

[Kaptain Klevtsov]

What camera are you going to use?

With a DSLR you don't want to use RGB filters as they're already in the camera so its pointless doing seperate colour shots anyway, same goes for a colour webcam or CCD imager.

Narrowband filters (OIII, Ha, SII etc) will not work very well with a DSLR or colour webcam, these work best with a mono webcam or CCD. The narrow bandpass filters out all the light except that of a very specific colour so for example, the Ha filter only lets some red light through so you dont get anything on the green or blue channel. As colour cameras have the RGB pixels split 25%:50%:25% (usually) you will only use 25% of the collected light as the rest will miss the red sensors. As narrow band filters by their nature filter out a lot of light you will struggle to get a useable image when using a colour camera.

HTH

Captain Chaos

[scotty365]

Okay I have a Toucam pro II (NOT modded) what would be my best option to make use of it?

Also, what affordable way forward should I take? Maybe buy a mono webcam or DSLR?

Scotty

[daz]

Either get your ToU modded for B&W and LX, or get one pre-done, or goto Astronomiser's web site - he does a range of commercial cameras that are the same guts as the ToU.

As the others have said, don't bother with the DSLR AND filters.

EDIT:

Bern at Modern Astronomy does a modded ToU Pro III for £179, plus either £249 for the narrowband filter set and £24 for the IR blocker, or £160 for normal LRGB.

How's your wallet feeling??? :)

[bern]

Definitely consider getting the Pro II LX modded for a cheap intro to deep sky imaging.

Once you get some experience I'd then recommend an entry level CCD camera like the new Atik 16IC or if you can get a cheap DSLR that's worth considering too.

bern

[Kaptain Klevtsov]

The Toucam will do wonders on bright planets and the moon. That's about where it stops.

With your existing kit you could go two ways, either DSLR or modified webcam. Here's the whys and wherefores for both.

DSLR

This has a relatively big chip so the image scale would be 1 1/2 moons high X 2 moons wide or thereabouts. If you can get a good view of Polaris then the HEQ5 polar scope will get you close enough to polar aligned for exposures up to 2 minutes without trailing. This will be good for most of the Messier objects although M31 will not fit as its too big. With this setup you can do a photographic Messier marathon and get pictures of the full set. The DSLR also does colour without a lot of faffing about which helps with things like the Dumbbell nebula which has pretty colours, M42 in Orion which is awesome (coming soon to a sky near you). Use the neodymium filter to get rid of light pollution

The downside with DSLRs is getting the focus spot on, unless you have it connected to either a seperate big preview screen or a computer. There are ways and means to get this sorted but its a pain.

Modified webcam

First off there are two types, the simpler ones do colour which is good, but the more modified ones are more sensitive with mono chips in them.

The webcams need to be connected to a computer so you need a way of getting the computer near the 'scope. A laptop is ideal.

The webcam chip is much much smaller than the DSLR chip so you will get really close up images (unless you get a focal reducer) and the image scale will be too big for a lot of Messier objects. The smaller M objects, such as the crab nebula, will fit the chip nicely.

Getting the object on the chip is quite difficult because of the small chip size, but you can use an eyepiece to find and centre the object first. Tracking is an issue with webcams as it is with DSLRs, but the image scale means that the image will fall off the chip much more easily.

Colour imaging is easy with the colour modified webcam, just point and shoot, whereas the B&W modified webcam has to do separate red green and blue images through coloured filters. This raises the issue of lining up the different images, so you then need a filter wheel where you can rotate a wheel under the camera having different coloured filters in the holder. As the filters don't have to be standard coloured filters you can use narrow band filters instead so that you don't suffer from light pollution and can still get (false) colour images.

As this has got rambly and messy, I'll pack it in now. If you need any more pointers just yell.

Captain Chaos

[scotty365]

As ever the info is fast and understandable, esp. from CC! Thanks everyone.

Right, I think I'd like to go for a lay down now.

Scotty

[bern]

Right, I think I'd like to go for a lay down now.

Good idea, just soak up info and wait 'til it all falls into place before making a decision.

bern, who likes to mix his metaphors as well as his drinks 8)

[Kaptain Klevtsov]

Don't mix your drinks, stick to straight snakebites (or Martinis for the ladies).

Captain Chaos (going to look up what a "meta" is for)

[FLO]

Good thread this - I am also trying to get my head around imaging!

If narrow-band filters such as OIII and Ha have limited use with a DSLR (because of its inbuilt Bayer filter array) is it at all possible/practical to photograph objects such as the the Veil Nebula (which responds well visually to an OIII) and similar, without filters?

Are there any filters that do work with a DSLR or colour CCD? Neodymium, or perhaps a UHC-S?

Thanks.

[Kaptain Klevtsov]

Filters that work well with colour webcams and DSLRs generally block bands rather than pass bands of frequencies. Good filters for DSLRs include deep sky, UHC, UHC-S, CLS, ALP and neodymium. The main reason for filters with colour imaging is to filter out light pollution which messes up the image. You can use narrow band filters with a DSLR if you run the exposures longer, you just have to make do with the lower resolution as you only get a proportion of the sensor being used.

Basically try it, with digital imaging the best thing is its free.

Captain Chaos

[FLO]

Thanks

[scotty365]

Thanks everyone for their input esp. C/C (always very informative) and an inspiration to me.

scotty