filters

f.n.g. i dont know a thin about optical transmittance or ir cut ect. but when i look at photos posted on the web there is usually some note about a filter or two. is there a beginner set or do i have to actually do research about this haha. im really more of a hands on guy. any thoughts thanks shiva

Are you talking about visual or photographic use? There are different filters used for each.

Photographic filters generally cut the UV and IR and may also only allow some specific wavelenghts pass. By cutting the UV/IR stars look sharper and smaller, the UV/IR would normally bloat the stars.

Visual filters are usually either coloured glass for viewing planetary details. There is also a cross over with light pollution filters which block wavelenghts which streetlights etc shine in. You also have UHC (Ultra High Contrast) filters which highlight some nebulae.

In short the filter needs to be targeted to a specific job. Identify the job and then look at what filters are available.

awesome concise answer. that is a good place to start from. thanks shiva

lets say i wanted to view and photograph andromeda with an etx 125at #497,5k 6.7 uwa 2x barlow, and canon rebel xti 10.1 mpx, sony cybershot 5.0 mpx. and lpi. in a heavily light polluted area with lots of moisture in the air (florida). would i use the magical aperture increasing, atmosphere clearing, power outage inducing. filter. if so how much is it.but seriously how much.

Well firstly the etx has a focal lenght of 1900mm so all you are going to get of the andromeda galkaxy is the bright nucleus. You need a much shorter focal length scope, even a camera lens, to fit in all of M31 in!

Lets forget the target for a moment.

Your rebel xti is the only camera to use out of that lot certainly for deep sky imaging. You should look at coupling this to the ETX by means of a t-ring and appropriate adaptor. i.e replacing the lens of the camera with the etx. The etx now becomes the lens. I really would not be too worried about filters until you've got this bit sorted. This is the 'prime focus' method and is defintely the way to go.

Next thing to worry about is getting sharp stars on your image. You've two things to worry about here, focus and tracking. Focus just takes paractice. Tracking (guiding) is another problem altogether. Although your scope may look like it tracks perfectly, anything more than a very short few seconds exposure will reveal stars as little lines rather than round. I'm afraid doing something about this with the ETX is gonna be a problem. With bigger scopes and mounts you would 'guide' the scope by some means (usually another telescope piggybacked on top) to correct for the drive errors. However you clearly can;t do that with the ETX.

So you need to use the ETX for what it is good at and that will be photography of the Moon and planets. Using your LPI you will get great results by taking video files and processing these with the magical and wonderful (and free Registax . Guiding won't be an issue here and neither will light pollution. So this looks like the perfect place to start since you already have everything you need to get up and running. Give it a go and you will be stunned at the results.

To answer specifically your question; for deep sky photography a good filter to start with is a 'Broadband Light Pollution Filter' (Orion USA do a good one). This will also help with visual views of nebulae (but not galaxies).

In summary start with planetary lunar imaging with the LPI and see where that takes you.

thanks for the advice bought a set of orion beginners 6 in all with a variable polarization. also a meade neutral density. the info page they came with was also very useful. think i will keep that handy. the set had your suggestions plus a couple. thanks shiva