Good Webcam IR/UV filter?

[Cragproductions]

Hi,

I have recently been trying astrophotography and had reasonable sucess with a webcam i bought off ebay. i was quite happy with the detail I got from a humble 130mm skywatcher explorer.

The problem I had was the filter that came with the webcam was an IR block filter (or whatever) that only allowed IR to pass, rather than block it out. This made my images B&W.

I took the filter off and tried some imagine, and have sucessfully been able to get colour - but the quality is very fuzzy and blurred. (with the best focus possible). The webcam footage with and without the filter looks identical, appart from the noticable increase in fuzz wihtout the filter, but when running through registax almost no new detail comes out without the filter, while with the filter detail just jumps out.

I was under the impression that newtonians didnt need these IR/UV filters, but seems they do.

can anyone advise whether i do need a filter, and if so, please advise what reasonable priced £20-30 filter I can buy that will 'crisp' up my images to a similar level I had with the IR limiter filter.

p.s. it is possible that it is seeing, however, the last few nights have been exceptionally clear. But im also aware that clear isnt always best.

many thanks.

[Cragproductions]

Here is the comparison. Ive gone a bit over the top with registax on the colour while trying to get some detail out.

These are my 3rd and 4th night imaging retrspectively so I do have some way to go.

It just feels like a step backwards now that im imaging in colour.

The only difference is the colour one has an added 2X barlow stacked (without the lense so its just the tube). I did try with just the TAL 3x, but its was just as bad.

Thanks

Dave

[Cragproductions]

Anyone?

Spent another night trying to image and still no sign of any detail.

It feels like the wavelets fo nothing except generate onion peel!

Many thanks

[Cragproductions]

I also notice that while capturing my colours are shifted quite a bit. Roughly 5 / -5 on the y axis (in registax RGB shift)

Could this be the cause?

If so, can it be resolved?

[JamesF]

The two problems are related.

It's probably easier to get focus in IR-only because you're only talking about a limited range of wavelengths. When the light reflected from a planet enters our atmosphere it is refracted by the atmosphere itself, just as with a lens (and if you have an achromatic refractor it happens in the lenses *as well*). All the light rays are bent, but some wavelengths more than others, making the image blurred and harder to focus.

Unless you're going to image in LRGB you probably have to live with this and just do the best you can at focusing time. A Bahtinov mask may well help, but personally I just do it by eye from the capture display.

Once you've aligned and stacked images in Registax there is an "RGB Align" option in the wavelets section. Click on that, extend the rectangle it pops up so it encloses the planet and then hit "Estimate". It normally does a pretty good job.

James

[JamesF]

Oh, to return to the original IR/UV filter question...

I use a Revelation/GSO IR filter on my webcam and find that to be sufficient. I don't filter UV to my knowledge. The reason for filtering IR in a "visible light" image is that webcam "red" sensors are quite sensitive to IR and without the IR filter you can end up with an image that's very over-exposed in the red channel.

James

[Cragproductions]

Cheers James.

I will pick a filter up and see if that helps clear the image up.

It could be that seeing hasn't been that great, even though it's been exceptionally clear the last few nights.

I bought an autofocuser which is invaluable for focussing, but it's really hard to tell if its in focus or not since its fairly fuzzy anyway. But I can see 2 bands quite clearly.

Thanks again.

[JamesF]

A filter might help push the image back towards a more "normal" visible light view. Unless you go for the full narrowband imaging gig then you're probably stuck with some of the blur unfortunately. The best way to combat it is to image objects when they're as high in the sky as possible because the atmospheric distortion is greater the lower they are.

James

[Tribal-Wolf]

You don't need an IR filter with a reflector telescope, I have one that came with the cam adapter and never use it as it kills the light too much for me.

I have no probs without it.

[JamesF]

You don't need an IR filter with a reflector telescope

I'd say it would be beneficial because the reflector would still capture the atmospherically refracted IR light and bring it to focus on the sensor (in the wrong place). The effect will presumably be far more pronounced when imaging something near the horizon than up near the zenith however.

That doesn't mean that some correction isn't possible after the fact, or that an IR component to an image is undesirable (a decent IR component may even contribute positively to the quality of an image).

Is there some property of reflectors that I've failed to take account of?

James