IR Blocking Filter

[gitchnz]

The webcam I had been using to take planetary images is one I've removed the IR blocking filter from. Despite an extensive search, I have no idea where I've put it. So its colours are more than a little messed up.

I did something stupid yesterday, and bought a webcam with the sole intention of dismantling it so I could use its IR blocking filter in my existing camera. Little did I know that you can buy IR blocking filters for a little more than what I paid for the webcam. Of course, I discovered this after I'd dismantled and destroyed the original camera (which, in case you're wondering, had limited driver support and I couldn't change the frame rate, hence why I didn't just use it in its original form). 

I see GSO make an IR cut filter, which looks perfect for me to use with my original camera. My question is, what sort of attachment does it need? Everything I've read says that it attaches to any webcam or eyepiece that supports filters. My webcam attachment is currently a piece of rolled up cardboard, and is shortly to get replaced by a film canister. Neither of these support filters, obviously. Looking at all my eyepieces, they have threads on the inside of the non-viewing side. I assume this is where you'd attach a filter. With webcam imaging, of course, you don't use eyepieces. So I checked my barlow lens for the same characteristic, but it doesn't really have a thread, other than the one that is used to ultimately hold the lens itself in place. 

My question is, what on earth do you attach the IR blocking filter to?

[Leveye]

They come in a plate, they come in 1/4 inch and 2' inch threaded for whatever barrel you have or if you have a Canon EOS series you can buy a pop in that goes into the body of the camera. Look at Astronomics and Baader they make some of the best.

[gitchnz]

While I have a Canon EOS camera, I don't think I'll go down that route. There's a few reasons why. 

Most importantly, the mount with my scope is a little on the wobbly side, so pushing the shutter release button would probably cause too much blur. Also, mine is an old 300D which shoots, in drive mode, about 5 images as a time. Nowhere near enough to use for decent stacking. Also, I imagine that the large sensor size would produce tiny images of planets.

I was more interested to know what those with homemade webcam setups without threaded barrels use.

[Cornelius Varley]

Normally a webcam would be adapted to astrophotography use by using a nosepiece like this one http://www.firstlightoptics.com/adaptors/125-nosepiece-to-webcam-lens-thread-toucam-pro-spc900nc.html . The nosepiece has an internal thread that matches the filter thread and this is where the filter goes. If your webcam isn't suitable for one of these adapters you might have to be more creative in your approach ie mounting the webcam in a small plastic box and glueing an adapter to the box ensuring the sensor and adapter are square to each other.

[gitchnz]

Thanks so much. That's absolutely what I need right now. Since writing my last post, I've managed to track down a suitable driver for my new camera that allows for manual control of the exposure setting. Looking at the size of the image sensor on it, compared to my first webcam, it looked smaller. So I did some comparisons between the image size on both cameras using the same lens, and bingo - the smaller sensor on the new camera makes for a larger image. I calculated that planetary images will be 1.75 times larger than what I'm getting at the moment. 

The beauty of the adapter you mentioned is that it takes the guesswork out of aligning the nosepiece as it's likely to be straight.