Follow Us


Altair Planet Killer 685nm IR Pass Filter – test with GPCAM camera

Home/Altair Planet Killer 685nm IR Pass Filter – test with GPCAM camera
Altair Planet Killer 685nm IR Pass Filter – test with GPCAM camera 2017-02-06T15:38:11+00:00

Ever looked through a telescope with a high power eyepiece? You’ll notice the air shimmer, kind of like a “heat haze”. What’s happening? Well, your telescope is magnifying air currents, as well as the distant object you’re trying to view. Heat causes convection currents in the air, changing the air density and that causes distortion by bending light passing through it.

By using your GPCAM in video mode you can “freeze” this apparent motion and capture a video file in either .SER or .AVI format. Once you have that you can process the file to discard the bad images and then stack and align the good ones into a much sharper image which averages out the distortion.

Of course if you start of with sharper images in the first place, you’re going to get an even sharper end result!

That’s where the Altair “Planet Killer” 685nm IR Pass Filter comes in handy, which is best used with a monochrome camera.


It allows infra-red light beyond 685 nanometre wavelength to pass through the filter and it blocks the shorter wavelengths.


Shorter wavelengths are the most affected by these air currents (often referred to as “seeing”), but the longer deep red and infra-red wavelengths aren’t as affected.

So your video appears noticeably sharper and more contrasty, making it easier to focus. And of course if you stack these images you get a much better end-result. Use AltairCapture or SharpCap to capture the video and Registax or AutoStakkert to stack and process this into sharp images.

What’s more, you can get better results that you otherwise would when the object is low on the horizon (you’re looking through more air after all). You can also get a darker background when imaging during the daytime.

We send an Altair Planet Killer filter to Robin Glover (author of the GPCAM-compatible SharpCap image processing software) to try out on his Altair GPCAM Mono camera. Robin used his Altair 10″ F5 Reflector without any Barlow lens to capture some video of the moon in the early morning.

According to Robin “Conditions were windy and I had to have the side of observatory folded down, so the scope was catching the wind quite a bit. The moon was fairly low by this time and the sky somewhat hazy at that altitude, so not perfect conditions by any means. The filter definitely has an impact on the moon – more contrast and easier to obtain a good focus and be sure that it is in focus.”

Lunar image without Altair Planet Killer filter:


Lunar image with Altair Planet Killer filter:


Both images were processed through AutoStakkert – best 100 frames selected from 1000, same settings used in both. No sharpening or other post-processing applied. The original 16 bit .PNG files were converted to .JPEG, with same compression to save space. Exposures 1.2-10ms.

Attaching the Planet Killer filter to your Altair camera couldn’t be simpler, just screw it on to the nosepiece. Mono cameras with lenses ship with two CS-Lens adapters with built in filters. Make sure you have the “clear” CS Adapter/Optical Window attached and not the UV/IR Blocking one (pinkish hue). Otherwise you will block out the IR light your’e trying to pass! Here’s a diagram:


Want to experiment? How about L-RGB planetary imaging with two cameras and one filter! 

You could use your Planet Killer filter as the Luminance filter when doing L-RGB imaging with a mono camera, filter wheel and Altair Premium Dichroic LRGB CCD filter set.

Or, instead of using a filter wheel, you could even combine the data from your mono GPCAM and Planet Killer filter with colour data from a colour GPCAM!

The possibilities are endless…