You are currently viewing archive for July 2011
Posted by: Tom How
Repair job today at the Curdridge observatory. Webcams are popular in astronomy. They take great pictures of the Moon and the planets. With some fiddly soldering you can actually modify them to take longer exposures, e.g. 10 or 20 seconds.

This makes them useful "starter" cameras for people just starting out in astrophotography. Their popularity as imaging devices has waned a bit in recent years due to the advent of inexpensive DSLRs and CCD cameras, however, they are still useful as a guide camera.

My telescope is guided using an Off Axis Guider (OAG) unit I made. This type of OAG requires a guide camera with the sensor mounted at the front of the a 1.25 inch barrel. Not compatible with a webcam you might think... Several years ago I made a small camera case that fulfilled this requirement and mounted the webcam circuit board and CCD sensor inside it. At the same time the standard colour sensor was replaced with a black and white ICX098 sensor which makes the camera three times more sensitive. A few firmware re-writes and you've got a pretty competent little guide camera.

After years of faithful service, it stopped working the other day. The basic webcam function was ok, but the modified long exposure system didn't work. This is usually caused by a wire becomming disconnected inside the camera. The long exposure modification involves cutting the tracks on the webcam circuit board and soldering on some extra wires - soldering things on a 0.1mm scale often results in fragile connections.

However, two evenings spent messing about with the circuit and it still didn't work. Lots of blue language. Without the guide-camera the new telescope mount is an expensive garden decoration. Useless. Today myself and Pete completely dismantled and rebuilt the camera using a new webcam board (I have a lot of spares) and after far too many hours I got it working again.

Products like the QHY5 camera are available for less than 200 these days, so using modified webcams for guiding telescopes is not such a money saving trick as it used to be, but still gives you the DIY satisfaction.

webcam guide camera

webcam guide camera

webcam guide camera

webcam guide camera
Posted by: Tom How
An unplanned visit to Greg Parker at the New Forest Observatory yesterday to configure the computer systems for the new telescope imaging array that Greg is putting together.

Whilst waiting for the weather to improve so that the dome can be delivered the process of interfacing all the components with the computers has started. I think both Greg and I had under-estimated the amount of good old-fashioned IT services required to get everything working. So I drove over to help and we ended up spending the entire day sorting everything out and testing everything.

telescope imaging array

The imaging array consists of two (eventually to be four) small refracting telescopes. Each scope has a 10 mega-pixel cooled astronomy colour CCD camera attached to it. These cameras from Starlight Xpress are a delight. Each weights about 1lb and are about 75mm diameter and 70mm long. Fantastic engineering. The can cool the sensor to well below freezing to reduce noise on long exposures. Each camera is interfaced to the telescope via a 5 position filter wheel which takes the large 2 inch filters required. On the top is an additional telescope with a guiding camera whose job is to keep the whole thing pointing in the right place.

Each scope has a motorised computer controlled focuser system as well - adding another layer of things to interface to the computers. Of course, the telescope mount needs to plug into a computer somewhere as well - again, another serial connection. USB to serial converters are most useful here!

Initially I was confident that we can run both scopes from a single PC. However, because the devices are essentially duplicates, the manufacturer gives them all the same USB identifier code. Whilst these can be changed it still remains a challange to tell the imaging software (Maxim DL) which devices pair up together. Additionally, focusing is performed by a complex piece of automation software called FocusMax. Doing this reliably for two scopes on one computer is not easy. In the end, I crumbled, and went for the dual computers. Greg was right all along! After a bit of a struggle the device drivers for all the cameras, focusers, filterwheels and telescope mount were installed on all the computers and the guider working. And on both computers as well!We tested everything with the array pointing at the neighbour's house: Perhaps the most complicated peeping Tom in history!

Much time was spent showing Greg how the dual computers (down in the observatory dome) can be controlled via Remote Desktop from the PC in the study. We've got a quad monitor system setup on the computer in the study. This allows us to have a full screen remote desktop session to each observatory computer visible and still have a couple free to do imaging processing. I spent a lot of time setting up saved RDP config files and configuring auto logins so that Greg has an easy set of shortcuts to access the computers.

Next step: When Greg gets the dome setup, he can move the rig down there and do all the wiring more neatly than our prototype setup.

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