In November 2003 I found myself at the showroom of Bray Imaging in Leighton Buzzard, Bedfordshire. They had recently taken delivery of a TMB 105 (4.1") apochromatic refractor with the new lightweight tube. TMB - Thomas M Back has a reputation for good optics, and the test figures on this unit were very good. The 650 mm focal length and f6.2 focal ratio were just what I was looking for to use with my MX camera for medium field imaging, and the lightweight assembly made it an ideal go anywhere 'scope since it would ride reasonably well on my EQ3 mount.

So I purchased the tube there and then and brought it home with me.

However I soon found that there was a problem with the design. The tube was very compact due to a sliding dew shield and draw tube, incorporating a truly excellent feather touch focusser. But the sleeve in which the drawtube slid was simply lined with thin felt which can wear and compress. Consequently after only a small amount of use the drawtube became sloppy and the eyepiece was able to move out of alignment to such an extent that the finder needed adjusting as the mount changed position, also the collimation was compromised.

Fortunately Bray were most obliging and engineered an excellent solution, although the original tube was from APM in Germany. They manufactured two rings which clamp to the front (internal) and rear projections of the drawtube sleeve, and locate the drawtube firmly with lockable nylon grub screws. Not only does this allow adjustment for wear, but enables the drawtube to be accurately aligned with the main tube axis. Many thanks to Chris and Geoff!

With the drawtube and dew shield retracted the unit is very compact. Don't worry - the grass was dry!

The telescope now performs as expected, with a textbook Airy disc and crisp images free of false colour. Earlier CCD images exhibited some artifacts - see for example the Running Man image which shows shadowy incursions into bright areas, but the first image taken since the modification is excellent - see the M65-66 image.