Amongst Lunt telescopes, there are a number of versions with different features. The model which is on offer can be deduced from the label.
An important price-influencing feature is the blocking filter size. There are 4 different blocking filters, with diameters of 4mm, 6mm, 12mm and 18mm. These are known as the B400, B600, B1200 and B1800. Unless otherwise stated in its name, an OTA does not include a blocking filter.
CaK or Ha indicate whether the devices are optimised for blue calcium spectral lines or for red H-alpha spectral lines. Over 90% of devices on sale are H-alpha devices, designated with Ha.
C or FT are used to distinguish between two versions of focusers. C is for standard focusers. FT is an improved model produced by FeatherTouch.
PT denotes devices with air pressure fine-tuning. Filters without PT use tilting for fine-tuning. Generally, air pressure models provide a more homogenous image field.
DS or DS50 are the identifiers for double stack. These devices have 2 etalon filters. These create narrower bandwidths and improved contrast.
2 numbers separated by a slash can also be found in the name. The first number denotes the diameter of the front lens. The second number is the focal length. So, a 60/500 is a telescope with an aperture of 60mm and a focal length of 500mm. Lens diameter generally refers to the diameter of the provided etalon.
(Bernd Gährken)
