Rainbow Optical and Baader Planetarium offer spectrum devices that come with a cylindrical lens, does your Type D unit come with a cylindrical lens for viewing star spectrums?
Cylindrical lenses are used to defocus/spread the spectrum perpendicular to its axis to make the spectral lines in the spectrum are more easily visible. These lenses are expensive and very generally quite inefficient and you need a lot of different ones to cover different combinations of stellar magnitudes, eyepieces (yes, you need to match it to your eyepiece) and telescope sizes (see the Next FAQ Question for more details). There are other more cost efficient ways to achieve the same effect without using a cylindrical lens, for this refer to our How to Focus FAQ Question. The Type D1/D3 Filters can be used with just about any eyepiece, that accepts standard 1.25″ filters, for strictly visual observations. The Type D Filter does not come with a cylindrical lens, as is supplied with similar products from competitors. The reason we don’t offer a cylindrical lens option is because no visual spectrum filter made by any manufacturer, no matter what they might say, will produce spectrums of
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