Used: Baader Fluorit Flatfield Converter 3x bis 8x Barlow Lens

Baader FFC - 2" T2 Fluorit Flatfield Converter

This interesting accessory was developed by one of the ZEISS AQ designers in cooperation with Baader. In our opinion the FFC is the best projective that was ever developed. Amongst others, two multi-coated fluorite lenses are used. The FFC offers best sharpness on the axis and allows even using cameras with large sensors up to medium format.

Photographic use:

The FFC provides a female T2-thread at the telescope side and a male T2-thread at the camera side. These threads, very popular in photography, turn the FFC into a versatile converter which fits to any telephoto lens with T2 mount. Via the adaptions which we offer in the accessories section, you can connect the FFC to any telescope. Photograpically, the FFX also offers the focal length extension of 3x to 8x, with full quality in the field.

Visual use:

The Fluorit Flatfield Converter (FFC) is the most versatile and highest-quality Barlow lens we know. It offers the possibility of changing the magnification between the factors 3x and 8x without visible loss of image quality. For example, turn your 2" 30 mm widefield eyepice with comfortable view into a 4 mm planetary eyepiece without losing field of view or viewing comfort.

How can I achieve the extension factors with the FFC:

The longer the distance of the FFC to the eyepiece or camera, the higher the extension factor. The distance can be extended by using T2 extension tubes or rings, but you can achieve the same effect by using a star diagonal.

If you attach the camera directly to the FFC, for example with a T2 ring, you get an extension factor of 3x. You get the same factor if the field stop of an eyepiece is placed approx. 55 mm behind the FFC.

If you add 40 mm, for example with a 40 mm T2 extension tube, the factor rises to approx. 4x. Another 40 mm will result in 5x, and so on.

There are quite complicated methods for calculating the magnification, but it is more simple to make a test exposure without the FFC and then one with the FFC. The different image scale shows the magnification factor.

One practical tip: The higher the extension factor, the further the focal plane is shifted outwards, so you will have to insert additional spacers (T2 extension or 2" extension) between focuser and FFC.

Important warning for usage:

The FFC must not be exposed to the direct, concentrated sunlight behind the telescope for solar projection, as with eyepieces, filters or normal barlow lenses: the optics might be damaged. However, using it behind a front solar filter or a Herschel prism is uncritical. Similarly, the FFC must not be subjected to sudden temperature changes - the fluorite (calcium fluoride) lenses could crack in this case, too.