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By reducing the focal length of the telescope (for example, a 500mm focal length becomes 300mm), this 0,6x reducer/flattener increases the area framed by the camera sensor. In addition, decreasing the focal ratio of the telescope (for example AIRY APO80 f/6.25 becomes f/3.75), it allows you to record weaker details. Designed for photographic use with AIRY telescopes, it offer an extended correct field and it can be used with many different refractors.
Focal reducers are used in long-exposure astrophotography of deep-sky objects like nebulae, star clusters and galaxies, and in order to get the best images, it is important that the field of view framed by you camera to be flat (that is, the stars have point shape in all the field). Since reducing the focal length also the field is generally reduced, in this table you will find not only the focal length and focal ratio created by the use of the 0,6x reducer/flattener but also the size of the corrected field. This way you can check whether your camera sensor will be suitable for use in astrophotography (eg Atik 428EX CCD camera has 11mm diagonal sensor so it needs at least 11mm of flat field to have images with pinpoint stars in all over the field):
|Focal length with con
|Focal ratio with con
|AIRY ED72||432mm||f/6||not available||not available|
|AIRY ED90||500mm||f/5.5||not available||not available|
|AIRY BLACK 90T||600mm||f/6.7||360mm||f/4||14mm|
|AIRY APO120||900mm||f/7.5||not available||not available|
|AIRY APO130T||860mm||f/6.6||not available||not available|
The 0,6x reducer/flattener into 50.8mm connection of the focuser (in front it has a thread for connecting 50,8mm diameter filters). Rear (camera side) it has a T2 male thread and therefore it can be screwed directly onto the DSLR cameras ( using a T2 ring of the camera brand) or to a CCD camera (with T2 female thread).
700Da camera connected to the AIRY ED100 refractor with reducer/flattener
This reducer/ flattener, in order to offer the best performance, requires that the camera sensor is positioned at 55mm distance from the reducer thread. This is precisely the distance provided by connecting the DSLR camera with T2 ring. For the use of CCD camera (that offer a sensor placed in more front position than the one of a DSLR camera) it is necessary to add a T2 extension. To calculate the required thickness, you can use the formula:
required T2 extension = 55mm required distance - CCD camera back focus
So, for example, if you use a QHY8L CCD camera that has 20 mm backfocus, the T2 you need will be: 55 - 20 = 35mm.
This focal reducer fit perfectly to my AT11EDT with the small sensor of my ZWO 178MM cooled. Stars are clear and round all over the field. No distortion are viewable. I just can't pronounce on the amount of light that is consumed by this accessory.
I am happy, now, I own a nice astrograph.