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5" Apo Refractor, Good for Imaging and Visual
Description
Askar's new 131F Flat-Field quad refractor offers sharp images and versatility at a reasonable price.
Like its smaller siblings, the 131F's optics cover full-frame imagers, without the need for a field flattener. Backfocus distance doesn't need to be precise, making astrophotography simpler when using filter drawers, OAGs, and other accessories.
The 131F's 983mm focal length gives you a 2.1° field of view on the long side of your full-frame imager, 1.4° with APS-C cameras, and 0.77° with a 1" (2.7x crop factor) camera.
NGC7293 | Askar 91F Flat-Field + ZWO ASI2600MC
Unlike astrograph refractors, the 131F can be used for visual observations, as well. (You'll need to provide your own finderscope, diagonal, and eyepieces.) With a 2" diagonal and a good 35mm wide-field eyepiece, you'd get about 28x and a 2.4° field—wide enough to fit a lovely view of the Andromeda Galaxy, or the Pleiades Cluster (M45). The 131F will respond very well to high-power views with a short eyepiece, too—great for planets!
Specifications
| Aperture size | 131mm | |
| Focal length | 983mm | |
| Focal ratio | f/7.5 | |
| Objective lens | Quadruplet air-spaced APO(including one ED glass) | |
| Image circle | 44mm | |
| Maximum accessory connection (with the focuser fully retreated) |
Imaging mode: 73mm (from the base of M48×0.75 male thread） 91mm（from the base of M54×0.75 male thread) |
Observing mode: 131mm（from the end of 1.25" eyepiece holder） 141mm（from the end of 2" eyepiece holder） |
| Minimum accessory connection (with the focuser fully extended) |
Imaging mode: 43mm (from the base of M48×0.75 male thread） 61mm（from the base of M54×0.75 male thread) |
Observing mode: 101mm（from the end of 1.25" eyepiece holder） 111mm（from the end of 2" eyepiece holder） |
| Total length |
878mm(including 1.25" adapter as dew shield contracted） 963mm(including 1.25" adapter as dew shield fully stretched） 941mm(including the photographic adapter as dew shield contracted） 1026mm(including the photographic adapter as dew shield fully stretched） |
|
| Focuser travel length | 30mm | |
| Net weight | 7.9kg | |
| Gross weight (Including tube ring&dovetail plate) | 9.4kg | |
| Rear-end thread type |
M78×1-M54×0.75 M54×0.75-M54×0.75 M54×0.75-M48×0.75 (with M48×0.75 filter thread) |
|
| Standard package items | A 131F OTA，a pair of tube rings, a handle, a 300mm Losmandy dovetail plate,a set of photographic adapters | |
