Off-Axis Guider - Tracking the stars the easy way
An off-axis guider provides an easy way of guiding the telescope for taking your astronomy photos. You do not need to mount a large and heavy guide scope, as this is easier - especially if your telescope cannot withstand much additional loading.
The off-axis guider is extremely compact and relatively lightweight. It is therefore also well suited for your photography using smaller telescopes / mounts.
An off-axis guider works really simply
The off-axis guider is easily slotted into your 2" focuser and clamped in place. It has a T2 thread on the camera side - standard for the easy adaptation of your camera. To take photos with a DSLR camera, you only need a matching T-ring - and that's everything.
When the light passes through the off-axis guider, a small amount is deflected via a small lateral prism. An additional 1.25" opening now lets you use your reticule eyepiece or an auto guider. You can then get started immediately after you have found a suitable guide star in the field of view.
Long exposures - Pin-sharp astronomy photos
You have probably seen many beautiful astronomy photos - magnificent galaxies with imposing spiral arms, red-glowing hydrogen nebulae, globular clusters whose countless stars look like they are embedded in velvet. All those photos were taken using long exposures - photos you can take using an off-axis guider.
You can now control the tracking precisely and achieve deep sky images with perfect pin-sharp stars.
Our expert comment:
The OAG comes with three T2 sleeves measuring 28 mm, 14 mm and 7 mm. These sleeves allow you to precisely adjust the distances between the off-axis guider, autoguiding camera and astro camera. The autoguider connection has a sliding focus with a travel of 7 mm. This allows you to compensate for any remaining focus differences.
On the telescope side, the OAG has a 2-inch plug-in sleeve. It has a T2 connection on the rear. The minimum installation height is 3 cm. The SC and most refractors have a back focus of 3 cm. For Newtonians, 3 cm is usually too much. In this case, you should measure before ordering to ensure that the 3 cm focus travel is actually available. The connections for the guiding camera and the astro camera can be rotated on the focuser without having to change the position of the OAG. The OAG can also be swivelled. It can be moved through an angle of about 100 degrees without having to rotate the camera. This allows the prism to cover a wide area, which significantly improves the chance of finding a guide star. In addition, the tilt angle of the prism can be adjusted by a few degrees, so that an additional area of the sky can be covered. The prism has an edge length of 9 mm. The chips of the guiding camera chips are usually smaller and are therefore sufficiently illuminated.
Suitable guiding cameras would be the Orion Starhoot or the Starlight Lodestar. If you do not want to work with an autoguider, you can use a classic reticle eyepiece. In addition to the reticle eyepiece, an eyepiece adaptor is required.
(Bernd Gährken)
