Product Description
New for 2024, this is a new field flattener designed for our 127 mm - 180 mm refractors. This is a full frame photographic field flattener.
Attaching the flattener to your focuser: The focuser attachment thread on this flattener is M75X1. We make numerous adapters so it will attach to any focuser used on all our 127 - 180 mm telescopes. When you order this flattener, select the focuser you use above, and we will provide you with the appropriate adapter. The flattener will thread to the adapter and the adapter will thread into your focuser.
Attaching the flattener to your camera: Cameras use various thread sizes. The SFFX-3 field flattener will come with a camera thread adapter that matches the thread on your camera. When you order the flattener, select the camera thread size you need, and we will provide the appropriate adapter.
To get optimal performance, photogrphic field flatteners must be placed at a precise distance from the camera's sensor. Most DSLR's and astronomy cameras have a sensor that is 55 mm from the camera's T-ring or attachment thread. This distance is often referred to as back-focus. It has nothing to do with focusing so many people get confused by this term. It simply means there is 55 mm from the camera's sensor to the camera's attachment thread (where the camera threads onto the field flattener). Recognizing that most cameras have a 55 mm back focus, we provide our field flattener with a 38 mm extension tube behind the flattener. With this 38 mm extension tube in place, the field flattener works best with the sensor 55 mm from the camera adapter on the field flattener. So, if you are using a DSLR camera with T-Ring or a camera with accessories that give you a 55 mm back focus, DO NOT remove the 38 mm extension. Merely screw the field flattener as it came into your camera system.
If your camera system with its accessories (filter wheel, off-axis guider, etc.) is more than 55 mm from its attachment thread to the sensor, you may increase the back-focus of the field flattener to compensate for this. To increase the back-focus of the flattener, remove the 38 mm extension and replace it with shorter extension tubes and spacer rings. You may obtain shorter extension tubes and spacer rings for this purpose on the M69 extension Tube Page on our website.
To better understand this, look at diagram-1. As you see, the 38 mm extension tube is in place and the camera sensor is 55 mm from the rear of the field flattener. Most cameras (with their included accessories or extension tubes in place) have this 55 mm distance from their attachment thread. So, in this case, one merely screws the field flattener to the camera system.
Now imagine your camera has accessories that increase the distance from the camera sensor to the camera's attachment thread to 59 mm. In this case you will need to remove the 38 mm extension tube from the field flattener and replace it with a shorter (34 mm) extension tube so that the field flattener has a 59 mm back focus, matching the camera. Looking at our webpage you will see that there is no 34 mm extension tube but there is a 33 mm extension tube and a 1 mm spacer ring. Buy one of each of these, install them in place of the 38 mm spacer and you will have the needed 59 mm back focus spacing.
We designed our field flattener with a longer back focus to accommodate those who want to add a camera rotator between their field flattener and camera. Using our 69mm to 68mm adapters and shorter extension tubes, one can add a rotator and still remain at the proper back focus.
Questions? Call us at (530) 823-7796 or email us at mail@stellarvue.com.
