Thanks to the many available adapters, you can easily use ESATTO as the new focuser for refractors and improve performance, especially in astrophotography. Refractors, and especially the apochromatic models, are perfect instruments for astrophotography since they haven’t a very long focal length (you can use them for very long exposures also with affordable mounts) and they combine very good performance with easy of use. But many refractors use a focuser that may not be able to adequately support your camera and the accessories used in astrophotography: let’s see how you can improve your refractor telescope by replacing the focuser with ESATTO.
Some of the problems you may have with standard focuser
Astrophotography, especially the one aimed at deep-sky objects, requests not only for specialized cameras (usually with large sensors and with a cooling system) but also for many accessories like large motorized filter wheels. When you have such a large “imaging train“, the first thing to consider is its weight: in fact most of the refractors (especially the ones with an affordable price) are not provided with a high weight load capacity focuser that is fundamental to perfectly keep the camera in the focus position during the long astrophotography exposures, especially when the telescope is pointed to the zenith (the vertical position). If your focuser has not enough weight load capacity, your camera and accessories will slip and will bring your sensor out of focus. But if we use ESATTO as focuser for refractors, we’ll have a high weight load capacity and you will be able to use also heavy imaging trains.
How to use ESATTO as focuser for refractors
ESATTO is available in different diameters and you have to choose the one that better fits your telescope based on your refractor specifications. If a compact refractor may use a standard 2″ focuser, a larger refractor may need for the ESATTO 3″ or 4″. ESATTO is designed to be used as new focuser for refractors, by replacing your standard focuser. So you can remove the original focuser from the tube of your refractor and connect the ESATTO. In order to make this as easy and straightforward as possible, we designed different adapters: first of all you connect the adapter to the tube of your telescope and then you connect the ESATTO robotic microfocuser.
Please note, if your refractor telescope has a built in corrector (field flattener or reducer), in order to use ESATTO first of all you have to check if the corrector is inserted in the focuser’s draw tube or if it’s separated from it. If the corrector is built in in the draw tube, by removing the original focuser you will remove the corrector too and in this case you can’t use the ESATTO. If your corrector is separated from the focuser (for example, like the Borg 90FL f3.9 and 107FL f3.9, the Takahashi FSQ-85/FSQ-106 or one of the many 65mm quadruplets available with different brand names), you can use the ESATTO as new focuser for refractor.
Application example and focus position of your refractor
Refractors usually have very long focuser’s draw tube while the ESATTO is a microfocuser designed for the small and precise movements requested in astrophotography. So, if you remove a focuser with long draw tube and you connect the ESATTO, in order to reach the focus you may need one or more extension tubes to install after the ESATTO focuser. For example, we can consider the ED 80 refractor telescope by SkyWatcher (EVOSTAR 80 ED) or Orion (80 ED).
For this telescope we can use the 2″ version of ESATTO and we designed a proper adapter (PL3600230) to connect it directly to the tube. By removing the 3 screws that fix the original focuser to the telescope tube, you can remove the original focuser (please note, sometimes manufacturers use thread lock so you may need to apply force to unscrew the locking screws), then install the PL3600230 adapter instead and finally connect ESATTO.
The adapter thickness is designed to make the ESATTO with adapter thickness to be equal to the one of the original focuser, this way you will never have problems to reach focus in the focuser’s draw tube inner position. But, while the original focuser has 75 mm draw tube travel, the ESATTO 2″ has 15mm travel. Since, when you focus on the stars, your sensor will be at 264mm from the telescope tube, based on the different instruments that you use to make astrophotography, you may need to add one or more extensions in order to reach focus position with ESATTO. Now your refractor telescope is ready to be used with the ESATTO focuser and you will be able to use heavy cameras and accessories even for the most difficult deep-sky astrophotography.