Takahashi Helical Focuser UpgradePosted By Michael Sandy |
I've just completed an upgrade to the focuser on my FRC-300 that I thought others might like to see (of course BRC-250 owners could do exactly the same thing). I have always had a love/hate relationship with the big Takahashi Helical focuser that comes with these scopes. The Tak helical focuser was very precise, strong, and well made, but it didn't lend itself at all to automated focusing. The standard fix or path to automated focusing with these scopes was to install a secondary focusing device like a FLI PDF focuser, and I did that myself for the past several years. But there were a few problems with that approach.
The secondary focusers are inserted into the light path on the camera side of the corrector lens. Focusing adjustments therefore change the metal back distance (MBD) between the corrector lens and the CCD. While it can be argued that the MBD change is so slight that it is unimportant, there have been several tests posted that show changes to the image quality with just a few mm's change in the MBD. I've also been a bit concerned about the ability of some of these devices to handle the increasing loads created by all the extra stuff and the larger cameras we are all hanging off them now. The final issue was the focuser consumes a lot of the MBD, and I wanted to free up enough room to be able to fit a remotely operated Camera Angle Adjuster.
My friend and I found the solution with a Clement Focuser (http://www.clementfocuser.com/home.html ). By having Don at Clement make a custom 4.25" focuser, we could remove the helical focuser all together, replace it with the Clement, and mount the corrector lens on the camera side of the focuser. Now we can maintain a consistent (and exact) MBD and free up room to install one of Astrodon’s TAKometers to handle the CAA function. It sounded too good to be true – but it wasn’t! For about the same cost as a PDF, Don made up one of his complete automated focusers.
I completed the installation a few weeks ago and couldn’t be happier. The Clement Focuser is very precise, on par with the original Takahashi Helical Design and with similar resolution to the PDF, and fits nicely in the original envelop. The appearance is a bit usual, but it grows on you, especially when you see it work. The automation interface is a Robofocus, so there is really nothing new to learn there. As a final plus, the nature of the focuser design gives it a very high load capacity, and since there are no pins or clearances there is virtually no chance of motion being introduced by the focuser. You can see a few pictures of the installation here:
http://www.darksights.com/Clements%20Focuser%20and%20TAKOMeter.htm
The secondary focusers are inserted into the light path on the camera side of the corrector lens. Focusing adjustments therefore change the metal back distance (MBD) between the corrector lens and the CCD. While it can be argued that the MBD change is so slight that it is unimportant, there have been several tests posted that show changes to the image quality with just a few mm's change in the MBD. I've also been a bit concerned about the ability of some of these devices to handle the increasing loads created by all the extra stuff and the larger cameras we are all hanging off them now. The final issue was the focuser consumes a lot of the MBD, and I wanted to free up enough room to be able to fit a remotely operated Camera Angle Adjuster.
My friend and I found the solution with a Clement Focuser (http://www.clementfocuser.com/home.html ). By having Don at Clement make a custom 4.25" focuser, we could remove the helical focuser all together, replace it with the Clement, and mount the corrector lens on the camera side of the focuser. Now we can maintain a consistent (and exact) MBD and free up room to install one of Astrodon’s TAKometers to handle the CAA function. It sounded too good to be true – but it wasn’t! For about the same cost as a PDF, Don made up one of his complete automated focusers.
I completed the installation a few weeks ago and couldn’t be happier. The Clement Focuser is very precise, on par with the original Takahashi Helical Design and with similar resolution to the PDF, and fits nicely in the original envelop. The appearance is a bit usual, but it grows on you, especially when you see it work. The automation interface is a Robofocus, so there is really nothing new to learn there. As a final plus, the nature of the focuser design gives it a very high load capacity, and since there are no pins or clearances there is virtually no chance of motion being introduced by the focuser. You can see a few pictures of the installation here:
http://www.darksights.com/Clements%20Focuser%20and%20TAKOMeter.htm
