This is a follow-up to a post I wrote a couple of years ago.
I recently upgraded to a full-frame ZWO ASI6200MC Pro camera, and have altered the adapters I use when connecting this camera to my RASA 11″. This post will detail the adapters I am now using.
First, to try and eliminate as much vignetting on this full-frame camera as possible, I use the screw-in Celestron Light Pollution Imaging Filter for the RASA 11″. I also still use the Baader UFC system, as the interior of these adapters is wide enough to ensure the light path isn’t obscured. Also, if I ever want to include other filters I can do so by using the Baader UFC filter slider.
However, there is a problem that occurs when attempting to use the Baader UFC RASA adapter with the Celestron Light Pollution Filter installed. As shown in the photo below, the top edge of the Celestron light pollution filter sits a couple of millimetres above the front tilt plate of the RASA. This means the Baader UFC RASA adapter is no longer able to lay flush on the tilt plate, as it sits on the top edge of the light pollution filter instead.
To enable the reliable use of this filter I ordered a custom RASA 11″ to Baader UFC adapter from PreciseParts that would provide space for the light pollution filter, and enable me to continue using the Baader UFC system:
The custom PreciseParts adapter doesn’t use the Celestron RASA clamp ring, and instead screws straight on to the front of the RASA. I ordered the adapter with an effective length of 12mm – I could have ordered it in a longer length, but I wanted to allow for any future UFC adapters I may install, such as the new Baader UFC Tilter detailed further on in this post.
When installed on the RASA, you can see the adapter has plenty of space within for the Celestron Light Pollution Filter:
The PreciseParts adapter provides a secure fit, but I did notice it needs to be screwed on fairly tight to ensure it doesn’t wiggle/tilt slightly (caused by slight looseness between the threads of the adapter and the threads of the RASA tilt plate). It is nice and secure once screwed on tight though.
With this type of custom adapter installed, it’s important to note it does obscure the collimation screws on the front of the RASA (which I’ve never adjusted, or wanted to adjust!), but Baader recently released a new tilt adapter for the UFC system which I went ahead and ordered. This allows for minor adjustments to the spacing and tilt without having to use the collimation screws on the RASA or the tilt screws on the camera (which are inaccessible when the camera is installed anyway). Here is the UFC Tilter:
The UFC Tilter consists of an outer and inner ring. The tilt of the inner ring can be adjusted (up to 1° of tilt) by using three pairs of push and pull screws located around the edge of the outer ring (shown below). The spacing of this adapter varies from 9.75mm to 10.50mm, depending on the extent of the tilt adjustment.
The inner ring is held in place by three pins that protrude from the outer ring, and this ensures it doesn’t come apart when adjusting the tilt! One of the pins is visible in this photo:
To complete the imaging train, I also use the Baader UFC VariLock adapter and the Baader UFC Base Filter Chamber. The ZWO ASI6200MC Pro is then attached using the Baader UFC M54 camera adapter, providing a configuration that is shown below. To ensure no stray light (or dust) enters the imaging train, I have an empty Baader UFC 50mm Filter Slider installed.
Once installed, I adjust the rotation of the camera so the bottom two corners of the sensor roughly line up with the positions of two of the push/pull screws on the UFC Tilter. I do this by performing a one-off adjustment of the angle of the Baader UFC Filter Slider Base, which sits on top of the UFC Tilter.
This combination of adapters provides a reasonably wide and unobstructed view to the full-frame camera sensor, as shown below.
With the cables and cable router installed, the setup looks like this:
To achieve the required back-focus distance of 72.8mm, the configuration and lengths of the adapters are listed below:
- 12mm – PreciseParts custom RASA 11″ to Baader UFC adapter – this is the custom adapter that gets attached to the front of the RASA 11″;
- 17.6mm – Baader UFC S70 VariLock (2459145) – a variable length extension that adjusts from 15-20mm, and can be locked in position once set. I have mine set to about 17.6mm – I measured mine using a digital caliper;
- 10mm – Baader UFC Tilter (2459146) – fine adjustments to the tilt can be easily made using this tilt adapter. The spacing of this adapter varies from 9.75mm to 10.50mm, depending on the extent of the tilt adjustment.
- 13mm – Baader UFC Base Filter Chamber (2459110) – the filter chamber that the filter slider is inserted in to (I have an empty 50mm filter slider installed most of the time, to eliminate any stray light and stop dust from entering the imaging train);
- 2mm – Baader UFC M54 Camera-Adapter (2459117) – the adapter plate that attaches to the filter slider base.
Then, on the camera side:
- 5mm – the ASI6200MC Pro camera comes installed with a 5mm-thick M54 tilt plate and this enables the attachment of the camera to the Baader slider base above;
- 12.5mm – camera back-focus – the camera sensor itself is positioned 12.5mm from the very front of the casing.
When you are calculating the total depth, remember that the filters themselves add a small amount to the total back-focus distance. The general rule of thumb is to add a third of the filter depth (the glass thickness) to the back-focus:
- 0.7mm – the Celestron Light Pollution filter thickness is 2.1mm, which equates to 0.7mm added to the back-focus.
Taking all the above measurements into account, the total comes to the required 72.8mm.
I hope this post was useful. Please let me know in the comments below if you have any feedback or questions!