Perfect coma correction with Baader-MPCC – but how to adapt eyepieces?

We received the following question and found it important to write an extensive answer for other customers.

QUESTION: I purchased the Hyperion Zoom and the MPCC Mark III. Can you tell me how to adapt the eyepiece to the coma corrector?
I also want to use other eyepieces. How do I know the right distance between fieldstop position and the MPCC?

It is easy to produce an adjustable 1¼" eyepiece adapter for the Baader-MPCC coma corrector, offering a variable optical length from 49 to 64 mm, by using the following two parts:

  1. Baader focusing eyepiece clamp 1¼"/T-2 (item no. 2458125 / # 8a)
  2. Baader VariLock 20-29 mm T-2/T-2 adapter (item no. 2956929 / # 25Y)

Combining these parts on top of the MPCC T-2-thread and rotating both adapters into the shortest optical length will provide an optical distance of 49 mm for an fully inserted eyepiece with 1¼" barrel. The MPCC is designer for a distance of 55mm to camera sensor or fieldstop.
That means, the fieldstop inside an eyepiece could be placed up to 6 mm above the (upper) end of the 1¼" eyepiece barrel, in order to adjust for the 55 mm optical distance of the MPCC, which is necessary for a coma free image.
Our Eudiascopic 35 mm eyepiece (having a field stop diameter larger than the 1¼" barrel diameter would allow) will exactly require these 6 mm inward travel, in order to position the eyepiece field stop at the 55 mm spacing required by the MPCC.


If the field stop of an eyepiece is exactly at the intersection between the 1¼" barrel and the eyepiece body, you only need to rotate the locking eyepiece clamp (#8a) all the way up to its upper end and use the locking screw to tighten the eyepiece clamp in that position. Now this mechanical combo would provide the required optical distance of 55 mm between the MPCC body and the start of the eyepiece body - this is the position were most eyepiece designers put their focus position / the field stop (= the image plane).

Our Hyperion Zoom MARK III has it´s field stop (image plane) also at the intersection were the 1¼" barrel ends and were the eyepiece body itself starts.

Part #8a is very convenient, primarily because it offers 6 mm of upward travel to adjust for another distance of the image plane very easily when changing eyepieces.

The VariLock-T-2/T-2 adapter offers another 9 mm of upward travel, with the ability to lock it down very strongly (with a steel locking tool supplied with the product). So in case an eyepiece has its image plane further down, inside the 1¼" barrel (as for instance our BCO / Baader Classic Ortho eyepieces with an 2 mm inward field stop, which are designed for Spotting scopes), then the VariLock can be expanded into a slightly longer extension, so that all 1¼" eyepieces of an existing collection could be brought to focus within the 6 mm travel range of the focusing eyepiece clamp #25Y. This will allow to precisely adjust all your 1¼" eyepieces to reach the necessary 55 mm MPCC-spacing, just by rotating the #8a focusing eyepiece holder.

Thanks to the locking provisions on both of these adapters, they can hold even the heaviest of 1¼" eyepiece designs. Note: the eyepiece will fit only if an eventual 2" eyepiece-barrel can be removed from the eyepiece!

If you need to find out the field stop position of competing brand eyepieces, we are sorry that we don't have all these data of such eyepieces (the market is all too big). Our competitors should have all such technical information on the web - just as everyone can find our technical info about our eyepieces (see here for Hyperion Zoom, Morpheus, Hyperion 68, Hyperion Aspheric and BCOs).

However – we are confident that the two Baader products explained above (# 2458125 and # 2956929) will provide enough flexibility for adapting most any 1¼" eyepiece onto the MPCC Mark III.