The original function of the optional "hole" was to provide a clear shot to the Primary center for those who want to supplement their collimation procedure with a laser. If you are using a laser in your collimation protocol, select the perforation size slightly larger than the projected area of the beam on your Primary. If you are using a "Barlowed" laser, the recommended hole size is 1/4".
With one exception, the hole is not needed when using any of the CATSEYETM Collimation System passive tools; however, the hole does provide visibility of the tool "pupil" that some folks use as an additional visual queue in their precision collimation protocol.
The exception is with the use of the INFINITY XLKTM autocollimator. When viewing through the offset pupil, the spot preforation provides additional visueal queue resolution in determining the presence or absense of axial error.
What about reflective "white" versus "red" for my center spot?
By design, "Red reflective" is the de facto and recommended reference media for the CATSEYETM Collimation System. The "Red" color provides excellent contrast for maximum visual resolution of the triangle inside the reflective white ring image of all of the CATSEYETM Cheshires when setting the Primary tilt.
On the other hand, reflective "White" has become quite popular with its ability to provide brighter "ghost image" queues in the CATSEYE INFINITYTM autocollimator series of tools.
Regardless of the choice, either color provides full functionality of the tools and it's a matter of personal preference.
Why do you offer a combination tool package that contains both the BLACKCAT XL-ATM and TELECAT XL/XLSTM ? Isn't that redundant?
Even though there is Cheshire functional redundancy, some folks like the multi-functionality of the TELECAT XL/XLSTM and prefer the convenience of leaving their sight tube at home and only having the more compact BLACKCAT XL-ATM taking up minimal room in their field eyepiece box.
What do I use the sight tube "cross-hairs for?
There are 2 uses of the cross hairs: 1) For the 1-time squaring of the focuser where the cross-hair intersection is aligned with a reference spot/hole placed excactly opposite the focuser on the side of the scope tube or UTA. 2) Some folks align the reflection of the intersection under itself as a way to do a preliminary set of the Primary tilt.
If I have a 2" focuser, will the 2" sight tube work in my scope?
The Diagonal must be at least as large as the inside diameter of the sight tube so as long as the Secondary (diagonal) mirror minor-axis size is larger than 1.8", the TELETUBE XL/XLSTM or TELECAT XL/XLSTM will work just fine.
Should I tighten the focuser set screws on collimation tools?
My recommendation is that the focuser set screw(s) NOT be tightened on the tools and that the user only hold the tool against the rim of the drawtube insuring the collimation tool and focuser axes are coincidental.
Some folks prefer to tighten the set screw (as they would an eyepiece), but this approach assumes all their 2" eyepieces & 1.25" adapters have the same barrel size and length (therefore they "tilt" at the same angle) which is highly unlikely.
If you must tighten a focuser setscrew, use only one. Additionally, I recommend you make a alignment registration mark of some sort on the tool and the focuser drawtube to insure repetitive orientation of the tool each time it is inserted in the focuser.
What's all this about merging "ghost" images in an autocollimator? Isn't just a "dark" view good enough?
Unfortunately there is an old misconception that a mere "dark" field in the autocollimator is proof enough of adequate alignment. We now know that one can have a single main reflection of the Primary spot in view in the A/C with a dark background and for a fast scopes (under f/5), this is typically not enough to satisfy collimation tolerances.
In the new protocols, once the "dark" view is obtained, the objective is to get the Secondary/focuser alignment even closer to pick up the multiple reflections of the center spot and then ultimately to get them all to merge as one. For an example of what you need to look for, see one of Vic Menard's movie sequences of going in and out of collimation and then back in at: "https://catseyecollimation.com/vicseq3.avi"
When all the images are merged (and there are 4), the accuracy of alignment is actually the best obtainable on the planet as a result of the 4th (faintest inverted) reflection being a result of multiple reflections totaling 7 focal lengths away from your eye - far more resolution than is attainable with a 2-pass laser.