Hello, by smooth barrel do you mean the entire thing has no "corners"(i don't know what you call them)? If so, can you tell me why I should make sure the Cheshire eyepiece has a smooth barrel?
There is one I can buy in here with minimal costs, but it looks like this:
By smooth I mean the insertion tube is 1.25" all the way up to the cheshire head of the tool. This tool pictured does not allow full insertion:
I have that much shorter combo tool you show a picture of. First read this:
There are 3 main Steps in collimation:
1. Center the secondary mirror under the focuser – done with a site tube or “combo tool”.
2. Align the focuser axis (secondary tilt) – done with a site tube w/cross hairs (combo tool), or thin beam laser.
3. Align primary axis – done with a Cheshire or collimating cap, combo tool (Cheshire portion), or barlowed laser.
Note that many combo tools are sold as “Cheshire eyepiece” or “collimating eyepiece”, but they are all 3 in 1 combo tools. They will only be as accurate as their fit in the focuser, which can be very sloppy.
A collimating cap is a derivative of a Cheshire – they both do the same thing.
The short combo tool that you posted a picture of sort of works, but has issues. For each of the above steps, that tool does the following:
Step 1. It works poorly to center the secondary. I'm not sure why but I can't get a good reading from it. It's too short as well, so you have to pull it out of the focuser, which causes a possible tilt in the tool. I get inconsistent readings from this short tool.
Step 2. It works poorly for aligning the focuser axis (secondary tilt). This is due to the very thin crosshairs they used. The crosshairs so thin that the tool will arrive with them slightly bent, and if you touch them they will bend further. They are too thin to get a good reading, even if they actually cross at the center.
Step 3. It works okay for aligning the primary. Most of these tools don't work well for step 3 because the newer center spots that are etched in the mirror are very small and black. So you are attempting to place a black ring under a black donut. The precision level is very poor with this method.
I'm using a sheet of green paper behind the secondary. You want to see the secondary through the tool, surrounded by a thin green circle (from the green paper). Getting this requires you to lift the tool out of the focuser a bit.
This is the short tool inserted but lifted out of the focuser by about 15 mm:
This is the view through that tool. The crosshairs are bent, and the "read" is very poor:
This is the SvBony tool I posted a link to, lifted out of the focuser to center the secondary:
The view through the lifted SvBony. Note that you can see a nice ring of green around the secondary, but you can't fully see the primary mirror. Ignore the crosshairs for this step:
Here we have it almost fully inserted, in order to see the edges of the primary mirror:
The view of the SvBony tool inserted fully in the focuser. This shows the full primary, and now the crosshair align with the center of the primary:
Finally the collimating cap view. Note that you can see the center spot (donut), and a black dot (the cap pupil) centered within the donut. This gets you far better precision when aligning the primary mirror (step #3).