Hi Astronut
You really have to practice for focus stacking. If you see something double, there must have been movement, even if it is only half a millimeter or less. With which program do you stack the photos? You have to focus only with the rail or only with the lens, not at the same time. Don't know what program you are using for stacking, but Helicon Focus or Zerene Stacker work best. From a rail or tripod, you have to use image stabilization on the camera.
I am lucky that my camera does it itself.
HOW TO MAKE YOUR PHOTOS SUITABLE FOR FOCUS STACKING
With some cameras it is now possible to apply focus stacking from the camera. The camera then takes the various photos, so that you can stack them later via Photoshop, for example. There are even cameras that do the merge in-camera! Most cameras do not have this function and you have to move the focus point and take the photos yourself. Taking a photo suitable for focus stacking therefore takes longer than taking a "normal" photo, because it involves multiple photos of the same subject.
Step 1: Place the tripod in a safe and secure place, where the camera can register as few movements as possible.
Step 2: Choose the right composition. If you have Live View you can easily frame.
Step 3: Set the camera to the M position. Try to keep the exposure the same for each photo. Is this not possible because of the alternation between sunlight and shade, for example? No problem, you can always perform post-processing (there is a greater risk of failure). Make sure that the camera also takes pictures in RAW to get the best out of the post-processing.
Step 4 Set the number of focus points to one. Think about what you want in focus and then take a picture of the center point of the object or subject. Take more pictures as desired to the furthest point of the subject and to the point closest to it. Remember, it's better to have too many than too few photos.
Tip: When you take several photos that belong together, you can eventually lose count. Take a picture of your hand or something else to be able to recognize the segments later on the computer.