With all the work done, how practical is this solution?
The ES-1 slide holder is designed for mounted slides, not for film strips, and handling the film is time consuming. It is difficult to advance the film strip and get the right crop, in particular because the eyesight only shows 95% of the frame, but I found a solution: Defocus slightly to see the entire frame beyond the crop, then advance the strip to the next frame and refocus.
The ES-1 is actually two tubes fitted such that it can be extended up to 25mm. This is great, exept that it is actually difficult to get the right distance for the best crop. I found that it needs to be extended at least 22mm to focus, and more than 23mm you will need to crop the image in post processing. that can be extended to get the right distance and crop. The problem is that the more it is extended, the less stable it becomes. When advancing the film, but also gravity can move the frame. THis has two problems: The film may not be entirely in focus because of a small tilt, and the frame may need to be retaken beacuse it moves after adjutment. This particular affects the bracket exposure method where the adapter may move slightly between exposures. A solution would be to get a 15-20mm tube extension, my local photo store didn't have one.
I initially tried using two Cokin filters to keep the film strip in place but it actually makes it much more difficult to place the film correctly. Since two filters are actually rather thick while they fit, the preasure from the clamps is hard. The preasure from the clamps on the filter may produce newton rings. Eventually I scracthed one of the Cokin filters and decided to work with just one to avoid the clamps scratching the film. This is much better, the filter can be slightly tilted to release the film strip while it is being placed or for advancing to the next frame.
If using the CTB gels, it is recommended, once the right gel combinnation is found, to stick the gels well to the slide adapter such that the light is filtered evenly across the entire frame.