JYC2

You don't need to keep holding shutter release button. After focusing by pressing shutter release button half way, take your finger off from shutter release button, and then press function button which is assigned to preview button. Then you will be able to easily check DOF. Of course focusing has to be done again by pressing shutter button half way again after checking DOF. But, it will not be that annoying.

Finally I have given up applying this hood. After I posted about LH-40N hood, I have suffered from the lack of sharpness, inaccurate focus and harsh bokeh. Now, without this hood, there isn't focus problem. The image is now tack sharp, and bokeh is soft.

I agree. B+W MRC Nano is all right for reverse mounting. (Kenko Zeta Quint is not all right although.) Unfortunately in my country the smallest size of MRC Nano is 43mm. They aren't selling 39mm version.

I also considered mounting 39mm filter from inner side. But, I gave it up because (1) I didn't want to attach filter in reverse direction due to the issue of coating and (2) Only 52mm filter was available for me. But, it is good idea.

I have been searching for small hood for my Zeiss Touit 32mm F1.8 because its included hood is too big. Especially it has caused big problem whenever I attach it to my X-Pro2. (Of course it doesn't cause problem when it is attached to X-T. But, still it is too big.) Yesterday I happened to know LH-40N hood for for Voigtländer ULTRON 40mm F2 SLIIN. It is screw-in type inner hood for 52mm filter thread. Immediately I visited Voigtländer shop and bought LH-40N. And, I tried it for Zeiss Touit 32mm. Yeah! It became compact! I worried about the vignetting. But, soon I noticed that the coverage of LH-40N is exactly the same as that of included 'big' hood. I took some shots, and I couldn't find vignetting at all even though I attached LH-40N on protector filter. I tried both of slim protector in above picture and thicker Zeiss UV filter. Both of those two were all right. One thing I don't like is 'Voighländer' text engraved on filter. But, at least its appearance is not bad. I also tested LH-40N on Zeiss 50mm F2.8 Macro and Fuji XF 35mm F1.4. LH-40N works very well on Zeiss 50mm F2.8 Macro. But, on Fuji XF 35mm F1.4, it caused noticeable vignetting. So it can't be used on Fuji XF 35mm F1.4.