English is not my mother tongue, and in my native language cathode is written with a 'k'.
I think we realised that. Rasch was just correcting your translation. It's OK.
You presume to know a lot of electronics, but what you are saying is wrong.
The terms anode and cathode are used to indicate which leg you have to connect with which pole of a source.
No, the terms are not - ever - used to indicate which pole of a power source is which.
Current is a movement of electrons, going from - to +.
They start from the - pole, where an oxidation occurs (anode), to the + pole, where a reduction occurs (that is the cathode).
A power source, like a battery or an accu, has a plus pole and a minus pole, hence a cathode and anode. But as the led will only light if it is correctly connected, they have given the legs a name.
Yes, you are referring to the function of electrodes in a cell (whereas a battery is a group of cells) and that is indeed relevant to the chemistry. But a battery is only one form of power source and once it is packaged it is referred to only by its positive and negative terminals, the terms "cathode" and "anode" are meaningless in this regard.
Similarly, the term "accu" does not exist in English, it is an abbreviation of an antique term "accumulator", now a "secondary" or storage battery. Just FYI!
Unless you have a solar installation with a storage battery your mains power source has nothing whatsoever to do with batteries but is produced by mechanical generators, so clearly the terms "cathode" and "anode" are entirely irrelevant.
I did indeed review the original article to which you referred and had attempted to replicate. It discusses - in passing but not in detail - the significance of the CTR but sadly goes on to cite the obsolete 4N26 part. Due to the wide manufacturing variability of the CTR the part he found presumably did work for him in the test circuit, but that is always the great danger of less-than-methodical "well, it worked for me" articles you find on the Web.
It seems you have the proper part now, the 4N35. Go ahead and use it.
My reference to a previous thread here was misplaced; the main discussion I had in mind was about using the flash trigger or "shoe" of the camera to synchronise other functions although the question of how to perform remote shutter control is most certainly discussed from time to time.
Actually I was confused until I saw your schematic.
Indeed. My original situation as well.