These are the worst affected leafs. Most of the leafs are affected, the older more than the younger ones

I have seven young plants and all of them are in the conservatory attached to my living room. They weren't having enough sun and had to much air humidity and soil was to moist probaply. Air temperatures were rather high. Also I may have given them to much fertilizer. It's the first time that I'm growing plants.

That being said, my other plants, cucumber, broccoli, aubergine, strawberry are doing great. They are all under the same conditions, I just put the cucumbers at a little more shady place.

I attached a photo so you can see the whole plants

It looks like sunscald and they also look very dry. Did you harden them off before putting them outside? If you gave them too much fertilizer, watering them some more will help to flush it out.

I didn't put them outside, they've had rather to much water and not enough sunlight so quite the opposite of what you suppose... Today I let the soil dry a little for the first time because I thought it might help

https://aggie-horticulture.tamu.edu/vegetable/problem-solvers/tomato-problem-solver/

http://vegetablemdonline.ppath.cornell.edu/DiagnosticKeys/TomWlt/TomWiltKey.html

One of these two should answer your questions.

These links are good still I am not sure which one it is. There are so many diseases yet non of the pictures looks exactly the same. All the tomato plants are affected likewise

I have read in a german forum that see-through leafs are supposedly necrosis oftenly caused by sunburning but that really doesnt make any sense.

I wwon't destroy my plants but let them grow and hope they get better eventually. My other plants are not affected by the disease as it seems.