Have you ever noticed how much an image's quality decreases when stacking a bunch of filters in front of the lens? No? Well, that's because nobody in their sane judgment tries to decrease stops of light with such a dumb technique.
But I did.
Stack Stack Stack… Oops
I had a really hard time finding a decent 77mm ND filter that allowed me to stop light down to 10 stops. So I had the brilliant idea of stacking 3 ND filters of 3 stops each and a circular polarizer that allowed me to get that extra stop to reach 10 stops of light reduced. After spending money on 3 poor quality filters and ruining some pictures, I began to wonder what was going on.
Finally, a friend of mine explained to me that even with high-quality filters stacked together, the beams of light passing through any lens began to fragment in a funny way. He also lent me a 77mm 10 stops ND filter when I went to Costa Rica. I was super excited because I wanted to capture some waterfalls with ghostly people surrounding the water.
After a few attempts, all I got were ugly overexposed photographs because I was rushing into things. And you know what was the saddest part? I didn't have time for making those pictures right because it suddenly started raining and I had to stop taking pictures.
The good lesson for me was that I shouldn't have taken ND filters for granted and I made some further research on how to actually use them.