"What is Focal Length?" - The science behind it explained.

Loved this type of content! Short, but to the point and explained very well!

Thanks for the graphics!

cool, thanks

I'm glad this came up high on my search results. Perfect explanation; I'm a visual guy and needed to see the lines to understand. Thanks!

If the camera lens flips the image, why is a pinhole camera (which has no lens) image also upside down?

Hint: It's because there is no point of convergence within the lens. The point of convergence is on the sensor itself, and the focal length is the distance from the entrance pupil, or aperture, to the image plane. The image flipping upside down has nothing to do with the lens, and that's why a pinhole camera inverts the image, too.

It is good.

Very well explained. You should be a teacher!

Super explanation. Very intuitive and clear. Thanks!

Ta.

I don’t understand what you mean with the focal point/convergation point, isn’t that what makes focus? Why would the convergation happen before hitting the sensor, isn’t it supposed to happen at the moment the rays/waves hit the sensor?

You just made everything perfectly clear thanks

Very nicely explained - well done!

I have a class about that but my teacher said that the focal length is the distance between the lens and the point where the originally parallel rays of lights converge, whereas in this video he says that its the distance between the point I just mentioned and the sensor. That seems like a pretty big deal so can anyone deny or confirm either of this versions?

Update: just saw a very insightful comment 58 comments (or something similar) below mine (when you filter them by release date) that confirms my teacher's version and contains a link to a complete scientific paper about it if you're interested!

Following physics this should mean that short focal lengths and wide sensors are much more sensitive to vignetting.

So basically what it does is that with larger focal length you have narrover field of view but with higher resolution, in relattion to same amount of space cropped from smaller focal length? Isnt it literlay zoom? for example if you take picture of face with smaller focal length from lets say 1m distance, you have wider field of view but with bigger perspective distortion of face proportions due to less surface of head being scanned (those funny faces with exagerated noses), while if you have larger focal length, to capture same lvl of surroundings, you have to go further from object (face) and difference is that you capture more from its surface which in finnal is less perspective distortion, as with distance perspective distortion exponentially decreasing. Sorry for my english, I hope you understand what I mean 😅

In answer to your question: Yes, I learnt something new!

Very well explained. Thanks.

Thank you

Dave, since you are talking about science. You need to learn the lens formula. Your information only correct when objects are far away. At closer distance, image formed is farther away than the focal length according to the lens formula, and what you said is no longer correct

So clear. So useful.

very very very good, good on ya bro

Wow! thank you so much

Great video. You cleared up some misconceptions that I had. Subbed. Thx!

24y

I hope you will notice me. Is point of convergence is the same with focal point?

Ver Well Explained, Thank you :)

Man ! Brilliant.....So easy....Luvved it ! Thanks

Absolutely cracking explanation! Thank you

Concise explanation, Thanks !

Agree with many here … never seen a better explanation of this subject, along with the overlays to articulate it soooo well!!! My 8 year old learning photography absolutely adored it!
Many thanks!

Thank you! Finally a good explanation on this topic!

Dude this explanation was PHENOMENAL

I have watched literally dozens of videos on focal length trying to get my head around it and this is hands down the best explaination.

Bravo! You just answered several longstanding, nagging questions I’ve had about this topic that all the textbooks don’t treat well or ignore entirely. Showing the path of the light and the point of convergence layered on an image of the camera and lens was a brilliant way to communicate this information. Thank you!

Excellent!!! Thanks

Well explained. 👌🏽

Great video

Thank you for taking the time to put the graphics on your hand movements during your excellent explanation. Tip top

FL well explained.. You win a sub.. Webale

Appreciate the detailed explanation. Could you make video longer by adding how the crop mode is affected effected and works? 4:3 with mirrorless (1.6) vs 16:9 and 3:2.... clear as mud?

That was the best video on focal length I have ever seen. Thanks so much, I learned a lot.

Thanks so much for the explanation! I was meaning to look this up sometime, and your video just came up. Great explanation!

I love it when content such as this gives you "Ohhhhhhhh" moment, connecting multiple concepts together forging an even stronger understanding. Thumbs up for that.

best explanation

THANK YOU SIR

Amazing bro looking for the right awnser and theory and you video was the awenser thanks so much well done explaned

Excellent my man! Been racking my brain. Thank you

AWESOME.....great work and masterfully explained ! 👍

As an optician it was very difficult for me to understand the meaning of focal length in photography and i was really confused
But you explained it very well and made me clear
Thank you bro
Uncle k1❤