# optics

This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.

#### sweetsaja

##### Full Member
10+ Year Member
ahhh this seems like an easy topic yet i always lose points on it i understand the difference between concave and convex, converging, diverging. for converging-positive, real, inverted; diverging-negative, virtual, upright. but i dont get it when something is wayy past the radius, or closer than the focal point, etc. can somoene summarize explain optics??

#### pandoraaj009

##### Full Member
10+ Year Member
ahhh this seems like an easy topic yet i always lose points on it i understand the difference between concave and convex, converging, diverging. for converging-positive, real, inverted; diverging-negative, virtual, upright. but i dont get it when something is wayy past the radius, or closer than the focal point, etc. can somoene summarize explain optics??

#### sweetsaja

##### Full Member
10+ Year Member
hmmm i already saw all the old posts about this topic on sdn, including that one..aahh i dont know why im getting these questions wrong. i guess i'll just practice more problems..

#### nanaschool2000

##### Junior Member
10+ Year Member
in my opinion, optic is not an easy topic. But it can be just me. I don't like physics in general.

I use 1/f = 1/0 + 1/i equation for the most problems. I'm not so good at mental picturing, so I prefer to use formula.

f is 1/2*r. If the object is too far (like the moon), we can put "infinity" to the object. Therefore, f needs to be equal to i. Depends on the type of lens, it can appear on the opposite side or same side.

When you are using converginig lens, the image usually appears real & inverted. However, if the object is within the focal point (so called pseudo focal point), the image will appear virtual upright. If you can't understand why, you should look at ray diagram.

Check out EK physics 1001 book. It helps me a lot.

correct me if I'm wrong.