Power of Lenses

[matth87]

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"If your left eye requires a lens power of -3.5D while your right eye requires a lens power of -3.25D then you left eye is weaker"

Am I understanding this correctly that a -3.5D lens is more powerful then a -3.25D lens?

The negative signs don't get factor in when talking about lens power if they are both negative?

What about a +2.5D lens vs a -3.5D lens, which would be more powerful?

 

[SuperSaiyan3]

"If your left eye requires a lens power of -3.5D while your right eye requires a lens power of -3.25D then you left eye is weaker"

Am I understanding this correctly that a -3.5D lens is more powerful then a -3.25D lens?

The negative signs don't get factor in when talking about lens power if they are both negative?

What about a +2.5D lens vs a -3.5D lens, which would be more powerful?

Where did you get this question?

I've yet to come across an optics passage that talked about power... although I did read about in my prep book.

 

[matth87]

Where did you get this question?

I've yet to come across an optics passage that talked about power... although I did read about in my prep book.

TPR Physical Sciences Review book

 

[thebillsfan]

TPR Physical Sciences Review book

the negative and positives signs are indicative of whether the focal length is positive or negative (a converging or diverging lens). when determining the strength of a lens (ie, which is more powerful), the magnitude of the power is what matters.

So a -5 diopter lens is more powerful than a +3
A +5 diopter lens is mower powerful than a -3
And so on.

 

[Seraph 84]

The first lens will diverge the light more because it's focal point is positioned closer to the lens; thus, it is more powerful than the -3.25 D lens.

For your second question, the -3.5 D lens will still bend the light more than the +2.5 D lens, so the -3.5 D lens is more powerful. The negative and positive signs just indicate where the focal point is relative to the lens (I know you know this), but the power is just a measure of the strength of the lens, or how much it can refract the incoming light.