# Distance between the luope and the virtual picture: I can not see any

I have a biconvex lens. f=45mm. (This is a loupe). I have an object (G). This object is G=64mm broad. When I place this object in a distance of g=42mm in front of the lens I get a virtual picture.

I have calculated the broad of this virtual picture (B) and the virtual distance (b) from the lens of this virtual picture:

distance from the lens: -(45*42)/(45-42)=630 -> -630mm -> -0.63 Meter

broad of the virtual picture: 630/42*64 = 960 -> 960mm -> 0.96 Meter

So my expectation was: When I make practical test (a practical experiment) I should see the virtual picture in a distance of 0.63 Meter.

So I position my smartphone in a distance of 42mm behind the loupe. Then I watch through the loupe to the smartphone display with my eyes. But I do not see my smartphone now in a distance of 0.63 Meter. It is much nearer.

Question: Can you explain me this contradiction between theory an experiment.

• Re, "...I do not see my smartphone now in a distance of 0.63 Meter." What do you mean, exactly? The virtual image of your phone, when seen through the loupe, should not only appear to be further away from your eye (or camera lens) than the actual phone, but it also should appear to be proportionately larger than the actual phone. That's why a loupe is also sometimes called a "magnifying" glass. How did you measure the distance to the virtual image? – Solomon Slow Feb 20 at 15:01
• Yes I agree, the virtual image should also be larger then the actual phone. But this is the other thing that is different in theorie and experiment. I have calculated that it should appear 0.96 Meter broad, but it looks max. like about 0.12 Meter. I was not able to measure the distance and the broad of my virtual image. I estimate them when looking through the loupe. And it is not what I have calculated. Maybe there is any fault in my calculation? Or there is any thinking error? Would appreciate some help. – Wogehu Feb 21 at 8:45