# Compound microscope

is magnification negative for a compound microscope at infinity

sophiecentaur
Gold Member
welcome to PF
Is this what you wanted? An inverted image implies a negative sign for the magnification.

I done a question where the formula was m=(-l0.25/fofe) as the final image was at infinty.
1. The angular magnification of a microscope is 400X when the final image is at infinity. The optical tube length is 16cm and the focal length of the objective is 5mm. What is the focal length of the eyepiece?

They took the magnification to be -400x not sure why? The only thing I could take from it was that when its a compound microscope at infinity the magnification is negative.

sophiecentaur
Gold Member
I done a question where the formula was m=(-l0.25/fofe) as the final image was at infinty.
1. The angular magnification of a microscope is 400X when the final image is at infinity. The optical tube length is 16cm and the focal length of the objective is 5mm. What is the focal length of the eyepiece?

They took the magnification to be -400x not sure why? The only thing I could take from it was that when its a compound microscope at infinity the magnification is negative.
Wherever you choose to put the final (virtual) image, the magnification will still have the same sign. Using infinity just makes the calculation easier.

So why is the magnification negative? It only seems to be for a compound microscope at infinity the magnification is negative. For a simple magnifier and astrological magnification remains positive

sophiecentaur