How is the focal length of an objective calculated?

In summary, the conversation discusses using an objective lens with a collimated beam to illuminate an object. The magnification and numerical aperture (NA) of the lens are known, but the focal length needs to be calculated. It is mentioned that the objective is not infinity corrected and typically has a tube length of 160mm, 170mm, or 180mm. The formula for calculating magnification is mentioned, and it is noted that the focal length is not the same as the front working distance. Ultimately, using the tube length in calculations is found to be successful.
  • #1
ppoonamk
28
0
Hi,

I am using an objective lens to illuminate my object by a collimated beam. The magnification and NA is available on the objective. How can I calculate the focal length from this information? The objective is not infinity corrected. Thank you
 
Physics news on Phys.org
  • #2
IIRC: You need to measure the LDDV.
 
  • #3
Non-infinity corrected microscope lenses are typically based on a tube length of either 160mm (RMS or DIN standard) or 170mm (JIS). Of course, just to be different, Olympus used 180mm...

The magnification is (tube length)/(lens focal length). Note the focal length is not the front working distance.
 
  • #4
... or you could just know how people build these things :)
 
  • #5
Thank you for all the answers. Using the tube length in my calculations worked. Thanks :)
 

1. What is the definition of focal length?

The focal length is the distance between the center of a lens or curved mirror and its focus point. It is a measure of the strength of the lens or mirror in bending light rays.

2. How is the focal length of a lens or mirror determined?

The focal length can be determined by measuring the distance between the lens or mirror and the point where a parallel beam of light converges, also known as the focus point. This is typically done by using a light source and measuring the distance between the lens or mirror and the point where the light converges.

3. What factors affect the focal length of a lens or mirror?

The focal length of a lens or mirror is affected by its shape, curvature, and refractive index. A thicker lens or a more curved mirror will have a shorter focal length, while a thinner lens or a flatter mirror will have a longer focal length. The refractive index of the material also plays a role, as materials with a higher refractive index will have a shorter focal length.

4. How is the focal length of an objective lens in a microscope calculated?

The focal length of an objective lens in a microscope is typically calculated by dividing the distance between the lens and the focus point by the magnification of the lens. For example, if the distance is 10mm and the magnification is 40x, the focal length would be 10mm/40 = 0.25mm.

5. Can the focal length of a lens or mirror be changed?

Yes, the focal length of a lens or mirror can be changed by altering its shape, curvature, or refractive index. This can be achieved through physical manipulation or by using different materials for the lens or mirror. In some cases, the focal length can also be adjusted by moving the lens or mirror closer or further from the object being viewed.

Similar threads

I How to calculate the focal length and focal point of collimator?
    • Other Physics Topics
Replies
3
Views
1K
I Total focal length and magnification
    • Optics
Replies
4
Views
1K
I Collimating an extended source to infinity?
    • Other Physics Topics
Replies
5
Views
20K
I Determining Appropriate Focal Length
    • Other Physics Topics
Replies
3
Views
1K
I Using simple lenses to image AFM Probes
    • Optics
Replies
10
Views
1K
What is the role of focal lengths in ray diagrams for telescopes?
    • Other Physics Topics
Replies
16
Views
27K
I How to calculate focal length?
    • Optics
Replies
8
Views
2K
I Difference between Working distance and object distance
    • Optics
Replies
1
Views
1K
I In a rifle scope, why is the reticle at the focal point?
    • Other Physics Topics
Replies
11
Views
3K
How do you know if the focal length is positive or negative?
    • Introductory Physics Homework Help
Replies
5
Views
1K

Hot Threads

Recent Insights

Back
Top