Wells Research & Development

Library

Technical Library and FAQs
Tests and Configurations

Technical Library

Basic FAQs

Question What if I want to test some other lens, such as..

  • ..negative lenses?
  • ..afocal modules, such as beam expanders, telescopes, etc?
  • ..virtual display devices with an eyepiece?
  • ..lenses which are designed to work at finite conjugates instead of at infinity?
  • ..very small lenses (as small as 0.25mm diameter)?

Answer The OS210 is part of the OpticStudio family, and can easily be expanded to measure all the above.

Question How does the OS210 differ from the OS200A?

Answer 1 We have eliminated some parts so the OS210 is a bit less flexible. Benefits: the OS210 is less expensive than the OS200A, and the OS210 is smaller and simpler to set up and operate.

Answer 2 Lenses are measured "in projection" so that no microscope objective is involved. Benefits: microscope lenses are the single largest source of wavefront error, so MTF measurements are more accurate with the OS210, and microscope lenses with a good wavefront for testing fast lenses are extremely expensive.

Answer 3 We added a large, robust pivoting telescope mount. Benefit: it is especially easy to measure lenses off-axis.

Question How well does the OS210 work for very short focal length lenses? You say it is suitable for lenses down to 10mm EFL - is this a hard limit?

Answer 1 The first issue is simple mechanics. The 3-jaw lens holder supplied with the OS210 is very flexible, but it isn't precise enough for very small lenses. (Many users will choose to make their own holders, so this may be moot.)

Others may wish to consider the lens holder system used on our OS220 microbench. This lens holder is optional on the OS210 and makes it possible to precisely hold lenses as small as 0.25mm.

Answer 2 Next is the issue of the reticle holder. The holder supplied with the OS210 presumes that the reticle will be physically moved to measure points across the FOV of the lens. THis means that any size FOV can be easily measured.

However, with a small enough lenses it may not be necessary to translate the reticle. In other words, a special reticle is made with multiple targets that span the entire FOV. This has obvious benefits, and the reticle holder supplied with the OS210 supports this arrangement.

Of course, small lenses have unique challences too. The working distance is often very small, sometimes less than a milimeter. The reticle holder supplied with the OS220 'microbench' is specially designed to address these issues. An example is the breakaway mount it features to protect the lens and reticle in case of accidental contact.

The reticle holder from the microbench is an option on the OS210. While not strictly required for testing small lenses, it may be convenient.

Answer 3 Finally, the standard 200mm telescope may give such high magnification that the useable FOV is very small. Again, this is a matter of convenience. When the telescope FOV is too small, it becomes necessary to re-center the target each time a new lens is loaded. When the telescope FOV is correctly sized, variations in centration from lens to lens simply mean the image will be shifted slightly.

Ideally, the collimator EFL should be 5-20 times greater than the lens under test. If you will be routinely measuring lenses with focal length shorter than 10mm, we recommend you consider purchasing an additional telescope tube with shorter EFL.

We supply short telescopes with EFL of 100mm, 45mm, and 20mm.

PDF FAQs

Fundamentals

Product Questions