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Science Forum Index » Optics Forum » A reasonable allowed change in tolerance
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| Guest |
 Posted: Tue Apr 29, 2008 7:12 pm |
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Hi y'all
What is a reasonable allowed change for a tolerance in wave RMS when
tolerance a system in Code V?
Is .0001 out of the question?
Thanks. |
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| Helpful person |
| Posted: Thu May 01, 2008 8:47 am |
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Joined: 22 Jun 2004
Posts: 659
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On May 1, 1:16 pm, "Richard F.L.R.Snashall" <rf...@notnotrcn.com>
wrote:
Quote: Philli...@yahoo.com wrote:
Hi y'all
What is a reasonable allowed change for a tolerance in wave RMS when
tolerance a system in Code V?
Is .0001 out of the question?
Thanks.
Why would a percentage not fit?
It all depends on many different items. In my opinion, tolerancing
(and mechanical mounting) are the most difficult, least taught and
most important items of lens design. It is too complex to answer in
this forum, however here is a list of points to consider to stimulate
your thoughts.
1. Is this a one off or a high volume production or somewhere in
between? Remember, tolerancing is a statistical process.
2. What is your nominal and required performance? If your system is
diffraction limited errrors introduced from various elements do not
add up in a linear manner. In other words, if you plot resolution
against wavefront aberration it is not a linear relationship.
3. How do you intend to mount your lens? Tolerancing cannot be
comnpleted before this is known.
4. How accurately do you know the dimensions of your parts? Instead
of relying on the drawing tolerances you can measure the parts and
adjust the design. For well corrected lenses this is often done with
glass data.
5. Remember that vendors will not usually supply parts with a
gaussian distribution about the nominal dimensions. For example, if
they do not need to rework lenses in their processes then all the
lenses are likely to be at the large end of the tolerances. (Room
left in case rework is necessary.)
6. Take care to include plus and minus field angles and full pupils
when performing tolerance analysis.
7. There is always a cost preformance trade off. This needs to be
considered not only when performing tolerance analysys but also in
deciding which lens construction to use. Certain lens designs are
extremely difficult to manufacture.
These are just a few points.
Has anyone written a book covering "real world" lens tolerancing? |
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| Richard F.L.R.Snashall |
| Posted: Thu May 01, 2008 12:16 pm |
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Guest
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PhillipKP@yahoo.com wrote:
Quote: Hi y'all
What is a reasonable allowed change for a tolerance in wave RMS when
tolerance a system in Code V?
Is .0001 out of the question?
Thanks.
Why would a percentage not fit? |
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