Re: What kind of lens combinations best for loupe'?
- From: "Harveyx" <removeh.rutt@xxxxxxxxxxxxxxx>
- Date: Fri, 6 May 2005 09:19:49 +0100
"Eric R Snow" <etpm@xxxxxxxxxxx> wrote in message
news:h7mi71toeiqs15b3h2jetjapsb96qe710t@xxxxxxxxxx
> Greetings All,
> I'm a machinist by trade and know very little about optics. I do know
> when using a simple lens that as magnification rises depth of field
> drops. However, looking at optics catalogs are lense systems that work
> better, a Hastings Triplet for example.
Just to clarify a point.
It doesnt matter what design of lens you use with regard to the depth of
field/magnification trade off.
The use of the Hastings etc reduces aberrations, you will get a much clearer
image, especially towards the edges, 'in focus all over', with less
distortion and less odd colour effects. But the depth of field is the same.
> But the Hastings Triplets I
> have seen have been considerably heavier for the same magnification
> than a simple lens. No surprise of course, it's a triplet. I use the
> type of loupe' that you screw into your eye socket most of the time so
> the extra weight may be a problem. So since I'm going to be making
> some of my own, for practice spinning the metal, I was hoping there
> might be some kind of compromise between the simple lens types and the
> heavy triplets. Any help is greatly appreciated. I might even be able
> to make a custom loupe' for someone.
There are other, simpler designs, such as the Coddington doublet, but it
uses a thick central component & is probably quite heavy too. Other standard
doublets would be worth a look. Its a trade off, more elements, better
performance in general.
There are also aspheric magnifiers, which can achieve very good performance
from a singlet (although Ive not used one and colour correction is not
possible.)
In fact it would be possible using standard optical software to optimise a
design including the weight as a factor to be minimised - important in many
applications, but not much considered for magnifiers I guess. Unfortunately
even if you get someone to design it for fun, getting it made & coated will
be very expensive.
The Coddington might be worth comparing to a Hastings for weight, or hunt
around for an aspheric magnifier.
Harvey
> Thanks,
> Eric R Snow,
> E T Precision Machine,
> Maybe someday Precision Spinning, or at least arty spinning.
.
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- From: Eric R Snow
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