Objective and magnification query

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Cyclops
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Objective and magnification query

Post by Cyclops »

I'm looking on ebay for a low power objective, and I have a found a few that are listed with its focal length, rather than the magnification, for example Beck 60mm .07 Microscope Objective.
(I take it that the longer focal length the lower the power)

How do I work out the magnification from the focal length, bearing in mind that my standard student compound scope has a tube length of 160mm
(I think so anyway. My objectives are marked 160/0.17)

I have found one that says 1X, but it looks awfully long!

Im hoping to get a final magnification of betwen 10-50X(plus the higher magnifications of 50-500)
My current set up is
eyepieces-5X, 10X and 12.5X
Objectives: 10 40 and 100X(oil,hoping to get rid of)
Many thanks
Larry
Canon 30D | Canon IXUS 265HS | Cosina 100mm f3.5 macro | EF 75-300 f4.5-5.6 USM III | EF 50 f1.8 II | Slik 88 tripod | Apex Practicioner monocular microscope

Charles Krebs
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Post by Charles Krebs »

Larry... a very rough approximation would be to divide the tube length by the focal length.

Just to give an idea from the specs I have Olympus (160 tube length) objectives:

2X: about 73mm
4X: about 34mm
10X: about 18mm
20X: about 8 mm
40X: about 4.2mm

Cyclops
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Joined: Sat Aug 05, 2006 5:18 pm
Location: North East of England
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Post by Cyclops »

So my 10X objective would effectively have a focal length of 16mm(tube length=160. Divide by 16=10)

Right so if I want a 4X Im looking for a obj. marked about 40mm, yea makes sense now!

My obj. lenses have no manufacturer markings but theyre pretty good, but what makes would you recommend and which should I avoid?
And how much should I expect to pay for a 4 or 5X obj.?
(Am hoping to sell my 100X oil on ebay to pay for the low power one)

Sorry about all the questions! :oops:
Canon 30D | Canon IXUS 265HS | Cosina 100mm f3.5 macro | EF 75-300 f4.5-5.6 USM III | EF 50 f1.8 II | Slik 88 tripod | Apex Practicioner monocular microscope

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