Magnification / Stage question

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Simonl
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Magnification / Stage question

Post by Simonl »

Hello,

I've been reading through so many posts on this fantastic forum, but a couple of things remain unclear.

1. Magnification=extension/focal length (so I'm told)
However this only makes sense to me if you factor in the length of the lens too.

e.g I own a 105 Nikkor Macro lens and have a 50mm 2.8 Enlarger lens coming soon (told you i'd been reading a lot of great posts on here :) )

Now my Nikkor 105 is 1:1
If I put 105mm of extension tubes between lens and camera I know I get greater than 1:1 but the equation says:

extension / focal Length= magnification
105/105=1

Please can someone explain.
Should it be 105 (extension) +105 (length of lens) /105 (focal length)?????

Also I've been looking on ebay(.co.uk) for a transition stage without any luck. (Want to put specimens on it instead of my camera) Anyone any idea what I should be searching for? Milling table? Microscope stage? Focus rail?

Hope this makes some kind of sense.

Thanks in advance, for any kind of answer

Regards

Simon

NikonUser
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Location: southern New Brunswick, Canada

Post by NikonUser »

My understanding is that you use the focal length of the lens at its infinity setting.
The 105mm Micro Nikkor has a built in extension of 105mm giving you 1:1. If you add another 105mm of extension tubes you have 210/105=2:1.
The older MF 105mm Micro Nikkor has only 52.5mm of extension built into the lens and thus it goes only to 1:2 mag. To get 1:1 with it you need the PN11 extension tube (52.5mm long).

The simplest, cheapest, and best (this could cause feedback) system is a microscope stand with a mechanical stage. Take your time and you could get one on E-bay for less than $100.00. It gives you superb control in all 3 axes, x, y, and z.
See my image near the bottom of page 2
SEE HERE
NU.
student of entomology
Quote – Holmes on ‘Entomology’
” I suppose you are an entomologist ? “
” Not quite so ambitious as that, sir. I should like to put my eyes on the individual entitled to that name.
No man can be truly called an entomologist,
sir; the subject is too vast for any single human intelligence to grasp.”
Oliver Wendell Holmes, Sr
The Poet at the Breakfast Table.

Nikon camera, lenses and objectives
Olympus microscope and objectives

rjlittlefield
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Post by rjlittlefield »

Simon,

The formula is correct for a lens set to focus at infinity when it is mounted directly on the camera.

If you set the lens itself to focus closer, then added extension will usually give more magnification than the formula says. But exactly how much more is difficult to predict. The wrinkle is that the focusing mechanism inside most macro lenses also shortens the focal length as you turn the ring toward higher magnifications. What makes prediction difficult is that lens manufacturers do not specify the reduction in focal length. You will find that the formula works much better with the enlarger lens, whose focal length is fixed.

About the stage, you don't want a focus rail -- the movements will be too coarse for high magnification stacking. I find that a milling table is adequate for everything up through 10X and 20X microscope objectives, though it does get fidgety at the upper end. As NikonUser suggests, a good microscope focusing block will handle even the higher magnifications with ease. Just be careful to get one that has enough range using the fine focus knob by itself. Some microscope stages have very limited travel with fine focus -- mine is only 0.15 mm!

--Rik

Simonl
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Location: Nottingham
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Post by Simonl »

Thanks so much for your quick responses.
Things are much clearer now. Can't wait to get my hands on my new 50m 2.8 enlarger lens. No doubt the step up ring I ordered will arrive at a different time - leaving me in limbo!

Also ordered bellows from hong kong - all this waiting is kiling me! at least it is too cold for insects at the moment.

Thanks again

Simon

DaveW
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Post by DaveW »

Hi Simon,

Is that Nottingham UK or USA?

If UK where abouts are you in Nottingham. I am in Mapperley.

DaveW

NikonUser
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Location: southern New Brunswick, Canada

Post by NikonUser »

rjlittlefield wrote:Simon,
Some microscope stages have very limited travel with fine focus -- mine is only 0.15 mm!

--Rik
Some Swift scope stands seems suitable for macro stacking; SEE HERE for one with a 25mm travel on the fine adjustment.

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NU.
student of entomology
Quote – Holmes on ‘Entomology’
” I suppose you are an entomologist ? “
” Not quite so ambitious as that, sir. I should like to put my eyes on the individual entitled to that name.
No man can be truly called an entomologist,
sir; the subject is too vast for any single human intelligence to grasp.”
Oliver Wendell Holmes, Sr
The Poet at the Breakfast Table.

Nikon camera, lenses and objectives
Olympus microscope and objectives

Simonl
Posts: 22
Joined: Fri Feb 22, 2008 5:06 am
Location: Nottingham
Contact:

Post by Simonl »

Thanks for the info NU.

Just down the road in Carlton, Dave.

DaveW
Posts: 1702
Joined: Fri Aug 04, 2006 4:29 am
Location: Nottingham, UK

Post by DaveW »

Not far away then Simon. I am on Moore Road.

DaveW

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