Telecentric combo at 0.8X to 1.69X

A forum to ask questions, post setups, and generally discuss anything having to do with photomacrography and photomicroscopy.

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TheLostVertex
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Location: Florida

Post by TheLostVertex »

Thanks Rik, this answers a lot of my questions. Now I need to got play with it some :D

-Steven

killes
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Joined: Thu Feb 14, 2013 7:36 am

Post by killes »

rjlittlefield wrote:
killes wrote:
rjlittlefield wrote:However, that lens has one very nice feature: the entrance pupil maintains a constant distance from the front of the lens as focus changes. This simplifies the added-lens approach because no change in separation is required as the lens ring is turned to change magnification/focus.
This is exactly the reason why I did not want the "lens in front" approach, I thought the changing distance would be a problem.
Well, it's a tradeoff. With the added aperture you have to change extension at the camera, where with the added lens you have to change extension between lenses. It seems the same amount of trouble either way, and with the other advantages of added-lens versus added-aperture, I see the scales tipping toward added-lens most of the time.
Hi Rik,

sorry for not getting back to you sooner!

I've now found my setup to be not very well working. There are two issues with it:

1) the extension. The extension helps with the magnification, but also takes away light. This makes it hard to do hand-held photo in 1:1.


2) the lens. The 50mm lens I used is old and the images aren't as sharp as I am used to from my macro lens.


So I guess I'll see if I can find a used Raynox somewhere.



Cheers,
killes

rjlittlefield
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Post by rjlittlefield »

Thanks for the follow-up. Yes, the old 50 mm lenses designed for landscape and street photography do not work well when extended around 1:1. They are very soft unless stopped down a lot, like f/11 or smaller (effective f/22, at 1:1).

--Rik

pierre
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Location: France, Var, Toulon

Post by pierre »

Rik

Sorry for the bother, but I was a bit puzzled seen the use of a 90mm for a Mity. I was guessing this big guy would not work righ under 150mm.

I am missing something ?
Regards

Pierre

rjlittlefield
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Post by rjlittlefield »

pierre wrote:Sorry for the bother, but I was a bit puzzled seen the use of a 90mm for a Mity. I was guessing this big guy would not work right under 150mm.
Using a Mitutoyo M Plan Apo on such a short tube lens will give soft and aberrated corners even on APS-C. Whether the limit is 150mm or 125mm or 100mm or 90mm is largely a matter of taste. If the subject fills the frame you'll need the longer lengths; if the edges and corners are mostly for context and don't have to be sharp then the shorter lengths will do. I've published tests of the 20X on 125mm HERE, and the 10X on 100 mm HERE.

--Rik

pierre
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Location: France, Var, Toulon

Post by pierre »

Oup!

I am afraid having missed this one.
Regards

Pierre

Guido
Posts: 184
Joined: Wed Jun 08, 2011 1:02 am

Post by Guido »

Hello Rik,

thx for the tip
A question. How did you find this out? Gues the only way are test pictures.

thx

rjlittlefield
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Post by rjlittlefield »

Guido wrote:Gues the only way are test pictures.
Yes, that's the only way I know.

--Rik

Guido
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Post by Guido »

This is all new to me, sorry for that many questions.

Is this comming Close, I notice focussing that there is a difference.

Image

rjlittlefield
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Post by rjlittlefield »

Guido wrote:Is this comming Close, I notice focussing that there is a difference.
This is not yet completely telecentric. If you shift and overlay the image, as shown below, you can see that the sticks still look bigger in the foreground than they do in the background. Notice that the cyan line lies smoothly along the edge of a stick, but the orange line has to break where the images are overlayed.

Image

This sort of test is very strong, but it works better if
1) the sticks run straight up and down in the photo (instead of diagonal), and
2) you stop down a lot when the picture is taken so that the background is pretty sharp too.

This sort of test can also tell you how to adjust the position of the achromat. If the foreground is bigger than the background (normal perspective), then move the achromat farther in front of the normal lens. If the foreground is smaller than the background (inverted perspective), then move the achromat closer to the normal lens. When the achromat is at the perfect place, foreground and background will be exactly the same size.

Your test indicates that the achromat needs to be moved farther in front.

--Rik

Guido
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Joined: Wed Jun 08, 2011 1:02 am

Post by Guido »

Thx Rik this explains it. I made this picture with a 100/2.8 macro and the canon 500D close-up lens in front.

RobbieC
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Joined: Sat May 06, 2017 5:20 pm
Location: Sonoma CA

Telecentric Lens

Post by RobbieC »

Can one make most lenses near telecentric by using combos such as a Raynox 250 or other combos? How does one test a lens setup for telecentricity?

Robbie

mawyatt
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Re: Telecentric Lens

Post by mawyatt »

RobbieC wrote:Can one make most lenses near telecentric by using combos such as a Raynox 250 or other combos? How does one test a lens setup for telecentricity?

Robbie
Robbie,

If you do a search here you'll find a number of threads on the subject. I believe Rik found that putting a Raynox 250 in front of a Canon 100mm macro produced a telecentric result, I tried with a Nikon 105mm macro and got a somewhat telecentric result.

A simple test is to look into the lens front with something with infinity focus, and look for the iris (stopped down so you can see it better) to be in focus. As Rik did, I used my long glasses and eyeballed it. But wasn't sure so I used another technique described here to use a long lens focused at infinity on another camera and look at the iris. I used a 300mm, and my eyeball was close.

Hope this helps,

Best,

Mike

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