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3D Printed hood for mitutuyo

 
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Yawns



Joined: 20 Dec 2015
Posts: 383
Location: Benavente, Portugal

PostPosted: Thu Nov 07, 2019 7:24 am    Post subject: 3D Printed hood for mitutuyo Reply with quote

A friend asked me to design a 3D printed hood for his mitutoyo lenses.
5x (0.14) 10X (0.28 ) and 20X (0.28 )

The problem is, I don't have any. If I had, I would draw a prototype, print it, and then see what happened.

I fetched the lens barrel dimensions from Mitutoyo's catalog and designed a CAD model with precise lens dimensions ...

My fear is that the hood will interfere with the entrance pupil (cone of light?)

So I checked the working distances of the lenses and the Na value of each one and calculated ArcSin (Na) to know the angle of each cone and drew a Hood whose front hole does not interfere with that calculated cone ...

But as my knowledge of apertures and light cones and entry pupils is close to zero.
I am not sure if my reasoning is correct and if the Hood will not cause problems .. change the Objectives Na or something ...

76179259_184516022714003_6558283604927971328_o by antonio caseiro, on Flickr

72967142_184516052714000_2793553188672765952_o by antonio caseiro, on Flickr
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 20085
Location: Richland, Washington State, USA

PostPosted: Thu Nov 07, 2019 10:28 am    Post subject: Reply with quote

The general approach looks correct, except I think you have implicitly paid attention only to the center point in the field of view.

It would be more correct to be sure that the hood does not intrude into the entire volume formed by connecting every point in the rectangular subject field with every point in the round front glass of the lens.

The optimum shape turns out to be a rectangle with rounded corners, as shown at https://www.photomacrography.net/forum/viewtopic.php?p=120423#120423 and discussed in the surrounding thread.

For you, the relative sizes of the round and rectangle will be reversed, and that causes the optimum shape to be much more rounded than shown in the diagrams of that thread. You would not be far off by allowing the opening to be round, but large enough to not intrude into the corners of the field.

--Rik
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Yawns



Joined: 20 Dec 2015
Posts: 383
Location: Benavente, Portugal

PostPosted: Thu Nov 07, 2019 4:01 pm    Post subject: Reply with quote

Thanks Rick .. I read that post about 4 or 5 times and I think I understand the reasoning explained .. but elaborate on my own all the reasoning and calculations on the other side of the lens .. I am not able ...

When I read that post about the baffles , I made myself a two-baffle tube with the help of the spreadsheet at the end ... and I also had to settle for an "imperfect solution" .... with rectangular openings (because I don't have the technology to cut round corners with such small arcs .. and because to be "perfect" I would have to make a specific tube for each lens, because they all have different exit pupils ... I thought it is best to cut a percentage of reflexes, than not cutting anything.

in this case I think I'll stick to the circular opening ...I can't do better... I will draw two or three with different openings and he decides which one suits him best (if any will be of any use) ..
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 20085
Location: Richland, Washington State, USA

PostPosted: Thu Nov 07, 2019 6:52 pm    Post subject: Reply with quote

Circular is good. It also has the advantage that the user won't have to worry about how to align the hood.

--Rik
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enricosavazzi



Joined: 21 Nov 2009
Posts: 1205
Location: Borgholm, Sweden

PostPosted: Fri Nov 08, 2019 12:03 am    Post subject: Reply with quote

I agree with Rik. I may add that, from a practical point of view, it may be useful to consider the size of the field of view of these objectives when focused on a subject.

For these objectives, based exclusively on magnification, we have the following subject-side circles of view if a full-frame (24*36 mm) sensor is used. I am aware that some of these Mitutoyo objectives do not satisfactorily cover a full-frame sensor (with a 200 mm tube lens) and that an APS-C or Micro 4/3 sensor is more appropriate, but considering a full-frame sensor helps to limit the incipient darkening in the image corners caused by the out-of-focus edge of the lens shade and adds a safety margin.

The full-frame sensor format has a diagonal of 43.3 mm, which we can take as the diameter of the image circle. Therefore, we get the following diameters of the circle of view on the subject side:

5x: 8.66 mm
10x: 4.33 mm
20x: 2.17 mm

In your model of lens shade, it seems you have tested whether the edge of the "cone of light" intersects the edge of the lens shade only when the vertex of the cone of light is at the center of the field of view. To test whether the lens shade causes vignetting, tilt the vertex of the cone out of the optical axis of the lens by an amount equal to half the diameter of the circles of view listed above, and test whether this tilted cone intersects the edge and inner surface of the lens shade.
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elf



Joined: 18 Nov 2007
Posts: 1383

PostPosted: Sat Nov 09, 2019 2:11 am    Post subject: Reply with quote

This hood has worked well for me. It's rectangular. Any light hitting the side is reflected back out.

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Yawns



Joined: 20 Dec 2015
Posts: 383
Location: Benavente, Portugal

PostPosted: Sun Nov 10, 2019 4:56 pm    Post subject: Reply with quote

Tahnk you all

after Savazzi's input now I understand what Rick meant to say

all I have to do is to put a sensor N times smaller in the focus plane (working distance) .. N is the magnification of the objective
then it's like the other post about the baffles in the tube.

.. draw a loft from the "mini sensor" to the base of the cone.
sections in the desired points to get the shapes of the baffle hole and design a shell around to support the baffles ...
with CAD I don't even need to do calculations, just have to draw everything with very precise measurements ...

[url=https://flic.kr
/p/2hJ2qEX]fig 01[/url] by antonio caseiro, on Flickr

fig 02 by antonio caseiro, on Flickr

OMG elf ... Very Happy Very Happy
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Christian67



Joined: 06 Oct 2019
Posts: 1
Location: Munich, Germany

PostPosted: Fri Nov 15, 2019 5:23 am    Post subject: Reply with quote

Does anybody have some files for 3D printing and experimenting to share?
Would like to run some tests also.
Best regards,
Christian
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