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Internal baffles for Thorlabs 3" tubes

 
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Andy Davies



Joined: 09 Dec 2014
Posts: 98

PostPosted: Thu Aug 16, 2018 4:00 am    Post subject: Internal baffles for Thorlabs 3" tubes Reply with quote

I'm looking for some suggestions for the design of a 3D printed baffle to fit inside Thorlabs 3" tubes.

The length from a recess just inside the camera bayont fitting to a another recess at the end of the tubes is 142mm.

Diameter of recess at camera bayonet is 48mm.

Diameter of recess at end of tubes is 63mm.

One option is to make a conical tube and flock inside.

Or, I guess it is better to have baffles - how many, what angle and what depth?

Many thanks

Andy
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enricosavazzi



Joined: 21 Nov 2009
Posts: 1089
Location: Stockholm, Sweden

PostPosted: Thu Aug 16, 2018 4:37 am    Post subject: Reply with quote

As a general comment, plane baffles should be as thin as possible, at least around the edge of their aperture. This is why well-made industrial baffles are laser-cut from a very thin steel sheet (a few tens of microns to perhaps 100 microns max, which is much thinner than ordinary 3D printers using a molten plastic filament can print).

The thicker the baffle material, the more light has a chance of striking the thickness of material exposed around the edge of the aperture, and to be reflected or diffused back into the optical path.

As another comment, it does not matter whether the baffle material is a flat sheet or conical. The only thing that matters is the size and shape of the aperture. However, a deeply conical baffle may allow light to bounce off its inner wall, so a broadly conical or flat baffle is preferable (unless the mechanics inside the lens barrel force the use of a conical baffle).
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Andy Davies



Joined: 09 Dec 2014
Posts: 98

PostPosted: Thu Aug 16, 2018 4:56 am    Post subject: Reply with quote

There is a Raynox 5320 with a 10x Mitty attached to the end of the Thorlabs tube and a Nikon D810 on the other end.
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enricosavazzi



Joined: 21 Nov 2009
Posts: 1089
Location: Stockholm, Sweden

PostPosted: Thu Aug 16, 2018 5:23 am    Post subject: Reply with quote

Andy Davies wrote:
There is a Raynox 5320 with a 10x Mitty attached to the end of the Thorlabs tube and a Nikon D810 on the other end.


Then I would start by drawing a diagram with a truncated cone that starts at the Mitty end with an opening slightly wider than the baffle at the rear of the Mitty and ends with an opening slightly wider than the Raynox glass. The diagram tells you the minimum diameter of a baffle opening for a baffle located at a specific distance within the tube. This guarantees that there can be no vignetting.

To further optimize, you may make the Raynox end of the cone narrower (exactly how narrow, depends on the distance of the Raynox to the sensor and on the sensor size, and it is easiest to find by trial and error than by computing it). Any baffle within the tube must become correspondingly narrow, depending on where they sit within the tube.

Baffle openings with a rounded rectangular shape make things more complicated, and are really needed only near the sensor plane.

The optimal shape and size of baffles can of course be computed with ray tracing, but trial-and-error with round baffles cut out of black cardboard is much easier if you only need one or a couple of baffles.

As long as other inner surfaces are not extremely reflective (paint them flat black or flock them in this case), just a single baffle roughly halfway in the tube, with the right opening size, thin and well blackened, could be enough to totally eliminate flare.
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mawyatt



Joined: 22 Aug 2013
Posts: 1665
Location: Clearwater

PostPosted: Thu Aug 16, 2018 5:43 am    Post subject: Reply with quote

Andy,

With the 3" Thor tubes I would think that a rolled up cylinder of Beetle Black card stock (blackest material I've found) would work well. Just blacken the edges of the card stock with a black pen since they aren't covered with the black velvet like material. I use double sided sticky tape or Protostar (has sticky backing) for the back sides of adapters interiors.

This may not be as good as a perfect baffle configuration, but is very easy to do and works quite well.

Best,
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Andy Davies



Joined: 09 Dec 2014
Posts: 98

PostPosted: Thu Aug 16, 2018 5:46 am    Post subject: Reply with quote

I have the Mitty very close to the Raynox as worked out by Nathan so no space for a baffle there.

I am talking about the tube between the camera and the back of the Raynox.

I am using Fusion 360 to do the design and it can "loft" between a circle and a rectangle a certain distance away and insert baffles inbetween. Depth, angle, number?

I understand from your post that the edges of the baffles should be as thin as possible.
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enricosavazzi



Joined: 21 Nov 2009
Posts: 1089
Location: Stockholm, Sweden

PostPosted: Thu Aug 16, 2018 10:12 am    Post subject: Reply with quote

Andy Davies wrote:
I have the Mitty very close to the Raynox as worked out by Nathan so no space for a baffle there.

I am talking about the tube between the camera and the back of the Raynox.

I am using Fusion 360 to do the design and it can "loft" between a circle and a rectangle a certain distance away and insert baffles inbetween. Depth, angle, number?

I understand from your post that the edges of the baffles should be as thin as possible.

For APS-C sensors, I would start with a rectangular baffle with rounded corners, with an opening roughly 28 x 23 mm somewhere close to the rear mount of the tube. Test for vignetting (e.g. by taking a shot with the Raynox mounted at the front of the tube and an illuminated diffusor right in front of the Raynox). If there is any vignetting, use a wider opening. You should not need a smaller opening.

For full-frame, I would start with a roughly 40 x 30 mm rounded rectangle, if it can fit within the tube.

For a second baffle, I would try putting one about one third of the length in from the front, circular and about 10 mm wider than the glass of the Raynox.

These two baffles may suffice, especially if you flock the inside of the tube. If not, I would place an additional baffle roughly two-thirds of the length from the front of the tube. I would start with a size and shape roughly the same as the rearmost baffle, or just a little smaller.

As mentioned earlier, you can do the testing with baffles cut out of a thin black matte cardboard (thick enough to completely block light, no more). This material can last indefinitely for a setup that is only used indoors, but a more humidity-resistant plastic sheet or metal sheet may be better for outdoors use.
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