A problem with "analog" lenticular 3d-stereo printing

Lenticular sheets are of several types and for several applications. The 3D ones are designed so that images can be viewed from a shorter or longer distance, and have larger or smaller angles at which images can be viewed, which must be more than two.
Many fractions of images can be placed under a single cylindrical lens, not just two, in which case the unused space beyond two images remains white, and is reserved for the rest of the images, which are missing.

All the specifications of the lenticular sheet must be known, not just the lenses density (lpi) to calculate what to do.

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In your particular case, respecting the projection distance, you can insert 5 images under the respective lenticular sheet.
You can photograph a subject from 5 different positions at equal distances from each other and then project them onto the sheet on all 5, at the interval chosen for the two used now.

In this case there will be no need for a fixed point from which 3D image can be seen.

Actually I suspected the multiview-related issue. But I want to stick to classic stereo - 2 views only.

The lens I'm using is intended for 3D, and the declared viewing angle is 35 degrees. Intuitively, the smaller viewing angle, the better - am I right?

3D smartphones apparently show only two views, and I'd like to reproduce it.

Turbguy1 wrote:

...good lenticular prints are made with a multitude of of views (four, or even more views).

I usually use 16 views for 3D lenticular prints.
Last time, the printing company used 400 lpi lenticular sheets (almost visually imperceptible) and a top high end printer.
This means that a space of ~4 microns was allocated for each fraction of a view, under each cylindrical lens.

Oleg L K wrote:

1. Actually I suspected the multiview-related issue. But I want to stick to classic stereo - 2 views only.

2. The lens I'm using is intended for 3D, and the declared viewing angle is 35 degrees. Intuitively, the smaller viewing angle, the better - am I right?

3. 3D smartphones apparently show only two views, and I'd like to reproduce it.

1. If you wants to stick to classic stereo - 2 views only - you need a proper lenticular sheet.
2. Yes, you need a much smaller viewing angle for only two views.
3. For 3D smartphones they have custom solutions.

3D Gunner wrote:

Oleg L K wrote:

1. Actually I suspected the multiview-related issue. But I want to stick to classic stereo - 2 views only.

2. The lens I'm using is intended for 3D, and the declared viewing angle is 35 degrees. Intuitively, the smaller viewing angle, the better - am I right?

3. 3D smartphones apparently show only two views, and I'd like to reproduce it.

1. If you wants to stick to classic stereo - 2 views only - you need a proper lenticular sheet.
2. Yes, you need a much smaller viewing angle for only two views.
3. For 3D smartphones they have custom solutions.

Does anybody know where I can buy more suitable lenticular lenses in small sizes and quantities nowdays?
Microlens.com went out of business, dplenticular.com sells only large sheets, vuethru.com handles only 60lpi.

Indeed, this method can potentially produce a better "filled" interlace, how much of it will actually reach the eyes?

Optics assumed to work symmetrically; if there are dead zones on the way towards the paper, they should arise in the opposite direction too, should they not?

I never saw those linear-prism sheets. Does anybody have experience with them? Are they available for purchase?

Intuitively (but not for sure) cylindrical lenses should work better.

Linear-prism sheets are exclusively for stereo pair 3D images, cylindrical lenses are best for multiple images mounted for 3D effect. I think that nobody made linear-prism sheets today.
Analog solution for lenticular 3D is not a good one, beyond some fun.

Oleg L K wrote:

The lenticular lens used is Vuethru "souvenir photo-frame" - 60lpi.
I do achieve stereo effect, and the best viewpoint is exactly in the center... So far so good.

But the resulting picture looks very dark when properly aligned with the lenticular plastic. Studying it with a loupe reveals that about half of its area is nearly white.

Any ideas on how to improve the prints? Maybe a different lenticular lens?

Thank you in advance,
Oleg.

The lowest angle for viewing 3D lenticular images is 25 degrees. Using a 25-degree lenticular plate will reduce the size of the white space between images.
To make the image brighter, you just need to expose the photo paper less. Without the lenticular plate the image looks brighter and more washed out (due to the white spaces interspersed), but that doesn't matter, it only matters how it is seen in the end, under the lenticular plate.

You can also try to reduce the white intermediate space by double exposure, through a more complicated technique, but effort is probably not justified.

Of cause I tried to reduce the exposure AND to brighten the original (darken the negative); the gain is insufficient.

Thus I want to employ all the means to improve the picture.

My current lenticular lens has ~35-degrees angle of view; going down to 25-degrees sounds attractive, but where I can purchase these lenses today?

In theory analog solution should be the best; that's why I try it.

Oleg L K wrote:

Of cause I tried to reduce the exposure AND to brighten the original (darken the negative); the gain is insufficient.

The gain is insufficient for what? The exposure in analog enlarging process can be set at any level.

It is very easy to to make good prints with analog/chemical process, for any purpose.

As you can see, the analogue solution is neither the best nor the easiest.
First of all, the whole process has a low optical quality. That means low resolution and high diffusion coefficient. Lenticular plates are OK for playback only.

Using digital printing technology you can insert hundreds of lines of clear and precise information under each cylindrical lens on the plates you use. With analog process you can insert only 4-5, even those with noticeable diffusion in areas exposed to more light.

With digital printing, you can perfectly fill the space under each cylindrical lens with just two images, compared to the hassle of the analogue process.