Auto focusing problem

[Timofey Gorlov]

I can show the real focused image through the same acrylic glass that has the same clarity as IMG_0380.JPG.
The focusing distance is about 150 mm.
The focusing distance for IMG_0380.JPG is about 1000mm.
The clarities and sharpness of both pictures are the same. May be illumination is different because of times.
The Focuses are different! So the problem not in quality of glass. I think I have a good logic.

 

[astroNikon]

To me I see a massive difference in quality. give me a few to show some crops

 

[Timofey Gorlov]

To me I see a massive difference in quality. give me a few to show some crops

There is another one with the glass that has a similar illumination

 

[astroNikon]

the original 038 shows details in the windows, the cross members and such. The other ones, including the one you just uploaded, with the acryliv have lost ALL detail.

It's even worse if you look at the house to the left. I thought they put a sheet of plastic over the house in one of the photos - zoom in and look at the windows.

 

[wfooshee]

You keep asking, "Why does the flat glass affect the pictures so much?" but you won't accept the answer, which is:

It's not glass. Acrylic is plastic. It's not transparent. It's "fuzzy."

Light bends every time it passes through a surface. The acrylic surface is not anywhere close to as smooth as a real glass surface, so the light entering and exiting the acrylic bends differently at every different point of the surface. Then there is the lack of transparency, the cloudiness of the acrylic. Every microscopic bubble or bit of uneven material density provides another light-bending surface.

A flat sheet of optical glass minimizes that by being pure. The surface is smooth with no irregularities, down to a microscopic flatness, and the material inside the surface is uniform and clear. A flat sheet of glass in front of the lens, and parallel to the focal plane, with no light behind it causing reflections, would have a minimal impact on the image clarity.

A sheet of plastic, though, cannot help but scatter the light. There's a difference between "I can see through it" and optically transparent.

Please stop asking, "Yeah, but why?" You've been told why. If you have a need for the acrylic sheet in order to protect yourself or the camera from something on the other side, then you have to accept the optical limitation, or go find something more transparent but still with impact protection, which will be expensive.

 

[astroNikon]

At first I thought the one picture with the acrylic that you just uploaded, the owners put plastic over the windows to keep drafts out. But when I checked the houses to the right it was the same problem.

But on the #62 image if you just look at the windows it looses all detail. Even the shutters are nearly gone in the image of the small window. The windows look like it has plastic over them.
The bricks has lost all detail. The roof. If you see the full image the trees are all fuzzy.

You may not be used to looking at photographs and comparing but once you do, you'll know the differences. this is all due to the "acrylic" not being "optical quality".

 

[Timofey Gorlov]

At first I thought the one picture with the acrylic that you just uploaded, the owners put plastic over the windows to keep drafts out. But when I checked the houses to the right it was the same problem.

But on the #62 image if you just look at the windows it looses all detail. Even the shutters are nearly gone in the image of the small window. The windows look like it has plastic over them.
The bricks has lost all detail. The roof. If you see the full image the trees are all fuzzy.

You may not be used to looking at photographs and comparing but once you do, you'll know the differences. this is all due to the "acrylic" not being "optical quality".
View attachment 94196 View attachment 94197

The post became little bit confusing. The last two pictures that you compare made in a different times of the day (that is my fault). Originally I supposed to show focusing issue. Just compare IMG_0380.JPG and IMG_0176.JPG that I attached that is still made in a different time-shades distribution.
Ok, forget about it.

 

[astroNikon]

but we're not talking about the light / time of day.
we're talking about the fuzziness of the image, or "washed" out image due to the acrylic.
The window detailed are totally different. bricks are washed out, and roof, trees .. not due to lighting variances.

 

[tecboy]

Take the acrylic glass off from your lens, and you will not have anymore problem.

 

[Timofey Gorlov]

Thanks for discussions. I'll continue this thread with more strict pictures/questions if I get one.

 

[Timofey Gorlov]

After all I figured out that infinite auto focusing gives a bad result and average distance focusing setting gives sharp image through the same acrylic glass. In this way I could resolve my problem without understanding why it happens. There is no real physical reason for it. I would assume that the glass somehow affects focusing mechanism or algorithm when focusing is setup for infinity. This is my big project and I cannot avoid using acrylic screen because it's a waterproof case for my camera.
I think my case can be useful for other people who use outdoor case. Just don't use "infinity" setting for it.

 

[astroNikon]

I use manual focus to shoot through any material. The Autofocus system wants to use any contrast to use for identifying where the object is. If the glass is not perfectly clear (to the camera and not to you), then it will have an issue with focusing and clarity.

and see post # 2

 

[wfooshee]

With a modern lens, you probably shouldn't ever use infinity anyway. To accommodate manufacturing tolerances, camera-to-camera differences, and so on, a lens set to infinity may actually be set past infinity.

You may well ask, "How can it be set farther???" but it's a simple answer. As you turn the focus ring towards infinity, the elements in the lens move physically. There is a point at which they are focused on something as far away as it's physically possible to focus on. Most lenses, however, can keep turning, and thus the elements move even farther, and move past the point of achieving focus at infinity, giving you your unexpectedly blurry image.

Just cranking the ring over to the stop is absolutely no guaranty of good focus at infinity!