Why is Window Glass So Bad to Shoot Through?

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Clickalot
Clickalot Regular Member • Posts: 444
Why is Window Glass So Bad to Shoot Through?

I guess it's a lesson in why optical glass costs buckets of dough, but I've learned that even freshly cleaned, streak-free window glass destroys fine detail and creates haze in pix taken through it no matter how scrupulously one chooses outdoor light conditions that obviate room/clothing reflections.

It's probably got to to with molecules and crystalline structure and stuff, no?

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FrancoD Forum Pro • Posts: 13,669
Re: Why is Window Glass So Bad to Shoot Through?
10

Because it's a pane.

Chris R-UK Forum Pro • Posts: 20,943
Re: Why is Window Glass So Bad to Shoot Through?
1

My guess is that window glass is not perfectly flat and that is what causes a lot of the problems.  Shooting at an angle to the glass makes things worse.  Dirt on the window doesn't seem to make much of a difference provided the front of the lens is very close to the glass and the target is some way off.

I posted this comparison a few years ago:
https://www.dpreview.com/forums/post/59574435

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Chris R

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David1961
David1961 Senior Member • Posts: 3,498
Re: Why is Window Glass So Bad to Shoot Through?
2

The refractive index of various types of glass also probably causes issues when photographing through it.

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Clickalot
OP Clickalot Regular Member • Posts: 444
Re: Why is Window Glass So Bad to Shoot Through?

Chris R, thanks for posting your examples. That is precisely what I'm getting: with the most fastidious technique to avoid reflections and with the lens hood flat upon the glass, I still get that slight blurring of finest details, sort of a lens glaucoma.

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Clickalot
OP Clickalot Regular Member • Posts: 444
Re: Why is Window Glass So Bad to Shoot Through?

"The refractive index of various types of glass also probably causes issues when photographing through it."

I agree it must be that because there was absolutely no surface residue on the glass and after several disappointing shots I simply placed the lens hood smack upon the window to ensure no reflections. Shots that way were properly contrasty but still a tick or two below the sharpness I'm accustomed to from my lenses.

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JasonTheBirder
JasonTheBirder Senior Member • Posts: 1,160
Re: Why is Window Glass So Bad to Shoot Through?

Clickalot wrote:

I guess it's a lesson in why optical glass costs buckets of dough, but I've learned that even freshly cleaned, streak-free window glass destroys fine detail and creates haze in pix taken through it no matter how scrupulously one chooses outdoor light conditions that obviate room/clothing reflections.

It's probably got to to with molecules and crystalline structure and stuff, no?

There are two reasons. The first is due to the light passing from air to glass. Part of the light through uncoated glass is reflected, no matter how clean it is, due to the way light waves pass through materials of different refractive indices. Coatings can reduce this reflection. Sort of like the difference between cheap and expensive UV/protective filters (which I never use).

Another cause can be a temperature differential and turbulent air flow due to the heating and cooling of air if your house is a  different temperature from outside.

However, I have some people post some pretty decent through the window shots so it is possible to minimize this effect.

FrancoD Forum Pro • Posts: 13,669
Re: Why is Window Glass So Bad to Shoot Through?
1

Yes, there are a few variables but occasionaly one can get a decent shot through glass. This is from pretty much where I am sitting,  looking out at a tree 2-3 metres away.

With that particular lens it is about as good as it gets.

BGD300V1
BGD300V1 Senior Member • Posts: 2,509
If you aren't perpendicular to the window

There will be some refraction.  You can also get internal reflections which are worse with thermopane where you will have 4 or 6 air to glass surfaces instead of the two of single pane.

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Leonard Migliore
Leonard Migliore Forum Pro • Posts: 18,332
Re: Why is Window Glass So Bad to Shoot Through?
3

Because it's not flat.

Windows are made out of float glass: https://en.wikipedia.org/wiki/Float_glass

where molten glass is poured onto a metal bed and slowly cooled. This makes it pretty flat. But in optics, we like things even flatter. Your customary optical surface is flat to 1/4 wave of light. So that's about a tenth of a micron. If it's not that flat, it messes up the wavefront of the light going through it. Now if you're stopped down to f/11 or so, window glass doesn't cause a lot of problems but if you're using some aperture, you get unsharpness.

As an aside, the Hubble telescope primary was accurate to 1/64 wave. But it was accurate to the wrong shape.

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lost alaskan
lost alaskan Senior Member • Posts: 1,542
Re: Why is Window Glass So Bad to Shoot Through?

That is a beautiful bird.

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A Marcus Regular Member • Posts: 120
Re: Why is Window Glass So Bad to Shoot Through?

While the optical flatness of window glass is likely poor, that is not the real reason for your disappointment.

The glass window has two surfaces, both reflect light. This reflectivity induces flare light.  Flair is misdirected light rays that intermingle with the image forming rays. Flare will reduce the reduce the image contrast. Additionally, your camera is attempting to focus on the main object being imaged. Sometimes, this automation will be foiled and the camera sets the focus distance, not of the subject but on the glass window. Thus the sharpness of the key objects being imaged will be  compromised.

FingerPainter Veteran Member • Posts: 9,501
Even if you are

Even if you are perpendicular to the window, unless you have a very narrow FOV, much of the light reaching your camera lens will not have been travelling perpendicular to the window when it passed through the window. This will cause refraction, which may vary by wavelength.

FrancoD Forum Pro • Posts: 13,669
Re: Why is Window Glass So Bad to Shoot Through?

lost alaskan wrote:

That is a beautiful bird.

It's the very common starling, a pest here in Australia. BUT it does not often look like that when they fly about.

BGD300V1
BGD300V1 Senior Member • Posts: 2,509
A bit of explanation

https://www1.curriculum.edu.au/sciencepd/readings/ligh_refraction.htm

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Doug Haag Senior Member • Posts: 2,343
Re: Why is Window Glass So Bad to Shoot Through?

Clickalot wrote:

I guess it's a lesson in why optical glass costs buckets of dough, but I've learned that even freshly cleaned, streak-free window glass destroys fine detail and creates haze in pix taken through it no matter how scrupulously one chooses outdoor light conditions that obviate room/clothing reflections.

It's probably got to to with molecules and crystalline structure and stuff, no?

Glass is a strange material in that even when cooled from its molten state to a solid it does not have a crystalline structure.  Although not a perfect analogy, think of it as a liquid that, at room temperature, has become so viscous that it seems rigid.  The reason this is not a perfect analogy is that it would appear to explain why some centuries old windows are thicker at the bottom than at the top -- the "liquid" having slumped over time.  But that is not the explanation for that phenomenon which can be Googled.

Anyway  https://www.google.com/search?client=firefox-b-d&sxsrf=ALeKk02EBerKbgFkDVPtThZWpgAagp98wQ%3A1603195959471&source=hp&ei=N9SOX42uGtGktQb88btA&q=does+glass+have+a+crystalline+structure&oq=does+glass+have&gs_lcp=CgZwc3ktYWIQARgAMgUIABDJAzICCAAyAggAMgIIADICCAAyAggAMgIIADICCAAyAggAMgIIADoECCMQJzoICC4QsQMQgwE6CAgAELEDEIMBOgsILhCxAxDHARCjAjoFCAAQsQM6CAgAELEDEMkDUOsOWJE_YNZWaABwAHgAgAFsiAHzCZIBBDE0LjGYAQCgAQGqAQdnd3Mtd2l6&sclient=psy-ab

Clickalot
OP Clickalot Regular Member • Posts: 444
Re: Why is Window Glass So Bad to Shoot Through?

Thanks for everyone's replies!

I had forgotten about the double-paned nature of modern window glass. Thats a non-optical glass-air-glass barrier in front of an already questionable UV filter all my lenses had.

They no longer have those filters; I'll just be more diligent in protecting the front elements.

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BGD300V1
BGD300V1 Senior Member • Posts: 2,509
Re: Why is Window Glass So Bad to Shoot Through?
2

FrancoD wrote:

lost alaskan wrote:

That is a beautiful bird.

It's the very common starling, a pest here in Australia. BUT it does not often look like that when they fly about.

And thanks to fans of Shakespeare a real problem in the US.

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FrancoD Forum Pro • Posts: 13,669
Re: Why is Window Glass So Bad to Shoot Through?
1

Doug Haag wrote:

Clickalot wrote:

I guess it's a lesson in why optical glass costs buckets of dough, but I've learned that even freshly cleaned, streak-free window glass destroys fine detail and creates haze in pix taken through it no matter how scrupulously one chooses outdoor light conditions that obviate room/clothing reflections.

It's probably got to to with molecules and crystalline structure and stuff, no?

Glass is a strange material in that even when cooled from its molten state to a solid it does not have a crystalline structure. Although not a perfect analogy, think of it as a liquid that, at room temperature, has become so viscous that it seems rigid. The reason this is not a perfect analogy is that it would appear to explain why some centuries old windows are thicker at the bottom than at the top -- the "liquid" having slumped over time. But that is not the explanation for that phenomenon which can be Googled.

Anyway https://www.google.com/search?client=firefox-b-d&sxsrf=ALeKk02EBerKbgFkDVPtThZWpgAagp98wQ%3A1603195959471&source=hp&ei=N9SOX42uGtGktQb88btA&q=does+glass+have+a+crystalline+structure&oq=does+glass+have&gs_lcp=CgZwc3ktYWIQARgAMgUIABDJAzICCAAyAggAMgIIADICCAAyAggAMgIIADICCAAyAggAMgIIADoECCMQJzoICC4QsQMQgwE6CAgAELEDEIMBOgsILhCxAxDHARCjAjoFCAAQsQM6CAgAELEDEMkDUOsOWJE_YNZWaABwAHgAgAFsiAHzCZIBBDE0LjGYAQCgAQGqAQdnd3Mtd2l6&sclient=psy-ab

No that is not true. Those glass panes were made like that.

Glass used to be span out by hand, so the outside became slightly thicker than the inside part. It seemed logical to put the thicker part always at the bottom.

Doug Haag Senior Member • Posts: 2,343
Re: Why is Window Glass So Bad to Shoot Through?

FrancoD wrote:

Doug Haag wrote:

Clickalot wrote:

I guess it's a lesson in why optical glass costs buckets of dough, but I've learned that even freshly cleaned, streak-free window glass destroys fine detail and creates haze in pix taken through it no matter how scrupulously one chooses outdoor light conditions that obviate room/clothing reflections.

It's probably got to to with molecules and crystalline structure and stuff, no?

Glass is a strange material in that even when cooled from its molten state to a solid it does not have a crystalline structure. Although not a perfect analogy, think of it as a liquid that, at room temperature, has become so viscous that it seems rigid. The reason this is not a perfect analogy is that it would appear to explain why some centuries old windows are thicker at the bottom than at the top -- the "liquid" having slumped over time. But that is not the explanation for that phenomenon which can be Googled.

Anyway https://www.google.com/search?client=firefox-b-d&sxsrf=ALeKk02EBerKbgFkDVPtThZWpgAagp98wQ%3A1603195959471&source=hp&ei=N9SOX42uGtGktQb88btA&q=does+glass+have+a+crystalline+structure&oq=does+glass+have&gs_lcp=CgZwc3ktYWIQARgAMgUIABDJAzICCAAyAggAMgIIADICCAAyAggAMgIIADICCAAyAggAMgIIADoECCMQJzoICC4QsQMQgwE6CAgAELEDEIMBOgsILhCxAxDHARCjAjoFCAAQsQM6CAgAELEDEMkDUOsOWJE_YNZWaABwAHgAgAFsiAHzCZIBBDE0LjGYAQCgAQGqAQdnd3Mtd2l6&sclient=psy-ab

No that is not true. Those glass panes were made like that.

Glass used to be span out by hand, so the outside became slightly thicker than the inside part. It seemed logical to put the thicker part always at the bottom.

Are you unable to read English and comprehend what you read?  I said that because glass at room temperature is like a very viscous fluid, that characteristic would "appear" to explain why ancient glass is thicker at the bottom."  I immediately followed that up by saying that is NOT the explanation for the phenomenon and that the real reason can be Googled.

You apparently did the Googling and discovered that I was correct about there being a different reason.  But then you bolded a portion of my text, ignored the rest of what I wrote, and proclaimed an error.  Brilliant.

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