How to "trick" my camera to focus through glass?

[roy_even_aune]

<p>Hi</p>

<p>I want to photograph a document behind a glass pane. The document is framed, so putting it in a scanner won't help, and I would like to avoid taking it out of the frame as it's old and fragile. </p>

<p>I have a Nikon D3200 with a kit lens (AF-S Nikkor 18-55mm 1:3,5-5,6G VR lens). The document is well lit so light is not an issue. The document is framed behind art glass - i.e. glass with low reflections - so there are only minimal reflections in the glass. The light is also positioned in such a way that lights are not reflected directly against the camera. The camera is on a tripod about 50 cm away from the document. </p>

<p>But all the photographs I take is slightly out of focus. When I hang a test sheet in <em>front</em> of the glass the resulting photograph is excellent, but when I try to photograph through the glass I get very poor results. It's a though the camera focuses on the front of the glass rather on what's behind the glass. I'm using auto-focus since the camera software is far better than I am to correctly focus on letters and make every letter on the document readable. </p>

<p>Does anybody know <em>how</em> the D3200 auto-focuses, and how to make it auto-focus on what's <em>behind</em> the glass instead of the glass pane itself?</p>

[bebu_lamar]

<p>If I were to shoot thru glass like a window I would put the lens against the glass or very close to it.<br>

In your case I would simply use manual focus.</p>

[Member69643]

<p>It could be the glass itself. If you had a similar piece of glass you could focus on a flat document, turn off the auto-focus, then set the glass down on top of the document. If the image is blurred it's the glass.</p>

<p>But really, if you shoot at nearly any f-stop, but use f8 for argument's sake, the thickness of a pane of glass simply won't matter, unless it's like an inch thick. The DOF will accommodate the slight focus difference.</p>

[SCL]

<p>Manual focus, tripod and f8 should do the trick.</p>

[Wouter Willemse]

<blockquote>

<p>I'm using auto-focus since the camera software is far better than I am to correctly focus on letters and make every letter on the document readable.</p>

</blockquote>

<p>Well, uhm, it apparently isn't ;-)<br>

You could try with a circular polariser filter to eliminate reflections even better, but good CP filters cost quite a bit. The solution given above is much easier, and cheaper. And I'd use the magnified view on Live View to see better if your manual focussing is spot-on. And I must say, the 18-55 does have a pretty horrible focus-ring, but for one-time use, it's useable enough.</p>

[roy_even_aune]

<blockquote>

<p>Well, uhm, it apparently isn't ;-)</p>

</blockquote>

<p>What I ment was that I usually get better results with auto-focus instead of manual focus. It's just that blasted glass that confuses the camera. But I've never used magnification on live view, which might give me better results for fine-tuning the manual focus. </p>

<blockquote>

<p>But really, if you shoot at nearly any f-stop, but use f8 for argument's sake, the thickness of a pane of glass simply won't matter, unless it's like an inch thick. The DOF will accommodate the slight focus difference.</p>

</blockquote>

<p>This is where things get embarassing (plus it's the reason why I post in the beginners forum :-) DOF? What is that? and f8? Why exactly f8?<br>

Thanks so much for helping me out with this - I'm really a noob where photography is concerned, but I'm trying to learn. </p>

[walter_degroot]

<p>this spounds like the problem a friend has with his panasonic<br>

digicam. he tahes his grandkids to the zoo and gets sharp photos of the fence,<br>

I offered him a MF film camera but he has switched to digital,<br>

there has to be a way. it irks him as he has mentioned it more than once.</p>

 

[ann_overland]

<p>I think you should be able to autofocus on the document if you can hang it up on a wall and make sure that the lens is pointed at the text in the middle of the dokument at an angel of 90 degrees. I think the problem you are encountering most likely has to do with dept of field. If you shoot in aperture priority mode and set the aperature to f/8, then I think you should be set to go. Check your manual for how you do that. And you would want to read up on the subject to be able to get dept of field and exposure right.</p>

[bebu_lamar]

<p>I don't see that auto focus is better than manual focus except when I don't have the 5 seconds to focus manually.</p>

[jcuknz]

<p>The usual problem is reflections of the camera and yourself in the glass. The answer here is simple although perhaps hard to implement. Glass reflects light which spoils the picture, if it reflects darkness the camera does pick up the reflections = good photo. So organise the balance of light between the framed subject and the areas the glass reflects so that on the camera and you is too little to register. I would also use as long a lens as you have to reduce the angle of reflections seen by the camera lens and likewise the amount of area you need to darken. In some situations a black cloth with just a hole for the lens to see through may be needed.<br>

If that is not possible then you may have to resort to using a polarising filter to supress reflections or shoot from an angle, correcting in editing ... but even then you need to have a dark area being reflected by the glass.<br>

So you have a lighting problem to sort out not a focusing problem :-)</p>

[norfolk_nsfw_maybee]

 

<blockquote>

<p>The usual problem is reflections of the camera and yourself in the glass.</p>

</blockquote>

 

<blockquote>

<p><img src="http://i1104.photobucket.com/albums/h332/sweetmk22/Photography/2012-10-14124622766x800_zps3aaba1ac.jpg" alt="" width="766" height="800" /></p>

<p>I never have problems with reflections off of glass! LOL<br>

Notice how the camera focused on me via reflection? I was photographing an insect on the window.</p>

</blockquote>

[dthew]

<blockquote>

<p>DOF? What is that? and f8? Why exactly f8?</p>

</blockquote>

<p><a href="http://www.shortcourses.com/use/using1-9.html">This page</a> explains aperture and depth of field (check out the animations down the left hand side)</p>

<p><a href="http://www.geofflawrence.com/depth_of_field.html">This page</a> by Geoff Lawrence goes into more detail and how it can be used creatively</p>

<p> </p>

[dthew]

<p>A while back, I took some pics of a ruler to help me understand Depth of Field (DoF), so I've dug them out. These were taken with a micro 4/3 camera with a 25mm lens at about 30cm. As you delve deeper into this you will fid out that sensor size, lens focal length and distance from subject will all have an effect on DoF, but we can ignore these for now. The point of focus was the number '7' on all pics.</p>

<p>At f/2 (wide aperture) only the 7 is in focus, with 6 and 8 out of focus and the near and far end of the ruler just being a blur. Very shallow DoF!</p>

<p><img src="http://d6d2h4gfvy8t8.cloudfront.net/16820697-lg.jpg" alt="" width="457" height="640" /></p>

<p>By f/4, the 6 and 8 are now in focus, but the near and far end are still blurry</p>

<p><img src="http://d6d2h4gfvy8t8.cloudfront.net/16820696-lg.jpg" alt="" width="457" height="640" /></p>

<p>Closing down to f/8 increases the DoF even more and the whole ruler is recognisable with only the near and far end being out of focus.</p>

<p><img src="http://d6d2h4gfvy8t8.cloudfront.net/16820695-lg.jpg" alt="" width="457" height="640" /></p>

<p>At f/16 (very small aperture), depth of field is at its greatest and the whole ruler is pretty much in focus.</p>

<p><img src="http://d6d2h4gfvy8t8.cloudfront.net/16820694-lg.jpg" alt="" width="457" height="640" /></p>

<p>Might be worth going through a similar exercise with your camera and lens.<br>

Also shoot at 18mm and 55m to see how that affects DoF.</p>

[bebu_lamar]

<blockquote>

<p>and f8? Why exactly f8?</p>

</blockquote>

<p> <br>

It's just a way of saying use a medium aperture, small enough to have decent DOF and not too small to cause lost of sharpness. I don't know about today but in the old days f/8 is about in the middle of the aperture range. </p>

[mendel_leisk]

<p>I always though DOF stood for Depth of <em>Focus</em>, grumble.</p>

<p>I'd concur with the glut of responses:</p>

<p>1. Most times I find auto-focus is <em>not</em> fooled by glass.</p>

<p>2. If it is a problem, switch to manual focus, if possible.</p>

[J.W. Wall]

<blockquote>

<p>Wikipedia: <strong>Depth of focus</strong> is a <a title="Lens (optics)" href="http://en.wikipedia.org/wiki/Lens_(optics)">lens</a> <a title="Optics" href="http://en.wikipedia.org/wiki/Optics">optics</a> concept that measures the tolerance of placement of the image plane (the <a title="Film" href="http://en.wikipedia.org/wiki/Film">film</a> plane in a camera) in relation to the lens. In a camera, depth of focus indicates the tolerance of the film's displacement within the camera, and is therefore sometimes referred to as "lens-to-film tolerance."....</p>

</blockquote>

[jcuknz]

<p>DoF can stand for Depth of Field or depth of focus .. either when outside the camera or inside the camera respectively.<br>

As for the foolish comment at the top of the page ... LOL ... Some knit trying to pick a non existant knit.</p>

[Wouter Willemse]

<p>Ron, In addition to David's excellent posts on how depth of field and aperture come together, what he has explained there is one of the "photography basics" and well worth knowing about, and getting very familiar with.<br>

If you want to dive deeper into photography, it could be very beneficial learning these basics. They're not specific to your camera or lens, so you can carry them with you all of your life :-) Depending on how you prefer to learn, you could look for a community college or local photo club doing photography courses, look up the <a href="/learn/">Learning section</a> here on photo.net, or a good book to get started: <a href="http://www.amazon.com/Understanding-Exposure-3rd-Edition-Photographs/dp/0817439390/ref=dp_ob_title_bk">Understanding Exposure</a>, by Bryan Peterson.<br>

These are just generic tips, but I hope they can help you a bit all the same.</p>

<p>As an aside note, the other reason to recommend F/8 is that your lens performs at its best at that aperture, and would give you the maximum amount of detail it is capable off. Not the biggest worry, but as you progress, you will find that these small differences can just help tip the scales.</p>

[scott_murphy5]

<p>Switching to manual focus is your best bet here. A canera's autofocus is "dumb", so to speak, no matter how sophisticated it is and will focus on what it thinks is the subject, though it may be different from what you want. One caution about shooting through glass, watch for reflections of other light sources and of course YOUR reflection as well!</p>

[jcuknz]

<p>Manual focusing is the old fashioned way and really unsuitable for the modern DSLR which are designed and built to use AF .. the trick is to know how to use AF and as Scott says the basic AF is just a dumb machine which needs help. The better cameras enable one to determine how AF works to get the results one wants. I haven't used Manual focus since I started shooting digital except for some very infrequent occasions, and usually it proved to be ineffective as neither AF or manual worked in some oddball situations :-( . But I do make AF work the way I would have manually focused in the past by selecting the point which I want to be my principle point of focus. Working at f/8 is probably a good aperture to work at with a DSLR though normally I would be at f/5.6 as I work with my smaller sensor and correspondingly shorter focal length lenses of M4/3 ... some of the old rules simply do not apply to the digital age. </p>

[bebu_lamar]

<blockquote>

<p>But I do make AF work the way I would have manually focused in the past by selecting the point which I want to be my principle point of focus<br>

</p>

</blockquote>

<p>I can't make AF work the way I would manually focus as I can manually focus at any point on the focusing screen not jut at some point.</p>

[jim_momary]

<p>" <em>The document is framed behind art glass - i.e. glass with low reflections - so there are only minimal reflections in the glass.</em> "</p>

<p>Doesn't that mean that the glass is sandblasted or roughened to be more diffuse?<br>

Doesn't that alone kill sharpness?</p>

<p>(I believe that anti-reflection coated glass is a lot more expensive and rare.)</p>

<p>Any reasonably priced frame I've seen with ' low reflectance' glass does reduce the clarity of the photo behind it by some noticeable measure. (even moreso if a mat spaces the paper further from the glass surface)<br>

<a href="http://en.wikipedia.org/wiki/Picture_framing_glass">http://en.wikipedia.org/wiki/Picture_framing_glass</a></p>

<p>Can't think a way around that without removing the glass.</p>

<p>Jim</p>

[James G. Dainis]

I have to agree with Mr. Momary. A friend of mine bought some anti-reflection glass to use on his 8x10 contact prints for an exhibit. He was upset at how much of the sharpness of the contact prints was loss due to the texture of the glass. If the glass has texture I would imagine the camera is focusing on that texture. At about 2 feet with f/3.5 and 55mm the DOF is less than 3/8 inch.

[jcuknz]

<p>You are behind the times BeBu .... With Panasonic I have a touch screen to select the focus point on, anywhere on it :-) The arguments people come up with to defend their antique way of working LOL</p>

[bebu_lamar]

<p>Oh sure! I am way behind the times as I am still using fully manual cameras and using film. I have no problem like the one the OP has. So much for improvement.</p>