francis_d

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<p><em>'D40 with the 18-55mm f/3.5-5.6 kit lens and his photos were MUCH sharper around the edges of people and eyes compared to mine'</em> "This is to be expected as the DOF is significantly greater. If you shot with your 35mm at the same aperture as the 18-55mm, the results would be virtually identical."</p>

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<p>Elliot, sorry I should have specified that my shots with my 18-200mm f/3.5-5.6 lens (shot in P mode as I was first learning) were not as sharp as my relative's D40 with the 18-55mm f/3.5-5.6 kit lens where he shoots in AUTO mode. To me that would seem like there's something off with either my lens (both of them though?) or the body in which case I think sending it in to Nikon would be a good idea.<br /> <br /> It seems that shooting the test chart may not be the best test, so next time I'll try taking shots with my lenses on the D40 to see if I'm able to shoot a real subject (people) wide open and get the eyes in focus vs on the D90.</p>

<p>Hi,</p>

<p>I would like to get some experienced user opinions on whether my D90 has back focusing issues.</p>

<p><strong>BACKSTORY</strong><br /> I got my D90 in Oct 2009 (first DSLR) and picked up a fair amount of knowledge in that short time IMO. I understand DoF concepts (where aperture, focal length, and subject distance affect DoF) and also having a fast enough shutter speed to avoid motion blur.</p>

<p>I wanted to be able to shoot indoors in lower lighting conditions, so I picked up a Tamron 17-50mm f/2.8 Di II (non-VC model). Shooting people wide open (f2.8) I wasn't able to get very many shots in focus. It seemed to be focusing a little behind the subject, so I'd have their hair on the side of the head in focus with the eyes blurred. I even used single point focus and focused on the eyes without recomposing to eliminate the possibility of the plane of focus being shifted. I read about people having front/back focus issues with the Tamron 17-50, so I ended up returning it because of that and the 2/3 of a stop didn't really let in that much more light.</p>

<p>I ended up getting a Nikon 35mm f/1.8G AF-S DX and discovered I was having the exact same back focus issues AGAIN while shooting wide open. I tried stopping down to 2.8 with no luck. Only when stopped down to about 3.5-5.6 was I able to get the subject's eyes in focus. My problem shots were even in the 1/60-1/80s shutter speed range for relatively still subjects (people). This led me to believe that it's not the two lenses with the back focus problem, but the D90 itself. I realize that each lens may not be perfectly calibrated with +/- variances (Ref: <a href="http://www.lensrentals.com/news/2008.12.22/this-lens-is-soft-and-other-myths">http://www.lensrentals.com/news/2008.12.22/this-lens-is-soft-and-other-myths</a>).</p>

<p>In comparing my printed photos with my relative's D40 with the 18-55mm f/3.5-5.6 kit lens and his photos were MUCH sharper around the edges of people and eyes compared to mine.</p>

<p><strong>TEST CHART SHOTS</strong><br /> I printed out a focus chart (from <a href="http://www.focustestchart.com/chart.html">here</a>) and ran the test on the 35mm and 18-200mm lenses. Of course with the latter I can't get as shallow DoF.<br /> I mounted my camera on a tripod and set a 2sec countdown with the shutter delay on and flash fired. I tried my best to eyeball a 45 degree angle down towards the paper on the floor. I even did some shots hand held at varying angles and in those cases, I still had back focus problems.</p>

<p>All shot with AF single point center, focused on the letter "h" in "Focus here").</p>

<p><strong>Nikon AF-S 35mm F1.8G DX</strong><br /> 35mm f/1.8, 1/80s, flash, tripod, Aperture Priority http://i265.photobucket.com/albums/ii240/dialeleven/D90%20test%20chart/DSC_4311.jpg</p>

<p>35mm f/2.5, 1/80s, flash, tripod, Manual Mode http://i265.photobucket.com/albums/ii240/dialeleven/D90%20test%20chart/DSC_4319.jpg</p>

<p>35mm f/3.5, 1/80s, flash, tripod, Manual Mode http://i265.photobucket.com/albums/ii240/dialeleven/D90%20test%20chart/DSC_4322.jpg</p>

<p>35mm f/1.8, 1/80s, flash, handheld, Aperture Priority http://i265.photobucket.com/albums/ii240/dialeleven/D90%20test%20chart/DSC_4342.jpg</p>

<p><strong>Nikon 18-200mm f/3.5-5.6G IF-ED AF-S VR DX</strong><br /> 18mm f/3.5 1/30s flash, tripod, Aperture Priority http://i265.photobucket.com/albums/ii240/dialeleven/D90%20test%20chart/DSC_4312.jpg</p>

<p>18mm f/3.5 1/30s flash, handheld, Aperture Priority http://i265.photobucket.com/albums/ii240/dialeleven/D90%20test%20chart/DSC_4333.jpg</p>

<p>From the samples, do you think the D90 has back focus issues and should be sent into Nikon for calibration?</p>

<p>P.S. I bounced back from Aperture Priority to Manual to see if I could get the 35mm shots brighter.</p>

<p>John, thanks for clearing up that up for me. I'll check out the 50mm F1.4G next time I'm at the camera store and compare what I see on my DX zoom lens at 50mm to get an idea. I had a feeling there was more to it than physically moving back, but I'm sure as you say it'll be easier for me to see it myself than read about the visual differences.</p>

<p>Ben, nice analogy with what happens with mounting a full frame lens on a crop sensor camera. I think that's the best explanation I've heard before.</p>

<p>Thanks for the responses everyone.</p>

<p>Just a quick follow up question taking the Nikon 50mm F1.4G example again. Below is the field of view of the 50mm lens on a full frame and crop sensor camera:</p>

<p>Full Frame: FL 50mm, FOV 40 degrees<br />Crop sensor: FL 50mm, FOV 27 degrees</p>

<p>Does that mean in order to get the same field of view as on a full frame camera, you'd have to physically move back from your subject X number of feet when used on a crop sensor camera? But by doing that you wouldn't get the same magnification of your shot (right?) compared to the FF camera.</p>

<p>Hi, I just picked up a Nikon D90 a few months ago and am progressively picking up things.<br /> <br /> I know that using a full frame lens on a crop sensor will result in a smaller angle of view. For example, take the Nikon 50mm F1.4G. When used on a DX body, the angle of view is equivalent to 75mm (50mm x 1.5) on a full frame body.<br /> <br /> Now, having that 75mm angle of view wouldn't change the focal length of 50mm to 75mm on a DX body would it?<br /> <br /> Just wanted to get that clear in my head.</p>