Focus on a DSLR vs. a point-and-shoot

jpreston4

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Hello all,

I've been an occasional browser on the forum, but this is my first post. I'm a casual DSLR owner - photography is a fun hobby for me, but I don't have an extensive knowledge of the craft. I've owned a point-and-shoot for years, and about three years ago, I upgraded to an entry-level DSLR (Nikon 3100). I started off using Auto, but I've slowly learned how to use other modes and adjusting photos for myself a bit.

I've noticed that I can get some outstanding photos using my DSLR. However, sometimes I'm unhappy with the focus on the edges of the photo. I'll explain using my files.

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This photo was taken several years ago in Munich using a point-and-shoot on auto mode. (ISO 160, f4, 1/250 speed...although the camera decided these, not me. I knew nothing of these options back then.) It's a gray day, yet the photo is sharp for an average photo. Edges of buildings are sharp and defined.

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Here is Quebec City last year with the Nikon, also on Auto mode. (ISO 140, f5.6, 1/125). Despite there not being an abundance of light, everything looks sharp.

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Now here's Paris a couple weeks ago. I put it on Auto for this picture, although I was also shooting a lot in other user-controlled modes on this trip, with varying degrees of success. The photos I will share are all Auto, in order to compare them to the shots I took in Auto when I was less experienced using the camera's features.

This one is ISO 100, f6.3, 1/160. If you look at the upper left corner of the top balcony, there is blurriness, as if the camera only focused on the center of the picture and not the upper edges. It's not sharp like the point-and-shoot or even like the very same DSLR was a year ago.

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Here's another one. The picture looks sharp, except for the dome in the upper left, it's out of focus. This despite being a beautiful, sunny day with an abundance of light.

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Finally, this last one of Italy. The hills in the left background are a bit blurry (Shot on Auto, f of 7.1).

Is there something I'm doing incorrectly? Is there something that requires cleaning or repair on my DSLR? I'm happy with most of my photos from this trip, but there are several photos that have this distracting and disappointing edge blurriness. I don't seem to recall this issue with any of my point-and-shoots or even with using my Nikon in the past - or maybe I'm just getting pickier with experience.

Thank you!
 
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Those shots look to me like they were made with a lens that has a slightly de-centered lens element, which can happen when a lens takes an impact or hard strike or blow, or the camera is dropped, etc..etc.. The problem seems worse on the left hand side of the frame. I have experienced this before myself.
 
Ok, so when your taking pictures like this, whatever you are using as a point of focus, that is what the camera will focus on. Think of that point in the [photograph as being a big horizonatal plane that is parallel to your lens. Any that is closer to, or further away from that point, will be less in focus the further away it gets.

Your depth of field is a measure of how much distance you can get away from that plane of focus (either nearer or farther away) and still be in focus. The wider your depth of field, the more objects further away or closer to your lens will still appear to be sharp and in focus.

Depth of field is determined by the focal length your shooting at, your distance to your subject and your F-Stop,. or in other words the aperture setting of your lens. You can increase your DOF by increasing your aperture setting, or ":stopping down" the lens. The higher that setting the more your DOF will increase, but of course it also means your letting less light into the lens so you'll need to shoot at lower shutter speeds or raise the ISO to get the same exposure.

Online Depth of Field Calculator
 
Could be two things unrelated to each other. You have not said what lens you used to take the shots with the D3100.

The point-and-shoot has a short lens, and therefore nearly everything will be in focus most of the time.

If your DSLR lens was set to anywhere longer than the short end (say; 18mm for instance) then your shots will suffer from a thin DOF.

If Derrel is correct, and the problem is inside your lens, you can borrow or rent another lens to compare. Or just send your lens to be repaired.
 
Great points, thanks everyone. And thank you for the detailed depth of focus breakdown, Robbins. I've experimented semi-successfully with f-stop, but I'm certainly a relative newbie at that.

For all of the shots, they were at 18mm using an 18-55, except the point and shoot.

The lens has never been dropped since I have owned it. I did buy it as a refurbished lens from an online camera store, however. So I'm not sure what happened before I bought it. I've had the same lens for two years, though, and this problem seems to be more recent - Quebec City (pic #2) was taken with the same lens a year ago, and I know the camera hasn't been dropped since.

Derrel - your info about de-centered lenses is completely foreign to me, and it opened up to me a lot of new info which taught me a lot. So thanks for that! While not every shot I take is resulting in the blurriness exhibited here, it seems to be happening every so often. Upon reading some more on this, it seems like this could be the issue.
 
Great points, thanks everyone. And thank you for the detailed depth of focus breakdown, Robbins. I've experimented semi-successfully with f-stop, but I'm certainly a relative newbie at that.

For all of the shots, they were at 18mm using an 18-55, except the point and shoot.

The lens has never been dropped since I have owned it. I did buy it as a refurbished lens from an online camera store, however. So I'm not sure what happened before I bought it. I've had the same lens for two years, though, and this problem seems to be more recent - Quebec City (pic #2) was taken with the same lens a year ago, and I know the camera hasn't been dropped since.

Derrel - your info about de-centered lenses is completely foreign to me, and it opened up to me a lot of new info which taught me a lot. So thanks for that! While not every shot I take is resulting in the blurriness exhibited here, it seems to be happening every so often. Upon reading some more on this, it seems like this could be the issue.

If you want to play around with it, put your camera in aperture mode. Take something simple like a soda can and sit it say on a fence post. Take some closeup shots and keep increasing the aperture. Then back up a ways, open your lens all the way up again, and do the same thing. Increase your distance a couple of times and take a couple more sets, Then compare the shots yourself and you'll get a really good feel for how aperture and distance from your subject will affect the final image.
 
De-centered lens elements often occur during the assembly process...MANY lenses ship from the factory with de-centered elements. The tolerances that must be maintained are very tight, and it's all too common for a zoom lens, or a prime lens even, to have minor de-centering due to a spacer not being quite right, or some minor, minor component not being in the exact, precise location needed to hold the lens element perfectly in the required position within the internal barrel.

One way to check for a de-centered element is the old brick wall test. The camera is set up square-on to a brick wall, with the height above ground being the right height to keep the back of the camera perfectly plano-parallel with the face of the wall, and then a series of photos made. Looking closely, if one corner of the wall, or one side of the wall looks fuzzy...well, there's a problem.

Lacking a brick wall, you can take newspaper pages and tape them up on a wall, and shoot that, and see if one side or one corner of the image area has an issue. it really helps if the test shots have everything at one, exact distance, so the flaw shows itself clearly. Your sample photos are not the best for detecting a de-centered element, but the one corner of the building, and the one hillside, show noticeably bad performance of the lens in the left, upper corner area of the frame.

In all fairness though: the 18-55 lenses are low-cost, and it's VERY common for the corners of wide-angle lenses to lag behind the central area in sharpness until the lens has been stopped down to f/8 or so. But, as you mentioned and I see also, the upper left corner is really lagging..which is a de-centered element kind of issue.
 
Thanks Derrel - extremely informative post. Along with that I did some research and it seems that is the case. I will definitely test it on a wall before jumping to any conclusions though. It's interesting that I've had the lens for probably 3 years and my photos never had this problem until recently. Is it likely that a lens can decenter over time with consistent use? It is a basic Nikkor 18-55, nothing special. I've never dropped it, but who knows, perhaps lots of movement and shifting over several years have caught up to it.

Looks like it's $93, not including shipping, to get the lens repaired by Nikon. I can get a 18-55 Nikkor online for around $100 with a warranty...so looks like that's the direction I'll be going if, in fact, it's decentered.
 
Robbins - I've enjoyed learning more about fstop over the past year or so, and I've really gotten some cool results changing it and producing different effects. Thanks for the practical tips!
 
Robbins - I've enjoyed learning more about fstop over the past year or so, and I've really gotten some cool results changing it and producing different effects. Thanks for the practical tips!

Varying the aperture can really produce some fun results. Glad you found some of what I posted of use :)
 
Another factor at play regarding a P&S and your Nikon is how, and how aggressively, the 2 post process the original image data particularly in regards to image sharpening. In the Nikon's menus you can change how much sharpening the camera does.
You can even select a file type, Raw (Nikon calls their Raw file .NEF), that does a minimum amount of post processing.

Note too that as things get further away we are looking through more air and air moves for a variety of reasons and can cause some blurring in the distance.

When the astronauts were on the moon they had great difficulty gauging longer distances because there is no atmosphere on the Moon to add that slight blurring we use here on earth to help us gauge distance.
 
Another factor at play regarding a P&S and your Nikon is how, and how aggressively, the 2 post process the original image data particularly in regards to image sharpening. In the Nikon's menus you can change how much sharpening the camera does.
You can even select a file type, Raw (Nikon calls their Raw file .NEF), that does a minimum amount of post processing.

Note too that as things get further away we are looking through more air and air moves for a variety of reasons and can cause some blurring in the distance.

When the astronauts were on the moon they had great difficulty gauging longer distances because there is no atmosphere on the Moon to add that slight blurring we use here on earth to help us gauge distance.

Good to know. I tried using Fine quality for the first time as well. It seems like that adds resolution to the picture, but could it also overpack the image with too many pixels and make parts of it blurry?
 
So I guess the only reason why one would not use Fine resolution is to simply save space? Seems like that's the only downside.
 
I agree with what's being said. It could be a variety of things between something up with the lens, to a DOF thing. You had mentioned that you used the 18-55 at 18mm, but if you shot it in auto, then if the lighting changed it may adjust your aperture automatically which could result in a shallower DOF. Plus, if you had it on say, center focus, then you focused on an area of the photo that would need a wider aperture or slower shutter speed, your camera would compensate to make the part that you focused on properly exposed and sharp. What made me think of that was your shot of Italy. It looks like the camera was metering for the buildings in the foreground, so in order to expose for them properly but also not blow out your highlights on the hills, you have a shallower depth of field. I hope that makes sense. I think what @robbins.photo recommends would be a great thing to do just so you can get a feel of DOF as well :) When I was in school, they had us do a whole project on depth of field so we could learn to understand it better.

Also, Shooting in the different resolutions won't affect how sharp one particular part of an image is. What it does is help record high quality information (hence the larger file size) that isn't as compressed. The higher quality the information, the less compression.. etc.
 

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