Sharpness problems please help

[abitfishy]

Hi all.

I've done a few shoots and can get some really sharp pic, and then some that look sharp until I view sections of them 100%, then its obvious they are pretty soft.

I decided to do a test with 3 lenses. Tamron 17-50, Tokina 50-135 and a Nikkor 50mm, all at 50mm focal length, at a variety of apertures. I've got 16 crops of the photo I took. All were done on a tripod.

I am not overly happy with any of them, although a couple I would say are acceptable.

Advice as to why these are all so soft would be great. The camera (D90) is near new with 1200 or so actuations on it. Am I expecting too much at full size to expect great sharpness???

Rather than post them all in a thread I've posted the link to the set on Flickr if people would be so kind as to take a look for me.

http://www.flickr.com/photos/49437235@N08/sets/72157624021795936/detail/

It would be appreciated as I'm getting a little put off about my photography not even being able to get sharp photos most of the time.

Thanks a lot.

[ricktas]

First off, all digital photos need to be sharpened.

Secondly, to get the very best results you need to have your lenses calibrated to your camera body. When lenses come out of the factory, they are all slightly different, and that can mean micro adjustments are needed to the focusing systems.

I am not sure if the D90 allows AF fine tuning, but check your manual and if it does, you can usually set it up and calibrate up to 5 lenses to your camera body.

You can also use manual focus if your eyes are good. Looking at your photos, focus is WAY off, you did not accidentally have it on manual focus and it just didnt focus in the first place?

[Adrian Fischer]

might help if there was exif embedded in them. Is the the only test youve done, as in the only subject matter?

[Roof]

I am not sure if the D90 allows AF fine tuning, but check your manual and if it does, you can usually set it up and calibrate up to 5 lenses to your camera body.


Sorry for half taking over this thread but Rick how do i do that ?

Or should i google this ?

[ricktas]

Sorry for half taking over this thread but Rick how do i do that ?

Or should i google this ?

It is NOT a feature of all DSLR out there, the more current models have it. It is called AF micro adjust. It lets you do a series of tests with your camera and lens combo, and adjust the AF system to ensure focus is accurate. The camera body can 'remember' up to 5 lenses and when that lens is attached it takes into account your settings and adjusts focus to ensure that focus accuracy is as accurate as possible.

Here is an instruction page : http://www.focustestchart.com/chart.html

[David]

It is NOT a feature of all DSLR out there, the more current models have it. It is called AF micro adjust. It lets you do a series of tests with your camera and lens combo, and adjust the AF system to ensure focus is accurate. The camera body can 'remember' up to 5 lenses and when that lens is attached it takes into account your settings and adjusts focus to ensure that focus accuracy is as accurate as possible.

Here is an instruction page : http://www.focustestchart.com/chart.html

Thanks to the OP and Rick for this thread: I think I have never read people talking about the need to have lenses calibrated to suit the camera body I have. Might explain some of the softness apparent in my shots more often than I want to remember.. will get them checked out when I take my body to the dust bunny assassin.

[arthurking83]

as someone already said... make sure the exif data is intact!

what software do you use?

if ViewNX( if not, then why not!?) open a file in ViewNX and make sure you click the 'show AF area' button at the top left of the toolbar, so that you can see where the focus point is.

Are you using a single(central) focusing spot?
Is the lens wide open? in very bright, harsh light some images will look a little bit more blurry if care isn't taken to minimise that risk. It's more of a lack of contrast than bluriness.. but it looks the same.
Try underexposing by -2/3Ev top see if that makes any difference.

The images in your link are way too small to form an opinion on whether there is an issue with any or all of your lenses, your camera, your technique or your processing ability.

Resizing an image(and not cropping it) makes it look much less sharp, so the resultant smaller puixels size image will need a teeny amount of 'output sharpneing too' ... but you have to keep that very minimal so you don't get haloing.

At 50mm all your lenses are capable of producing super detailed images.

Tammy17-50 @ f/2.8 and beyond, Tokina(I have no idea, but many folks rave about how good this lens is), Tammy 18-270 is very capable up to about 100mm and at one stop down from max aperture it should produce excellent detail, Nikon 50/1.5 is excellent from f/2.8 and beyond in hard light.
make sure you're using lens hoods if there's any chance of getting light directly onto the front of the lens.

name your tripod!!! weak tripods can be a frustrating source of confusion as to their misunderstood ability(depending on camera setings of course).

D90 doesn't have focus calibration/micro adjust.. but I doubt that'd help anyhow given the described symptom.

IF!!! there's an issue, it could be camera related.. but ATM I'm inclinded to assume it's operator error.. or more accurately operator misunderstanding.

As an example of how to tell what's going on with some of these images:

Image #10 in your series looks to be back focused. Probably shot with the 50mm f/1.8 @ very wide aperture(up to about f/2).
Reason: a lot of lateral CA. Red fringing along the fence palings, and the focus point seems to be on or just behind th every last paling on the RHS, where it seems to get slight sharper.
(lens used could also be the Tammy18-270 wide open as you'd expect to see a bit of fringing with that lens too).
My suspicion is that if you used the 50/1.8 wide open in that shot, there'll be some green fringing starting to show behind the point of best focus.

Are these images all crops of the originals?

etc, etc.... more info will help us to help you.

:)

[abitfishy]

Looking at your photos, focus is WAY off

Exactly the point of this thread! :D All done on AF, with the focus point shown in Viewnx as the leaf you see in them middle of the crops. I couldn't believe it when I zoomed into full size.

And yes, they are crops, not resized images so there shouldn't be loss of quality from resizing.

All exif data as far as I know is intact and shown when I choose 'properties' in the Flickr link.

Single point AF, taken at a variety of apertures from 1.8 (for the 50mm) all the way down to 22 (or maybe 32).

Lack of PP sharpening aside, and just using my Slik tripod, I really think they should still be a lot sharper than they are.

[ricktas]

How windy was it, how steady is your tripod, etc! This could also be caused by movement of the camera/lens during exposure. Did you do mirror lock-up, prior to taking the photos?

[abitfishy]

Maybe I'm expecting too much at full size. These 2 photos at full size cropped on the face were badly soft too, but resized to these sizes I think are perfectly acceptable (and I quite like the photos too). So is some lack of sharpness at full size really an issue? Should I resize the images down somewhat before I supply them to a model? I'm pretty new to all this....

Edit: After looking at the second one I think thats a bit soft too.

[abitfishy]

After having a think and a look at some of my photos I think I might be having trouble, particularly with my portraits, by using too large an aperture (usually 2.8), not having perfect focus on the eyes and therefore having such a shallow DOF I'm not getting all of the models face in focus.

I've played around with my lenses with a model on Saturday and much prefer my 50-135 as being more practical, so might give it a go next time I head out trying to stick to around F4 and see how I go.

Any suggestions for in camera mode to do with sharpening etc? I've been using Portrait Picture mode (not to be confused with the program exposure mode), and wondering if I should stick to Standard or Neutral? I assume portrait mode probably decreases the sharpness.

In addition, if I did happen to want a better portraiture lens, will a 90mm Tamron Macro be a good choice for something pretty sharp at larger apertures?? Or should I go for the famous Nikkor 85mm? I like this type of photography so definitely think I will stick to trying to get attractive young ladies in focus! :)

[ricktas]

f2.8 is way to shallow depth of field. Try about f8.

[PerfectPicture]

It is NOT a feature of all DSLR out there, the more current models have it. It is called AF micro adjust. It lets you do a series of tests with your camera and lens combo, and adjust the AF system to ensure focus is accurate. The camera body can 'remember' up to 5 lenses and when that lens is attached it takes into account your settings and adjusts focus to ensure that focus accuracy is as accurate as possible.

Here is an instruction page : http://www.focustestchart.com/chart.html

ohh Geez .. THANK YOU soo much for this info, l was feeling sometimes my pictures were not sharp at all, and blaming myself .. never heard of AF Micro Adjusting your Lens to the Camera Body before!

thanks for the original post and everybody who replied, have to re-read it again.
after l googling the heck out of "AF Micro Adjust" .

Now how do you do it on the Canon 50D??

life's a learning experience .. all right :D

[farmer_rob]

... Am I expecting too much at full size to expect great sharpness???

... It would be appreciated as I'm getting a little put off about my photography not even being able to get sharp photos most of the time.

Thanks a lot.

Firstly, DON'T GIVE UP. It is solveable, and it is likely to be straightforward. You have a good camera, and good lenses.

It seems to me that you are taking on a lot very quickly. It is difficult to track a problem when there are so many variables. I've had a look at your photos on flickr, and there are so many variations, it is hard to get an idea of what is what.

Spend some (more) time on subjects that don't move (e.g. a brick wall) and work it out before trying to take photos you want. I find autofocus a deceptive beast - it promises a lot, but will not actually deliver unless you work at it.

So, some suggestions and comments:

1. At 100%, it is hard to get a really sharp photo - although not impossible - and pointless. You've got heaps of pixels in the D90 - don't waste them on parts of the shot that you will drop later - move closer, zoom in or change lenses. (I try to avoid cropping as much as possible, as the image is invariably degraded.)

2. Sharpening can be issue - if you are using RAW, you must sharpen in PP. If not, you have to be really careful about the picture presets (I do understand the ones you mean.) In the camera menu, you will find some adjustments available for the picture presets. Sharpening is one of these. You may find that portraits have less sharpening. (I don't know - I shoot raw and do sharpening in PP.)

3. Softness can come from
i) wide aperture and hence thin DOF, and then missing focus on the point you want.
ii) Camera shake. VR helps, but you should be at a shutter speed over 1/60 hand held.
iii) Camera shake 2 - mirror slap, light tripod, wind: often apparent at slower shutter speeds (which is why you use the tripod :confused013)
iv) small aperture. Above f16 you get diffraction problems on most DSLRs. I noticed some of your flickr samples were f22. There will definitely be diffraction at f22 on a D90, which will appear as softness. Open up (rule of thumb - no smaller than f11.)
v) focus error - the focus points in the camera are not absolutely spot on in the viewfinder on all cameras. This can be a problem at wide apertures (see i).
vi) focus error 2 - back/front alignment. Adjustable on some cameras. Best checked with a focus chart - and I don't think this will be your problem.
vii) bad focus - you just aren't focussing on what you should be.

4. With your test shots, you have a subject (fence?) that will have some parts in focus and others not. Pick a picture with an aperture of f8. Look at the whole picture. Are there sharp spots? If not, then you have a problem with camera shake. If there are sharp spots, are they forward or back from where you want focus? Then you have a focus error problem. (Your lens should have a point in focus - it is just a matter of making sure the focus point is where you want. If there is no point in focus, it is typically because of camera movement.)

5. Work with one lens first. Choose an easy subject that will show something in focus. Work to focus on what you want. Work on a mid-range aperture - f8. Work with a fast shutter speed (1/125 at least.) Get consistent test images, then move on to other apertures and other lenses.

It seems that you manage the light and composition well - getting the sharpness is well worth the effort.

[kiwi]

AF micro adjusting is a massive furfy

The issue here as Farmer_Rob pointed out could be a range of things, unlikely to be a gear issue at all

Where are you anyhow ? Perhaps you could hook up with a local more experienced photographer who can review your technique

[ricktas]

AF micro adjusting is a massive furfy



I disagree with this comment. In some circumstances AF fine tuning can make a world of difference. Agree that it may not be the case in this instance, but AF fine tuning is not a massive furfy in my opinion.

[ricktas]

Sharpening can help : http://www.ausphotography.net.au/forum/showthread.php?t=8579

[kiwi]

I disagree with this comment. In some circumstances AF fine tuning can make a world of difference. Agree that it may not be the case in this instance, but AF fine tuning is not a massive furfy in my opinion.

quote "sometimes its sharp and sometimes its not":confused013

adjust the microfocus ? Hows this help ?

[farmer_rob]

OT - it is furphy, not furfy. Derived from Furphy and Sons in Shepparton, who produced a portable farm water tank used widely in the 1st World War. (They are still made.) It's not clear why a furphy is a furphy.

[abitfishy]

Thanks all.

I am definitely thinking the issue is more likely down to too large an aperture. Hence they are a little soft as well as too shallow DOF to always get all parts of the face in focus. Particularly as there is also the added slight change considering I centre focus and re-compose as well with the possibility of slight movement of the model (and me) prior to the shutter button being pressed. I also think I'm not paying enough attention to ensure the eyes are the focus point always, sometimes I'm just ensuring the focus is somewhere on the model prior to recomposing.

I did another similar test but this time in front of a flat box with text on it. There were a few that were a tad soft (particularly the Nikkor 50mm at F1.8) but even at full size it was all pretty good (and at smaller image sizes was as sharp as a tack), and even a couple at full size were surprisingly sharp indeed. Considering the DOF isn't an issue with that test and I got good results then I think I've solved the issue - that I CAN take sharp images.

Next time I'm out I will give larger apertures a go. I did notice F10 with the 50-135 to be brilliant, although I'm thinking to ensure the background is sufficiently out of focus it might be a little too small an aperture.

[ricktas]

quote "sometimes its sharp and sometimes its not":confused013

adjust the microfocus ? Hows this help ?

As I said in my post, it might not help in this case, but your comment "AF micro adjusting is a massive furfy" (full stop) is what I replied to. As a statement by itself it is incorrect, and if I took it as a global, overall statement about the benefits of AF fine tuning, others might have as well, and I wanted to correct that. :D

[farmer_rob]

Why do you use center focus and recompose? (I'm sure this causes your random softness wide open.) With 11 focus sensors on the D90, you should be able to have a focus point on the subject.

[abitfishy]

I was using the multipoint where it chooses for me, but found too often it chose the wrong spot.

What method do you suggest Farmer Rob?

Would changing to center point 'wide' assist?

[farmer_rob]

I'm guessing manual selection of the point using the selector on the back. I am wary of "automatic" selection without looking at "how" it chooses the focus point. What options do you have? Can you use multipoint and then use the selector to change the point if it is wrong? (ie use Multipoint as a shortcut then override?) I tend to feel that the automatic settings (in general) are to give people upgrading from a P&S a bit of a safety net, and are often not going to give the optimum result - because we are still smarter than cameras :).

Note that I can't talk from experience on a fancier camera here: my D40x only has 3 focus points, and I choose which one manually - while looking though the viewfinder. If I let the camera choose, it doesn't always do what I want.

[abitfishy]

Yes, I can do all that with manual selection, but it all sounds too much like hard work. :)

Single point and recompose seems pretty common, so I should be able to do that. If I keep an aperture that gives me some depth I should be OK.

Or maybe I'll just stick to P&S. :)

[MarkChap]

Yes, I can do all that with manual selection, but it all sounds too much like hard work. :)

Single point and recompose seems pretty common, so I should be able to do that. If I keep an aperture that gives me some depth I should be OK.

Or maybe I'll just stick to P&S. :)

Hard Work ????????

Are you kidding, look at all the work you have put in already, in an effort to solve your problem ??
Find this hard to accept, you either want sharp images, and need to work at getting them, or you don't, in which case this whole exercise has been a waste of time.

If you want consistent results, particularly at wide apertures, use manual selection of a single focus point.
Use the focus point as close as possible to the area that is critical, the eyes in the case of a portrait.

Using single centre point and recomposing can have an effect on focus, particularly at wide apertures with shallow DoF.

Not sure of the Nikon, but the Canon has a dedicated button just near my thumb, press the button, spin the dial and the focus point I want is selected, slide my thumb to the AF button and away I go.

[abitfishy]

I was waiting for a reply like that. You were quick!

I've read about it in the manual but not attempted it, so will take a look. I guess its also just getting used to the procedure too, once its second nature it won't be 'hard work'.

Oh, and thanks for biting. :)

[MarkChap]

Another thought I just had.

Does the D90 have a rear button for focus ??
If you are focusing and recomposing by holding the shutter button halfway whilst recomposing, maybe you are sometimes releasing that and then refocusing on the wrong area ?

I use rear button focus on my Canons exclusively now, press the button for focus and when I release the button the focus won't change until I press the button again.

[abitfishy]

Yes, I'm sure it has an AF lock. There are a few that has happened to, but the majority I've been pretty steady.

[kiwi]

forget af lock, focus recompose and all that stuff

Have you actually looked in View NX for example of what the focus point in your OOF shots actually is ?

Are you using AF-S or AF-C ?

[abitfishy]

Hey Kiwi.

I'm using AF-A.

Yes, checked a lot in ViewNX, many are great, a few are off, but then there are some like the attached. Within the focus area its pretty soft to me. 1/1000 and F3.2 as you can see.

Just scrolled through a lot in ViewNX and the only pattern I can see is ANY at 135 aren't great at full size. Particularly at higher shutter speeds. Most of the better ones are between 55-75mm with mid range shutter speeds, 1/125 - 1/500. Using the Tokina 50-135 lens. I know there tends to be sweet spots with lenses, but I didn't expect it to be quite so limited.

Would love to hear from anyone else with that lens.

[jaqson]

Just like me I am sure many amateurs who are reading this are very thankful for this discussion because It is exactly what I am going through at the moment and probably what all amateurs go through when starting out. Sometimes it is so overwhelming what you have to think about and set up even before you take a single image.

So many of my shots have sharp focus on certain areas of the face and sightly out of focus on others (I take close up candid shots) It is very frustrating at times.

[kiwi]

OK, well, obviously focussing on the mouth is the wrong plan, always focus on the nearest eye, select the focus point manually, use af-continous, af-c, I have no idea what af-a is ? so that if you or the subject move it's tracking. make sure focus is acquired (there should be a indicator in the viewfinder at least) before you push the shutter

Step down the lens to two stops more than wide open

Ensure you have good shutter technique - ie - dont stab the shutter button like you are pressing some quiz show thing, roll your finger over the shutter to release. Hold the camera properly - just google it if not sure

any shutter speed 1/100s + 1/focal length should be OK

Try that

[abitfishy]

So many of my shots have sharp focus on certain areas of the face and sightly out of focus on others (I take close up candid shots) It is very frustrating at times.

Um, yes, frustrating it is. I do think you will find for the close up candids it is a too wide an aperture. I have a few great photos like that with the eyes perfect but everything else off. Have you checked the Exif info for aperture details?

[Travelm8]

all great advice but there is a known fault with some
d9o's back focusing which you can search on google and see if you are having those issues (as mine was) it can be repaired under warranty if that is an issue. My d90 would only get crisp shots on my 18-200 at 155mm either side of that focus was very poor. I do think we expect too much from digital it is limited in sharpness whilst a brilliant medium it's not the ultimate for certain styles of photography.

Cheers
John

[abitfishy]

OK, well, obviously focussing on the mouth is the wrong plan,

Yes, accepted, but nonetheless, you can see how bad that screen shot is.

AF-A automatically selects the correct mode between AF-S and AF-C.

Will try that out.

1st Option Plan of attack: Few stops wider, AF-C and either manual focus point or single point and recompose (prefered!)

2nd Option Plan of attack: Forget photography and stick to fishing. :eek:

[kiwi]

1st option is better, D90 only makes a good weight

The screen shot of a 100% unsharpened raw file is a bit meaningless, ive seen worse

[abitfishy]

1st option is better, D90 only makes a good weight


Absolutely Kiwi. Fishing is good, but taking photos of pretty girls........ :umm:

:lol:

[kiwi]

all great advice but there is a known fault with some
d9o's back focusing which you can search on google and see if you are having those issues (as mine was) it can be repaired under warranty if that is an issue. My d90 would only get crisp shots on my 18-200 at 155mm either side of that focus was very poor. I do think we expect too much from digital it is limited in sharpness whilst a brilliant medium it's not the ultimate for certain styles of photography.

Cheers
John


Disagree, I expect every shot to be razor sharp. If it's not it's not a limitation of digital, it's a limitaion of me or the gear I am using

There is zero excuse for soft photos

[RLeadbetter]

hmm this might be an answer to the same problem im having.

Thanks

[kiwi]

As said before if anyone really thinks you have a problem with your gear (ie backfocussing etc) then its very simple to do a controlled test - DO NOT TEST ON A PERSON OR A MOVING OBJECT OF ANY KIND OR HANDHELD

Use a tripod, or put camera on a steady surface, a table etc
Use either a remote release or the timer
Make sure you focus exactly on the object
line up a few objects in front and behind the main focus point (use cans or boxes etc) or a focus test chart (google it)
use flash so that your s/s is at least 1/200s
Shoot JPEG
Shoot at ISO200

etc

Do a controlled test before even thinking about blaming cameras or lenses for OOF shots


Story - about a year ago a friend had bought a brand new d300 with 24-70 lens as she claimed her d80 and 18-200 was too soft. I could still use her old gear and get sharper shots, and her d300 and 24-70 and get nothing sharper. She couldnt get sharp shots with either combo. Its hardly ever the equipment

[swifty]

Just a few tidbits that might help. Try kiwi's controlled test first. Maybe use a 30cm ruler and shoot from an angle on the 15cm mark using centre focus spot. Repeat and see if it consistently focus on the same spot. If so, is the focus in front or behind the 15cm mark.
A potential problem is sometimes the actual AF sensor is not exactly where it is indicated in your viewfinder.
Never ask the camera to choose your focus spot. I always choose my own with the back selector when I had my D80 and now on my S5.
Shallow DOF can be a limitation or it can be a tool. If f2.8 is too wide then why do so many lust after super fast exotic primes with apertures 2-3 stops faster than f2.8. But I do agree f2.8 may be too wide for a lock and recompose method of shooting at close distances. As others have suggested, I also choose the AF point closest to what I want to focus on, trigger AF with the AF-ON button (not shutter release), recompose a little if necessary then take the shot (shutter release does not trigger AF again..it is disabled on my setup).
Hope that helps a little.

[abitfishy]

Well, I did a very quick ruler test and it seems that it was sharper just in front of the focus mark (as in away from the camera) on the ruler, less obvious at smaller apertures for obvious reasons. Wonder if I do have an issue with the lens/body.

Quick question, I was concerned about the portrait exposure mode making a difference, but I assume the RAW files don't have any of the mode settings in regards to sharpness and saturation etc applied to them?

[farmer_rob]

The RAW files record the mode settings, and apply them non-destructively if you use ViewNX/CaptureNX - and you can then override them if you want (one of the real benefits of using RAW and ViewNX/CaptureNX) before you convert the file to jpeg. Photoshop/ACR does not use the mode AFAIK.

Is it sharper in a consistent manner relative to the focus point? Often the focus points are not as accurately aligned as you might think - which is not a front/back focus issue. Try it with the ruler on various angles.

[abitfishy]

Thanks. Is there any reason I shouldn't turn it off if I am going to PP with Lightroom initially anyway? Thinking of just setting it to Neutral to take any issue of softening (particularly on Portrait mode which I have been using) out of the equation.

[etherial]

Firstly, DON'T GIVE UP. It is solveable, and it is likely to be straightforward. You have a good camera, and good lenses.

It seems to me that ...

It seems that you manage the light and composition well - getting the sharpness is well worth the effort.

Great post Rob, I appreciate the effort you have put into this thread, your advice seems very logical and well thought out to me. :th3:

Good discussion everyone, very helpful!

[arthurking83]

Yes, I can do all that with manual selection, but it all sounds too much like hard work. :)

Single point and recompose seems pretty common, so I should be able to do that. If I keep an aperture that gives me some depth I should be OK.

Or maybe I'll just stick to P&S. :)

:p

focus and recompose can be difficult to do properly if you don't fully understand it.
Some lenses.. in fact most lenses have what's called 'feild curvature'(look it up to get a good understanding of the term).
What happens when you focus and recompose:

1. you focus at point A(eg. eyes) and use the center spot to do so(in the old, manual days you had a micro prism/split prism to help aid that focusing ability). When you then recompose, you automagically change the distance from the sensor to point A(read up on triangulation theory).
I wish I could draw a diagram for ya, but the topic has been done to death in many books and probably on some websites already, that there's no need to reinvent the wheel! Unless your ability to rotate left to right is absolutely spot on(which, with luck, can be.... sometimes!)you will inadvertently move either closer or further from Point A.
By implication, will recomposing will usually mean placing Point A closer to the edge of the frame. At wider aperutures the thin DOF will make a worlkd of diffference. If you want to use focus and recompose, learn how to best do so, with specific types of gear(ie. lenses).
If the lens is affected with feild curvature, then you're only multiplying the effect of thin DOF+subject to sensor distance error+lens abberations!
2. Lens abberations! While the lens's edge sharpness ability is usually set by the design, it;s not really an abberation, but a simple limitation of the design of the lens. Lens abberations is a different topic, where I previously described how a wide aperture will give that lateral chromatic abberation(the red colouring in one of your fence images). Cheap lenses like the 50/1.8 are made to a price, so you woudl expect a lens like that not to be of the highest calibre in soem respects. have a look at Photozone (http://www.photozone.de/nikon--nikkor-aps-c-lens-tests) for an easy to use database of how good/bad lenses can be, in terms of overall performance.
In particular!!!!! have a look at the Tamron 17-50mm f/2.8 review on that link I posted. Why? Because on the 'analysis' page they briefly refer to feild curvature, with a simple diagram so that you can see what effect it can have on your images.
Field curvature is usually not a problem tho.. you should just be aware that it can affect your images. if you're doing flat field work, then FC will be an issue. Flat feild photography is like taking a photo of something that exists only in 2D, like a photo or a page captured from directly in front of the subject.

Bookmark that link and refer to it, as you begin to get a better understanding of gear/technique/etc.. and then it'll all click one day. Don't take those results literally! Use them as aguide to understand your gear better, and go forth and multiply.... your knowledge.

very quickly: farmer_rob described how Picture Control settings work. By default, if you use Portrait sharpness is set to 2, Standard is set to 3 and Vivid is set to 4. it all makes a difference, but usually to the jpgs captured in camera. If you shoot raw, the Picture Control should make no difference to the final result, because as Rob said it can be changed.
One thing i'm not overly impressed with is in camera sharpening and sharpening in ViewNX(CaptureNX's USM is much nicer quality). But you should still get OK quality with using sharening in ViewNX.. but I still think that in camera sharpening is to harsh/coarse.
Set all of the Picture Control sharpening setings to zero, use ViewNX to process your NEF files into TIFF files for further processing in PS/CS/LR. If you want better quality NEFs I suggest using CaptureNX(if you want to maintain them as procesed NEFs that is).

So back to the 50/1.8(only as an example.. this could hold true for any other or all of your lenses!). If you focused from the central focus point on your camera, and then recomposed the scene, then a quick look at the review of the 50/1.8 will show you in an instant, that the edges of the frame when using the 50/1.8 at wide-ish apertures is going to be abysmal(when compared with the centre of the frame). Add that knowledge to your inability to rotate in a perfect arc when you recompose(unless you are a fully automated robot of course! :D) and the possibility that the lens is affected by FC.. and the end result will be :confused013 ... something like a thread asking why your images are not sharp :p

With 50mm f/1.8. if you use the central focusing point at f/1.8 you should get image sharpness that you will be happy with, at f/1.8, but remember Photozone are in a studio environment, using controlled lighting to maximise the contrast(which is sharpness spelled differently! :D) in the image. in harsh light such as sunshine, you'll get more glare andhence loss of contrast(which, remember!... is another way to spell... etc, etc ;)).

Very few lenses operate optimally at full wide aperture in bright light(they can tho), and the operator will usually have a good knowledge of how to best use that situation and also great PP knowlegde too.
Great lens(in Nikon terms) in harsh light at widest aperture is the Nikon 24-70(that's a lens that you can afford!.. the other ones are generaly the lenses that retail in the $3000+ end of the scale).

So lets asume that the Tammy 17-50 is affected by FC(I hate typing the full term.. it hurts my fingers!). and you want the subject at the edge of the frame, which I've done many times with good to great results with my version... and if the lens is affected by FC, then when you recompose the subject at the edge of the frame is almost certain to be outside the DOF zone.

Now (maybe??)I'm about to introduce an element of envy/regret in your decision of camera body.. and one small and possibly insignificant reason why I sometimes reckon the camera body is more important than the lens when choosing gear.
The D300(and higher) cameras have a focus mode called 3D tracking. This is where you focus and recompose the 'proper way' ... but only when/if it actually works.. which is usually here'n'there. No matter what focus point you choose(and there are 51 of them on the D300 and up models) you focus on the subject, and using AF-C(continuous focus mode) you recompose the frame, and the camera will(should!) keep the subject in the focused area all the time. As you move/pan/tilt fall/stumble/trip/etc the focusing point moves across the viewfinder of it's own accord, still maintaining a single point.
(not the automatic focus point choosing mode in auto auto focusig mode.. D300 and up has that mode too) This focus tracking mode lets you decide the subject(ie. not allow the camera too decide for you) and then helps you to keep track of it.
other alternatives for using focus and recompose is to get an alternative focus screen matte for your D90.

But! If you want to shoot with the subject at the edge of the frame.. now, with the D90, for best focus(sharpness) results you would preselct the focus point that places the subject in the right area(and experience will help there), and:

using AF-C mode; you would focus for a brief moment to allow the camera to settle a little before exposure, then expose.

using AF-S mode(and using the shutter button for both focusing and exposure);- you shouldn't half press(to focus) and then full press(to expose)! Do the full press in one movement and wait for the camera to eventaally take the exposure. Reason is that in the split second that you focus and then expose you are very likely to sway back/forth just enough to get out of focus again. if you press the shutter all the way to expose in one action, the camera takes the exposure in a much quicker split second than you ever could which helps to ensure that the subject distance is where it's supposed to be. using a tripod it should make no difference, but the body naturally sways a little bit, especially when using only one eye, and through a 5x10mm peep hole!
Kiwi mentioned that you should use AF-C mode.. it's a lot better and more consistent(I rarely use AF-S mode.

Your camera has the ability to set the AE-L button(near your thumb) to act as the focusing activation for the camera. Can't remember what setting you need to change to do that, but I highly recommend that mode. What you then do is to set camera to AF-C mode, and use your thumb to activate focusing. The shutter button(called the 'release') will no longer operate the focusing for the camera. Now you focus when you want, and not when the camera wants too, and you're free to shoot as you please. The button falls perfectly to where your thumb probably rests anyhow, so once you're used to it, it feels very natural. :th3:

As Kiwi said too, if you're in an area close to any meetups about to happen, it'd be a good point to make it to one and get first hand help from someone that can help.
i reckon that kind of help would be worth a thousand questions, in a forum.