Real sharpness vs viewfinder...

[Uffe]

Hi all,

I have a small problem, but I'm not sure if it is just me or if it is a more general problem...

95% of my photographs are available (low!) light portraits. For this I mostly use the 28/1.8 and the 50/1.4. I have been taking this kind of shots with SLR's for more than 20 years now. (Although with film based cameras I used 50 and 85 mm instead.)

Due to lack of time, my darkroom hasn't been used for almost 5 years - and neither have my SLR's. I've had a few digitals in between, including a G1 I still have. But, basically, until I bought my D30 last year I haven't used any SLR regularly for several years. In the mean time, I have gotten reading glasses...

Now to my problem: When I look through the viewfinder, the image appears sharp as a knife - I even think I can count the eylashes on the person in front of the camera. But when it comes up on screen, it turns out that a disappointing amount of the images are a little off focus.

I know that I can stop down the lens a couple of steps to get better DOF, but I'd rather not... I like the ultra-ultra-narrow DOF, and as I said, we're talking *really* low light here... :)

I've also tried diopter-adjusting the camera - autofocusing on something, adjusting until it's sharp, focusing on something else, readjusting etc until the autofocus and I agree upon what's sharp...

This problem effectively stops me from using manual focus, but it also appears using autofocus. I let the camera focus, and look through the viewfinder. Image appears very sharp where I want it to be, so I release the shutter. When it comes up on the PC screen, it turns out that the focus was on the ears rather than the eyes of the subject...

Maybe I just need to find a way to work better with the camera. I have an ST-E2 on order, we'll see if that helps.

In the back of my head I have a very faint suspicion though, that the CMOS sensor may be a little out of position or something... But then *no* pictures would be sharp, would they?

What do you guys think?

BR,

/Uffe.

[Pekka]

You could do a small test if your camera focuses where you want it to:

Take a deck of cards and place the cards vertically on a table (supported by e.g. matchboxes) on a row going away from your viewpoint . Then start taking photos from same spot, focusing to a different card, using the center focus point only (frame subject to the center, too).

After each photo write down the filename and where you set the focus point (like queen of hearts, top right corner) and compare the notes to what you see on PC screen.

Deck of cards set up like that is also a great tutorial on DoF.

Test also manual focus so that you frame subject to the edges of the view area.

Note that after focusing, even a slight change of angle of camera relative to the subject might tilt the DoF 'box' far away from the focus point you intended - this is always a problem with f1.4 and similar open apertures.

I hope you get you problem solved!

Pekka

[KHogan]

Hi Uffe,

Great idea suggested by Pekka. Also, I would add a second suggestion, this one just to make sure that it's indeed a focusing problem and not the camera settings. Perhaps you have done this already but have you tried a few shots with the in-camera sharpening set to "normal" (or even "high")? Since you are saying that your pictures all appear just slightly out of focus, perhaps what you are seeing are soft images which would be normal if you have the camera set to "low" for sharpening. Thought I'd mention this just in case...

Regards,
Kharim

[Uffe]

Pekka,

thanks for the suggested test setup. I had some serious testing in mind, but given my laziness I first wanted to hear if it was a common problem... :)

I will do some really extensive testing to see what might be the problem. Not tonight though, I'm in Sweden so my clock is almost as late as yours... :)

Kharim,

thanks for the suggestion! Unfortunately, my pictures aren't soft in that way. I probably wasn't clear in explaining. I *do* get amazingly sharp pictures! Especially in broad daylight, when I can afford to stop down a couple of stops. The problem is that in lower light, with fully open lens, 30-40 % of my pictures are slightly out of focus, but they look ok in the viewfinder.

I can accept that the autofocus with all three focuspoints enabled in low light prefers the subjects contrast to the background before something like eyes. Practically meaning that the autofoucus sets focus on the ears rather than the eyes. But I should be able to see that in the viewfinder and correct it - which I don't! It looks ok until the onscreen magnification kicks in - then there's no doubt that the ears on the subject are ultrasharp, but the eyes are out of focus...

I'll post my findings after my extensive testing!

Thanks,

/Uffe.

[oops]

I'm sure this is not related to your situation but I want to share a kind of "Oops" I experienced with my 50/f1.4.

Coming from SLR and G1, the D30 1.6x factor really caught me by surprise. I was taking portrait shots in available light @ f1.4 with a 80mm lens! Each factor alone could spell the kiss of death for DOF but combined they were a disaster. In addition, I was hand holding a 80mm lens @ 1/60 and 1/30 shutter speeds. Not a good idea. Also a glasses wearer, my viewfinder looked great but I was probably concentrating on the main focal point and couldn't imagine the ears would be out of focus.

I performed some DOF experiments and was floored by my findings. Focal length, in my tests, was a much bigger factor than f/stop in spoiling my shots. Since then I have not regarded my 50mm as a "portrait" lens at all until I can get better at predicting the results.

I am going to try the card experiment with all my lenses before I miss any more opportunities.

[AJSJones]

Do you need to use all three focus points because it is low light? How does it work if you only use one and put it on where you want you focus to be?
Isn't there a CF that allows you fix the AF and then move it to recompose if none of the three is in the exact right spot for your shot?
Or are you using only one and still having this problem????

Andy

[chris maddock]

AJSJones wrote:
Isn't there a CF that allows you fix the AF and then move it to recompose if none of the three is in the exact right spot for your shot?


There isn't a custom function as such (AFAIK) - just set the AF to single shot, focus where you want then recompose - WITHOUT releasing the shutter button. Note that the exposure will be calculated for the new coposition, unless you use the AE Lock button (*)

HTH
Chris

[Uffe]

Hi all,

and thank you for suggestions and comments. I haven't had the time to do the 'deck-of-cards'-test yet, and probably won't in the next few days either.

During lunch hour though, I annoyed a couple of my coworkers by using them for target practise. Setup was me and the target sitting on chairs opposite each other, about a meter apart. Only lightsource a north-facing window, about a meter to the side. Using 50/1.4 this gave me shutter speeds between 1/15 and 1/30 at f 1.4. (ISO 100.)

I have a very steady hand, so these are actually pretty long shutter speeds for me, even at the effective focal length of 80 mm. Here's what I found:

Manual focus: Not a single sharp shot. Keeping the subject 'correctly' framed, and manually focusing for the eyes. The eyes of the subject looked sharpest in the viewfinder, but in the pc the focus plane was always somewhere else. (On the ears, the tip of the nose or the fringe...)

Auto focus: With all three focusing points enabled, having one of them over the eyes of the subject, pressing halfway to get focus lock, releasing and repressing if the eyes didn't look in focus gave me about 60% focused shots and the rest with focus off, just like when manually focusing.

Selecting the middle focusing point, aiming for the eyes of the subject, locking the AF and recomposing gave me 80-90 % of the shots in focus.

99% of my shots are sharp, just not where I want them to be... So it's not a camera shake blur or anything like that, its just that what looks to be in focus in the viewfinder isn't really in focus for the CMOS...

Is it my eyes? Or could it be that the viewfinder is a little bit out of position? Or the CMOS sensor?

Shouldn't you be able to use *any* part of the viewfinder to determine whether or not the image is in focus?

I will do a very extensive test, with other lenses as well. It really haunts me though, because with film based SLR's I've always preferred lenses 85-100 mm, always focused manually in available light, and always had very sharp shots coming out of the darkroom... :)

Anyway, thanks for your time and all your kind suggestions.

BR,

/Uffe.

[romeozulu]

Maybe I'm not understanding you, but are you saying you hand-held at 1/30 and 1/15? If so (and I don't care how steady you can hold the camera) you are not going to get sharp pictures. If you are using this as the basis for sharpness, you should really try the same thing with a tripod.

When I first got my D30, I resisted using a tripod for the longest time because it destroyed my spontaneity. Once I realized the dramatic different a tripod made, I use it all the time with anything less that 1/125 and even that is borderline.

RZ

[miro]

To test the CCD position, you should photograph some text on the wall (newspaper?) directly in front of the camera 2-3 meters away, using tripod, different f numbers and focal lengths. Use manual focus. Examine the photos to see which part of the picture is actually in focus. If sharpness of the text changes other than being the sharpest in the center and *slightly* blurring (uniformly) towards the edges, you might have a problem with the placing of the CCD.

Hope this helps,
-Miro

[Uffe]

Hi all,

and thanks for all your suggestions and comments. Finally I've found the time to do some serious testing according to your suggestions. And, I've solved it!

Turned out to be the diopter adjustment after all...

Here's what I found:

I had done the diopter adjustment this way: Use autofocus to focus on something, then adjust the diopter until it was really sharp for my eye in the viewfinder. Focus on something else, readjust if necessary, etc, until the autofocus and I agreed on what was sharp. My serious mistake here was that I kept using the center focusing point.

What I should have done (and have done now :) ) is this: Set focus with auto, and then move the camera so that the point you set focus on is in one of the corners of the viewfinder. Adjust the diopter until the selected point is sharp in its new position. Repeat for all four corners, and fine tune by focusing on something else etc.

(Hint if you want to try this - use your fastest lens to get as shallow DOF as possible.)

It appears as if the center of the viewfinder is more forgiving than the corners, almost as if it has a greater DOF in the middle...

After having adjusted the diopter this way, I can use manual focus again! What I see in the viewfinder is what I get in the image!

Thank you for all your suggestions, without your ideas I might not have gotten around to do as extensive testing.

BR,

/Uffe.

[JoMo]

>What I should have done (and have done now ) is >this: Set focus with auto, and then move the camera >so that the point you set focus on is in one of the >corners of the viewfinder. Adjust the diopter until the >selected point is sharp in its new position. Repeat for >all four corners, and fine tune by focusing on >something else etc.

Did you wear your glasses or use your naked eyes?

[Uffe]

I didn't wear glasses - I never do when I photograph. Since I used cameras for 20 years before I got glasses, I can't learn not to slam the eyepiece into the glasses... :)

/Uffe.

[gerry]

if you want a great alternative to glasses, which you can wear while you're photo taking, i recommend ciba progressive focus dailies.