a way to judge what F-number to use?

[scraggles]

I'm quite new to photography with a DSLR and I tend to screw up a number of shots by using the wrong F-number. Is there a way to figure out what the f-number I'm using is going to pull into focus without snapping a bad shot first?

The camera is a Rebel XT, and the only lens I own at the moment is the EF 50mm f/1.8 II

[RbrtPtikLeoSeny]

There's a DOF preview button on your camera located on the left side of the lens attatchment area. It's meant to be accesable to your left thumb when holding the lens. You set the f stop number you want, focus the lens, then press that button. The viewfinder will become darker (unless your at max apeture) and you will notice what is, and is not in focus. Then you further adjust the f/ stop to get what you want, or if it's all good leave it at what it is. Go look at your camera and see if that's there. Give it a try. I own a 20D so I'm not sure if it's the same on an XT, but I think it should be....

[RbrtPtikLeoSeny]

.

[cfcRebel]

When u said u screwed up a number of shots, you mean they are OOF? Too bright, too dark?

The bigger the aperture(smaller f value) the smaller DOF. If u r shooting a subject that is close to you (~ 5 ft), then low f value (f1.8?) will blurr the background and create nice "bokeh" but it might also blurr part of your subject. So it depends on what u want the picture to look like.

[scraggles]

Out of focus. Brightness is fine.

I tend to get pretty good results when using a preset mode, but I really want to get better with the manual modes.

[idofotos]

in general, the smallest number say f 1.8 will not allow alot of focus or depth of field, say you focused on the nose the eyes might be out of focus, if you use f8 and do the same the whole head might be in focus, f 11-f22 will allow the most depth of field, now each of these rules works differently depending on weather its a tele or wide angle, wide angle gives great depth of field at f 5.6 while a 300 @ 5.6 is pretty shallow, find a fence and focus on one post and shoot a series of photos at different f stops always focusing on the exact same spot, but fstops are determined by the amount of light available, say you want to shoot at f1.8 on a sunny day, cant do it because there isnt enough shutterspeed to allow it, on a bright sunny day with 100 asa set on camera your correct exposure would be f16@125th of a second this is the sunny 16 rule, on a sunny day set f @16 shutter speed will be same or as close to ASA # so f16 with 400 would be f16@1/500th of a second, so you have to control the amount of light in order to control depth of field, decide what is most important, depth of field or shutterspeed, if you are shooting 1 person 1.8-5.6 should workif its a group and they are 3-5 deep go at least f8-11, its a little complicated but when you figure it out you will see why you need it to change, when I first learned I couldnt figure out why anyone would want to use anything but f 1.4, but after years of shooting I rarly use 1.4 altho I have been experimenting with my 85 1.2 at 1.2 and love the out of focus background, sorry to be so long winded but its ahard question to answer
dennis@idofotos.com feel free to email me if you need more help

[RbrtPtikLeoSeny]

Your probably shooting at to large an apeture ( example f/1.8) try stopping it down a bit to like, f/4, or f/5.6. I typically shoot everything between f/4 and f/8 with all my lenses including my 50mm f/1.8 that I have. Also, shoot AV mode. Works great, very easy to use. And like I said, use the DOF preview button!

Your OOF shots aren't possibly caused by slow shutter speeds are they? Because that could be another contributor. If so, you may need to learn how to take advantage of ISO settings to get the higher shutter speeds you need to obtain sharp images.

[jfrancho]

This may help you: http://www.dofmaster.com/

[scraggles]

Alright, here is a crop, these are the kind of results I'm getting.

The cropped image(The white circle is what was focused perfectly before shooting)
http://24.195.234.44/0666crop.jpg

and the properties of the pic:
http://24.195.234.44/0666settings.jpg

What am I doing wrong? The picture looks horrible.

[RbrtPtikLeoSeny]

There's also this website that you could check out. If you have a PDA, downloading the DOF calculator from the website that jfrancho posted would be a good idea since it's free and all.

http://www.dofmaster.com/dofjs.html

[RbrtPtikLeoSeny]

Huh, the picture does look very soft...... then again, you are shooting with a 70 dollar lens...... all your settings seem to be alright.... not sure what pattern metering is though. Don't think I have that on my 20D, and what focal point are you using? You know how there's 7 points and you can choose them? Did you use the center point? Right side point on the sign?

[lostdoggy]

Your said that you shot at f/11 and 1/120 with that it should pretty much get everything in focus. Can you post an uncropped picture???

[scraggles]

Huh, the picture does look very soft...... then again, you are shooting with a 70 dollar lens...... all your settings seem to be alright.... not sure what pattern metering is though. Don't think I have that on my 20D, and what focal point are you using? You know how there's 7 points and you can choose them? Did you use the center point? Right side point on the sign?

It was focused on the center point. However, keep in mind, I cropped the picture. In the original, the sign was dead center.

I've seen countless pictures on pbase taken with this lens, and a 300D and they look MUCH better than mine.

[scraggles]

go to http://24.195.234.44/_MG_0666.jpg for the full size, uncropped pic.

[RbrtPtikLeoSeny]

Uh... don't know what to say here.... you say that when shooting in auto settings you get better results with this lens? Could you post the results? Full shot, uncropped, unedited like you did with the link? :-)

[scraggles]

Well, now I seem to be getting horrible results here too.

http://24.195.234.44/IMG_0668.jpg

It does look like it's in focus right around the window on the van. :-(

[cfcRebel]

The uncropped version does look a little soft. Here is a sample of mine taken with my 50mm f1.8.


Cloudy, ISO100. f5.6, 1/125s handheld.

[slin100]

IMHO, the picture looks fine. You might try opening up the aperture a bit. At f/8 diffraction starts to kick in on 1.6x-size sensors. This image was taken f/11.

Try taking the shot at f/4 or f/5.6. The result should be very sharp.

Don't knock the $70 50/1.8. It's a fantastic lens.

[CyberPet]

I'd recommend a book called "Undestanding exposure" by Bryan Peterson (I think that's his name), it gives you many ideas on how to understand apertures and shutterspeeds. I did learn a lot from that book.

[jfrancho]

Scraggles,
Did you take this through a window?

[scraggles]

Scraggles,
Did you take this through a window?

No, I was out on my front steps when I took them. Nothing blocking the view.

[Tom W]

IMHO, the picture looks fine. You might try opening up the aperture a bit. At f/8 diffraction starts to kick in on 1.6x-size sensors. This image was taken f/11.

Try taking the shot at f/4 or f/5.6. The result should be very sharp.

Don't knock the $70 50/1.8. It's a fantastic lens.

Yes, f/8 would be a better choice, though f/11 is still highly useable on this camera. At f/4 or 5.6, you are limiting your depth-of-field quite a bit. And try a focus point a little farther into the scene as well, such as the street sign (Van Buren St.) or even a little farther away. The back of that sign is considerably closer to you than most of the scene and you may be pushing the limit on DOF on distant objects.

Some of this depth-of-field stuff is more about developing a feel for what happens at various apertures and focus points, but do study up on depth-of-field and hyperfocal points. It will give you the background to make educated guesses at where to set your aperture and your focus point. And don't be afraid to take a great number of shots to compare - digital is free.

There's some other things that could improve the image a bit like contrast, sharpness, and saturation but I know that wasn't what you asked and it won't help the DOF at all.

[jfrancho]

No, I was out on my front steps when I took them. Nothing blocking the view.Kind of looks like out my front window...gotta trim the bushes. Anyway, the pic looks sharp. If you were 15 feet away from the sign your DOF would be around 14 feet. About 4.5 feet in front of the sign would be in focus and 9.5 behind the sign still in focus. Problem is there is a too much going on and that is what is distracting to you. Look at some of the other elements in the pic. I can see that you are near the corner of Van Buren St and 2nd St. I can even make out the bricks an the farthest building in the shot. The Jeep's tag is CZE 9504 and is from New York. I can see 14 stars in the obscured flag on your neighbors porch. This is all before I tried applying some USM in ps. There's even more here, such the climbing roses on the fence. Try a little post processing, and think you'll be satisfied.

[blue_max]

Sometimes it's easy to move the whole camera when you press the shutter button.

Try and crank up the ISO to 800 and try again and see if it improves and try to squeeze the shutter gently. This might help rule out any operator error. Sorry if this is sucking eggs for you, but you have to have the basics right.

Hope it is as simple as that!

Graham

[steibeldj]

No depth of color, soft throughout, overexposed, hazy. Usually when I see a picture like this, the lens is fogged, like taking it out from a cold car into a hot summer day. Otherwise, I would say that between the ISO, shutter speed and f stop something let in too little light in to charge the CCD properly, like low ISO and fast shutter, but everything looks ok from you listing?!?

[DavidEB]

to me, the white house behind the sign looks in-focus and quite sharp, so does the wire hanging slightly above the sign (further away) and the van, and the sign looks out-of-focus. My guess is that the camera was set to use all focus points rather than just the center focus point, and it selected the remote objects on the peripheral points because there's not enough contrast in the gray signpost at center.

The 50mm is a great little lens and can take sharp pictures if focused properly, but the slow focus motor does make it hard to get good focus.

try this - put the camera on a tripod. set to use only center focus point. retake the picture. Now take again without moving camera, but focus by hand. Do this at f 1,8 which will really demonstrate differences in where the focus is set to.



good luck

[SAZABI]

ok... n00b question. :o


after pressing that DOF button, i do see some area becomes darker. How do I interpret that result? How do i see what is in focus? thanx...

[RbrtPtikLeoSeny]

You look very closely. :-) I like to start at a maximum apeture, like f/4, then press that DOF preview button and start making the apeture smaller while looking through the view finder. That way, you can see the picture becomming more and more in focus even though it's really dark. When you get it where you want it, stop there and press that shutter. :-)

Hm, I have a quick Q for everone.... does the 1d MkII darken the view finder when using the DOF preview button...?

[cmM]

there's something wrong there. you should have plenty DOF at that aperture and you were shooting at a pretty high shutter speed so camera shake is pretty much out of question... something wrong with your camera or lens.. perhaps back/front focusing. Do some focus tests just in case.

[scraggles]

Thats what I was thinking cmM. However, at the moment, I don't have a printer to print out any of the tests online that I found, but my brother does, so hopefully I'll print something out soon.

I also don't have any other lenses at the moment, so testing another lens isn't possible. I don't know where a big enough camera store is around here. All the camera stores around here that I know of don't have lenses, they just have a few cameras, bags, and option to develop there. :-/

[jfrancho]

Scraggles, How far away from the sign were you? I'm going to guess about 15 ft. Total DOF would be 13.7 ft. at those settings. Does everyone realize they are looking at a 100% crop? The full size files look fine, as far as sharpness out of the camera, is concerned. Scraggles, may I post a version optimized for web output on a monitor?

[scraggles]

Feel free to post any edits you do. The whole purpose of this thread is that I'm just trying to get the sharpest image out of my camera that I possibly can. My A80 put out much sharper images and I think the 600$ price difference between cameras should also mean that the images would come out clearer. I know the issue is most likely MY fault, and if that is the case, I would like to find out what I am doing wrong. If it isn't my fault, I would like to get the camera or lens fixed asap.

[jfrancho]

Ok. Here is the photo with the changes.

http://plan-b.smugmug.com/photos/25108848-L.jpg

Here are the 100% crops:

http://plan-b.smugmug.com/photos/25108843-L.jpg

http://plan-b.smugmug.com/photos/25108845-L.jpg

http://plan-b.smugmug.com/photos/25108846-L.jpg

Here is what I did:
Open in PS/CS2
Unsharp Mask:Amount: 251%
Radius 1.6 px.
Threshold: 1 level.
I then converted the color profile to sRGB.
Saved as jpeg Quality 12.
Upload to the smugmug account.
Linked to the Large(High Bandwidth) file in this post.

You can visit the gallery directly here (http://plan-b.smugmug.com/gallery/596865/1/25108846).

Here is what I think. Don't take any offense, please. It's a terrible photo with several things wrong with the composition if it is to be used to test lens sharpness. As I explained, at 15' (just a guess on my part) the DOF is 13.7 ft. The focus point was in the sign post. So, 4.2 ft. in front of the sign and 9.5 ft. behind it will be in focus. There isn't much more than some ashphalt that falls in this plane. Therefore, the soft assessment. That said, I think every image should be sharpened a little. It probably should be color corrected, and a few more things, but that isn't the question.

[scraggles]

No offense taken. I just took a quick picture to show the problem. No serious thought went behind it. I stepped onto the porch, and clicked.

I'm just trying to figure out the camera. With my A80, I had no DoF, so taking pictures was a walk in the park.

[jfrancho]

I don't think there is a problem with your lens, nor do I think there is a serious problem with scraggles' pics...take a look at two great posts:
http://photography-on-the.net/forum/showthread.php?t=60650
http://photography-on-the.net/forum/showthread.php?t=79211

[montreal]

I think every image should be sharpened a little.

I think jfrancho nailed it, with his DOF explanation. And digital pictures need to be sharpened because of the way the sensor works.

[scraggles]

So, who here thinks the problem is my fault, who thinks its the camera/lens's fault, and who thinks its a combination of both?

I'm voting on me. I can fix me in time, I'll learn from experience, but if I have to pay to have something repaired, I'll be pissed, especially considering everything is 2 days old.

[DavidEB]

I think you had the blank white part of the sign lined up in the center focus spot at the exact moment you acquired focus, so the camera didn't use the center focus point because it had no contrast, and it instead used the outer focus points to focus on the house in the background.

[jfrancho]

So, who here thinks the problem is my fault, who thinks its the camera/lens's fault, and who thinks its a combination of both?

I'm voting on me. I can fix me in time, I'll learn from experience, but if I have to pay to have something repaired, I'll be pissed, especially considering everything is 2 days old.I don't think it's your fault, or that it's a bad camera/lens combo. I just think it isn't a great example to judge for sharpness.

[scraggles]

I'll just keep practicing. I'm not used to the flexibility. If I still have problems, I'll definitely come back here for help.

[wiselion]

There's a DOF preview button on your camera located on the left side of the lens attatchment area. It's meant to be accesable to your left thumb when holding the lens. You set the f stop number you want, focus the lens, then press that button. The viewfinder will become darker (unless your at max apeture) and you will notice what is, and is not in focus. Then you further adjust the f/ stop to get what you want, or if it's all good leave it at what it is. Go look at your camera and see if that's there. Give it a try. I own a 20D so I'm not sure if it's the same on an XT, but I think it should be..

I played with this button today when testing my 300f/4 L at 30 ft on a magazine cover taped to the side of my house. I set apeture to f/8, and pressed the DOF preview button. Everything in the viewfinder was dark. I couldn't tell what was in focus and what was not. The picture did come out crystal however. What am I really supposed to see when I click the preview button?

[wiselion]

I think I just found my explanation on another post.



In an SLR camera, the lens is normally wide open for better viewing in the viewfinder. When you push the DOF button, you stop the lens down to the actual aperture you will use when you take the picture.
If the actual lens aperture is close to wide open, you won't see much if any difference with the DOF button. If the lens is stopped way down, you will see the difference including the depth of field. When you see this difference you will also see sometimes that any detail in the viewfinder is difficult to see because you have limited the light coming in. That's why it is normally opened up for focusing, etc.
Jim

[SimonBl]

I'd recommend a book called "Undestanding exposure" by Bryan Peterson (I think that's his name), it gives you many ideas on how to understand apertures and shutterspeeds. I did learn a lot from that book.
Petra, just a quick note to say that I went out to order this book yesterday and ended up finding 1 in stock, so I have it to read over the weekend. Thanks for that. I've also been recommended another called something like "The National Geographic Field Guide", have you heard of that?

I need to get my head around f-stops and exposure and stop using the auto modes as much.

Simon....