Another sharp question part II rebel XTI

wheresdavid

I have a follow up question to my yet another sharp question. When you zoom in on the lcd of a rebel xti should you be able to zoom in to the smallest and still have the photo be in focused? :scratch i hope that makes sense, I cant seem to get a photo that i can keep sharp until maybe three or four clicks (push of the zoom button) away from the smallest and this is when i should on the highest resolution. :dunno

Thanks

Dave

LuckyBob

I'm not sure on the particulars with the XTI, but on my original Rebel I know that the image used for preview is a ~3MP preview JPEG embeded into the RAW image, so my experience follows yours. I've taught myself how sharp the preview image should be relative to the actual RAW file, so I can pretty accurately guess what the final image should look like.

Edit: I saw online that BreeseBrowser can extract the built-in JPEG image so you can compare what the JPEG looks like versus the RAW image.

wxwax

The more you zoom in on your camera's LCD, the blurrier the image will get.

It's perfectly natural, happens even on the 1 series.

pathfinder

You cannot depend on looking at the camera LCD to verify focus. I have tried to do that with several Canon cameras, and until I can see the image on a computer screen at 100%, I never REALLY know if the image is critically sharp until then. You can set the camera to display the AF point used to aquire AF on the LCD image, but just do not place your trust on it too firmly.

I can get a pretty good idea about focus, from how easily the camera aquires autofocus with the AF point I have chosen to use.

The trick is to not allow the camera to choose the AF point - you must do that yourself, very precisely. This is more true for an XT than a 1 series camera, but it is true for all of them.

The cameras will look for sharp, straight, contrasty lines and focus on them, rather than soft eyelids and facial features if you let them. Cameras also tend to choose closer over more distant points of focus. If you want to focus on the more distant focus point, behind a near, sharp linear point, like the fibres of a hat, you must be precise in your choice of AF points.

Zanotti

Pathfinder is exactly right.

Letting the camera choose:




You doing the choosing:



Easy!?!

Z

wheresdavid

pathfinder wrote:

You cannot depend on looking at the camera LCD to verify focus. I have tried to do that with several Canon cameras, and until I can see the image on a computer screen at 100%, I never REALLY know if the image is critically sharp until then. You can set the camera to display the AF point used to aquire AF on the LCD image, but just do not place your trust on it too firmly.

I can get a pretty good idea about focus, from how easily the camera aquires autofocus with the AF point I have chosen to use.

The trick is to not allow the camera to choose the AF point - you must do that yourself, very precisely. This is more true for an XT than a 1 series camera, but it is true for all of them.

The cameras will look for sharp, straight, contrasty lines and focus on them, rather than soft eyelids and facial features if you let them. Cameras also tend to choose closer over more distant points of focus. If you want to focus on the more distant focus point, behind a near, sharp linear point, like the fibres of a hat, you must be precise in your choice of AF points.

I am not exactly sure what you mean when you say dont let the camera choose for you. does that mean change the autofocus to only the center point and focus on that one point??

Rhuarc

wheresdavid wrote:

I am not exactly sure what you mean when you say dont let the camera choose for you. does that mean change the autofocus to only the center point and focus on that one point??

Exactly... Point the center focus point at what you want to focus on, then either use the focus lock, or press the shutter halfway down to lock the focus, then recompose the shot before pressing the rest of the way down. This way you decide what is in focus, regardless of whether it is in the center of the frame or not.

LuckyBob

Rhuarc wrote:

Exactly... Point the center focus point at what you want to focus on, then either use the focus lock, or press the shutter halfway down to lock the focus, then recompose the shot before pressing the rest of the way down. This way you decide what is in focus, regardless of whether it is in the center of the frame or not.

, but keep in mind that (a) you have more focus points than just the center, although on most dSLRs it is the most accurate focus point, and (b) that recomposing can cause many focus issues due to focal plane shift.

Rhuarc

LuckyBob wrote:

, but keep in mind that (a) you have more focus points than just the center, although on most dSLRs it is the most accurate focus point, and (b) that recomposing can cause many focus issues due to focal plane shift.

From my understanding the focus plane issues happen more often the closer you are to the subject, and the shallower your depth of field.

LuckyBob

Rhuarc wrote:

From my understanding the focus plane issues happen more often the closer you are to the subject, and the shallower your depth of field.

True dat. People just need to be aware of it.

Terrence

Be careful with using the center point only. If you focus, lock, re-compose, there is a good chance you won't be sharp on what you want. For example, if your subject is in the right half of your composition, you are better off choosing a focus point to the right than using the center and re-composing. There is a great discussion of that here: http://visual-vacations.com/Photography/focus-recompose_sucks.htm.

pathfinder

Good on ya, Terrence!!

Focus (with the center AF point), recompose, yields poor focus if you are focusing on on a subject less than 12-15 feet away. The closer you are, the more error there is in focus, recompose.

Focus, recompose works fairly well with long teles at very large lens to subject distances. Like shooting birds with long glass.

Instead.... Choose the appropriate single AF point from among the many ( 9 -15 -45) in your camera, put it on the specific area of the subject that needs to be dead on in focus, half press the shutter to achieve AF lock, and then press the shutter carefully. Do not move the camera around, do not release the half pressed shutter. If you are shooting with lenses at wide apertures, where depth of focus is shallow, and accuaracy of focus is critical, CHOOSE the AF point used carefully, and place it carefully, and then shoot the picture.

If you allow the camera to shoose the AF point used, it will frequently not be the point in the subject you might prefer. Cameras are just not that smart. They have a very small brain.

Autofocus is a great focusing aid, that can truly improve the quality and focus of your images if used properly. Autofocus is not a "Press the Button and everything will be fine" button. It needs to be used with skill and attention.

Rhuarc

pathfinder wrote:

Autofocus is a great focusing aid, that can truly improve the quality and focus of your images if used properly. Autofocus is not a "Press the Button and everything will be fine" button. It needs to be used with skill and attention.

Well put PF!!

Terrence

Rhuarc wrote:

Well put PF!!

HUMONGOUS +1. I have been beating my head against a wall for a long time thinking AF is a "fire and forget" tool, until I found that link on AF and re-composing. After a full year I am just now "getting it" and starting to improve my pictures. Learn from those who have gone before you.

wheresdavid

thanks for the link!

Terrence wrote:

Be careful with using the center point only. If you focus, lock, re-compose, there is a good chance you won't be sharp on what you want. For example, if your subject is in the right half of your composition, you are better off choosing a focus point to the right than using the center and re-composing. There is a great discussion of that here: http://visual-vacations.com/Photography/focus-recompose_sucks.htm.

thanks for the link!!