Davejwatts From United Kingdom, joined Dec 2005, 42 posts, RR: 0 Posted (3 years 10 months 1 week 4 days 9 hours ago) and read 392 times:
If you have read my post on my pictures that have the front in focus but the back not, I have figured it is not the lens but indeed the way it focuses I used my 18-55 and 75-300 lenses to photograph some black text on a white background and noted that when straight on it is all in focus with both lenses and were sharp but at a 45 degree angle the nearer text was in focus but the more distant text was blurred. So I am wondering could this be a depth of field/technique problem rather than a lens problem???
DC10Tim From United Kingdom, joined Jan 2005, 1394 posts, RR: 21 Reply 2, posted (3 years 10 months 1 week 4 days 7 hours ago) and read 367 times:
Quoting JeffM (Reply 1): Duh, that is what DOF does. Use your center point and do the same test. Some in front, and some in the back will be in focus.
Surely you mean some infront and some at the back will be out of focus at a 45 degree angle and using centre focus?
Dave, if I were a gambling man I would say it is down to technique, but the 738 shot you linked to in the last thread was kinda hard to judge as it was more or less at 90 degrees to you and actually on the runway, not turning or anything and it was more or less in front of you, so the relative movement of the aircraft would be pretty much uniform throughout its length, making it hard to understand why the front half was so out of focus. Are you making sure that you keep pressing the shutter half way to re-focus on the aircraft as it moves infront of you?
Dendrobatid From United Kingdom, joined Nov 2004, 1353 posts, RR: 70 Reply 4, posted (3 years 10 months 1 week 4 days 1 hour ago) and read 308 times:
AIRLINERS.NET CREW PHOTO SCREENER
Dave
That is exactly what is meant by depth of field,
JeffM is being his usual subtle self - always makes me smile and I am sure he cultivates that impression !
Anyway....
If an object is angled away from you and you focus on the middle, only one point, the focus point is PERFECTLY in focus. There is an area forward of that point and behind that point that is ACCEPTABLY in focus. The two extremes are the depth of field. As the lens is closed down(higher f number) that range increases.
The test on your lens should have been conducted with the subject at 90 degrees to the lens axis as anything else would be meaningless. If you have done that and everything is sharp the the lens is okay.
Your shutter speed was rather low for the original photo and the problem was then probably camera shake. The original aircraft photo was very square on to the lens making that a less likely candidate than a lens problem. However, due to the way the shutter works it is possible to get shake on part of the image but not all of it. The usual old photographic adage is to not use a shutter speed lower than the reciprocal of the focal length (which you did)
Not wishing to sound like JeffM, but a good book on photography might be an idea.
Mick Bajcar
DC10Tim From United Kingdom, joined Jan 2005, 1394 posts, RR: 21 Reply 6, posted (3 years 10 months 1 week 3 days 19 hours ago) and read 264 times:
Quoting JeffM (Reply 3): No. My statement is accurate as written. Some in front of the focus point, and some behind it will be IN focus.
Is that hard to understand?
Not now you've elaborated a little. The confusion arose because obviously you will have two areas beyond the extremities of the DoF that are out of focus when doing that test and it wasn't clear you were talking about the area around the point of focus.
On days when it is cloudy as such, it's a trade-off between having a smaller aperture, giving a bigger depth of field and a higher shutter speed, giving sharper images within the DoF. Though the lens doesn't perform as well at it's extremities, in this instance I would have been inclined to open up the aperture as far as possible (f5.6 at full stretch?) and use the higher shutter speed. For everyday stuff, I wouldn't bump the ISO above 200 on the 300D as the results are very grainy.
Davejwatts From United Kingdom, joined Dec 2005, 42 posts, RR: 0 Reply 7, posted (3 years 10 months 1 week 3 days 17 hours ago) and read 253 times:
Just to say thanks alot guys I really appreciate it!! Peoples own experiances can often be better than that of a book. Anyway will try what has been said and hope for a clearer day preferably with a little more sunshine, grey British weather is not ideal fpr sharp photos!!
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