Sharpness reduces with distance

[pasoviennese]

Hi,

I've been playing around with my Canon 50mm f1.8 on EOS 30D today. Took a few shots with the subject 1meter infront of me (crisp sharp) and with subject 5 meters infront of me (blury/fuzzy).

ISO 400
shutter 1/200
f 1.8

Focus is automatic centre point.

I'm confused

[OsmosisStudios]

When you shoot at large apertures (like f/1.8), you end up with a shallow Depth of Field. Usually this is done on purpose to help isolate a subject from a background. In your case, you need a smaller aperture (larger f/#) to get a deeper Depth of Field.

[pasoviennese]

Originally Posted by OsmosisStudios

When you shoot at large apertures (like f/1.8), you end up with a shallow Depth of Field. Usually this is done on purpose to help isolate a subject from a background. In your case, you need a smaller aperture (larger f/#) to get a deeper Depth of Field.

I don't understand what's that got to do with DOF, because i am focusing on the subject tha's 5meters away from me, not the on that's 1 meter away from me.

[teaking]

I think OS is saying because the DOF is smaller at F1.8 and the subject is further (distance narrowing the focus range as does magnification) any error in focus is punished and anything on the wrong side of the focus point wont be tack sharp.

If your not already doing so try using one focus point if possible the centre focus point and a tripod make sure the focus point is exactly what you want to focus on this may be a case for manual focus.

If possible tape the subject to something so they cant move lol im joking but with such limits in focus range the smallest shift can cause lack of focus some people use burst mode in situations like this its hit and hope but sometimes works

[pasoviennese]

Hmm...from my understanding, distance expands the focus range.

1.6x DSLR 50mm f1.8

For object distance = 1m
DOF = 2.5cm

For object distance = 5m
DOF = 66cm

This was done using a online DOF calculator.
Depth of Field Calculator

If your not already doing so try using one focus point if possible the centre focus point and a tripod make sure the focus point is exactly what you want to focus on this may be a case for manual focus.

I am already using the center point as my only focus point.
Shutter was at 1/200sec so I didn't think camera shake would be a problem, the subject was a fruit bowl...don't think it would move that much.

[RichardTaylor]

Just a thought. Did the lens have a filter on it?

[pasoviennese]

Originally Posted by RichardTaylor

Just a thought. Did the lens have a filter on it?

No filter.

[Vagebond]

Just another thought: do you have "auto lighting optimizer" on your camera? It's found under custom functions on my 450D and it's ON by default. Under certain light conditions it can cause noise. It might be worth a try to turn it off.

[teaking]

Haha .. yeah messed that up it is the other way round I confuse my self sometimes I mix up focal range with how far in front and behind is out of focus you can tell in my exposure triangle apreture is last

Nail down that fruit bowl that will solve all problems haha

Hope you manage to find a solution would be interesting to see what was causing it good luck!

[OsmosisStudios]

Originally Posted by pasoviennese

I don't understand what's that got to do with DOF, because i am focusing on the subject tha's 5meters away from me, not the on that's 1 meter away from me.

Thats not what you said in the first post.

The way your original post is worded, you had 2 subjects: one at a distance of 1m and one at a distance of 5m. The subject at 1m was the one that was focused on.

In either case, 4m is going to be well beyond DoF for f/1.8, regardless of what you focused on. The other subject will always be blurry.

You need to better explain the situation