Sigma 30mm f/1.4 - manual focusing help!

[kiso]

Hi guys, so I have a Sigma 30mm f/1.4 lens (on a Canon Rebel XTi) and whenever I decide to do nighttime photos of landscapes, I have to manually focus to get the background. Not a problem.

The problem is every time I do so and I turn the focus ring as much as I can to let the whole background in focus (it appears so in my viewfinder), the photos turn out unfocused when they take.

Does this lens only focus so far?!! Am I turning it wrong?

 

[Gavjenks]

How can you tell it's in focus at night through your viewfinder? Are you focusing on a nice bright point source of light like a street lamp far away? or at you just trying to focus on a dark hillside or something?

Hillside: Your viewfinder probably is just too dark and crappy to focus at night on dark objects. DSLRs aren't meant to do this, and they don't have microprisms and so forth like old manuals did to aid in focusing visually. ESPECIALLY if you're using that lens wide open at f/1.4 You don't stand a snowball's chance in hell at focusing on dark objects at night with the super thin DOF of f/1.4 Not gonna happen, no matter what.

Street lamp, etc.: If you're focusing on a light, then it should be working, and something else is probably wrong. One possibility is that the diopter wheel on your viewfinder is badly adjusted. it's a tiny little wheel next to the viewfinder on most Canons, that moves lenses around to compensate for people who wear eyeglasses. If it's way off, it can make the viewfinder not match the photos very well (like if you have it set for thick glasses, but you don't wear glasses). Try messing around with it during the day with a nice high contrast object, and see if you can adjust it to where the viewfinder agrees with the final image.

The problem is every time I do so and I turn the focus ring as much as I can to let the whole background in focus (it appears so in my viewfinder), the photos turn out unfocused when they take.

Also this is a suspicious comment.

What do you mean by this? If you turn the focus all the way, it shouldn't automatically make everything in focus... It just makes things at "infinity" or close enough to infinity (about 100 feet and beyond at 30mm, f/1.4) in focus.

Look up articles on "depth of field" if you don't know what that means already.
Also look up "hyperfocal distance."

 

[Big Mike]

Most lenses can focus just a little past 'infinity'. I believe this is just to accommodate some expansion and contraction that may occur due to temperature changes etc. So you can't just manually turn the lens all the way...you do actually have to focus at or to something. I used to have that lens, but I don't remember if it has a distance scale on it...if it does, then there is your focusing tool when in the dark.

 

[kiso]

Sometimes it's at a light, for once the other night it was in a darker area but I was looking toward a bright parting in the sky.

I'm also not shooting at f/1.4 but f/8+ (yes, I know about DoF).

"What do you mean by this?" > That's actually what I was getting on about. I'll focus it to infinity and beyond I guess but it doesn't stretch as far as the night sky.

I've shot the same landscapes in the daytime but I'll use autofocus and it works fine butwon't work in darker situations (fair enough), I just can't get the manual focus to cooperate in those situations.

Thank you though

How can you tell it's in focus at night through your viewfinder? Are you focusing on a nice bright point source of light like a street lamp far away? or at you just trying to focus on a dark hillside or something?

Hillside: Your viewfinder probably is just too dark and crappy to focus at night on dark objects. DSLRs aren't meant to do this, and they don't have microprisms and so forth like old manuals did to aid in focusing visually. ESPECIALLY if you're using that lens wide open at f/1.4 You don't stand a snowball's chance in hell at focusing on dark objects at night with the super thin DOF of f/1.4 Not gonna happen, no matter what.

Street lamp, etc.: If you're focusing on a light, then it should be working, and something else is probably wrong. One possibility is that the diopter wheel on your viewfinder is badly adjusted. it's a tiny little wheel next to the viewfinder on most Canons, that moves lenses around to compensate for people who wear eyeglasses. If it's way off, it can make the viewfinder not match the photos very well (like if you have it set for thick glasses, but you don't wear glasses). Try messing around with it during the day with a nice high contrast object, and see if you can adjust it to where the viewfinder agrees with the final image.

The problem is every time I do so and I turn the focus ring as much as I can to let the whole background in focus (it appears so in my viewfinder), the photos turn out unfocused when they take.

Also this is a suspicious comment.

What do you mean by this? If you turn the focus all the way, it shouldn't automatically make everything in focus... It just makes things at "infinity" or close enough to infinity (about 100 feet and beyond at 30mm, f/1.4) in focus.

Look up articles on "depth of field" if you don't know what that means already.
Also look up "hyperfocal distance."