Focusing Question

I have had bad luck with focusing in dark situations. I have the 580EXII, so brightness of the result is never an issue.
However the focusing is a big issue, I am wondering if the larger the aperture the easier the lens can focus easier as well as suck more light in.
Now, imagine using the same lens with a wider aperture, would this be alright to focus under the same circumstances.

If so I could hopefully focus with larger aperture and change my settings and then switch to manual focus before taking a shot, unless there is a better way of doing this.

Can anybody help me?

I would think not - a lens keeps its aperture wide open anyway until you fire the shutter. So, for example, a f/2.8 lens set to f/8 will focus etc at f/2.8 and then switch to f/8 once the shutter is fired.

michaelgreen78 is correct. Your camera is focusing the lens at its widest aperture (f4 or f/3.5 depending on which lens you have in your sig is being used.)

Your 580EX's AF Assist light should help you focus. But since your fastest lens is f/3.5 you don't have anything as fast as f/2.8 that your 40D's AF sensors can take advantage of.

If the 580EX isn't enough to help you focus, consider a flash light or laser pointer. Or worse case, a faster lens.

(Also consider where you are focusing as well. Pick out high contrast areas, consider using your center AF only, etc...)

What kind of problems are you having? With my 580 and my 17-85, I've never had a problem shooting in low/dim light. The AF-Assist beam of the 580 helps a ton, and the 17-85 focuses fairly quickly in any light.

egordon99 wrote in post #7533079
What kind of problems are you having? With my 580 and my 17-85, I've never had a problem shooting in low/dim light. The AF-Assist beam of the 580 helps a ton, and the 17-85 focuses fairly quickly in any light.

What if the subject is beyond the AF assist range ?

vadim_c wrote in post #7536122
What if the subject is beyond the AF assist range ?

Flash light or laser pointer or some other aid with longer reach

blssdwlf wrote in post #7537725
Flash light or laser pointer or some other aid with longer reach

I understand this is a joke, but you have to be careful with it as some might take it as an advice. You can end up in jail with your laser pointer.

vadim_c wrote in post #7539393
I understand this is a joke, but you have to be careful with it as some might take it as an advice. You can end up in jail with your laser pointer.

Actually no joke. However, you are correct that the OP should check their local laws to make sure they can legally use a laser pointer (and also not cause harm as in pointing at someone's eyes or use in a manner that would create a hazard to others.)

A flashlight is very useful in giving enough illumination to focus where the AF assist light doesn't reach. A laser pointer gives you much more range than most flashlights. I prefer a vertical laser line pointer though since you don't have to do much corrective aiming.

Each of my lenses aren't great in fluorescent light. The 17-85 usually works fine.
My intention was to purchase a 50mm Prime (1.8 MkII) to counter all possibilities for the occasions where it doesn't work. I never use flash assist.

I was wanting to focus perfectly in a black night with stadium lighting at a distance. I am aware I should need more than 1.8, but I can't afford more, and it should do loads better than 3.5 or 5.6 with focus.

Besides, I am becoming very fond of the sharpness primes are getting, my standards are always increasing

Your most sensitive AF sensor on your 40D is your center point which is sensitive to f/2.8. An f/1.8 lens will help with your shutterspeed though

The 50mm f/1.8 is a decent lens but its motor is not very accurate and compound that with low light+distance you will get frustrated. The 85mm f/1.8 has gotten some good feedback and you could look at a constant f/2.8 lens.

Night time focusing can be difficult without some type of AF assist or high contrast target though.

fubarhouse wrote in post #7540298
Each of my lenses aren't great in fluorescent light. The 17-85 usually works fine.
My intention was to purchase a 50mm Prime (1.8 MkII) to counter all possibilities for the occasions where it doesn't work. I never use flash assist.

I was wanting to focus perfectly in a black night with stadium lighting at a distance. I am aware I should need more than 1.8, but I can't afford more, and it should do loads better than 3.5 or 5.6 with focus.

Besides, I am becoming very fond of the sharpness primes are getting, my standards are always increasing

blssdwlf wrote in post #7539653
Actually no joke. However, you are correct that the OP should check their local laws to make sure they can legally use a laser pointer (and also not cause harm as in pointing at someone's eyes or use in a manner that would create a hazard to others.)

A flashlight is very useful in giving enough illumination to focus where the AF assist light doesn't reach. A laser pointer gives you much more range than most flashlights. I prefer a vertical laser line pointer though since you don't have to do much corrective aiming.

http://www.hps.org …tions/articles/​laser.html
In 1997 the FDA issued a warning on misuse of laser pointers (see Consumer Information on CDRH Topics). In some states such as California, it is a criminal misdemeanor to shine a laser pointer at individuals who perceive they are at risk, and it is a felony to aim one at an aircraft.
and...
Common sense dictates that users should never direct a laser pointer beam at another person.

vadim_c wrote in post #7541610
http://www.hps.org …tions/articles/​laser.html
In 1997 the FDA issued a warning on misuse of laser pointers (see Consumer Information on CDRH Topics). In some states such as California, it is a criminal misdemeanor to shine a laser pointer at individuals who perceive they are at risk, and it is a felony to aim one at an aircraft.
and...
Common sense dictates that users should never direct a laser pointer beam at another person.

Absolutely. Like I said in my previous post:

Actually no joke. However, you are correct that the OP should check their local laws to make sure they can legally use a laser pointer (and also not cause harm as in pointing at someone's eyes or use in a manner that would create a hazard to others.)

Used safely, legally and with common sense a laser pointer can also work as a focusing aid.

blssdwlf wrote in post #7543275
Absolutely. Like I said in my previous post:

Actually no joke. However, you are correct that the OP should check their local laws to make sure they can legally use a laser pointer (and also not cause harm as in pointing at someone's eyes or use in a manner that would create a hazard to others.)

Used safely, legally and with common sense a laser pointer can also work as a focusing aid.

Wdo you point the focusing point when photographing people ? Sure it is the eyes. Even if not it is very easy to forget about the laser pointer and still point it into somebody's eyes.
Now if you just play with the ponter it is very unlikely that the point would be directed in the eyes for more than a fracture of second. But if used as a focus assist it could stay there for a second even more thus permanently damaging the eyes. Laser as a focus assist seems like a very attractive and cheap solution but no camera manufactures uses it. There is a reason for that. If you want to play Russian Rulette fine. But suggesting it to others is a bit unresponsible.

Hmm. You said point at the eyes.

That goes against what I said: "not cause harm as in pointing at someone's eyes or use in a manner that would create a hazard to others". Why are you insisting that I am being irresponsible when you're deliberately trying to use the laser in a manner I did not write?

You are advocating focusing on the eyes (deliberately or by accident). I am not (and I never indicated that in my posts.)

A laser can produce a sharp contrast point on a subject (the body, a tree, a distant building, etc) where it can help the AF system focus.

And as to "no camera manufacturer uses it", check out the old Sony DSC-F707 which uses a laser AF system.

http://www.dpreview.co​m/reviews/SonyDSCF707/​page4.asp

Quoted from dpreview.com:

Hologram AF

"Now I know you gonna dig this". Here's a neat party trick to wow your friends (are the guys on STF going to love this or what), aim the camera at a dark wall and half-press the shutter release, the camera will paint a pretty laser pattern on the wall.


This pattern is used to assist the contrast detect AF system in locking AF in low light situations. The pattern appears for approximately one second and does appear to work (in most circumstances). We'll test it in a bit more detail later in the review. I'm told by Sony that this class 1 laser is completely safe to aim directly at a persons face (yes, really).

vadim_c wrote in post #7543381
Wdo you point the focusing point when photographing people ? Sure it is the eyes. Even if not it is very easy to forget about the laser pointer and still point it into somebody's eyes.
Now if you just play with the ponter it is very unlikely that the point would be directed in the eyes for more than a fracture of second. But if used as a focus assist it could stay there for a second even more thus permanently damaging the eyes. Laser as a focus assist seems like a very attractive and cheap solution but no camera manufactures uses it. There is a reason for that. If you want to play Russian Rulette fine. But suggesting it to others is a bit unresponsible.