Hi all,

i've just bought the Canon 85mm f/1.8 lens. i'm so loving it now!! the DOF can make a photo more awesome!

anyway, i'm having some problem now. how do you set the focus to infinity without relying on Autofocus??

one example of situation is when i'm taking a photo of the night sky, i want to focus on the clouds in the sky, but because it's too dark, Autofocus can't manage to focus on it. so my solution is to target a faraway light source (e.g. lightpost -20km away), then i turn to Manual focus, and shoot at my night clouds, but it's still not sharp enuf and there's no other way for me to adjust my focus.

so does anyone have any solution to my problems??

thanks.

inkle.
Pls check out my photos, & give some critics.
http://www.flickr.com/photos/patrickcheng/

How about shooting 10 shots while turning the focus ring a little bit each time?

isnt focus to infinity just means turning the focus ring all the way to the end?

Yeah, just set your lens to MF(manual focus) and turn it all the way to the end for infinity (right? ).

I thot the manual said u turn in clock wise rotation till the end?

Accurate AF cannot be guaranteed by turning lens all the way. Every lens has 'beyond infinity' focussing to tolerate non-ideal environment. You must always look at the subject when focussing manually.

Even if it's the (night)sky?

i wouldn't bothered
i just turn it to infinity and then shoot loh

Well, if you use narrow aperture, the little inaccuracy doesn't matter.


Not all lens have focussing meter right? For Canon, usually only the L lens have the meter. If you observe the meter, there is a lot more space after the infinity mark.

oppss i didnt know that
all my AFD and AiS lenses have

actually not all the way to the end is the infinity.. u wont get sharp images..

trust and focus with ur eyes.. when your eyes thru the viewfinder say it is sharp.. then it will be..

Turn to the end and then slowly inch your way through the ring. Generally the only way. Even with a focus distance meter, doing it on Canon lenses is quite hard (infinity tolerance still too large). Short of buying an MF Canon FD lense, you can help yourself by getting a brighter focusing screen.

I find that starlight photography is only decent on an MF lense as there's a guesswork element involved in using normal AF lenses.

mengsuan,

your info on the lens focusing 'beyond infinity' actually made me realise that i've been turning the lens all the way to the end, no wonder all my photo is not sharp on MF. i've just tried it again and now i turn the focus ring to point exactly on the 'infinity' mark, no more no less, and the lamp post that is 20km away is very sharp. Thanks!!

so i was wondering, under what situation can i use the 'beyond infinity focus'??

inkle.

When your lens is heated up, you'll realise that you need to focus beyond infinity.

buy a flash then u no need to worry about it ^^

You even read the TS's post ah?

I'd like to see a flash that illuminate the clouds that doesn't involve a thermonuclear explosion.

this must be the most out-of-topic reply i've ever seen in this forum

ts, i agree with mindkiller. trust ur eyes when focusing. in an slr, what u see is what u'll get

A scientific way to focus on infinity is to put a closeup filter on and take out a ruler.

+4 means that if your lens is at infinity, the lens will focus on something 25cm close.

+2 - 50cm.
+1 - 100cm.

So you set the ruler with the 0 mark at the front of the closeup filter, and focus until 25cm, if you're using a +4 filter.

Happy collimating!

If you want to go the unscientific way, well, use your peripheral vision (that means, use the sides of your eyes). I've read that it's better for focusing on stars.

On an unrelated note, the Minolta/Sony system always resets any AF lens you mount on it, to infinity. Even when the camera is set to manual focus. So I guess there's ONE advantage to that feature...

Try to get acquainted with your len's hyperfocal distance.
Just focus on an object far enough to be in the hyperfocal distance.
No need to look up numerical tables. Just review the 'at infinity' objects and if they are sharp enough, you have hit hyperfocal.

far enuf means set it to 50mm according to my 40D manual...

yesterday i also used 85mm at zoo..........added filter one.......when i use MF,also hard to F.........haha

Are you sure they're blur because of focusing issues, or blur because of cloud drift?

Maybe Canon not expecting 40D users to have a 1000mm f/4 lens?

actually its regarding checking dust. not sure why 50mm though..

Hmm, maybe it's to move some internal mechanism away for the user to check for dust more easily.

But hyperfocal distances vary according to focal length, focal distance, aperture size, and film/sensor size.

Generally, if your focal length is short, focal distance is long, aperture size is small, and sensor size is small, the focal distance which you start to hit hyperfocal will be nearer to you.

Speaking of filters, try getting a cross star filter. Not for the effect... but for the obvious visual effect it has on stars. You can see the 'thickness' of the star lines. The thinner, the more in focus you are.

After focusing, remove the filter.

The star lines also get thinner with smaller aperture...

How do the 'stars' know what are you focusing on?

This is a crop.

As you can see, the focus is further to the back (left of the picture) and the lines get thinner there. The photographer would have the benefit of adjusting focus with the lens wide open anyway.

If I have time to put on and take off a star filter, I'd have time to shoot and review the LCD and then shoot again (with adjusted manual focal distance)...