focus beyond infinity?

[airpix]

Does anyone know if it's posible to focus beyon infinity with the Canon 1Ds and Canon 24-70, 2.8 lens? I took some distance shots and focused as far as the lens would allow. All the images were out of focus!
Thanks, Airpix

[Titus213]

Does anyone know if it's posible to focus beyon infinity with the Canon 1Ds and Canon 24-70, 2.8 lens? I took some distance shots and focused as far as the lens would allow. All the images were out of focus!
Thanks, Airpix

I'm not sure there is anything there to focus on...:lol:

But I have seen the problem you are talking about I think. My old FD 100-300 seemed capable of focusing past infinity which threw everything out. I chalked it up to an issue with the lens age rather than design. I don't think it is meant to happen.

[Andy_T]

So it's a 'Chuck Lightyear' lens ... to infinity AND BEYOND :lol:

I remember reading that some lenses do allow that feature, but not in order to focus on things farther than infinity, but rather for use in very cold conditions, so that infinity focus can be achieved even if the lens contracts because of the temperature.

Best regards,
Andy

[Jon]

Some, especially long focal length, lenses will focus beyond infinity, but AFAIK the 24-70 isn't one of them. Did you use manual focus or AF? Is it possible that haze in the air led you to believe the subject was out of focus? Thermals may also lead to fuzzy images. Are you using a filter on the 24-70? If so, what kind (make, model, type)?

[robertwgross]

Does anyone know if it's posible to focus beyon infinity with the Canon 1Ds and Canon 24-70, 2.8 lens? I took some distance shots and focused as far as the lens would allow. All the images were out of focus!
Thanks, Airpix

It is impossible to focus beyond infinity. Infinity is as far as it gets.

If the lens actually tried to focus on a spot at 25 feet, then objects on the horizon would look out of focus.

---Bob Gross---

[Jon]

It is impossible to focus beyond infinity. Infinity is as far as it gets.

True, but . . . (there's always a "but")
Some long lenses will allow you to "focus" the lens past the infinity mark, even though under some conditions this would leave your 500 mm lens trying to form an image on a sensor 498 mm from the rear nodal point, effectively trying to focus beyond infinity, and giving you an out-of-focus image (think "far-sighted" vision). As Andy said, they do this to allow for thermal expansion/contraction. Under different conditions, "beyond infinity" may allow you to focus at infinity.

[Titus213]

So it's a 'Chuck Lightyear' lens ... to infinity AND BEYOND :lol:

I remember reading that some lenses do allow that feature, but not in order to focus on things farther than infinity, but rather for use in very cold conditions, so that infinity focus can be achieved even if the lens contracts because of the temperature.

Best regards,
Andy

Hey Andy, thanks for this info. I'll use it when I try to sell my FD lenses. I actually never thought too much about this since manual focus puts the onus on me to fix it but it sounds like it should be logical. Anybody in Alaska want to buy an FD lens?

[pierrot]

It is impossible to focus beyond infinity. Infinity is as far as it gets.
Oh yes it is! The lens actually can focus on a imaginary point beyond of infinity: the focusing group just have to move beyond the position in which the projected image (of a target situated at the infinity) is well focused on the sensor/film.

Be it a flaw, or on purpose, or under severe climatic conditions or whatever.

Of course, a well behaving AF system will never drive the lens into this situation and a well designed AF system should not allow it either.

But there is no optic law against "beyond infinity" focusing. ;)

[PacAce]

Does anyone know if it's posible to focus beyon infinity with the Canon 1Ds and Canon 24-70, 2.8 lens? I took some distance shots and focused as far as the lens would allow. All the images were out of focus!
Thanks, Airpix
Canon made it possible to focus beyond infinity on purpose. That's to allow for expansion/contraction due to heat/cold. It's all explained in the little pamphlet/booklet that comes with the lenses.

[SkipD]

Does anyone know if it's posible to focus beyon infinity with the Canon 1Ds and Canon 24-70, 2.8 lens? I took some distance shots and focused as far as the lens would allow. All the images were out of focus!I just checked into this with my 24-70 f2.8 and 20D body. If I autofocussed on an "infinity" subject (1/2 mile away), the lens would stop with the white index on the lens about in line with the short part of the "L" that is next to the infinity symbol on the inner ring. I could, in fact, turn the focus ring further and get out of focus "beyond infinity".

Lenses for my old cameras (Nikon, 1968 vintage and Pentax, 1995 vintage - manual focus only) used to have a hard stop right at the infinity setting and you couldn't turn the ring any further. This one is different. I don't have time right now, but will test my other two L lenses (16-35 f2.8 and 70-200 f2.8) when I get a chance. I got about the same action for any focal length setting.

Because autofocus is the "intended" way for these lenses to operate, I suspect that this may be the way they were designed - with a little overtravel possible. Why? The book refers to focus shifting with temperature variations on page E-6.

[airpix]

Yes, I tried the camera / lens for aerial photography, shut off the AF (switched to MF) and taped the lens after turning it as far as I could towards infinity. All images were out of focus!

Airpix

[SkipD]

Yes, I tried the camera / lens for aerial photography, shut off the AF (switched to MF) and taped the lens after turning it as far as I could towards infinity. All images were out of focus!I would suggest either leaving AF on or acquiring a good focus in manual and verifying it in the viewfinder and maybe a sample picture before taping the ring. It's obvious that running to the ring's limit was your problem.

[rdenney]

I'll assume that the lens is done that way on purpose. If so, thermal expansion may be one reason, though it seems unlikely given the short focal length.

But I'll bet Canon put that little bit of overtravel headroom in there for a reason they would not admit to. They don't want the autofocus ramming the focus mechanism against a hard stop when you point it at an infinity target. I know that this happens a lot at close focus, but the close focus point is arbitrary and they can just put an electrical limit on the focus motor before reaching a hard stop. Providing a bit of slop on the infinity end lets the autofocus mechanism work without running into mechanical limits, even if true infinity focus points on the lens do vary a bit with temperature changes. If there was a hard stop, I'll bet there would be a loud click every time you focused on a distant object.

Rick "who doesn't trust the infinity stop on any of his lenses of any brand or heritage" Denney

[ScottE]

I believe there are at least three reasons to allow the lens to focus past the infinity focus.

Any lens with a metal body will change in length with changes in temperature. At hot temperatures the length will be longer so the lens has to be brought closer than would be calibrated for infinity in cold conditions when the lens is shorter.

If a lens is used for infra-red photography it will be necessary to adjust the focal length since lenses are designed to have a common (as possible) focal point for light in the visible spectrum. Infra-red is beyond the design parameters so focus distance has to be adjusted. (You can see this effect by shining a beam of light through a prism and seeing the colours of light separate to from a spectrum.)

No manufacturing process is perfect so tolerances have to be built in for manufacturing variances. If the lens was designed to only focus to infinity and turned out to be a little too long you would not be able to focus on distant objects.

Scott

[lancea]

The 17-40 F/4L also has the mark beyond infinity. It is referred to in the lens's manual. As stated above, you're supposed to use that above a certain temperature (as in very hot).

[robertwgross]

Of course, a well behaving AF system will never drive the lens into this situation and a well designed AF system should not allow it either.

At the last time I checked, these are autofocus cameras and lenses!

---Bob Gross---

[ron chappel]

As many have stated above ,many lenses can indeed focus past infinity.And it does sound like what has happened in you case (assuming other obvious possible errors such as camera movement,etc are eliminated)

So basically it sounds like your camera missfocused-simple as that
Wether this is a potential problem (back focus) or just an odd rare incident would require more checking.
Just one possible theory (assuming the camera and lens are perfect)-in some situations it's possible for the camera to take a picture without any focus lock.The first-pic--in-a-series from focus tracking is one example,there may be others.
Maybe the camera didn't lock on this occasion and took pics anyway?
(yes several things would have to go wrong at once and you'd prob notice-it's just a possibility,not fact :))

[Jon]

Well, he says he used MF and taped the lens down after cranking it as far as it'd go. So if the lens allows focus beyond infinity, that's where he was. I think I'd either MF on a distant subject while on the ground with a focus magnifier or rely on AF in this situation.

[ron chappel]

:o Oops ok

I was abit tired last night and totally missed that one,lol