roger55 Loc: Tampa Bay Florida

Question...When I want to focus on an object which should fall beyond infinity my lens i not in focus. I have to refocus. Why so ?

stogieboy Loc: Marlboro, NY

When you say "should fall beyond infinity" what exactly are you talking about? The infinity mark on the lens's focus ring? Not all lenses are built the same way, so sometimes the infinity mark is not precise, so you'll need to finesse the focus a little bit to get the result you're looking for.

BullMoose Loc: Southwest Michigan

"Infinity and beyond".

agillot

i dont thing there is anything behind infinity, most lenses will want to focus slightly beyond focus when put at max position , this become a problem on a wide 10 mm or so at wide open . , now if you shoot at f8 or so , this out of focus will go away , but at wide open it wont .like doing astro photo at wide open .

BlueMorel Loc: Southwest Michigan

Every lens has optimal focus distances, usually not at the near or far end. My tendency also runs to the extremes, and I'm trying to break that habit.

Mac Loc: Pittsburgh, Philadelphia now Hernando Co. Fl.

What can be beyond infinity?

amfoto1 Loc: San Jose, Calif. USA

Buzz Lightyear.

But to try to answer the original question, which I'm not sure I completely understand...

If you focus a lens "all the way to it's infinity stop" (if it has one), you will be de-focusing closer objects. It's usually better to focus only so that the "range of sharp focus" just barely reaches infinity, if that's what you want kept sharp.

But it depends upon the lens focal length and aperture being used. Shorter focal lengths naturally render greater depth of field. And smaller lens apertures also make for greater depth of field.

And a lot of lenses these days don't have distance and depth of field scales, which are needed to make these focus adjustments "on the fly". With zooms it's impractical to have a distance/DoF scale due to the variable focal lengths.

Short of stopping and getting out a calculator, a tape measure and spending a lot of time working with those, the best we can do a lot of the time is estimate the ideal "hyperfocal focusing distance".

https://en.wikipedia.org/wiki/Hyperfocal_distance
https://www.cambridgeincolour.com/tutorials/hyperfocal-distance.htm
https://photographylife.com/landscapes/hyperfocal-distance-explained
https://www.youtube.com/watch?v=FY1bLdeBN_U
https://www.youtube.com/watch?v=YmlhVZrcsbY
https://www.youtube.com/watch?v=KB7FR8u830Y

While it applies to a large extent to landscape photography, hyperfocal distance can be important when doing other types of shots, too.

I hope this answers your question.

roger55 Loc: Tampa Bay Florida

Let me reword this...If I point my camera towards the moon for example ,I would think putting my lens at infinity . then the moon should be in focus. Not so, i have to "back"and refocus the lens. I don't remember having that issue with film cameras.

roger55 Loc: Tampa Bay Florida

hmmmmmm

Mac Loc: Pittsburgh, Philadelphia now Hernando Co. Fl.

DWU2 Loc: Phoenix Arizona area

Update: Added link I referred to, but failed to paste in.


Here's an article that, I believe, addresses your question. I have a lens (Tamron 90mm), which can be focused beyond the infinity mark.

https://www.bhphotovideo.com/explora/photography/features/who-killed-infinity-focus%3F

Photocraig

We worked our film cameras differently, didn't we. No Chimping, then. and only Auto focus system knew for not so sure. Correlating the focus distance to the "reference" scale on the lens barrel isn't nor is it meant to be a precise thing. Focus by auto focus system confirmation of visual confirmation is what focus is. Adding aperture, DOF etc. to the analysis changes the issue from the focus plane--as in there is only one at a time, to "Apparent" focus.

Infinity is more of a philosophical concept adopted by Math theoreticians. Kinda slippery thing to achieve, then theoretical/philosophical concepts in a quantitative world.

amfoto1 Loc: San Jose, Calif. USA

Many modern lenses focus "beyond infinity" by design. Especially autofocus lenses. In some cases, this is done to be able to compensate for changes in how the lens focuses at different temperatures.

In addition, some lenses simply aren't marked all that accurately.

Used to be that lenses had an "infinity stop". Particularly manual focus lenses. That stop was adjustable and needed to be calibrated using special optical testing gear. So it also may be a time and cost savings to lens makers, not having a hard infinity stop, but simply allowing the lens to focus past it a little bit.

Essentially, the lens makers feel that the automation of AF will make up for the manufacturing/cost shortcuts.

It's very probably similar cost and complexity reductions that have led to many zoom lenses today being "varifocal", which means that they don't maintain focus when the focal length is changed with the zoom. If you change the focal length, you have to remember to refocus the lens afterward. Early zooms were varifocal... as were some cheaper ones in later years. Higher quality zooms were "parfocal", which maintained accurate focus throughout their zoom range. For example, you could zoom in on a subject to focus accurately, then zoom out to get the composition you want and depend upon the lens to still be in focus. But true parfocal designs are more complex and require more exacting calibration.

For example, look at the cost of cinema zooms sometime... which are often highly developed parfocal designs. A Canon 70-200mm f/4L IS USM lens for their EOS cameras costs about $1100. A Canon CN-E 70-200mm T4.4 Compact Cine Zoom costs $5000 (other factors, such as power zoom, also add to the cost).

With modern autofocus, more and more zooms are varifocal to keep the cost down, since the AF will sort of "auto correct" any loss of focus (though it depends upon the focusing mode being used in many cameras). Some zooms are also only partially panfocal... They maintain focus through much of the range, but not when shooting really close.

It's much the same with an accurate infinity hard stop.... It adds to the cost to have one in a lens.... But is relatively unimportant with autofocus.

John Gerlach Loc: Island Park, Idaho

I shoot plenty of landscapes where everything in the scene is at infinity focus. I have no trouble at all getting everything sharp. Be aware that all the lenses I know can focus past infinity as ambient temperature can alter where infinity focus is, so lenses are made to account for wide extremes of ambient temperature. I simply use a magnified live view image and manually focus on an object at infinity, and use f/8 when everything is already at infinity. Stopping down more gains you nothing but more diffraction. If some objects are closer than infinity, then you do need to stop down more, use hyperfocal, or as I normally do, simply focus stack at f/8. Hope these ideas help you.

Rich1939 Loc: Pike County Penna.

Plus an auto focus lens needs to go beyond the best focus point and return to be sure it does have optimal focus. Come to think of it, so do I!