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12-08-2017, 08:50 PM   #1
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Focus on infinity

Just trying to get some clarification on something I read.

When setting up a macro shot, I've read on a couple of occasions that the lens should be focused to infinity. Admittedly when I've tried Macro I have tried focusing the lens on a couple of occasions but there was no real difference and I've never intentionally focued to infinity.

So is it good information?

12-08-2017, 09:18 PM - 1 Like   #2
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What lens are we talking about here?

If you have a "macro" lens, you would focus it as with any lens such that the subject is in sharp focus. That normally wouldn't be infinity for any close-up subject.

Are you talking about using another lens in front of a non-macro lens (perhaps reversed) to capture close-up subjects? If that's the case, it doesn't make too much difference what that lens is set to focus-wise (as you've learned). It would depend on the supplementary lens construction and what distance it was designed for (usually "infinite conjugate" for most camera lenses) so it wouldn't hurt to leave it at its infinity focus, but the difference will be small, and for many lens designs, negligible. Ideally, if you are using a reversed lens in front of a regular lens, best performance would be obtained if both are focused to infinity and focus is obtained by moving the camera or subject, but that doesn't need to be the rule.
12-08-2017, 09:21 PM   #3
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If you have a bare lens mounted directly on the camera focused at infinity then everything up close will be blurry, so this won't work.

Are you using bellows or extension tubes? Close up adapters? These things will adjust your focus, so this advice is in with a chance (but not necessarily the way to go). List the equipment you're using and better advice will follow!
12-08-2017, 09:49 PM   #4
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QuoteOriginally posted by Liney Quote
So is it good information?
Its good information if your subject is a few hundred yards away from you, but I wouldn't quite call that "macro" photography.

12-08-2017, 10:16 PM - 1 Like   #5
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Instruction booklets for macro bellows say to set prime lenses to infinity. This is mainly for the purpose of determining the extension factor.

If you are using a prime macro lens without a bellows or extension tubes setting the focus to infinity means the focus is on objects at "infinity" and not close objects.

When using close-up lenses, stacked or reversed lenses setting the lenses at infinity can reduce or eliminate vignetting if any. It also reduces the stress the additional weights can put on the helical threads of the lenses.
12-08-2017, 11:48 PM   #6
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OK my fault for not being clear enough.

Currently I'm using extension tubes, but of the lenses I currently own two are zoom lenses with a "macro" end of the focus. What tends to happen with these is that I select the "macro" end of the focus and end up adjusting the distance to the target to get a clear and focused image.
12-09-2017, 06:40 AM - 2 Likes   #7
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QuoteOriginally posted by Liney Quote
When setting up a macro shot, I've read on a couple of occasions that the lens should be focused to infinity.
In a nutshell: it really doesn't matter where the lens is focused.

Macrophotography with extension tubes on primes the old way of thinking is that by using the lens set at infinity, it was easier to calculate precisely how much light was being lost at the focal plane from just measuring the amount of extension*. But TTL light meters do a pretty good job of compensating for that these days so it isn't a relevant issue anymore.

QuoteOriginally posted by Liney Quote
So is it good information?
No, in the age of TTL metering its complete crap.

QuoteOriginally posted by Liney Quote
I currently own two are zoom lenses with a "macro" end of the focus. What tends to happen with these is that I select the "macro" end of the focus and end up adjusting the distance to the target to get a clear and focused image.
FYI: Most zoom lenses are perform pretty badly when used at what is considered for a zoom "macro" focus. Primes or better yet, dedicated Macro lenses offer superior image quality.



* Infinity focus is also where the lenses transmission or T-stop is calculated. As the focus point moves away from infinity on some lenses, the entire optical assembly moves away from the focal plane and light is lost. During normal use the amount of light lost at MFD Vs infinity focus is not much, but coupled with extension tubes, and older non-IF telephoto primes the light loss can really stack up.

Last edited by Digitalis; 12-09-2017 at 10:12 PM.
12-09-2017, 03:05 PM   #8
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Also remember that, depending on the lens design, all the elements could move as a whole, or just some of them.
In the first case (which is applicable to, e.g. the SMC-M 50-1.7 and most old lenses), the focus ring is useless when the lens is inverted (well... you could use it to decide how much of the barrel to use as an impromptu lens shade...), and when the lens is on bellows/tubes focusing the lens just changes the distance of the optical elements from the sensor, so +1cm focusing -1cm tube = -1cm focusing +1cm tube, it doesn't matter how you move 'em as long as the distance is the same.

12-09-2017, 03:13 PM   #9
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It's also possible to shoot macro with a lens set to infinity focus when using a diopter (e.g. Raynox) in front of the lens.
12-09-2017, 04:06 PM   #10
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Many thanks for clarifying that, much appreciated
12-25-2017, 02:11 PM   #11
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Many modern lenses have some compensatory element(s) when focusing at a shorter distance, and therefore shouldn't be use at infinity on a below or with tube extender.

Most belows instructions predate this kind of lens and ignore this problem.
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