Extension Tube on a6000 won't Focus

[Donde]

I bought a set of Vello Auto Focus Extension tubes and the camera will not focus with one or both attached in front of a Sony Zeiss 24 1.8 lens . The focus shifts a little bit when I depress the shutter button but not much and won't bring anything into focus. What's the trick? The little instruction booklet doesn't address the issue.

 

[480sparky]

Are there electrical connections in the tubes?

Also, maybe it's too dark with the tubes on for the AF module to work.

 

[tirediron]

Agree ^^ Have you tried testing them in bright sunlight at max aperture? It's also possible that you got a duff pair and they need to be returned.

 

[petrochemist]

The trick is to change the distance between the lens & the subject.
Tubes make the lens focus closer than normal how much closer depends on the focal length.
With 24mm of extension on that lens the maximum focal distance will be about 50mm in front of the lens.

When first getting the hang of tubes It's easiest to use just the shortest tube & a slightly longer focal length - these are both factors which will make the effect less drastic.

If the lens is not within the right distance range from the subject no amount of varying the AF will create a sharp image.

 

[Derrel]

Wait a second!!!! With a 24mm lens, and a longish extension tube, the focus point is VERY likely to be ___inside the lens itself____.

When you use a short focal length lens with an extension tube, it needs to be an incredibly short tube: Nikon made some VERY short tubes, in the 1mm to 5mm length, for use with wide-angles. Most all normal-length extension tubes will NOT allow you to do close-up shots with a 24mm lens. That is just the way it works.

(The Nikon set of VERY short tubes has K1,K2,K3,K4,and K5 tubes in the complete 5-tube set.**EXCELLENT** Nikon K Series Extension Tubes, Set of 5 - K1, K2, K3, K4, K5 • $39.07) and pre-dates digital photography by decades. THIS is the type of extension ring needed to allow close-up shooting with short focal length lenses. As you can imagine, these extension tubes are very short; so short they do not look like "tubes" as much as "shims".

NIKON-K1-K2-K3-K4-K5-Ring-set-_1.jpg

Try it for yourself and see. If you have a 24-70mm zoom, mount the tube....it's VERY likely that you will find it impossible to focus at 24 to 35mm with a longer tube, like say an 11mm tube, because the focusing range will be, literally, INSIDE THE LENS (a dentro!). However, at the longer focal lengths, from 50 to 70mm, the tube will allow you to shoot close-up subjects.

It's very likely that there is nothing wrong with the tube whatsoever, but you are using it with an incompatible lens.

 

[TreeofLifeStairs]

I had tubes for the NEX-7 and Derrel is right, I had to use my 55mm with some of the tubes and it was still inches away from the subject.


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[Donde]

Bingo Derrel! I tried the 10mm tube on my Batis 85 1.8 and it works. However it turns out it will only focus when the camera is between 35mm and 80mm from the subject, Closer or further are a no go. Both the 10mm and 16mm could be useful for bugs under the right but rather specialized circumstances. Some test examples below. I focused more or less on the horizontal reflection in front of the F (for frio) and the camera was set at f5.6. It was a quickie test and I didn't take pains to adjust settings.

Closest focus possible with no tubes

Closest focus with 10mm tube

Closest focus with 16mm tube

The point made about light reduction is clearly illustrated.

 

[Derrel]

Yes, you are correct, that when an extension tube is placed on a lens, there is a new Minimum Focusing Distance, and there is also a Maximum Focusing Distance, so...as with all extension tubes, there's an actual range of near to far, in which the tube works.

 

[TreeofLifeStairs]

Also, you probably noticed that your depth of field shrinks. Many times when I used my tubes I was shooting f16 and above. So strong light is helpful. Also you might try some focus stacking in ps. I don’t know if Lightroom let’s you ficus stack.


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[petrochemist]

Yes, you are correct, that when an extension tube is placed on a lens, there is a new Minimum Focusing Distance, and there is also a Maximum Focusing Distance, so...as with all extension tubes, there's an actual range of near to far, in which the tube works.

The thin lens formula will give some idea of what these distances are:

1/focal length = 1/subject distance + 1/image distance (all in the same units, usually mm)

Image distance is effectively the added extension plus the focal length of the lens (when focused at infinity), at minimum focus the image distance would be increased by the amount necessary for the lens to focus to it's normal minimum. In reality it's not quite as simple as that as both distances will be from the lenses nodal points - this is why the subject distance can be within the lens. Other bits of lens design can add further complications too - many macro lenses change their focal length drastically as focused closer...

 

[Braineack]

yeah, even with a 12mm extension tube on my 58mm lens, the focus is CRAZY close to the lens.

 

[arso96]

Extension tubes basically work like a simple macro lens. They reduce the minimum focal length of your lens. That means that when mounted, your lens won't achieve focus to infinity, but might reduce the CLOSEST you can focus from 4 feet to 15 inches.

AND it creates a very shallow depth of field (focal plane). More background separation. Much "like" a macro lens. For cheap.

When working with macro... It usually is best to manually focus. Why trust AF? The slightest shift in focus between an antenna and a head/thorax of an ant or butterfly can make or break a 'keeper' while shooting in the macro world.

I humbly suggest understanding some basic macro principles. Usually one stops down to f/8 or f/11. Not always, depends on your pre-vision. But the shallow focus might require it.
regards

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