Is added adapter similar to extension tube?

Started 3 months ago | Questions
grsnovi
grsnovi Senior Member • Posts: 1,229
Is added adapter similar to extension tube?

Wondering to what degree adding an adapter is similar to adding an extension tube between the lens and the sensor. Isn't doing so going to change the apparent focal length of the adapted lens?

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ANSWER:
Aoi Usagi Senior Member • Posts: 2,547
Re: Is added adapter similar to extension tube?
2

Adapters are made to fill in the gap of the flange distance of specific lens mount. For instance, adapters made for using SLR/DSLR lenses to mirrorless cameras, just fill in the gap that was usually occupied by the reflex mirror. Of course, some mirrorless camera lenses can be adapted to other mirrorless cameras such as LTM to Sony E, etc.

A better explanation might be with numbers. The Canon EF mount flange distance (SLR?DSLR mount) is 44mm. The Sony E mount (mirrorless) is 18mm. The adapter thickness should be the Canon EF flange, subtracted by the Sony E mount flange distance. 44-18=26mm. The focal length of the lens doesn't change.

Here is the wiki page for flange distances for each camera mount. Link.

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grsnovi
OP grsnovi Senior Member • Posts: 1,229
Re: Is added adapter similar to extension tube?

Thanks for the link!

I was specifically interested in the Minolta/Sony A mount to their E mount. The adapters look so huge! Interesting to see that the E mount is 18mm while the A mount is 44mm. That explains it!

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Dem Bell Contributing Member • Posts: 563
Re: Is added adapter similar to extension tube?
1

grsnovi wrote:

Wondering to what degree adding an adapter is similar to adding an extension tube between the lens and the sensor. Isn't doing so going to change the apparent focal length of the adapted lens?

Neither changes focal length.

Both are designed to hold the lens at a specific distance from the sensor.

The difference is that the adapter is supposed to "zero" the position of the lens, whereas the extension tube moves the lens mount further away from the sensor by a specified distance (10 mm, 16 mm etc...).

grsnovi
OP grsnovi Senior Member • Posts: 1,229
Re: Is added adapter similar to extension tube?

Paraphrasing Wikipedia , I understand that extension tubes:

Contain no optical elements...

and they move the lens farther away from the focal plane results in:
- closer focus,
- greater magnification,
- and greater loss of light.

Lens adapters may unintentionally have an effect similar to an extension tube.

(I had extension tubes for my FTb in 1970).

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fferreres Veteran Member • Posts: 6,440
Re: Is added adapter similar to extension tube?

grsnovi wrote:

Paraphrasing Wikipedia , I understand that extension tubes:

Contain no optical elements...

and they move the lens farther away from the focal plane results in:
- closer focus,
- greater magnification,
- and greater loss of light.

Lens adapters may unintentionally have an effect similar to an extension tube.

(I had extension tubes for my FTb in 1970).

You can use a macro tube to focus a lens. Or you can use a mount with the wrong distance and focus past infinity or much closer. There’s nothing special about adapting fully manual lenses.

However, many mounts can operate or read info from the lens, either change lens options, instruct focus, change aperture, etc. So an adapter may have more features, and likewise, and extension tube may have more features.

The important thing to know is the lens and the sensor do not care one bit what’s around the optics. The lens always does the same thing (unless with floating parts) regardless of anything else, so at the right distance from the sensor it will always show the same thing regardless of sensor type, maker, or astrological sign of the photographer.

The only thing we need is for a sensor and lens to be the right distance apart, to make the same image. Of course, we need to also prevent light not coming from the lens from going into the sensor.

grsnovi
OP grsnovi Senior Member • Posts: 1,229
Re: Is added adapter similar to extension tube?

Having used extension tubes in the 1970's I was familiar with the simple mechanical difference in the distance from the lens to the camera. My question was prompted by the possibility of purchasing a new (Sony) camera and the need to use a new (Sony) adapter to use my 8 year old (Sony) lenses. I understand the additional functionality provided by the electrical connections in facilitating AF and AE, what I was curious about was the impact of the added (mechanical) offset between the lens and the body/sensor.

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fferreres Veteran Member • Posts: 6,440
Re: Is added adapter similar to extension tube?

grsnovi wrote:

Having used extension tubes in the 1970's I was familiar with the simple mechanical difference in the distance from the lens to the camera. My question was prompted by the possibility of purchasing a new (Sony) camera and the need to use a new (Sony) adapter to use my 8 year old (Sony) lenses. I understand the additional functionality provided by the electrical connections in facilitating AF and AE, what I was curious about was the impact of the added (mechanical) offset between the lens and the body/sensor.

Ah, zero impact other than how precise it's machined.

SimonOL Senior Member • Posts: 1,956
Re: Is added adapter similar to extension tube?
1

grsnovi wrote:

Paraphrasing Wikipedia , I understand that extension tubes:

Contain no optical elements...

and they move the lens farther away from the focal plane results in:
- closer focus,
- greater magnification,
- and greater loss of light.

Lens adapters may unintentionally have an effect similar to an extension tube.

An well-made adapter won't do that - it will be the right length for the camera & lens combination

That's assuming it is possible to adapt that lens to that particular camera. Generally, the lens needs to have a longer flange focal distance than the camera body; that difference provides enough physical space for the adapter to position the lens the correct distance from the sensor so that everything works normally.

Very occasionally -  particularly with the very cheapest, no brand adapters - you can get a poorly-made adapter that is just a bit longer than it should be. Then it would act like a very thin extension tube.

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Lightshow
Lightshow Veteran Member • Posts: 7,474
Re: Is added adapter similar to extension tube?

In summation, an adapter is a device designed to place the adapted lens at its designed/engineered distance from the sensor/focal plane (ie. infinity focus at the infinity position of the focus ring) also known as flange back distance and back focus among other things, they are basically the same thing but they reference different things of the lens (the mount and the optical centre of the lens). An adapter is just a glorified shim.

So, if the adapter places the lens too close to the sensor, the lenses focus range is shifted away from the camera, out past infinity which decreases focus range because anything past infinity by definition is impossible and will be out of focus.

On the flip side, placing the lens too far from the sensor will end up with the lenses focus range being shifted closer to the camera, and like with an extension tube, it includes the loss of infinity focus.

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E Dinkla Senior Member • Posts: 2,260
Re: Is added adapter similar to extension tube?

grsnovi wrote:

Thanks for the link!

I was specifically interested in the Minolta/Sony A mount to their E mount. The adapters look so huge! Interesting to see that the E mount is 18mm while the A mount is 44mm. That explains it!

I think the A mount register distance is 44,5mm. And that 0,5mm difference counts in adaptation.

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