# Does anybody make extension tubes shorter then 12mm



## kphoto99 (Feb 27, 2016)

Short version:
I want to change the zoom range on the Canon 8-15 on my 70D so at 8mm the entire frame is covered.

Long version:
A while back I got the Rokinon 8mm fisheye lens. This lens covered the entire sensor on my crop camera. I liked the effect, but I didn't like the all manual lens. Fast-forward to this fall and I got the Canon 8-15 fisheye. I made an assumption (yes I know that is stupid) that Canon's 8mm is the same as Rokinon's 8mm. To cover the entire sensor I have to zoom to 11 on Canon. I don't know who is correct, but I suspect it is more Canon then Rokinon.

I'm guessing that since Rokinon makes the same lens for different mounts they effectively use different extension tubes to correct for the different flange distance. The difference between Canon and Nikon flange distance is about 2mm. I was thinking that if I could add an extension tube I could gain the 3mm of the zoom.
The 12mm (the shortest tube I have) is way to much.


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## Zeidora (Feb 27, 2016)

That does not work, unfortunately. An extension ring mainly changes closest close focus, but has very little effect on focal length or area of coverage, particularly with small extension rings.

Also note that focal length is not giving you field of view necessarily. It also depends on the lens design. For instance, the Zeiss F-Distagon 16 mm is a 180 degree rectangular fisheye (180 degree FOV in diagonal of image), but the Zeiss Distagon 15 mm is a 110 degree/diagonal rectilinear wide angle.


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## Random Orbits (Feb 27, 2016)

I don't understand why you are looking to cover the entire sensor at 8mm. The Rokinon has an AOV of 167 degrees, while the 8-15 goes to 180 deg.


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## ajfotofilmagem (Feb 27, 2016)

Canon 8-15mm (8mm) projects a circular image with the rest of the full frame sensor turning black.
When used in APS-C (8mm), will design an almost rectangular image, but only the corners of the rectangle will remain black.

An extension tube does not solve the problem, and will only allow to focus closer than 15.7 centimeters.

The solution to cover the entire APS-C frame is using between 11mm and 15mm.


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## rs (Feb 27, 2016)

Extension tubes are to change the focus range, not the focal length. What you're after is either a teleconverter or a zoom ring. Seeing as the 8-15 is equipped with a zoom ring, I'd go with that.

The difference in focal length and angle of view between the Samyang/Rokinon and Canon fisheyes is all down to projection and the sensor size they're designed for.

The Samyang/Rokinon 8mm is a stereographic fisheye designed for a 1.5x crop sensor. On a sensor that size it offers a 180' field of view (diagonal), and due to its stereographic projection the middle isn't as pronounced or bulbous as a more conventional fisheye. If you use it on a smaller Canon 1.6x crop sensor, you won't get the full 180' FoV it was designed to do.

Canon fisheyes, like almost every other fisheye out there has a much more conventional equidistant projection. This creates a more distorted image with the centre appearing larger and the corners more squashed up. This more magnified centre is the key to these lenses typically having a longer focal length to gain the same AoV.


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## Mt Spokane Photography (Feb 27, 2016)

Expanding the image to cover the entire frame is basically zooming to a longer focal length. You have a zoom ring to do that.

As others have said, extension rings merely alter the focus distance.


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## kphoto99 (Feb 29, 2016)

Thank you to everyone who replied (especially Zeidora). Now I understand that knowing the FL of a lens it is not enough to know what the lens sees. The FoV in degrees is the deciding factor. Unfortunately the crappy lens simulator on Canon's website is a work of fiction.

Some replies stated incorrectly that extension tubes do not change the FL, it should be intuitively obvious that if you move the lens further from the sensor then the image circle will get bigger. The photo attached shows the effect of a 12mm extension tube. The camera and the object are stationary, the lens is fixed at 135mm. Left without a tube, right with a 12mm tube.

Back to the original question, does anybody make tubes that are shorter then 12mm?

BTW, I have started looking at the Canon 11-22 and Tokina 10-22 lens.


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## rs (Feb 29, 2016)

kphoto99 said:


> Thank you to everyone who replied (especially Zeidora). Now I understand that knowing the FL of a lens it is not enough to know what the lens sees. The FoV in degrees is the deciding factor. Unfortunately the crappy lens simulator on Canon's website is a work of fiction.
> 
> Some replies stated incorrectly that extension tubes do not change the FL, it should be intuitively obvious that if you move the lens further from the sensor then the image circle will get bigger. The photo attached shows the effect of a 12mm extension tube. The camera and the object are stationary, the lens is fixed at 135mm. Left without a tube, right with a 12mm tube.
> 
> ...



You have a zoom ring - why not use that? As previously stated, the primary function of an extension tube is to alter the focus range - you're very likely to lose infinity focus using them. If you really want to solve the dilemma of having a fisheye that you can use without mechanical vignetting when set to its widest setting, either go for an APS-C designed fisheye, or simply engage the limit switch on your 8-15

Looking at rectilinear lenses is not a solution to this particular problem, especially when one of them is EF-M mount and you have a 70D


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## Valvebounce (Feb 29, 2016)

Hi kphoto. 
Just looking at this from an engineering standpoint, I would estimate (I looked, held side by side but did no measurements or calculations) that the shortest tube possible would be no less than 6mm and possibly 8mm. This would allow a functioning lens catch and enough material between each side of the bayonet for it not to be a significant risk of failure. 
From using a set of tubes it is possible that the macro increase from smaller than 12mm would not be significant enough to warrant making a thinner tube, not enough people want what you want! 

Cheers, Graham.


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## rs (Feb 29, 2016)

6mm is possible if you're into your DIY:

http://www.4photos.de/camera-diy/Shortest-Canon-EF-Extension-Tube.html

However, as this lens already has 0.39x MM with a working distance of 23mm, uses for an extension tube on this lens are likely to be limited.


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## ajfotofilmagem (Feb 29, 2016)

If you find an extension tube, shorter than 12mm (or do it yourself), you will find that the viewing angle is exactly the same as your 8-15mm in 70D in 11mm.

Do yourself a favor to yourself, and simulate a short extension tube, using black tape between the lens and the camera. You will find a minimum difference in viewing angle, and will lose the ability to focus at infinity.

In short, you could use extension tube and a 8-15mm in 10.5mm to obtain the same angle of view with only a 11mm lens. After all, you are using a zoom lens anyway ...


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## neuroanatomist (Feb 29, 2016)

I'm picturing the Geico commercial where the old lady's 'Facebook wall' is a bunch of prints in her living room, and when she verbally tells her friend, "I unfriend you," the friend states, "That's not how it works...that's not how any of this works!"


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## Don Haines (Feb 29, 2016)

7mm?

http://www.bhphotovideo.com/c/product/888030-REG/vello_ext_cem_manual_extension_tube_set.html


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## ajfotofilmagem (Feb 29, 2016)

Don Haines said:


> 7mm?
> 
> http://www.bhphotovideo.com/c/product/888030-REG/vello_ext_cem_manual_extension_tube_set.html


In fact, 7mm segment will be added to the front mounting and bayonet trazeira (through screw), total something like 12mm.


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## kphoto99 (Feb 29, 2016)

rs said:


> kphoto99 said:
> 
> 
> > Thank you to everyone who replied (especially Zeidora). Now I understand that knowing the FL of a lens it is not enough to know what the lens sees. The FoV in degrees is the deciding factor. Unfortunately the crappy lens simulator on Canon's website is a work of fiction.
> ...


My mistake, I was thinking of the EF-S 10-22. Also the Tokina is 11-20.

I already use the limit switch, so effectively I have a 11-15 lens. Was just thinking of a way of making the 8-15 into 11-18 lens.


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## Zeidora (Feb 29, 2016)

There are some adapter rings that are thinner. Those are mainly to mount a lens from a different manufacturer on an EOS body. I have some Haoda CY -> EOS adapters, and those are about 2-3 mm thick. HOWEVER. The point is not that of an extension ring, but to adjust the flange focal distance and to make the lens usable on a different system. EOS has a very short FF-distance, while you cannot mount old Zeisses on a Nikon.

BTW: Focal length is not changed by any amount of extension. Teleconverters change FL. What is changed is field of view. You project a larger, more expanded image generated by a lens with given FL over a wide area, and the sensor only captures the central part. Notice that e.g. TS lenses have inherently larger image circles, as do most large format camera lenses, to permit movements. However, as mentioned before, with very thin extension rings (10-20% of FL), The change in FOV is minimal.

With WA lenses, excessive extension can move the focal plane inside the lens. Seen that with the Zeiss 21 mm.


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## fish_shooter (Feb 29, 2016)

kphoto99 said:


> Some replies stated incorrectly that extension tubes do not change the FL, it should be intuitively obvious that if you move the lens further from the sensor then the image circle will get bigger. The photo attached shows the effect of a 12mm extension tube. The camera and the object are stationary, the lens is fixed at 135mm. Left without a tube, right with a 12mm tube.



Focal length is defined when the lens is focused on infinity and in air or space (refractive index = 1.0). 

Many lenses focus-breath; objects get larger or smaller as one focuses (stationary camera & viewpoint). Lenses with zero focus breathing have been designed for cinematography and are quite expensive.


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