# How to work out magnification ratio for macro?



## Valvebounce (May 17, 2018)

Hi Folks.
I have been doing some macro shots and I wondered if anyone knows a simple way to know what magnification a lens and tube combo will give, for example I have a (cheap) tube set, 13mm 21mm and 31mm tubes, if I add each to a 24-105mm lens what magnification will I see. 
I don’t really want the answer so much as a formula or a recommendation for an app to calculate this if anyone knows of one? 

Cheers, Graham.


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## neuroanatomist (May 17, 2018)

https://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm

The wider the focal length, the greater the benefit of tubes.


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## AlanF (May 17, 2018)

neuroanatomist said:


> https://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm
> 
> The wider the focal length, the greater the benefit of tubes.



I think you meant shorter the focal length.


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## Valvebounce (May 17, 2018)

Hi Neuro. 
Thank you for the link, I am now looking through the Canon site to try to find the native magnification of my lenses. 

Cheers, Graham.


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## magarity (May 18, 2018)

Valvebounce said:


> Hi Neuro.
> Thank you for the link, I am now looking through the Canon site to try to find the native magnification of my lenses.
> 
> Cheers, Graham.


Canon's own site doesn't always list it in an easy to find spot. It's usually easier to look it up on a good vendor's website. Adorama is pretty good about listing max magnification under 'specs' for pretty much all the lenses. Probably B&H too.


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## neuroanatomist (May 19, 2018)

Valvebounce said:


> Hi Neuro.
> Thank you for the link, I am now looking through the Canon site to try to find the native magnification of my lenses.
> 
> Cheers, Graham.



It's near the end of the instructions booklet.


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## Valvebounce (May 19, 2018)

Hi magarity. 
Thanks for the tip, I managed to find the info for all my lenses on the Canon site except the 24-105 f4L and 50 f1.8 II as these have been superseded / discontinued and I found these on popular review sites! 
Just as an FYI, the Canon site gives the magnification as well as other data with the 1.4x and 2x installed for lenses compatible with tele converters. 
It is bloody difficult to get to the lens spec, use the lenses link in the bottom left Products column of the small print at the very bottom of the page to skip the lens optimiser junk! 

Cheers, Graham. 



magarity said:


> Valvebounce said:
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> > Hi Neuro.
> ...


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## Valvebounce (May 19, 2018)

Hi Neuro. 
Never thought to look there for the lenses that I do have the booklet for, and as some of my lenses are previously enjoyed (ok secondhand  ) I do not have the booklets for them, plus it was easier to find this info on the web than to access the booklets in the lens boxes at the back of a cupboard with a ton more stuff in front of them! 

Cheers, Graham. 



neuroanatomist said:


> Valvebounce said:
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> 
> > Hi Neuro.
> ...


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## neuroanatomist (May 19, 2018)

Valvebounce said:


> Hi Neuro.
> Never thought to look there for the lenses that I do have the booklet for, and as some of my lenses are previously enjoyed (ok secondhand  ) I do not have the booklets for them, plus it was easier to find this info on the web than to access the booklets in the lens boxes at the back of a cupboard with a ton more stuff in front of them!
> 
> Cheers, Graham.
> ...



They are all online as PDFs, linked from the page for each lens – my point was, that's where to find them on the Canon website. Moreover, for the Canon-length extension tubes (12 and 25mm), the instruction booklets give you the actual magnification (which is in many cases more accurate than an online generic calculator), and also give you the working distances (which the calculator does not).


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## stevelee (May 19, 2018)

I bought a 100-400mm II lens this spring. I didn't find an instruction booklet in the package. I was surprised that the most expensive lens I have didn't come with a booklet. Maybe I was so excited that I misplaced some of the stuff in the box, I thought.

I later went to Canon's web site and downloaded the instructions. I'm glad I did, since I had guessed wrong about what some of the gizmos do.

Days later I went back to the coffee table near where I had unboxed the lens and looked under the warranty card, and there was a little folded up tissue like what usually warns you not to use under water, scrub with scouring powder, or take internally. But as I unfolded it, that turned out to be the instructions. Out of curiosity, I will look to see if it gives magnification stats.


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## Zeidora (May 19, 2018)

With some WA and UWA lenses, extension rings will put focal plane inside lens! 
Re figuring out magnification ranges, photograph a ruler or some other object of known size.
Additional complications arise when working with different sensor sizes, then printing, or even displaying on web on different size displays. That is why in science publications, you hardly ever see magnification indications these days, but rather a scale bar, because magnification always depends on size of capture medium AND size of output medium. For LF there are targets you can put on subject, then measure on ground glass (or camera LCD) the size of the target.


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## AlanF (May 19, 2018)

Zeidora said:


> With some WA and UWA lenses, extension rings will put focal plane inside lens!
> Re figuring out magnification ranges, photograph a ruler or some other object of known size.
> Additional complications arise when working with different sensor sizes, then printing, or even displaying on web on different size displays. That is why in science publications, you hardly ever see magnification indications these days, but rather a scale bar, because magnification always depends on size of capture medium AND size of output medium. For LF there are targets you can put on subject, then measure on ground glass (or camera LCD) the size of the target.



How does an extension ring put the focal plane inside a lens? I naively thought the ring just moved the lens further away from the sensor.


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## Valvebounce (May 19, 2018)

Hi Alan. 
I have had it happen where with 65mm of stacked extension ring the point of focus got so close I had to remove the hood, I don’t remember which lens it was, I guess some other lens might happen to have the point of focus recede ‘inside the lens’. 

Cheers, Graham. 



AlanF said:


> Zeidora said:
> 
> 
> > With some WA and UWA lenses, extension rings will put focal plane inside lens!
> ...


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## Zeidora (May 19, 2018)

AlanF said:


> Zeidora said:
> 
> 
> > With some WA and UWA lenses, extension rings will put focal plane inside lens!
> ...



Just try it. I think it was the Zeiss 21 mm with 13 mm ring. Most likely it has to do with position of nodal point and focal plane being closer to nodal point than front element. 

You can use WA lenses for macro (extension rings, even bellows), but then you reverse them and retrofocus design gives you little bit of clearance between rear element and object.


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## AlanF (May 19, 2018)

It would seem to me that you haven't moved the focal plane to within the lens but you have moved it too far away to focus on the sensor.


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## Zeidora (May 19, 2018)

AlanF said:


> It would seem to me that you haven't moved the focal plane to within the lens but you have moved it too far away to focus on the sensor.



Don't understand what you mean. Focal plane is too far =hyperinfinity. But with extension rings, you get focal plane closer. If you try to say that if I would focus on lens to hyperinfinity, that then the subject would be in focus outside lens with extension ring, sure. However, that is not how it works with quality lenses that stop focus at true infinity. 

What I notice is, if specimen touches front glass, it is still not sharp. I move specimen further away, it gets blurrier. Accordingly, I can never achieve focus with specimen in front of lens. Only conclusion is, that focal plane is inside lens. I use both live view and proper matt focusing screens. Have been doing MF for ~35 years. 

Or just try it. I'd think it should show with most UWA lenses (14-21 mm). Put a bellows behind it, and try to focus. I suspect it has to do with retrofocus design of those lenses.


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## Valvebounce (May 20, 2018)

Hi Alan. 
It seems to me this may be about confusion over terms, I suspect that you are thinking in terms of the focal plane being at the sensor end where we are using it to describe the focus plane of the subject? 
If I’m mistaken I apologise. 

Cheers, Graham. 



AlanF said:


> It would seem to me that you haven't moved the focal plane to within the lens but you have moved it too far away to focus on the sensor.


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## Valvebounce (May 20, 2018)

Hi Neuro. 
D’oh!  I never thought to go there! :
I found them under the specifications section for new lenses! 

Cheers, Graham. 



neuroanatomist said:


> They are all online as PDFs, linked from the page for each lens – my point was, that's where to find them on the Canon website.


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## neuroanatomist (May 20, 2018)

Zeidora said:


> AlanF said:
> 
> 
> > It would seem to me that you haven't moved the focal plane to within the lens but you have moved it too far away to focus on the sensor.
> ...



It's a pedantic thing – the focal plane cannot be inside the lens, because if you can't achieve focus, the focal plane doesn't exist. 

For the pedants: an extension tube reduces the minimum focus distance, and the shorter the focal length the greater the reduction in the MFD. Since the MFD is measured from the sensor, a sufficient length of extension tube(s) coupled with a sufficiently short focal length can result in the MFD being behind the front element, meaning focus cannot be achieved.


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## AlanF (May 20, 2018)

neuroanatomist said:


> Zeidora said:
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> > AlanF said:
> ...



That wasn’t the problem. It wasn’t pedantry. I take focal plane to be the plane where the image is in focus. I now see from their explanations that Graham et al mean that the plane in which the object would have to be in to focus would have to be within the lens. Thanks for the clarification.


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