Magnification vs Focal Lenght in Macro Shooting

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enstaUK
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Magnification vs Focal Lenght in Macro Shooting

Post by enstaUK »

HI,

Can anyone shed light on the difference between magnification (ratio) and focal length (mm) in terms of practical results?
Am trying to unpick lens selection, and likely reproduction outcomes

Many thanks in advance
N*

rjlittlefield
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Re: Magnification vs Focal Lenght in Macro Shooting

Post by rjlittlefield »

enstaUK, welcome aboard!
Can anyone shed light on the difference between magnification (ratio) and focal length (mm) in terms of practical results?
Am trying to unpick lens selection, and likely reproduction outcomes
Magnification is key -- that determines what size subject will fill your sensor.
Example: if you have a sensor with width 23 mm (APS-C), and your lens focuses from infinity to 2:1, then the smallest subject that will fill your sensor is 23/2 = 11.5 mm.

Focal length does not matter much -- that only affects how far you can be from your subject ("working distance"), at any specified magnification.
No single example is very meaningful. Working distance varies a lot between lenses, even at the same nominal focal length.

What is your application?

--Rik

enstaUK
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Re: Magnification vs Focal Lenght in Macro Shooting

Post by enstaUK »

Thanks for this

So, where all things are equal, distance to subject and mag ratio, how does focal length affect things if at all?
A 50mm and a 100mm at same mag, distance and subject will give the same size reproduction? Or diff

For me, the application in this case is sugar. Framing a composition thats an inch square or so, and having the resolution to zoom in and see the individual crystals, sharp.
Body is a Sony A7R

Cheers,
N*
rjlittlefield wrote:
Tue Jan 21, 2025 5:29 pm
enstaUK, welcome aboard!
Can anyone shed light on the difference between magnification (ratio) and focal length (mm) in terms of practical results?
Am trying to unpick lens selection, and likely reproduction outcomes
Magnification is key -- that determines what size subject will fill your sensor.
Example: if you have a sensor with width 23 mm (APS-C), and your lens focuses from infinity to 2:1, then the smallest subject that will fill your sensor is 23/2 = 11.5 mm.

Focal length does not matter much -- that only affects how far you can be from your subject ("working distance"), at any specified magnification.
No single example is very meaningful. Working distance varies a lot between lenses, even at the same nominal focal length.

What is your application?

--Rik

rjlittlefield
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Re: Magnification vs Focal Lenght in Macro Shooting

Post by rjlittlefield »

enstaUK wrote:
Wed Jan 22, 2025 5:30 am
So, where all things are equal, distance to subject and mag ratio, how does focal length affect things if at all?
Distance to subject will make some difference in perspective. But the difference will not be obvious unless you also have structures visible in the far background, like bushes behind mushrooms.

In general, longer lenses will give you more working distance at same magnification. But modern lenses actually change their focal length as they focus closer, some more than others, so it is difficult to predict from lens specifications exactly how this will work out.
For me, the application in this case is sugar. Framing a composition thats an inch square or so, and having the resolution to zoom in and see the individual crystals, sharp.
Body is a Sony A7R
Sony A7R has a full-frame sensor, very close to 24 x 36 mm. A one inch square will need about 1X to fill the center square of the sensor. Any modern macro lens should do that job with no problem.

If you want to have everything in the image sharp, then probably you will need to use focus stacking. The only exception would be if you were shooting straight down on a thin flat layer of crystals.

--Rik

enstaUK
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Re: Magnification vs Focal Lenght in Macro Shooting

Post by enstaUK »

Thanks

Yes, will be focus stacking.

So why is it with telephoto that focal length has so much impact, and none, for macro?
Beyond DoF type consideration?

Cheers

rjlittlefield
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Re: Magnification vs Focal Lenght in Macro Shooting

Post by rjlittlefield »

enstaUK wrote:
Thu Jan 23, 2025 2:32 am
So why is it with telephoto that focal length has so much impact, and none, for macro?
It's mostly a matter of how you use the lens: what you decide to hold constant, what to change, and what to pay attention to.

Please tell me your thoughts about how focal length has big impact with telephoto, and I'll compare and contrast with macro.

--Rik

MarkSturtevant
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Re: Magnification vs Focal Lenght in Macro Shooting

Post by MarkSturtevant »

There are variables that complicate the picture, but as a general rule a shorter focal length macro lens will require a shorter working distance for the same magnification. Such a lens will also present a wider angle of view of the surroundings, and this can be either a good or less good thing, depending on what one wants. There is a good chance that the shorter focal length lens will be lighter in weight, but will also cost less. Given a closer working distance, lighting on the subject can be more challenging with a shorter focal length lens.

Some of these things may be important for your application, while others are not. 90-100 mm macro lenses are a very popular focal length since they strike a good balance of qualities for a lot of people.
Mark Sturtevant
Dept. of Still Waters

mbf
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Re: Magnification vs Focal Lenght in Macro Shooting

Post by mbf »

enstaUK wrote:
Thu Jan 23, 2025 2:32 am
So why is it with telephoto that focal length has so much impact, and none, for macro?
Beyond DoF type consideration?
I think, everything relevant had been addressed. For a visual explanation, please have a look at this video, I think it covers most of the aspects of the different focal lengths: https://www.youtube.com/watch?v=aJXDVDXvD44 , including graphics and pictures to show the effects.

So I wouldn't say, the impact in "none". Yes, you can reach, let's say 1:1 magnification with nearly every focal length, but that does not mean that all lenses will give the same final result. It may be true if you are taking pictures of flat objects. But if the z-axis cones into play, you have to consider the focal length.
-- Matthias

CrispyBee
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Re: Magnification vs Focal Lenght in Macro Shooting

Post by CrispyBee »

enstaUK wrote:
Thu Jan 23, 2025 2:32 am
Thanks

Yes, will be focus stacking.

So why is it with telephoto that focal length has so much impact, and none, for macro?
Beyond DoF type consideration?

Cheers
Just to clear up one thing: there's not DoF consideration when it comes to focal length in macro applications (or anywhere else).
DoF depends on the magnification and aperture, regardless of the focal length used. So you'll get the same DoF with a 5mm or 50mm or 500mm lens at 1x at f4.0.

What changes are - as others have already mentioned - working distance and extension if you're working with bellows.

That being said there's one more aspect that's very important when it comes to focal length and macro photography: background rendition.
With a long focal length you can get a smoother background due to a narrower perspective/compression. That can be very pleasing, especially outdoors. However that is mostly relevant when it comes to lower magnifications and when you can't isolate your subject from a very busy background otherwise.

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