# Macro vs. Flat Field ?



## JumboShrimp (Mar 10, 2015)

Years ago in the film days, I was under the impression that a "macro" lens was synonymous with a "flat field" lens, which was of key importance when photographing art work and other flat objects. (EBay has several film-era Vivitar Flat Field 90-180 Macro Zooms, for instance.)

When I looked at the Canon web page describing macro lenses, the phrase "flat field" was not used. It led me to wonder if modern-day macro lenses are not flat field and if that characteristic was no longer a concern or design objective. With the advent of quality scanners, perhaps flat field lenses are just no longer needed.

So, for the stupid question of the day, do we still have (or even want) flat field lenses?


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## neuroanatomist (Mar 10, 2015)

Yes, we want them – and for the most part we have them, thanks to modern computerized lens design. Some lenses suffer from notable field curvature (e.g. the original 24-70/2.8L), but not many. 

Some lens makers still highlight it, the 'planar' designation in Zeiss nomenclature refers to flat field (shortened to Plan sometimes, at least in microscope objectives). 

'Macro' generally refers to achieving a 1:1 magnification, or at least 1:2 (Canon and Zeiss both have 1:2 macro lenses).


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## jeffa4444 (Mar 10, 2015)

The main purpose when I first bought my Canon EF 100 f2.8L Macro was to photograph a large number of documents which were old (from WWII). I found this lens to be completely flat field and whilst Canon doesnt state that I would be surprised if they did not make that a criteria of a purpose macro lens.


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## Mt Spokane Photography (Mar 11, 2015)

A Macro lens can have a flat field, and most do, but a flat field is not necessarily a Macro lens. Macro lenses are close focusing lenses, and some manufacturers like Vivitar advertised lenses as Macro because they supposedly focused at a shorter distance than some lenses.

Most photographers consider a lens to be a Macro lens if it places a image on thye film or sensor that is full sized, so a small bug, for example, would be life sized. Some Macro lenses are 1:2 or half sized, and some are more like a low power microscope and can magnify tiny objects by up to 5X.


However, the old Vivitar zoom lenses are not and never did meet the definition of a true Macro lens.

Flat field lenses are great as projection lenses or for reproducing art or anything that is flat. Technical copy lenses are flat field.


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## JumboShrimp (Mar 11, 2015)

So, since Canon does not mention flat field in their macro descriptions, does that mean that they are not flat field? Or are we to assume that they are?


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## neuroanatomist (Mar 11, 2015)

JumboShrimp said:


> So, since Canon does not mention flat field in their macro descriptions, does that mean that they are not flat field? Or are we to assume that they are?



Since Canon does not mention distortion free in their TS-E descriptions, does that mean they have substantial distortion? They have almost none. Interestingly, they don't mention distortion in their 24-105/4L description either...I wonder why? 

In fact, Canon does mention a flat field in their descriptions of the 50 mm and 60 mm macro lenses, possibly because those are suitable focal lengths for a copy work. They used to put that sort of information in their technical reports, unfortunately they have removed all of the older ones from their website so none are available for the current macro lenses.

Read lens reviews, the better technical ones (PZ, Lenstip) will call out field curvature when present.


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## LDS (Mar 11, 2015)

JumboShrimp said:


> So, for the stupid question of the day, do we still have (or even want) flat field lenses?



In macro lens, field curvature would become clearly noticeable at short distances (because of the very shallow DOF). Moreover, macro lens are often used to take images of "flat", or almost, subjects, bugs & C. are just one use.
That's why they have been used as "repro" lens as well. Thereby I guess most (if not all) macro lens are still designed to obtain a "flat field", even if the "repro" work is far less advertised today.


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## Arty (Mar 22, 2015)

I don't know if this is true, but one book I read stated that the only true flat field macro lens among the Canon family is the 50F2.5.


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## BeenThere (Jun 29, 2018)

Could the dual pixel “focus adjust” be used (theoretically) to algorithm correct a lens to a flatter focus field in post processing? Obviously it would require a lot of measurement work and software development.
Just wondering out loud.


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## neuroanatomist (Jun 29, 2018)

BeenThere said:


> Could the dual pixel “focus adjust” be used (theoretically) to algorithm correct a lens to a flatter focus field in post processing? Obviously it would require a lot of measurement work and software development.
> Just wondering out loud.



I believe it could, yes. That would be a great application for dual pixel RAW, to correct the minor but predictable focus variance resulting from mild field curvature.


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## Mt Spokane Photography (Jun 29, 2018)

neuroanatomist said:


> BeenThere said:
> 
> 
> > Could the dual pixel “focus adjust” be used (theoretically) to algorithm correct a lens to a flatter focus field in post processing? Obviously it would require a lot of measurement work and software development.
> ...


That got me thinking about stacking software that uses the two images from the dual pixels. They can be recovered using DPR Split, and stacking software should select the portions of the two or three if you include the combined image.
https://www.fastrawviewer.com/DPRSplit


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