Macro magnification explained?

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#1
Hi Guys I'm wondering if you can explain macro magnification to me?
I understand if I take a picture of a penny at 1:1 magnification it projects the penny at a 1:1 ratio on a full frame sensor... (1.5x on a nikon crop)
Now when I bring this to a PC and zoom In 100% the image will appear larger than 1:1 on screen...

How is this on screen size calculated?
 

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#2
Number of pixels. At 100% on screen presumably 1 sensor pixel (photosite) = 1 screen pixel
 
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#3
1:1 ratio on *any* sensor as I understand it regardless of crop size.
The relationship to on screen is variable, but basically, without zooming to 100%, it's scaling your sensor size up to your monitor size (assuming full screen display), so in my case approx 28mm corner to corner on sensor up to 685mm corner to corner on monitor (with some correction to aspect ratios). Different it you have a 21" monitor, 24" etc, and whether you have all the screen realestate or just a part for the image etc.

Zooming in to 100% further complicates this (100% meaning 1 screen pixel = 1 image pixel), as different displays have different pixel densities, so a 5K 27" display will be different to a 4K one etc, also bearing in mind some displays also include scaling modes.

So basically - the only one that matters if 1:1 on sensor!
 
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#4
Sorry, I think I've got this a bit mixed up with things... I don't mean 100% to fill the screen.. I mean 100% in lightroom... I know the camera sensor is small, but an image zoomed in fully on lightroom is much bigger...
 

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#5
Suppose for arguments sake your sensor is 5000 "pixels" wide and has a physical height of 35mm and you photograph a tape measure at 1:1 macro. So in theory you would see 35mm of the tape measure on the resulting image across 5000 pixels, each pixel would represent 0.007mm. If you then display that at 100% (in LR or anything else) on a screen that is 1920 pixels wide, you would see 1920x0.007mm of the tape measure which would be 13.44mm. So the 100% view, full screen would show just over 13mm of the tape measure out of the total 35mm image
 
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#6
Hi Guys I'm wondering if you can explain macro magnification to me?
I understand if I take a picture of a penny at 1:1 magnification it projects the penny at a 1:1 ratio on a full frame sensor... (1.5x on a nikon crop)
Now when I bring this to a PC and zoom In 100% the image will appear larger than 1:1 on screen...

How is this on screen size calculated?
You're mixing things up - macro magnification is nothing to do with display screen magnification. (And nothing to do with crop-factor, either.)

A 'magnification ratio' of 1:1 means the subject is recorded life-size on the sensor. If you photograph a bug 25mm long, the image will cover 25mm on the sensor. If the sensor is actually smaller than 25mm, only part of the bug will be recorded - magnification ratios are independent of sensor format. 1:2 is half life-size, 1:4 is quarter and so on.

You may also see the term 'macro magnification' which is the same thing expressed differently. 1:1 is the same as 1x, 1:2 is 0.5x, 1:4 is 0.25x etc.
 
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#7
I think I can better explain what I was trying to get at...
My sensor is 23.50mm x 15.60 mm
If I open up a d3300 and take a 1:1 ratio image of the opened cameras sensor... my cameras sensor would fill the frame and create an edge to edge image of the opened sensor...

Now if I bring that to screen at 6000px x 4000px (240dpi as standard) the image will be 635mm x 423mm (if printed)
That translates to a multiple of 27.11 for screen... So a postage stamp T a 1:1 ratio would look 27x larger on screen... I think?
 

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#8
Did you read my post above?

It depends on how many pixels your screen has. 100% means one sensor pixel is displayed as one screen pixel
 
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#9
I think I can better explain what I was trying to get at...
My sensor is 23.50mm x 15.60 mm
If I open up a d3300 and take a 1:1 ratio image of the opened cameras sensor... my cameras sensor would fill the frame and create an edge to edge image of the opened sensor...

Now if I bring that to screen at 6000px x 4000px (240dpi as standard) the image will be 635mm x 423mm (if printed)
That translates to a multiple of 27.11 for screen... So a postage stamp T a 1:1 ratio would look 27x larger on screen... I think?
If that's how the maths for your camera and screen work then yes, fine. But you are talking about sensor/screen/print magnification, which is a different thing to lens magnification (as has already been said). You may as well just say "if I take a postage stamp and enlarge it to 27 times bigger then it will be 27 times bigger", no need to worry about lens at all.
 

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#10
I think I can better explain what I was trying to get at...
My sensor is 23.50mm x 15.60 mm
If I open up a d3300 and take a 1:1 ratio image of the opened cameras sensor... my cameras sensor would fill the frame and create an edge to edge image of the opened sensor...

Now if I bring that to screen at 6000px x 4000px (240dpi as standard) the image will be 635mm x 423mm (if printed)
That translates to a multiple of 27.11 for screen... So a postage stamp T a 1:1 ratio would look 27x larger on screen... I think?
No. Your error here is that 240dpi figure. It's quite unlikely that your screen resolution is 240 pixels per inch: most desktop monitors run at about 100 pixels per inch.

I think the easiest way to think of this is to look at pixel size. A pixel is a pixel is a pixel, so if we know how big the pixels are on your sensor, and we know how big they are on your viewing device - be that a screen, a projector, or a print - then the magnification is easily calculated.

You say your camera has 6000 pixels on a sensor which is 23.50mm wide. That's 255 pixels per mm, which is 6485 pixels per inch (ppi). OK so far?
The monitor I'm using here in my study uses a standard HDTV resolution, 1920 x 1080 pixels, and I've just measured the screen to be 510mm wide. So that's 3.76 pixels per mm, or 96 ppi.
Hence if I look at an image at "100%" on screen, the effective magnification is 6485 / 96 = approximately 67x.

You can easily generalise this to cases where you're not using a macro lens. For example my trusty Canon 100-400 Mk II has a minimum focus distance of 1 metre, and at that distance the magnification is 0.31x.
So an image taken using that lens and your sensor, and viewed at 100% on my screen, will have a magnification of 0.31 x 6485 / 96 = approximately 21x.

You can also easily generalise this to cases where the image is not displayed at "100%" on screen.
 

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#11
It can be fun calculating the magnification ratio of macro photos. A couple of years ago I did a project at camera club, where I took photos of common household objects using a Canon MP-E 65mm 1-5x macro lens. I did a mini presentation whereby they were displayed on the projector screen at the club. Here's an example; it's a rivet on a pair of jeans.

upload_2019-1-4_8-23-47.png

This image was taken at 5x magnification.
The camera I used was a Canon 40D which has 3888 x 2592 pixels on a sensor measuring 22.2 x 14.8 mm, so that's 175 pixels per mm.
However I had to reduce the image to 1050 x 1050 pixels for projection, so the reduced image had 175 * 1050 / 2588 = 71 pixels per mm of sensor.
The projector displayed 1400 x 1050 pixels, and the screen was roughly 6 feet x 4 feet, so the resolution there was 233 pixels per foot which is 0.76 pixels per mm of screen.
Hence the projected display was 5 x 71 / 0.76 = 467 times life size (in linear dimensions).
 
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#12
Interesting thread thanks for the explanations guys
I see where Andy is coming from
I spend all spring and summer doing macro but didn't really understand how it related to viewing a macro image on my computer screen
I've always thought of it in the simplest way, a small butterfly at minimum focus distance on my macro lens will be very approximately full screen on the computer display
 
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#13
My subject...;) Magnification only really has any relevance at the taking stage and/or at the printing stage and is probably best ignored on a pixel based viewing device. I used to produce images at a precise magnification for inclusion in scientific journals and publications and all specimens were photographed with a scale (most often a very accurate graticule) and sized accurately for output.

Given that many different devices can be used to view images perhaps the only 'fairly' accurate way is to include a scale (which should be on the plane of focus) in your image that you can take a direct measurement from or, if you are only interested in the magnification of an image at 1:1 filling your screen simply photograph a rule (metal preferably) and measure that (easiest to use the same edge of each line), you then know that say 2.5cm measures 25cm the magnification is x10.
 
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#14
Interesting thread thanks for the explanations guys
I see where Andy is coming from
I spend all spring and summer doing macro but didn't really understand how it related to viewing a macro image on my computer screen
I've always thought of it in the simplest way, a small butterfly at minimum focus distance on my macro lens will be very approximately full screen on the computer display
Macro magnification has no direct relation ship to image magnification.
If I take a 1:1 macro shot the macro magnification remains 1x if I'm viewing it on the cameras 3" rear screen, in the smaller EVF, on a 17" monitor or projecting it to fill a wall 20' across. (I only project my shots to a maximum of about 5' across, but will use all these others too)
In each of these cases a magnified view would also be available instead of a fill the frame view but that doesn't change the macro magnification either - nor does cropping the image in post...

Cropping & the size of the final image can be used to determine the overall magnification (it used to be called print magnification but with digital files that's no longer quite relevant until its actually printed)
If you know the extra magnification of your standard display system you can get a combined magnification but this isn't generally to useful.

Macro magnification is purely a function of the lenses used their arrangement and relative spacing (including distance to sensor).

Phil's comment on photographing rulers is an excellent point. I do this when experimenting with new macro set-ups but they can make boring photos:
Here's a mm scale that's about 6mm across the frame
full magnification in mm (unedited)
by Mike Kanssen, on Flickr
 
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#15
Thanks guys... As daft as it seems I've never actually thought of the sensor as pixels... But it does make sense when thinking of it as the sensor been a very tiny screen with very tiny pixels (6485ppi)
I know this isn't physically 'magnified' when converted to screen as an exact science but I understand better now how it works.. And I get that most images on normal websites are at 72 dpi.

Thanks guys.
 
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#16
I always thought the answer was as Hoppy explained above and had nothing to do with screen size, resolution, etc - actual size of object is the same size on the sensor, so a 30mm long screw photographed on a full frame (24x36mm) sensor would be recorded as 30mm long, ie 1:1.

If the same screw is recorded on a crop camera, the screw size on the sensor (18 x 24mm) would be the same, so part of the screw would be cropped as the sensor width (24mm) is less than the screw length (30mm).

My opinion only, but what I always understood to be the meaning of 1:1.
 

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#17
And I get that most images on normal websites are at 72 dpi.
Not so, sorry.

All images on websites are at whatever your display device offers. On my desktop monitor, that's 96 ppi. On my phone, it's allegedly 577 ppi, but phones do funny tricks with their displays and I think it effectively behaves as if it's 144 ppi. That figure of 72 ppi comes from display technology in the 1980s and it has absolutely zero meaning or relevance today.
 
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#18
That figure of 72 ppi comes from display technology in the 1980s and it has absolutely zero meaning or relevance today.
I'm only thinking of this from my day to day job for the company I work for... I know google rankings are affected by loads of things, image size is one of them so every single image for the website we create and upload is created at 72dpi as we have found this is generates the smallest image for acceptable viewing on screen.
 
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#19
72dpi as we have found this is generates the smallest image for acceptable viewing on screen.
That is in fact incorrect, all that matters for display on a screen are the pixel dimensions. The same file saved at 800 x 600 pixels at 72ppi (not dpi) will be exactly the same file size if it is saved at 800 x 600 pixels at 300ppi, indeed it will be the same size if saved at 1ppi or 1000ppi.
 
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#20
I'm only thinking of this from my day to day job for the company I work for... I know google rankings are affected by loads of things, image size is one of them so every single image for the website we create and upload is created at 72dpi as we have found this is generates the smallest image for acceptable viewing on screen.
Afraid it doesn't. The PPI has no impact on file size at all. The only thing the PPI sets, is the default print size. 3000px @ 300ppi = 10".

The only things that impact file size are:
  • Number of pixels in the image
  • Colour depth of the image
  • Compression (quality) applied to the jpeg.
Obviously the Colour depth is out of your control, but it's why high key, low key and B&W images tend to be much smaller than others.
 
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#21
Afraid it doesn't. The PPI has no impact on file size at all. The only thing the PPI sets, is the default print size. 3000px @ 300ppi = 10".

The only things that impact file size are:
  • Number of pixels in the image
  • Colour depth of the image
  • Compression (quality) applied to the jpeg.
Obviously the Colour depth is out of your control, but it's why high key, low key and B&W images tend to be much smaller than others.
I gather there are software packages that allow you to save images at a fixed size & dpi, which effectively makes them calculate the number of pixels to save the image at. This is a remnant of old print based thinking & should have been done away with years ago!
Computer displays completely ignore DPI settings, & most printers ignore them too scaling to the size specified by the print operator (fit to A4 etc)

Specifying the pixel dimensions yourself is simpler & makes more sense. I usually save photos for the web at 1000 pixels in the longest dimension, but if I want smaller file sizes & there's no great detail to show I might drop that to 800 or even lower.
 
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#22
Macro magnification has no direct relation ship to image magnification.
If I take a 1:1 macro shot the macro magnification remains 1x if I'm viewing it on the cameras 3" rear screen, in the smaller EVF, on a 17" monitor or projecting it to fill a wall 20' across. (I only project my shots to a maximum of about 5' across, but will use all these others too)
In each of these cases a magnified view would also be available instead of a fill the frame view but that doesn't change the macro magnification either - nor does cropping the image in post...

Cropping & the size of the final image can be used to determine the overall magnification (it used to be called print magnification but with digital files that's no longer quite relevant until its actually printed)
If you know the extra magnification of your standard display system you can get a combined magnification but this isn't generally to useful.

Macro magnification is purely a function of the lenses used their arrangement and relative spacing (including distance to sensor).

Phil's comment on photographing rulers is an excellent point. I do this when experimenting with new macro set-ups but they can make boring photos:
Here's a mm scale that's about 6mm across the frame
full magnification in mm (unedited)
by Mike Kanssen, on Flickr
Thanks Mike
I see what you mean
 
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