Thread moved to Lens forum.

[newarts]

So, how is magnification (1:1), min. focussing distance and dof related.

DOF/WOF=Constant*F-Stop*(1+1/m)

Where WOF is width of field, m is magnification. The constant is the "circle of confusion" (which is related to how much fuzziness you can tolerate) divided by the width of the sensor.

The distance from the sensor to the subject, D, is related to magnification and focal length, F, through:

D=F(1+m)(1+m)/m

For m=1, D=4F; m=3, D=5.3F; m=5, D=7.2F...

Dave

[vinzer]

Here's another take on the significance of 1:1; things get harder to do as you magnify beyond 1:1 - not only harder, but different. It is because of the physics involved.

The distance from the back of the camera to the subject goes through a minimum at 1:1; as magnifcation gets bigger than 1:1 the camera back moves *away* from the subject fast so elaborate helicon movements, bellows, or extension tubes are required to get the sensor far enough from the lens.

Another example is Depth of Field as a % of Width of Field; at high magnifications it stops changing, while at low magnifications it changes with magnification.

For most casual close-up work it is more useful to talk in terms of field width rather than magnification now that there are small sensor cameras around.

Dave

I think it used to be that 1:2 was considered macro territory already back then. Of course, with a lot of zoom lenses now being able to do 1:2, macro standards became stricter.

My understanding (for what that's worth) on the technicalities of it is that:

a) Macro begins at 1:1 and goes to 10:1
b) Micro begins at 10:1 goes to 100:1
c) anything under 1:1, like 1:2, is merely "close up". Where things change from close up to "normal" I don't know...
d) anything over 100:1 is really frikkin small, dude!

So, lenses marketed as "macro" or "tele-macro" with ratios of 1:2 or 1:3.9 aren't technically macro at all. They merely have close focus (under 18" or so) capability.

Think your numbers are reversed for micro. 10 to one or ten times the original size I don't think is micro

1:1 is read as one to one or same size . 1:2 is one to two or half size. 1:4 is one to four or quarter size.

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Last edited by graphicgr8s; 01-29-2009 at 09:51 PM.

[Miserere]

A misconception was thrown out concerning depth of field, so I would like to clarify it for the original poster:

If you are photographing a bug at a magnification of 1:1, it doesn't matter what the focal length of the lens is, the depth of field will depend only on the aperture you use, although perspective might fool you into thinking otherwise.

Thank you.

[pentaxman]

If the 1:1 is a full frame lens, it is 1:1 on a 35mm negative. This means that with a APSC crop factor, it will have more apparent magnification. It will actually be 1.5:1

[Miserere]

If the 1:1 is a full frame lens, it is 1:1 on a 35mm negative. This means that with a APSC crop factor, it will have more apparent magnification. It will actually be 1.5:1

Not really. 1:1 just means that the lens is capable of magnifying a bug the length of the sensor to fit in the sensor. So a 35mm long bug will take up the whole width of a film camera frame, while a 24.5mm long bug will take up the whole width of an APS-C camera sensor. Just because there's a crop factor doesn't make the macro ratio 1:1.5; it's still 1:1.

[Blue]

A misconception was thrown out concerning depth of field, so I would like to clarify it for the original poster:

If you are photographing a bug at a magnification of 1:1, it doesn't matter what the focal length of the lens is, the depth of field will depend only on the aperture you use, although perspective might fool you into thinking otherwise.

Thank you.

Actually DOF is calculated using the focal length, f-stop, and subject distance.

Edit: http://www.dofmaster.com/dofjs.html

[Sean Nelson]

Actually DOF is calculated using the focal length, f-stop, and subject distance.

Miserere is correct regarding depth of field for macro shots. The reason for this is that you move closer or further to get the same subject size in the image frame - therefore the greater depth of field you'd usually see with a wide lens is countered by the fact you have to be closer to the subject. This means that focal length and distance cancel each other out and the only thing that remains to control DOF is the aperture.

[Sean Nelson]

If the 1:1 is a full frame lens, it is 1:1 on a 35mm negative. This means that with a APSC crop factor, it will have more apparent magnification. It will actually be 1.5:1

Miserere is correct on this one too. The actual magnification of the final image will be greater because you have to enlarge the image from an APS-C sensor 50% more than from a full-frame sensor. But "1:1" doesn't refer to the size of the final image - it refers to the size of the subject compared to the size of the image projected onto the sensor/film. In other words, a subject 10mm long is rendered 10mm long at the sensor.

Saying that a 1:1 macro lens becomes a 1.5:1 on APS-C is akin to saying that a 100mm lens becomes a 150mm lens. In actual fact, the focal length (or magnification ratio in the case of a macro lens) doesn't change - only the field of view changes.

[Miserere]

Thanks Sean, for both posts. That's exactly what's going on.

[Blue]

Miserere is correct regarding depth of field for macro shots. The reason for this is that you move closer or further to get the same subject size in the image frame - therefore the greater depth of field you'd usually see with a wide lens is countered by the fact you have to be closer to the subject. This means that focal length and distance cancel each other out and the only thing that remains to control DOF is the aperture.

You are changing the distance. This is straight up algebra. For a 35mm lens to have the same DOF as a 105mm lens at the same aperture, the distance has to change.

. . .
Saying that a 1:1 macro lens becomes a 1.5:1 on APS-C is akin to saying that a 100mm lens becomes a 150mm lens. In actual fact, the focal length (or magnification ratio in the case of a macro lens) doesn't change - only the field of view changes.

You are correct on the sensor. What it changes is the angle of view.

Thanks Sean, for both posts. That's exactly what's going on.

This is straight up algebra. For a 35mm lens to have the same DOF as a 105mm lens at the same aperture, the distance has to change.
If they were the same, the distance would be the same!

[Miserere]

This is straight up algebra. For a 35mm lens to have the same DOF as a 105mm lens at the same aperture, the distance has to change.
If they were the same, the distance would be the same!

For the same subject size on the sensor, the DoF is determined ONLY by the aperture being used.

Say your subject is filling the frame lengthwise, and you're using a 50mm lens. If you use a 100mm lens and stand twice the distance away from the subject, it will still fill the frame. If you use a 200mm lens and stand 4 times as far, again, the subject will fill your frame. In all these situations the DoF will be exactly the same if you use the same aperture with every lens. That's just photography physics.

Macro at 1:1 means that a 24.5 mm long bug will fill the frame lengthwise (on an APS-C camera). Whether you're using the DA 35mm Ltd, 50mm or 100mm macro lenses doesn't matter for the DoF. If the bug fills the frame, the DoF is determined exclusively by the aperture you shoot at.

[Blue]

For the same subject size on the sensor, the DoF is determined ONLY by the aperture being used.

Say your subject is filling the frame lengthwise, and you're using a 50mm lens. If you use a 100mm lens and stand twice the distance away from the subject, it will still fill the frame. If you use a 200mm lens and stand 4 times as far, again, the subject will fill your frame. In all these situations the DoF will be exactly the same if you use the same aperture with every lens. That's just photography physics.

Macro at 1:1 means that a 24.5 mm long bug will fill the frame lengthwise (on an APS-C camera). Whether you're using the DA 35mm Ltd, 50mm or 100mm macro lenses doesn't matter for the DoF. If the bug fills the frame, the DoF is determined exclusively by the aperture you shoot at.

You are missing the issue Missere. For the DA 35mm ltd and the Sigma 105mm macro to get 1:1, at the same aperture, the working distance has to change because the focal length is different.


Edit: What you should be saying is that the DOF is controlled by the aperture on a given lens. Even 105mm lenses of different designs won't be exactly the same so the working distance could be slightly different.

If focal length didn't matter, I wouldn't be using a DA 35mm ltd macro and a Sigma 105mm macro. To get 1:1 and similar depth of fields from them, the working distance changes.

I don't know why you dragged the sensor back in since I agreed with you on that. the sensor size effects the angle of view or field of view. That will only change the DOF if you go back and forth with the same lens from film to 1.53x body because of the changing circle of confusion.

Edit: Edit: Did you even go to this link that has the spread sheet set up? Edit: http://www.dofmaster.com/dofjs.html

[pentaxman]

Miserere is correct on this one too. The actual magnification of the final image will be greater because you have to enlarge the image from an APS-C sensor 50% more than from a full-frame sensor. But "1:1" doesn't refer to the size of the final image - it refers to the size of the subject compared to the size of the image projected onto the sensor/film. In other words, a subject 10mm long is rendered 10mm long at the sensor.

Saying that a 1:1 macro lens becomes a 1.5:1 on APS-C is akin to saying that a 100mm lens becomes a 150mm lens. In actual fact, the focal length (or magnification ratio in the case of a macro lens) doesn't change - only the field of view changes.

I guess my point is that if you are taking a picture of a 24mm bug with a FF 10Mp camera and you are taking a picture of the same bug with a 10Mp APSC camera, you will have more pixels and therefore greater resolution with the APSC camera. You will be able to enlarge the bug more with less loss in resolution with the APSC camera. Of course I am only talking about sensor resolution, not lens resolution - the lens resolution would remain the same.