Got my first macro lens yesterday. Tokina 100mm. It dawned on me, I don't know what I'm doing. Mainly I don't understand minimum focus distance. I thought I would be unable to focus when I got a foot from the subject. I was able to nearly fit the lens up the rear end of the subject. Apparently I can focus all the way to a couple of inches. So how do macro pros do it? Get as close as the subject allows? ty
Focus distance.
- Thread starter snj979s
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The minimum focus distance is measured from your sensor to the subject, not from the end of the lens to the subject.
Like Blacktop said, distance to the sensor. Once in awhile, you will come across a macro that lists 'working distance', that would be from the front of the lens. Its a more meaningful number when comparing lenses.
As for distance, I back up a bit. I try for the highest aperture possible, usually use flash to get that high aperture. Depth of field is very thin, even at higher apertures. Backing up a bit gets more in focus. Most of our cameras have enough pixels to crop a good bit and still have a decent image. Getting as close as possible isn't always the best way.
As for distance, I back up a bit. I try for the highest aperture possible, usually use flash to get that high aperture. Depth of field is very thin, even at higher apertures. Backing up a bit gets more in focus. Most of our cameras have enough pixels to crop a good bit and still have a decent image. Getting as close as possible isn't always the best way.
B&H lists the specs for the Tokina M100 lens as Minimum Focus Distance: 11.8 inches. Focus distance is measured to the sensor. The Nikon DSLR camera has a marking of a circle with line through it (like a greek Theta type mark θ ) near the rear corner of the top LCD to indicate this focal plane. Focus distance is measured to it.
The distance in front of the lens is called Working Distance, and this Tokina does 1:2, and it is reported for the Tokina M100 lens to be 215 mm (8.46 inches), in front of the lens at 1:2
The distance in front of the lens is called Working Distance, and this Tokina does 1:2, and it is reported for the Tokina M100 lens to be 215 mm (8.46 inches), in front of the lens at 1:2
Hmmm. Making me think hard. The minimum focus distance of this lens is 11.8" to the sensor. The length of the lens is listed as 3.74". Trim off about 3/8" of that lens length for the rear element poking passed the mount, so we'll call it 3.4" for lens length. So we calculate working distance as 11.8 - 3.4 = 8.4" It sounds good on paper, but I think this is an external focus lens, meaning the length grows as you focus close. So my calculations are useless, lol. Having that lens extended would probably put you in the 4" range for working distance to get 1:1.
I found this:
Tokina 100mm f/2.8 Macro Review
I know some people are not fans of Ken Rockwell, but I trust that he can measure. He says this lens is a measured 4.5" working distance.
Focal length appears to go out the window at minimum focus distance on macro lenses. My Sigma 100mm gives me maybe 2" over my Tamron 60mm at minimum distance. The 100mm shows its stuff though as soon as I back off a little.
Tokina 100mm f/2.8 Macro Review
I know some people are not fans of Ken Rockwell, but I trust that he can measure. He says this lens is a measured 4.5" working distance.
Focal length appears to go out the window at minimum focus distance on macro lenses. My Sigma 100mm gives me maybe 2" over my Tamron 60mm at minimum distance. The 100mm shows its stuff though as soon as I back off a little.
You forgot to subtract the distance from mounting flange to sensor (the thickness of the camera body). For Nikon, that is 46.5 mm, 1.83 inches.
I got the 215 mm working distance from this chart
Macro lens calculations
which is normally pretty good, but it says the M100 lens does 1:2, but B&H says specs are 1:1. Could be some kind of mix up there.
Yes, I totally forgot camera thickness. The extending lens barrel is an unknown anyway to figure the distance from the front of lens to the subject at the closest distance. That website you listed has two charts, one for 1:1, and the 2nd chart for backing away to get 1:2, if I am reading it correctly. So that makes sense: WD of 115mm (4.5") for 1:1 and 206mm (8.1") when backing up to get 1:2.
You're right, my mistake was not seeing this Tokina M100 in the 1:1 section (not even realizing I was looking for M100), so I landed on the second 1:2 section. It does say at 1:1, the M100 working distance is 115 mm (4.5 inches).
It is an excellent site, but my complaint is that the table is an image (probably screen capture from Excel) so it is not text searchable.
The page (on its Excel worksheet) says it uses a ruler to measure to the filter ring on the lens. That can be said to be the "front" of the lens, same as the specs show lens length as the overall, including extension inside the camera at the mount end.
But actually, in the math (of the 1:1 magnification), "subject distance" is computed to the nodal plane normally inside the lens somewhere.
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Then be glad you bought a 100mm lens, and got 4.5 inches at 1:1. If it had been a 55 or 60mm macro lens, it would have been more like 2 inches. This is simply the normal thing for macro lenses at 1:1.
Because, the meaning of 1:1 is that the distance in front of the lens is equal to the distance behind the lens. 1:1 means the image is same as real life size. So that is just a similar triangle, to be 1:1 means the subject height and distance must equal the focal length and image height, same triangles.
This is not measured from the exact front edge of the lens, but instead is measured to a principle point inside the lens somewhere. You have a 100mm lens (meaning, when focused at infinity, it is 100 mm). At 1:1 the lens is racked out some to focus closer, and the focal length is technically 2x longer at 1:1, or 200 mm. This also means the equivalent aperture will be 2 stops smaller then, actual maximum will be f/4 instead of f/2.8 (because f/stop is focal length / aperture diameter, and focal length is 2x longer at 1:1). Lenses and bodies today surely report the f/4 then, instead of f/2.8, but in old days, they didn't. Internal focusing lenses shift things inside, and can slightly vary this, maybe f/3.8 instead of f/4.
So at 1:1, the distance in front is necessarily equal to the focal length, let's say 200 mm. However, that is measured to the principle point inside the lens body, maybe an inch or two inside, so it is less distance to the actual front filter ring.
The 100 or 105 mm macro lens is often considered a plus due its slightly longer working distance. The difference between 2 and 4 inches is a lot. The closer camera can block the light, or it could scare the bug.
But the 55 and 60 mm has advantages too. For example, if you wanted to use 100mm for a table top scene, perhaps 18 or 20 inches wide, the 100 mm would have to stand back maybe 7 feet to get all of that in. The space in the room might not allow that. Similarly, copying documents on a copy stand would prefer the shorter lens, because its height column might not be that tall, and we couldn't reach the camera if it were.
The 55 or 60 mm lens is likely better suited for casual closeups (like 2 or 3 feet instead of 1:1), because they don't have to stand back so much farther.
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Not sure I understand about the hood, but the main problem with a very close focus distance is that the lens may block the light on the subject. A lens hood would greatly aggravate that.
And the crop body does not change anything (except cropped field of view). This is true of both macro and the general case.
Saying, camera on a tripod and focused for 1:1. Switch out the bodies, and it is still at 1:1. This is true at 30 feet also, still focused at 30 feet. The lens is not affected by the sensor crop.
Full frame shows a larger frame and field, cropped frame shows a smaller frame and field, but the image inside the frame depends only on what the lens can do. Appearance of sensor cropping looks the same as if cropping later in the computer. Cropping only changes frame size, but not the contained image. Cropping in the computer loses that many pixels, but smaller cropped sensors can be built with more pixels to make up for that aspect.
1:1 magnification is entirely about the lens. 1:1 is the same 1:1 regardless of sensor crop. 1:1 is about magnification, i.e., object size. Cropped "equivalent focal length" is instead about field of view, it crops the object (instead of magnifying it). Equivalent focal length is simply to maintain the same field size.
In every case (macro or not), sensor crop only crops the total field of view size size, but does not affect the object size projected by the lens. In every case, the object image size is whatever the lens can do. Saying, sensor crop does not affect whatever the lens can do, it merely crops that image (due to the smaller sensor).
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Yes, as compared to cropping later in an editor, the DX image has many more pixels.
The lens projects the same image regardless of what sensor is present. If you can remember back to film days, it is exactly like a movie projector or a slide projector, projecting an image. Regardless of what size projection screen we might place at say the same 10 feet, the projector projects the same image on it. A smaller screen would be like a cropped sensor, seeing only a smaller view of that larger projected image. We could call that a "cropped screen".
But it is exactly the same concept as the cropped sensor. The sensor is merely a projection screen for the projected lens image.Let's say that our FX camera lens projects a circular image about 44mm diameter. That projected image falls on whatever sensor is present.
The 36x24mm full frame sensor has a diagonal of 43.27 mm. It captures a photo image that size.
The 24x16mm DX sensor has a diagonal 28.8 mm. The FX image is 43.27 / 28.8 = 1.5x larger. The DX sensor simply crops the view of the full lens image. The lens image is not affected in any way by the sensor that is present (regardless if the focus distance is 1:1 macro, or 30 feet distant). The cropped result is affected by the smaller sensor, but the lens is not affected. There is no magic, the cropped DX sensor is simply smaller.
The cropped DX sensor might have 24 megapixels, and yes, of course it retains those 24 megapixels.
The full FX image may have 24 megapixels too, but if cropped to the the same smaller size later (2/3 width and 2/3 height, because 1/1.5 is 2/3), it only has about 44% of its original pixels remaining then. So cropping later is the same "view", but the pixel count suffers seriously. Depending on use, may or may not have enough pixels remaining.
A 50mm DX is said to be an "Equivalent Focal Length" as 75 mm FX. The way we say this is misleading, causes confusion. It is only the FX body that sees the Equivalent focal length, not the DX body which only sees 50 mm. All it actually means is that the 50 mm DX body sees the same Field of View as a 75 mm FX body (assuming both at the same distance). These are different magnifications, since the FX sees the scene 36 mm wide, and the DX sees the same Field of View to be 24 mm wide. The FX body can duplicate that 50mm DX field of view either by using the 1.5x longer lens, or standing 1.5x closer. This is only because its sensor is 1.5x larger, so its field of view is larger.
So we imagine the DX lens as being somehow magically 1.5x longer than it actually is, like a 1.5x telephoto lens would see on a FX body, but only applies if we are comparing in terms of what FX sees. Not true if thinking about that the DX body sees. A 50 mm lens is always 50mm. And the smaller DX image does have to be enlarged half again more to be "equal" size of the FX image, so all things are still not equal.
Anyway, the point was, if the lens is projecting a 1:1 macro image, it is 1:1 regardless of which sensor is seeing it. The FX field of view will be 1.5x larger than the DX, since the DX image is a cropped smaller area of it, but the magnification is the same 1:1.
So the original point was that the 1:1 is itself a magnification, and there is not even this sense of Equivalent (field of view). If the lens is focused to 1:1, both sensors see 1:1. meaning the subject details are reproduced life size on the sensor. However at same magnification, now they see different fields of view (the DX is a smaller cropped field of view).