Longest working distance lens @ 1:1 range?

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l2oBiN
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Post by l2oBiN »

In which way do the macros achieve 1:1. If its by shortening focal length I guess they would be doing that by shortening their focal length and extending the optical group as has been suggested?

ChrisR
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Post by ChrisR »

the macros

Which macros ?
Again, old lenses usually did it all by extension, later ones often do it by shortening the FL as well as extension and moving internal elements.
Test reports & reviews will sometimes tell you which/how much.

ray_parkhurst
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Post by ray_parkhurst »

Shortening of the FL approaching 1:1 is a design/marketing concession to keep from having an excessively long extension. From what I've read, most if not all "internally focused" lenses do this. If the lens extends physically when you focus, it's likely to have minimal FL shortening, though there may still be some adjustment going on in the name of "close focus control" or some other goal to improve image quality at higher magnifications. A byproduct of the FL shortening is magnification "pumping" as the lens is focused. I personally find this very annoying.

I suppose this means that a change from 1.4x to 2.0x teleconverter will have a disproportionate increase in WD since the lens FL will be increased, assuming you are using a 200mm Macro that has this characteristic.

Using a 2x teleconverter with macro extension would also help this, allowing you to get some of the extra magnification through extension rather than FL reduction.

seta666
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Post by seta666 »

In the digitalpicture.com you have a list of different macro lenses and the magnification the offer with several extension tubes, making easy to calculate the FL at 1:1

http://www.the-digital-picture.com/Revi ... eview.aspx

I have used the 25mm extension magnification value to determine the FL at 1:1, should give a more aproximate value

EF-S 60mm f/2.8 USM ( 12mm Ext) 1.28x (25mm ext) 1.61x FL at 1X 41mm aprox
EF 100mm f/2.8 USM ( 12mm Ext )1.19x (25mm ext) 1.39x FL at 1X 65mm aprox
EF 100mm f/2.8 L IS ( 12mm Ext) 1.17x (25mm ext) 1.37x FL at 1X 68mm aprox
EF 180mm f/3.5 L ( 12mm Ext) 1.09x (25mm ext) 1.21x FL at 1X 120mm aprox

So, acording to this a 120mm bellows lens should give a WD similar to a canon 180mm macro lens at 1:1; a 150mm bellows lens would give better WD but the extension needed would make it a bit uncomfortable to use

Regards
Javier

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Post by rjlittlefield »

ray_parkhurst wrote:Shortening of the FL approaching 1:1 is a design/marketing concession to keep from having an excessively long extension.
The reason is more fundamental.

If the focal length were fixed, and all focusing were done by extension, than around 1:1 the system would stop working intuitively. Under these conditions, as you approach 1:1 changing extension has less and less effect on focus (with camera and subject in fixed positions). Exactly at 1:1, changing extension has no effect on focus -- it only changes magnification.(!) Beyond 1:1, increasing extension moves the focus point outward (not inward), while magnification continues to rise.

All this in intrinsic in the basic lens equation that 1/f = 1/o + 1/i, with fixed f.

Allowing the focal length to shorten does reduce the required extension, but more fundamentally it allows the focus ring to behave "sanely", such that even at 1:1 it has the same type of effect that it does at lower magnifications.

--Rik

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Post by ray_parkhurst »

rjlittlefield wrote: The reason is more fundamental.
...
Allowing the focal length to shorten does reduce the required extension, but more fundamentally it allows the focus ring to behave "sanely", such that even at 1:1 it has the same type of effect that it does at lower magnifications.

--Rik
I'd like to review the patent literature from around the time the IF lenses were developed to see if this was an intentional effect and considered novel enough to be granted as IP. Does anyone have a reference that might describe IF lens FL shortening? Does anyone know who made the first lens to apply this principle?

I'd still wager that the practical aspects of limiting extension was the core reason for FL shortening. Making a compact, 1:1-capable telephoto lens seems to be the compelling value proposition. Were there accounts in the 70s and 80's of folks having such issues with focusing near 1:1? I was not doing much serious photography, and certainly no macro work, at that time so don't have any practical experience with being annoyed.

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Post by rjlittlefield »

ray_parkhurst wrote:Were there accounts in the 70s and 80's of folks having such issues with focusing near 1:1?
I have no idea if anybody bothered to write it up. I was doing lots of both macro and darkroom enlarging work at the time. The effect was well known in both areas. The problem is straightforward: at 1:1 with a fixed FL lens it doesn't work to focus by front bellows movement. Scale changes a lot, focus changes only a little near 1:1 and not at all exactly at 1:1. If you're into calculus you can do the derivatives, or make a table of numbers in a spreadsheet, or best of all hook up a bellows and a lens and play with it yourself.

--Rik

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Post by morfa »

ray_parkhurst wrote:If the lens extends physically when you focus, it's likely to have minimal FL shortening, though there may still be some adjustment going on in the name of "close focus control"
I think this is an oversimplification. For instance, I'm not aware of a lens in the 100mm range capable of achieving 1:1 on its own without exhibiting focal length shortening. I have two non-IF lenses in this range in my possession right now: A modern Tokina AT-X Pro 100/2.8D and a Kiron 105/2.8 (from the 1980's). The first extends 47 mm and the latter 65 mm. Their measured focal lengths at 1:1 are 69 mm and 72 mm respectively.

According to Bjørn Rørslett here (a page well worth reading) the "old" (non-IF) AF-Micro-Nikkor 105/2.8 has a focal length of merely 60 mm at 1:1. Incidentally Bjørn adds: "The design also means it is awkward to use on a tripod if the needed magnification is between 1:2 and 1:1. In this case, one cannot focus the lens without changing magnification, so framing the subject can be frustratingly difficult". So at least in this case the FL-changing design does not seem to have been chosen to target the problem Rik mentions (at least not very successfully).

There are a few older/simpler lenses in this range (such as the Micro-Nikkor 105/4) which are entirely focused by extension but these are only able to deliver 1:2 without additional accessories. Evidently, even some of these 1:2 lenses used FL-shortening close to the near limit. Bjørn reports that the MF Micro-Nikkor 105/2.8 is 88 mm at 1:2.

**Edit** Just to clarify: I think Ray's statement is widely accepted and indeed it does seem intuitively sound. It's just that my attempts at confirming it have been surprisingly unsuccessful.

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Post by ray_parkhurst »

morfa wrote: ...
There are a few older/simpler lenses in this range (such as the Micro-Nikkor 105/4) which are entirely focused by extension but these are only able to deliver 1:2 without additional accessories. Evidently, even some of these 1:2 lenses used FL-shortening close to the near limit. Bjørn reports that the MF Micro-Nikkor 105/2.8 is 88 mm at 1:2.
I think this minor shortening of FL on the older lenses was Nikon's CRC (or whatever they called it) that was intended to improve field flatness for close-focusing. The 55mm and 105mm use this principle.

Thinking about Rik's hypothesis, I am wondering if the reason wasn't so much that users of manual focus macro lenses had issues with focusing, but that the requirements of auto-focus algorithms forced FL shortening in order to have sufficent focusing gradient for the algorithms to work. Can anyone think of a 1:1 capable, manual focus lens that was produced prior to 1:1 capable AF lenses? All the manual focus macro lenses I know of went only to 1:2, with extensions or adapters required for 1:1. Could the reason for FL shortening be due to the advent of AF?

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Re: Longest working distance lens @ 1:1 range?

Post by ray_parkhurst »

l2oBiN wrote:What is the longest high quality objective for photographing bugs/insects at 1:1. The combo I have been using is 1.4TC+Nikon 200mm macro. Any way of achieving longer working distance without increasing the TC mag??
So, what did you decide?

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Post by rjlittlefield »

ray_parkhurst wrote:A byproduct of the FL shortening is magnification "pumping" as the lens is focused. I personally find this very annoying.
I've been wondering about this phrase since I first saw it.

Googling for "magnification pumping" doesn't give me anything helpful.

Can you clarify for me exactly what effect you're talking about?

--Rik

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Post by ray_parkhurst »

rjlittlefield wrote:
ray_parkhurst wrote:A byproduct of the FL shortening is magnification "pumping" as the lens is focused. I personally find this very annoying.
I've been wondering about this phrase since I first saw it.

Googling for "magnification pumping" doesn't give me anything helpful.

Can you clarify for me exactly what effect you're talking about?

--Rik
I see this most in my 105VR. I am very particular in framing my shots when photographing coins so that the pictures all show a given coin size to have the same diameter. When using the 105VR, while the lens is focusing, the apparent size of the coin changes. This makes it very difficult to frame the shot correctly. If the focus locks onto the top surface of the coin, the lens magnification is different than if it locks onto the surface of the field, even though the depth of field is sufficient to make both planes in reasonable focus. So as the lens is deciding on what plane to focus on, the magnification vacillates a bit, which is the "pumping" I referred to. This is at around 0.75:1 for a Cent with 19mm diameter on a D7000.

edited to add...the solution to this is turning off autofocus and adjusting focus with distance from the coin...sort of negates a lot of the advantage the lens offers and is one of the reasons I don't use it any more.

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Post by rjlittlefield »

I see. So we're talking about the field of view changing as focus changes.

Almost all my lenses and lens systems do that, so I'm curious: what lenses do you have for macro applications that do not change FOV as their focus ring is turned?

--Rik

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Post by ray_parkhurst »

rjlittlefield wrote:I see. So we're talking about the field of view changing as focus changes.

Almost all my lenses and lens systems do that, so I'm curious: what lenses do you have for macro applications that do not change FOV as their focus ring is turned?

--Rik
As you imply, this happens for all dedicated macro lenses, but what I am bothered by is the degree or magnitude of the change. Small adjustments in focus produce noticeable changes in mag/FOV with the 105VR, while using a 105AI I don't see the same magnitude of change. The changes are even smaller when the extension/focus is fixed, and are inverted when back focus is used. So it's all a matter of how much can be tolerated, and I find the FL shortening lenses intolerable if a fixed magnification is desired.

paganel
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Post by paganel »

The LOMO Mikroplanar 100/4.5 gives 1:1 on distance 180mm and 2:1 on distance 130mm.
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