Why does my 24-105 have a different magnification (macro ratio) from a 105mm macro lens at same MFD?

Started 6 months ago | Questions
ThrillaMozilla Veteran Member • Posts: 7,468
Re: Why does my 24-105 have a different magnification (macro ratio)

I'm going to try to give you a simple answer. Just read on. (It's not substantially different from the answers you have received, but you may find it simpler. Do read to the end. You don't need to understand all of it.) By the way, Tom Axford's reply was spot-on. Bill Claff's reply also was, albeit a little more complicated.

The magnification is the height of the image on the sensor, divided by the height of the subject. One lens gives you a maximum magnification of 1, while the other is limited to 0.5, or half the magnification. You knew that already.

You asked why two lenses have different magnfications at approximately the same minimum focal distance. A simplified answer is that the magnification is determined by the distance from the front focal point, not from the sensor. The front focal point can be almost anywhere, but the minimum focal distance is measured from the sensor. Because some lenses are long, with lots and lots of lens elements inside, but others are short, the two numbers bear no relation to each other. So the minimum focal distance is not much help.

(Incidentally, cameras used to have a mark at the film plane, and that made sense when the distance from film to subject was marked on the lens barrel. But most modern cameras don't have that mark, and most modern lenses lack the scale, so the minimum focal distance is not as useful as it used to be.)

Now here's the hard part. It sounds like you want to know the working distance, which is simply unknown at this point. That depends not only on how thick the lens is (which Bill Claff can help with), but also on how much metal and plastic is on the front side of the lens at maximum magnification. Even something as simple as a lens hood or a filter would change the working distance.

If that's what you need, there may be a slight possibility of calculating that information. Maybe the manufacturer gives specifications for the length of the lens from flange to the end of the lens, and maybe someone can guess the state of the lens corresponding to that measurement. If the length is specified from end to end, maybe someone knows or can guess the last few millimeters, the distance from flange to the back of the lens. The distance from flange to sensor is known. From all that information maybe Bill Claff can estimate the distance from the front nodal point to the subject position at maximum magnification, and from that, estimate the working distance.

You see, it's not so simple to calculate the minimum working distance from the available information. Maybe you can ask the manufacturers.  They should actually specify that, even if they don't.

 ThrillaMozilla's gear list:ThrillaMozilla's gear list
Canon EOS Rebel SL1 Canon EOS M6 II Canon EF 400mm f/5.6L USM
ThrillaMozilla Veteran Member • Posts: 7,468
Re: Why does my 24-105 have a different magnification ... ?

bclaff wrote:

ThrillaMozilla wrote:

John Sheehy wrote:

That's why max magnification needs to be stated as a lens spec.

Yes, I hardly ever need to know the specification for the minimum focusing distance. The maximum magnification, however, is crucial, and cannot be derived from the minimum focal distance without considerable additional information.

Arguably working distance (to the front of the lens) is more useful information than subject distance (to sensor/film).

Absolutely.  I just wrote a reply that states that in many more words.  There's a chance that it could be calculated from available specifications, for someone who's handsome and really talented.  It could also be a fool's errand.

 ThrillaMozilla's gear list:ThrillaMozilla's gear list
Canon EOS Rebel SL1 Canon EOS M6 II Canon EF 400mm f/5.6L USM
Monicaa
OP Monicaa Junior Member • Posts: 42
Re: Why does my 24-105 have a different magnification (macro ratio)

ThrillaMozilla wrote:

the magnification is determined by the distance from the front focal point, not from the sensor. The front focal point can be almost anywhere

Right. This made it click in my head, I've connected the dots from the other replies now. At infinity the difference is negligible beween "a 105mm focal length" lens where that focal length is measured starting from 5cm or 15cm in front of the sensor, but if the subject is 30cm away from the sensor that's going to have a significant impact on the appearance of the image.

I have felt this difference in focal points before but I never really made the connection to how it would affect the image. In fact, even using the 24-105 at macro distances it "feels" off compared to some other lenses. You have a very tight image but the way the focus and framing changes as you move doesn't feel quite consistent with other lenses.

Of course it makes sense that the focal length is relative to the focal point and not from the sensor, so different focal point placement will make a different image... I'm surprised I didnt make that connection.

I now see this exact thing written in the other replies, but worded in a way that didnt quite click in my head. Reading is hard

 Monicaa's gear list:Monicaa's gear list
Panasonic Lumix DC-S5 Fujifilm X-E3 Panasonic S 24-105mm F4 Macro OIS Sigma 105mm F2.8 DG DN Macro Sigma 35mm F2 DG DN
bclaff Forum Pro • Posts: 13,750
Re: Why does my 24-105 have a different magnification (macro ratio)

ThrillaMozilla wrote:

...

Now here's the hard part. It sounds like you want to know the working distance, which is simply unknown at this point. That depends not only on how thick the lens is (which Bill Claff can help with), but also on how much metal and plastic is on the front side of the lens at maximum magnification. Even something as simple as a lens hood or a filter would change the working distance.

...

Distance to the front lens vertex is provided in my previous Optical Bench screen shots.

Panasonic Lumix S 24-105mm F4 Macro OIS 117.41mm
Sigma Macro 105mm F2.8 EX DG OS HSM 144.49mm

These values are also not intuitive as you might think the close working distance would be the higher magnification.

-- hide signature --

Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

bclaff Forum Pro • Posts: 13,750
Re: Why does my 24-105 have a different magnification (macro ratio)

Monicaa wrote:

ThrillaMozilla wrote:

the magnification is determined by the distance from the front focal point, not from the sensor. The front focal point can be almost anywhere

... I'm surprised I didnt make that connection.

I now see this exact thing written in the other replies, but worded in a way that didnt quite click in my head. Reading is hard

There is also a Thick Lens Optical Bench at PhotonsToPhotos.

Here's the Panasonic and SIgma as displayed there (with specific options chosen).

Best viewed "original size"

Best viewed "original size"

The horizontal lines underneath are are labelled with how they contribute to the total distance.

It's the green line, the internal distance (i), that makes the big difference.

-- hide signature --

Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

ThrillaMozilla Veteran Member • Posts: 7,468
Re: Why does my 24-105 have a different magnification (macro ratio)

bclaff wrote:

ThrillaMozilla wrote:

...

Now here's the hard part. It sounds like you want to know the working distance, which is simply unknown at this point. That depends not only on how thick the lens is (which Bill Claff can help with), but also on how much metal and plastic is on the front side of the lens at maximum magnification. Even something as simple as a lens hood or a filter would change the working distance.

...

Distance to the front lens vertex is provided in my previous Optical Bench screen shots.

Panasonic Lumix S 24-105mm F4 Macro OIS 117.41mm
Sigma Macro 105mm F2.8 EX DG OS HSM 144.49mm

These values are also not intuitive as you might think the close working distance would be the higher magnification.

Excellent.  Now, for a fair comparison of the two lenses, the working distance at a magnification of 0.5 would be the pertinent value.

 ThrillaMozilla's gear list:ThrillaMozilla's gear list
Canon EOS Rebel SL1 Canon EOS M6 II Canon EF 400mm f/5.6L USM
bclaff Forum Pro • Posts: 13,750
Re: Why does my 24-105 have a different magnification (macro ratio)

ThrillaMozilla wrote:

bclaff wrote:

ThrillaMozilla wrote:

...

Now here's the hard part. It sounds like you want to know the working distance, which is simply unknown at this point. That depends not only on how thick the lens is (which Bill Claff can help with), but also on how much metal and plastic is on the front side of the lens at maximum magnification. Even something as simple as a lens hood or a filter would change the working distance.

...

Distance to the front lens vertex is provided in my previous Optical Bench screen shots.

Panasonic Lumix S 24-105mm F4 Macro OIS 117.41mm
Sigma Macro 105mm F2.8 EX DG OS HSM 144.49mm

These values are also not intuitive as you might think the close working distance would be the higher magnification.

Excellent. Now, for a fair comparison of the two lenses, the working distance at a magnification of 0.5 would be the pertinent value.

FWIW (and you can get this yourself using the link above)  the Sigma at 0.5x is 228.10mm

-- hide signature --

Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

ThrillaMozilla Veteran Member • Posts: 7,468
Re: Why does my 24-105 have a different magnification (macro ratio)

Oh, I see. You actually have the working distance calculated automatically.  Very handy.

I see how you zoom, but how do you focus the zoom lens?

 ThrillaMozilla's gear list:ThrillaMozilla's gear list
Canon EOS Rebel SL1 Canon EOS M6 II Canon EF 400mm f/5.6L USM
bclaff Forum Pro • Posts: 13,750
Re: Why does my 24-105 have a different magnification (macro ratio)

ThrillaMozilla wrote:

Oh, I see. You actually have the working distance calculated automatically. Very handy.

I see how you zoom, but how do you focus the zoom lens?

For that lens Panasonic Lumix S 24-105mm F4 Macro OIS (and many others) you need to consult other scenarios. Normally I only have enough information to do zoom or focus and usually zoom takes precedence.
Look for the Previous and Next Scenario buttons.

-- hide signature --

Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

ThrillaMozilla Veteran Member • Posts: 7,468
Re: Why does my 24-105 have a different magnification (macro ratio)

bclaff wrote:

ThrillaMozilla wrote:

Oh, I see. You actually have the working distance calculated automatically. Very handy.

I see how you zoom, but how do you focus the zoom lens?

For that lens Panasonic Lumix S 24-105mm F4 Macro OIS (and many others) you need to consult other scenarios. Normally I only have enough information to do zoom or focus and usually zoom takes precedence.
Look for the Previous and Next Scenario buttons.

Oh, I see. It's Scenario 4. Thanks.

Nice tool.  I hadn't really looked at it much before.

 ThrillaMozilla's gear list:ThrillaMozilla's gear list
Canon EOS Rebel SL1 Canon EOS M6 II Canon EF 400mm f/5.6L USM
bclaff Forum Pro • Posts: 13,750
Re: Why does my 24-105 have a different magnification (macro ratio)

ThrillaMozilla wrote:

bclaff wrote:

ThrillaMozilla wrote:

Oh, I see. You actually have the working distance calculated automatically. Very handy.

I see how you zoom, but how do you focus the zoom lens?

For that lens Panasonic Lumix S 24-105mm F4 Macro OIS (and many others) you need to consult other scenarios. Normally I only have enough information to do zoom or focus and usually zoom takes precedence.
Look for the Previous and Next Scenario buttons.

Oh, I see. It's Scenario 4. Thanks.

Right that's the 0.5x for that lens

Nice tool. I hadn't really looked at it much before.

Thanks. Spread the word

It was a significant effort to code the ray tracer.

And it's a significant and ongoing effort to enter optical prescriptions (almost exclusively) from patents. For example I entered the Fujifilm Fujinon GF35-70mm F4.5-5.6 WR yesterday

If you're interested in hearing about new entries the best place right now is this dpreview thread .

-- hide signature --

Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

FrancoD Forum Pro • Posts: 18,963
Re: Why does my 24-105 have a different magnification (macro ratio)

I suggest you look at the article I linked to  and the video clip in and just take it from me that a lot of lenses, particularly zoom lenses, do the same as your lens does.

bclaff Forum Pro • Posts: 13,750
Re: Why does my 24-105 have a different magnification (macro ratio)

FrancoD wrote:

I suggest you look at the article I linked to and the video clip in and just take it from me that a lot of lenses, particularly zoom lenses, do the same as your lens does.

However, be aware that focus breathing has nothing to do with the original observation.

-- hide signature --

Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

QuietOC
QuietOC Veteran Member • Posts: 6,676
Re: Why does my 24-105 have a different magnification (macro ratio)

Note that the macro lens you ordered (DN) has different optics than the one shown in the other posts. I am not sure if he has the new mirrorless lens in the optical bench.

 QuietOC's gear list:QuietOC's gear list
Pentax Q7 Sony a7R IV NEX-5T Sony a77 II Sony DT 16-50mm F2.8 SSM +107 more
bclaff Forum Pro • Posts: 13,750
Re: Why does my 24-105 have a different magnification (macro ratio)

QuietOC wrote:

Note that the macro lens you ordered (DN) has different optics than the one shown in the other posts. I am not sure if he has the new mirrorless lens in the optical bench.

Yes, the designs are quite different

Macro 105mm F2.8 EX DG OS HSM

105mm F2.8 DG DN MACRO Art

I haven't located a patent corresponding to the later lens.
This is quite close and I have to reexamine it to see if it's actually a match.

-- hide signature --

Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

Monicaa
OP Monicaa Junior Member • Posts: 42
Re: Why does my 24-105 have a different magnification (macro ratio)

I now have both in hand. The panasonic exhibits basically no focus breathing, including at macro ranges, but the sigma exhibits extreme breathing at the macro range. I'm not sure exactly what specifically in your tool would show this, but I do think that breathing does seem to play quite a large part, but I am not sure whether as a symptom or a cause.

As a side note, this lens is quite exceptional. I've scanned some film and the detail is quite great, and the corners are just as flawless as the center even wide open, not something I've seen in other macro lenses I've used. I'll need to do some specific testing to see how it performs in 96MP pixel shift high res mode, but from quick tests it appears to still have very high pixel level detail at that resolution. Very impressed.

 Monicaa's gear list:Monicaa's gear list
Panasonic Lumix DC-S5 Fujifilm X-E3 Panasonic S 24-105mm F4 Macro OIS Sigma 105mm F2.8 DG DN Macro Sigma 35mm F2 DG DN
bclaff Forum Pro • Posts: 13,750
Re: Why does my 24-105 have a different magnification (macro ratio)
2

Monicaa wrote:

I now have both in hand. The panasonic exhibits basically no focus breathing, including at macro ranges, but the sigma exhibits extreme breathing at the macro range. I'm not sure exactly what specifically in your tool would show this,

Sure the Optical Bench shows Pansonic at 105mm is 24 degrees at infinity and 21 degrees at 0.5x whereas the SIgma is 24 degrees at infinity and 9 degrees at 1x.

This makes sense since the Sigma working distance is larger so the angle would be smaller.

but I do think that breathing does seem to play quite a large part, but I am not sure whether as a symptom or a cause.

Neither. It's just different lens designs and the large difference in internodal distance (hiatus) is what results in your original observation.

As a side note, this lens is quite exceptional. I've scanned some film and the detail is quite great, and the corners are just as flawless as the center even wide open, not something I've seen in other macro lenses I've used. I'll need to do some specific testing to see how it performs in 96MP pixel shift high res mode, but from quick tests it appears to still have very high pixel level detail at that resolution. Very impressed.

Both the Panasonic and Sigma exhibit similar distortion according to the Optical Bench; about 3% pincushion. Comparing sharpness requires an actual rather than virtual optical bench ! 

-- hide signature --

Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

Keyboard shortcuts:
FForum MMy threads