Is my thinking about equivalence right?

Started 5 months ago | Questions
Bassam Guy Veteran Member • Posts: 3,118
TLDNR - Take Pix Instead
3

C'mon, this is photography, not science class. Take some pictures instead of fretting over this.

Get an m43 body and 43 adapter. Replace lenses with MFTs at your leisure.

Muster Mark wrote:

Hi all, I realize this is NOT the topic everyone loves to discuss and I totally understand. I hope no-one feels annoyed by this post. That said, after some investigation I have come to the conclusion that "traditional" equivalence math is only useful as a rough heuristic to get a sense of what DOF will be and NOT a reasonable way to compare individual lenses or judge cost/performance of lenses in different systems. I wanted to see what other geeky 4/3 sensor users think and if I am missing something in my calculations. I should add I fully understand the traditional argument that total light is 4x on FF camera (for example) at the same aperture since we need to multiply (integrate, actually) brightness by the sensor size to calculate S/N. This idea only works if you have an IDEAL lens and an ideal sensor. Lenses are never ideal though, so I wanted to dig deeper.

For the sake of simplicity let's limit ourselves to looking at "normal" lenses: e.g. fov roughly 1 radian. This FoV tends to "favor" larger formats as far as I can tell especially if the goal is to maximize bokeh-ball size/$. Furthermore, to limit permutations I only looked at examples of lenses for m43 and Sony E mount, specifically trying to find an "equivalent" lens to the M.Zuiko 25mm f1.2

My analysis boils down to 2 points:

1: No two lenses are actually "equivalent". This seems obvious. There is more to evaluating a lens than pupil diameter and FoV. People seem to forget this when comparing between systems.

2: Talking about "total light" without accounting for vingetting is either lazy or disingenuous. I am guessing this is 100% laziness as calculus is annoying. However FF lenses have much worse vingetting than m43 lenses for obvious reasons. Is this a hugely important aspect to image quality? No not really, IMHO, it's pretty easy to correct in post if you have the lens profile, but you are losing some of the signal to noise ratio advantage in the process. How much? that's what I wanted to figure out. By my calculation (of course it depends on lens a huge deal) FF lenses at 50mm lose about half a stop of light to vingetting MORE than the 25 f1.2. Specifically, the Sony GM 50mm 1.2 at 1.2 gathers about 2.9x the total light gathered by the olympus 25mm 1.2 (at 1.2). Is this a huge deal? No probably not, but it's not quite as impressive as the 4x factor everyone is repeating is it? I just thought it was interesting, mainly.

Calculating total light (for point 2): This is pretty handwavey, but after squinting at the data on lenstip.com, and specifically the level curves for brightness I thought it looked remarkably parabolic. Thus I approximated the brightness function of a lens wide open as a decreasing parabaloid -(x^2+y^2)K, where K is a constant that depends on the specific lens (I compared contour plots of these functions to the level curves provided by lens tip and they are remarkably close). When comparing between lenses of different aperture, there is a shift applied: e.g. approximating 1.4 as half a stop slower than 1.2, we would shift by -1/2. We then exponentiate and integrate over the frame. For these calculations I am assuming Fstop equals Tstop. Which is not correct, though lenses with similar numbers of elements will not have much difference in T stop I don't think (am no expert!). I couldn't find information on T stops for a lot of lenses which is why I left it out of consideration. I also couldn't find information on how it's measured (are they integrating total lite or measuring intensity at the center of the frame?) which further complicated trying to incorporate it.

Comparing lenses holistically: When more is taken into account than just pupil diameter, it seems to me at least, m43 lenses are not overpriced. For example the 25mm1.2 is optically pretty amazing when it comes to corner to corner sharpness, longitudinal CA correction (which is hard to correct in post, if my understanding is correct) and bokeh quality (not size).

For half the price one could use the Sony 50mm 2.5. This amounts to being about half a stop dimmer due to vingetting, the bokeh while the same size is much busier. Longitudinal CA is only a smidge worse though. Oh and yeah if you want a sharp full frame you need to stop down to f4 (the 50mm 1.8 by sony is not really worth looking at if optical performance is something you care about).

The Sony GM 50mm 1.2 lens performs very well when stopped down (and is pretty good wide open), but now we are back to being much heavier and costlier than the olympus. I am NOT saying it's a rip off, but I also don't think the lens needs defending as no one seems to doubt it.

The Zeiss 55mm 1.8 has lovely bokeh, but bad Long. CA and needs to be stopped down to 2.8 to be sharp.

Sigma ART lenses start to really shine honestly. Generally very well corrected optically, much less vingetting on FF than other lenses when wide open, and even slightly cheaper priced to the olympus. They are significantly bigger though (the 50mm 1.4 is 815g, versus 410g for the oly).

So what do we make of all this? My take away is that there is no free lunch. All lenses are compromises and on a system-wide level nobody is scamming anyone. If size of the bokeh balls is not your biggest concern, and you care about system size/weight and optical performance, m43 makes a lot of sense. I guess you already know that

I personally am shopping around at the moment (trying to decide if I want to adapt old 4/3 glass to m4/3 bodies, or buy new lenses and potentially change systems or buy new m4/3 lenses) and thus did this analysis to try to compare systems more accurately. Hopefully it was moderately interesting?

If there is anything I should be accounting for that I am not (and you know how I might, e.g. t stops) I'd be curious to hear.
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Bassam Guy Veteran Member • Posts: 3,118
Un-equivalence
2

jwilliams wrote:

Muster Mark wrote:

Hi all, I realize this is NOT the topic everyone loves to discuss and I totally understand. I hope no-one feels annoyed by this post. That said, after some investigation I have come to the conclusion that "traditional" equivalence math is only useful as a rough heuristic to get a sense of what DOF will be and NOT a reasonable way to compare individual lenses or judge cost/performance of lenses in different systems.

No, not really. Equivalence is more than DOF or even mainly about DOF. I'll not go into any long winded discussion, but here's an article on this site that is a good read on the subject.

Equivalence is useful if you have any interest in light (and as a photographer, you probably should): Digital Photography Review (dpreview.com)

That is not true. 'Equivalence' implies at least two things. If 43 is your only sensor size then equivalence is meaningless.

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OP Muster Mark Contributing Member • Posts: 588
Re: TLDNR - Take Pix Instead
2

Bassam Guy wrote:

C'mon, this is photography, not science class. Take some pictures instead of fretting over this.

Get an m43 body and 43 adapter. Replace lenses with MFTs at your leisure.

Best response yet, I think. I didn't realize there was a photographic science and tech forum, I really should have posted this there.

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Cheers,
-Ian

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Mark Ransom
Mark Ransom Veteran Member • Posts: 7,670
Re: TLDNR - Take Pix Instead
9

Muster Mark wrote:

Bassam Guy wrote:

C'mon, this is photography, not science class. Take some pictures instead of fretting over this.

Get an m43 body and 43 adapter. Replace lenses with MFTs at your leisure.

Best response yet, I think. I didn't realize there was a photographic science and tech forum, I really should have posted this there.

Like it or not, equivalence comes up far more often in the m4/3 forum than anyplace else.  And this post in the photographic science and tech forum would probably get you roasted alive.

At least you had the grace to put "equivalence" in the title so those tired of the subject could pass it by.

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dkyl Contributing Member • Posts: 967
Re: Is my thinking about equivalence right?
6

Muster Mark wrote:

Just look at the lenstip data. The Sony 50mm 2.5 has vignetting of 2.29 stops in the corners. The olympus 25mm1.2 has at most 1.3 stops of vignetting. Th Sony GM 50 1.2 has almost 3 stops of vignetting wide open.
Normal equivalence would say FF at 1.2 is gathering 4x the light as m43 at 1.2. That's not true if it's falling off so much more. Is the difference big? No I don't think so. I don't think most people care so much about vignetting, but it makes the "total light" calculation rather different.

Sure, but you're cherry picking a little here. The Sony 50mm f/1.2 is excellent but one of its design consideration is keeping it relatively compact. So of course something has to give.

I know you wanted to limit the scope of comparison to just Sony since it makes things a little easier, but if you expand your scope there are plenty of examples where FF is not any more prone to vignetting. It's just a design compromise depending on what the designers want to achieve.

Take the Nikon Z 50mm f/1.8 S as an example. Lenstip didn't do a review for the Nikon but DXOMark has a measurements for both the Nikon 50mm f/1.8 and the Olympus 25mm f/1.2.

The Nikon has a T-stop of T1.9 and vignetting at -1.6EV whilst the Olympus comes in at a T-stop of T1.8 and vignetting of -1.2EV.

So now they have practically the same transmission in the middle and only 1/3 stop difference on the peripheral whilst the Nikon covers an imaging area 4 times the size. And the two don't differ that much in size either.

I'm not here to preach FF or anything. I'm happy using both my m43 and FF gear. At the end of the day there are benefits to both system when looking at actual lenses and cameras that are being produced, not just theoretical benefits.

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LevAizik Regular Member • Posts: 164
Re: Is my thinking about equivalence right?
3

Don't go down this rabbit hole. It is pointless and doesn't advance your skills as a photographer in any way or form. The equivalence topic is used mostly by YouTubers looking for more clicks and internet trolls looking to start a virtual fight.

Think about your budget. Think about how much weight you are willing to carry and if you want to change lenses. Think about what you are photographing (Family, travel, portraits, wedding, etc) Check if the system you want to use has the specialty lenses you might need. (Macro, long telephoto, wide-angle, etc) Check the ergonomics of the camera.

This is what is important and not all the endless internet chatter about noise (overrated), DOF (feature and not an advantage), and vignetting (can be used creatively).

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rgs_45
rgs_45 Senior Member • Posts: 1,357
Re: Is my thinking about equivalence right?
3

A retired seasoned outdoor photographer told me that don't fret with the "equivalency crap.

He told me, take a light meter and meter a subject (at the time a flower). I just bought my EM-5 mk i with 12-50 kit lens and he had the Nikon 3DS with 24-120/4.0 G (if I can remember correctly). He metered the subject in Aperture priority and chooses F5.6, the shutter speed came to be 1/600th of a second. He then told me to set my my settings at F5.6 and 1/600th of a second and he did the same. Took the photo and when we compare the result through the lcd screen, I could not find any difference in the colors, brightness etc. The only thing I could see different is the DoF. The Nikon 3DS has a much better bokeh (subject to background separation than my m4/3 gear.

Since then, I totally erased all equivalency thoughts I had. Been shooting m4/3 since then. Have a EM1 mk i, EM5 mk ii and just recently the EMX1 since Friday. I also have a Nikon Z6 i with the 24-70/4.0 kit lens just for the heck of it.

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David Fell Regular Member • Posts: 203
Re: Is my thinking about equivalence right?

rogerstpierre wrote:

I understand equivalency, but I just don't see the purpose if all you got is one system.

I think I do understand and wonder why M43 gets hammered but not APS-C cameras or maybe it's my cognitive bias

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bobn2
bobn2 Forum Pro • Posts: 69,811
Re: Is my thinking about equivalence right?
23

Muster Mark wrote:

Hi all, I realize this is NOT the topic everyone loves to discuss and I totally understand. I hope no-one feels annoyed by this post. That said, after some investigation I have come to the conclusion that "traditional" equivalence math is only useful as a rough heuristic to get a sense of what DOF will be and NOT a reasonable way to compare individual lenses or judge cost/performance of lenses in different systems. I wanted to see what other geeky 4/3 sensor users think and if I am missing something in my calculations. I should add I fully understand the traditional argument that total light is 4x on FF camera (for example) at the same aperture since we need to multiply (integrate, actually) brightness by the sensor size to calculate S/N. This idea only works if you have an IDEAL lens and an ideal sensor. Lenses are never ideal though, so I wanted to dig deeper.

OK, a thoughtful, detailed post which deserves a detailed response. So here it is.

For the sake of simplicity let's limit ourselves to looking at "normal" lenses: e.g. fov roughly 1 radian. This FoV tends to "favor" larger formats as far as I can tell especially if the goal is to maximize bokeh-ball size/$. Furthermore, to limit permutations I only looked at examples of lenses for m43 and Sony E mount, specifically trying to find an "equivalent" lens to the M.Zuiko 25mm f1.2

My analysis boils down to 2 points:

1: No two lenses are actually "equivalent". This seems obvious. There is more to evaluating a lens than pupil diameter and FoV. People seem to forget this when comparing between systems.

That's what is called a 'semantic argument'. Before you argue about whether things are, or are not equivalent, you need to agree on what the word 'equivalent' is going to mean. This is a very common practice in science and engineering, we give every day word very precise definition so as to avoid that kind of lack of clarity. For photographic equivalence, the word 'equivalent' is defined with respect to 'equivalent photographs' which are defined to have the:

Same Perspective
Same Framing
Same Exposure Time
Same DOF / Diffraction / Total Amount of Light Projected on the Sensor
Same Lightness
Same Display Dimensions.

That's it. There's no point arguing with whether or not that's the right definition. In the context of the discussion, the is the definition. Choose a different definition, and you end up with a different discussion.

2: Talking about "total light" without accounting for vingetting is either lazy or disingenuous. I am guessing this is 100% laziness as calculus is annoying. However FF lenses have much worse vingetting than m43 lenses for obvious reasons. Is this a hugely important aspect to image quality? No not really, IMHO, it's pretty easy to correct in post if you have the lens profile, but you are losing some of the signal to noise ratio advantage in the process. How much? that's what I wanted to figure out. By my calculation (of course it depends on lens a huge deal) FF lenses at 50mm lose about half a stop of light to vingetting MORE than the 25 f1.2. Specifically, the Sony GM 50mm 1.2 at 1.2 gathers about 2.9x the total light gathered by the olympus 25mm 1.2 (at 1.2). Is this a huge deal? No probably not, but it's not quite as impressive as the 4x factor everyone is repeating is it? I just thought it was interesting, mainly.

It's no more 'lazy' or 'disingenuous' that talking about exposure without accounting for vignetting.

Calculating total light (for point 2): This is pretty handwavey, but after squinting at the data on lenstip.com, and specifically the level curves for brightness I thought it looked remarkably parabolic. Thus I approximated the brightness function of a lens wide open as a decreasing parabaloid -(x^2+y^2)K, where K is a constant that depends on the specific lens (I compared contour plots of these functions to the level curves provided by lens tip and they are remarkably close). When comparing between lenses of different aperture, there is a shift applied: e.g. approximating 1.4 as half a stop slower than 1.2, we would shift by -1/2. We then exponentiate and integrate over the frame. For these calculations I am assuming Fstop equals Tstop. Which is not correct, though lenses with similar numbers of elements will not have much difference in T stop I don't think (am no expert!). I couldn't find information on T stops for a lot of lenses which is why I left it out of consideration. I also couldn't find information on how it's measured (are they integrating total lite or measuring intensity at the center of the frame?) which further complicated trying to incorporate it.

In the end, if we apply your argument to exposure, what you're saying is that f/2 ≠ f/2 ≠ f/2. Well, fine. Things are more accurate if we use T-stops, and more accurate still if we abandon T-stops and use some kind if exposure map for each individual lens. And when you said 'For these calculations I am assuming Fstop equals Tstop' you rather undercut the whole point you were making, because you applied exactly the 'lazy' or 'disingenuous' thinking as you were arguing against.

Comparing lenses holistically: When more is taken into account than just pupil diameter, it seems to me at least, m43 lenses are not overpriced. For example the 25mm1.2 is optically pretty amazing when it comes to corner to corner sharpness, longitudinal CA correction (which is hard to correct in post, if my understanding is correct) and bokeh quality (not size).

For half the price one could use the Sony 50mm 2.5. This amounts to being about half a stop dimmer due to vingetting, the bokeh while the same size is much busier. Longitudinal CA is only a smidge worse though. Oh and yeah if you want a sharp full frame you need to stop down to f4 (the 50mm 1.8 by sony is not really worth looking at if optical performance is something you care about).

The Sony GM 50mm 1.2 lens performs very well when stopped down (and is pretty good wide open), but now we are back to being much heavier and costlier than the olympus. I am NOT saying it's a rip off, but I also don't think the lens needs defending as no one seems to doubt it.

The Zeiss 55mm 1.8 has lovely bokeh, but bad Long. CA and needs to be stopped down to 2.8 to be sharp.

Sigma ART lenses start to really shine honestly. Generally very well corrected optically, much less vingetting on FF than other lenses when wide open, and even slightly cheaper priced to the olympus. They are significantly bigger though (the 50mm 1.4 is 815g, versus 410g for the oly).

So what do we make of all this? My take away is that there is no free lunch. All lenses are compromises and on a system-wide level nobody is scamming anyone. If size of the bokeh balls is not your biggest concern, and you care about system size/weight and optical performance, m43 makes a lot of sense. I guess you already know that

I personally am shopping around at the moment (trying to decide if I want to adapt old 4/3 glass to m4/3 bodies, or buy new lenses and potentially change systems or buy new m4/3 lenses) and thus did this analysis to try to compare systems more accurately. Hopefully it was moderately interesting?

If there is anything I should be accounting for that I am not (and you know how I might, e.g. t stops) I'd be curious to hear.

This has now stopped being a careful and precise argument, and has diverged in to a randomised set of views, some of which cannot be sustained with evidence, about different cherry-picked lenses. Mostly it is irrelevant to the issue of Equivalence, because that has nothing to say at all about image quality, bokeh quality and such like. Sometimes well done testing doesn't produce the results you would think. For instance, here is the Lens Rentals test of the Olympus 25mm f/1.2 which you say is 'pretty amazing'.

And here is the smaller, cheaper, lighter Sony ZA 55mm f/1.8, which gives a larger entrance pupil.

We can see that the Sony is as sharp, and at the centre sharper than the Olympus. And remember that these are absolute resolution tests. Considering that the Olympus has to produce double the resolution of the Sony just to match it in a final image, due to being magnified twice as much, then there's not much of a comparison. You have to compare the Olympus lines with the lined for half the lp/mm on the Sony. On FF 10 lp/mm corresponds to 215 lp/ph, whilst on FF that final resolution is given by 20 lp/mm, so if we compare the two at the same final resolution, we find that the Sony gives an MTF of 0.93 in the centre and 0.85 at the edge, whilst the Olympus gives 0.77 in the centre and 0.69 at the edge.

The Sony lens costs $700, and is 65x71mm and weighs 281g. The Olympus costs $1100, and is 70x87mm and weighs 410g. The Olympus costs a lot more, is bigger, weighs a lot more, delivers less light to the sensor and produces a less sharp final image across the field.

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James Stirling
James Stirling Senior Member • Posts: 8,266
Re: Un-equivalence
10

Bassam Guy wrote:

jwilliams wrote:

Muster Mark wrote:

Hi all, I realize this is NOT the topic everyone loves to discuss and I totally understand. I hope no-one feels annoyed by this post. That said, after some investigation I have come to the conclusion that "traditional" equivalence math is only useful as a rough heuristic to get a sense of what DOF will be and NOT a reasonable way to compare individual lenses or judge cost/performance of lenses in different systems.

No, not really. Equivalence is more than DOF or even mainly about DOF. I'll not go into any long winded discussion, but here's an article on this site that is a good read on the subject.

Equivalence is useful if you have any interest in light (and as a photographer, you probably should): Digital Photography Review (dpreview.com)

That is not true. 'Equivalence' implies at least two things. If 43 is your only sensor size then equivalence is meaningless.

Facts are facts whether you use them or not and it applies equally to all systems . People who buy the the £1100 40-150mm F/2.8 pro as opposed to the £195 40-150mm f4-5.6 , presumably appreciate the abilities that two extra stops of light gathering bring at the long end. Or perhaps they just like carrying larger heavier gear.

The problem here is not those who understand equivalence and conclude not unreasonably that it is not of much importance to them . But those who endlessly post factually inaccurate statements about it some of whom amusingly get stroppy when they are called on it. There are some posters here who have been posting BS about equivalence going all the way back to the start of FT despite being corrected literally 100's if not 1000's of times.

That demonstrates an impressive degree of ignorance , denial or straight up lying. As I find it hard to accept that anyone could struggle to comprehend what is after all a simple concept.

For anyone actually interested in the facts about equivalence this post below by Bob covers it very nicely

https://www.dpreview.com/forums/post/65329546

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SonyX
SonyX Contributing Member • Posts: 747
Re: Is my thinking about equivalence right?
1

rgs_45 wrote:

A retired seasoned outdoor photographer told me that don't fret with the "equivalency crap.

He told me, take a light meter and meter a subject (at the time a flower). I just bought my EM-5 mk i with 12-50 kit lens and he had the Nikon 3DS with 24-120/4.0 G (if I can remember correctly). He metered the subject in Aperture priority and chooses F5.6, the shutter speed came to be 1/600th of a second. He then told me to set my my settings at F5.6 and 1/600th of a second and he did the same. Took the photo and when we compare the result through the lcd screen, I could not find any difference in the colors, brightness etc. The only thing I could see different is the DoF. The Nikon 3DS has a much better bokeh (subject to background separation than my m4/3 gear.

Since then, I totally erased all equivalency thoughts I had. Been shooting m4/3 since then. Have a EM1 mk i, EM5 mk ii and just recently the EMX1 since Friday. I also have a Nikon Z6 i with the 24-70/4.0 kit lens just for the heck of it.

If he would use ISO 2 stops higher, and f/5.6 1/2400 - you would not find any difference in the colors, brightness etc. too.

1/2400 vs 1/600 with "a much smaller DOF/ not always better bokeh" - this is where equivalency thoughts are coming back

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JosephScha Veteran Member • Posts: 6,660
Re: Is my thinking about equivalence right?
1

On page 3 of the 2014 article about Equivalence, it says:

"There are a number of factors in play here, most likely dominated by differences in sensor performance, but with other complications such as differences in transmission between lenses. This is why we tend to state that, although equivalence can be used as a guide to low light performance (and a very good guide in most instances), it can't be used to completely predict the differences."

I think this quote basically supports your (the original post's) point.

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js

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Bassam Guy Veteran Member • Posts: 3,118
My mistake

James Stirling wrote:

Bassam Guy wrote:

jwilliams wrote:

Muster Mark wrote:

Hi all, I realize this is NOT the topic everyone loves to discuss and I totally understand. I hope no-one feels annoyed by this post. That said, after some investigation I have come to the conclusion that "traditional" equivalence math is only useful as a rough heuristic to get a sense of what DOF will be and NOT a reasonable way to compare individual lenses or judge cost/performance of lenses in different systems.

No, not really. Equivalence is more than DOF or even mainly about DOF. I'll not go into any long winded discussion, but here's an article on this site that is a good read on the subject.

Equivalence is useful if you have any interest in light (and as a photographer, you probably should): Digital Photography Review (dpreview.com)

That is not true. 'Equivalence' implies at least two things. If 43 is your only sensor size then equivalence is meaningless.

Facts are facts whether you use them or not and it applies equally to all systems . People who buy the the £1100 40-150mm F/2.8 pro as opposed to the £195 40-150mm f4-5.6 , presumably appreciate the abilities that two extra stops of light gathering bring at the long end. Or perhaps they just like carrying larger heavier gear.

Perhaps, then, I don't understand 'equivalence' in digital photography. I thought it was about differences between various sensor sizes, not about differences between different apertures, like the $99 plastic fantastic at 5.6 and the 40-150 pro at 2.8 (which seems to me like common blasé knowledge).

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pinnacle Senior Member • Posts: 2,597
Re: Is my thinking about equivalence right?
4

You were correct that very few want to talk equivalence. It is a beyond useless and worn out topic. There are much, much better ways to invest your time.

Dan

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SrMi
SrMi Senior Member • Posts: 2,397
Re: Is my thinking about equivalence right?
1

I wonder, why do people care about equivalence, and how do they use it?

I am used to FF focal length and FF aperture (DOF) numbers and use the equivalence to select my m43/APS-C/MF lens and aperture. SImilar like (still) translating Fahrenheits into Celsius.

Mark Ransom
Mark Ransom Veteran Member • Posts: 7,670
Re: Is my thinking about equivalence right?
5

David Fell wrote:

rogerstpierre wrote:

I understand equivalency, but I just don't see the purpose if all you got is one system.

I think I do understand and wonder why M43 gets hammered but not APS-C cameras or maybe it's my cognitive bias

I think it's because people find it easy to multiply or divide by 2.  1.5 is harder, and 1.3 (the difference between M4/3 and APS-C) is harder still.

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OP Muster Mark Contributing Member • Posts: 588
Re: Is my thinking about equivalence right?

dkyl wrote:

Muster Mark wrote:

Just look at the lenstip data. The Sony 50mm 2.5 has vignetting of 2.29 stops in the corners. The olympus 25mm1.2 has at most 1.3 stops of vignetting. Th Sony GM 50 1.2 has almost 3 stops of vignetting wide open.
Normal equivalence would say FF at 1.2 is gathering 4x the light as m43 at 1.2. That's not true if it's falling off so much more. Is the difference big? No I don't think so. I don't think most people care so much about vignetting, but it makes the "total light" calculation rather different.

Sure, but you're cherry picking a little here. The Sony 50mm f/1.2 is excellent but one of its design consideration is keeping it relatively compact. So of course something has to give.

I know you wanted to limit the scope of comparison to just Sony since it makes things a little easier, but if you expand your scope there are plenty of examples where FF is not any more prone to vignetting. It's just a design compromise depending on what the designers want to achieve.

Take the Nikon Z 50mm f/1.8 S as an example. Lenstip didn't do a review for the Nikon but DXOMark has a measurements for both the Nikon 50mm f/1.8 and the Olympus 25mm f/1.2.

The Nikon has a T-stop of T1.9 and vignetting at -1.6EV whilst the Olympus comes in at a T-stop of T1.8 and vignetting of -1.2EV.

So now they have practically the same transmission in the middle and only 1/3 stop difference on the peripheral whilst the Nikon covers an imaging area 4 times the size. And the two don't differ that much in size either.

I'm not here to preach FF or anything. I'm happy using both my m43 and FF gear. At the end of the day there are benefits to both system when looking at actual lenses and cameras that are being produced, not just theoretical benefits.

All very good info! My point was just to demonstrate the kind of analysis you need to do to actually compare total light of an exposure and why the equivalence formula (pupil area x sensor area) doesn't actually work in practice.

That Nikon in particular looks like a good argument for the system. It's nice to see weather resistant lenses/cameras becoming the norm.

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-Ian

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OP Muster Mark Contributing Member • Posts: 588
Re: Is my thinking about equivalence right?
1

JosephScha wrote:

On page 3 of the 2014 article about Equivalence, it says:

"There are a number of factors in play here, most likely dominated by differences in sensor performance, but with other complications such as differences in transmission between lenses. This is why we tend to state that, although equivalence can be used as a guide to low light performance (and a very good guide in most instances), it can't be used to completely predict the differences."

I think this quote basically supports your (the original post's) point.

You are spot on. I guess I missed this when I skimmed the article and just payed attention to the equations they used.

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-Ian

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bobn2
bobn2 Forum Pro • Posts: 69,811
Re: Is my thinking about equivalence right?
6

Muster Mark wrote:

All very good info! My point was just to demonstrate the kind of analysis you need to do to actually compare total light of an exposure and why the equivalence formula (pupil area x sensor area) doesn't actually work in practice.

In practice, it works just as well and no better that exposure. When you calculate exposure, you also don't generally take account of factors such as vignetting and lens transmission.

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bobn2
bobn2 Forum Pro • Posts: 69,811
Re: Is my thinking about equivalence right?
1

Muster Mark wrote:

JosephScha wrote:

On page 3 of the 2014 article about Equivalence, it says:

"There are a number of factors in play here, most likely dominated by differences in sensor performance, but with other complications such as differences in transmission between lenses. This is why we tend to state that, although equivalence can be used as a guide to low light performance (and a very good guide in most instances), it can't be used to completely predict the differences."

I think this quote basically supports your (the original post's) point.

You are spot on. I guess I missed this when I skimmed the article and just payed attention to the equations they used.

Better to read it rather than skimming if you want to make any kind of decent critique.

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Is it always wrong
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