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m4/3 and aperture settings: whats the deal?!
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PostPosted: Thu Mar 10, 2011 4:38 pm    Post subject: m4/3 and aperture settings: whats the deal?! Reply with quote

maybe it just takes me longer to catch on than it takes others, but i have been shooting a lot of film lately, a good portion indoors/low light so with open apertures, most typically 1.4.

what i started noticing was that, at the same iso, and at the same aperture setting, i could shoot full frame film at much higher shutter speeds than i could my m4/3 ep2. at first i thought the film cams metering was off, but after experimenting with different film cams, i kept finding the same thing: 1.4 means something different on film vs m4/3!

so, three questions: am i nuts, if not why is this so, and most importantly is there a formula that one could use to determine what the 'actual' aperture setting is (vs what it says on the lens at any given time) on m4/3 cams? is it like multiplied by 2 because of the 2x crop factor, making 1.4 actually 2.8 etc?

thanks!


PostPosted: Fri Mar 11, 2011 10:17 pm    Post subject: Reply with quote

There really should be no difference. If you use the same lens at the same aperture on m4/3 and film to record a given subject, then clearly the photons per unit area in the image must be the same. The difference in sensor size is irrelevant.

I would say any difference would be due to either or both of two factors:
1) The ISO ratings are not correct (either of the film, the sensor or both)
2) The metering of the two cameras is different (e.g film camera tries to preserve highlights whilst digital goes for correct mid-tones). Depending on the scene, it is perfectly possible to use a 1-stop difference in overall exposure without things looking really wrong.

Mark


PostPosted: Fri Mar 11, 2011 10:30 pm    Post subject: Reply with quote

well mark, first thanks for your post, and thats what i thought. i have read though that because the image circle is smaller, not the same amount of light gets through to smaller sensors, like taking a small center crop of large photo. dont know if that makes sense, if the writer knew what he was talking about, or if i interpreted the theory correctly...

all i can say is i definitely notice at least a one stop difference. also, i do recall other random posts on this forum that allude to, though do not directly address, the expectation that one or another fast lens wouldnt be as fast on m4/3.

anyone else want to weigh in? it would be interesting to hear from some of our science majors! Laughing


PostPosted: Fri Mar 11, 2011 11:29 pm    Post subject: Reply with quote

Well, I do have a degree in physics, but it may take me a while to think through the problem from all angles. It's also getting late in the Uk so I will have to pick this up tomorrow.

However, the size of the image circle should not be relevant. The brightness of the lens is determined by the size of the aperture stop, whilst the size of the image circle is determined by the field stop. Reducing the field stop to reduce the image circle does not change the brightness of the image on-axis.

Mark


PostPosted: Fri Mar 25, 2011 9:34 pm    Post subject: Reply with quote

Could be due to the difference in metering. if you use the same lens on a crop body vs a FF, the FF would have a wider angle of view and might lead to a brighter image and shorter shutter speed. Example: ultrawide's exposure.

Also, if you remember in the early days of m4/3, people often comment on the difference in the definition of ISO between Panny and Oly: at the same shutter speed, same brightness, same aperture, Oly has higher reported ISO. So, at the same ISO, Oly would have a slower shutter speed. But I don't know whether Panny or Oly's definition of ISO is closer to film bodies.


PostPosted: Tue Mar 29, 2011 4:08 am    Post subject: Reply with quote

I am afraid that most of us think that there is indeed a difference! I had hoped someone else would tell you but I see this unanswered.

The angle of incidence again! If you were flush enough to use an M8 then the difference would be less....

ANSWER:
Fast lenses with current sensor designs are a luxury that produces flare, smearing and less useful light than the f1.8 version! I base this on my own obs, very restricted and on article from DXO or Luminous, whichever. Manufacturers have a dirty secret. The wider the rear glass, the less is actually picked up as information while some is picked up as noise. This will, I hope, eventually be rectified! Baffling!!!!!! The more the light is baffled, the better behaved is the usual light equation....

One question: do C-Mount lenses obey this queer law you have found? They produce a brighter image that is more telecentric, I hope that is the word, with less indirect light? They should then perhaps be even more valuable than the 35mm lens equivalent, if there could be one!

Google away to find the article. I expect the manufacturers will address this deceit on their part? Not intentional, just regrettable!


PostPosted: Tue Mar 29, 2011 12:39 pm    Post subject: Reply with quote

pat im not quite sure where youre coming out on this? i think you are agreeing that same aperture, same iso, same shutter speed, same subject/lighting, FF comes out brighter than m4/3, indicating for example that 1.4 on FF is really 1.4, but 1.4 on m4/3 is NOT really 1.4, but more like2.0+.

in answer to your question, yes, c mount lenses seem to perform darker (require slower SS) than same aperture on FF...

funny, i think this is both a really interesting and really important topic, so im kind of amazed also at the lack of responses. i mean what could be more important to a photographer than fully understanding how his cam utilizes aperture/SS settings?


PostPosted: Tue Mar 29, 2011 9:01 pm    Post subject: Reply with quote

I still think that there is no fundamental difference.

Consider:
I put a lens on a 35mm camera and point it at a subject. I use spot metering at the centre of the image and it tells me to use a shutter speed of (say) 1/200s with film of ISO200.

I now replace the 35mm camera with a 4/3 camera, but leave the lens fixed. The light intensity at the centre of the picture is obviously IDENTICAL to before. If the camera is at ISO200 it will give me 1/200s shutter speed provided that:
Both cameras are metering to get the same exposure
ISO200 on the film has the same sensitivity to light as ISO200 on the sensor.

But, the pictures I take will obviously be different because the 4/3 sensor will only record about half the height and half the width as the film camera. The first point to note is, if I am using metering averaged of the whole image plane, then I will get a different result simply because the image is different in the two cases.

If I then move the 4/3 camera back so I can record the same image, then the situation between the two cameras is again different and so why should the shutter speed be the same?

Other points:

The f-number of a lens is simply the ratio of two numbers (the focal length and the aperture diameter). If a lens is set to f2, it means the focal length is twice as big as the aperture diameter. This will (I bet) be set very accurately on a modern lens. Who's to say the old manual lens will be so accurately calibrated? Maybe f2 is actually f1.8? On the other hand, maybe the old manual lens has a 20-blade diaphragm that gives a perfect circle whilst the modern lens gives a polygon. How is the "diameter" of the polygon measured? Is the actual aperture area comparable?

Further more, the f-number does not tell you how much light the lens transmits since it does not take into account losses through optics. Modern lenses have such good multi-caotings that transmission is probably above 95% even with a complex zoom lens. Nevertheless, there is scope for two lens of the same focal length set to the same f-number to give different amounts of light in the image.

I believe many camera test web sites measure actual sensitivity of camera sensors. There can be differences between the set sensitivity and the actual sensitivity. I am sure the same applies to film.

In summary:
There is no crop sensor fiddle with regards to aperture and shutter speed. Any differences are due to
    Differences in actual sensitivity
    Differences in metering
    Differences in actual area of aperture
    Differences in light transmission
    Differences in composition


This gives ample scope for big differences in shutter speed to build up.

Mark


PostPosted: Tue Mar 29, 2011 10:08 pm    Post subject: Reply with quote

well, im not sure about your first point, because actual sensitivity of a given roll of film is not relevent to metering of a camera.

here is a more accurate state of the situation: i meter a given scene exactly the same way with the same lens at the same aperture. i have experimented with 3 film cameras and all meter the scene essetntially the same way, while the m4/3 cam meters it over a stop slower.

i am not talking about the RESULTING image, in fact there is no resulting image, im just comparing the metering. so i think that effects your second point. and since i am comparing the SAME lens across different cameras, i think that effects your third and f ourth points.

perhaps im wrong or do not understand your points sufficiently, but i wanted to make sure we are talking about the same scenario.

now think of this: when you put a 2x converter on any cam, it double the maximum aperture you can use on any lens, eg making a 2.0 a 4.0. m4/3 doubles the focal length, like a 2x converter. does it therefore have the same effect on the max aperture?

now it could be that the ep2 meters differently, but over a stop is really differently. it woud be intersting if those who have other m4/3 models try this quick test and see what happens.


PostPosted: Wed Mar 30, 2011 9:08 pm    Post subject: Reply with quote

rbelyell wrote:
now think of this: when you put a 2x converter on any cam, it double the maximum aperture you can use on any lens, eg making a 2.0 a 4.0. m4/3 doubles the focal length, like a 2x converter. does it therefore have the same effect on the max aperture?.



No, this is a not how it works. A teleconverter works by spreading the central portion of the image over a larger area. Since it cannot create light as it does this, the existing light is spread more thinly and so the image gets dimmer. The 4/3 sensor is just recording a smaller part of the image, but the brightness of the image is the same. If I put a mask the size of the 4/3 sensor just in front of the shutter in your film camera, would the unmasked part of the image suddenly get dimmer? Obviously not!

Let's go back to the set-up you are using. You have a lens which is focused on a subject of fixed brightness. The lens forms an image, which could be captured on film, or on the sensor of your m4/3 camera (or on a piece of paper for that matter). The light intensity in that image is what it is. It does not change whatever it is captured on. The light intensity, all else being fixed, is a function only of the lens aperture.

Now try a "thought experiment". Let us suppose that both film and digital cameras have the metering (spot mode to negate the effects of the different format size) set-up so that a neutral grey card is recorded as exactly neutral grey. The shutter speed is calculated from the light intensity and the sensitivity of the film / sensor. If the film and sensor have the same sensitivity, then the shutter speed MUST be the same. There is simply no way there can be a difference. The light is the same, the sensitivity to that light is the same, the end result is the same.....the shutter speed must be the same.

Conclusion: There is no "aperture loss" with m4/3 relative to 35mm. An f2 lens is as bright on m4/3 as it is on 35mm. How can it be otherwise?

If you say there is a difference, then it can only be the result of a difference in metering or in sensitivity. I don't think the ISO rating of your EP2 can be out by one stop (ISO100 is actually ISO50); that would be illegal, and of course in complete contravention of the ISO standard. We are therefore down to metering differences, or (dare I say it) experimental error. Unfortunately I do not have a film camera to make the comparison with.

Mark


PostPosted: Wed Mar 30, 2011 11:45 pm    Post subject: Reply with quote

SXR_Mark wrote:


I believe many camera test web sites measure actual sensitivity of camera sensors. There can be differences between the set sensitivity and the actual sensitivity.



dxomark makes such measurements... http://www.dxomark.com/index.php/eng/Camera-Sensor/Compare/Compare-sensors/

If you compare the Olympus EP2 with, for example, the Panasonic G1 there's a difference of about a stop between the measured sensitivities of the two cameras at the same settings.


PostPosted: Thu Mar 31, 2011 6:17 pm    Post subject: Reply with quote

thanks john, looking at this chart my personal findings finally make some sense. what doesnt make sense is how olymous can make a sensor that meters exactly the same at iso 200 as it does at iso 100! and how it can consistently meter 3/4 stop slower at all iso,s over 100! that is truly amazing and frankly it pisses me off! one needs to have confidence in ones settings, and to be off by this much across the board is just awful. they must do it to improve their IQ numbers relative to iso, because their iso 800 IQ is really closer to FF iso 400 IQ! so their proclaimed 'high' iso performane is just a lie.


PostPosted: Thu Mar 31, 2011 8:25 pm    Post subject: Reply with quote

sichko wrote:
dxomark makes such measurements...


If there measurements are real, it is quite scandalous (that Olympus can make their ISO so wrong).

But, surely there is something very obviously wrong with the DXO measurements. For all the recent Olympus cameras they say that the camera at ISO200 has the same sensitivity as at ISO100. Well, I have an EPL1 and I can say categorically that this is not the case. Tripod mounting the camera and pointing it at a target illuminated with a lamp I get an exact doubling of shutter speed going from ISO200 to ISO100

I have also compared my E3 (which DXO measure to have an accurate trend) and the EPL1 using the same lens. The two cameras give a shutter speed that is never more than 1/3 stop different (and mostly identical) no matter how many times I repeat the test. I certainly do not see the considerable difference between the EPL1 and E3 that DXO report.

I do not know how DXO make their measurements, but they look like BS to me.

Mark


PostPosted: Thu Mar 31, 2011 8:44 pm    Post subject: Reply with quote

mark i think a comparison you could make with a non olympus sensored camera might be more meaningful.

your finding on the differences between iso 100 and 200 on epl1 vs dxo is interesting. i did same test with ep2 and got same result you did, the sensitivity reacted as it should when increasing iso by 1 stop.


PostPosted: Thu Mar 31, 2011 9:01 pm    Post subject: Reply with quote

rbelyell wrote:
mark i think a comparison you could make with a non olympus sensored camera might be more meaningful.


And if I had one, I would do so.'Laughing'

Mark


PostPosted: Thu Mar 31, 2011 9:36 pm    Post subject: Reply with quote

you like olympus, no? Very Happy mee too!


PostPosted: Thu Mar 31, 2011 9:58 pm    Post subject: Reply with quote

Oh Yes!! Such nice colour rendition, saturated but not artificial. And great glass as well - so sharp. I still think the E3 is a truly great camera (though not perfect of course).

Mind you, for my EPL1 the only true m4/3 lenses I have are the Panasonic 20mm and 14mm pancakes (both of which I really like). Although I have the 4/3 to m4/3 adapter, I don't use it now I have both pancakes. If I want something different, I will go for a MF lens.

Mark


PostPosted: Thu Mar 31, 2011 11:10 pm    Post subject: Reply with quote

SXR_Mark wrote:
sichko wrote:
dxomark makes such measurements...

If there measurements are real, it is quite scandalous (that Olympus can make their ISO so wrong).


I agree - but Olympus is not the only guilty party.

Quote:
But, surely there is something very obviously wrong with the DXO measurements. For all the recent Olympus cameras they say that the camera at ISO200 has the same sensitivity as at ISO100.

Similar behaviour is seen for other cameras such as the Nikon D300. If the DXO measurements are true then it implies that the native or base ISO is 200 - or maybe something less. The DXO measurements for the D300 include a point for ISO 100. In fact this is not an option in the D300 settings. The available ISO settings go down to ISO 200 and are the listed (AFAIK - I haven't actually checked the manual) as "Lo 0.3", "Lo 0.7" and "Lo 1.0". Presumably "Lo 1.0" corresponds to ISO 100. The manual (again AFAIK) warns against difficulties when using these settings. Presumably they exist to allow long shutter times when you don't have an ND filter. Some have suggested that the native ISO of the D300 is ~ 160 so that use of "Lo 0.3" may be optimum.

Quote:
Tripod mounting the camera and pointing it at a target illuminated with a lamp I get an exact doubling of shutter speed going from ISO200 to ISO100

What do the histograms look like ?

A Google search reveals lots of discussion about "camera sensor native ISO". There has been some discussion on this forum. The problem is not confined to Olympus - or Nikon. So, for example, the Canon 1Ds MkII shows a lower S/N ratio at ISO 50 than it does at ISO 100 (measurements not made by DXO).


PostPosted: Tue Apr 05, 2011 11:30 pm    Post subject: Reply with quote

Thanks, John for referring to the article I mentioned in my earlier reply.

The sensor is at the bottom of a small well that blocks oblique light from registering with the sensor.

Those who wish to test this should use a slow lens, not a fast lens on a large aperture! The point of the tests is that a f1.4 lens is effectively "wasted", apart from arty flare, as the camera sensors, except M8 (and M9?) cannot pick up the extra light.

This is due to the design limitations of all cheap sensors, used in most cameras! Not confined to Olympus!

The sensor is at the bottom of a small well that blocks oblique light from registering with the sensor. As fast lenses have very large exit apertures, allowing all that light onto film, it only registers as a slow lens on a sensor!

Sell me all your fast glass! As designs improve, sensors will pick up the extra light, but until then, a f2 lens, wide open, is maybe as "fast" as f1.4 lens wide open. Those measurements are a guess, but you see the point? The sensor is at the bottom of a small well that blocks oblique light from registering with the sensor.

I triplicated the relevant sentence as it is a design flaw! Telecentric lenses, as some c-mounts, should give a truer result on these sensors? The light is parallel to the axis and more of it strikes the sensor, less is killed by the walls of the recess in which the sensor is embedded?

That is my understanding, but some tests I performed on 4/3, not m4/3, sensors showed greater sensitivity!!! The distance from the sensor meant that more of the transmitted light hit a similarly recessed sensor? The m4/3 sensor is very close to the exit opening of the lens and more of the light is lost due to acute angle of incidence.

Does anyone disagree?


PostPosted: Wed Apr 06, 2011 1:06 am    Post subject: Reply with quote

pat, are you saying only m4/3 sensors exist 'at the bottom of a well' and so lose this 'oblique' light from large apertures? because ive had a lot of cameras w lots of sensors and never noted this effect before...just referring to rebcent cams, didnt happen on sony a100, sigma sd14 or canon 5d...


PostPosted: Thu Oct 27, 2011 1:39 pm    Post subject: Reply with quote

Glad to find this olympus thread


PostPosted: Thu Oct 27, 2011 1:57 pm    Post subject: Reply with quote

I realize this is an old thread, but I only spotted it now as it was bumped, and can't help myself:

pat donnelly wrote:

The sensor is at the bottom of a small well that blocks oblique light from registering with the sensor.

Those who wish to test this should use a slow lens, not a fast lens on a large aperture! The point of the tests is that a f1.4 lens is effectively "wasted", apart from arty flare, as the camera sensors, except M8 (and M9?) cannot pick up the extra light.

This is due to the design limitations of all cheap sensors, used in most cameras! Not confined to Olympus!


The angle of incidence issue only concerns the edges of a sensor when the rear of the lens is close to it. This is why it's a problem with Leica M8/M9 in particular, because they are full frame and have the lenses often nearly touching the sensor (due to no mirror & rangefinder lenses designed to take advantage of this).

However, with adapted lenses the adapter adds the necessary thickness to place the lens at the exact same distance it would normally be from the film/sensor, i.e. 4/3 vs other camera makes absolutely no difference here. An M42 lens adapted to 4/3 is exactly the same distance from the sensor as when adapted to Canon EOS, hence there is no difference in angle of incidence.

Furthermore, the light at the centre of the frame hits the sensor straight on, and only becomes shallower when moving away from the centre, meaning that the smaller sensor in 4/3 cameras actually has much less issues here since only the centre portion of the image is recorded. So even if you adapt RF lenses (like Leica) to 4/3, the issues are much less severe on the edges of the small 4/3 sensor than on the edges of the FF Leica M8 sensor.

Remember that the lens does not know the size of the sensor and draws the same image regardless of what camera, if any, it is on, so the light coming in to the camera is exactly the same, same distance, and same angle, independent of sensor size.

pat donnelly wrote:

The sensor is at the bottom of a small well that blocks oblique light from registering with the sensor. As fast lenses have very large exit apertures, allowing all that light onto film, it only registers as a slow lens on a sensor!


The smaller opening in 4/3 cameras may indeed block some light, but not light that would register with the sensor. The blocked light comes in at an angle that would not have hit the smaller sensor anyhowit would have hit the edges of a larger sensor, e.g. FF, and hence the total amount of light hitting the FF sensor would have been greater (which is why larger sensors are better!), but the amount of light in a given area is the same (which is what matters for exposure).

Also, if a camera blocks some light in a way to serve as an additional aperture stop, it will be instantly visible in out of focus circles of confusiondo your f/1.4 lenses give rectangular bokeh on 4/3? If not, light is not being blocked in a way that would darken the recorded area of the image.


PostPosted: Sat Oct 29, 2011 12:27 am    Post subject: Reply with quote

Er, this has got me a bit confused - perhaps because I should be in bed by now! It seems that

at the same iso, and at the same aperture setting, i could shoot full frame film at much higher shutter speeds than i could my m4/3 ep2. at first i thought the film cams metering was off, but after experimenting with different film cams, i kept finding the same thing: 1.4 means something different on film vs m4/3!

But you then say that

i am not talking about the RESULTING image, in fact there is no resulting image, im just comparing the metering.[...using...] the SAME lens across different cameras

With the greatest respect and regard to everyone who has considered the theory of lenses and exposure here, surely without actual results to compare this is an incompletely-informed discussion. If you use a constantly illuminated subject and expose colour reversal film in the film cameras, and then use the digital camera at the same setting, then - and only then - will you know how they are all actually behaving. Except you may introduce some small variables in the film cameras' comparisons because of shutter speed variations or whatever, but hopefully they'll be relatively small.

If you get correctly exposed results from all the cameras, then you know that either the EP2's meter is somehow calibrated differently, or its sensor's "ISO sensitivity" differs in some way. But the key thing is - do its results concur with the other cameras or not.

I hope this doesn't come over as pedantic or even a bit dim - it is way past my bed-time . Smile


PostPosted: Sat Oct 29, 2011 12:46 am    Post subject: Reply with quote

sichko wrote:
So, for example, the Canon 1Ds MkII shows a lower S/N ratio at ISO 50 than it does at ISO 100 (measurements not made by DXO).


That's because Canon's 50 ISO is a resampled 100 ISO.

Reg. the original question, there is only one way to find out, and that is, to meter the scene appropriately with a hand meter.
Then set the cameras in manual mode, apply manually the time to the cameras and the aperture on the lenses,
and verify the results (shooting obviously in a controlled light environment and on a tripod).