Is the Panasonic 25mm a real f/1.4 lens?

Started 8 months ago | Discussions
Pixnat2
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Is the Panasonic 25mm a real f/1.4 lens?
8 months ago

I'm interested on a 25mm for my E-M1. We have two native 25mm now : a f/1.4 and a f/1.8 lens.

But there's some questions about the fact the Panasonic 25mm is a real f/1.4 lens :

What do you think? Is it possible that the Panaleica is more a f/1.7 rather than a f/1.4 lens?

What are your thoughts about it?

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007peter
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*Realistic Expectation*, slight 0.3ev T-Stop lost it to be expected
In reply to Pixnat2, 8 months ago

I share the same thought as you (for the most part). However, you must keep your Expectation Realistic & Reasonable. A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

For example, the DXO Tested T Stops are:

  • 2.0 T-Stop for Panasonic 20mm F1.7 (II) | -0.3ev
  • 2.1 T-Stop for Panasonic 20mm F1.7 (I) | -0.4ev
  • 2.2 T-Stop for Olympus 12mm F2 | -0.2ev
  • 2.0 T-Stop for Olympus 45mm F1.8 | -0.2ev
  • 2.0 T-Stop for Olympus 75mm F1.8 | -0.2ev

Based on DXO results,  I would say Olympus is more consistent with narrower gap between Lab Tested "claimed" vs real-world tested results.  It would surprise me if the new Olympus 25/1.8 is tested exactly at 2.0 T-Stop.

Either way, I wouldn't worry about it.  Since Olympus is the cheaper of the two, I just buy it over Panasonic.

Pixnat2 wrote:

I'm interested on a 25mm for my E-M1. We have two native 25mm now : a f/1.4 and a f/1.8 lens.

But there's some questions about the fact the Panasonic 25mm is a real f/1.4 lens :

What do you think? Is it possible that the Panaleica is more a f/1.7 rather than a f/1.4 lens?

What are your thoughts about it

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Pixnat2
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Agree.
In reply to 007peter, 8 months ago

007peter wrote:

Hi Peter, thanks for your answer

I share the same thought as you (for the most part). However, you must keep your Expectation Realistic & Reasonable. A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

For example, the DXO Tested T Stops are:

  • 2.0 T-Stop for Panasonic 20mm F1.7 (II) | -0.3ev
  • 2.1 T-Stop for Panasonic 20mm F1.7 (I) | -0.4ev
  • 2.2 T-Stop for Olympus 12mm F2 | -0.2ev
  • 2.0 T-Stop for Olympus 45mm F1.8 | -0.2ev
  • 2.0 T-Stop for Olympus 75mm F1.8 | -0.2ev

Yes, I've seen it. Panasonic primes seems to be consistently 0.3ev darker than the claims, while Olympus 0.2ev.

Based on DXO results, I would say Olympus is more consistent with narrower gap between Lab Tested "claimed" vs real-world tested results. It would surprise me if the new Olympus 25/1.8 is tested exactly at 2.0 T-Stop.

Robin Wong seems to think that it's actually brighter than its claims. It would be a good surprise if DXO confirms it (though I doubt it).

Either way, I wouldn't worry about it. Since Olympus is the cheaper of the two, I just buy it over Panasonic.

That's my thinking now, though I like the pictures I've seen with the Panasonic. I think I'll buy the Olympus, but I'm curious about the diffrences between both.

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tt321
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Re: *Realistic Expectation*, slight 0.3ev T-Stop lost it to be expected
In reply to 007peter, 8 months ago

007peter wrote:

I share the same thought as you (for the most part). However, you must keep your Expectation Realistic & Reasonable. A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

For example, the DXO Tested T Stops are:

  • 2.0 T-Stop for Panasonic 20mm F1.7 (II) | -0.3ev
  • 2.1 T-Stop for Panasonic 20mm F1.7 (I) | -0.4ev
  • 2.2 T-Stop for Olympus 12mm F2 | -0.2ev
  • 2.0 T-Stop for Olympus 45mm F1.8 | -0.2ev
  • 2.0 T-Stop for Olympus 75mm F1.8 | -0.2ev

Based on DXO results, I would say Olympus is more consistent with narrower gap between Lab Tested "claimed" vs real-world tested results. It would surprise me if the new Olympus 25/1.8 is tested exactly at 2.0 T-Stop.

Either way, I wouldn't worry about it. Since Olympus is the cheaper of the two, I just buy it over Panasonic.

You are right.

I looked at a number of FF 50/1.4 lenses (Canon, two versions of Nikkors, and a Sony) and they are all T1.6 so the PL25 is a bit worse in class, but not too radically different.

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EarthQuake
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Re: Agree.
In reply to Pixnat2, 8 months ago

Pixnat2 wrote:

007peter wrote:

Hi Peter, thanks for your answer

I share the same thought as you (for the most part). However, you must keep your Expectation Realistic & Reasonable. A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

For example, the DXO Tested T Stops are:

  • 2.0 T-Stop for Panasonic 20mm F1.7 (II) | -0.3ev
  • 2.1 T-Stop for Panasonic 20mm F1.7 (I) | -0.4ev
  • 2.2 T-Stop for Olympus 12mm F2 | -0.2ev
  • 2.0 T-Stop for Olympus 45mm F1.8 | -0.2ev
  • 2.0 T-Stop for Olympus 75mm F1.8 | -0.2ev

Yes, I've seen it. Panasonic primes seems to be consistently 0.3ev darker than the claims, while Olympus 0.2ev.

Based on DXO results, I would say Olympus is more consistent with narrower gap between Lab Tested "claimed" vs real-world tested results. It would surprise me if the new Olympus 25/1.8 is tested exactly at 2.0 T-Stop.

Robin Wong seems to think that it's actually brighter than its claims. It would be a good surprise if DXO confirms it (though I doubt it).

Either way, I wouldn't worry about it. Since Olympus is the cheaper of the two, I just buy it over Panasonic.

That's my thinking now, though I like the pictures I've seen with the Panasonic. I think I'll buy the Olympus, but I'm curious about the diffrences between both.

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Fstop and tstop are two different concepts, Fstop is the physical size ratio of the aperture to focal length, tstop is how much light the lens lets through, and varies by the type of glass elements used and the optical design, no lenses have a 1:1 tstop to fstop ratio nor are any manufacturers "lying" about tstops when they list fstops. This is why cine lenses are rated as t-stops not f-stops.

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Pixnat2
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At those apertures 0.1ev is significant
In reply to tt321, 8 months ago

tt321 wrote:

007peter wrote:

I share the same thought as you (for the most part). However, you must keep your Expectation Realistic & Reasonable. A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

For example, the DXO Tested T Stops are:

  • 2.0 T-Stop for Panasonic 20mm F1.7 (II) | -0.3ev
  • 2.1 T-Stop for Panasonic 20mm F1.7 (I) | -0.4ev
  • 2.2 T-Stop for Olympus 12mm F2 | -0.2ev
  • 2.0 T-Stop for Olympus 45mm F1.8 | -0.2ev
  • 2.0 T-Stop for Olympus 75mm F1.8 | -0.2ev

Based on DXO results, I would say Olympus is more consistent with narrower gap between Lab Tested "claimed" vs real-world tested results. It would surprise me if the new Olympus 25/1.8 is tested exactly at 2.0 T-Stop.

Either way, I wouldn't worry about it. Since Olympus is the cheaper of the two, I just buy it over Panasonic.

You are right.

I looked at a number of FF 50/1.4 lenses (Canon, two versions of Nikkors, and a Sony) and they are all T1.6 so the PL25 is a bit worse in class, but not too radically different.

When we think about the price difference between, a f/1.4 and f/1.2 lens, it's like 500$ for 0.1 EV

More seriously, the claimed difference between f/1.4 and f/1.8 is 0.4ev. It's not a good surprise if it's reduced to 0.3EV in reality (supposing the Oly 25mm will be 2 Tstop)

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Pixnat2
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Re: Agree.
In reply to EarthQuake, 8 months ago

EarthQuake wrote:

Pixnat2 wrote:

007peter wrote:

Hi Peter, thanks for your answer

I share the same thought as you (for the most part). However, you must keep your Expectation Realistic & Reasonable. A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

For example, the DXO Tested T Stops are:

  • 2.0 T-Stop for Panasonic 20mm F1.7 (II) | -0.3ev
  • 2.1 T-Stop for Panasonic 20mm F1.7 (I) | -0.4ev
  • 2.2 T-Stop for Olympus 12mm F2 | -0.2ev
  • 2.0 T-Stop for Olympus 45mm F1.8 | -0.2ev
  • 2.0 T-Stop for Olympus 75mm F1.8 | -0.2ev

Yes, I've seen it. Panasonic primes seems to be consistently 0.3ev darker than the claims, while Olympus 0.2ev.

Based on DXO results, I would say Olympus is more consistent with narrower gap between Lab Tested "claimed" vs real-world tested results. It would surprise me if the new Olympus 25/1.8 is tested exactly at 2.0 T-Stop.

Robin Wong seems to think that it's actually brighter than its claims. It would be a good surprise if DXO confirms it (though I doubt it).

Either way, I wouldn't worry about it. Since Olympus is the cheaper of the two, I just buy it over Panasonic.

That's my thinking now, though I like the pictures I've seen with the Panasonic. I think I'll buy the Olympus, but I'm curious about the diffrences between both.

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Fstop and tstop are two different concepts, Fstop is the physical size ratio of the aperture to focal length, tstop is how much light the lens lets through, and varies but the type of glass elements used, no lenses have a 1:1 tstop to fstop ratio nor are any manufacturers "lying" about tstops when they list fstops. This is why cine lenses are rated as t-stops not f-stops.

Yes, I'm aware of that, though some lenses have 1:1 Tstop for Fstop : http://www.dxomark.com/Lenses/Canon/Canon-EF-35mm-F2-IS-USM. Transmission can be influenced by many things like elements and coating as you said, but it could be influenced by the actual aperture of the lens too.

If it was only this DXO measure, It wouldn't have raised the question. But Robin Wong (I think he is honest) and other threads seems to find that the Panasonic is a bit darker than it claims.

Moreover, I never imply someone is lying, I'm just curious.

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tt321
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Re: At those apertures 0.1ev is significant
In reply to Pixnat2, 8 months ago

Pixnat2 wrote:

tt321 wrote:

007peter wrote:

I share the same thought as you (for the most part). However, you must keep your Expectation Realistic & Reasonable. A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

For example, the DXO Tested T Stops are:

  • 2.0 T-Stop for Panasonic 20mm F1.7 (II) | -0.3ev
  • 2.1 T-Stop for Panasonic 20mm F1.7 (I) | -0.4ev
  • 2.2 T-Stop for Olympus 12mm F2 | -0.2ev
  • 2.0 T-Stop for Olympus 45mm F1.8 | -0.2ev
  • 2.0 T-Stop for Olympus 75mm F1.8 | -0.2ev

Based on DXO results, I would say Olympus is more consistent with narrower gap between Lab Tested "claimed" vs real-world tested results. It would surprise me if the new Olympus 25/1.8 is tested exactly at 2.0 T-Stop.

Either way, I wouldn't worry about it. Since Olympus is the cheaper of the two, I just buy it over Panasonic.

You are right.

I looked at a number of FF 50/1.4 lenses (Canon, two versions of Nikkors, and a Sony) and they are all T1.6 so the PL25 is a bit worse in class, but not too radically different.

When we think about the price difference between, a f/1.4 and f/1.2 lens, it's like 500$ for 0.1 EV

More seriously, the claimed difference between f/1.4 and f/1.8 is 0.4ev. It's not a good surprise if it's reduced to 0.3EV is reality (supposing the Oly 25mm will be 2 Tstop)

This also depends on how the manufacturers and DXO do their rounding. If you put the PL25 on a camera and monitor the F stops the camera can set, you will see 1.4, 1.6, 1.8 and 2. So in their terminology 1.4 is 1/3 EV faster than 1.6 which is again 1/3 EV faster than 1.8 which is 1/3 EV faster than 2.0. There is no 1.7 in spite of Panasonic liking that number - and disliking 1.8, on their primes. On the other hand, presumably DXO has no such obligations and puts their T numbers where the nearest approximate is. So T1.7 is better than T1.8, but this 'better' could be between almost 0 and almost 0.2 because of the precision of the reported T numbers.

According to this patent, the PL25 is actually F1.44319, any narrower it should be called F1.5! It's also slightly longer than 25, at 25.6692. So if the Olympus turns out to be 23.5571 and F1.75812 just to throw some arbitrary numbers around there could be only F0.3 in the difference. And this gets translated to T0.3 difference with one at 1.7 and the other at 2, very roughly speaking and massively into the realms of speculation now...

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Steen Bay
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The t-stop also depends on the camera used
In reply to 007peter, 8 months ago

007peter wrote:

I share the same thought as you (for the most part). However, you must keep your Expectation Realistic & Reasonable. A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

For example, the DXO Tested T Stops are:

  • 2.0 T-Stop for Panasonic 20mm F1.7 (II) | -0.3ev
  • 2.1 T-Stop for Panasonic 20mm F1.7 (I) | -0.4ev
  • 2.2 T-Stop for Olympus 12mm F2 | -0.2ev
  • 2.0 T-Stop for Olympus 45mm F1.8 | -0.2ev
  • 2.0 T-Stop for Olympus 75mm F1.8 | -0.2ev

Based on DXO results, I would say Olympus is more consistent with narrower gap between Lab Tested "claimed" vs real-world tested results. It would surprise me if the new Olympus 25/1.8 is tested exactly at 2.0 T-Stop.

We don't really know what the t-stop is for the lens itself. DxO's tests show the t-stop for a given camera/lens combination. For example, the t-stop of the 25/1.4 is 1.7 on E-M1 and 1.8 on E-M5. The article below shows how the t-stop of the same lens can vary considerably from camera to camera. The t-stop of the 25/1.4 could theoretically be 1.4 if it was tested on a camera without ' pixel vignetting'.

http://www.dxomark.com/Reviews/F-stop-blues

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Pixnat2
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Re: At those apertures 0.1ev is significant
In reply to tt321, 8 months ago

tt321 wrote:

Pixnat2 wrote:

tt321 wrote:

007peter wrote:

I share the same thought as you (for the most part). However, you must keep your Expectation Realistic & Reasonable. A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

For example, the DXO Tested T Stops are:

  • 2.0 T-Stop for Panasonic 20mm F1.7 (II) | -0.3ev
  • 2.1 T-Stop for Panasonic 20mm F1.7 (I) | -0.4ev
  • 2.2 T-Stop for Olympus 12mm F2 | -0.2ev
  • 2.0 T-Stop for Olympus 45mm F1.8 | -0.2ev
  • 2.0 T-Stop for Olympus 75mm F1.8 | -0.2ev

Based on DXO results, I would say Olympus is more consistent with narrower gap between Lab Tested "claimed" vs real-world tested results. It would surprise me if the new Olympus 25/1.8 is tested exactly at 2.0 T-Stop.

Either way, I wouldn't worry about it. Since Olympus is the cheaper of the two, I just buy it over Panasonic.

You are right.

I looked at a number of FF 50/1.4 lenses (Canon, two versions of Nikkors, and a Sony) and they are all T1.6 so the PL25 is a bit worse in class, but not too radically different.

When we think about the price difference between, a f/1.4 and f/1.2 lens, it's like 500$ for 0.1 EV

More seriously, the claimed difference between f/1.4 and f/1.8 is 0.4ev. It's not a good surprise if it's reduced to 0.3EV is reality (supposing the Oly 25mm will be 2 Tstop)

This also depends on how the manufacturers and DXO do their rounding. If you put the PL25 on a camera and monitor the F stops the camera can set, you will see 1.4, 1.6, 1.8 and 2. So in their terminology 1.4 is 1/3 EV faster than 1.6 which is again 1/3 EV faster than 1.8 which is 1/3 EV faster than 2.0. There is no 1.7 in spite of Panasonic liking that number - and disliking 1.8, on their primes. On the other hand, presumably DXO has no such obligations and puts their T numbers where the nearest approximate is. So T1.7 is better than T1.8, but this 'better' could be between almost 0 and almost 0.2 because of the precision of the reported T numbers.

According to this patent, the PL25 is actually F1.44319, any narrower it should be called F1.5! It's also slightly longer than 25, at 25.6692. So if the Olympus turns out to be 23.5571 and F1.75812 just to throw some arbitrary numbers around there could be only F0.3 in the difference. And this gets translated to T0.3 difference with one at 1.7 and the other at 2, very roughly speaking and massively into the realms of speculation now...

Very interesting insight, even if it's speculation, thanks for that!

We're in the world of fractions and decimals :-). It may seem insignificant for some, but important (and interesting) for others.

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Pixnat2
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Very interesting!
In reply to Steen Bay, 8 months ago

Steen Bay wrote:

007peter wrote:

I share the same thought as you (for the most part). However, you must keep your Expectation Realistic & Reasonable. A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

For example, the DXO Tested T Stops are:

  • 2.0 T-Stop for Panasonic 20mm F1.7 (II) | -0.3ev
  • 2.1 T-Stop for Panasonic 20mm F1.7 (I) | -0.4ev
  • 2.2 T-Stop for Olympus 12mm F2 | -0.2ev
  • 2.0 T-Stop for Olympus 45mm F1.8 | -0.2ev
  • 2.0 T-Stop for Olympus 75mm F1.8 | -0.2ev

Based on DXO results, I would say Olympus is more consistent with narrower gap between Lab Tested "claimed" vs real-world tested results. It would surprise me if the new Olympus 25/1.8 is tested exactly at 2.0 T-Stop.

We don't really know what the t-stop is for the lens itself. DxO's tests show the t-stop for a given camera/lens combination. For example, the t-stop of the 25/1.4 is 1.7 on E-M1 and 1.8 on E-M5. The article below shows how the t-stop of the same lens can vary considerably from camera to camera. The t-stop of the 25/1.4 could theoretically be 1.4 if it was tested on a camera without ' pixel vignetting'.

http://www.dxomark.com/Reviews/F-stop-blues

Thanks Steen Bay for your insight and link. The DXO article is very interesting. Their conclusion should keep us aware :

DxO Mark measurements are based on an assessment of the effective T-stop for every camera-lens combination. T-stop, a measurement widely used in the industry, especially the motion picture industry, is a measurement of the effective quantity of light transmitted by the lens at a certain f-stop. Thus, T-stop takes into account every reflection or absorption due to the lens. It can be considered as an effective (versus theoretical) way of measuring the aperture.

A possible conclusion of DxO Labs’ measurements is that photographers should consider with caution the maximum f-numbers advertised for lenses. Indeed, depending on the performance of their camera body and sensor, they may not effectively benefit as they expect from such wide apertures.

Enlightning

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Dr_Jon
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Re: Agree.
In reply to Pixnat2, 8 months ago

I would assume Canon just rounded the F-stop up, perhaps not to compete too closely with the 35/1.4 (it's probably a f1.8/1.9 really). That is really interesting though. Do note faster lenses will always loose more light going from F to T stops as the light hits the sensor at a bigger range of angles and less makes it down to the pixels (which are quite a way down).

I don't personally believe Robin Wong about the Olympus being faster. I also wonder if he was using a camera with a sensor which is particularly bad for high incidence angle light rays. That would then be bad with all fast lenses. I will be very interested to see the T-rating of the Panny f1.2 on a bunch of sensors.

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duartix
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Re: Is the Panasonic 25mm a real f/1.4 lens?
In reply to Pixnat2, 8 months ago

Pixnat2 wrote:

What are your thoughts about it?

Cheers!

My thoughts are that this thread is too much focused on numbers (even though there is a very interesting reply on how the differences in precise focal length may add up to that).

The best of Robin Wong's test is the the pictures themselves. Personally I think the bokeh on the Oly is far superior to the Panny. The CA is also something that jumps into your eyes, but I guess that could be inverted if you changed bodies. In the end, the F-stop, is what matters less...

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Fygaren
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Re: Is the Panasonic 25mm a real f/1.4 lens?
In reply to Pixnat2, 8 months ago

The f-stop has to do with the actual size of the aperture compared to focal lenght, and not with light transmission. The DoF should be "f1.4" no matter what the T-stop is. Im guessing its between f1.35 and 1.49.

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Fygaren
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Re: Is the Panasonic 25mm a real f/1.4 lens?
In reply to Fygaren, 8 months ago

Sorry, f1.35-f1.44

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Ulfric M Douglas
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Re: At those apertures 0.1ev is significant
In reply to tt321, 8 months ago

tt321 wrote:

Pixnat2 wrote:

tt...

This also depends on how the manufacturers and DXO do their rounding. If you put the PL25 on a camera and monitor the F stops the camera can set, you will see 1.4, 1.6, 1.8 and 2. So in their terminology 1.4 is 1/3 EV faster than 1.6 which is again 1/3 EV faster than 1.8 which is 1/3 EV faster than 2.0. There is no 1.7 in spite of Panasonic liking that number - and disliking 1.8, on their primes. On the other hand, presumably DXO has no such obligations and puts their T numbers where the nearest approximate is. So T1.7 is better than T1.8, but this 'better' could be between almost 0 and almost 0.2 because of the precision of the reported T numbers.

According to this patent, the PL25 is actually F1.44319, any narrower it should be called F1.5! It's also slightly longer than 25, at 25.6692. So if the Olympus turns out to be 23.5571 and F1.75812 just to throw some arbitrary numbers around there could be only F0.3 in the difference. And this gets translated to T0.3 difference with one at 1.7 and the other at 2, very roughly speaking and massively into the realms of speculation now...

Good post TT,

(On m4/3rds forum a lot of posters got the wrong end of the stick and assumed Robin was saying the PLF1.4 was dimmer than the new Olympus.)

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Managarm
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F-Stop = theoretical value, T-Stop = practical value
In reply to 007peter, 8 months ago

007peter wrote:

A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

Doesn't have to do with different testing conditions or manufacturers cheating. F- and T-Stops are simply the results of two different kinds of methods.

F-Stops are just calculated from the diameter of the entrance pupil and the focal length of the lens. F = focal length / diameter of entrance pupil

T-Stops are actually measured values of the transmission of light trough the lens.

Since you will always lose some light when it travels through lenses (due to reflection & absorbtion & vignetting) the F-Stop is at best equal to the T-Stop. The more complex the lens design (more elements) and the greater the aperture, the higher the loss of light and hence the difference between F-Stop and T-Stop.

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Pixnat2
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Interesting answers. DXO as THE reliable source?
In reply to Pixnat2, 8 months ago

Thanks for all those interesting answers.

I think the most interesting thing is the DXO article pointed by Steen Bay :

http://www.dxomark.com/Reviews/F-stop-blues

DXO shows that Tstop (measurement of the effective quantity of light transmitted by the lens at a certain f-stop) is a an effective (versus theoretical) way of measuring the aperture.

If a f/1.4 (theoretical aperture) lens behave like an f/1.7 (effective aperture) lens, the gain of speed is less than the manufacturer advertise.

This may be not so important for f/1.8 and above lenses, but very important for really fast and expensive lenses like f/1.2 or 1.4. Don't we buy them because they are ... fast?

What about the Canon 50mm f/1.2 (1500$) being 1.4Tstop vs the Canon 50mm f/1.4 (350$) being 1.5 Tstop on a 6D? 1200$ for 0.1Tstop difference?

Let's be aware of this when we buy ultra-fast lenses! (If it's important for you of course!)

So, is DXO the realiable source?

Let's see what they'll find about our Nocticron!

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Dheorl
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Re: Is the Panasonic 25mm a real f/1.4 lens?
In reply to Pixnat2, 8 months ago

Pixnat2 wrote:

I'm interested on a 25mm for my E-M1. We have two native 25mm now : a f/1.4 and a f/1.8 lens.

But there's some questions about the fact the Panasonic 25mm is a real f/1.4 lens :

That was in a very uncontrolled environment making it hard to tell how much was down to the camera making correction or just metering slightly differently. For example is the olympus does stronger vignetting correction on it's own lenses than the panny the metering in total will measure the scene differently.

I'm very doubtful of that test. For instance different looking bokeh can cause the DoF to look different. If someone took a photo of a target with a front/back ruler like lenstip (and probably other review sites use) then we might actually be able to compare them accurately.

Lenses t-stop should never match their f-stop.

What do you think? Is it possible that the Panaleica is more a f/1.7 rather than a f/1.4 lens?

No.

What are your thoughts about it?

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Dheorl
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Re: Agree.
In reply to Pixnat2, 8 months ago

Pixnat2 wrote:

EarthQuake wrote:

Pixnat2 wrote:

007peter wrote:

Hi Peter, thanks for your answer

I share the same thought as you (for the most part). However, you must keep your Expectation Realistic & Reasonable. A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

For example, the DXO Tested T Stops are:

  • 2.0 T-Stop for Panasonic 20mm F1.7 (II) | -0.3ev
  • 2.1 T-Stop for Panasonic 20mm F1.7 (I) | -0.4ev
  • 2.2 T-Stop for Olympus 12mm F2 | -0.2ev
  • 2.0 T-Stop for Olympus 45mm F1.8 | -0.2ev
  • 2.0 T-Stop for Olympus 75mm F1.8 | -0.2ev

Yes, I've seen it. Panasonic primes seems to be consistently 0.3ev darker than the claims, while Olympus 0.2ev.

Based on DXO results, I would say Olympus is more consistent with narrower gap between Lab Tested "claimed" vs real-world tested results. It would surprise me if the new Olympus 25/1.8 is tested exactly at 2.0 T-Stop.

Robin Wong seems to think that it's actually brighter than its claims. It would be a good surprise if DXO confirms it (though I doubt it).

Either way, I wouldn't worry about it. Since Olympus is the cheaper of the two, I just buy it over Panasonic.

That's my thinking now, though I like the pictures I've seen with the Panasonic. I think I'll buy the Olympus, but I'm curious about the diffrences between both.

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Fstop and tstop are two different concepts, Fstop is the physical size ratio of the aperture to focal length, tstop is how much light the lens lets through, and varies but the type of glass elements used, no lenses have a 1:1 tstop to fstop ratio nor are any manufacturers "lying" about tstops when they list fstops. This is why cine lenses are rated as t-stops not f-stops.

Yes, I'm aware of that, though some lenses have 1:1 Tstop for Fstop : http://www.dxomark.com/Lenses/Canon/Canon-EF-35mm-F2-IS-USM.

Then canon are misrepresenting the f-stop of the lens, DXO are measuring it wrong or rounding errors are coming in to play.

Transmission can be influenced by many things like elements and coating as you said, but it could be influenced by the actual aperture of the lens too.

If it was only this DXO measure, It wouldn't have raised the question. But Robin Wong (I think he is honest) and other threads seems to find that the Panasonic is a bit darker than it claims.

Moreover, I never imply someone is lying, I'm just curious.

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