TTArtisan 23mm f/1.4 lens for $99

Henry Richardson wrote:

This popped up on my youtube recommended list today. Tested on a Sony APS-C so the results would be even better on m4/3 since it only uses the best central area of the image circle.

Surely if only uses the centre part of the optic for m43, the light gathering will not be equal to f1.4 will it?

TTArtisans 23mm f/1.4 lens review with samples

https://www.youtube.com/watch?v=dMlMZo3PBwc

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Henry Richardson
http://www.bakubo.com

Adrian Harris wrote:

Henry Richardson wrote:

This popped up on my youtube recommended list today. Tested on a Sony APS-C so the results would be even better on m4/3 since it only uses the best central area of the image circle.

Surely if only uses the centre part of the optic for m43, the light gathering will not be equal to f1.4 will it?

The light gathering of a lens is a function of the lens. If I run with the reasoning that it somehow depends on the sensor, then:

• an unmounted lens would gather no light
• a lens which I hold in front of a white wall (large sensor) would gather a huge amount of light.

Neither is true. The lens did not change, it's just a piece of glass.
A smaller sensor simply discards the edges of the image. So the nett amount of used light is lower.

But the aperture does not change depending on where the image is projected or on what a sensor chooses to do with it.

Your reasoning comes from the rule-of-thumb that a cropped image appears as an image with a longer lens on a larger sensor - but that imaginary focal length is not used in the calculation of the aperture number, only the actual focal length of the chunk of glass we call a lens.

techie takes pics wrote:

Adrian Harris wrote:

Henry Richardson wrote:

This popped up on my youtube recommended list today. Tested on a Sony APS-C so the results would be even better on m4/3 since it only uses the best central area of the image circle.

Surely if only uses the centre part of the optic for m43, the light gathering will not be equal to f1.4 will it?

The light gathering of a lens is a function of the lens. If I run with the reasoning that it somehow depends on the sensor, then:

• an unmounted lens would gather no light
• a lens which I hold in front of a white wall (large sensor) would gather a huge amount of light.

Neither is true. The lens did not change, it's just a piece of glass.
A smaller sensor simply discards the edges of the image. So the nett amount of used light is lower.

But the aperture does not change depending on where the image is projected or on what a sensor chooses to do with it.

Your reasoning comes from the rule-of-thumb that a cropped image appears as an image with a longer lens on a larger sensor - but that imaginary focal length is not used in the calculation of the aperture number, only the actual focal length of the chunk of glass we call a lens.

My thinking was that as people were discussing and excited about this 'f1.4' lenses light gathering ability (not the focal length equivalence). However like you said all the light collected doesn't fall on the m43 sensor. Therefore a lot of the light collected by the lens if using a crop sensor, is actually wasted. ... Because it is not designed to focus it all onto a smaller than FF sensor.

Therefore my question is querying is it still the equivalent of an f1.4 in light gathering when it is fitted to a crop camera.

Adrian Harris wrote:

techie takes pics wrote:

Adrian Harris wrote:

Henry Richardson wrote:

This popped up on my youtube recommended list today. Tested on a Sony APS-C so the results would be even better on m4/3 since it only uses the best central area of the image circle.

Surely if only uses the centre part of the optic for m43, the light gathering will not be equal to f1.4 will it?

The light gathering of a lens is a function of the lens. If I run with the reasoning that it somehow depends on the sensor, then:

• an unmounted lens would gather no light
• a lens which I hold in front of a white wall (large sensor) would gather a huge amount of light.

Neither is true. The lens did not change, it's just a piece of glass.
A smaller sensor simply discards the edges of the image. So the nett amount of used light is lower.

But the aperture does not change depending on where the image is projected or on what a sensor chooses to do with it.

Your reasoning comes from the rule-of-thumb that a cropped image appears as an image with a longer lens on a larger sensor - but that imaginary focal length is not used in the calculation of the aperture number, only the actual focal length of the chunk of glass we call a lens.

My thinking was that as people were discussing and excited about this 'f1.4' lenses light gathering ability (not the focal length equivalence). However like you said all the light collected doesn't fall on the m43 sensor. Therefore a lot of the light collected by the lens if using a crop sensor, is actually wasted. ... Because it is not designed to focus it all onto a smaller than FF sensor.

Therefore my question is querying is it still the equivalent of an f1.4 in light gathering when it is fitted to a crop camera.

I see your point... but we (as photographers) are really dancing around the bush. We are abusing numbers to mean things they were not intended to.

We abuse focal lenght to mean angle-of-view. That was fine for a long time until we got many different sensor formats, and the field of view changes between them while the focal length stays the same.

The aperture is simply a calculation done on the lens.
We abuse that number to get an indication of the amount of light we receive.

Then we run with that f-number as if it is some absolute amount of light, and we start reasoning that this must mean something when it is spread out over a sensor - not unlike peanut butter on bread.

So when you say "is it still the equivalent of an f1.4", context is lost.  I think you are trying to ask: Can I expect different shutterspeeds and ISO settings on my MFT camera as someone will on his Sony A6100?    Or more specifically: Do I get as much as the other guy?

This is a dangerous topic and it leads to heated debates. But to start, you get a different scene than the other guy. The Sony-APSC sensor gives a wider field of view. It shows the edges of the image that the MFT will not. 
You'd use the lens slightly different; on MFT it's a short standard lens, on APS-C it's the standard 35mm-view (now I'm doing it myself!  Refering to focal length as if it defines a field of view!)

But think about it, the center of the image is the same for both cameras.  The fact that the Sony sensor is larger does not mean that more or less light falls on the center.
It is like a table with a book on it:  A certain amount of light falls on the table.  If I cut the table in half, you may be surprised I can still read the book.  "How is that possible?" you may ask. "The amount of light hitting the table has been halved!".  Yeah, but that does not matter for that book, does it?

Here is where wars start: Only if you want exactly the same image on an MFT sensor, you have to use a different focal length. Thus, a different lens, different focal length... different f-number calculation.  Here is where it goes wring, as you can not use the f-numbers over different lenses to compare the 'total amount of light'.

My honest and well meant advice is to forget about it.

An f1.4 will provide a lot of light, low ISO, high shutterspeeds and a shallow depth of field. The 23mm is close to a 'standard' lens.
Those are the things you need to know if you are contemplating buying a lens.  It does not matter if the lens gives a different image or different parameters on another system.