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Does using a FF lens with adapter lose light?

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dpyy

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It has been mentioned a few times here on the forum that if you use a FF A lens with one of the EA adapters you are basically going to crop the image. As a result, you really have to move your location to frame the subject the same way, effectively "changing" the focal length. I think I understood that correctly.

However, what I'm not sure is, wouldn't this mean you are losing light through this cropping step? If so, would it total up to something significant? Say one stop of light? If my guess is right, does that mean if you use a 80mm/2.8 with EA2 you are really "effectively" using a 50mm/4.0 at the widest aperture?
 
dpyy said:
dpyy wrote:

It has been mentioned a few times here on the forum that if you use a FF A lens with one of the EA adapters you are basically going to crop the image. As a result, you really have to move your location to frame the subject the same way, effectively "changing" the focal length. I think I understood that correctly.

However, what I'm not sure is, wouldn't this mean you are losing light through this cropping step? If so, would it total up to something significant? Say one stop of light? If my guess is right, does that mean if you use a 80mm/2.8 with EA2 you are really "effectively" using a 50mm/4.0 at the widest aperture?
Click to expand...
Ah, this comes up all too often. So I'll distill it down using an arbitrary 50mm f/2 lens for discussion:
  • The lens is a 50mm f/2 regardless of what camera it is put on
  • Due to the crop factor of APS-C, the 50mm will give the same FIELD-OF-VIEW (not the same as focal length) as a 75mm lens on FF. This doesn't matter if the lens was designed for APS-C or not.
  • The amount of light hitting the sensor is always f/2, however the crop factor does have an effect on bokeh. In general, the 50mm f/2 on APS-C will behave like a 75mm f/2.8 on FF with regards only to depth-of-field/bokeh.
  • However, it is known that the translucent mirror in the LAEA2 blocks about 1/3-1/2 EV of light to the sensor. Depth-of-field is still the same, of course.
Make more sense? :)

http://matthewdurrphotography.com
 
I think you're asking about crop factor using full frame lenses? The focal length remains the same as does the light coming in, what changes is your field of view because your lens in projecting a circle larger than needed to light the sensor. so at the middle of the image the same amount of light is striking the middle of the sensor no matter what. That being said the EA2 adapter is an SLT design and there is a mirror in there that deflects part of the light to the AF sensors so the phase detect auto focus can function. that mirror does use about 1/3 of a stop which for all practical purposes you won't miss. The SLT cameras are set to be more sensitive so it doesn't affect exposure at all, but I'm not sure if that is done also on the NEX cameras with the adapter or not. I assume it would be. The NEX cameras being APS-C have a physically smaller sensor than a 35mm film frame would be. the factor is 1.5, so looking through the lens of 100mm it will seem like your looking through 150mm lens on a 35mm full frame camera. I've you've never shot 35mm then you won't know any better anyway.




-

 
El Matadurr said:
  • The lens is a 50mm f/2 regardless of what camera it is put on
  • Due to the crop factor of APS-C, the 50mm will give the same FIELD-OF-VIEW (not the same as focal length) as a 75mm lens on FF. This doesn't matter if the lens was designed for APS-C or not.
  • The amount of light hitting the sensor is always f/2, however the crop factor does have an effect on bokeh. In general, the 50mm f/2 on APS-C will behave like a 75mm f/2.8 on FF with regards only to depth-of-field/bokeh.
  • However, it is known that the translucent mirror in the LAEA2 blocks about 1/3-1/2 EV of light to the sensor. Depth-of-field is still the same, of course.
Make more sense? :)

http://matthewdurrphotography.com
Click to expand...
Yep the first two points made sense to me. Sorry for the language, I meant that the FOV changes, not the FL. Or put another way, the FOV becomes that of a multiplied FL.

The third point was where I was confused. If some light is left out of the image why is there no lost of light? But now it makes sense because the area of the image is also smaller. Same amount of light goes into the center no matter what.

thanks for explaining!
 
There's no lost light because the projected image circle is evenly "bright" across its entire surface. Only a part of that circle is being used but the whole circle is still say, f2.

Because the centre is the strongest part of a lens' circle, using an FF lens on APS-C can avoid light fall-off and desharpening in the corners of your images which can happen with large-aperture lenses.

And yes, if you're using the LA-EA2 adapter then a small amount of light (I think 1/3 of a stop) will be diverted by the translucent mirror for the phase-detection autofocus.
 
dpyy said:
dpyy wrote:

It has been mentioned a few times here on the forum that if you use a FF A lens with one of the EA adapters you are basically going to crop the image. As a result, you really have to move your location to frame the subject the same way, effectively "changing" the focal length. I think I understood that correctly.

However, what I'm not sure is, wouldn't this mean you are losing light through this cropping step? If so, would it total up to something significant? Say one stop of light? If my guess is right, does that mean if you use a 80mm/2.8 with EA2 you are really "effectively" using a 50mm/4.0 at the widest aperture?
Click to expand...



Light shining through diffusor on front of lens mounted at flange distance from paper sensor models.




Even smaller image circle (not quite centered), Sony has been tending to run the image circle on the smaller side (this is from a Samsung lens)




The inner rectangle is approximately APS-C sized, the outer rectangle approximately Full Frame size. This lens happens to be an APS-C lens so it doesn't quite cover full frame.

The point being is that if you shoot full frame, the total light hitting the sensor is greater than the APS-C sensor. The intensity is the same at the same aperture.

This is why the APS-C is considered a crop sensor, it is exactly the same as cropping away part of the full frame image.

To correct for this, you adjust by the crop factor, 1.52 or so for Sony APS-C, and so a 35mm lens will be fairly close to a 50mm lens on full frame for field of view. However, a 50mm has shallower depth of field at the same aperture as a 35mm, so to get the same composition depth of field you also need to adjust the aperture by the crop factor, so if you were at f/1.8 you would take that * 1.52 which is about f/2.8. However, if you do this, the light intensity on the full frame camera is now 1 and 1/3 or so stops darker than the APS-C. To compensate for this you also need to adjust the ISO by the same amount, so if you were at 100 on the APS-C you would adjust to 250 on the full frame. Since you don't have to enlarge the full frame image as much to reach some screen or print size, the noise is the same at the image level between the two (given similar technology sensors, e.g. Sony 16 MP 4/3" sensor, Sony 16/24 MP APS-C sensor, or Sony 24/36 MP full frame sensor).

Eric

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dpyy said:
dpyy wrote:

It has been mentioned a few times here on the forum that if you use a FF A lens with one of the EA adapters you are basically going to crop the image. As a result, you really have to move your location to frame the subject the same way, effectively "changing" the focal length. I think I understood that correctly.

However, what I'm not sure is, wouldn't this mean you are losing light through this cropping step? If so, would it total up to something significant? Say one stop of light? If my guess is right, does that mean if you use a 80mm/2.8 with EA2 you are really "effectively" using a 50mm/4.0 at the widest aperture?
Click to expand...



You only loose light if you use the LAEA2 that has the translucent mirror, that takes more or les 1/3rd of light, or if you use an adapter that has any kind of glass (Cant tell there, every case is specific.




Hollow adapters dont loose light.




Some people talk about steps or speed, and sometimes they are refering to light, and sometimes they are refering to DoF. While in a given lens, they are related (you open the lens, you have more light and less DoF, inverse related) when you use a lens from full frame on APS-C only the DoF changes. The ammount of light is the same.




There are other factros that makes you loose light. It has been proven that from 2 to 1.4 on the nex cameras you dont get 1 stop of light. You get more or less 2/3. And from 1.4 to 1.2 even less thatn what it should. this is a problem of the sensor, that I dont remember exactly why it is. IT is only on the light part. The DoF will work as expected. Thats why more than 1.4 is really an overkill ont he nex. You wont get more light, at least not much, and you will have such a narrow DoF that would make it very hard to work. It is considered that 1.8 is the sweet spot on the Nex.




There is a lot of misunderstanding on lenses and different sensor sizes, and unfortunatelly, people dont talk/write correctly and confuse more.




Hope this helps.
 
dpyy said:
dpyy wrote:

It has been mentioned a few times here on the forum that if you use a FF A lens with one of the EA adapters you are basically going to crop the image. As a result, you really have to move your location to frame the subject the same way, effectively "changing" the focal length. I think I understood that correctly.

However, what I'm not sure is, wouldn't this mean you are losing light through this cropping step? If so, would it total up to something significant? Say one stop of light? If my guess is right, does that mean if you use a 80mm/2.8 with EA2 you are really "effectively" using a 50mm/4.0 at the widest aperture?
Click to expand...
Losing light is not a precisely defined term. What happens is that the intensity of light from a FF lens will be the same on an APS-C sensor and on the equivalent area of the FF sensor - think of just swapping sensors rather than cameras. However, more light will fall outside the sensor with APS-C than FF and in this sense will be lost. This fact is exploited by the Metabones FF to APS-C speed adapters which "refocus" the light so all (or most) of the light that would fall on an FF sensor now falls on the APS-C sensor, increasing the intensity and hence the "speed" .
 
"Hollow adapters dont loose light."




The "hollow" adapter between my legacy lens and the sensor moves the lens almost an inch away from the sensor plane. I'm pretty sure that light intensity falls off as a square of the distance, if high school physics serves me right. Perhaps not a big deal in this case, but worth noting as clarification.
 
Richie Beans said:
Richie Beans wrote:

"Hollow adapters dont loose light."

The "hollow" adapter between my legacy lens and the sensor moves the lens almost an inch away from the sensor plane. I'm pretty sure that light intensity falls off as a square of the distance, if high school physics serves me right. Perhaps not a big deal in this case, but worth noting as clarification.
Click to expand...
The 'fall-off' you refer to ... is when a lens is moved AWAY from it's normal register (flange/sensor distance) - i.e. use of teleconvertors/extension tubes - both of which extend the light path.

In this scenario, FF lenses are being located at the CORRECT distance (due to narrower NEX body) - hence no light path extension/no light fall-off. In the case of the SpeedBooster - which 'compresses' the light path down to APS dimensions, this actually increases/speeds-up the light transmission.
 
blakninja said:
blakninja wrote:

Why does crop sensor reduce bokeh?
Click to expand...
Technically speaking, the crop sensor does not reduce bokeh. That is, a crop sensor doesn't affect the depth of field of an image. Taken from the same spot, of the same subject, a 50mm/f2 lens will give the same depth of field on a FF or APS-C camera. It's just that the APS-C image will be cropped. However, the depth of field is increased (and bokeh reduced), when you walk backwards to get a 50mm lens on an APS-C to have the same field of view as a 50mm on a FF. This is because depth of field is influenced by distance from the subjeact. So, it is a practical implication that generally speaking, the smaller the sensor, the harder it is to achieve a thin depth of field in conjuction with a desired field of view.
 
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Technically speaking DOF (depth of field) and bokeh are not the same thing. Bokeh is the visual appearance or quality of the out of focus areas of the image.
  • John :)
Puddleglum said:
Puddleglum wrote:
Puddleglum said:
blakninja wrote:

Why does crop sensor reduce bokeh?
Click to expand...
Technically speaking, the crop sensor does not reduce bokeh. That is, a crop sensor doesn't affect the depth of field of an image. Taken from the same spot, of the same subject, a 50mm/f2 lens will give the same depth of field on a FF or APS-C camera. It's just that the APS-C image will be cropped. However, the depth of field is increased (and bokeh reduced), when you walk backwards to get a 50mm lens on an APS-C to have the same field of view as a 50mm on a FF. This is because depth of field is influenced by distance from the subjeact. So, it is a practical implication that generally speaking, the smaller the sensor, the harder it is to achieve a thin depth of field in conjuction with a desired field of view.
Click to expand...
 
fotowbert said:
fotowbert wrote:

Technically speaking DOF (depth of field) and bokeh are not the same thing. Bokeh is the visual appearance or quality of the out of focus areas of the image.
  • John :)
fotowbert said:
Puddleglum wrote:
fotowbert said:
blakninja wrote:

Why does crop sensor reduce bokeh?
Click to expand...
Technically speaking, the crop sensor does not reduce bokeh. That is, a crop sensor doesn't affect the depth of field of an image. Taken from the same spot, of the same subject, a 50mm/f2 lens will give the same depth of field on a FF or APS-C camera. It's just that the APS-C image will be cropped. However, the depth of field is increased (and bokeh reduced), when you walk backwards to get a 50mm lens on an APS-C to have the same field of view as a 50mm on a FF. This is because depth of field is influenced by distance from the subjeact. So, it is a practical implication that generally speaking, the smaller the sensor, the harder it is to achieve a thin depth of field in conjuction with a desired field of view.
Click to expand...
Click to expand...

You're correct of course.
 
dpyy said:
dpyy wrote:
dpyy said:
  • The lens is a 50mm f/2 regardless of what camera it is put on
  • Due to the crop factor of APS-C, the 50mm will give the same FIELD-OF-VIEW (not the same as focal length) as a 75mm lens on FF. This doesn't matter if the lens was designed for APS-C or not.
Click to expand...
Click to expand...
100% agree



dpyy said:
dpyy said:
  • The amount of light hitting the sensor is always f/2, however the crop factor does have an effect on bokeh.
Click to expand...
Click to expand...
Only if you change focus distance like when you re-frame the subject to cover the frame as with the longer lens on a larger format.(Refer to your first point, and my bottom comment)



dpyy said:
dpyy said:
  • In general, the 50mm f/2 on APS-C will behave like a 75mm f/2.8 on FF with regards only to depth-of-field/bokeh.
  • However, it is known that the translucent mirror in the LAEA2 blocks about 1/3-1/2 EV of light to the sensor. Depth-of-field is still the same, of course.
Click to expand...
Click to expand...
dpyy said:
dpyy said:
Make more sense? :)

http://matthewdurrphotography.com
Click to expand...
Yep the first two points made sense to me. Sorry for the language, I meant that the FOV changes, not the FL. Or put another way, the FOV becomes that of a multiplied FL.

The third point was where I was confused. If some light is left out of the image why is there no lost of light? But now it makes sense because the area of the image is also smaller. Same amount of light goes into the center no matter what.

thanks for explaining!
Click to expand...
Think of it like Cropping your picture while editing in post.
 
Puddleglum said:
Puddleglum wrote:
Puddleglum said:
blakninja wrote:

Why does crop sensor reduce bokeh?
Click to expand...
Technically speaking, the crop sensor does not reduce bokeh. That is, a crop sensor doesn't affect the depth of field of an image. Taken from the same spot, of the same subject, a 50mm/f2 lens will give the same depth of field on a FF or APS-C camera. It's just that the APS-C image will be cropped. However, the depth of field is increased (and bokeh reduced), when you walk backwards to get a 50mm lens on an APS-C to have the same field of view as a 50mm on a FF. This is because depth of field is influenced by distance from the subjeact. So, it is a practical implication that generally speaking, the smaller the sensor, the harder it is to achieve a thin depth of field in conjuction with a desired field of view.
Click to expand...
I think it's more like, you stand in the same place to get the same framing and perspective, but to match the framing between the two camera types, you must swap to a wider lens for APS-C. Now you have greater DOF (and thus less bokeh as well).

Although you're right about walking backwards, now you've got a lot of variables, such as "how far away am I from my subject?" that just seems confusing to me. So I prefer to think of the example of, "everything is the same but now I have to change lenses."
 
Puddleglum said:
Puddleglum wrote:
Puddleglum said:
fotowbert wrote:

Technically speaking DOF (depth of field) and bokeh are not the same thing. Bokeh is the visual appearance or quality of the out of focus areas of the image.
  • John :)
Click to expand...
You're correct of course.
Click to expand...

True that bokeh can be considered the "quality" of the OOF area, but I think it's a bit obvious that, all else being equal, you get less of it as you have less OOF. I suppose you could argue that you're getting both less and poorer bokeh, but you might swap to a different lens that gets better bokeh quality, but just that you have less of it. Which really doesn't help to understand the difference between the two camera formats, but is a fun technical point to sidetrack the thread. ;-)
 
Richie Beans said:
Richie Beans wrote:

"Hollow adapters dont loose light."

The "hollow" adapter between my legacy lens and the sensor moves the lens almost an inch away from the sensor plane. I'm pretty sure that light intensity falls off as a square of the distance, if high school physics serves me right. Perhaps not a big deal in this case, but worth noting as clarification.
Click to expand...
This is old and maybe you are not reading this but.




The adaptor doesnt move the lens away from the lens. It put it at the designed distance for this lens. So at its designed distance, it will work as the aperture it says it has, so, no loose light. At least for an adapter. If you are talking about extension tubes, that is another thing. They may look the same but they are not the same.




You only loose light with an adapter if there is something in the middle, as I already said, with the LAEA2 , or if there is glass in the middle.
 
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