Speed booster confusion in DOF

Started Jun 6, 2013 | Discussions
kkx
kkx
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Speed booster confusion in DOF
Jun 6, 2013

Hi,

I am trying to understand this before buying the adapter.

Read many posts and articles here and on the net in general, but still not certain.

I hope someone who understand this can help me out. Best of all, if you have the adaptor, so test will be fantastic.

Say I have 100mm 2.8 lens mounted on tri-pod. Focus and framing is fixed.

If I mount a FF camera (say 6D?) and expose at ISO 100 f2.8 1/1200 I will get a photo that I will use as reference.

Now swapping the camera (550D or Nex via simple no lens adaptor) and expose at ISO 100 f2.8 1/1200, I will theoretically get a photo with the same exposure (brightness), absolute DOF as the ref photo above, but the framing will be different, it will be cropped (1.6 or 1.5).

If I know swap the camera with nex + the speech booster and I expose at ISO 100 f2.8 1/2400: I will get a photo that is exactly the same (brightness, DOF and framing) as the first reference photo.

I.e, I can use faster shutter because of the 1-stop of light increase, and the framing is the same as FF. But the DOF is aslo the same as FF.

There are a lot of "info" saying that the lens will be effectively f2.0 because of the light/speed increase of 1-stop. So I am confused.

Is my expectation correct? From what I have "learn" from internet with 2x tele-converter, if you don't change the framing, using the same lens with and with-out the tele-converter will mean exposure difference of 2-stops, but DOF is not changed. DOF is only affected by FL vs entry pupil size.

Can anyone help me confirm this?

Thanks in advance.

-kk

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EinsteinsGhost
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Re: Speed booster confusion in DOF
In reply to kkx, Jun 6, 2013

kkx wrote:

Hi,

I am trying to understand this before buying the adapter.

Read many posts and articles here and on the net in general, but still not certain.

I hope someone who understand this can help me out. Best of all, if you have the adaptor, so test will be fantastic.

Say I have 100mm 2.8 lens mounted on tri-pod. Focus and framing is fixed.

If I mount a FF camera (say 6D?) and expose at ISO 100 f2.8 1/1200 I will get a photo that I will use as reference.

Now swapping the camera (550D or Nex via simple no lens adaptor) and expose at ISO 100 f2.8 1/1200, I will theoretically get a photo with the same exposure (brightness), absolute DOF as the ref photo above, but the framing will be different, it will be cropped (1.6 or 1.5).

Same exposure - Yes. Narrower field of view (comparable to 150mm on FF) - Yes. Absolute DOF? Depends on what you mean by it. But the DOF will actually be shallower (150mm f/4.2 lens on a FF camera will have a shallower DOF compared to 100mm f/2.8 lens on that camera).

If I know swap the camera with nex + the speech booster and I expose at ISO 100 f2.8 1/2400: I will get a photo that is exactly the same (brightness, DOF and framing) as the first reference photo.

I.e, I can use faster shutter because of the 1-stop of light increase, and the framing is the same as FF. But the DOF is aslo the same as FF.

Yes.

There are a lot of "info" saying that the lens will be effectively f2.0 because of the light/speed increase of 1-stop. So I am confused.

That is reflected in faster shutter speed (1/2400s versus 1/1200s). However, DOF will be the same. All of this assumes that f-stop is as good representative of t-stop as well.

Is my expectation correct? From what I have "learn" from internet with 2x tele-converter, if you don't change the framing, using the same lens with and with-out the tele-converter will mean exposure difference of 2-stops, but DOF is not changed. DOF is only affected by FL vs entry pupil size.

Can anyone help me confirm this?

DOF will decrease. The effect of FL is greater than that of f-stop. If you use a 2X TC on 100mm/2.8, you'd have 200mm/5.6. But just because 2.8 is now 5.6 does not compensate for the effect of doubling of focal length. In fact, doubling the focal length reduces by the DOF by four times (the factor is: square). Whereas, f-stop is linear (increase from 2.8 to 5.6 will increase the DOF by 2 times). So, your effective reduction in DOF will be by a factor of 2.

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DtEW
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Re: Speed booster confusion in DOF
In reply to kkx, Jun 6, 2013

kkx wrote:

Hi,

I am trying to understand this before buying the adapter.

Read many posts and articles here and on the net in general, but still not certain.

I hope someone who understand this can help me out. Best of all, if you have the adaptor, so test will be fantastic.

Say I have 100mm 2.8 lens mounted on tri-pod. Focus and framing is fixed.

If I mount a FF camera (say 6D?) and expose at ISO 100 f2.8 1/1200 I will get a photo that I will use as reference.

Now swapping the camera (550D or Nex via simple no lens adaptor) and expose at ISO 100 f2.8 1/1200, I will theoretically get a photo with the same exposure (brightness), absolute DOF as the ref photo above, but the framing will be different, it will be cropped (1.6 or 1.5).

Let's start here.  There is one other thing that is different that you omitted:  the photo's SNR.  It will be like the FF's SNR at ~ISO200.  Remember that you are losing/wasting light with a light circle way too big for the sensor.

If I know swap the camera with nex + the speech booster and I expose at ISO 100 f2.8 1/2400: I will get a photo that is exactly the same (brightness, DOF and framing) as the first reference photo.

You might begin to see what the prior statement was heading toward.  It actually won't be exactly like the reference photo, because it's SNR will be like if the reference FF camera is shooting at ~ISO200.  This now explains why it is shooting one stop faster than the reference photo.

(this is all assuming that the sensor technologies are comparable)

This is why I tell people that the Speed Booster more-or-lessy makes the NEX into a slow-focusing/manual-focusing FF, but stuck on ISO200 and greater.  All the shooting parameters are the same (just ignore all the "adds one stop" conversions, which is only true if you're thinking in APS-C terms), except you can never drop the camera down into a FF's ISO100 creamy smoothness and signal integrity.  It is a partial simulation of the performance envelope of a FF camera.  It does not exceed it in any way.

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saintz
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Re: Speed booster confusion in DOF
In reply to kkx, Jun 6, 2013

kkx wrote:

Hi,

I am trying to understand this before buying the adapter.

Read many posts and articles here and on the net in general, but still not certain.

I hope someone who understand this can help me out. Best of all, if you have the adaptor, so test will be fantastic.

Say I have 100mm 2.8 lens mounted on tri-pod. Focus and framing is fixed.

If I mount a FF camera (say 6D?) and expose at ISO 100 f2.8 1/1200 I will get a photo that I will use as reference.

Now swapping the camera (550D or Nex via simple no lens adaptor) and expose at ISO 100 f2.8 1/1200, I will theoretically get a photo with the same exposure (brightness), absolute DOF as the ref photo above, but the framing will be different, it will be cropped (1.6 or 1.5).

If I know swap the camera with nex + the speech booster and I expose at ISO 100 f2.8 1/2400: I will get a photo that is exactly the same (brightness, DOF and framing) as the first reference photo.

I.e, I can use faster shutter because of the 1-stop of light increase, and the framing is the same as FF. But the DOF is aslo the same as FF.

There are a lot of "info" saying that the lens will be effectively f2.0 because of the light/speed increase of 1-stop. So I am confused.

Is my expectation correct? From what I have "learn" from internet with 2x tele-converter, if you don't change the framing, using the same lens with and with-out the tele-converter will mean exposure difference of 2-stops, but DOF is not changed. DOF is only affected by FL vs entry pupil size.

Can anyone help me confirm this?

Thanks in advance.

-kk

You got it!

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kkx
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Re: Speed booster confusion in DOF
In reply to EinsteinsGhost, Jun 7, 2013

EinsteinsGhost wrote:

kkx wrote:

Hi,

I am trying to understand this before buying the adapter.

Read many posts and articles here and on the net in general, but still not certain.

I hope someone who understand this can help me out. Best of all, if you have the adaptor, so test will be fantastic.

Say I have 100mm 2.8 lens mounted on tri-pod. Focus and framing is fixed.

If I mount a FF camera (say 6D?) and expose at ISO 100 f2.8 1/1200 I will get a photo that I will use as reference.

Now swapping the camera (550D or Nex via simple no lens adaptor) and expose at ISO 100 f2.8 1/1200, I will theoretically get a photo with the same exposure (brightness), absolute DOF as the ref photo above, but the framing will be different, it will be cropped (1.6 or 1.5).

Same exposure - Yes. Narrower field of view (comparable to 150mm on FF) - Yes. Absolute DOF? Depends on what you mean by it. But the DOF will actually be shallower (150mm f/4.2 lens on a FF camera will have a shallower DOF compared to 100mm f/2.8 lens on that camera).

Since I did not change the framing, I assume the DOF will be the same.

For example, if my photo is of a ruller, if in the FF ref, the DOF cover inch 2 to inch 4 making (I focus on inch 3 and the DOF is 2 inches)

The crop camera photo will still show that inch 2 to inch 4 is in focus. The framing has change, but I still focus on inch 3 and DOF is (absolute) still 2 inches center around the marking of inch 3.

I know you can assume that you have an "effective" 150mm F4.2 lens, but since I did not change the framing, relative (to FL)distance to subject for the FF and crop photo is different. And this result in the same area in focus.

Please correct me if I have any misunderstanding.

If I know swap the camera with nex + the speech booster and I expose at ISO 100 f2.8 1/2400: I will get a photo that is exactly the same (brightness, DOF and framing) as the first reference photo.

I.e, I can use faster shutter because of the 1-stop of light increase, and the framing is the same as FF. But the DOF is aslo the same as FF.

Yes.

There are a lot of "info" saying that the lens will be effectively f2.0 because of the light/speed increase of 1-stop. So I am confused.

That is reflected in faster shutter speed (1/2400s versus 1/1200s). However, DOF will be the same. All of this assumes that f-stop is as good representative of t-stop as well.

Is my expectation correct? From what I have "learn" from internet with 2x tele-converter, if you don't change the framing, using the same lens with and with-out the tele-converter will mean exposure difference of 2-stops, but DOF is not changed. DOF is only affected by FL vs entry pupil size.

Can anyone help me confirm this?

DOF will decrease. The effect of FL is greater than that of f-stop. If you use a 2X TC on 100mm/2.8, you'd have 200mm/5.6. But just because 2.8 is now 5.6 does not compensate for the effect of doubling of focal length. In fact, doubling the focal length reduces by the DOF by four times (the factor is: square). Whereas, f-stop is linear (increase from 2.8 to 5.6 will increase the DOF by 2 times). So, your effective reduction in DOF will be by a factor of 2.

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kkx
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Re: Speed booster confusion in DOF
In reply to DtEW, Jun 7, 2013

DtEW wrote:

kkx wrote:

Hi,

I am trying to understand this before buying the adapter.

Read many posts and articles here and on the net in general, but still not certain.

I hope someone who understand this can help me out. Best of all, if you have the adaptor, so test will be fantastic.

Say I have 100mm 2.8 lens mounted on tri-pod. Focus and framing is fixed.

If I mount a FF camera (say 6D?) and expose at ISO 100 f2.8 1/1200 I will get a photo that I will use as reference.

Now swapping the camera (550D or Nex via simple no lens adaptor) and expose at ISO 100 f2.8 1/1200, I will theoretically get a photo with the same exposure (brightness), absolute DOF as the ref photo above, but the framing will be different, it will be cropped (1.6 or 1.5).

Let's start here.  There is one other thing that is different that you omitted:  the photo's SNR.  It will be like the FF's SNR at ~ISO200.  Remember that you are losing/wasting light with a light circle way too big for the sensor.

I don't quite follow, please help. I might got some of this mixed up. Trying to understand what you are telling me.

The crop sensor is smaller, but the per-mm-square light energy should be the same (same shutter speed).

I can understand that due to denser pixel the crop sensor have a lower SNR compare to the FF sensor at the same ISO and light energy per-mm-square. Is that what you are referring to?

If I know swap the camera with nex + the speech booster and I expose at ISO 100 f2.8 1/2400: I will get a photo that is exactly the same (brightness, DOF and framing) as the first reference photo.

You might begin to see what the prior statement was heading toward.  It actually won't be exactly like the reference photo, because it's SNR will be like if the reference FF camera is shooting at ~ISO200.  This now explains why it is shooting one stop faster than the reference photo.

(this is all assuming that the sensor technologies are comparable)

This is why I tell people that the Speed Booster more-or-lessy makes the NEX into a slow-focusing/manual-focusing FF, but stuck on ISO200 and greater.  All the shooting parameters are the same (just ignore all the "adds one stop" conversions, which is only true if you're thinking in APS-C terms), except you can never drop the camera down into a FF's ISO100 creamy smoothness and signal integrity.  It is a partial simulation of the performance envelope of a FF camera.  It does not exceed it in any way.

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EinsteinsGhost
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Re: Speed booster confusion in DOF
In reply to kkx, Jun 7, 2013

kkx wrote:

EinsteinsGhost wrote:

kkx wrote:

Hi,

I am trying to understand this before buying the adapter.

Read many posts and articles here and on the net in general, but still not certain.

I hope someone who understand this can help me out. Best of all, if you have the adaptor, so test will be fantastic.

Say I have 100mm 2.8 lens mounted on tri-pod. Focus and framing is fixed.

If I mount a FF camera (say 6D?) and expose at ISO 100 f2.8 1/1200 I will get a photo that I will use as reference.

Now swapping the camera (550D or Nex via simple no lens adaptor) and expose at ISO 100 f2.8 1/1200, I will theoretically get a photo with the same exposure (brightness), absolute DOF as the ref photo above, but the framing will be different, it will be cropped (1.6 or 1.5).

Same exposure - Yes. Narrower field of view (comparable to 150mm on FF) - Yes. Absolute DOF? Depends on what you mean by it. But the DOF will actually be shallower (150mm f/4.2 lens on a FF camera will have a shallower DOF compared to 100mm f/2.8 lens on that camera).

Since I did not change the framing, I assume the DOF will be the same.

For example, if my photo is of a ruller, if in the FF ref, the DOF cover inch 2 to inch 4 making (I focus on inch 3 and the DOF is 2 inches)

The crop camera photo will still show that inch 2 to inch 4 is in focus. The framing has change, but I still focus on inch 3 and DOF is (absolute) still 2 inches center around the marking of inch 3.

I know you can assume that you have an "effective" 150mm F4.2 lens, but since I did not change the framing, relative (to FL)distance to subject for the FF and crop photo is different. And this result in the same area in focus.

Please correct me if I have any misunderstanding.

Here I was addressing your point on framing being different. To have the same framing (FOV) as 100mm f/2.8 on a FF and the same lens on APS-C, your focusing distance will have to change (increase) accordingly which will affect DOF.

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Hye
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Re: Speed booster confusion in DOF
In reply to kkx, Jun 7, 2013

kkx wrote:

I.e, I can use faster shutter because of the 1-stop of light increase, and the framing is the same as FF. But the DOF is aslo the same as FF.

There are a lot of "info" saying that the lens will be effectively f2.0 because of the light/speed increase of 1-stop. So I am confused.

I think the confusion is in trying to compare across different systems: your 100mm f/2.8 lens on APS-C *with* speed-booster performs like a 67mm f/2.0 lens on APS-C *without* speed-booster. This makes sense if you are comparing to other lenses mounted on APS-C and not to FF equivalents.

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kkx
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Re: Speed booster confusion in DOF
In reply to EinsteinsGhost, Jun 7, 2013

EinsteinsGhost wrote:

kkx wrote:

EinsteinsGhost wrote:

kkx wrote:

Hi,

I am trying to understand this before buying the adapter.

Read many posts and articles here and on the net in general, but still not certain.

I hope someone who understand this can help me out. Best of all, if you have the adaptor, so test will be fantastic.

Say I have 100mm 2.8 lens mounted on tri-pod. Focus and framing is fixed.

If I mount a FF camera (say 6D?) and expose at ISO 100 f2.8 1/1200 I will get a photo that I will use as reference.

Now swapping the camera (550D or Nex via simple no lens adaptor) and expose at ISO 100 f2.8 1/1200, I will theoretically get a photo with the same exposure (brightness), absolute DOF as the ref photo above, but the framing will be different, it will be cropped (1.6 or 1.5).

Same exposure - Yes. Narrower field of view (comparable to 150mm on FF) - Yes. Absolute DOF? Depends on what you mean by it. But the DOF will actually be shallower (150mm f/4.2 lens on a FF camera will have a shallower DOF compared to 100mm f/2.8 lens on that camera).

Since I did not change the framing, I assume the DOF will be the same.

For example, if my photo is of a ruller, if in the FF ref, the DOF cover inch 2 to inch 4 making (I focus on inch 3 and the DOF is 2 inches)

The crop camera photo will still show that inch 2 to inch 4 is in focus. The framing has change, but I still focus on inch 3 and DOF is (absolute) still 2 inches center around the marking of inch 3.

I know you can assume that you have an "effective" 150mm F4.2 lens, but since I did not change the framing, relative (to FL)distance to subject for the FF and crop photo is different. And this result in the same area in focus.

Please correct me if I have any misunderstanding.

Here I was addressing your point on framing being different. To have the same framing (FOV) as 100mm f/2.8 on a FF and the same lens on APS-C, your focusing distance will have to change (increase) accordingly which will affect DOF.

I see. My bad. I use the term "framing" inconsistently.

In my original post, I said "framing will be different" but just now I said "framing will be the same".

In both cases, I mean to say that, I do not reframe the photo between FF and crop. Keeping the focus distant the same, and just let the photo from crop sensor be a crop from photo of the FF sensor/camera.

Sorry for the confusion.

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EinsteinsGhost
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Re: Speed booster confusion in DOF
In reply to kkx, Jun 7, 2013

kkx wrote:

EinsteinsGhost wrote:

kkx wrote:

EinsteinsGhost wrote:

kkx wrote:

Hi,

I am trying to understand this before buying the adapter.

Read many posts and articles here and on the net in general, but still not certain.

I hope someone who understand this can help me out. Best of all, if you have the adaptor, so test will be fantastic.

Say I have 100mm 2.8 lens mounted on tri-pod. Focus and framing is fixed.

If I mount a FF camera (say 6D?) and expose at ISO 100 f2.8 1/1200 I will get a photo that I will use as reference.

Now swapping the camera (550D or Nex via simple no lens adaptor) and expose at ISO 100 f2.8 1/1200, I will theoretically get a photo with the same exposure (brightness), absolute DOF as the ref photo above, but the framing will be different, it will be cropped (1.6 or 1.5).

Same exposure - Yes. Narrower field of view (comparable to 150mm on FF) - Yes. Absolute DOF? Depends on what you mean by it. But the DOF will actually be shallower (150mm f/4.2 lens on a FF camera will have a shallower DOF compared to 100mm f/2.8 lens on that camera).

Since I did not change the framing, I assume the DOF will be the same.

For example, if my photo is of a ruller, if in the FF ref, the DOF cover inch 2 to inch 4 making (I focus on inch 3 and the DOF is 2 inches)

The crop camera photo will still show that inch 2 to inch 4 is in focus. The framing has change, but I still focus on inch 3 and DOF is (absolute) still 2 inches center around the marking of inch 3.

I know you can assume that you have an "effective" 150mm F4.2 lens, but since I did not change the framing, relative (to FL)distance to subject for the FF and crop photo is different. And this result in the same area in focus.

Please correct me if I have any misunderstanding.

Here I was addressing your point on framing being different. To have the same framing (FOV) as 100mm f/2.8 on a FF and the same lens on APS-C, your focusing distance will have to change (increase) accordingly which will affect DOF.

I see. My bad. I use the term "framing" inconsistently.

In my original post, I said "framing will be different" but just now I said "framing will be the same".

In both cases, I mean to say that, I do not reframe the photo between FF and crop. Keeping the focus distant the same, and just let the photo from crop sensor be a crop from photo of the FF sensor/camera.

Sorry for the confusion.

If you keep the focus distance the same, you will get shallower DOF with APS-C (and narrower FOV).

If you replace non-optical (non-SB) adapter with optical (SB), and do the same, you will get the same DOF and FOV, but gain about a stop in exposure.

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Re: Speed booster confusion in DOF
In reply to EinsteinsGhost, Jun 7, 2013

EinsteinsGhost wrote:

If you keep the focus distance the same, you will get shallower DOF with APS-C (and narrower FOV).

If you replace non-optical (non-SB) adapter with optical (SB), and do the same, you will get the same DOF and FOV, but gain about a stop in exposure.

Shallower than what?

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EinsteinsGhost
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Re: Speed booster confusion in DOF
In reply to pmow, Jun 7, 2013

pmow wrote:

EinsteinsGhost wrote:

If you keep the focus distance the same, you will get shallower DOF with APS-C (and narrower FOV).

If you replace non-optical (non-SB) adapter with optical (SB), and do the same, you will get the same DOF and FOV, but gain about a stop in exposure.

Shallower than what?

The comparison is between: 100mm f/2.8 on FF and 100mm f/2.8 on APS-C, without changing focusing distance. The DOF will be shallower on the APS-C set up.

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viking79
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Re: Speed booster confusion in DOF
In reply to kkx, Jun 7, 2013

To get exact same images between APS-C and 135 format full frame:

APS-C: 35mm f/1.8 1/100 ISO 100

Full Frame: 50mm f/2.8 1/100 ISO 250

This will give you the same noise performance (given similar sensor performance, like Sony 16 MP vs Sony 24 or 36 MP full frame) same field of view same shutter speed and same depth of field.  These are "equivalent" settings.

To figure these out, use the crop factor to get effective aperture and focal length and for ISO is it crop factor^2?  So if your crop factor is 1.52 you would multiply ISO by 2.31, rounding up to 250 since that is closest 1/3rd stop.  I haven't thought about the ISO one much, but instead just use an ISO chart and go up or down 1 1/3 stops [1] (actual is like 1.23 stops, but 1 1/3 is rounded).

The speed booster basically converts your lens focal length and aperture to a full frame equivalent (or nearly).  This is actually changing the physical focal length and f/stop, but the net result is it is a full frame converter for the camera.

Eric

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EinsteinsGhost
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Re: Speed booster confusion in DOF
In reply to viking79, Jun 7, 2013

viking79 wrote:

To get exact same images between APS-C and 135 format full frame:

APS-C: 35mm f/1.8 1/100 ISO 100

Full Frame: 50mm f/2.8 1/100 ISO 250

This will give you the same noise performance (given similar sensor performance, like Sony 16 MP vs Sony 24 or 36 MP full frame) same field of view same shutter speed and same depth of field.  These are "equivalent" settings.

To figure these out, use the crop factor to get effective aperture and focal length and for ISO is it crop factor^2?  So if your crop factor is 1.52 you would multiply ISO by 2.31, rounding up to 250 since that is closest 1/3rd stop.  I haven't thought about the ISO one much, but instead just use an ISO chart and go up or down 1 1/3 stops [1] (actual is like 1.23 stops, but 1 1/3 is rounded).

The speed booster basically converts your lens focal length and aperture to a full frame equivalent (or nearly).  This is actually changing the physical focal length and f/stop, but the net result is it is a full frame converter for the camera.

Eric

You're also increasing the amount of light reaching the sensor by using a lens as a concentrator, which would otherwise be spread over a larger area. Consequently, increasing exposure.

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viking79
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Re: Speed booster confusion in DOF
In reply to EinsteinsGhost, Jun 7, 2013

EinsteinsGhost wrote:

viking79 wrote:

To get exact same images between APS-C and 135 format full frame:

APS-C: 35mm f/1.8 1/100 ISO 100

Full Frame: 50mm f/2.8 1/100 ISO 250

This will give you the same noise performance (given similar sensor performance, like Sony 16 MP vs Sony 24 or 36 MP full frame) same field of view same shutter speed and same depth of field.  These are "equivalent" settings.

To figure these out, use the crop factor to get effective aperture and focal length and for ISO is it crop factor^2?  So if your crop factor is 1.52 you would multiply ISO by 2.31, rounding up to 250 since that is closest 1/3rd stop.  I haven't thought about the ISO one much, but instead just use an ISO chart and go up or down 1 1/3 stops [1] (actual is like 1.23 stops, but 1 1/3 is rounded).

The speed booster basically converts your lens focal length and aperture to a full frame equivalent (or nearly).  This is actually changing the physical focal length and f/stop, but the net result is it is a full frame converter for the camera.

Eric

You're also increasing the amount of light reaching the sensor by using a lens as a concentrator, which would otherwise be spread over a larger area. Consequently, increasing exposure.

Correct, that is the how, by compressing the image circle you enlarge the f/stop of the lens, remembering f/stop is focal length divided by aperture.  If you decrease the focal length of the lens with a rear converter (not with a front converter) your aperture remains the same apparent size from the front.  This means your f/stop increases and more light is hitting the sensor.

A teleconverter is the opposite.  A 1.5x TC converts your APS-C lens into a lens usable on full frame.  I.e. you could mount any APS-C lens and get a full frame image circle on a 1.5x TC and use it on your full frame camera.  This direction is usually less desirable though

Eric

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EinsteinsGhost
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Re: Speed booster confusion in DOF
In reply to viking79, Jun 7, 2013

viking79 wrote:

EinsteinsGhost wrote:

viking79 wrote:

To get exact same images between APS-C and 135 format full frame:

APS-C: 35mm f/1.8 1/100 ISO 100

Full Frame: 50mm f/2.8 1/100 ISO 250

This will give you the same noise performance (given similar sensor performance, like Sony 16 MP vs Sony 24 or 36 MP full frame) same field of view same shutter speed and same depth of field.  These are "equivalent" settings.

To figure these out, use the crop factor to get effective aperture and focal length and for ISO is it crop factor^2?  So if your crop factor is 1.52 you would multiply ISO by 2.31, rounding up to 250 since that is closest 1/3rd stop.  I haven't thought about the ISO one much, but instead just use an ISO chart and go up or down 1 1/3 stops [1] (actual is like 1.23 stops, but 1 1/3 is rounded).

The speed booster basically converts your lens focal length and aperture to a full frame equivalent (or nearly).  This is actually changing the physical focal length and f/stop, but the net result is it is a full frame converter for the camera.

Eric

You're also increasing the amount of light reaching the sensor by using a lens as a concentrator, which would otherwise be spread over a larger area. Consequently, increasing exposure.

Correct, that is the how, by compressing the image circle you enlarge the f/stop of the lens, remembering f/stop is focal length divided by aperture.  If you decrease the focal length of the lens with a rear converter (not with a front converter) your aperture remains the same apparent size from the front.  This means your f/stop increases and more light is hitting the sensor.

A teleconverter is the opposite.  A 1.5x TC converts your APS-C lens into a lens usable on full frame.  I.e. you could mount any APS-C lens and get a full frame image circle on a 1.5x TC and use it on your full frame camera.  This direction is usually less desirable though

Eric

Actually, it is about more light hitting over a smaller area than before, that increases the exposure, the lens in the adapter serving as a light collector. Each pixel is now getting more photons than would be available without the lens element in the adapter, or on FF.

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kkx
kkx
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Re: Speed booster confusion in DOF
In reply to EinsteinsGhost, Jun 7, 2013

EinsteinsGhost wrote:

viking79 wrote:

EinsteinsGhost wrote:

viking79 wrote:

To get exact same images between APS-C and 135 format full frame:

APS-C: 35mm f/1.8 1/100 ISO 100

Full Frame: 50mm f/2.8 1/100 ISO 250

This will give you the same noise performance (given similar sensor performance, like Sony 16 MP vs Sony 24 or 36 MP full frame) same field of view same shutter speed and same depth of field.  These are "equivalent" settings.

To figure these out, use the crop factor to get effective aperture and focal length and for ISO is it crop factor^2?  So if your crop factor is 1.52 you would multiply ISO by 2.31, rounding up to 250 since that is closest 1/3rd stop.  I haven't thought about the ISO one much, but instead just use an ISO chart and go up or down 1 1/3 stops [1] (actual is like 1.23 stops, but 1 1/3 is rounded).

The speed booster basically converts your lens focal length and aperture to a full frame equivalent (or nearly).  This is actually changing the physical focal length and f/stop, but the net result is it is a full frame converter for the camera.

Eric

You're also increasing the amount of light reaching the sensor by using a lens as a concentrator, which would otherwise be spread over a larger area. Consequently, increasing exposure.

Correct, that is the how, by compressing the image circle you enlarge the f/stop of the lens, remembering f/stop is focal length divided by aperture.  If you decrease the focal length of the lens with a rear converter (not with a front converter) your aperture remains the same apparent size from the front.  This means your f/stop increases and more light is hitting the sensor.

A teleconverter is the opposite.  A 1.5x TC converts your APS-C lens into a lens usable on full frame.  I.e. you could mount any APS-C lens and get a full frame image circle on a 1.5x TC and use it on your full frame camera.  This direction is usually less desirable though

Eric

Actually, it is about more light hitting over a smaller area than before, that increases the exposure, the lens in the adapter serving as a light collector. Each pixel is now getting more photons than would be available without the lens element in the adapter, or on FF.

That was my understanding too.

But Eric's explanation is also very popular and seems logical so I am still a bit confused now.

Adding the speech booster to a 100mm F2.8 lens will give an effective 100/1.5 mm F2 lens for my nex-6 ?

using DOF calculator at : http://www.dofmaster.com/dofjs.html

on nex-7/nex-6:

no speed booster: 100mm F2.8 at 10f DOF = 0.33f

with speed booster: 66.7mm F2 at 10f DOF = 0.54f

FOV will be 1.5 crop vs FF, at ISO 100, shutter speed for second case (with speed booster) will be faster (2x) due to effective F2 on the lens.

IS this correct?

I was thinking :

no speed booster: 100mm F2.8 at 10f DOF = 0.33f

shutter speed = 1/1200, ISO 100

with speed booster: 100mm F2.8 at 10f DOF = 0.33f

shutter speed = 1/2400, ISO 100

give the same exposure, FOV of 1.5 crop vs FF (because I lock the focus distance at 10f for both). Same DOF.

Shutter speed is faster because light is concentrated so per-mm-square on the sensor will get more light.

So I am now not sure which is correct. Maybe these are just two view of the same thing, but I am still missing something, I think.

Because, for view 1, DOF change from 0.33 to 0.54, but view two DOF is constant. Help me to clarify this please. If I have the speed booster, I could run some test (shooting a ruller). But I have yet to buy one.

-kk

edit: spacing was messed up, fixed

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