Answer this one question!

joe mama · May 21, 2007

peteb said:
At least as far as the front element goes.

http://forums.dpreview.com/forums/read.asp?forum=1032&message=21528198

In the above post I outline how it is obvious that the outer edge
of a lens impacts the light at the center of the frame.

Good practical example!

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my photos. If you wish to use any of my photos for any purpose other than editing in these forums, please ask.

joe mama · May 21, 2007

Member said:
Member said:

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23296470

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23297008

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23301485

I mean, that's pretty hard core evidence to the contrary.

Click to expand...

Member said:
Not only it is a bad test but total waste of time because he used
two totally different lenses.

You don't use the same lenses on FF in the same way as you do on 1.6x, so a "proper" test uses the lenses that you would use on each system.

In the first link, using the 135 / 2L on the 5D and the 85 / 1.2L on the 30D, I mean, I cannot even imagine a more fair comparison. Seriously, that's as good a comparison as you can get.

Now, the second test, comparing the 16-35 / 2.8L on FF with the 17-55 / 2.8 IS, is not the perfect match-up, I'll agree. But you know what? The test actually favors 1.6x, 'cause the 17-55 / 2.8 IS is sharper than the 10-22 / 3.5-4.5 at 21mm, which is what the comparison should have used (but he doesn't have the 10-22):

10-22 / 3.5-4.5:

http://www.photozone.de/8Reviews/lenses/canon_1022_3545/index.htm

17-55 / 2.8 IS:

http://www.photozone.de/8Reviews/lenses/canon_1755_28/index.htm

In any case, the 17-55 / 2.8 at f / 4 has virtually the same sharpness as the 16-35 / 2.8L at f / 6.3:

http://www.photozone.de/8Reviews/lenses/canon_1635_28/index.htm

In any event, a "proper" comparison would never use the same lens on each format. You do not evaluate a system by the lens or the sensor -- you evaluate the system .

Now, in the first test, the 5D + 135 / 2L vs 30D + 85 / 1.2L, the two lenses are as equivalent as you will ever get between the two systems. Most of the time, the lens choices will not be so clear cut.

So, while the 10-22 / 3.5-4.5 on the 30D "should have" been paired up against the 17-40 / 4L on the 5D, the fact that he used the 17-55 / 2.8 IS on the 30D, which is sharper than the 10-22, only serves to strengthen the conclusion that FF does not have worse corners. In fact, they are actually better.

Please don't tell me a "valid" comparison would be using the same lens on each camera. That's just pure bunk. If I have a 16-35 / 2.8L on my 5D (which I often do), I would be using a 10-22 / 3.5-4.5 on a 30D (which is what I did do).

To make an analogy, if we are comparing two motorcycles, say the Yamaha R1 (1000cc) against the Yamaha R6 (600cc), we most certainly would not use the same tires on each bike.

His test was as valid as a test could be.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my photos. If you wish to use any of my photos for any purpose other than editing in these forums, please ask.

Molokai_fiords · May 21, 2007

I must say I find the discussion quite interesting - and I have learned a few things. Most notably a bit more about the specific issues that come into play to cause the difference in DOF between 1.6x and FF.

As far as I can tell it seems that both sides arguing are in many ways right, but put weight on different things.

And to answer you Brok; firstly as was noted in one of the other replies, the outer part of the glass does matter! All parts of the lens glass comes into play to create all parts of the image - this is also why you when you have spots on your glass generally will get reduced contranst all over - and not the same blotches on your images (dust on the sensor is of course another matter entirely).

But if you have a lens you can probably hold it so that light goes through it and a picture is displayed on something below/behind the lens. What you will see is what we refer to as the image circle. The difference between a 1.6x crop and a fullframe is that the sensor which would be placed where that image cirlce is, is smaller on the 1.6x.

Which means that if you use the SAME lens on FF and on 1.6x, shooting at the SAME aperture, you will get a "crop" of the image circle on 1.6x compared to FF.

Which means that in the specific scenario, on the 1.6X crop you get to use the central portion of the image circle - which has less vignetting and is sharper than the edges that your sensor cannot see.

Which means that you DO use the "sweet-spot" - not of the "glass" but of the image circle.

On another note you also get the same DOF and perspective with both cameras - using the exact same shutter speed/aperture if you are at the SAME DISTANCE from the subject. However you will then have different images since the 1.6x gets a crop of the image circle.

This is where Joe Mama is right in all his views (as far as I can tell) in that his basic statement is that you are now comparing apples and oranges, since if you want the same image with both cameras, you can't use the same lenses - either you will get different FOV - or you must change your camera-subject distance which affects DOF, perspective etc..

So in order to retain the same perspective AND the same DOF, you need to stay put - which means using different focal lengths - so for example using 85mm and 135mm. However since you now have different FLs - but you are at the same distance, you will have different DOF on the same F-stop (larger FL - smaller DOF) - and hence you need to vary the F-stop as well to get similar DOF.

You can use the same lens, same settings, and get the same exposure - but at least 1 or 2 of these will vary: FOV, perspective, DOF.

OR you can do what Joe says, and you can (in many situations, not all) get the exact same picture with both FF and 1.6.

Brok said:
Am I correct in assuming, that a 20D, due to it's 1.6x crop factor,
actually uses "less" of the lens' glass and therefore does not
"see" deteriorating edge IQ?
--
Flemming

Molokai_fiords · May 21, 2007

Eugene Powers said:
That is because you need to read the whole idea behind it but as
usual in these forums it gets separated in to small pieces and I
don't think he explains it in layman terms.
Let's see if I can do it.
First, you have to understand that the smaller the sensor the wider
the DOF is. Just like on PS cameras you just can't get shallow DOF
because of the small sensor.
Second, in order to match DOF from FF to crop camera you need to
stop down FF camera.
Third, if you stop down FF camera you get less light coming in so
you need to increase ISO or slow down shutter to match the same
exposure.

Understand now? It is all based on DOF. Joe just went backwards
explaining exactly the same thing.

--
Eugene

The only time a smaller sensor with the same pixel count is
superior to a larger sensor (aka higher pixel density) is when you
are focal-length limited.

Lee Jay

Molokai_fiords · May 21, 2007

Something went wrong with the post.. so my whole big point was lost.

Oh well I try again, short and sweet this time:

1. Cameras with smaller sensors have more DOF than cameras with larger sensors
2. Sensor size does not in any way change DOF

3. However, sensor size changes FOV at a given focal length, meaning you need a shorter FL with a smaller sensor to have the same FOV
4. DOF is determined by focal length and distance to subject ONLY

5. since smaller sensor cameras have shorter focal lenghts for same FOV as larger sensor cameras, you change the FL and thus you get more DOF
6. hence, sensor size has an INDIRECT impact on DOF

Hope that is helpful. My point being that there is nothing magical about different sensor sizes, but that they change the FOV and if you want a similar picture from the same position with cameras of different sensor sizes (a pretty fair request I would think) then you need to change some parameters (like FL) and that impacts other parameters (like DOF).

Hope this is helpful to some

Lee Jay · May 21, 2007

Eugene Powers said:
Are you saying that crop factor camera "sees" all of the glass in
the lens including corners?
The answer could be only Yes or No.

Well, it's actually a bit less than yes. ;-)

Each pixel sees the entire aperture, except for pixels affected by vignetting (not light falloff, vignetting). Those see a portion of the aperture blocked by internal or external physical elements.

--
Lee Jay
(see profile for equipment)

Lee Jay · May 21, 2007

Amin Sabet said:
Less of an image circle does use less of the glass despite looking
through the entire aperture. If that's not true, please explain.

It's mostly not true. See my response to Eugene.

--
Lee Jay
(see profile for equipment)

Eugene Powers · May 21, 2007

your DOF matching theory got to do with corner sharpness?
That is right. Identical lens should be used on both cameras.

We are not talking about DOF again, are we? We are talking about if crop camera sees all of the lens. The answer is, it does not see most of the last element in the lens.

Original tester could not possibly know how sharp corners are on both lenses so he could not possibly compare one to another. As you know one copy of the lens could be better than another even if it is the same lens.

I went through 6 copies of the 16-35mm to get one because of the corner sharpness.
This right here invalidates the test.

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

Eugene Powers · May 21, 2007

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

Eugene Powers · May 21, 2007

Your #1 contradicts with #2 and #6

Of course sensor size changes DOF and FOV if the same lens is employed.

You need to stop down this lens on FF camera to get the same DOF as on the crop camera.

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

Eugene Powers · May 21, 2007

If crop factor camera needs all of the glass in the lens designed for FF camera why bother making crop factor camera lenses. And I should be able to use crop factor camera lenses on my 1DS2 like Sigma 50-150mm F2.8 DC for example. Right?

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

Eugene Powers · May 21, 2007

I wish I could say I understand you but I can't.
How can it be less than Yes?

Think about it. If crop factor camera needs all of the glass elements in the lens why bother making EFS, DC (Sigma) lenses. In fact Sigma just converted some of their FF lenses to 4/3 system. All they did is change the mount.

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

pcunite · May 21, 2007

UziY said:
In your shooting situatuion, would you like a 15-44/1.8L lens? Are
you willing to spend over $2000 for it?

Well because of the clarity that Eugene has stated, no, not at this time. I have no potential customers or myself complaining about the DOF I am currently getting. When I control the shooting situation I can use a 70-200 f2.8L on my 1.6 crop and get excellent DOF by placing the subject and background where I want.

What I am starting to see the value in with a 1.6 crop when shooting in situations that I don't control. I get excellent shutter speed without having to go to ISO3200 when the light is dim.

As I stated in my original question:

If I am using my 24-70 at f2.8 ISO1600 on a 30D so that I get shutter speeds around 1/125 would it be wise for me to go full frame?

Now I know that full frame won't help "IN THIS ONE SITUATION". In my above question, I can not go any faster than f2.8 (lense limitation) and don't want noise any worse than ISO1600, AND can not use a shutter slower than 1/125 otherwise the subject will blur...

Eugene Powers said:
... in order to match DOF from FF to crop camera you need to
stop down FF camera.
... if you stop down FF camera you get less light coming in so
you need to increase ISO or slow down shutter to match the same
exposure.
... It is all based on DOF

Lee Jay · May 21, 2007

Eugene Powers said:
If crop factor camera needs all of the glass in the lens designed
for FF camera why bother making crop factor camera lenses. And I
should be able to use crop factor camera lenses on my 1DS2 like
Sigma 50-150mm F2.8 DC for example. Right?

The reason for EF-s lenses is the "s" standing for short back-focus distance. The reason to make crop-camera lenses that aren't "s" (like the Sigmas and Tamrons) is to reduce cost by making the barrel vignette the image to a narrower image circle, thereby reducing the cost of the barrel and relaxing the constraints on optical quality by eliminating the need for them to be sharp to the edges of the 35mm frame.

--
Lee Jay
(see profile for equipment)

Lee Jay · May 21, 2007

Eugene Powers said:
I wish I could say I understand you but I can't.
How can it be less than Yes?
Think about it. If crop factor camera needs all of the glass
elements in the lens why bother making EFS, DC (Sigma) lenses. In
fact Sigma just converted some of their FF lenses to 4/3 system.
All they did is change the mount.

I answered below.

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23311239

--
Lee Jay
(see profile for equipment)

Atlantian · May 21, 2007

I think I know where you are coming from, but I feel it is a bit of a blackart, and in my feeling, it doesn't
quite work that way.

Molokai_fiords said:
Something went wrong with the post.. so my whole big point was lost.

Molokai_fiords said:
Oh well I try again, short and sweet this time:

Molokai_fiords said:
1. Cameras with smaller sensors have more DOF than cameras with larger sensors

Err... May I ask why? I think smaller sensors have the same DOF as the larger sensors at the same aperture.

Molokai_fiords said:
2. Sensor size does not in any way change DOF

Yes, I agree with you, but doesn't your (2) seem to contradict with your (1)?

Molokai_fiords said:
3. However, sensor size changes FOV at a given focal length, meaning you need a shorter FL with a smaller sensor to have the same FOV

Yes, fully agree with you. I am still with you so far.

Molokai_fiords said:
4. DOF is determined by focal length and distance to subject ONLY

Aperture don't?

Molokai_fiords said:
5. since smaller sensor cameras have shorter focal lenghts for same FOV as larger sensor cameras, you change the FL and thus you get more DOF

If I change my FL, I get the same FOV like the larger sensor camera, but my DOF is still governed by my aperture, no?

Molokai_fiords said:
6. hence, sensor size has an INDIRECT impact on DOF

I still don't see how you can arrive at this conclusion.

Molokai_fiords said:
Hope that is helpful. My point being that there is nothing magical about different sensor sizes, but that they change the FOV and if you want a similar picture from the same position with cameras of different sensor sizes (a pretty fair request I would think) then you need to change some parameters (like FL) and that impacts other parameters (like DOF).

Only if my Aperture is forced to change when I change my FL.

Lee Jay · May 21, 2007

Molokai_fiords said:
2. Sensor size does not in any way change DOF

Yes it does. It changes enlargement ratio, which changed CoC, which changes DOF. Smaller sensors have smaller DOF when the lens is not changed.

30D, 100mm, f2.8, 10 feet, DOF = 0.32 feet
5D, 100mm, f2.8, 10 feet, DOF = 0.50 feet

I think the most counter-intuitive thing in photography (that's also correct) is that taking a pair of scissors and trimming the edges of a film negative will change the DOF of the image on that negative.

The reason is, you're still going to print the final image at the same size (say, 8x10). Enlarging it more makes blur more visible which makes the DOF shallower.

--
Lee Jay
(see profile for equipment)

joe mama · May 21, 2007

Member said:
your DOF matching theory got to do with corner sharpness?

If you match the DOF, then you will be using the lens stopped down on FF. Stopping the lens down, of course, improves the corner sharpness.

When you compare two different systems, you cust compare equivalent images. One of the big plusses of FF, is that you get to used the lens stopped down for an equivalent image, which yields a sharper image.

Member said:
That is right. Identical lens should be used on both cameras.

So identical tires should be used on car tests? Identical shoes should be used on foot races? No. I mean, I can't fathom why you think the same lens should be used on the different camera formats, when the photographer would not use the same lens on the two formats for the same situation in real life.

Member said:
We are not talking about DOF again, are we?

Not per se. But we are talking about equivalent images.

Member said:
We are talking about if crop camera sees all of the lens.

I'm not talking about that at all. It has no bearing on what I'm talking about. I apologize for the confusion which comes from this link:

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23307714

I said:

Member said:
Member said:

Actually, the whole of the optics are used, but I, myself, am unclear
of the specifics, so I'll let Lee Jay answer that.

Click to expand...

However, that was incidental to my point and simply a response to one of Amin's points. My main thrust was:

Member said:
Member said:

No one denies that FF does not suffer on the edges, but certainly no
more so than cropped cameras do. The evidence is pretty
overwhelming:

Click to expand...

Which, again, is not related to the lens using the whole of the glass.

Member said:
Original tester could not possibly know how sharp corners are on
both lenses so he could not possibly compare one to another.

That's totally besides the point. I'm comparing the pics that the two formats take.

Member said:
As you know one copy of the lens could be better than another even if
it is the same lens.
I went through 6 copies of the 16-35mm to get one because of the
corner sharpness.
This right here invalidates the test.

You lost me. A test is posted that shows the corners of FF to be sharper than the corners of 1.6x for equivalent images, and no test to the contrary is posted.

What does your hunt for a sharp copy have to do with this?

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my photos. If you wish to use any of my photos for any purpose other than editing in these forums, please ask.

Eugene Powers · May 21, 2007

joe mama said:
joe mama said:

That is right. Identical lens should be used on both cameras.

Click to expand...

joe mama said:
Which, again, is not related to the lens using the whole of the glass.

joe mama said:

Original tester could not possibly know how sharp corners are on
both lenses so he could not possibly compare one to another.

Click to expand...

That's totally besides the point. I'm comparing the pics that
the two formats take.

You can't. Just like in car and tires example.

joe mama said:
joe mama said:

As you know one copy of the lens could be better than another even if
it is the same lens.
I went through 6 copies of the 16-35mm to get one because of the
corner sharpness.
This right here invalidates the test.

Click to expand...

You lost me. A test is posted that shows the corners of FF to be
sharper than the corners of 1.6x for equivalent images, and no
test to the contrary is posted.

Does not matter. Still not valid.

joe mama said:
What does your hunt for a sharp copy have to do with this?

Because lenses he used for test vary in quality.

joe mama said:
--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my
photos. If you wish to use any of my photos for any purpose other
than editing in these forums, please ask.

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

joe mama · May 21, 2007

Member said:
Member said:

That's totally besides the point. I'm comparing the pics that
the two formats take.

Click to expand...

Member said:
You can't. Just like in car and tires example.

Let me get this straight -- you're saying that you can't compare pics taken from FF and 1.6x?! If so, there's no need to read more or respond. That represents such a fundamental difference in outlook that it cannot be breached.

Member said:
Member said:

You lost me. A test is posted that shows the corners of FF to be
sharper than the corners of 1.6x for equivalent images, and no
test to the contrary is posted.

Click to expand...

Member said:
Does not matter. Still not valid.

Ditto what I just said above.

Member said:
Member said:

What does your hunt for a sharp copy have to do with this?

Click to expand...

Member said:
Because lenses he used for test vary in quality.

Which has nothing to do with which format produces sharper corners. I honestly don't get you, but don't trouble yourself with an explanation if you feel that you can't compare 1.6x to FF.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my photos. If you wish to use any of my photos for any purpose other than editing in these forums, please ask.

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