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iq and sensor size

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strawman
strawman  1022006 forum posts United Kingdom16 Constructive Critique Points
21 May 2013 - 5:25 PM

Hi Mike I think it comes and goes in waves or trends. And like everything it can be over used. I have seen images where a massive depth of field has created an image of stunning depth, and others where the low depth of field has pulled a subjected from its background. It is a parameter I like to play with and I think is one of the fun elements of photography. The moment everyone has something some people will pull the other way, and long may it continue.

For the original poster, I think lots of compact cameras can create excellent A4 sized prints, I use one myself, as well as an SLR. But I also like the freedom to play with DoF and focal length plus focus point. So yes some images you will struggle to tell, others you will spot a low DoF

For me the different formats bring different things and it is great to be able to play with them and decide what you want. For me photography is about playing, for others it is serious. And if you are playing, enjoy the toys 

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21 May 2013 - 5:25 PM

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Paul Morgan
Paul Morgan e2 Member 1315366 forum postsPaul Morgan vcard England6 Constructive Critique Points
21 May 2013 - 5:28 PM


Quote: This gave me food for thought

http://theonlinephotographer.typepad.com/the_online_photographer/2012/06/in-defe...

Good dof once meant great dof, I`m glad i`m old fashioned.

This really belong in the other thread Smile

strawman
strawman  1022006 forum posts United Kingdom16 Constructive Critique Points
21 May 2013 - 5:29 PM

This is the best photography magazine I have seen lately

cyclist magazine Smile

A good mix of photo's with lots of depth and interesting landscapes and some others. Sometimes in a shot you have something sharp in the foreground with an out o focus background interest. It is the mix that intrigues me.

Last Modified By strawman at 21 May 2013 - 5:30 PM
Paul Morgan
Paul Morgan e2 Member 1315366 forum postsPaul Morgan vcard England6 Constructive Critique Points
21 May 2013 - 8:55 PM


Quote: This is the best photography magazine I have seen lately

Ideal for those with tight Lycra fetishes Smile

strawman
strawman  1022006 forum posts United Kingdom16 Constructive Critique Points
21 May 2013 - 10:37 PM

You have got to get it where you can Paul Smile

Paul Morgan
Paul Morgan e2 Member 1315366 forum postsPaul Morgan vcard England6 Constructive Critique Points
21 May 2013 - 11:24 PM

Lol Smile

MichaelMelb_AU
22 May 2013 - 5:38 AM


Quote: I'm getting a bit confused with this. Although I can accept it's used as a ground measurement, I can't understand what size of enlargement has to do with it except perceptually - unless you are cropping a portion of the image [in which case you are of course effectively altering the format]. The way I look at it, pixel density could be seen as analogous to film speed, since slower/finer grained films would yield more detail. I don't know for sure, but I don't think this had any bearing on the DoF calculation for any given format...

Pixel density does not have much to do with enlargement - sensor size does, no mater how many Mp is there. Finer grained film gets more detail, but useable density of either film or digital sensor is limited to the lens resolution, i.e minimal airy disk lens is able to produce. Circle of confusion in it's turn, is also in proportion to sensor size, not megapixel count. You are getting crossed between camera resolution and DOF - that is what I see as the source of confusion. Megapixels simply don't count in this matter. Also, sensors are very unlike the film. ISO100 film has the same grain in 18/24mm and 10/12cm, the sensors don't.

Last Modified By MichaelMelb_AU at 22 May 2013 - 5:41 AM
LenShepherd
LenShepherd e2 Member 62479 forum postsLenShepherd vcard United Kingdom
22 May 2013 - 7:01 AM


Quote:

You lot have gone way of subject.

All I know is, my old 50mm zuiko gives a whole lot more DOF on a film camera than it does on one of my Pens, focused at the same distance Smile

I agree the topic has got way off subject.
However comparing a different angle of view, (100mm equivalent on the Pen) which is what you are doing, is perhaps adding to the confusion.
Changing magnifications has a dramatic effect on depth of field

Putting the 50mm on the Pen from the same focus distance gives you a lot more magnification, and reduces dof compared to the OM film body by 4 stops - a reduction of depth of field to one quarter.
If you maintain the same angle of view with a 25mm on the Pen you get more dof than with the 50mm on the film body.
Summing up same angle of view (with a wider angle lens) from the same distance gives more depth of field with a smaller format.
Increasing magnification from the same focus distance by not changing the focal length gives less dof with a smaller camera.
On a detail if you increase focus distance using the same lens on a smaller format camera to get the same angle of view as on the larger format camera you also get more dof.

LenShepherd
LenShepherd e2 Member 62479 forum postsLenShepherd vcard United Kingdom
22 May 2013 - 7:38 AM


Quote:
Pixel density does not have much to do with enlargement - sensor size does, no mater how many Mp is there. Finer grained film gets more detail, but useable density of either film or digital sensor is limited to the lens resolution,

There is reality, and there are web myths.
Sorry but digital sensor or film resolution is NEVER limited by lens resolution.
The optical formula and field use clarify that image resolution is made up of sensor/film resolution measured in isolation, and lens resolution measured in isolation.
If you increase either sensor resolution or lens resolution you get more image resolution Smile
If you increase both at the same time you get even more image resolution- including at aberration limited apertures Smile Smile
MP can have a lot to do with maximum print magnification possible.
Large format film cameras are generally capable of more print magnification when prints are viewed close up because there are were more usable film grains.
Higher MP digital cameras are capable of more print magnifications when viewed close up because there are more pixels to use.
Comparing a 12 MP Nikon D3 to a 36 MP D800 it is widely accepted the D800 sensor at base ISO has about double the independently measured resolution of a good lens used at its optimum aperture. The optical formula predicts this should result in about 33% more image resolution with the 36 MP camera, which is less than some might presume. My experience comparing D3 to D800 is 33% is about right much of the time using pro lenses.
Whether you print big enough to see the extra detail possible is another topic - in much the same way as is there an quality difference between a high end compact and an entry level crop sensor body and lens when making a small print seems to be a forgotten topic - even though this is where this thread started 9 pages ago Smile

MichaelMelb_AU
22 May 2013 - 8:03 AM

Post was edited - see below. Sorry for the inconvenience.

Last Modified By MichaelMelb_AU at 22 May 2013 - 8:09 AM
MichaelMelb_AU
22 May 2013 - 8:06 AM


Quote: ...

Putting the 50mm on the Pen from the same focus distance gives you a lot more magnification, and reduces dof compared to the OM film body by 4 stops - a reduction of depth of field to one quarter.
If you maintain the same angle of view with a 25mm on the Pen you get more dof than with the 50mm on the film body.
Summing up same angle of view (with a wider angle lens) from the same distance gives more depth of field with a smaller format.
Increasing magnification from the same focus distance by not changing the focal length gives less dof with a smaller camera.
...

Sorry Len, but it's a really puzzling mix you produced. First of all - what do you mean by "magnification"? Is it the scaling of the sensor format to fit the image into screen/print or narrowing of the field of view of the lens because of the smaller sensor format? They are not the same. Second - depth of field in your example should decrease about two times - it is in proportion to the linear size of sensor's diagonal ( as COC), but not to the sensor's surface area. Hence 2, not 4.

Quote:
On a detail if you increase focus distance using the same lens on a smaller format camera to get the same angle of view as on the larger format camera you also get more DOF.

That is not possible altogether - one can get the same linear field of view in small sensor camera by standing further from the subject, but not the same angle of view - this does not change and is a rigid combination of lens focus length and sensor diagonal. Though you will get the same look of image front plane - the image prospective will change dramatically. That will be entirely different image with flatter prospective. DOF comparison becomes pretty much pointless with prospective change.

Last Modified By MichaelMelb_AU at 22 May 2013 - 8:15 AM
LenShepherd
LenShepherd e2 Member 62479 forum postsLenShepherd vcard United Kingdom
22 May 2013 - 8:35 AM


Quote: Sorry Len, but it's a really puzzling mix you produced. First of all - what do you mean by "magnification"?

If a lens on 24x36 covers a subject 12x8 feet putting the same lens on 4/3 at the same focus distance covers approximately 6x4 feet, which is commonly known as more magnification.

Quote: On a detail if you increase focus distance using the same lens on a smaller format camera to get the same angle of view as on the larger format camera you also get more DOF.[/quote/]
Agreed - as in the last line of my post at 7.01 am
[quote]That is not possible altogether - one can get the same linear field of view in small sensor camera by standing further from the subject, but not the same angle of view - this does not change and is a rigid combination of lens focus length and sensor diagonal. Though you will get the same size of image front plane - the image prospective will change dramatically. That will be entirely different image with flatter prospective. DOF comparison becomes pretty much pointless with prospective change.

I part agree and part disagree. If you keep the same focus distance and use a wider angle on the smaller format you get similar perspective, ignoring small differences because one format is 4/3 and one is 3/2 format. Formats I am more familiar with are 24mm onNikon FX and 17mm on Nikon DX)
Although dof is different marked aperture for marked aperture, changing aperture on one camera can often achieve the same dof.

Steppenwolf
22 May 2013 - 1:57 PM

OK, so the reason that the larger sensor camera has a greater DOF (in the on-line calculators, when using the same lens) is because the image taken with a smaller sensor camera needs to be blown up to print at the same size. I'm a bit dubious about comparing DoF on two pictures with a different AoV, but never mind - I can now see how they arrive at the result they do.

However, it does mean that these DoF calculations need to be treated with a lot of caution when comparing different sensor sizes. For example, MichaelMelb said earlier in this thread that:

"But, EOS5D with 25mm, f1.8 and subject distance of 5m will produce whole 5.2m DOF! Sure you need to do 2X crop to get the same picture as 4/3 camera? Can we minimise the crop? Yes, we can! With a 35mm lens we get 2.27m DOF - pretty much the same as 25mm lens with 4/3 camera. And it is just 35/25=1.4 crop that would be needed to get absolutely the same result as one of the best 4/3s!
This is what I meant by creating a DOF one needs for their image."

He has used the on-line DoF calculators to attempt to try to prove that the FF camera can generate the same DoF as the M4/3 camera. His argument is that the FF camera has the same DoF as the M4/3 camera because you can achieve the same result by cropping the FF image from a 35mm lens. Unfortunately he has misunderstood the way that the DoF calculators work. When the FF picture is cropped to the AoV of the M4/3 camera it will end up smaller (obviously). So the image will need blowing up - at which point the DoF of the image becomes smaller. Basically as soon as you crop the FF image you need to magnify the image, at which point the DoF becomes smaller.

ChrisV
ChrisV  7786 forum posts United Kingdom26 Constructive Critique Points
22 May 2013 - 4:24 PM


Quote: I'm getting a bit confused with this. Although I can accept it's used as a ground measurement, I can't understand what size of enlargement has to do with it except perceptually - unless you are cropping a portion of the image [in which case you are of course effectively altering the format]. The way I look at it, pixel density could be seen as analogous to film speed, since slower/finer grained films would yield more detail. I don't know for sure, but I don't think this had any bearing on the DoF calculation for any given format...
Pixel density does not have much to do with enlargement - sensor size does, no mater how many Mp is there. Finer grained film gets more detail, but useable density of either film or digital sensor is limited to the lens resolution, i.e minimal airy disk lens is able to produce. Circle of confusion in it's turn, is also in proportion to sensor size, not megapixel count. You are getting crossed between camera resolution and DOF - that is what I see as the source of confusion. Megapixels simply don't count in this matter. Also, sensors are very unlike the film. ISO100 film has the same grain in 18/24mm and 10/12cm, the sensors don't.

Apart from the thing Len mentions about lens resolution not absolutely limiting sensor resolution [which I believe is true], I am actually largely agreeing with you that it is sensor size and not sensor resolution which will determine DoF at any given equivalent AoV and aperture value.

I don't know for sure, but I would imagine that a 10x8 print from a D3 and one produced from a D800 taken with the same aperture from the same position [without any crop of either's full frame of view] would appear more or less identical in terms of how they render DoF. Perhaps someone could test that? Len?

MichaelMelb_AU
22 May 2013 - 9:00 PM


Quote:
He has used the on-line DoF calculators to attempt to try to prove that the FF camera can generate the same DoF as the M4/3 camera. His argument is that the FF camera has the same DoF as the M4/3 camera because you can achieve the same result by cropping the FF image from a 35mm lens. Unfortunately he has misunderstood the way that the DoF calculators work. When the FF picture is cropped to the AoV of the M4/3 camera it will end up smaller (obviously). So the image will need blowing up - at which point the DoF of the image becomes smaller. Basically as soon as you crop the FF image you need to magnify the image, at which point the DoF becomes smaller.

DOF does not change when you crop the image - it stays the same. When you crop full frame to a smaller format it just means that this cropped image cannot be magnified to the format larger than smaller sensor allows, and quite often - less than small sensor allows. It is irrelevant however in the small print an on the computer screen. DOF is defined by combination of optics and sensor size (COC). Stop confusing people with your inability to grapple with the basics (i.e resolution and DOF)- your statement that online calculator wrong is ridiculous! Better read some good photography books...Tongue

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