DOF and Cropping take 2

Started 9 months ago | Discussions
moving_comfort
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Re: DOF and Cropping take 2
In reply to awaldram, 9 months ago

awaldram wrote:

moving_comfort wrote:

Q: Does cropping FF (to ap-sc, for example) change DOF when displayed at the same sizes? Because I think you used to hold the position that it does not.

Simple question  how can it.?

It absolutely does.  Remember, we're displaying the image at the same size after the crop - we're not doing something like cropping an 8x10 to 5x7 and then just looking at the 5x7!  Cropping the FF image to aps-c size changes the DOF of the original FF image to match what an aps-c shot would have had when the crop is displayed at the same size.

You are stuck on this issue, and I suspect you're thinking of the image staying in the same dimensions as you cropped it to, which isn't the case when you either view or print the crop.  None of the 'good' information you've managed to reference supports your error, if you pay attention.

Here - please read carefully through what I wrote in this thread , which I'll past below - please take the time to read, understand and answer it paying attention to the last paragraph:

. . . pasted below ...

...Actually, I don't think you do agree with that point, unless I'm misreading you.  Let's try a simple test to see where you stand:

We know that a 300mm f/4 shot on FF and then shot on aps-c from the same position would have different DOF in the final image, from:

• Using the same lens on a APS-C crop sensor camera and a 35mm full frame body, the APS-C crop sensor camera image has 1.5x LESS depth of field than the 35mm image would have

Now, take that 300mm f/4 FF shot, and crop it so that it has the same FOV as the aps-c shot, and display both images (aps-c uncropped and FF cropped) at, say, 8x10. Do the images show the same DOF now?

If the answer is yes**, how could that be true if cropping does not change DOF? Remember, focal length and distance to subject didn't change, the only thing that changed was that the FF image was cropped.

** spoiler alert - the answer is yes

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moving_comfort
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Re: DOF and Cropping take 2
In reply to MightyMike, 9 months ago

MightyMike wrote:

awaldram wrote:

You missed the point!

Does cropping FF (to ap-sc, for example) change DOF when displayed at the same sizes?

To crop and then display at the same size the magnification must change and therefore the appearance of DOF will change!

It's the same mistake he always makes, look at that thread I linked form three months ago.

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James O'Neill
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Re: Back to basics
In reply to awaldram, 9 months ago

awaldram wrote:

I think your right there are a lot of simplification in play in photography that break under some circumstances.

If you check that MIT slide deck I linked there is some interesting material on simplifications and covers off both distance shooting and indeed macro shooting where its also busted

I know that there is a slight error in the formula because the circle size is always based on the focus distance error as a fraction of the correct focus distance which is always assumed to be the focal length. That's close enough most of the time but for 1:1 (i.e. true macro) the lens to subject and lens to image distances are both 2xf so the formulae for near and far point [ HD/(H-D) and HD/(H+D) ] don't work properly. I've got a vague memory that you use D+F  instead of D and when F is 50mm and D is 5M the error really doesn't matter.  When D is 100mm ....

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awaldram
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Re: DOF and Cropping take 2
In reply to moving_comfort, 9 months ago

moving_comfort wrote:


• Using the same lens on a APS-C crop sensor camera and a 35mm full frame body, the APS-C crop sensor camera image has 1.5x LESS depth of field than the 35mm image would have

The answer in NO it doesn't, the image created on the aps-c sensor is identical to the middle 66.6% of the FF sensor.

With an identical lens same F -stop and same registration the images painted onto the film plane is identical therefore the DoF is identical , DoF is a function of the Lens.

Perceived DoF varies because you alter the viewing distance (something that happens after your above statement)....i.e CoC is altered. i.e you will magnify the aps-c image 1.5 times therefore reducing CoC and increases apparent DoF.

Turn it all round look at  it this way

if you want maintain image size between formats you need to optically magnify the larger sensor by the crop factor of the smaller sensor.

If you use a larger magnifying lens (say for aps-c 200 ff 300) you have reduced the physical aperture by reducing the entry pupil... ergo your DoF will reduce by 1.5.

So whether you use 1.5x optical magnification or 1.5x digital enlargement the result is the same CoC reduces DoF changes.

Hence why in my first statement which you took such exception to and spawned this thread  about DoF and cropping I altered the viewing distance and crop at the same time to ensure it was correct.

But your statement above is 100% wrong became its incomplete and as it stands inferes a 300mm F2.8 lens causes a different DoF depending on how big a proportion of its projection you take and you have categorically stated that is true which it obviously isn;t and has to break the laws of physics to be so.

You may as well tell me you believe in fairies.!

The danger is your statement will lead others to believe in fairies as well.

So lets be clear a 300 F2.8 on FF is exactly the same as a 300 f2.8 on aps-c shutter iso and f-stop will be the same for any given exposure.

DoF captured will be the same but because you will veiw the ff image 1.5 time closer it will appear to have less DoF.

You can easily prove this by taking a magnifying glass to an image and note where the DoF extends vs without it.

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moving_comfort
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Re: DOF and Cropping take 2
In reply to awaldram, 9 months ago

awaldram wrote:

moving_comfort wrote:

• Using the same lens on a APS-C crop sensor camera and a 35mm full frame body, the APS-C crop sensor camera image has 1.5x LESS depth of field than the 35mm image would have

The answer in NO it doesn't, the image created on the aps-c sensor is identical to the middle 66.6% of the FF sensor.

mod edit: removed personal attack

Read what I and others have said above - you're not cutting out the middle 66% of the image and displaying it at those dimensions, you're cutting it out and magnifying it, which is what changes DOF.

.

So lets be clear a 300 F2.8 on FF is exactly the same as a 300 f2.8 on aps-c shutter iso and f-stop will be the same for any given exposure.

300 f/2.8 aps-c vs 300 f/2.8 FF? FOV will be different, DOF will be different, and if you shoot at the same ISO, noise will be different. You're shooting blanks now

Some apropos points to ponder:

• For an equivalent field of view, an APS-C crop sensor camera has at least 1.5x MORE depth of field that a 35mm full frame camera would have - when the focus distance is significantly less then the hyperfocal distance (but the 35mm format needs a lens with 1.5x the focal length to give the same view).

• Using the same lens on a APS-C crop sensor camera and a 35mm full frame body, the APS-C crop sensor camera image has 1.5x LESS depth of field than the 35mm image would have (but they would be different images of course since the field of view would be different)

If you use the same lens on an APS-C crop sensor camera and a 35mm full frame body and crop the full frame 35mm image to give the same view as the APS-C crop image, the depth of field is IDENTICAL

• If you use the same lens on an APS-C crop sensor camera and a 35mm full frame body, then shoot from different distances so that the view is the same, the APS-C crop sensor camera image will have 1.5x MORE DOF then the full frame image.

• Close to the hyperfocal distance, the APS-C crop sensor camera has a much more than 1.5x the DOF of a 35mm full frame camera. The hyperfocal distance of an APS-C crop sensor camera is 1.5x less than that of a 35mm full frame camera when used with a lens giving the same field of view.

.

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Ian Stuart Forsyth
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Re: DOF and Cropping take 2
In reply to moving_comfort, 9 months ago

moving_comfort wrote:

Ian Stuart Forsyth wrote:

http://www.dpreview.com/forums/post/53084843

continued from the post above

Just a highlight key points I would like to address

red is Ian

Green is GossCTP

and Black awaldram

But I see it as equivalent please see below

Do you really believe this website above , I mean really ?

How accurate is the information they provide ?

.

That Cambridge Tutorials page is not very accurate, and that site has been debunked in the Nikon fora before.

Some folks are just not careful with their googling, and they still try to source it, adding to their confusion

.

As you can see that it calculates the same equivalent of lens and F stop as I had calc’d

Here is a quote from the site

“As sensor size increases, the depth of field will decrease for a given aperture (when filling the frame with a subject of the same size and distance). This is because larger sensors require one to get closer to their subject, or to use a longer focal length in order to fill the frame with that subject. This means that one has to use progressively smaller aperture sizes in order to maintain the same depth of field on larger sensors. The following calculator predicts the required aperture and focal length in order to achieve the same depth of field (while maintaining perspective).

As an example calculation, if one wanted to reproduce the same perspective and depth of field on a full frame sensor as that attained using a 10 mm lens at f/11 on a camera with a 1.6X crop factor, one would need to use a 16 mm lens and an aperture of roughly f/18. Alternatively, if one used a 50 mm f/1.4 lens on a full frame sensor, this would produce a depth of field so shallow it would require an aperture of 0.9 on a camera with a 1.6X crop factor — not possible with consumer lenses!”

And a reminder that whether you crop an image in the camera or in post with PS you are altering the size of the format, just as many do with a D7100 or a D800 in camera or during post

Now which site do I believe yours or mine?

Yours is of course correct.

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

Its kind of funny as Cambridge Tutorials has got this right and even their calculator is correct as this is what I used who would have thunk EH

& it looks like I am late to the party

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awaldram
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Re: DOF and Cropping take 2
In reply to moving_comfort, 9 months ago

As they say proof is in the eating

Bit rough and ready but as your both saying the Q will show 4X more DoF than the K3 precision isn't required to prove your wrong

I didn't use a tripod as the results are as conclusive as the logic of the facts.!

One is a crop from a large sensor one straight of a (very) small sensor

Both using same lens same F-stop same shooting distance

1 is cropped to match the other

so which has the massively less DoF as you argument states ?

The only things done to these images is one cropped and both have had there niose profile equalised.

So does cropping give the same DoF if the same lens is use irrelvant of sensor?

This proves without any doubt in my opinion a lens characteristic do not alter by sensor size.

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awaldram
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Re: DOF and Cropping take 2
In reply to Ian Stuart Forsyth, 9 months ago

Ian Stuart Forsyth wrote:

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

Its kind of funny as Cambridge Tutorials has got this right and even their calculator is correct as this is what I used who would have thunk EH

Yep they seem to know what there talking about despite MC's bunk

as they say on the page you refer

"Be warned that both of these terms can be somewhat misleading. The lens focal length does not change just because a lens is used on a different sized sensor — just its angle of view. A 50 mm lens is always a 50 mm lens, regardless of the sensor type."

And just above they state exactly the point I;ve been making

"As sensor size increases, the depth of field will decrease for a given aperture (when filling the frame with a subject of the same size and distance). This is because larger sensors require one to get closer to their subject, or to use a longer focal length in order to fill the frame with that subject."

i.e you alter the magnification to maintain size therefore altering CoC and intern reducing DoF.

as they state

"Note that the above calculator assumes that you have a lens on the new sensor (#2) which can reproduce the same angle of view as on the original sensor (#1). If you instead use the same lens, then the aperture requirements remain the same (but you will have to get closer to your subject)."

Again exactly what I've been saying

& it looks like I am late to the party

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moving_comfort
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Re: DOF and Cropping take 2
In reply to awaldram, 9 months ago

awaldram wrote:

As they say proof is in the eating

Bit rough and ready but as your both saying the Q will show 4X more DoF than the K3 precision isn't required to prove your wrong

Where has anyone said that?

.

So does cropping give the same DoF if the same lens is use irrelvant of sensor?

This proves without any doubt in my opinion a lens characteristic do not alter by sensor size.

I'm not quite sure what point you're trying to make with that comparison, and can't know for sure what angle and position you took the shot from, but doesn't the above speak to the following? :

* If you use the same lens on an APS-C crop sensor camera and a 35mm full frame body and crop the full frame 35mm image to give the same view as the APS-C crop image, the depth of field is IDENTICAL

(in this case you're not comparing aps-c to FF, you're comparing Q to aps-c, but same principle.)

In which case the act of cropping (and enlarging) is equalizing things from the original, uncropped image (ie - changing DOF from the original) - as expected, and described by me, Ian, Bob Atkins, Cambridge Tutorials (the 'good' link ) and everyone else who knows what they're talking about?

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awaldram
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Re: DOF and Cropping take 2
In reply to moving_comfort, 9 months ago

moving_comfort wrote:

awaldram wrote:

moving_comfort wrote:

• Using the same lens on a APS-C crop sensor camera and a 35mm full frame body, the APS-C crop sensor camera image has 1.5x LESS depth of field than the 35mm image would have

The answer in NO it doesn't, the image created on the aps-c sensor is identical to the middle 66.6% of the FF sensor.

Are you just being dense now, or willfully deceptive? Because you're repeating the same incorrect things without even reading what I wrote.

Well someone here is being dense but given Ian's source was the same as mine and both vindicate everyone of my statements I guess its not me.

hopefully you;ll put it to bed now given the easy to digest photographic evidence I've provided .

so yes cropping a larger sensor image to the same as the cropped sensor does indeed give identical DoF

Or can you think of anything else for me to shoot down in flames, Your coming across as desperate now.

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moving_comfort
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Re: DOF and Cropping take 2
In reply to awaldram, 9 months ago

awaldram wrote:

Ian Stuart Forsyth wrote:

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

Its kind of funny as Cambridge Tutorials has got this right and even their calculator is correct as this is what I used who would have thunk EH

Yep they seem to know what there talking about despite MC's bunk

The link Ian gave was for a different tutorial than what you linked (same site.) You missed his joke a bit I'm afraid.

.

as they say on the page you refer

"Be warned that both of these terms can be somewhat misleading. The lens focal length does not change just because a lens is used on a different sized sensor — just its angle of view. A 50 mm lens is always a 50 mm lens, regardless of the sensor type."

And just above they state exactly the point I;ve been making

Yes, just like a 5mm lens is a 5mm lens, regardless of sensor type - but they give radically different FOV when you move up in size from P&S. Not sure how this fits into your confusion or how it applies directly to things you've said so far.

.

"As sensor size increases, the depth of field will decrease for a given aperture (when filling the frame with a subject of the same size and distance). This is because larger sensors require one to get closer to their subject, or to use a longer focal length in order to fill the frame with that subject."

i.e you alter the magnification to maintain size therefore altering CoC and intern reducing DoF.

as they state

"Note that the above calculator assumes that you have a lens on the new sensor (#2) which can reproduce the same angle of view as on the original sensor (#1). If you instead use the same lens, then the aperture requirements remain the same (but you will have to get closer to your subject)."

Again exactly what I've been saying

Actually it's not what you've been saying - you've been saying that cropping FF to aps-c of a shot taken from the same position and then displaying the same size does not alter DOF - and it does. It makes the FF shot equal the aps-c shot in DOF, when before (uncropped) it had less DOF. See how the DOF changed there, by cropping and enlarging to the same viewing size? I guess we can keep repeating it until it takes

.

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MightyMike
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Re: DOF and Cropping take 2
In reply to moving_comfort, 9 months ago

moving_comfort wrote:

MightyMike wrote:

awaldram wrote:

You missed the point!

Does cropping FF (to ap-sc, for example) change DOF when displayed at the same sizes?

To crop and then display at the same size the magnification must change and therefore the appearance of DOF will change!

It's the same mistake he always makes, look at that thread I linked form three months ago.

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To be honest i doubt its really a mistake of knowledge but of mis-interpretation... I think you both can agree that you both understand the subject but sometimes you both misfire on the little niggles in the subject. Best to always be very clear and try to avoid the small niggles that will confuse the average joe.

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awaldram
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Re: DOF and Cropping take 2
In reply to moving_comfort, 9 months ago

moving_comfort wrote:

awaldram wrote:

As they say proof is in the eating

Bit rough and ready but as your both saying the Q will show 4X more DoF than the K3 precision isn't required to prove your wrong

Where has anyone said that?

.

So does cropping give the same DoF if the same lens is use irrelvant of sensor?

This proves without any doubt in my opinion a lens characteristic do not alter by sensor size.

I'm not quite sure what point you're trying to make with that comparison, and can't know for sure what angle and position you took the shot from, but doesn't the above speak to the following? :

* If you use the same lens on an APS-C crop sensor camera and a 35mm full frame body and crop the full frame 35mm image to give the same view as the APS-C crop image, the depth of field is IDENTICAL

(in this case you're not comparing aps-c to FF, you're comparing Q to aps-c, but same principle.)

In which case the act of cropping (and enlarging) is equalizing things from the original, uncropped image (ie - changing DOF from the original) - as expected, and described by me, Ian, Bob Atkins, Cambridge Tutorials (the 'good' link ) and everyone else who knows what they're talking about?

So why did you contest me here.?

http://www.dpreview.com/forums/post/53081062

Are you now admiting you were talking rubbish and f2.8 on mf,ff,aps-c or indeed Q will not effect exposure ?

and that to say f2.8 = f2.8 is not crazy but correct.?

and this
?

http://www.dpreview.com/forums/post/53082172

or from the thread that started it all 3months ago

http://www.dpreview.com/forums/post/52527488

so lets try and make it clearer

In photography, the circle of confusion (“CoC”) is used to determine the depth of field, the part of an image that is acceptably sharp. A standard value of CoC is often associated with each image format, but the most appropriate value depends on visual acuity

Nothing todo with sensor sizes at all !!

So if you finally agree then maybe you've learnt something ?

Unfortunately your obsession with proving everybody needs FF blinds you in everything and prevent you being objective or even understanding any other viewpoint.

Even when that viewpoint is the same as yours but from the other side as in Cambridge in colours two page references you slander the same author for one yet laud him for the other. When both say the same thing only your to blind to see.

.

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awaldram
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Re: DOF and Cropping take 2
In reply to moving_comfort, 9 months ago

moving_comfort wrote:

Actually it's not what you've been saying - you've been saying that cropping FF to aps-c of a shot taken from the same position and then displaying the same size does not alter DOF - and it does. It makes the FF shot equal the aps-c shot in DOF, when before (uncropped) it had less DOF. See how the DOF changed there, by cropping and enlarging to the same viewing size?

it never ever had less or more DoF it always had the same DoF if you don't understand that point I'm close to giving up.

a lens of X length at aperture Y delivers DoF Z always it a characteristic of the lens nothing else it has to the entry pupils and hence magnification and hence f-stop remain constant so any image projected onto whatever target at the same distance  has a constant CoC.!

What you do with the resulting image affects CoC and so effects perceived DoF

I guess we can keep repeating it until it takes

At last something we can agree on

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Ian Stuart Forsyth
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Re: DOF and Cropping take 2
In reply to awaldram, 9 months ago

awaldram wrote:

“As sensor size increases, the depth of field will decrease for a given aperture (when filling the frame with a subject of the same size and distance). This is because larger sensors require one to get closer to their subject, or to use a longer focal length in order to fill the frame with that subject. This means that one has to use progressively smaller aperture sizes in order to maintain the same depth of field on larger sensors. The following calculator predicts the required aperture and focal length in order to achieve the same depth of field (while maintaining perspective).

This nothing different to what I've been saying or Cambridge in color for that matter if your using the longer focal length to deliver greater magnification on larger sensors the the DoF will alter i.e you will need to shrink the aperture.

But doing this is not giving you any advantage and will come at a cost to ISO and/or shutter speed.

Of course you have to go to a higher 225 iso if you want to have the same DOF but FF has the advantage that it has a better SNR and can give it up and go to a higher iso without losing anything and hold the same SNR as a cropped sensor at iso 100

Sensor size is nothing but the expected viewing size in reverse.

?

If you concern is to maintain perceived DoF at he same viewing angle then of cause you need to alter focal length and aperture and take the hit in ISO and shutter.

again

Of course you have to go to a higher 225 iso if you want to have the same DOF but FF has the advantage that it has a better SNR and can give it up and go to a higher iso without losing anything and hold the same SNR as a cropped sensor at iso 100

(with the addition) If I take a hit on iso then my shutter speed will be the same so I can still freeze the subject as a cropped camera would under the same conditions. This is why we say FF 300 F4.2

will share the same DOF and FOV and total light ( Same noise level) as a Cropped with a FL of 200 F2.8

Most people myself included could not give to hoots about DoF as its to narrow on aps-C and even worse on FF, So I care about shutter speed and target size not DoF.

i.e Fast shutter, plenty of reach and bags of sharp area controllable noise

they are mutually exclusive and you can do very little to gain anything

I could use a 5.5 crop camera this would give me loads of reach, massive DoF (shorter focal length for same target size) but I'd still be shooting in the iso1600 range and the sensor noise can't cope.

because with the great DOF less light will falls on the 5.5 crop thus more noise. I f you where to get into the DOF shooting with your cropped 1.5 camera that a compact can achieve the same DOF then many times the compact can give you better IQ than the cropped 1.5 camera as some of those compact cameras have QE over 65%

So how about FF, this would be me issues with DoF , focal lengths requiring faster shutter than the target required leading to higher ISO than the ambient light indicated driving up ISO beyond the possible stop gained by the format.

A FF with the same FOV as a Cropped camera's FOV would require the same shutter speed on both formats to freeze the subject & iso 100 on cropped would give us the same noise as iso 225 on FF so you lose nothing

APS-C allows me to shoot at subject stopping speeds which are also-in the ball park 1/x for camera induced blur whilst maintain an ISO in 1600-3200 range giving noise that Ir can cope with.

exmples

q = 50mm (f-stop irrelevant) have to shoot >1/250 to freeze subject so in in 800-1600 range noise uncontrollable.

k3 = 300mm F4 shutter 1/250ish iso 1600-3200

FF = 450mm (have to shoot F5.6 for cost and DoF) shutter has to be >1/400 for consistent non camera blur this pushes iso into the 128,000 -256,000 range resulting in a poorer IQ than the aps-C will deliver.

As stated above if you need a SS of 1/250 to freeze motion on a cropped then the FF at 1/250 will freeze the same image movement

Cropped FOV 300 x1.5=FOV of a FF 450 mm Same FOV same shutter speed to freeze the same object as it moves the same size of FOV framing.

so with FF shooting at 450mm at F5.6 1/250 3200-7200 will give you the same noise levels to work with because they capture the same amount of light. If you don't believe me look up the SNR of a FF at iso3200 to a cropped at iso 1600

I find it kind of funny how you for your k3 state that all you need is a SS 1/250 but when moving over to FF you now included that need more shutter speed to make for camera shake, you know most lenses tele's in production have IS built into them ?

Everything is a balancing act and what works for one may not work for another, In very bright light I can see Q type sensor delivering better Images than either FF or Aps-C due to its reach.

Yes a Q with a 100mm F2.8 (5.64 crop factor) can give you pretty good IQ but how often do people with a FF shoot at 560mm F 16 or a cropped at 400mm F11 we are in the territory that diffraction starts to hamper IQ and not to mention for the Q and the 100 mm F2.8 would have to 5.64 times sharp than a FF equivalent 600 or 3.7 times sharper than cropped 400mm lens. You have to also remember that lens is wide open( at its worst for IQ) just to achieve the F16 ff equivalent .

Yes if could have FF with a 200-400 f4 or the 400 f2.8 then yes I could realize the FF Dream but I don't have £10,000 to cover that aspect of my hobby.!

A FF 400mm F5.6 is in the same ball park as for cost and weight as a 300 F4 any guesses why?

Of cause of Blurred backgrounds are all you care about then MF is the better option.

not really as I don't see anything in production that pentax can give us the DOF as a FF 24 F1.4, 28 F1.8 35mm F1.4 50mm F1.4, 50mm F 1.2 or 85mm F1.4

To achieve the same blur a portrait can deliver in MF on a FF camera if you were shooting a 300 f2.8 on MF

135mm f1.2

nothing pentax produces can do this

For a pentax 645 d with 300 F2.8 all it would take is a FF 200 F 2 lens that is in production

and if you were using a 135 f4 land camera (8x10) to get the same shots you need a 14mm f.4 on a Nikon FF body.

Hence my opinion that basing purchasing decisions on DoF equivalence is doomed to despair.

Not really when you look at what equivalent lenses between FF and crop most of the time they are at the same price point , IQ and weight

And even considering DoF equivalence outside academia is fruitless.

Not when you look at the versatility FF has to offer.

The only equivalence that makes some sense today is FoV where it can be used to roughly understand what magnification factor you might perceive based off something you know.

and what does this mean? with magnification comes light loose

Given proliferation of small sensor image taking devices even that is becoming pointless.

Not really now that FF body is becoming cheaper to afford and updated with the latest technology  as a cropped sensor.

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Re: DOF and Cropping take 2
In reply to moving_comfort, 9 months ago

moving_comfort wrote:

awaldram wrote:

As they say proof is in the eating

Bit rough and ready but as your both saying the Q will show 4X more DoF than the K3 precision isn't required to prove your wrong

Where has anyone said that?

.

So does cropping give the same DoF if the same lens is use irrelvant of sensor?

This proves without any doubt in my opinion a lens characteristic do not alter by sensor size.

I'm not quite sure what point you're trying to make with that comparison, and can't know for sure what angle and position you took the shot from, but doesn't the above speak to the following? :

* If you use the same lens on an APS-C crop sensor camera and a 35mm full frame body and crop the full frame 35mm image to give the same view as the APS-C crop image, the depth of field is IDENTICAL

(in this case you're not comparing aps-c to FF, you're comparing Q to aps-c, but same principle.)

In which case the act of cropping (and enlarging) is equalizing things from the original, uncropped image (ie - changing DOF from the original) - as expected, and described by me, Ian, Bob Atkins, Cambridge Tutorials (the 'good' link ) and everyone else who knows what they're talking about?

you for got the great B too!

.

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MightyMike
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Re: DOF and Cropping take 2
In reply to awaldram, 9 months ago

awaldram wrote:

Are you now admiting you were talking rubbish and f2.8 on mf,ff,aps-c or indeed Q will not effect exposure ?

Just a little niggle... The exposure can be very different as the FOV of the area being projected onto the sensor or metering device can vary greatly, a 40mm lens at F2.8 on a 5.5x crop factor Q and a 40mm lens at F2.8 on an APS-C when shot from the same distance can have significantly different exposures as the scene can be quite different than a part of the scene.

and that to say f2.8 = f2.8 is not crazy but correct.?

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Re: DOF and Cropping take 2
In reply to Ian Stuart Forsyth, 9 months ago

Ian Stuart Forsyth wrote:

awaldram wrote:

The only equivalence that makes some sense today is FoV where it can be used to roughly understand what magnification factor you might perceive based off something you know.

and what does this mean? with magnification comes light loose

I mean equivalence for DoF etc don't really tell someone anything about the image as most shooters have no terms of reference

Given proliferation of small sensor image taking devices even that is becoming pointless.

Not really now that FF body is becoming cheaper to afford and updated with the latest technology as a cropped sensor.

By small Sensor I mean camera phones.! now that proliferation and what your average shooter has as a term of reference the Film shooters from yesteryear are a dying breed (literally) and when were all gone what point a FoV based on a sensor size in the minority.?

I don't see any format as the new nirvana they all have strengths and weakness , at present with the aps-c current pixel density it fits my needs.

A 36-50 Mp FF would also work but not give me any massive gains to what I have today but would set be back £10,000+ in replacement glass.

I expect the Pentax FF to be 24Mp and though I'll watch with interest it won't be on my Christmas list for the reasons I've covered in this thread.

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Re: DOF and Cropping take 2
In reply to MightyMike, 9 months ago

MightyMike wrote:

awaldram wrote:

Are you now admiting you were talking rubbish and f2.8 on mf,ff,aps-c or indeed Q will not effect exposure ?

Just a little niggle... The exposure can be very different as the FOV of the area being projected onto the sensor or metering device can vary greatly, a 40mm lens at F2.8 on a 5.5x crop factor Q and a 40mm lens at F2.8 on an APS-C when shot from the same distance can have significantly different exposures as the scene can be quite different than a part of the scene.

Give you that , maybe I should add against a flat 18% grey target

and that to say f2.8 = f2.8 is not crazy but correct.?

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James O'Neill
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Confusion and mispeaking.
In reply to awaldram, 9 months ago

awaldram wrote:

moving_comfort wrote:

Actually it's not what you've been saying - you've been saying that cropping FF to aps-c of a shot taken from the same position and then displaying the same size does not alter DOF - and it does. It makes the FF shot equal the aps-c shot in DOF, when before (uncropped) it had less DOF. See how the DOF changed there, by cropping and enlarging to the same viewing size?

This is back to front. If you have a full frame image, and crop it (magnifying what is left by greater margin), smaller amounts of misfocus are visible, i.e. the depth of field is shallower.

If you use a smaller image area the circle of confusion where you can see something isn't in focus gets smaller. If you change the focal length of the lens to give the same angle of view, because circle size is proportional to square of focal length the change in focal length more than compensates for the change in circle size.

it never ever had less or more DoF it always had the same DoF if you don't understand that point I'm close to giving up.

The size of the circle of confusion remains constant.  If you have an image the size of the side of house the c of c where you notice the image is out of focus is bigger than in the image is the size of a finger nail.

a lens of X length at aperture Y delivers DoF Z always it a characteristic of the lens nothing else it has to the entry pupils and hence magnification and hence f-stop remain constant so any image projected onto whatever target at the same distance has a constant CoC.!

Again , I think you mean "C of C, Z"

What you do with the resulting image affects CoC and so effects perceived DoF

It affects the C of C size which is visible as a circle rather than a point, not the size of the circle laid down by the lens. But I think that's what you meant.

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