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stupid 1.6 multipler question

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John Mason said:
There were some massive threads on this over the past year. I will
try to summarize below.

1. It's a simple crop because of the smaller sensor.
Click to expand...
Right
Member said:
2. Perspective is not a factor of focal length but of distance to
your subject.
Click to expand...
Right
Member said:
3. Depth of Field. This is were the rubber meets the road. This
is the only thing the crop factor doesn't change. At 24mm lens or
a 80mm lens on a 35mm camera will show the 24mm lens has much more
depth of field. This is not just because of the fact you have a
wider angle view. I used to think that wide angles just looked
like they had more depth of field because they were as if you had
"stepped back". This is totally wrong as these massive threads
show. If you take a shot with a 24mm and an 80mm and then crop
them so they show the same subject matter at the same size you will
see and prove to yourself that the wider the lens the more depth of
field there is. So the range of focus does not change simply
because you crop the picture.
Click to expand...
Wrong, BECAUSE the DoF is DEFINED in terms of the OUTPUT image, NOT what is captured on the Sensor. With a SMALLER format you have to ENLARGE the image more to get the same size output. The more you enlarge an image, the less in-focus it will appear to be (this assumes "simple optical enlarging" you can "cheat" with a more advance algorithm to maintain appararent sharpness). When you enlarge an image anything slightly out of focus will appear to be very out of focus. Thus the problem of trying to tell whether you shot is in-focus by looking at the LCD display on the back of the camera (you can only tell if the picture is grossly out of focus, but not if it is in focus). I think this is what you are missing.
Member said:
So - bottom line from a practical shooters standpoint, or another
way to put it, how to change your shooting decisions when working
with a D30/D60 is:

1. You get a image that is cropped or magnified once you print it
by a factor of 1.6. So your 50mm lens behaves as a 80mm lens in
terms of your angle of view. Angle of view equates to a higher
focal length. So it is ok to think of your 50 as an 80 and so one
in terms of the amount of subject matter you will get in your frame.
Click to expand...
The DoF will be about 1.6X GREATER with the D60 in this example. If you open up the F-number by 1.6X then the DoF will be about the same.
Member said:
2. Perspective is a function of distance so in this regard also
your 50mm lens will act just like an 80mm would have on a 35mm film
camera
Click to expand...
Yep
Member said:
3. the only area your lens will not be behaving just like it's
longer counterpart is DOF which remains the same.
Click to expand...
You are right that the Lens id not change but wrong on DoF. DoF is based on the Final Output Size and not just the image captured. The Fact that a smaller sensor image will have to be blown up more affects the sharpness and has to be taken into account. I suggest you review the DoF forumla and learn that it is based on an assumed output size.
Member said:
I hope that helps. The longer massive threads had people that
posted very carefully done example shots that proved the 3 points
with no doubt what-so-ever. I always understood point 1 but I was
totally wrong on points 2 and 3. That's why this forum is so
great. It's a wonderful learning tool.

disclaimer:

(before you flame me and disagree with what I've said here search
the earlier posts and find the examples and see all the
discussion.) or (take the shots yourself carefully and you'll prove
it to yourself)
Click to expand...
I am not try to Flame you, just correcting you factual errors. You can search ealier posts and get all kinds of incorrect information. That does not change the facts or the DoF formula.

There are many people on this forum that are confused about the DoF formula, many of which have never taken the time to learn how it really works and the ASSUMPTIONS made by the forumla. Adding to the confusion is that so many of the older books just Assumed 35mm Film format without stating that it was assumed.

--
Karl
 
Karl Guttag said:
Enjoy the photo shooting, but please stop spouting your ignorance
on subjects for which you do understand.
Click to expand...
I'm not going to dignify that with a response other than to point out that you can't even write a sentence as you intend Karl. I think you neglected to insert the KEY negative adverb, 'not', towards the end of your sentence.

I have no desire to get into a flame war, least of all with someone who enjoys trying to belittle other people. I could sit here and point out that while you say I have no ability to read or understand things you are so GREATLY lavished with knowledge of, your poor spelling and grammar weaken the fabric your argument so greatly it becomes laughable.

However, I do not wish to continue a conversation on this, you will only drive me to further sarcasm.

Please no more.
 
the focal length is by far the largest factor in depth of field

the formulas show that

so the practical effect of the lower focal length for a given perspective is the majority of the effect on DOF

CoC calcs also get into pixel size and grain size of film not just the sensor size. There are effects there but no where close to the obvious effects of the smaller focal length needed to achieve any given perspective with a smaller sensor as compared to a larger sensor.

Look at the forumlas, I already have fcalc. Use fcalc and play with the variables and you'll see this is true.
 
not sure what the argument is about. fcalc will show

1. for a given output size depth of field will be most dependent on the focal length of the lens - period. are you saying you disagree with that?
 
Yes true, because f is second order and all other variable are first order.

Janksta;
John Mason said:
not sure what the argument is about. fcalc will show

1. for a given output size depth of field will be most dependent on
the focal length of the lens - period. are you saying you
disagree with that?
Click to expand...
 
Member said:
3. Depth of Field. This is were the rubber meets the road. This
is the only thing the crop factor doesn't change.
Click to expand...
You forgot to include the veiwing of the print in your discussion of DoF. If you view the same size prints at the same distance, then D60 prints must be enlarged more than 1Ds prints. Enlargement affects CoC which affects DoF.

Here's something that may help. Everything is out of fucos except those objects that are precisely on the focus plane. In other words, DoF includes the notion of perception; that is, objects that "appear" to be in focus. For objects to "appear" to be in focus, you must view them. To standardize the DoF calculations, you must standardize the viewing methodology (e.g. 8x10 at two feet). If you don't standardize the viewing methodology, then it is not possible to discuss what "appears" to be in focus.
  • Christopher
 
Member said:
not sure what the argument is about. fcalc will show
Click to expand...
Don't know which calculator you are using, but please be aware than many DoF calculators on the web have been simplified to assume 35 mm negative film. If you are changing film (sensor) size, then it is important to use a DoF calculator that takes this variable into account.
  • Christopher
 
fcalc has all the variables involved including sensor/film size

John Mason - Lafayette, IN
 
I have to agree that the DoF does change.

A 16mm lens on a 35mm camera focusing on an object 10ft away would have a near limit of acceptable sharpness of ~ 5ft and a far limit of acceptable sharpness to infinity.

A 16mm lens on a D60 camera focusing on an object 10ft away would have a near limit of acceptable sharpness of ~ 6.1ft and a far limit of acceptable sharpness to 27.5 ft.
The difference being the circle of confusion.

Steve C.
Christopher Glaeser said:
Christopher Glaeser said:
not sure what the argument is about. fcalc will show
Click to expand...
Don't know which calculator you are using, but please be aware than
many DoF calculators on the web have been simplified to assume 35
mm negative film. If you are changing film (sensor) size, then it
is important to use a DoF calculator that takes this variable into
account.
  • Christopher
Click to expand...
 
the whole DOF question is a statistical method for determining what is acceptable focus.

this reminds of standard deviation discussions.

that's why I like to bring discussions back to what is operationally practical for the majority

Given same output size AND viewing distance - focal length of the lens is, by far, the largest variable in DOF.
 
print size and viewing size being the same

if a subject is at 8 feet and lens is a f1.8

you get the following:

24mm 50mm
DOF DOF
APS 3.13 feet .68 feet
35mm 2.46 feet .54 feet

So the CoC does change based on film/sensor dimensions, but the huge overiding factor in all this as shown above is the focal length of the lens.

Hopefully this will put some perspective on the discussion. I don't disagree with the people that want to state that the size of the sensor as a factor, but I think that detracts from the actual main issue which is not the sensor size - as shown above - but the focal length.

As you go from 50mm to 24mm you see a 460% improvement in DOF solely related to focal length for APS film. You see 455% improvement in DOF with 35mm film.

Leaving the focal length the same but changing the sensor size from 35mm to APS sized you get an improvement of 20% improvment instead of a 460% improvment or 1/23rd as much effect as changing the focal length.

I hope this puts some perspective on the discussion as to why this statement is true from:

The depth of field does not change with sensor size (will it does but not very much)

or this statement

The depth of field varies because of the focal length change of the lens (well it does, but its not the only factor)

from a practical standpoint DOF changes by far and mostly with the lenses focal length.

also from a practical standpoint, if you shoot with a ps digital with a little sensor it will have great DOF mostly because it's using a wider angle lens cropped to a smaller part of it's view.

Oh well, now I'm rehashing very old ground. So everyone has truth to what they are saying. I just wanted to put up something objective to show how much more important focal length is than the other factor's people are bringing up. I'm not saying the other things are true because they are true. I'm just putting proper perspective on it.
 
Most of the DOF calculators seem to use 0.033 as the standard COC for 35mm. In the digital world, however, the smallest point that can be registered and seen is a single pixel.

Purely as an exercise, I created a 3072x2048 pixel image (D60 pixel dimensions) in PS and sized the output dimensions to be 8x12.

I placed several black pixel clusters on the page, 1x1, 2x2, 3x3, 4x4, 5x5, and then printed it on my 2200 using enhanced matte paper.

At a viewing distance of 2-3 ft, I can clearly discern the single pixel (1x1) clusters.

For the D60, then, the COC would seem to be 0.0074mm, assuming of course, that a lens could resolve to that point. And upon examining some D60 shots, I do see single pixel-level detail.

To be fair, the 2x2 cluster does seem to be more of a point, yielding a coc of 0.0148. Still a major difference from 0.033.

On 35mm, with a 100mm lens at f/2.8 at a distance of 5m, a coc of 0.033 yields of DOF of 0.454m. A D60, with a 100mm lens at f/2.8 at a distance of 5m, a coc of 0.0074 yields a DOF of 0.102m. A big difference.

Incidentally, shooting the same setup at a distance of 8m gives a DOF of 0.262. This corresponds to backing up with a D60/100mm lens to frame the subject giving the same proportions as that of the 35mm/100mm lens.
 
John Mason said:
http://tangentsoft.net/fcalc/
Click to expand...
Couldn't get through to that site...

Using the depth of field calculator found here:
http://www.dudak.baka.com/dofcalc.html

Let's assume a .033mm "circle of confusion" for 35mm film
vs a .021mm CoC for a D60 (.021 = .033/1.6) to allow for the
fact that the smaller digital sensor cropping also enlarges
the "out-of-focus-ness" when enlarging to a given size print
(this ignores an inherently subjective discussion of how
"out of focus" is perceived differently on different media).

If you take a picture with a 35mm film camera, and then want to
shoot the exact same in-camera composition with a D60, you either
have to use the same lens and move further away from the subject,
or else maintain your distance and use a wider angle lens.

Using the above calculator, here are the results for each of the
"same lens, longer distance" and "wider lens, same distance"
for 100mm, 35mm, and 300mm lens scenarios, all shots
assuming f/8.

---

35mm film camera, 100mm lens, 15 ft distance:
1.62ft near, 2.06ft far

D60, 100mm lens, 24 ft distance:
2.63ft near, 3.4ft far

D60, 62.5mm lens, 15 ft distance:
2.46ft near, 3.62ft far

---

35mm film camera, 35mm lens, 5 ft distance:
1.24ft near, 2.45ft far

D60, 35mm lens, 8 ft distance:
2.00ft near, 4.02ft far

D60, 21.9mm lens, 5 ft distance:
1.74ft near, 5.73ft far

---

35mm film camera, 300mm lens, 40ft distance:
1.38ft near, 1.49ft far
D60, 300mm lens, 64ft distance:
2.25ft near, 2.40ft far
D60, 187mm lens, 40ft distance:
2.21ft near, 2.49 ft far
 
...couldn't help noticing that you hassle Karl because he;
Tim Lozinski said:
"neglected to insert the KEY negative adverb, 'not',
towards the end of (his) sentence".
Click to expand...
"Tim Lozinski said:
...
I'm not going to dignify that with a response other than to point
out that you can't even write a sentence as you intend Karl. I
think you neglected to insert the KEY negative adverb, 'not',
towards the end of your sentence.
Click to expand...
...and then turn around and "neglect to insert the preposition "of", toward the end of your sentence(between "fabric" and "your").
Tim Lozinski said:
I have no desire to get into a flame war, least of all with someone
who enjoys trying to belittle other people. I could sit here and
point out that while you say I have no ability to read or
understand things you are so GREATLY lavished with knowledge of,
your poor spelling and grammar weaken the fabric your argument so
greatly it becomes laughable.
Click to expand...
People and glass houses and stones, ...oh my! :-)

Larry
 
Ya know, someone with both a D60 and an EOS film SLR could easily put this to bed by taking photos of the same subject with the same lens on both cameras. Take the digital photo at various apertures, then move the camera forward 'til the field-of-view with the film camera is identical (which you can verify by looking at the digital photos on the D60's LCD screen), then take the film shots. Get the film developed, scan the frames and compare the files.

-Dave-
 
Tim Lozinski said:
Canon had a 'more technical' engineer phone me up the next day - so
I presume he was someone who REALLY knew his stuff.
Click to expand...
No he didn't know his stuff, and here's some simple proof for people who have problems with the 1.6x factor.

Does the G2 have more DOF than film? Everyone would answer "yes, of course!" Well, the G2 is NO different than the D60, just a smaller crop. Not at all different in any relevant way.

Jason
 
John Mason said:
Given same output size AND viewing distance - focal length of the
lens is, by far, the largest variable in DOF.
Click to expand...
This is an over simplification to the point of being untrue.

To a first approximation:

1. DoF goes down by the Square of the Focal Length - so yes it does have a big effect.

2. DoF goes up by the Square of the distance -- so it is just as important as the Focal length!

3. DoF goes up linearly with the F-number

4. DoF goes up linearly with the CoC (which for simple purposes follows the sensor size).

Note that 1 and 2 above roughly offset each other. So that if you say double the distance AND go double the focal length, the subject at the Focus distance in the viewfinder will stay the same size and the DoF will be the Same at the same F-number (and assuming the CoC is constant). The DoF will thus stay the same (the "perspective" or relative size of everything not at the same distance as the subject will change since the camera has moved thus changing the relative distances).

This is a well known issue to experience photographers, namely that since the Focal Length and Subject Distance offset each other if you keep the subject at the focus point the same size, the ONLY variable you can control DoF with is the F-number.

--
Karl
 
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