Depth Of Feild

Discussion in 'Digital SLR' started by Edward Holt, Feb 27, 2005.

1. Edward HoltGuest

Are the depth of field markers on a 35mm film lens correct when the lens is
used on a DSLR with a 1.6x magnification factor?

If I have a depth of field of three metres to infinity using a 50mm lens on
a film SLR and I put it on a DSLR, does the DSLR still have a depth of field
of three metres to infinity or does the magnification factor impact it?

Edward Holt, Feb 27, 2005

2. dylanGuest

No. Look for various threads in this group eg RE: DSLR Depth fo field 10/2
2005 . I learnt a lot from the group, in particuilar that the DOF scale is
only correct for 10x8 print when using 35mm film !

dylan, Feb 27, 2005

3. Don FGuest

-----------
As mentioned before, there are many tutorials and threads pertaining to
your question. Depth of Field and Depth of Focus are commonly misunderstood
terms and much has been written about it.
An excellent (not too technical) source is:
www.luminous-landscape.com

Look under "Tutorials" and "Understanding Series". You will have a better
understanding of what you are looking for.
Regards,
Don F

Don F, Feb 27, 2005
4. Roland KarlssonGuest

Hmmmm ... no ... not really. Look at this ...

It says the CoC is defined as 5 l/mm for a 10x8. This will
result in CoC being d/1625, where d is the diagonal.

But the value 1625 can be used for any size, so - the DOF
scale on your lens is correct for any print size. It is
just to change the viewing distance.

OK - for smaller prints you need a magnifying glass and
vary good photo paper - so there is a limit for smaller prints.

/Roland

Roland Karlsson, Feb 27, 2005
5. dylanGuest

so the reply (below) I got to an early post is wrong then ?
Confused !!

dylan, Feb 27, 2005
6. SheldonGuest

IMO logic would dictate that the magnification factor is only for your use
in determining what size your image will be. Keep in mind the focal length
of the lens does not change. The image is being "cropped" by a specific
ratio due to the smaller size of the image sensor. It is not being
magnified in any way. Therefore, the DOF should be the same.

As for the second statement: What difference should it make how large you
print your image? The DOF is in the image. The image does not change when
you blow it up, except for size, so how could DOF change? Your image is
only two dimensional. That's like saying if you take a photo of your
daughter and blow it up larger than 8x10 she will become your son.

Somebody correct me if I'm wrong.

Sheldon, Feb 27, 2005
7. CrownfieldGuest

correction: you are wrong.

to quote:

It says the CoC is defined as 5 l/mm for a 10x8. This will
result in CoC being d/1625, where d is the diagonal.

But the value 1625 can be used for any size, so - the DOF
scale on your lens is correct for any print size. It is
just to change the viewing distance.

note that sex changes are not mentioned anywhere.

Crownfield, Feb 27, 2005
8. BubbabobGuest

You'll have less depth of field with the DSLR. People will give you all
sorts of bullshit reasons why this isn't so but experimention bears this
out. It has to do with the difference in sensor size requiring a smaller
COC in order to maintain the same depth of field in indentically sized
prints. You'll get the same DOF that you'd have if you cut the
approprately sized piece out of the middle of one of your film camera
prints and enlarged it to the original print's size. DOF is a nebulous
term and requires that you standardize your print size and viewing
distance before any sort of meaningful numbers for comparison can be
generated.

Bubbabob, Feb 27, 2005
9. BubbabobGuest

Images are 'perfectly' sharp only at a single distance. As you magnify
the print, objects in front and in back of this plane become unacceptably
unsharp. If you alter your viewing distance so that the image subtends
the same number of degrees as the smaller image, this is effectively
negated. If you don't back off, larger prints have less depth of field
because you're magnifying the COF.

Bubbabob, Feb 27, 2005
10. dylanGuest

might be useful http://www.dofmaster.com/dofjs.html

PS. I originally didn't believe it either !!

dylan, Feb 27, 2005
11. Roland KarlssonGuest

Yes - it is wrong IMHO. Read the web page I gave in my reply.
There is it explained. And as far as I can see - the 10x8 is
just an example. If you use 10x8 and look at it at 25 cm (called
normal viewing distance), then the eye resolution is supposed to
be 1/5 mm. Therefore - this is used as the definition of DOF.
But - if you make a larger print at look at it further away you
get the same figure 1625 - and thus the same DOF. If you make a smaller
print - then it is problems though - and the DOF will in practice
increase.

/Roland

Roland Karlsson, Feb 27, 2005
12. Roland KarlssonGuest

You are both right

The definition is that the CoC is 1/1625 of the diagonal.
Then - it does not matter the slightest how large or
small the print is. The DOF scale on the lens is the same
for all print sizes. This is according to the defintion
of DOF - so - if we are talking about DOF - it does not
matter what print size you have.

But - it does matter in practice what print size you have.
In smaller prints you cannot see small details and when
viewing larger prints you can go nearer. So - the actual
sharpness needed usually change with print size. So - in
practice the definition used for DOF might not be all that
useful - and you could use another CoC. But - this is __NOT__
according to the definition of DOF - it is another value,
maybe more useful in some circumstances.

/Roland

Roland Karlsson, Feb 27, 2005
13. dylanGuest

Thanks, makes sense now.

dylan, Feb 27, 2005
14. Paul MitchumGuest

You're saying that it's possible for the circle of confusion to be
equivalent if you change the size of the paper *and* the viewing
distance to maintain that relationship between them.

And in that circumstance, yes, the DoF would be the same for the two
prints. However, unless you somehow make it so that the larger image can
only be viewed from a certain distance, the DoF will change as people
get closer to it.

Paul Mitchum, Feb 27, 2005
15. Paul MitchumGuest

DoF resides in the capacity of your eye to see detail in the finished
print, not in the lens. So regardless of what the DoF indicators on the
lens says, different print sizes will result in different DoF.
Again, DoF is *perceived,* it is not 'in the image.' If you take a
blurry image and shrink it, the shrunken image will appear to be
sharper. This is because the DoF has *changed.*
No, it's like saying that if you take a photo of your daughter and blow
it up larger than [whatever dimensions] it will become an image of your
daughter where the parts that are out of focus will appear much more out
of focus.
OK, will do.

(Sorry, I couldn't resist.)

Paul Mitchum, Feb 27, 2005
16. Paul MitchumGuest

....of an 8x10 print viewed at 25cm.
....as long as it's an 8x10 print at 25cm.
....that happen to be 8x10 viewed at 25cm.
I think that if you look for more definitions of DoF, you'll find more
accurate information. '1/1625 of diagonal' is only part-way there. It's
like saying that the theory of relativity is equal to 3, because you can
solve e=mc^2 for e=3.
The CoC doesn't change; your eyes' capacity to see detail is really only
going to be affected by disease or old age. Relative to the constant
CoC, the DoF changes as you alter print size and viewing distance.

Paul Mitchum, Feb 27, 2005
17. Paul MitchumGuest

I think you have confused 'Depth of Field' with 'Field of Vision.'

Paul Mitchum, Feb 27, 2005
18. BubbabobGuest

0m (Paul Mitchum) wrote:

In what way?

Bubbabob, Feb 28, 2005
19. stephen zimic via PhotoKB.comGuest

Technically I agree with Bubbabob. Personally, I've always used the depth
of field preview button and then close down one additional stop for
insurance. It hasn't failed me yet regardless of format. I guess you might
need to use the scale on the lens for really low light photography where
the button is impracticle.

stephen zimic via PhotoKB.com, Feb 28, 2005
20. BubbabobGuest

I've experimentally determined the same thing. One additional stop seems to
do it.

Bubbabob, Feb 28, 2005