toxdoc42

I should know the answer to this and am embarrassed to ask, but I just want to be surw.

Using depth of field tables to determine what will be "in focus" uses the focal length of the lens, the distance to the object photographed and the aperture ( f stop for those who are even more basic then I). If one has a crop sensor, do you use the "adjusted" lens focal length of the native one. To clarify, a 50 mm prime lens on my Nikon crop sensor camera is a native 50 mm, but is effectively functional as about a 70-80 mm one when using the crop factor. I have to be further away from the subject to achieve the photo I am trying to achieve, so the distance would be correct, but would the depth of field be that of the 50 mm lens, which is wider, or that of the 70-80 mm lens?

rmalarz Loc: Tempe, Arizona

https://neilvn.com/tangents/full-frame-vs-crop-sensor-cameras-comparison-depth-of-field/
--Bob

jederick Loc: Northern Utah

Great, well written info and examples at that link, Bob...thanks for posting!!

NCMtnMan Loc: N. Fork New River, Ashe Co., NC

I would suggest that you spend $10 if you have a smart phone and purchase the PhotoPills app. There is so much info in it about not only shooting astrophotography, sunrises and sunsets, but depth of field etc. for pretty much any camera and lens combination. It is the best $10 you'll spend for this type of info.

toxdoc42

I have one, but I question whether to use the native focal length of the lens or the adjusted one for the crop factor.

selmslie Loc: Fernandina Beach, FL, USA

Use the native focal length.

A 35mm lens on a 1.5 crop sensor camera will give you a field of view similar to a 52.5mm lens but you need to use 35mm as the focal length in the DOF calculator.

User ID

As usual .... the answer to an incomplete
question depends on knowing the missing
information. So, I'll start from scratch ...
DoF derived from circle of confusion ;-)

Ultimate image magnification determines
what size circle of confusion is needed. It
doesn't matter how you get there. Take a
tight head shot as example, and print/view
it as an 8x10. You can shoot it on an 8mm
movie camera and blow up a movie frame
40X. You can shoot it on Nikon F and blow
it up 8X. You can shoot it on a Graphic and
blow it up 2X. The ultimate magnification
is always 0.5X [face in an 8x10 tight head
shot is about 1/2 life size].

If all of the above are to have the identical
DoF then the C of C size AS PRINTED must
be the same in all the prints. And that size
we'll call "Z" [cuz it's near the shift key and
I'm a lousy typist].

So the in-focus C of C measures "Z" in all of
the 8x10 prints. Therefor, on film the C of C
measures Z/40 on 8mm film, Z/8 on 135
film in the Nikon F, and Z/2 on the 4x5 film.

The C of C is the image of the physical lens
aperture projected onto the film. The long
FL of the 4x5 projects a bigger CoC but that
is OK cuz we will only enlarge it 2X. The lens
on the Nikon, looking at the SAME SIZE hole
as the Graphic, projects a CoC 1/4 as big as
did the lens on the Graphic ... cuz it has a
shorter FL. The lens on the 8mm movie cam
is also looking at the same size hole and it
projects over its dinky little distance a CoC
on 1/5 as big as did the lens on the Nikon F.

Surely you have noticed "same size HOLE"
is stated, but not the f/stop. As the FL gets
shorter that same size hole represents ever
faster f/stops. That hole can be f/45 on the
Graphic and f/11 on the Nikon F, and f/2.3
on the movie cam.

So yes, for identical DoF at identical viewing
sizes [all 8x10 tight heads in the example]
the smaller the format the faster the f/stop.
In the example, f/2.2 for 8mm movies is the
same DoF as f/11 for a Nikon, and the same
DoF as f/45 for a Speed Graphic.

Notice that the Nikon format [24x30mm for
an 8x10 print] is 1/4 the size of the Graphic
format. Notice that the f/stop number used
for the Nikon is 11, which is 1/4 of 45, the
f/stop number for the Graphic. That same
simple formula holds for the movie cam, as
1/20 of 45 is 2.3. And acoarst it holds for all
format and f/stop comparisons. An OMD-1
sensor is 1/2 the size of the Nikon F format
so if we include m4/3 here, the f/11 on the
Nikon equals f/5.6 on the Olympus.

As to equivalent FLs from format to format,
or changes in subject distance if the same
lens is used for different format sizes, or for
any and all combinations of FL, distance and
format size, only one thing determines DoF
and that is ultimate image magnification, as
stated in line one, paragraph one, so we've
come full circle [of confusion, fun pun !]

So, you can use your calculator. If it's set for
FF, and you're shooting APSC, just set your
f/number at about 2/3 of what the calculator
wants for FF. Calculator says f/16 for FF, use
f/11 for APSC.

And acoarst if you are cropping to get more
reach cuz you've outdistanced your 600mm,
don't forget that this all works in reverse.
IOW, say you crop to about 12x18mm for a
shot with the 600mm. If the moose is 1000
yards away, you use 500 ft subject distance
to calculate the DoF for the MARKED f/stop
on the long lens. That chart wants a higher
f/number for 500yd than for 1000yd, which
is cuz you need more DoF cuz you cropped,
and cropping increases your ultimate image
magnification.

.

toxdoc42

I assume the other poster and my original assumption are correct, use the native lens focal length?

Now, the $64,000 question, why did the manufacturers stop putting the DoF indications on the lenses?

selmslie Loc: Fernandina Beach, FL, USA

1. Because they are misleading - not enough information.
2. Because with autofocus lenses they are too close together.

larryepage Loc: North Texas area

3. And because for zoom lenses, except for "push-pull" models, there is no way to do it.

selmslie Loc: Fernandina Beach, FL, USA

But the curved colored lines are pretty.

User ID

Becuz you now understand HOW to use
the native lens FL, yes you use it.

======================

All math is fungible, so there will surely
be those who explain that you use the
equivalent rather than the native FL. It
all depends on what data is input along
with the FL number. IOW when you turn
socks inside out, they still fit the same !

.

User ID

`

DoF is subjective.
Use LV MF magnifier.

And don't squint or your
face will freeze like that !


.

toxdoc42

I don't see why you say DoF is "subjective," I assume that everyone would see the out of focus objects as out of focus, and those within the circle of the depth of field as in focus. Yes, I do use LV and the magnifier, but usually only after I have taken a "test photo," to check focus, and exposure. But that is only when the timing allows it to be done.

I rarely use LV. In so many circumstances, it is either impossible or inconvenient.

User ID

`



Avoid using LV when impossible or inconvenient.

It's unreasonable to assume everyone would see the
out of focus objects as out of focus, and those within
the circle of the depth of field as in focus. It's a very
subjective call as to where margins of the "in focus"
zone actually lie. What's verrry OUT is not subjective
but DoF is about deciding where IN is "IN enuf".

Declaring what size CoC represents "IN enuf" derives
from analyzing many samples of viewers' subjective
personal impressions of "sharp enuf".

.