Close up filter question

Krzys · Sep 15, 2009

I am going to use a x2 close up filter on my Hasselblad 80mm and was just wondering how this affects the depth of field. Will if half the depth? Should I be stopping down heaps to say.. f/8 if I want to get all of the features of a person's face in focus?

Q.G. · Sep 15, 2009

It will change depth of field, as image scale changes.
By how much depends on what the lens is set to, i.e. the image scale used at the time.

Sirius Glass · Sep 15, 2009

Use the preview button. It will be no worse that what you can see with the close up lens on the camera lens wide open.

Steve

Larry.Manuel · Sep 15, 2009

http://www.dofmaster.com/dofjs.html

For this calculation, I have assumed a subject distance of 30 inches. Closer, the D.O.F. will be smaller. Also assumed: 80mm lens, f/8. A handy rule of thumb: 80mm lens at f/8 has the same D.O.F. as a 50mm lens has at f/4.

Subject distance 30 in

Depth of field
Near limit 28.9 in
Far limit 31.2 in
Total 2.31 in

In front of subject 1.11 in (48%)
Behind subject 1.2 in (52%)

Hyperfocal distance 703.1 in
Circle of confusion 0.045 mm

Larry.Manuel · Sep 15, 2009

For the calculation, omit any consideration of the close-up lens. The subject distance is what matters. Close-up lenses don't change the focal length of the camera's lens, they allow closer focusing. Probably yours has a 0.5 meter focal length, which means your 80mm lens will focus at 20" when set at infinity. Maybe consider f/22 when at 20" subject distance with an 80mm lens.

Marco B · Sep 15, 2009

Maybe these examples will help a bit. Camera was a Minolta Dynax 7 (35mm), with an F1.7/50 mm lens and a 4x times close up lens.

First, a photo at F22:

Next one is at F4:

As you can see, the F4 picture has almost zero depth of field, while the F22 pictures manages to have maybe 1-2 centimeters...

Please note that these two pictures were taken at about the exact limit of the close focusing distance. Of course, if you back away, the available depth of field will be bigger.

Marco

Q.G. · Sep 15, 2009

Larry.Manuel said:
[...] Close-up lenses don't change the focal length of the camera's lens, [...]

That is exactly what they do: they shorten the focal length of the lens (or rather: the combined focal length is shorter), so that with the same amount of extension, you focus closer.

It is correct, though, that for DOF considerations only the scale and aperture matter

Larry.Manuel · Sep 15, 2009

Quote:
Originally Posted by Larry.Manuel View Post
[...] Close-up lenses don't change the focal length of the camera's lens, [...]
That is exactly what they do: they shorten the focal length of the lens (or rather: the combined focal length is shorter), so that with the same amount of extension, you focus closer.

Respectful disagreement follows:

The close-up lens -"filter" in OP - makes a more-strongly converging cone of light enter the camera's lens, thus the [macro-esque] image will focus on the film, using the same focus travel. If the lenses' combined focal length was shorter [or longer] the image scale - size of objects on film - would be affected, and it's not.

The close-up lens [Rolleinar for Rollei users] is like a reading glass for you eyeball. Without it, the image of the newspaper /now Facebook/ you're trying to read would focus behind your retina. Ergo: blurry vision. The correct eyeglass lens begins converging the light before it enters the eye. Ergo: clear vision.

Larry.Manuel · Sep 15, 2009

This may be handy for planning the exposure, as the FL of the lens is the same, and it gives at a glance what requires many iterations with DOFmaster.com. Note also the subject area/field - handy, too.

Considering the "strength" of the close-up lens is not required. The object distance and aperture are all that matter.

http://www.stutterheim.nl/rolleigraphy/dof75.htm

polyglot · Sep 15, 2009

Sorry Larry, QG is right on this one. A close up lens is measured in diopters, which are the inverse of focal length (1/m). Say you have a 100mm lens, that's +10 dioptres. Put a +2 closeup lens on it, the net effect is like you have a +12 = 83mm lens. For the same extension with a shorter lens, you get more magnification.

Anyway, all that matters for DOF is magnification (ratio of image size to subject size) and relative aperture (f-number), not the focal length. You can rearrange all those terms to also come to the conclusion that all that matters for DOF is how far you are from the subject and what the physical diameter of the effective aperture is - think about the cone of rays entering the lens from a focused point.

Q.G. · Sep 16, 2009

Larry, you respectfully disagree with yourself too:

Larry.Manuel said:
The close-up lens [Rolleinar for Rollei users] is like a reading glass for you eyeball. Without it, the image of the newspaper /now Facebook/ you're trying to read would focus behind your retina. Ergo: blurry vision. The correct eyeglass lens begins converging the light before it enters the eye. Ergo: clear vision.

So the light focuses a shorter distance behind the lens with, than without close up lens.

See?

Sirius Glass · Sep 16, 2009

There are only two ways of knowing what the DOF is for a subject:

1) Stop down the lens and look through the viewfinder/prism - 35mm and MF SLRs
2) Stop down the lens and look at the ground glass - LF and some MF

Using a tape measure and charts is less than fun and prone to errors.
Using the hyper-focus is not real accurate when very close up.

Steve

Krzys · Sep 16, 2009

I know how to judge with distance scales ect. I was just wondering if there was a calculation for the filter.

Sirius Glass · Sep 16, 2009

Close up filters do not require an exposure compensation.

Extension tubes and bellows do. But if you are using a metering prism, then the meter takes care of the exposure.

For exposure compensation see:
http://www.hasselbladhistorical.eu/HT/HTComp.aspx
http://www.hasselbladhistorical.eu/HT/HTCuC.aspx

Steve

Q.G. · Sep 16, 2009

Krzys said:
I know how to judge with distance scales ect. I was just wondering if there was a calculation for the filter.

(there was a url link here which no longer exists) gave the formula to use to find the new focal length.
Use that focal length in the 'usual' DOF formulae, add in aperture and distance, and you'll get an answer.

Close up filter question

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