Enlarger height/Magnification formula?
Ian Dodd
information. A search on dejanews.com gives several conflicting
formulas. Can anybody give me the correct formula for determining the
enlarger height needed for various size prints?
I will be building a new darkroom when I move in a few weeks. I want to
be able to enlarge to 16X20" from 4X5" with a 150mm lens. How much
distance from the negative to the paper do I need? And if if I want to
go to 20X24"?
Private e-mail is fine. Thanks in advance.
Ian Dodd
c._downs
wrote:
Michael Gudzinowicz answered a similar question for me by stating:
The formula is:
easel_to_carrier_distance = focal_length * (2 + 1/M + M)
where M is the negative to print magnification.
For a 7.2 X enlargement, the distance with a 300 mm lens would be
300 * 9.34 = 2801 mm = 110.3 inches. For a 240, the distance would be
240 * 9.34 = 2241 mm = 88.25 inches.
Hope just pluging in your lens and film size will help
Good luck in the new darkroom!
C. Downs
Tim Mathers
However, this is from the rear nodal point of the lens.
And another factor is that most enlargers focus by moving
the lens. An additional "fly in the ointment" is the focal
length of the lens (is it 150.00mm FL?).
At "face value", you have a 4x5 negative and you want to
make a 16x20 print, so that's 4X magnification. So "we" do
the math and it comes out 29.5 "and change" inches.
In the "real world", you'll probably be "higher" because
a 4x5 negative isn't 4x5 inches. And if it were, the film carrier
"masks" some of it (so the film won't "fall out" when you
remove the dark slide - I hate it when that happens!).
And even if the image was 4x5 inches, the negative carrier
in your enlarger "masks" some of that (most carriers that I've
measured have an aperture of somewhere near 3.6" by 4.6").
And, of course, you cropped the image to the absolute edge
of the negative.
So, in reality, you'll most likely be something like 34" or 36"
lens-to-easel distance.
Hope this helps. .......... Timmy
PS The inverse (R+1)*FL will give the lens-to-film distance.
Very useful to calculate bellows draw for exposure compensation.
"Ian Dodd" <ian...@mediaone.net> wrote in message
news:39AD559D...@mediaone.net...
Ian Dodd
Currently I raise the head to about 31-33", depending on cropping, to make
an 11X14" from 4X5" through a 150mm lens (the math says it should be 30.5"
but, as another person pointed out, I'm losing a bit around the edges to the
carrier and cropping). That suggests that a 16X20" enlargement needs 37" of
negative to paper distance and 20X24" will need 42.5". Figuring in a bit
for cropping, I had better build my enlarging table with at lest 44" of
distance available. Thanks again.
Ian
C., Downs wrote:
> On Wed, 30 Aug 2000 18:44:20 GMT, Ian Dodd <ian...@mediaone.net>
> wrote:
>
> >I know this question has been asked before but I can't seem to find the
> >information. A search on dejanews.com gives several conflicting
> >formulas. Can anybody give me the correct formula for determining the
> >enlarger height needed for various size prints?
> >
> >I will be building a new darkroom when I move in a few weeks. I want to
> >be able to enlarge to 16X20" from 4X5" with a 150mm lens. How much
> >distance from the negative to the paper do I need? And if if I want to
> >go to 20X24"?
> >
> >Private e-mail is fine. Thanks in advance.
> >
> >Ian Dodd
>
c._downs
wrote:
>Thanks for the formula. Checking it with my own enlarger, it seems to fit.
>Currently I raise the head to about 31-33", depending on cropping, to make
>an 11X14" from 4X5" through a 150mm lens (the math says it should be 30.5"
>but, as another person pointed out, I'm losing a bit around the edges to the
>carrier and cropping). That suggests that a 16X20" enlargement needs 37" of
>negative to paper distance and 20X24" will need 42.5". Figuring in a bit
>for cropping, I had better build my enlarging table with at lest 44" of
>distance available. Thanks again.
>
>Ian
One of the things you might do is build the enlarger table so that the
"baseboard" is removable and build slots on either side to slide it
into. That way you can have an easy working distance for 8x10's and
lower the baseboard to print 20x24 or larger sizes. I've mounted my
enlargers on the wall so that the baseboard can go all the way to the
floor and have a track up the wall that allows the enlarger to be
raised to the ceiling if necessary....but then I do love big prints!
Beseler has a table like this you might look at to get ideas.
Ian Dodd
will wall mount the enlarger (and gain the extra stability) and build a
baseboard that is adjustable. Indeed, I am going to install some leveling
screws on each corner and a bubble levels in the X and Y directions so it can be
precisely leveled at any working height.
Ian