Bellows extension

[holmburgers]

I'm familiar with that, but it seems cumbersome, at least for "field" stuff. (as if taking a monorail into the field isn't cumbersome enough)

My reasoning for wanting to have a table with subject distances is the ability to take some measurement-standard on your body. For instance, the "hang ten" sign with your hand; that distance won't change, and if you know what it is you could quite accurately measure distances in the field w/o a ruler or anything. The distance from your elbow to fingertips could be another measurement, and so on.

Come to think of it, I'm just gonna get a huge ruler tattooed down the length of my arm and a yardstick down my leg....

 

[Ian C]

Quick & Easy Bellows Compensation with a Calculator

The easy way is to program a pocket calculator and take it with you. If you have trouble programming it there are many high school or college students who’d do it for you in a minute. You likely know at least one such person who’d do it for you.

Once that’s done you carry a metric roll-up tape measure or a dressmaker’s tape (they have metric versions very cheap at any fabric shop). Here’s all you do.


1. Compose and focus

2. Measure the distance E from film plane to diaphragm in millimeters (this isn’t fussy)

3. Enter f, E, and press the execution key to display the answer in f stops


What could be simpler?


The equation is

x = 2*ln(E/f)/ln2

where x = number of additional f stops for the bellows extension, E = bellows extension measured from the film plane to the diaphragm, and f = focal length of your lens.


It isn’t rocket science and you really don’t need to know any math to use it.

 

[holmburgers]

Thanks everyone, I know that you all have very good reasons for doing it the traditional way. It's simple and straightforward... I'll do it already!! However, I'm also wanting to take a fresh look at this and explore something different. Let's leave it at that. Besides, the more exposure mistakes I make, the more film I use and the more I'm feeding the market!

I really believe that having an intuitive grasp of how subject distance relates to bellows factor would result in near instantaneous exposure compensations, in your head. It's much easier to estimate distances on the scale of feet and inches rather than mm or cm.

Now, what was it that Robert Frost said?...

 

[John Koehrer]

IMO Greg's got the easiest solution and is more or less what I use.
My method(?) goes like this:
With a 150mm/6" lens,
infinity=0,
275mm/9"=1 stop,
300mm/12"=2 stops.
Halfway between gets half the correction 1/3 gets 1/3 the correction. Plus or minus depending which side you're measuring from.
With my hand, 9" is the spread from thumb to little finger whilst hanging ten.

 

[RodKlukas]

To all,
Here is a simple way to calculate compensation requiring only an inch tape measure.
take the focal length of your lens in inches and the extension of the bellows in inches and using these numbers change the unit to Fstops.
What is the difference? that is the number of stops you must compensate.
example a 210mm is approximately an 8" lens and with a 16" extension you derive f8 and f16. What is the difference between F8 and F16? 2 stops!
You're done. BTW, wide angles are terrible for closeup due to excessive lateral chromatic aberration. Questions see RodKlukas.com
Should help you all. 75mm= 3"= F2.8 1/3, 90mm = 3.5"=F3.5(2.8 2/3), 135mm = 5.6"=F5.6(close enough) etc
Thanks,
Rod

 

[Q.G.]

To all,
Here is a simple way to calculate compensation requiring only an inch tape measure.
take the focal length of your lens in inches and the extension of the bellows in inches and using these numbers change the unit to Fstops.
What is the difference? that is the number of stops you must compensate.
example a 210mm is approximately an 8" lens and with a 16" extension you derive f8 and f16. What is the difference between F8 and F16? 2 stops!
You're done.

Remember though that the extension in this methode is the full lens to film distance.

I mention that, because when SLRs are involved it is normal practice to use only the extra extension (the length of an extension tube, or bellows put between lens and camera) in calculations.
So when using the above method to calculate the compensation you need for an X" focal length lens with an Y" length tube, you have to add those X" to the length of the tube Y before 'converting' them into f-numbers.

 

[Q.G.]

IMO Greg's got the easiest solution and is more or less what I use.
My method(?) goes like this:
With a 150mm/6" lens,
infinity=0,
275mm/9"=1 stop,
300mm/12"=2 stops.
Halfway between gets half the correction 1/3 gets 1/3 the correction. Plus or minus depending which side you're measuring from.
With my hand, 9" is the spread from thumb to little finger whilst hanging ten.

Your "275mm/9"=1 stop" is off target by as much as 0.75 stops (should be 1.75 stops).
1 stop would be at 212 (and a bit) mm.

 

[steelneck]

http://www.youtube.com/watch?v=vwfRA615Mx8

I just came across this video on youtube that kind of explains bellows extension compensation. Thanks jason Brunner. Hope this helps someone else.

I just had to see it again. Jason is really good at doing those videos, they are both fun and educative.

 

[cowanw]

perhaps he meant 225mm

 

[hcm]

As the lens gets further from the film the light passing though the lens is spread over a wider area and proportionately less falls on any given area. The proportion is based on the square of the change in distance. Thus if the lens were twice as far away the light would be diffused over an area twice as high and twice as wide so the adjustment would be based on one quarter of the light hitting any area of film and the adjustment would be 2 f stops.

 

[stradibarrius]

I .tried measuring my bellows extension for this shot the bellows from the film plane to the lensboard is 16". My lens is 180mm. If I square the extension and divid by the square of my lens length I come up with 5 stop bellows factor??? Is this right?
Obviously this is a very close up shot. This is the total extension of the bellows.

 

[johnielvis]

16" extension / 180mm lens

that's the bellows FACTOR...not the stops--

FACTOR is used to multiply exposure TIME...

you want STOPS, what you really want is to know how many doublings it takes to get to that number

so if you get 5 for the FACTOR, you want to solve

2^n = 5 (where n=the Number of stops)

take logarithm of both sides: n*log2 = log5--this gives n = log5/log2 = 2.3

so you need 2 and one third stops compensation for this setup

 

[rmolson]

The Kodak Master Photoguide has a very comprehensive f number computer and simple way of determining exposure correction I have one taped to the back of my view camera glass cover.That and a pocket tape measure and you can figure the correction in seconds with out all the math. If I have a 6 inch lens 8 inches from the film plane my exposure should be increased by one stop.

 

[Bruce Osgood]

Strad,

I did the math and keep a copy in my bag


FILTER FACTOR & STOPS

FACTOR.. ..STOPS
1 0.0
1.5 0.6
2 1.0
2.5 1.3
3 1.6
3.5 1.8
4 2.0
4.5 2.2
5 2.3
5.5 2.5
6 2.6
6.5 2.7
7 2.8
7.5 2.9
8 3.0
8.5 3.1
9 3.2

 

[Bruce Osgood]

OOP'S

the format did not hold up.

The FACTOR should read as a number and decimal point, IE: factor of 1 is 1.0, 1-1/2 is 1.5.
The STOP numbers are one decimal point also, IE: STOP of 1 is 0, STOP of 1.5 is 0.6

Sorry the column spacing between the numbers didn't work.

 

[johnielvis]

well....that's basically a table of logaritms base 2....I prefer to just do something I call the "effective f stop"

you measure the lens extension then you divide by the lens focal length (the infinity "marked" focal length)

this give you a multiplier for the fstops on the lens...for instance if you have an extension of 140mm and the lens is 100mm then your muliplier is 1.4...so f5.6 as marked on the lens is now an "effective fstop" of 5.6*1.4 = 8

so I call it "f8 effective" when the lens is set at f5.6 at that bellows extension....

 

[Bruce Osgood]

John, I agree.

I made the all to common mistake of answering the wrong question.

I was addressing filter factors and not bellows extension.

 

[RalphLambrecht]

Is anyone out there able to give me an easy to understand explanation of this 'bellows extension compensation' that I have been hearing about. Just bought my first 4x5 camera (Zone VI) with a 210mm and 80mm lens. I haven't taken any photos yet, but like to be prepared for when I do.

try thisand start on pge 192!

 

[artonpaper]

My method is to measure the bellows extension, from the ground glass to the lens board, which, believe me is close enough, then divide that number by the focal length of the lens, square that number, which yields your Bellows Extension Factor, BEF, then divide your ISO by your BEF and set that into the meter and take your reading. Being super precise is not usually necessary, although when shooting chromes it can't hurt.

Example: 11 inch bellows extension, 8 inch lens, = 1.375 X 1.375 = 1.89. ISO 100 divided by 1.89 = 52.9, for a working exposure index (EI) of 50, which in this case will yield a one stop correction. All of this will keep you in a 1/3 f-stop tolerance, an industry standard.

 

[artonpaper]

PS - Here's a handout that I give to my large format students.

http://dl.dropbox.com/u/16205118/View camera procedure.doc

 

[PanaDP]

I know this has been well and thoroughly covered but perhaps the way I prefer to do it will be of use to somebody. I don't really care for doing math in the field. I want everything prepared for me. I just sit down at my computer and fogure out the bellows extensions for a given focal length that will evenly correspond to stop corrections in 1/3 stop increments going out as far as the bellows on my camera will allow. I then make a small table with P-Touch tape and stick it to the lensboard for that lens. That ensures that I can simply set up the photograph I want and then choose the closest stop correction from the table.

Here's how the tables look, this one is for a 90mm:

90mm

+1/3 - 106mm (4 3/16")

+2/3 - 121mm (4 3/4")

+1 - 127mm (5")

+1 1/3 - 142mm (5 9/16")

+1 2/3 - 156mm (6 1/8")

+2 - 180mm (7 1/16")

+2 1/3 - 202mm (7 15/16")

+2 2/3 - 226mm (8 7/8")

+3 - 255mm (10")

+3 1/3 - 285mm (11 1/4")

+3 2/3 - 321mm (12 5/8")

+4 - 360mm (14 3/16")

+4 1/3 - 404mm (15 15/16")

+4 2/3 - 454mm (17 7/8")

 

[Larry L]

I use Kodak photoguides for all my lens extension calculations since they have a dial system in the back of the books that will provide the exposure correction by you indicating what focal length of lens is being used along with how much extension you are experiencing. No math (calculator, etc.) is required. Both the Kodak Pocket Photoguide and the Kodak Professional Photoguide have this. The latter also has an extensive section on view camera perspective and depth-of-field controls as well as guides on camera movements. These can be found on E-Bay for reasonable prices as I'm sure they're out of print.

 

[pbromaghin]

The Cambo Legend conveniently has a scale printed on the rail that indicates the distance between front and rear standards.

 

[DanG]

Is anyone out there able to give me an easy to understand explanation of this 'bellows extension compensation' that I have been hearing about. Just bought my first 4x5 camera (Zone VI) with a 210mm and 80mm lens. I haven't taken any photos yet, but like to be prepared for when I do.

To keep it really simple: for B&W film especially, the exposure compensation that works well in the field is: add 1/3 of a stop for every inch of bellows extension over the focal length of the lens that you are using. EG.: with a 6" lens (150 mm) on the camera and with a bellows extension of 9" (film plane to nodal point of the lens) the exposure compensation would be plus 1 stop. I have used this "rule of thumb" for 49 years and it has served me well.
(PS: I don't like thin negs. in BW. If in doubt give a little extra exposure: develop according to the scene brightness ratio.

I use a Zone VI, 4x5 with 75, 150 and 240 Nikkor lenses. I also use a 6x7 roll film back which is especially good with the 75 mm Nikkor.

Enjoy, don't over think it, keep it simple. Shoot film, print lots!

Dan Gordon

 

[RalphLambrecht]

the easiest way to deal with this is to place a target discinto the subject and measure it with a special disc ruler on the view screen. the ruler will tell you how the exposure has tobe xhanged to compensate for the bellows extenson. send a private email to rlambrec@ymail.com and I'll send you a free pdf of the whole thing