I don't get it - Please help the newbie

[Digidurst]

Hi everyone! I have recently aquired a Horseman LE and I sure do love it. But as I have never used a LF before in my life, I'm having a hard time with getting my exposures right due to bellows extension. I downloaded this thing called a QuickDisk that's supposed to help and while the measuring part is easy, I don't understand what the numbers mean on the little "ruler" or how to apply them. Sometimes the simplist things boggle my brain!

I would be eternally grateful if someone could explain it to me (like I'm three). For example, lets say I've metered my scene and the results indicate that the correct exposure is f25 @ 1/60th of a second (using strobes). I measure the QuickDisk on my ground glass and get the numbers 0,5. So my correct f stop would be ?????

I have a feeling I'm making this overly complicated but I just don't get what the numbers mean on the QuickDisk 'ruler' or how to translate them to a working exposure.

Thanks for the help and thanks for not laughing at the newbie, or at least in front of the newbie!

 

[John Bartley]

Just out of curiosity, what sort of scenes are you having trouble with? And what size of lens do you have? I understood bellows extension exposure compensation was required when doing extreme closeups, or in any other situation where long bellows draw was being used.
cheers

 

[Nick Zentena]

F/25 + 1/2 a stop. I guess that's pretty close to F/32.

 

[Digidurst]

Just out of curiosity, what sort of scenes are you having trouble with? And what size of lens do you have? I understood bellows extension exposure compensation was required when doing extreme closeups, or in any other situation where long bellows draw was being used.
cheers

Oh shoot! I'm sorry I forgot to include that important information!

I'm using a 210mm lens in my (small) studio, shooting a floral scene. Does that help?

 

[Digidurst]

F/25 + 1/2 a stop. I guess that's pretty close to F/32.

???? Wouldn't f32 underexpose?

 

[mikeb_z5]

yes, you would need to open up a stop. not close down

 

[Nick Zentena]

Sorry-) I'll try and redeem myself. You're using lights. If you've decided you need F/25 for DOF then you'll need to increase the lights enough that the meter reads that extra 1/2 stop.

 

[lee]

I would think F22 closer by one stop

lee\c

 

[Digidurst]

Okay, so again what do the numbers mean on the QuickDisk 'ruler' and how do I translate them to a working exposure?

 

[Baxter Bradford]

There should be instructions with the download. The Quickdisk is a great tool which is used solely to calculate Bellows factor.

The numbers on the Quickdisk ruler give the extra exposure you have to add due to bellows factor. Measure the longest axis of the Disk on the GG (distortion can make the circle appear elliptical). Then use your light meter as normal to get your basic exposure for the shot; to which you then add whatever bellows factor was given from the ruler before making the actual exposure.

Simple, free and works really well.

 

[Nick Zentena]

You've got two scales.

Scale #1 is time. xT. Multiple the meter reading by the factor on that scale.

The F/stop scale is the amount of F/stops you're increasing the F/stop. If you had a meter set at F/stop priority you'd change the F/stop you're telling the meter by the amount in that scale.

Hope I didn't screw that up to.

 

[rbarker]

Let's use your example. To start, your meter tells you f/25@1/60. F/25 would be about 1/3 stop smaller (toward f/32) than the f/22 marked on the lens.

As mentioned, the ruler has two colums of adjustment factors: XT for time, and f-stops. Unless you're good at mentally multiplying fractions, I'd forget the XT column, and think in terms of f-stops.

You measure the widest axis of the disc on the ground glass, and it comes closest to the +0.5 (+0,5 in Euro terms), which means you need to add (open up) a half stop to whatever your exposure is. So, your adjusted exposure would be not quite 1/3 stop the other side of f/22 (toward f/16). Depending on how your lens is marked between full stops (some have half-stop marks, others 1/3 stop marks, some none), you just have to interpolate the fractional stops.

For close-up work, however, the chosen f-stop is often more critical than the shutter speed (assuming continuous lighting), insofar as controlling DOF. So, you might actually want to adjust the metered exposure first to give greater DOF - 1/30 at f/32-1/3 (1/3 stop toward f/45), and then make the compensation for bellows factor to that, moving the aperture bar back toward f/22 by the half stop compensation factor.

If, however, you're using electronic flash, the shutter speed has almost no effect on exposure (except to include or exclude any contribution of ambient light), so you can't reduce the shutter speed and close down the f-stop to gain additional DOF. You can, however, do multiple "pops" of the strobes, adjusting the f-stop accordingly, by carefully re-cocking the shutter for the additional pops. For example, two pops would allow you to close down a full f-stop, and four pops would allow you to close down two full f-stops. Beyond two pops, some reciprocity failure often starts to creep in, however. So, depending on the film, you might actually need five pops to close down two full f-stops on the aperture.

 

[steve simmons]

Forget the math. Here is a fool proof sysem.

If you have a 210mm/8.25" lens and the bellows extesion is rght at 210mm/8.25 there is no extension factor. If the bellows extension is 10.5 nches add 1/2 stop of expsure. You can do this by opening up 1/2 stop or adding light. If you are using strobe slowing the shutter won't make any difference. If the bellows is extended to 12 to 12.5" add one stop(open up on stop) or add light. If you have an extension of 14" add 1.5 stops. If you have 16" of extension add two stops.

Here is the rule that will work for all focal length lenses and all films

for each 25% you extend the bellows beyond an infinity focus add 1/2 top

if you go 50% beyond infinity add one stop

if you go 75% beyod the infiinty extension add 1.5 stops

for twice the infnity extension add two stops

If you are using Polaroid film to check your exposures the same rule applies but the Pola-meter will take this into account or you.

steve simmons
www.viewcamera.com

 

[NikoSperi]

or... bellows extension^2/focal length^2 = exposure factor

 

[noseoil]

As steve has stated, it isn't rocket science. If you have a 5" lens (125mm) and infinity is on the ground glass, there is no bellows factor. If you are focusing on an object which results in a measured 7 1/2" (not the normal 5"), then you have increased the lens focal length by a factor of 1/2 (7.5"-5"=2.5" 2.5"/5"=.5). Just double the difference and you are there, or add a stop of exposure (make the hole bigger). That's all there is to it.

The actual relationship is the "inverse square law" which states that light falls off as a function of distance from the light source. The actual math is done with squares of distances, but I don't do squares in my head as well as multiplying by 2. For printing I do use a calculator. tim

 

[Bruce Osgood]

First of all, I did away with the Quick Disc because I didn't feel it was accurate.

To figure out Bellows Extension Compensation (it is not a Factor) you need to determine if compensation is required. If the subject distance to the ground glass (film plane) is LESS the 10 time the focal length of the lense, compensation is needed. Otherwise it is not.

In your case, with a 210mm (8.25") lens when the subject is less than 82.5" (10 X 8.25") compensation is needed.

The amount of compensation is calculated by:
Lens Length ^2 (8.25 X 8.25 = 68.06 [68])

DIVIDED BY:

Bellows Extension (Distance from film plane (ground glass) to shutter plane) ^2.
(Suppose 6" draw ^2, = 36)

This would equal: 68/36 = 1.88 or +/- 1-1/2 to 2 stops more light.

With your measured f-25 @ 1/60 I would compensate to f-8-2/3 @ 1/60.

Now, if the f-25 was important to your Depth of Field considerations you may wish to make the Bellows Compensation to the time. In this case the exposure would be f-25 between 1/15 and 1/30 of a second.

This becomes intuitive after a while and I kept loosing that damn little ruler for the Quick Disc.

 

[NikoSperi]

In your case, with a 210mm (8.25") lens when the subject is less than 82.5" (10 X 8.25") compensation is needed.

The amount of compensation is calculated by:
Lens Length ^2 (8.25 X 8.25 = 68.06 [68])

DIVIDED BY:

Bellows Extension (Distance from film plane (ground glass) to shutter plane) ^2.
(Suppose 6" draw ^2, = 36)

This would equal: 68/36 = 1.88 or +/- 1-1/2 to 2 stops more light.

Bruce, now you're confusing me. First of all, I've been taught the denominator is focal length, not bellows draw.
Secondly, in your example, how could you possibly have only 6 inches between film plane and shutter plane with an 8.25" focal length? (Telephoto lens excluded)

 

[Bruce Osgood]

Bruce, now you're confusing me. First of all, I've been taught the denominator is focal length, not bellows draw.
Secondly, in your example, how could you possibly have only 6 inches between film plane and shutter plane with an 8.25" focal length? (Telephoto lens excluded)

Niko
I just used 6" as an example, I have no idea what the real life situation is.
Well, if you're right then 36/68 would produce .09 compensation, not measurable... OH! You're right. MY MISTAKE. Using the example of a 6" extension screwed me up. Sorry 'bout that.

Maybe it ain't so intuitive afterall. I apologize.

 

[Digidurst]

With your measured f-25 @ 1/60 I would compensate to f-8-2/3 @ 1/60.

This becomes intuitive after a while and I kept loosing that damn little ruler for the Quick Disc.

You'd go all the way to f-8-2/3?!? Oh dear... I'm lost

Just for more info I measured my bellows extension from the center of the lens to the center of the GG - I got 17 inches. And I was no more than 2 - 2 1/2 feet from my subject.

p.s. I keep the QuickDisk thingie in a baggie thumb-tacked to the wall so I don't loose it as otherwise, that thing would be a goner! Being the visual type (i.e. if I can't see it than I forget where it is), I have lots of crap in baggies thumb-tacked to the walls of my studio. LOL

 

[NikoSperi]

For some reason, there are seemingly at least six different ways to get to the same point, and everyone uses their own, to the mutual confusion of most other methods.

I simply use a ruler to measure the distance between nodal plane and film plane; say 297mm. If I've got a normal 210mm lens on the board that means my extension factor would be:

297mm^2/210mm^2 = 2.0x

As if I had a one stop factor filter on my lens. Now, because getting everything into focus, tilts and swings included is a sufficient PITA that I don't want to mess with aperture, I'll apply that 2x factor to the shutter speed (reciprocity factors added later as applicable). But, if you're using strobes, you're going to have to convert that 2x into f/stops. So your 2x bellows extension factor is going to require your f/25 metered exposure to become f/19 roughly, or one stop more light.
Yes, I need a calculator most of the time to do the math, but most of the time when shooting something so macro I'm inside anyway. But that's the simplest way for me to work it out. Now for you to find yours.

 

[steve simmons]

If you have 17" of extension wth an 8.25/210 lens then add two stops.

steve simmons
www.viewcamera.com

 

[NikoSperi]

You'd go all the way to f-8-2/3?!? Oh dear... I'm lost

Just for more info I measured my bellows extension from the center of the lens to the center of the GG - I got 17 inches. And I was no more than 2 - 2 1/2 feet from my subject.

Ok, 17 inches bellows draw... on what focal length lens? 8.25" (210mm)? That would mean a 4.25x factor, or just over two stops. So f/25 would need to become f/11 about.

 

[Bruce Osgood]

You'd go all the way to f-8-2/3?!? Oh dear... I'm lost

Just for more info I measured my bellows extension from the center of the lens to the center of the GG - I got 17 inches. And I was no more than 2 - 2 1/2 feet from my subject.

Okay, let me get the numbers right. You're 24" - 30" from the subject. This only means you are less than ten times the F.L., so compensation is needed.

The formula is: EXTENSION LENGTH^2 / LENS LENGTH ^2

The draw you measured is 17". Squared is 289
Your lens (210mm) = 8.25 inch or rounded 8". Squared is 64

289/64 = 4.5 stops compensation

So, an exposure of f-25 @ 1/60 would or could be either f-25 @ 1/3 second OR f- between 5.6 and 8 @ 1/60, OR a combination of each.

In my earlier message I simply picked a number out of the air as bellows draw, not thinking, I'm sorry I did that.

 

[Gary892]

Jim, I am looking for 12x20 film holders for a 12x20 korona. If you see any please let me know.

Thanks

Gary

 

[Gary892]

Sorry

Whoops, wrong thread. A senior moment. cheeezz.

Gary