An easy way to figure bellows factor

[ImSoNegative]

I know there are several ways to do this but this one I read about works great and its easy for me and that is what counts :p someone else posted this in a thread on here someplace and im just reposting it for future searches by others, so cheers to the OP.

step 1: convert the mm of your lens to inches ex. 90mm lens is roughly 3 1/2 inches
step 2: convert that to an f stop 3 1/2 inches is close to f4 the number 3 1/2 is close to the number 4 get it?
step 3: when doing a close up measure from the lensboard (roughly) to the film plane ex. say its ten inches to the film plane convert that to an fstop which would be
f11 (closest f stop to the number 10)
step 4: figure the difference between the two fstops ex. between f4 and f11 3 stops
step 5 add 3 stops of exposure

this of course will only work accurately if you don't use tilts

[C. D. Keth]

It'll be close enough if you use tilts. When was the last time you tilted so much it was more than a few mm difference between the top and bottom of the lensboard?

I just calculate the bellows extensions that correspond to full 1/3-stop corrections. I make a table of those out to the maximum my camera can do and I stick that on the lensboard. Simply measure and choose the closest correction. I don't like doing math when I'm making a photograph.

Here's what is stuck to the lensboard of my 150mm caltar (with the formatting all messed up by the forum software):

150mm

+1/3 - 168mm
+2/3 - 190mm
+1 - 212mm
+1 1/3 - 237mm
+1 2/3 - 268mm
+2 - 300mm
+2 1/3 - 335mm
+2 2/3 - 379mm
+3 - 424mm
+3 1/3 - 477mm
+3 2/3 - 535mm

Say you measure your bellows for the current shot at 229mm, you'll see that 1-1/3 stops is the closest correction.

[redshift]

There's an app for that for $2.00. https://itunes.apple.com/au/app/reciprocity-timer/id459691262?mt=8 I like the way it that it works specifically for each brand of film and includes filter factors. It doesn't replace knowing how to do it though.

[Leigh]

I like the way it that it works specifically for each brand of film...
Since when does bellows factor care about what film you're shooting?

- Leigh

[Robert Oliver]

I use that same method... Learned it from Bruce Barlow's manual. I just carry a big plastic ruler with the mm conversion of my lenses written on it.

[redshift]

Since when does bellows factor care about what film you're shooting?

- Leigh

I thought reciprocity failure varied with the film and that extended exposure due to bellows extension brought reciprocity failure into play. I'll leave that discussion to the know it alls.

[ImSoNegative]

yes it can definitely bring it into play depending on far you stop your lens down and how long your exposure is, I use ilford film which there failure starts at 1 sec. I normally use the delta and rate it at box speed, so usually I have to add time, found a really cool formula for figuring reciprocity for the ilford films,
(1.7 x metered time) + (.12 x metered time squared) = corrected time. this has worked perfectly for me every time. for example if my metered time is 8 sec. 1.7 x 8=13.6 sec or just round it off to 14 sec. then .12 x 64=7.68 round it off to 8. add 14+8=22. 8 sec metered time is 22 sec corrected time.

[ImSoNegative]

It'll be close enough if you use tilts. When was the last time you tilted so much it was more than a few mm difference between the top and bottom of the lensboard?

I just calculate the bellows extensions that correspond to full 1/3-stop corrections. I make a table of those out to the maximum my camera can do and I stick that on the lensboard. Simply measure and choose the closest correction. I don't like doing math when I'm making a photograph.

Here's what is stuck to the lensboard of my 150mm caltar (with the formatting all messed up by the forum software):

150mm

+1/3 - 168mm
+2/3 - 190mm
+1 - 212mm
+1 1/3 - 237mm
+1 2/3 - 268mm
+2 - 300mm
+2 1/3 - 335mm
+2 2/3 - 379mm
+3 - 424mm
+3 1/3 - 477mm
+3 2/3 - 535mm

Say you measure your bellows for the current shot at 229mm, you'll see that 1-1/3 stops is the closest correction.

150 is a 6 inch lens so convert that to fstop 5.6 229mm is 9 inches plus a bit. so yes if you convert that to f9 the correct difference between 5.6 and f9 would be 1 1/3
this type of math can be pretty much done in your head as long as you know that 25mm is an inch and one knows the f stop numbers. you can get the exposure really close using any lens.

[StoneNYC]

yes it can definitely bring it into play depending on far you stop your lens down and how long your exposure is, I use ilford film which there failure starts at 1 sec. I normally use the delta and rate it at box speed, so usually I have to add time, found a really cool formula for figuring reciprocity for the ilford films,
(1.7 x metered time) + (.12 x metered time squared) = corrected time. this has worked perfectly for me every time. for example if my metered time is 8 sec. 1.7 x 8=13.6 sec or just round it off to 14 sec. then .12 x 64=7.68 round it off to 8. add 14+8=22. 8 sec metered time is 22 sec corrected time.

Delta films reciprocity starts at 1/2 not 1 according to ilfords documents FYI

[ImSoNegative]

Thanks I always thought it started at 1sec.

[Brian Ellis]

I thought reciprocity failure varied with the film and that extended exposure due to bellows extension brought reciprocity failure into play. I'll leave that discussion to the know it alls.

Reciprocity failure does vary with films, though for b&w film the tables I use only separate TMax films from all others (TMax films can be exposed for a longer time than others before reciprocity starts to fail - see http://www.largeformatphotography.info/articles/sexton-tmax.html - written before Kodak changed the TMax films to their current state but the principles presumably remain the same). However I would think, without really knowing, that bellows factor may or may not also be important. If you're making a 20 or 30 minute exposure it might be insignificant. If you're making a 4 or 5 second exposure, maybe not. Since there seem to be formulas for everything these days there's perhaps a formula for this somewhere.

As reciprocity failure sets in and you increase exposure time with b&w film you'll also increase contrast if you use the same development time as you use without that increase. So if you want a normal negative ("N" in zone system terms) it's necessary to reduce development time to take the contrast increase into account. Some reciprocity tables provide the amount of decrease for varying amounts of exposure increase.

[StoneNYC]

Reciprocity failure does vary with films, though for b&w film the tables I use only separate TMax films from all others (TMax films can be exposed for a longer time than others before reciprocity starts to fail - see http://www.largeformatphotography.info/articles/sexton-tmax.html - written before Kodak changed the TMax films to their current state but the principles presumably remain the same). However I would think, without really knowing, that bellows factor may or may not also be important. If you're making a 20 or 30 minute exposure it might be insignificant. If you're making a 4 or 5 second exposure, maybe not. Since there seem to be formulas for everything these days there's perhaps a formula for this somewhere.

As reciprocity failure sets in and you increase exposure time with b&w film you'll also increase contrast if you use the same development time as you use without that increase. So if you want a normal negative ("N" in zone system terms) it's necessary to reduce development time to take the contrast increase into account. Some reciprocity tables provide the amount of decrease for varying amounts of exposure increase.

I have to disagree with you here, the Kodak chart

http://www.kodak.com/global/en/professional/support/techPubs/f4016/f4016.pdf

States that reciprocity correction starts at 1 second which is no different than many other films, whereas Acros100 starts at 2 minutes...

http://www.digitaltruth.com/products/fuji_tech/NeopanAcros100.pdf

So to say that Tmax has a much better reciprocity failure rate than most other films is false and misleading, especially to those who are less experience at long exposure and reciprocity correction.

Tmax's rate of failure after failure begins, over the long term, compared to many other films does seem better, but you need to be clear about the difference.

[Drew Bedo]

I mostly use either a 150mm or a 210mm lens.

The 150mm = 6 inches. For each inch of extension beyond infinity the bellows correction in 1/3 stop.

The 210mm = ~8 inches. For each inch of extension beyond infinity the correction is 1/4 stop extra exposure.

I can do this in my head all day long. When another lens is on the camera, a run through the arithmatic gets me where I need to go.

[redshift]

"So to say that Tmax has a much better reciprocity failure rate than most other films is false and misleading, especially to those who are less experience at long exposure and reciprocity correction."

Why do people have to be so friggin judgmental?

Both of you cited documentation.

Brian added a caveat, "written before Kodak changed the TMax films to their current state".

Why can't a person try to add to a discussion without someone crawling up their butt with accusations of being false and misleading?

So many fora seem to be about little dick disease instead of a place to share experience.

[StoneNYC]

"So to say that Tmax has a much better reciprocity failure rate than most other films is false and misleading, especially to those who are less experience at long exposure and reciprocity correction."

Why do people have to be so friggin judgmental?

Both of you cited documentation.

Brian added a caveat, "written before Kodak changed the TMax films to their current state".

Why can't a person try to add to a discussion without someone crawling up their butt with accusations of being false and misleading?

So many fora seem to be about little dick disease instead of a place to share experience.

Because when you say something, people with less information and understanding often read it and then aren't properly informed.

I'm guilty of doing this a lot on here, and people correct me. And that's ok. If I say something misleading I want someone to point it out so that others who don't know as much, don't go down the wrong path, who then spreads his "knowledge" to his friends who know even less, it's just better to try and keep info good from the start.

[Terry Christian]

There's absolutely no judgement of the person intended necessarily when someone calls something false or misleading. There's no need to take it as a personal affront.
If, hypothetically speaking, Stone were to day that Rodinal is a solvent developer, it would be false and definitely misleading to someone who might be looking for a fine-grain developer, but my telling him he's incorrect doesn't mean I've assaulted his character.
So keep calm... (and praise Rodinal). ;-)

[BrianShaw]

I can do this in my head all day long.

I wish I could, but I just can't. I think it is a lack of experience (and perhaps insecurity) on my part since I do close-up work very seldom. For extension factor I use a tool similar to these rulers:

http://www.cookseytalbottgallery.com/photo_blog_article.php?blRecordNumber=24

http://www.southbristolviews.com/pics/Graphic/SBVCALC.pdf

[StoneNYC]

There's absolutely no judgement of the person intended necessarily when someone calls something false or misleading. There's no need to take it as a personal affront.
If, hypothetically speaking, Stone were to day that Rodinal is a solvent developer, it would be false and definitely misleading to someone who might be looking for a fine-grain developer, but my telling him he's incorrect doesn't mean I've assaulted his character.
So keep calm... (and praise Rodinal). ;-)

Rodinal!!!!! :)

I recently saw someone post that "Rodinal is a great fine grained developer" .... I let that one slide... Hehe

[BrianShaw]

Because when you say something, people with less information and understanding often read it and then aren't properly informed.

I'm guilty of doing this a lot on here, and people correct me. And that's ok. If I say something misleading I want someone to point it out so that others who don't know as much, don't go down the wrong path, who then spreads his "knowledge" to his friends who know even less, it's just better to try and keep info good from the start.

No, Stone... you are completely wrong on this one. Absolutely and utterly incorrect. You don't do it a lot; you only occasionally do that. :p

[Bob Salomon]

You are making this very simple thing very complicated.

It does not matter wht focal length lens you are using. All you need to know is the size of the object you are shooting and how big it is on the ground glass.

If it is the same size on both open up 2 stops. If it is half as large on the gg open up 1 stop. If it is a quarter the size open up 1/2 stop. If it is 1/8 the size don't worry about it.
If it is twice the size open up 4 stops.

Or put a ruler in the scene where the subject will be and compare the size of an inch on the gg. Same rules apply as above. Works with or without movements.

[Leigh]

Reciprocity failure does vary with films, though for b&w film the tables I use only separate TMax films from all others
With Fuji Acros, reciprocity law failure only begins at 120 seconds.
It requires only 1/2 stop compensation from 120 to 1000 seconds.

- Leigh

[Leigh]

I'm guilty of doing this a lot on here, and people correct me. And that's ok. If I say something misleading I want someone to point it out so that others who don't know as much, don't go down the wrong path...
It's interesting how a particular sentence can be read two or more different ways.

In some cases it's simply due to emphasis being placed on different words by the author and the reader.
In other cases it's due to multiple meanings of words, ambiguity, or other problems attributable to the language itself.

English is a weird language, full of traps for the unsuspecting. :D

- Leigh

[StoneNYC]

It's interesting how a particular sentence can be read two or more different ways.

In some cases it's simply due to emphasis being placed on different words by the author and the reader.
In other cases it's due to multiple meanings of words, ambiguity, or other problems attributable to the language itself.

English is a weird language, full of traps for the unsuspecting. :D

- Leigh

It's true, I don't know if at 8 hours, tmax overtakes acros or not, so it could be that tmax is better "in the long run" which would make him correct. But I think even there, that Acros100 is better than tmax.

Anyway, language IS funny, :) English is one of the worst when it comes to insinuation/interpretation/double meanings, etc. But we decided to use it for science anyway :)

[redshift]

Yes, maybe I misread things. To me, someone that has the facts wrong can simply be making a mistake, being false and misleading implies bad intent.

I also missed the undercurrent of Team Arcos100 versus Team Tmax.

Stone, if I misinterpreted your reply to Brian I apologize.

[C. D. Keth]

150 is a 6 inch lens so convert that to fstop 5.6 229mm is 9 inches plus a bit. so yes if you convert that to f9 the correct difference between 5.6 and f9 would be 1 1/3
this type of math can be pretty much done in your head as long as you know that 25mm is an inch and one knows the f stop numbers. you can get the exposure really close using any lens.

I know the math is easy. I just know about myself that I can think well creatively or I can think well technically. When I do both, they each tend to suffer a little so I take all the math out of it that I can.

[Jim Noel]

I don't know about reciprocity departure over 8 hours, but through testing I know that the departure at 4 hours is far less, as much as 1 1/2 stops, for Acros than for T-Max.

[Colin Robertson]

http://www.salzgeber.at/disc/

[Jerry Bodine]

I know the math is easy. I just know about myself that I can think well creatively or I can think well technically. When I do both, they each tend to suffer a little so I take all the math out of it that I can.

That's the safe approach. A wise move. When the math is wrong, it's definitely WRONG. When the creativity is questioned, there's no right or wrong because of it's SUBJECTIVE.

[Mark Sawyer]

I never understood the odd contortions people go through to figure bellows extension factors. The f/stop is a simple ratio of aperture diameter to focal length, (bellows extension).

1.) Measure your bellows extension (A).
2.) Measure your aperture through the front element (B).
3.) Divide A by B.

That's your f/stop.

[Drew Bedo]

I wish I could, but I just can't. I think it is a lack of experience (and perhaps insecurity) on my part since I do close-up work very seldom. For extension factor I use a tool similar to these rulers:

http://www.cookseytalbottgallery.com/photo_blog_article.php?blRecordNumber=24

http://www.southbristolviews.com/pics/Graphic/SBVCALC.pdf

Brian: You do the arithmatic at home using as much time and whatever calculator you wish. You just have one thing to remember about each lense. I have put a label with a note on it on the lensboard at times.

For any 150mm lens

for each inch of bellows extension beyond 6inches, add 1/3 stop of exposure.

For any 210mm lens

For each inch of belows extension beyond 8 inches, add 1/4 stop of exposure.

Easy-Peasy its a breezy.

[Heroique]

I also keep it simple. KISS, as they say:

A useful rule of thumb – I don’t worry too much about “correction” unless the distance to my subject is 10x my focal length, or closer.

If this is the case, my next rule of thumb is to add 1/2 stop for every 25% increase in bellows extension (beyond infinity).

Example: I’m using a 240mm lens. 10 x 240mm = 2400mm (or 2.4 meters). So I will consider BC when my subject is 2.4 meters from the camera, or closer. Depending on film choice and (any) adjusted exposure time, I will also consider reciprocity correction.

[Drew Bedo]

KISS—right.

For any thumb you may use, it comes out the same:
Infinity +1 focal length = 2 stops.
Infinity +1/2 focal length = 1 stop.

With this relationshipm in mind, any bellows extension may be corrected for.

[Leigh]

Infinity +1 focal length = 2 stops.
Infinity +1/2 focal length = 1 stop.
And it's linear, so...
Infinity + 1 focal length = 2 stops.
Infinity + 7/8 focal length = 1¾ stops.
Infinity + 3/4 focal length = 1½ stops.
Infinity + 5/8 focal length = 1¼ stops.
Infinity + 1/2 focal length = 1 stop.
Infinity + 3/8 focal length = ¾ stops.
Infinity + 1/4 focal length = ½ stop.
Infinity + 1/8 focal length = ¼ stops.

Every 1/8 focal length = ¼ stop.

It's pretty unusual to need exposure accuracy tighter than ¼ stop, even with chromes.

- Leigh

[StoneNYC]

Yes, maybe I misread things. To me, someone that has the facts wrong can simply be making a mistake, being false and misleading implies bad intent.

I also missed the undercurrent of Team Arcos100 versus Team Tmax.

Stone, if I misinterpreted your reply to Brian I apologize.

Really no worries, there's probably a perceived understanding that "misleading" is intentional, I actually don't know if the word specifically has to include intent to be used correctly, I should look it up. But I wasn't using it in that way, but I can see how someone might read it that way, so I'm also sorry for that.

We're good ;)

[StoneNYC]

Re-math...

My head hurts...

Glad I have an app...

[Wayne]

Its amazing what some people find simple. For me simple is having the conversion for my 8x10 lenses written on my measuring tape so when I measure my extension there it is. One step. I've put labels on the camera rack on my Wista 45SP, so I don't even need to measure.

[Leigh]

That works fine for a couple of lenses.

My 4x5 kit has about 18 lenses in roughly 15 different focal lengths.

- Leigh

[Corran]

All I do is eyeball the total extension of the camera, and divide by the focal length of the lens. Square that number for a direct multiplication factor. Never understood the big deal. The OP's formula is a lot harder to wrap my head around.

Example: 300mm ext. of 150mm lens for 1:1 = (300/150)^2, or 4X the exposure length. Done. I use inches though generally - easier to estimate.

[Leigh]

All I do is eyeball the total extension of the camera, and divide by the focal length of the lens. That's how many stops I need to compensate. Square that number for a direct multiplication factor. Never understood the big deal. The OP's formula is a lot harder to wrap my head around.

Example: 300mm ext. of 150mm lens for 1:1 = 300/150, or 2 STOPS, square that it's 4X the exposure length. Done. I use inches though generally - easier to estimate.
Sorry... wrong.

At infinity: 150/150 = 1 stop, when in fact the compensation should be 0 stops.

- Leigh

Edited to include the entire previous post, since he deleted key sentences thereof.

[Corran]

(150/150)^2 = 1X multiplication

I always square it and don't think about the stops adjustment so whatever. The formula is (EXT/FL)^2 regardless, which is correct for the multiplication. In my effort to explain things easier I should have just not mentioned stops*.

*Edited the post above for clarity

[Leigh]

Yeah. When you go back and edit your previous post, you can correct any mistake with impunity.

"Edited the post above for clarity."???
More like correcting an error and covering your posterior.

So I edited my reply and included your entire previous post as it was before you edited it.
Caches are awfully handy. :D

- Leigh

[Corran]

Whatever Leigh. I never think of it in stops. In my example it was 2 stops, as noted, which is why I put it in there.

The formula is correct. Get over it.

[Corran]

And you'll have to get on Ken Lee's case about it too. And I quote from his site:



How Many More f/stops are Required ?
Compensation = (B / F) stops
where B = Bellows extension and F = Focal length

Given a 300mm lens, 450mm of bellows draw and a 2-second exposure, by how many f/stops should we adjust the exposure ?

Compensation = (450 / 300) stops
Compensation = 1.5 stops

We adjust exposure by an additional 1.5 f/stops


http://www.kenleegallery.com/html/tech/bellows.php

[ImSoNegative]

its cool how everyone pretty much has there own way of figuring it and how it all comes out about the same :)

[Joe Smigiel]

:eek: OMG! Math! Fractions! Exponents!

Leave the calculator home. There's also a way to visually determine extension corrections using a light meter dial. (I've posted a pic of one below to follow along with.) If using a 150mm lens focused at 300mm think of the distances as f-stop readings. (See the red dots on the pic.) Think of 150mm as f/15 and note the shutter speed. Then think of 300mm as f/30. Whatever shutter speed is aligned with f/30 will be your corrected exposure for the bellows extension. In that example, if your meter read 25 seconds at f/15 (see the pic below), you should find the shutter speed at f/30 to be 100 seconds (= 1 2/3 minutes) and that would be the corrected exposure time for the extension factor at the original f/stop. Your exposure becomes 100 seconds @ f/15 (or equivalent). I've picked these numbers because I know an extension of twice the lens focal length gives an extension factor of 4x or 2-stops and if you look at the numbers in the example you'll see that the corrected exposure (100 seconds @ f/15) is 2-stops different than the original meter reading (25 seconds @ f/15). (I apologize for not having a scan with simpler alignments to post.) A Pentax Spotmeter V is great for this. I'd never buy a digital meter because of this trick.

If you can use such a meter dial you don't really have to calculate anything. You just need to know your lens focal length and the total extension and you can eyeball it on the meter face. For example a 90mm lens @ 120mm extension with an original meter reading of 9 seconds @ f/9 produces the corrected result of about 15 seconds at f/9 just eyeballing the meter.

http://www.collodion.com/uploads/54/Pentax_V_face_272.jpg

[EOTS]

Hi guys,

why not use the QuickDisc?
Simply print this out and measure on the ground glass: http://www.salzgeber.at/disc/disc.pdf

Best regards,
Martin

[Wayne]

Rofl. Then you can afford to cart around a full-time assistant to do your calculations for you.


That works fine for a couple of lenses.

My 4x5 kit has about 18 lenses in roughly 15 different focal lengths.

- Leigh

[StoneNYC]

Rofl. Then you can afford to cart around a full-time assistant to do your calculations for you.

Yea, holy shit man haha

[vinny]

Hi guys,

why not use the QuickDisc?
Simply print this out and measure on the ground glass: http://www.salzgeber.at/disc/disc.pdf

Best regards,
Martin
doesn't work well over water, sand, snow, or anything else you don't want disturbed. I have one and use a cloth measuring tape instead.

[EOTS]

doesn't work well over water, sand, snow, or anything else you don't want disturbed. I have one and use a cloth measuring tape instead.

Yeah, that's right ...
I also have a spreadsheet printed (x axis extensions, y axis focal lengths) and measure with a tape and look it up ...