1st time 4x5 user: exposure compensation?

[scott_russell2]

Hi, I recently purchased a super graphic with a rodenstock f4.5 optar 135mm

lens. Now, I have a good amount of experience with medium format but I'm really

kinda lost when it comes with this camera. I've become familiar with the camera

and have figured out most of the buttons and operations of it, I've practiced

taking pictures with it, but before I go and shoot a couple test shots I had

somethings that were confusing me that I hope someone could clear up. What is

the purpose of the infinity stops? Are they specific to the lens you are using?

They seem to be set about halfway on the bellows track right now. What I'm

essentially trying to figure out is how close I can focus before I have to start

figuring out exposure compensation. I know on my Mamiya RB67, there was a scale

on the side of the bellows, telling me that at 2" (example) I need to add .5

stops, and that at 4", I had to add a full stop etc. There's no scale on the

side, or anywhere around the bellows. The only one I found is the focusing scale

on top. I can extend the bellows only a few (3 or 4) inches from the body of the

camera before the focusing scale goes past the shortest distance at 3.5'. So is

the minimum distance before compensation 3.5 feet? After that, what will I have

to do? My girlfriend tried to help me, but she's a little rusty since college.

She said I have to take a ruler or something, measure how far the bellows is

extended, and do some sort of math equation to figure out compensation. I have

the manual, but its missing a few pages and some of the words are smeared on it.

[BrianS1664879711]

Scott - congratulations on getting a super graphic... you'll really like it. You have a lot of questions. Let me suggest that you visit www.graflex.org soon.

 

The infinity stops will, indeed, be set up for a particular lens - most likely the one on the camera. When you pull the lensboard out of the camera you'll want to pull it up to the infinity stop and lock it down. Then focus with the knobs.

 

To check if the infinity stops are correctly adjusted for the lens you are using you can focus on something really far away using the ground glass and then check to see that the focus scale on the bed and top of the caemra agree - all should indicate infinity.

 

For close-up exposrue information, visit the following site and read up:

 

http://www.largeformatphotography.info/bellows-factor.html

[ronald_moravec1]

4x5 inch subject requires 2 extra stops. 8x10 1 extra, 16x20 1/2 extra.

 

It is as simple as that. Life size is 2 stops, 1/2 life size 1 stop .

 

Any format as long as you use a symetrical lens.

[michael_briggs2]

The first rule is very easy: if the subject that you are focused on is farther than ten times the focal length of the lens, you don't have to bother with exposure compensation. So for a 150 mm lens, if the subject is 1500 mm = 1.5 m (i.e., about 1.5 yards) or more away, you don't have to bother. At these distances, the correction will be less than 1/3 of a stop and can be ignored.

 

 

Here is an equation that you can use for closer distances. You could make tables for your lenses in advance. If you don't have a scientific calculator, google will do the calculation. The correction in stops for a lens of focal length F with bellows extension B is 6.64 * log (B/F), with log base 10. Use the same units for B and F. For example, for a 180 mm lens at 260 mm extension: 6.64 * log (260 / 180) = 1.06 stops. You could round this to 1 stop. If you don't have a calculator with the log function, you can enter "6.64 * log (260 / 180)" (without the quotation marks) into the search field of google and google will do the calculation. You don't have to have understand the equation to make a table -- just use google repeatedly with a successive values for B. It is generally accurate enough to measure B from the ground glass to the center of the lens. (The exact measurement is from the ground glass to the rear principal plane.)

 

True telephoto lenses are more complicated.

 

There are previous discussion in the forum of other ways, if you don't like this method.

[paul_hoyt]

As you focus closer (extend the bellows) your effective f/stop decreases, larger the f/stop number the less light is transmitted through the lens. An 8" lens should measure 8 inches from the lens board to the film plane when focused at infinite. If you extend the lens and the lens board is 11 inches from the film plane, you have lost 1 f/stop of light, your f/8 is now f/11. That is one way to figure your exposure compensation; convert your lens size to inches and measure your extension in inches. Your exposure meter will tell you how many f/stop compensations you will need by substituting the inches to f/stops. A 2 inch lens extended to 4 inches has a 2X exposure compensation; f/2 to f/4 is 2 f/stops increase. A light meter and a tape measure are required, both you should have as part of your equipment already. You must know how far the lens has been extended to calculate the exposure compensation. You don't need log tables, scientific calculator or google.

 

Paul

[obakesan]

Scott

<P>

Michael's responce of "<i>if the subject that you are focused on is farther than ten times the focal length of the lens, you don't have to bother with exposure compensation</i>"

<br>

is just the neatest formula I've ever heard.

<P>

However to what I was going to say ... do you have a palm pilot (or any Palm OS device)? If you then grab a copy of vade mecum (email me for a copy if you like). While 99% of it is hard core stuff, there are some useful bellows factor bits in there which can help.

<P>

alternatively I carry a bit of paper for each lens, cut to 1cm wide and double the focal length of the lens. I've marked the BF points on that in 1/2 fstop adjustments. I just hold it to the rail and voila

<P>

HTH

[Monophoto]

If you are focusing on the ground glass, the infinity stops aren't all that important. They were really intended for use in conjunction with the rangefinder.

 

I suspect that the bellows on your camera doesn't allow enough extension to have to worry about compensation. However, it never hurts to know what the compensation rules are. The "ten times focal length" rule is one of the better rules. The life size rule (see Ronald's post) is also a good one. Beyond that, you are into exotica. There are a number of aps that run on PDAs that will calculate an exact compensation - I have something called LF exp that converts a metered exposure into an actual exposure taking into account filters, extension, film reciprocity, and perhaps even the phase of the moon.

[frankz]

I'd like to throw a, perhaps, simpler version of the calculations into to soup if I may.

 

F "stops" are no more than a ratio of a given lens' clear-glass diameter to its focal lenth AT INFINITY. (Remember, your trig teacher probably never called that a ratio, either - the witch).

 

Example - conventional wisdom says your 4 X 5 has a 'normal' (I hate that word) focal length of 150 mm and clear glass measures 31mm (I'm doing this in sillymeters 'cause I don't know where you live). Anyhow - 150mm / 31mm = f4.83 in this example.

 

Now - with that same lens and the bellows racked out to 190mm, your (f4.83 at infinity focus) lens suddenly becomes a f6.12 lens because of the extension needed to focus closer.

 

Remember - this is only a ratio of lens focal length/clear diameter and so far I've only given examples of clear lens diameters and haven't brushed on the lens' aperture settings but it figures the same way and only adds one extra calculation to the mix to find out where you are re: real aperture.

 

This is my method for caculating 'real' aperture. It's really simple for me but all I was good at in school was math and beer drinking.

[rodeo_joe1]

Basically, you don't have to worry about anything less than a quarter stop of compensation, and this kicks in at 1.28 metres (4 ft) subject distance with your 135mm lens.

 

One third of a stop extra exposure is required at 1 metre, and a half stop at 735mm subject-to-lens distance.

 

This simple guide should be enough unless you're into serious close-up work.

[thirteenthumbs]

Take everything the other posters have told you so far with a grain of salt, go to <a href=http://www.cameraeccentric.com/html/info/supergraphic/supergraphic.html> The Camera Eccentric/Super Graphic Manual </a>, download all the pages, then if you have the <a href=http://www.cameraeccentric.com/html/info/shuttera/shuttera.html>

Graflex 1000 Speed Shutter</a> download the operating instructions for it.<br>

Now work thru the instructions then come back and reread the others post and ask more questions as needed to clear up anything that is still fuzzy.

[friedemann_pistorius]

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

 

<p>No headache anymore, and always perfect results.

<br>It's just that simple.

[rodeo_joe1]

Charles: I don't think that page 20 of the "official" manual explains how to calculate exposure compensation any better than other posters here have tried to do. In fact the example given in the manual is about as clear as mud!

 

It's easier, IMHO, to take the bellows extension factor (as described in the manual) and just multiply the marked aperture number by it. This gives you the effective aperture directly, and you can simply set that aperture on your lightmeter to get the correct exposure time.

 

For example: If you've set the aperture pointer on the lens to f/16, and your bellows factor is 1.4, then your effective aperture is(16*1.4) = f/22. Look up the time on your meter opposite f/22 and you'll have the perfect exposure. Simple, and no need to carry any tables or charts around with you. In fact you could just paste a pre worked out compensation scale to the bed of the camera alongside the focusing scale.

 

There are many methods of calculating exposure compensation, some more accurate than others. But simplicity should be the key. It's no use fumbling for the square function on your calculator, or trying to read a chart or disc while your subject starts to fidget or crawl away or the light's changing fast. You need a method you can easily remember and work out in your head in seconds.

 

Personally, I removed the focusing scale from my own technical camera and substituted a millimetre scale instead, with zero set at the film plane. I can now read the bellows extension directly from the focusing pointer, which makes exposure compensation quite easy, regardless of which lens I've got fitted.

[thirteenthumbs]

Rodeo Joe,<br> Scott states in the first few lines that he does not know how to fully use the camera and is, IMO, making an assumption that he needs to figure in bellows extension for his exposures. My post was to direct him to the Instruction Manual, have him to pause on the bellows extension, read and figure out the operation of the camera then come back and reread the bellows compensation posts, which are very good, so that the information would make more sense to him. Hopefully he has a good footing of how to use the camera and when and how to apply bellows extension factor.<br> I keep a tape measure handy when I'm doing close up work.