Sinar Booster 1, Minolta meter, conversion?

Dazzer123

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Hi folks,

I'm a real noob with metering, so be gentle!

I'm facing the following issue:

When i take a meter reading with the Sinar Booster 1 / Minolta Flash Meter IV, if i get an F number of 5.6-0, all is hunky-dory, i just read the shutter time and I'm ready to rumba.

But sometimes i get an F number like 5.7-7. (the third number is showing a multiplier of 0.1 of a stop).

Ok, i dive into the Minolta manual and it tells me i need to adjust my lighting until the reading is 5.6-0
Well that's no good, maybe i don't want to do that, perhaps i'm working with natural light or lots of other lights and i don't want to adjust them all.

So then i need to adjust my shutter time instead. But strangely, the Minolta won't let me do this adjustment (dial the F number back to 5.6, then it shows me the corrected shutter time). I'm guessing this is because back in the day, it was expected that you would stick to one of a certain number of discrete shutter times, there were no in between shutter times considered?

But this is 2023 baby, i think we can be more flexible about this!

So to my questions:

Is what i wrote above correct, or am i completely misunderstanding something?

Am i being silly about this, should i just adjust my lighing so my middle grey reading will be 5.6 and deal with it?

Is there an online converter available somewhere. I mean one where you tell it an F# and shutter time, then if you change the F#, it tells you the new shutter time?

Alternatively, if someone knows the equation, i can hack the converter together myself in Excel?

If i understand correctly, the F number of 5.6-9 is extremely close to F8?

I should also mention i'm using long shutter times, 2 seconds+, i appreciate that at fast shutter time you need to stick to the standard times.

Thanks in advance!
 

MattKing

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Most apertures allow you to set them to in between positions.
If the display is meant to indicate 5.6 + 0.7 stops, then you just push the aperture indicator about 7/10 of the way toward f/8.
 

Eff64

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I agree with MattKing-just set the aperture in between. On any LF lens I ever used, the f-stops were variable.

Separate issue is using 5.6. That is wide open-or almost-on many LF lenses.

Are you trying to have minimal depth of field?
 
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Dazzer123

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Thanks guys.

I guess the question is, is setting an in between aperture going to be as precise as adjusting your shutter speed? Actually, i guess it doesn't matter because you're at the mercy of the accuracy of your "normal" aperture settings anyway.

If anyone knows it, i'd still like to know the equation for conversion, because i have two different Minolta meters, and it would help with comparing the readings they take.

About f5.6: that's just how the Booster 1 / Minolta combo works: you measure stopped down, but you always keep the meter at f5.6, and the meter will tell you the required shutter time.
 

wiltw

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Unless you have click stops, any setting in between is an ESTIMATION (and even the click stops themselves are typically an approximation!). The way you adjust with 0.1EV precision is to change the power of the flash either by
  1. moving the flash closer/farther from the subject, or
  2. by dialing down the flash power with the variator that permits fractional EV adjustment (commonly 0.1EV precision on studio flash)
 
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_T_

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Adjusting the aperture is much more precise than adjusting the shutter speed. On large format shutters you generally have a precision of 1 stop, whereas when setting your aperture you generally have the ability to measure down to 0.1 stops by estimating the placement of the indicator between the marked stops.

Doing this is basically unavoidable. Full stop increments like those found on your shutter speed dial are nowhere near precise enough to ensure proper exposure.

As for the formula for converting partial stops to shutter speed it's 2^(log2(shutter speed) ± (partial stop))

But it's not that important. As long as you're within 1/3 of a stop from the correct setting it's close enough. For most applications 1/2 stops are close enough.
 
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reddesert

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Honestly I think a film plane meter like the Sinar booster is not the easiest way to learn about light metering. If you have an incident or reflected light meter you can point it at different light sources (for incident) or different parts of the field of view (for reflected) and watch how the readings move around. You can do this with a film plane meter too, in a precise and time consuming manner where the instructions are written for someone who already has experience with handheld meters.

Most camera shutters and lens shutters are not really designed to allow intermediate shutter speeds (the exception being later electronically controlled shutters with a control dial rather than click stops). However, nearly all lens apertures do allow setting intermediate apertures. Thus it is easier to think about "f/5.6 plus a half stop" than "1/30 plus a half stop" (which would be about 1/40, but you can't predictably set most mechanical cameras to 1/40).
 
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Dazzer123

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Film plane metering seems to me to be the simplest form of metering, because you don't have to take anything else into account apart from your reading, and you can focus in very accurately to the different parts of the scene for a measurement! But yeah, I'm a total noob so it could be that you're 100% right!
 

Eff64

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If adjusting by shutter speed, that will be in full stops only, so I don’t see how that is being more precise than adjusting your aperture to an in between setting. Some of this discussion has gotten theoretical because the mechanisms, and the film sensitivity are not going to notice.

If you take any 2 lenses and time their actual shutters, I doubt they will be closer than 1/3 stop to each other.

But beyond that, you sort of have to pick your poison. In another comment you say that reading from the film plane is the simplest way to work, but the meter you are using has to be set at 5.6 only, according to that same comment. Unless that is your taking aperture, you have to convert that, so not so simple.

Use an incident reading. Accurate and simple combined. If you have bellows extension or are using a filter then off the ground glass might be better, but that is user preference.

In the film days we always used Polaroid to gauge exposure. Oops, no more Polaroid!
 
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Dazzer123

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Thanks for the info!

About the 5.6 thing: that really is how the Booster / Minolta work together. You take your reading, and as long as the ISO is set correctly and the Minolta is set to the f5.6, it will tell you the correct shutter speed to whatever aperture you're stopped down to. On the Auto Meter you need to manually dial the aperture setting back to 5.6 to read the shutter time, on the Flash Meter IV it tells you directly as it has f priority mode.
I don't have the technical explanation for you about why they chose 5.6 as their magic number!
 

Ian C

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A meter reading such as f/5.6 + 0.7 means that there is sufficient light for 0.7 stops more exposure than an f/5.6 exposure at the selected shutter speed.

If you were shooting narrow-latitude transparency film and wanted to “nail” the exposure, you’d set the aperture index to 0.7 of the distance from f/5.6 towards f/8 for correct exposure.

Although you can easily calculate a new exposure time to compensate for the fractional f-stop increment, it’s impractical with a camera shutter because nearly all of them are designed to provide full stop increments only. There are a few exceptions, such as the Mamiya RZ67 Pro II and Pro IID, which provides half-stop time increments.

For enlarging and using a digital timer, it's easy to set exposure times to the nearest 0.1 second. But in practice, this is rarely done, as it’s not practical in most cases.

Here’s how to calculate an exposure time T that is a function of a meter reading A + Δf, where

A = standard f-number displayed and

Δf = fractional part of a stop displayed in 0.1-stop increments and

t0 is the time displayed on the meter.

T = t0*2^Δf (at the displayed aperture number A)

For example, if you had a reading of f/5.6 + 0.7 at t0 = 2 seconds, then

T = 2 seconds*2^0.7 = 3.25 seconds (to the nearest 0.01 second).

Or, to state this another way, the exposure difference from 2 seconds to 3.25 seconds is 0.7 stops.

I use this calculation in enlarging, such as discussed in the thread for determining a new exposure time at a preferred aperture when changing from one projection size to another on the same paper stock.

https://www.photrio.com/forum/threa...-on-the-same-paper-stock.203076/#post-2743311
 

Eff64

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I have not used any of those meters myself, so happy to hear they are a good solution for you. Minolta always had a great reputation.

You didn’t say if you are using these with flash or continuous lighting. As you know, the shutter speed will not affect the exposure for flash, and will sync at any speed on a view camera lens.
 
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Dazzer123

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Only continous!!!
 

Chan Tran

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The meter doesn't want to display the information the way you like it then you should calculate it yourself. By the way I don't think the meter would ever display the f/5.7 (even though f/5.7 is actually a more correct number).
 

Chan Tran

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If the meter reading is f/5.6 and 7/10th of a stop and shutter speed is 2s then if you use f/5.6 the shutter speed is 2s / (2^0.7)= 1.23s. A division and not a multiplication. You use a larger aperture and thus the exposure time is shorter.
 

Ian C

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The sequence of aperture numbers: 1, 2, 4, 8, 16, 32, 64, 128, . . . are exact. They are the result computing the square root of 2 to the even integer powers of 2: 0, 2, 4, 6, 8, 16, 32, 64, . . .

The aperture sequence: 1.4, 2.8, 5.6, 11, 22, 45, 90, . . . are conventional truncations—not roundoffs. They are the result of taking the square root of 2 to the odd integer powers: 1, 3, 5, 7, 9, 11, 13, . . .

The results of the odd powers are irrational (cannot be expressed as the ratio of two integers). For the following powers their actual values are (rounded to the 5th decimal place):

1, 1.4142

3, 2.82843

5, 5.65685

7, 11.31371

9, 22.62742

11, 45.25483

13, 90.50967

In practice, this usually causes no problems, unless you perform a calculation in which you need the full numerical value. In that case, you can convert a standard aperture number to its exact value to the degree of accuracy needed.

You can also convert a meter reading to an aperture number, which is usually a non-standard value. For example, a light meter reading, such as f/5.6 + 0.7 stops, can be converted its equivalent exact value.

Thus, f/5.6 + 0.7 stops = f/7.21

This might look odd but is sensible when we note that 0.7 stops greater than f/5.6 is nearly f/8.
 
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Chan Tran

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Conventionally (not mathematically) the f/5.6 and 7/10th is called f/7.1. It's a setting on most modern cameras.
 
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Dazzer123

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Hi guys,

Any chance anyone could put this together in excel for me, im really useless at math and just can't work it out?!

This is what i'd like it to do as an example:

--------------------------------------------------------------

Reading one:

shutter time: 4 seconds ....... aperture: f/5.6 + 0.7

Reading two:

shutter time: 1 second........aperture: f/5.6 + 0.2

Difference in number of stops between readings one & two is: X

-------------------------------------------------------------

So basically, i'm only really interested in X, the number of stops difference between the two measurements.
 

MattKing

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The difference between those two is 0.7 stops - 0.2 stops = 0.5 stops.
That ubiquitous "Y.X" display of a reading is simply because digital displays can't be easily used to display things like 1/16, 1/8, 1/4, 1/3 or 1/2 stops.
And by the way, you wouldn't get encounter those two measurements unless the light or the subject changed between them.
 
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Dazzer123

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That doesn't sound right! (only 0.5 stops difference between a 1 & 4 second shutter time?)

But perhaps i'm over-thinking this and it's actually quite simple?

So the difference in my example is simply 2.5 stops?

And the following example is 1.2 stops?

Reading one:

shutter time: 2 seconds ....... aperture: f/5.6 + 0.1

Reading two:

shutter time: 4 seconds........aperture: f/5.6 + 0.3
 

MattKing

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Your question was capable of being read in multiple ways.
It wasn't a question about two different readings of the same lighting, it was a question about comparing two different light levels.
And yes, 2.5 stops difference in the light.
 

Ian C

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Regarding post #19

Determine the difference in light meter readings of

A: 4 seconds at f/5.6 + 0.7 stops to

B: 1 second at f/5.6 + 0.2 stops,

This is easier to see if you first note that the second reading shows an increasing light level. First, make both times the same. Think of the second reading in terms of the original 4-second metering. Translate reading #2 as

4 seconds at f/11 + 0.2 stops.

That should make it clear that the difference between 4 seconds at f/5.6 + 0.7 stops and 4 seconds at f/11 + 0.2 stops is an increase in light intensity.

That is an increase of f/5.6 to f/11 = 2 stops in terms of the difference in aperture numbers.

The fractional parts of a stop of increase are 0.7 stops – 0.2 stops = + 0.5 stops.

The total increase is +2 stops + 0.5 stops = +2.5 stops.


If the order of readings were reversed, (from 4 seconds at f/5.6 + 0.2 stops to 1 second at f/5.6 + 0.7 stops), the difference would be a DECREASE of -2.5 stops.

You would have less trouble in reading the difference between meter readings by simply selecting the SAME TIME on the meter for both readings. Then the difference is obvious.


In the example at the end of post 21, convert the first reading to the same 2 seconds as that of the first reading. Now we are comparing.

2 seconds at f/5.6 + 0.1 stops to

2 seconds at f/4 + 0.3 stops.

This is a decrease in light value.

The difference in aperture values is f/5.6 – f/4 = -1 stop (negative, because it is a decrease)

The fractional difference is an INCREASE of 0.3 – 0.1 = + 0.2 stops.

(The difference from the fractional part of the first reading to that of the second is 0.2 stops greater)

Thus, the total difference is -1 stop + 0.2 stop = - 0.8 stop.

It is a 0.8-stop decrease in light intensity from the first to the second meter reading.


I’ve programed my HP48GX so that I enter 5.6, 0.1, 4, 0.3, and press a single key. The display then reads -.79999999996, which is its approximation to -0.8, the number of stops difference from the first to the second meter reading.
 
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Chan Tran

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I attached an Excel file that can do the same.
Enter the aperture as the aperture
Enter the 1/10th of a stop in whole number. For example .1 enter as 1
Enter the Time as time. So if you want 1/250 enter as =1/250 which the cell will have the value of 0.004
There is a slight error because the Aperture number as well as Shutter speed numbers by convention are not rounded off correctly.
For example f/5.6 would be more correctly f/5.7. Shutter speed of 1/125 should be 1/128.
To make it more correct I would have to enumerate the number. That is assign a value to each f number and shutter value rather than calculate.
 

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