New Lens Scale: How To Convert Milliseconds To Standard Camera Fractions?

[Doremus Scudder]

Andy,

There are a range of shutter speeds; some of them are off more than others, e.g., some are 2/3 stop too slow, some only 1/3 stop too slow. If you can get your head around my method, I'll do the other work for you. Here's the list of your shutter speed indications and the actual shutter speeds from the sheet you posted in your first post (with note about how much too slow they are that you could also use as factors).

Just remember, the + and - signs refer to the numbers, so end up being the opposite of what you might think. E.g., 1/4+ is something like 1/5 or 1/6, so is less exposure than 1/4. Plus is less exposure, minus is more.

1 sec. = 1.35 sec. (1/3 stop slow)
1/2 sec. = 1- sec. (2/3 stop slow)
1/4 sec. = 1/2+ sec. (2/3 stop slow)
1/8 sec. = 1/4+ sec. (2/3 stop slow)
1/15 sec. = 1/8+ sec. (2/3 stop slow)
1/30 sec. = 1/15+ sec. (2/3 stop slow)
1/60 sec. = 1/30+ sec. (2/3 stop slow)
1/125 sec. = 1/125- sec. (1/3 stop slow)
1/250 sec. = 1/125+ sec. (2/3 stop slow)
1/400 sec. = 1/250 sec. (2/3+ stop slow)

You could just print these out, paste them on your lens board and use the plus and minus signs as factors. Minus means More exposure, so give less at the aperture by stopping down the appropriate amount. Plus means Less exposure, so give more with the aperture by opening the appropriate amount.

Example: your meter wants 1/15th at f/22. You don't have a true 1/15 available, the closest is 1/15+ that you get when you set your shutter to the 1/30 mark, So do that, note the "+" sign, which means the shutter is giving you 1/3 stop less exposure than 1/15 and close your aperture to (correction!) f/22 minus (1/3 stop more exposure) to compensate.

Note that if there's a "+" on the shutter speed, you compensate with a "-" at the aperture and vice-versa. It's really easy once you get used to it.

Alternately, in this particular case, you could just underexpose everything 2/3 stop from the actual setting, which would only be about 1/3 stop off in the worst case. Still, that's not as precise nor does it really allow finding optimum shutter-speed/aperture combinations.

Best,

Doremus

[Alan Klein]

Here's my table of shutter speeds in milliseconds with corresponding approximate 1/3-stop fractions.

When I get my shutters tested, I convert the time in milliseconds to the closest 1/3-stop shutter speed. I'll then make a sticker to paste on the lensboard with the corrected shutter speed.

So, for example, let's say the 1/15th-second setting on the shutter comes in at 83 milliseconds. On my table, that's closest to 80 milliseconds, which is 1/12 second, which is 1/3 stop slower than the standard 1/15th second. So, I'll mark that as 1/15- (using the "minus" sign). And say that my 1/125th-setting comes in at around 14 milliseconds. That's closest to 12.7 milliseconds on the chart, which is 1/80th second, which is 1/3 stop faster than the standard 1/60th setting (i.e., my 1/125 setting is about 2/3-stop slow). So, I'll mark that 1/60+ (using the "plus" sign) on my sticker. Just remember that the plus and minus signs refer to the numbers: Minus means More exposure and Plus is Less exposure when working with the fractions-of-a-second shutter speeds.

Then, when setting the exposure, I'll just adjust with the aperture. Say my meter wants 1/60th at f/22. I'll set my shutter at 1/125th, which is 1/60+ (1/3 stop less exposure than 1/60th) and then set the aperture to 1/3 stop more open than f/22 to compensate. (if there are no 1/3-stop hash marks on the shutter, I just estimate). This method gets me to within 1/6 stop overall, close enough for color transparency work even.

I work in 1/3-stop increments when metering anyway, since my meters are all marked with third-stop hash marks. I'd notate the above in my exposure record as "f/22- at 1/60+." The good thing about this is that the minus sign for both shutter speeds and aperture means more exposure and the plus sign for both means less exposure.

Hope that all makes sense; it will after looking at the chart and going through the above examples again.

Best,

Doremus

I've got enough trouble remembering to remove the dark slide. But thanks for the the ideas.

[acrobatic_citron]

"and close your aperture to f/8 minus "

Do you not mean f22- ( minus) , open up 22 a third to compensate for the 3rd lost on 15+? f8 is alsmost 3 stops away! Or did I miss something

[Andy F]

Hi everyone,

Thanks for all the help. I am writing notes on my lens board and light meter based on peoples advice. I just want to confirm the strategies I can take with this lens. The strategies for this lens, based on the person's advice would be as follows:

-Adjust the light meter’s ASA. (Mark’s and others suggestion)
-Adjust the aperture by stopping down by the corresponding 10ths of a stop. (Neil’s suggestion)
-Rewrite the scale to get as close as you can but also indicate that use a plus (+) or minus (-) sign to indicate that it will need an aperture adjustment as well. (Doremus Suggestion)

So here is my first question. And clearly I suck at math. If I was to follow Mark's advice and adjust the meter, what would my new ASA be if I was shooting plus one third of a stop and plus two thirds of a stop. Let’s say it is box speed at 400asa, what would my new ASA be? Let's say I was shooting HP5 at 300 ASA. What would the new ASA be?

My second question is about Mark's method. I guess here you just eyeball things to the closest 10th because the apertures are not that precise. So if it is going to be closed down by .7 tenths you are moving down past the midpoint and close to the next stop. Is that correct?

My third question is about Doremus' suggestion. What occurs here is that must indicate not just the closest shutter speed but also the individual aperture adjustment for each f stop. Is that correct? You must somehow indicate that it will need a third or two thirds less light I believe. Is that correct?

Let me know if I am understanding all of these methods correctly? I will probably move forward using each method depending on the situation.

Thanks everyone,
Andrew

[BrianShaw]

https://books.google.com/books/about...d=Q7uyzakcUrAC

Shopping around you can get this as inexpensive as $1 (plus nominal shipping charge). Worth its weight in gold for complete understand and long-term photography knowledge.

[Doremus Scudder]

"and close your aperture to f/8 minus "

Do you not mean f22- ( minus) , open up 22 a third to compensate for the 3rd lost on 15+? f8 is alsmost 3 stops away! Or did I miss something

Thanks for the correction! Typing too fast and not thinking clearly, obviously. Yes, f/22- , which is 1/3 stop more light than f/22.

I apologize to the OP and the rest following this thread for any confusion.

Correction made.

Doremus

[Doremus Scudder]

Hi everyone,

...

My third question is about Doremus' suggestion. What occurs here is that must indicate not just the closest shutter speed but also the individual aperture adjustment for each f stop. Is that correct? You must somehow indicate that it will need a third or two thirds less light I believe. Is that correct?

Let me know if I am understanding all of these methods correctly? I will probably move forward using each method depending on the situation.

Thanks everyone,
Andrew

Andrew,

I'll just address your question to me. First, though, please note the correction in post #11, pointed out by acrobatic_citron (thanks a_c). I hope that didn't confuse the issue for you.

On to your question:

Making a list of actual shutter speeds to the closest 1/3 stop (however you do in, with + or - signs or whatever) gets you in the margin of error for just about any exposure situation. Use the millisecond to fractional shutter speed chart I posted as a pdf attachment in my original post #7.

Once you have that, you just use your meter as usual, but compensate for the 1/3-stop difference in shutter speeds (if there are any) with the aperture. If the shutter is giving you 1/3 stop less exposure than the setting, then you need to open the aperture 1/3 stop and vice-versa.

All the light meters that I have used indicate exposure in full stops with 1/3-stop divisions marked by small lines. Most aperture scales on shutters have 1/3-stop increments marked with lines between the full numbered stops as well; if not, it's easy to estimate the position of the pointer between stops. (Note that LF shutters just have whole-stop settings!) It should be easy to make 1/3-stop adjustments with the aperture. If your light meter reads out in something different, like decimal values, you will have to convert. Using .3 and .6 is close enough for third-stop increments (e.g., f/16.3 is about 1/3-stop more closed than f/16).

With my system, I use + and - signs to indicate the change in the actual numbers they follow. E.g., 1/15- means 1/12 second (12 is less than 15), but be aware that 1/12 second is a slower shutter speed than 1/15 second and lets in more light. If you felt like labeling that slow 1/15th-second something else, like "1/15 +1/3 stop" or 1/12 or whatever to make it easier for you to remember which way is more exposure and which way less, then please do whatever seems most intuitive to you. If you feel like memorizing the whole list of fractional shutter speeds in 1/3-stop intervals, they are in the pdf conversion chart I posted in post #7.

Bottom line: make a list of your actual shutter speeds to the closest 1/3 stop (I do for all my lenses). Make a sticker for your lens board with these. Then, in the field, use the list to make a 1/3 stop compensation with the aperture for whichever actual shutter speeds are faster or slower than the setting. Say you set your shutter to 1/8 second, but the actual shutter speed is slower by a third of a stop (however you want to indicate that). Then you'd need to close the aperture by 1/3 stop from the reading on your meter for 1/8 second.

In practice, I meter and find the shutter speed I need opposite the aperture I choose (I almost always give the aperture priority). Let's say I need around f/32 for depth of field. My meter tells me that the closest combination is 1/3 stop more open than f/32 at 1/4 second. Great! I set that speed and aperture (one hash mark more open than f/32) on the shutter. Then, I look at my list of actual shutter speeds. I tells me that 1/4 on my lens is really 1/3 stop slower than the setting. So I go back and close my aperture 1/3 stop (back to f/32 proper). EZPZ

Best,

Doremus