View Full Version : Determining shutter speed

Calamity Jane
15-Jun-2005, 08:19
When checking shutter speed, at what point on the rise/fall curve is the time measured?

I.E. the illumination behind the shutter will be of the shape ___/^^^___

Is the time measured from dark-to-dark, from 50% full open, 100% full open ???

James E Galvin
15-Jun-2005, 08:49
You want the equivalent rectangle, so 50%. Note that the 50% point changes when you change the aperture (stopped well down, the shutter needs to open only a bit to clear the diaghram, wide open the shutter has to fully open to clear). But the difference between your three measurements is small at the usual slow speeds we use, the time it takes the shutter to open or close is small compared to say 1/15 second (the curve is almost a rectangle). However, if you are using the fastest speeds, the curve is nearly a triangle, the shutter starts closing almost as soon as it gets open, so use 50% at your typical f stop.

Calamity Jane
15-Jun-2005, 09:05
Thanks Jim. Makes sense . . film is sensitive to the TOTAL amount of light falling on it so 50% SHOULD give the same as "instant open" for the 50% time period.

I have an old pneumatic B&L shutter that runs down to 3 Seconds - which is just perfect for my tintypes - but, because it's pneumatic, the opening and closing s quite slow and I imagine the "rise" and "Fall" will be different shapes and non-linear. I might have to dust off my calculus books :-(

Jay Lnch
15-Jun-2005, 10:38
Ms Jane, I have a question for you....

How do you make your plates for the Tintypes? Where do you get the tin, what size do you normaly use and how to you make the black finnish for the starting plates?

thanks, jay...

Dan Fromm
15-Jun-2005, 11:54
C'lamity, what are you trying to accomplish? It your goal is finding actual shutter speed, why calculate and model when you can measure?

One way to find actual shutter speed is to shoot test strips. I did this when I first got a Speed Graphic and had no other way of checking what its focal plane shutter did.

Calamity Jane
15-Jun-2005, 12:20
Jay: Do you REALLY expect me to give away all the secrets of my process on a public board? ;-) Not to be rude but I'm trying to make some money at this and working out the processes has COST me a substantial amount of money and time. If I were to freely give out all my "tricks of the trade", I could have competition spring up and benefit from my investment to take business away from me. Once I have established a clientele and recovered my start-up costs, I will be much more generous with information but so far I am $2,000 in the red since last fall.

I will say: I use steel, 0.005" thick, and it is painted. I currently shoot 4x5 but will be trying my hand at 8x10 shortly.

Dan: I am trying to calculate the effective shutter speed so I have an accurate starting point for test exposures. I have tried "test strips" in tintype and they don't work very good. At the cost of 4x5 tintype plates, I try VERY HARD to minimize the number of "experimental" plates. Although the metal can be reused, it only accounts for a small fraction of the cost per plate - all the rest is lost.

Dan Fromm
15-Jun-2005, 13:34
Jane, for finding shutter speed film of known speed is as good as y'r tintype plates as long as you know the plates' speed.

Be calm, be rational, you'll find an inexpensive way.

Donald Hutton
15-Jun-2005, 13:42
Wow Calamity

That's really generous of you to refuse to offer up some of your knowledge to Jay on your area of expertise - especially when one considers the hours of sound FREE advice you have received here from other members. I hardly see how divulging a little imformation to Jay is going to impact your business... You do realize that several professionals regularly provide you with all sorts of advice on this forum without the same apparent fear that your newfound enlightenment will severly impact their business. The idea of this forum is actually about information sharing, not hoarding.

Calamity Jane
15-Jun-2005, 14:16

What comes to me free, I pass on for free. If information is already in the public relm, I gladly direct people to the source. On the other hand, what I have to work hard to perfect, I am very cautious with. I have already shared a great deal of what I have learned on the Tintype process on this and other boards and shared even more with those who have contacted me privately. Rocklands has not shared with me their formula for Liquid Light - though I would LOVE to know I do not expect them to tell me.

John Coffer charges $550 per student to learn his process - would he not receive the wisdom of those on this board unless he revealed all his "trade secrets" publicly?

I mentioned "a public board". This board is available for all to read, both those who contribute and those who only take.

I would presume at a professional photographer who freely shares his knowledge on a public board already has a developed skill set and a market share and has probably recovered some or all of his startup costs.

Finally, you will notice I DID answer his questions ;-)

If anybody wants details on how I do this step or do that process, they can e-mail me. If that's not good enough then I've been hanging out in the worng place.

15-Jun-2005, 14:25
Don please leave well enough alone. It is nice to see someones true colors. It speaks volumes to their character. Jay if you are interested, there is a man by the name of Dennis Waters who is one of the foremost authorities on Daguerreotypes in the U.S. and one of the largest collectors in the world. He also does restorations on Dags and is quite knowledgable in the tin process also. He manages a web site.......www.finedags.com... and he is more than willing to share his expertise and take the time to answer your questions. Now I'm sure if you start producing some of the finest Tintypes in the world all that he would ask is a little acknowledgement for his mentoring. Hope this is of some help to you

Dan Jolicoeur
15-Jun-2005, 14:44
Wow, Sorry, I could not leave well enough alone. I found it quite rud myself after frequenting this site daily for the last few years and seeing the questions asked. Information hoarding, you hit the nail on the head Don!

Jim Galli
15-Jun-2005, 15:00
CJ I'll stand with you on this and say I also choose what and sometimes what not to reveal for free. Sorry folks, we're all stranded in the real world. Hopefully we all enjoy some remaining freedoms. Like choice? Let all the big names that charge $800 for workshops come here and tell everything they teach in those for free. I think Don's attack is entirely un-warranted. I've got a process I designed by hours and hours of trial and error and a little knowledge thrown in where I can get beautiful tones on Ortho / Lith films for pennies a sheet in the ULF sizes. If you want to know how I do that come on out to Tonopah and pay me about $800 bucks for a workshop and I'll teach you. I share much of what I've learned about LF freely here and enjoy doing so but I feel Don and others are out of line if they feel I OWE some debt that must be repaid and I have no choice in it. Get real. My true colors are flying. end rant.

Struan Gray
15-Jun-2005, 15:09
I'll tell you everything I know about Tintypes *and* contone use of Lith film. And I'll do it for $500. And I'll only take up five minutes of your time. Can't say fairer than that.

CJ: do you have some way of plotting traces from a photodiode or phototransistor? If so, the classic way of integrating them (previously known to a sect of scientists so secret even Dan Brown hasn't heard of them) is to plot the trace, cut it out and weigh the resulting piece of paper. The 'shutter speed' is then the length of a similar-height rectangle of the same weight/area. Digital oscilloscopes spoil the fun.

Donald Hutton
15-Jun-2005, 15:21

1. I'm not trying to attack anyone.
2. CJ solicits information on this forum on a very regular basis. She is offered a wealth of excellent advice and experience on every occassion. On the only occassion I have ever seen her advice solicited, she publically dismisses it out of hand (much easier to place a posting saying "drop me an email"). I think that's mean spirited. Only my opinion, but if everyone on this forum reacted in the same manner to every question asked on this forum, we would all be the poorer. I'm also not suggesting that every participant here divulge everything they know at every opportunity. I'm simply suggesting that if anyone finds the content on this forum useful, they should make the effort to contribute.

Calamity Jane
15-Jun-2005, 15:59
Struan: I have a digital storage scope. Although I don't have the ability to plot from the scope, it is easy to do a basic integration on-screen and get a good read on the time between 50% points.

Don: I hope I have contributed where and when I can, though I am certainly not a wealth of knowledge on the traditional field of photography - the vast majority of contributors to this board know WAY more than I do.

Jay: Sorry if I was a bit short but trying to develop tintypes into a viable business has been a he!! of a struggle. It has taken a LOT of time and a fair amount of money. I should have simply answered you question and omitted further comment. I guess the wink got lost too.

There is LOTS of basic information around that's readily available and there are quite a few tintype photographers, but few have truly mastered the art - I am no where close (yet). Those who have mastered the art don't give ANYTHING away for free (believe me, I have tried to solicit their guidaence without success!). Most of what I have learned that ISN'T widely published I have already posted in public places and I can certainly provide a LONG list of things that DON'T work. What I haven't posted, any dedicated student of tintypes can ferrit out for themselves, deduce from what IS posted, or learn by doing.

I try to be a generous capitalist but I am a capitalist nonetheless.

Today I saw a handfull of tintypes that were made in the 1880s by a professional of that period. I had a chance to examine them closely and I am in absolute AWE! They had contrast and sharpness way beyond what I have achieved to date. From my examination I have learned a few things that I will try to in an effort to improve my own tintypes in the future. What did I learn? I'M NOT TELLING! ;-)

(It's a JOKE fellas, a JOKE!)

M. J. Rossano
15-Jun-2005, 16:24
... plot the trace, cut it out and weigh the resulting piece of paper.


You're joking, right?

Scientists and engineers have had a marvelous invention, the planimeter, available for over a hundred years! In fact, they're still manufactured to this day.

Conrad Hoffman
15-Jun-2005, 18:09
Struan, that's an absolutely cool technique. Yes, planimeters (sp?) have been around forever, and were really popular for doing area under the curve when analyzing steam engine cycles, but there's nothing wrong with the weighing technique.

I do my shutters with nothing more than a photo diode and an ancient 545B oscilloscope. This is a 10% process, not a 1% process, so eyeballing the 50% point works just fine.

IMO, CJ has been very clear in other posts that her hard earned knowledge is hers until she deems otherwise. Almost all the information people share on the web is easily available in a secret and soon to be unreadable format known as "books", if you know where to look. When someone develops (no pun intended) a difficult process where much of the info has been lost, and intends to use it for commercial gain, I don't see anything wrong with holding it close. I share almost everything I know that's been gained from others here and/or comes from a technical library that I've spent thousands of dollars assembling, however, I have a few tricks from about 30 years of study that help me make a living, and I try not to make those too public unless the public is paying :-)

Dan Fromm
15-Jun-2005, 18:41
Arrgh! Please cool it folks, I'm the only one authorized to be obnoxious here.

Jane, all kidding aside, if you know the exposure index you use when exposing the tintype plates that are the fruit of your trade secret, reasoning from film to them is pretty easy.

Cheers, and plagues on all of your houses,


Paul Fitzgerald
15-Jun-2005, 20:08

Why not make a posterboard baffle for the back of your camera that quarters the frame? Rotate it around and do 4 shots on 1 plate to test the exposure for that lens on your tintypes. It just seems a more direct test for the tintypes' UV sensitivity <-> lens UV transmission.

Just a thought

Calamity Jane
15-Jun-2005, 20:14
That's a brilliant idea Paul!

I've been trying to figure out how I was going to proof the 8x10s - 8x10 tintpye plates represent a considerable investment in time and money. Getting 4 exposures per plate cuts the cost to the same as 4x5 test plates.

Jay Lnch
15-Jun-2005, 21:15
Thank you Calamity .... and yes you did answer my question about the plates you use. The plate size was very helpful. Also I didn't know if you were Japanning as opposed to painting them black. The former seems tough to say the least.

Robert, thanks for the info and web site.

Now I am off to order a roll of steel sheet metal.......

Struan Gray
16-Jun-2005, 01:18
M.J.: the advantage of the weighing technique is that you have an immediate visual indication of the error in your measurement. Better, someone else (such as your thesis supervisor) also has an immediate visual record of the error in your measurement. With a planimeter you need to learn your own particular biases when tracing a shape, and other people just have to trust your numbers.

I used this technique as an undergraduate and postgraduate Physicist. During the course of my PhD (87-91) the availability and price of A-D convertor chips changed dramatically, as did the ways of gettnig the converted numbers into a PC. What was a neat trick became just another piece of technological history.

C.J. The reason to care about the curve shape is that many of the old C19th shutters have low 'efficiency' - they are fully open only for a short part of the shutter cycle. The plate doesn't care (if you ignore reciprocity failure at low light levels) but it can be worth making a table of 'real' shutter speeds verses marked, especially for the shutter's top speeds when working at full aperture. With a storage scope you'll see straight away how significant the rise and fall times are, and if they are so badly non-linear that you need to use something other than a simple 50% value. FWIW, if your scope can gang up several traces, it's a good way to see the repeatability of the shutter, which is probably more important than its accuracy.