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 ???
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 ???
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.
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 :-(
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...
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.
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.
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.
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.
Don,
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.
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
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