A great way to test shutter speed accuracy

<p>I have discovered a great and precise way to measure shutter speed. I have read about using a microphone and recording to a computer to analyze the shutter speeds. What I did is I took my D700 and positioned it behind my "new" Crown Graphic with my lens pointed to the ground glass. It does not matter if the image is in focus or not. I made a type of funnel out of a dark towel so that no other light got between the DSLR lens and the ground glass. Point the camera at a constantly lit scene (my kitchen) and shoot at the slowest speed (i.e. 1 second) on the LF lens, while holding the DSLR shutter open with Bulb setting. After the first 1 second shot, set the LF camera lens to compose, and set DSLR to the matching speed (1 second). Compare the two shots with histogram, and if it is slightly off, adjust DSLR shutter speed and shoot until the two match up. This will give you any correction factors required. Do the same for every shutter speed setting on the lens you are testing. I just tried this on my "new" Schneider Symar 135mm f/5.6 and found it was dead on at all shutter speeds except 1/500 sec. which is actually exposing at 1/400 sec. It doesn't take that long to do, and with all DSLRs electronic shutters being as accurate as they are, this method really works. You could do the same with a point and shoot. Just remember to adjust ISO and F/stop settings as you go, you don't want the image to be too bright or too dark to get good comparisons on. Hope this helps.</p>

<p>It took me a while to comprehend your description, but now it makes perfect sense (I think). You're using the Crown Graphic's shutter as if it were the DSLR's, and the DSLR doesn't know it's the Crown Graphic's shutter. It thinks it's own shutter is firing. Is that it? Sounds great, but how do you compare the histograms? Do you toggle back and forth from one to the other? I have an inexpensive shutter tester that I bought on fleabay that runs on the Audacity program in a similar fashion. W/ Audacity it's possible to stop the histogram and measure it's length. I usually aim the camera at the computer monitor (google, because there's no ads and it's mostly a bright white screen). Not sure it would be bright enough for your system. Thanks for posting this.</p>

<p>Well, essentially you are correct, you are basically using the large format lens shutter, at various speeds, and comparing the exposure to the DSLR set to the same speed, all while pointing the DSLR at the large format camera's ground glass. Most DSLRs have an option to view the histogram on the LCD. You compare the LF lens exposure to the DSLR shutter exposure histograms and make sure they look the same. If the LF lens shutter shot is brighter or dimmer than the DSLR exposure, then adjust the DSLR shutter speed until they match. For example, I fired the Schneider lens shutter at 1/500 second with my DSLR exposing at 1 second (ensuring the DSLR shutter is open long enough to get the Schneider lens shot). Then I set the Schneider lens to open for composing and set my DSLR to the same shutter speed, 1/500 second. I saw that the Schneider exposure was slightly darker than the DSLR exposure, so I changed the DSLR shutter speed to 1/400 second. By comparing the histograms, I saw that the 1/400 second exposure exactly matched the 1/500 second Schneider lens exposure, therefore the actual shutter speed of the Schneider lens set at 1/500 second is actually exposing at 1/400 second. All other shutter speeds were dead on. It takes more to describe all of this, but is quite easy to do and will tell you a lot about your lens. As far as a test scene, I recommend shooting out your window on a bright sunny day where there are no clouds passing that will change the brightness outside.</p>

<p>Should work, but make sure that you correct for bellows extension.</p>

<p> </p>

<p>Robert,<br>

Based on Nathan's description, there would be no need to "correct" for bellows extension, since each image being taken by the digital camera is of the ground glass, and the bellows extension, in each instance would presumably be the same.</p>

<p>Nathan,<br>

Great idea. I will give it a try. Did you use any particular material to create your light funnel, and do you recommend any particular design?</p>

<p>It sounds like you are comparing your LF's shutter to another cameras shutter (dslr); and assuming it is correct; thus your sole reference is another camera. Hopefully will will check your reference too; maybe your dslr is really at 1/450 second or 1/400th ?<br>

<br /> An ancient method that is almost 100 years old is to use a record. One places a chaulk line on it and gets the rpm/pitch correct and one shoots an imge of it; then one measures the arc with a protractor. Records were once available with 440 C; one could adjust the rpm to a tuning fork; that is before turnetables had a neon strobe to set rpm.<br>

<br /> Shutter speeds on the higher ends typically are lower; it going to vary too by the fstop used when one uses a leaf shutter. One has the ramp up and ramp down time; true shutter speeds are defined at the 50 percent points.<br>

<br /> Shutters of all types are a tad slower if the camera has set around awhile; and work up into a groove after the shutter is exercised. This tends to be the case with a purely mechanical shutter; and electronically timed shutter has a reference; or maybe just a capacitor to be charged up on an Instamatic X-30.<br>

<br /> With some leaf shutters at say 1/500 second; there are two springs in place; a higher tension helper spring to increase the tension. If only the top end is low; it might be due to a helper spring that has creeped due to time and temperature.<br>

Creep in mechanical engineering is where a metal that is say in tension or compression has its stress drop over time. Music wire is often used as a quality spring material; but will creep if some goober left the camera cocked at 1/500 in a hot car for a few days. Even if the spring barely creeps one has the issues of greases outgassing a tad and adding some internal fog. Music wire sperings is not used in hydraulics usually due to creep.</p>

<p>That really is lateral thinking, nice one! Even if your DSLR is not quite spot on, you should be able to compare different LF lenses.</p>

<p>If your dslr is consistant to itself; you have a precise reference; that maybe accurate; or maybe not.<br /> Accuracy means how close it is the target; precise means one has a small grouping with not much scatter in the data.<br>

<br /> Thus your dslr might be really at 1/450 second; but you think it is 1/500. You might measure a LF shutter to be 1/550 with your settup referenced to the dslr that is off; and then declare the LF shutter is too fast; when it is really spot on at 1/500 second..<br>

<br /> Try testing your dslr to see if it is correct too; then one knows what your reference is.<br>

<br /> You are are really just testing watch #1 to watch #2 and assuming watch #2 is correct.<br>

A record player's arc on a record with a turntables strobe set is a radically more precise reference than an unknown camera. You want to feel your data is tied to some actual traceable reference; ie WWV; the 60 HZ power line at least; or a calibrated shutter tester. Your dslr maybe too be spot one too; but assuming can get one in hot water at times!</p>

<p> </p>

<p>You guys seem to really making mountains out of a molehill. It's simple and cheap to make an extremely accurate shutter tester with a photo transistor that plugs into the sound card port of almost any late model PC or Mac. Using one of these with freeware, you can time shutters to an extreme degree of accuracy. I've got all of $20 and an hour's work into mine.</p>

<p>Ivan, that sounds like how my shutter tester works. Mine was bought on fleabay, but the seller doesn't seem to be selling them anymore. There are lots of diagrams on the web for building a tester that works off the sound card on your computer, as this one does, but being electronically challenged I bought one ready built. I keep a log book of all my cameras/shutters and know exactly at what speed they're firing. Doesn't matter if they're slow or fast as long as I know the actual speeds. Kelly's right on the shutters needing exercise. Many of mine have come up on their speeds by firing them a dozen times or so. Once a month I take the cameras out and fire the shutters at all their speeds 10 times on each setting.</p>

<p>You are aware that the industry standard for shutter speeds is ±30% aren't you?</p>

<p>Bob, I was not aware of that. But it does make sense, as 30% is only 1/3 f-stop and that small deviation is easily correctable in printing. It is nice to know though, that my LF lens is very accurate compared to my Nikon D700, so I can have faith in the shutter speeds and focus on other, more important things, especially since I am brand new to large format photography. In fact I am so new, that I have not even had a chance to expose my first 4x5 negative yet ( I have been working 12 hours a day, often 7 days a week building a prototype airplane).</p>

<p>Nathan,<br>

But how do you know if your Nikon is up to 30% fast or 30% slow?<br>

In fact, your Nikon could be 30% fast and your LF lens 30% slow. <br>

Why not use a good exposure meter, photograph an 18% grey card and process it the way you normally would. Then adjust your film speed to compensate for any corrections that you would like?</p>

<p>Nathan,<br>

But how do you know if your Nikon is up to 30% fast or 30% slow?<br>

In fact, your Nikon could be 30% fast and your LF lens 30% slow. <br>

Why not use a good exposure meter, photograph an 18% grey card and process it the way you normally would. Then adjust your film speed to compensate for any corrections that you would like?</p>

<p>Nathan... Brilliant! (Except for the 30% thing.) Somehow I want to believe that a modern shutter on a DSLR is better than 30% but then Bob is the expert.<br>

So Ivan are you going to share the plans for your $20 tester?</p>

<p>Best,<br>

Bill</p>

<p>I mean the testing to be used as a reference, not necessarily as die-hard spec ratings for the lens, just to make sure that the mechanical shutter is good. I do intend on doing zone system tests for each lens and film type as Ansel Adams describes in "The Negative" when I have time to do so, but for now I feel confident in being able to shoot at specified shutter speeds due to my comparison test. I do have a great light meter, I just got a excellent used Sekonic L758-DR which I have been playing with and learning to use with consistency with my D700 until I have time to get back into the darkroom. </p>

<p>Kelly</p>

<p>Record????<br>

I can't get the bellows and lens inside the CD player. How do you manage it???</p>

 

<p>If the DSLR alone gives the same output (easy to check) at different pairs "aperture/shutter speed" (same EV) then the only chance for the "30% issue" is to state that all that shutter speeds have the same systematic error. But this is very unlikely. So we can safely assume that the DSLR speeds can be considered as the true speeds.<br /><br />If the DSLR alone gives slightly different output, we can average the results and find out the errors of any partucular DSLR shutter speed. And then use that corrections in LF lens testing.<br /><br />Finally the questions about LF lens accuracy arise mostly in case of old lenses, where shutter can be way off. The suggested method is cheap and quick in comparison with test film shooting.<br>

I only want to add that the method can be used not only for LF shutter testing, but also for medium and small format shutters.</p>

<p>Looks like techno geeks from DP Review have invaded the LF Forum. </p>

<p>Testing shutter speed of Tessina twln lens reflex 35mm camera:</p>

<p>http://www.photo.net/minox-camera-forum/00djtU</p>

 

<p>Test the speed of an electric fan. Use the sort of tachometer that is for testing speed of lathes and mills. Remove the guard of the fan and spray the blades matt black. Paint a clear white line on one of the blades. Take a photograph at each speed. The white line will appear as a blur covering a larger sector at lower shutter speeds. For a 1200rpm fan, for example, 1/125 would be 57.6 degrees. I realise that it is yesterday's technology, but I use yesterday's cameras.</p>