Calculating Shutter speeds for Guillotine shutters

[EastCityStudios]

I have built a guillotine shutter for my Dallmeyer 3A, I am trying to figure out the shutter speed for it but have not been able to find any information online? I started by filming the drop with my phone camera at 240 frames a second and counting the frames to see when the lens is open, but when I tried using that as my shutter speed I ended up getting incredibly under exposed results. I am wondering if it is possibly because the slit in the shutter is smaller than the Front element of the lens and it is somehow effecting the aperture? or is it just that counting frames on a video isn't accurate enough? or is there a second step after counting frames? I would really appreciate any help

 

[Donald Qualls]

What you need to get off that slo-mo video instead is the time between the first panel uncovering a reference point (a particular letter in the lens legend, if there is one, or a piece of tape applied to the rim of the barrel), and the second panel covering the same reference point. This will give the length of time any particular fraction of the field is open, and should give you a much more accurate value for the shutter speed. If your shutter has the option of different opening widths, you'll want to do this for each setting.

 

[Chan Tran]

Try this
https://www.largeformatphotography.info/guillotine-shutter/guillotine-shutter-speeds.html

 

[Richard Man]

I have made a couple shutters for my Pinkham and Smith Visual Quality IV lens. See my post here at the LF Camera subforum. The formula I use is derived from the LFPF article

Slot Width is "=POWER(1/B3 + SQRT(A3*0.00518), 2) / 0.00518 - A3"

 

[Richard Man]

I even compared the highlight shape difference between a Packard Shutter and a guillotine shutter

 

[EastCityStudios]

What you need to get off that slo-mo video instead is the time between the first panel uncovering a reference point (a particular letter in the lens legend, if there is one, or a piece of tape applied to the rim of the barrel), and the second panel covering the same reference point. This will give the length of time any particular fraction of the field is open, and should give you a much more accurate value for the shutter speed. If your shutter has the option of different opening widths, you'll want to do this for each setting.

Thanks,

that's helpful, I used the same video's and used the edge of the lens counting the frames from when it first got revealed to when it closed. I counted four- three frames when it was exposed which I thin gives me a speed of around 1/60-1/80 since it was a 240 frame per second video. I did a test exposure this morning at 1/60 which looks maybe a stop underexposed but pretty close so I think its now about 1/80 of a second

 

[EastCityStudios]

I even compared the highlight shape difference between a Packard Shutter and a guillotine shutter

Yes I think I saw your thread when I was looking earlier, If the shutter affects out of focus areas does that mean that the shutter is affecting the aperture of the lens?

 

[Donald Qualls]

Thanks,

that's helpful, I used the same video's and used the edge of the lens counting the frames from when it first got revealed to when it closed. I counted four- three frames when it was exposed which I thin gives me a speed of around 1/60-1/80 since it was a 240 frame per second video. I did a test exposure this morning at 1/60 which looks maybe a stop underexposed but pretty close so I think its now about 1/80 of a second

And unless you know for certain the frame rate your phone can shoot, that's about as good as you're going to get. If the claimed 240 fps is only 180 fps, it'll make that much difference.

Of course, now that you know, you can adjust. Widening the slot 25% will get you back to a real 1/60 (which will be an easier figure to use with light meters).

 

[Richard Man]

I made a 1/8th shutter (full disclosure, I have not verified their actual speeds, but do know for sure that the 1/60 is faster than the packard and the 1/8 is slower) and saw no problem with the highlight shape. I think we need an optical engineer to explain the phenomena. I can't do further testing until I get more films though.

 

[Donald Qualls]

A Packard might tend to give a little "wedge" shape to highlights or bokeh -- because the top stays open longer than the bottom. A guillotine type shouldn't exhibit any special highlight shape or effect on the bokeh, because the exposure is even across the whole lens.

 

[cowanw]

Thanks,

that's helpful, I used the same video's and used the edge of the lens counting the frames from when it first got revealed to when it closed. I counted four- three frames when it was exposed which I thin gives me a speed of around 1/60-1/80 since it was a 240 frame per second video. I did a test exposure this morning at 1/60 which looks maybe a stop underexposed but pretty close so I think its now about 1/80 of a second

I was going to say that you could photograph and bracket a grey card at different fstops until you matched the grey card to the negative grey card and the shutter speed /fstop combo of that negative would match a meter reading of the original grey card.

 

[Ian Grant]

Always astound me why people don't just buy a decent British contemporary shutter Don't think Packard think Pickard , Thornton Pickard

This is one of my largest on the front of a 20" Rapid Rectilinear.

Test you Guillotine shutter with a DSLR, make an exposure at say f11 and the shutter with the camera set on B, then make a series of exposres using the cameras shutter at roughly slower and faster speeds, it's easy to match

Here in the UK TP shutters were standard on many new camears and retro-fiited yo older until leaf shutter became reliable and dominated, although the Limited company was liquidated and wound down i the late 1930's they were still made up to about 1960. In fact Kodak sold TP shutters in 1940, They where sold in the US by B&J who seemed to prefer the Luminium cased versons but Aluminium alloys of taht era corroded.

John Thornton was pushed out of TP by the Pickard family, he lived of Royalties from Kodak, they used his Film PAck system and his additive colour process they called Kodachtome, not the later version.

Ian

 

[Bob S]

Thanks,

that's helpful, I used the same video's and used the edge of the lens counting the frames from when it first got revealed to when it closed. I counted four- three frames when it was exposed which I thin gives me a speed of around 1/60-1/80 since it was a 240 frame per second video. I did a test exposure this morning at 1/60 which looks maybe a stop underexposed but pretty close so I think its now about 1/80 of a second

If you are a stop off at 1/60 you will be a stop off at 1/80. A stop from 1/60 is 1/120!!!

 

[jim10219]

The best way I've discovered to test shutter speeds of stuff like that is to attach the shutter to your large format camera body (or the mounted lens, however you intend to use it), and take a digital camera with manual controls and place it inside the camera, preferably near where the film is inserted. . Then what you do is set the camera for a long exposure, say 5-30 seconds, with the self timer activated, trip the self timer, and close up the LF camera box the digital camera is in. Now wait for the self timer to quite beeping, letting you know it's starting the 5-30 second exposure. During that 5-30 second exposure, trip the shutter you made or are testing. Wait out the rest of the 5-30 seconds. What you should now have is a digital exposure with a known ISO, and a known aperture. From there, you remove the digital camera from the box and take a series of photos of whatever you were trying to photograph before, with the same ISO and aperture, only now you're using a series of known times. Compare the known times with the unknown times, and where the two photos look identical, you now know your shutter speed. Test it again a few more times, this time setting the aperture or ISO to get a better exposure during the test, and with some different variables (like a difference scene or different light source).

It would be a lot easier to explain with a video or some diagrams. It sounds difficult and time consuming, but it really only takes like 5 minutes. And the results are very accurate (assuming your digital camera is accurate), and doesn't require any math or special tools (other than the camera).

Or you could build a shutter speed tester. They're simple to make, so long as you have a computer to hook it up to and some basic soldering skills.

 

[btaylor]

Or you could build a shutter speed tester.

Or you can buy one. There is one that hooks up to a phone, and stand alone units. I bought a home built one from a guy who I think used to post here, I think it was $80 or so all in. There are probably cheaper ones now. One of the best photo investments for me- I have a number of cameras and a lot of leaf shuttered lenses. It is great to run through a shutter's speeds and know exactly what I am getting and if it is consistent. Then I make up a little chart of the actual speeds and keep it with that camera or shutter. If the speeds are inconsistent it's time for a CLA. Helps take an unknown out of the equation.

 

[Bill Burk]

I would certainly use a film test with step wedge exposed on one sheet and he camera shot of a gray card (but focus at infinity) and measure the density of the developed film. I’d plot the curve and mark the “point” where the gray landed... then I would find how far the gray landed compared to where I thought it would land... messy I know, but it would work. Luckily gravity doesn’t change much over time so you should be good for a while. Until you point the camera down

 

[Richard Man]

I would love to try a Thornton shutter! Now if I can get a large enough one in clean shape.

 

[Richard Man]

... but there doesn't seem to be a lot of (any?) Thornton with opening as large as 3 1/2"?

 

[Ian Grant]

... but there doesn't seem to be a lot of (any?) Thornton with opening as large as 3 1/2"?

I have at least 3 TP shutter for 3½" and slightly larger lenses but they are a lot less common than the smaller ones. But with T & I and a shutter speeds of 1/10 to 1/90 - 170 with the largest, they are a practical proposition. I've restored and passed on 3 other alrge TP shutters. I should add all my large ones are now paired to lenses.

Ian

 

[Richard Man]

@Ian Grant, if you ever want to sell one of your 3 1/2 shutter, let me know. Thanks

 

[Ian Grant]

@Ian Grant, if you ever want to sell one of your 3 1/2 shutter, let me know. Thanks

I'll keep my eyes open Richard, I don't need any more large ones myself well at the moment I restore these shutters on a regular basis so condition is less important as long as the spring in the tension roller works.

So if I come across one I'll let you know, I don't think there's a large one in my pending/part restored box, I think I have 20+ just waiting on my making new curtains and reassembly

Ian

 

[Minarik]

Old post but someone might be interested.
Free fall calculator where you can punch in the initial velocity and calculate the drop for each shutter speeds.

https://www.omnicalculator.com/physics/free-fall