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FORUMS Canon Cameras, Lenses & Accessories Canon EOS Digital Cameras 
Thread started 09 Mar 2014 (Sunday) 19:45
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Opening aperture during exposure

 
kfreels
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Mar 10, 2014 09:10 |  #16

pwm2 wrote in post #16746693 (external link)
And the really big problem is that a varying aperture doesn't work well with our sliding shutter curtains - we don't expose the full image at the same time, so a varying aperture while the shutter curtains moves would result in the top and bottom of the image to be taken with different aperture. And that would require the shutter curtains to also move with different speeds so they move quick when the lens is fully open and move slowly when the lens is stopped down.

This is the major problem. You end up with an open slit traveling across the sensor and as it does, you have different apertures running. So you would get decreasing exposure as the shutter traveled and end up with a light to dark image. Assuming you have some kind of computer control that could compensate by varying the time that each aperture was open to give an even exposure, you would have a depth of field that expands as the shutter travels down the image.

On longer exposures, the effect would be different. Assuming the shutter opens completely and then the aperture makes its run, then you might be getting somethign interesting. You would need to do some calculating but it would be straighforward. As others mentioned, a manual camera with a manual lens on film would be the easiest way to do it and see what you get. I would guess that the result would be basically a multiple exposure image with partial exposures combining to add up to the proper exposure. I also guess that taking multiple images and blending them in post would product the same result. So for example, you have 5 images at f2.8, 4, 5.6, 8, and 11 and you do all 5 as layers in photoshop with 20% opacity.

But hey, we're all speculating. Part of the fun in photography is the experimentation. Get out there and do it!


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DutchinCLE
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Mar 10, 2014 09:31 |  #17

Interesting Idea.. I have a manual Takumar I will try this with tonight.. The only problem I see is that the Aperture ring, "clicks" when it selects the aperture, so I might get some movement.. I'll post the result.


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Gobeatty
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Mar 10, 2014 10:43 as a reply to  @ DutchinCLE's post |  #18

I guess I assumed (I know, I know) that the exposure is at least longish so the aperture would only be changed while the shutter was fully open. But hey - if there is a way to change aperture quickly during a short exposure, go for it.

Also fun to be had zooming during exposures.


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Lowner
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Mar 10, 2014 10:56 |  #19

Sorry, but I just don't see the point. Its got so many negatives and I cannot see a single positive factor anywhere.


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kfreels
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Mar 10, 2014 13:27 |  #20

Lowner wrote in post #16747919 (external link)
Sorry, but I just don't see the point. Its got so many negatives and I cannot see a single positive factor anywhere.

Most likely you're right. But all the great discoveries are made by people who don't assume and instead, experiment outside the box. You won't see me experimenting with it because I'm fairly certain it would be a waste of time, but I'm certainly not going to dissuade someone else from it. Even if the result it total crap, you still come out of such an experiment with more knowledge than you went in with. And who knows what unexpected things you might think of along they way while you're exploring?


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Mar 10, 2014 14:35 as a reply to  @ kfreels's post |  #21

I would expect that you would end up with something that looks like the lens baby image. The center point of the field in focus would be crisp but as you moved away from that toward the edges of the DOF and beyond, everything would be hazy or ghostly, because as you opened up the aperture, more of what used to be in focus would now be out of focus until you get to wide-open.

It would make for creative images, much like focus zooming, but not sure what other specific applications would benefit.

Image this, but instead of objects moving away from the center, focus/ghost imaging would increase the farther out.

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groundloop
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Mar 10, 2014 14:39 |  #22

kfreels wrote in post #16748329 (external link)
But all the great discoveries are made by people who don't assume and instead, experiment outside the box.....

Right you are. I too am fairly certain the results would look like crap, but the idea is so outlandish that I may just try it in Photoshop with multiple exposures and see what it looks like.




  
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Mar 10, 2014 16:18 |  #23

OP, you can get a much more interesting effect by zooming during a long exposure, especially if there are some lights in the frame.


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DutchinCLE
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Mar 10, 2014 19:59 |  #24

allright, I gave it a try:
I used a T3i in combination with a 55mm Takumar f2.2, andfocused on the second "animal"

First one was done with 4 second exposure and changed the aperture from 2.2 to 22, second was done at f2.2 - 1/20sec and the last on at f22 - 20sec.

What I think happens, other then getting a blurred image due to the snapping of the aperture ring, is that the DOF becomes a bit larger than wide open, but the transition from "sharp" to blurred becomes shorter. No way to control it by hand though.


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DutchinCLE
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Mar 10, 2014 20:00 |  #25

and the f22


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tat3406
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Mar 10, 2014 20:28 |  #26

good experiment. just wonder start with F22 and open to F2.2, what the image look like?


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DutchinCLE
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Mar 10, 2014 20:34 |  #27

I tried, I ran into the problem that it would overexpose.. Didn't have a lot of time to play with it.. My parental duties got in the way.. :)


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Tom ­ Reichner
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Mar 10, 2014 23:10 |  #28

Snydremark wrote in post #16746970 (external link)
Given that the aperture and shutter are electronically controlled and the camera locks control out during an exposure, I don't even see how this would be possible

Exactly right. I think the only way to do this is with gear that is not current, mainstream Canon stuff. And if you're doing it manually, how would you control exactly how long the aperture is at each setting? I mean, we're talking about hundredths and thousandths of a second here, unless you're doing some weird long-exposure stuff when it's practically nighttime outside. How do you make your fingers turn an aperture ring exactly 1/125th of a second into an exposure? Or exactly 1/500th of a second, etc?


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xarqi
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Mar 11, 2014 00:13 |  #29

Tom Reichner wrote in post #16749612 (external link)
Exactly right. I think the only way to do this is with gear that is not current, mainstream Canon stuff. And if you're doing it manually, how would you control exactly how long the aperture is at each setting? I mean, we're talking about hundredths and thousandths of a second here, unless you're doing some weird long-exposure stuff when it's practically nighttime outside.

ND10 filter and a stop watch.

How do you make your fingers turn an aperture ring exactly 1/125th of a second into an exposure? Or exactly 1/500th of a second, etc?

It's more complicated than that. If each aperture is to contribute equally to the final result, the time spent at that aperture must be inversely proportional to it. So instead of rotating the aperture ring at a constant angular velocity, it must be accelerated or decelerated depending on whether the aperture is going from small to large or vice versa. Not doing that would mean that the final result would be much the same as the maximum aperture result.

So - it's long exposures, with ND filters probably, a stopwatch, and a set of precalculated times, or simulate the process by merging exposures of the same scene at different apertures.




  
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Xerxes
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Mar 12, 2014 13:33 |  #30

Thanks for testing DutchinCLE! That is pretty neat, turned out better than I expected and the result makes sense




  
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Opening aperture during exposure
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