workaround for 360 shutter below 24 fps

[jbeale]

As several people mentioned on this thread, http://www.reduser.net/forum/showthread.php?t=17105 there seems to be no way currently (Build 16) to get a shutter slower than 1/24 sec (360 degrees at 24 fps) without using the timelapse mode, which in turn limits you to 1 fps or slower (at least with the internal intervalometer).

Perhaps this limitation will change with firmware updates yet to come. But in the meantime, if you wanted, say 18 fps with 360 shutter it should be possible to get close to this, just by shooting in Varispeed mode at 36 fps with 360 shutter and then stacking together pairs of frames in post to create 18 fps.

While this is not exactly the same thing as true 18 fps (finite read/reset time means not a true 360 shutter, and readout + quantization noise on the one hand, but double the data rate on the other hand) and it means extra time in post, still it may be "good enough" for most purposes.

(I know there were posts about this here some time ago; just wanted to mention it again for reference- and so someone can correct me if this doesn't actually work).

 

[Justin Anderson]

Wouldn't shooting at 36fps @360deg and then converting it to 18fps look exactly the same as shooting 18fps @180deg?

 

[jbeale]

Shutter angle in degrees measures exposure relative to the fps rate. 360 means the shutter is open all the time, so two full 1/36 sec intervals equals one full 1/18 interval.

Combining two frames at 36 fps, 360 deg. should exactly match one frame at 18 fps, 360 deg. with a "theoretically perfect" camera. With a real camera there are some slight differences:

1) there is some finite time taken to readout the sensor and reset it so you cannot get truly 360 shutter. Maybe it's 359, I'm not sure, but there will be a short unexposed gap between frames. Maybe not big enough to see, but I haven't tried it and I don't know.

2) there should be a noise advantage (both thermal noise and quantization error) to using one longer exposure instead of two shorter ones, but it may not be significant in practice.

In fact, since you are combining two independently-compressed Redcode frames into one in post, you should actually reduce some compression artifacts. However Redcode now apparently has few or no visible artifacts anyway, so that's probably not a real advantage.

 

[Justin Anderson]

Shutter angle in degrees measures exposure relative to the fps rate. 360 means the shutter is open all the time, so two full 1/36 sec intervals equals one full 1/18 interval.

Combining two frames at 36 fps, 360 deg. should exactly match one frame at 18 fps, 360 deg. with a "theoretically perfect" camera. With a real camera there are some slight differences:

1) there is some finite time taken to readout the sensor and reset it so you cannot get truly 360 shutter. Maybe it's 359, I'm not sure, but there will be a short unexposed gap between frames. Maybe not big enough to see, but I haven't tried it and I don't know.

2) there should be a noise advantage (both thermal noise and quantization error) to using one longer exposure instead of two shorter ones, but it may not be significant in practice.

In fact, since you are combining two independently-compressed Redcode frames into one in post, you should actually reduce some compression artifacts. However Redcode now apparently has few or no visible artifacts anyway, so that's probably not a real advantage.

Oh, I see. That sounds like a good idea!

Anyone care to post a test? :innocent:

 

[Stuart English]

Shutter Speed

Shutter Speed

Yes it works fine in Build 16 .. try this

Set Shutter DISPLAY = 1/sec format

Set TIME BASE = 23.98 fps and SHUTTER to 1/24 fps

Set shutter MODE = RELATIVE

Enable VARISPEED and set FRAME RATE to 18 fps

Camera will show 1/18 sec ( which is 360 degrees at 18 fps )

 

[David Wilson]

Stuart,

I think I am following but sadly won't have a camera (God Willing) till next week to try it out.

But...

Would this pattern hold true for even slower frames per second and longer exposure times?

For example:
Set Shutter DISPLAY = 1/sec format

Set TIME BASE = 23.98 fps and SHUTTER to 1/24 fps

Set shutter MODE = RELATIVE

Enable VARISPEED and set FRAME RATE to **6** fps

Camera will show 1/6 sec ( which is 360 degrees at **6** fps )???

Does this work?

Many thanks.

 

[Kenn Michael]

Yes, this does work.

 

[Pawel Achtel]

I haven't tested it, but what is the longest exposure (slowest shutter) one can set? Would this work at 1fps and 1s (360 deg) shutter?

 

[David Wilson]

Thank you Kenn, great relief to me to hear this. I wonder as well with Pawel if this will work all the way down to 1fps/1 sec exposure.

 

[Stuart English]

Yes, it will work at all framerates

 

[I Bloom]

Relative shutter is bad ass. I leave it on all the time.