Improving CHDK ND filter support

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Offline lapser

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Re: Improving CHDK ND filter support
« Reply #30 on: 16 / September / 2017, 14:06:13 »
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On both elph130 and d10, I noticed that the zoom level seems to change very slightly with/without ND.
Same on G1x….
Another interesting think is changing of noise in the video when the cam goes from ISO1000 to ISO130. I don’t use any noise reduction
Adding a filter moves the focal point back a small amount, depending on the thickness of the filter.
http://www.lcas-astronomy.org/articles/display.php?filename=filters_and_focus_shift

I've noticed a slight magnification change, and slight blurring, in my time lapses before and after an ND filter switch. It's not very noticeable to most people, so I haven't done anything to fix it. I suppose the way to correct it would be to change the focus after an ND switch, but I'm not sure it's worth the hassle.

I have two G1X cameras. I usually set the focus at the hyperfocal point, which works with one camera. But the other camera gets too blurry with the ND filter in, so I set that camera to infinity focus.

The way to correct your time lapse video would be to zoom slightly in or out after an ND filter switch.

Here's an example video:

Watch the tree on the right after the Sun goes down in the above time lapse. The filter switches out around 40 seconds, which moves the tree slightly, and changes the sky pattern a little. Nobody has ever noticed it (except me).

Regarding the ISO change, I switched the filter in at 1/500 sec 100 ISO in this video. I switched back out at 1/34.6 sec 100 ISO, which makes the first shot without the filter 1/250 sec 100 ISO. Note the ISO is always at minimum if you set your switch point to a fast enough shutter speed.

Here's the part of my log file for this video that shows the ND filter switch:
Code: [Select]
Shot# dEV sEV Shutter  ISO   Bv* IntD PD mV°F  >50  >90 H-M1 Hist   M#1  IMG_
 1115  -4 274  1/34.6  100  615*   51  3 7849    0    0   38   -3«  -42« 9821
Auto OUT (274) 273« -1
 1116  -1  -1~  1/250  100  614    53  8   80    0    0   38   -5«  -43« 9822
 1117  -4   0   1/248  100  615    49  1 7859    0    0   38   -3«  -42« 9823
EOS-M3_120f / SX50_100b / SX260_101a / G1X_100g / D20_100b
https://www.youtube.com/user/DrLapser/videos

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Offline reyalp

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Re: Improving CHDK ND filter support
« Reply #31 on: 16 / September / 2017, 16:18:28 »
On both elph130 and d10, I noticed that the zoom level seems to change very slightly with/without ND.
Same on G1x….
One way to deal with this would be to use log to determine when the ND changed and crop / scale the images to match. Wouldn't address the focus change lapser mentioned though.
Don't forget what the H stands for.

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Offline lapser

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Re: Improving CHDK ND filter support
« Reply #32 on: 16 / September / 2017, 21:26:53 »
One way to deal with this would be to use log to determine when the ND changed and crop / scale the images to match. Wouldn't address the focus change lapser mentioned though.
There's usually enough depth of field to handle the small focus change from the ND filter. I had a problem when I got too fancy and set the focus at the hyperfocal distance computed by CHDK. That's as close as you can set the focus and still have infinity in acceptable focus.

But when you switch the ND filter from out to in, the focus moves in even further, causing the blur. The solution was to focus on infinity in the first place, and not use the hyperfocal point.

You can see the blurring when the filter switches in at 1:16 in this sunrise time lapse (starting at 1:06)

https://youtu.be/fZ7V9Wy2UN4?t=66
« Last Edit: 16 / September / 2017, 21:34:07 by lapser »
EOS-M3_120f / SX50_100b / SX260_101a / G1X_100g / D20_100b
https://www.youtube.com/user/DrLapser/videos

Re: Improving CHDK ND filter support
« Reply #33 on: 18 / September / 2017, 03:01:32 »
The way to correct your time lapse video would be to zoom slightly in or out after an ND filter switch.

This is probably the easiest way…

I have tried a lot of stabilization algorithms; strangely they all fail in such simple situations.

Nobody has ever noticed it (except me).

I've noticed that sometimes. I just thought it was a gust of wind. ;)
The more you deal with the subject, the more you pay attention.


What you can also see very well at the log file is that the ND value from the props works very well.


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Offline lapser

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Re: Improving CHDK ND filter support
« Reply #34 on: 29 / September / 2017, 13:23:06 »
The way to correct your time lapse video would be to zoom slightly in or out after an ND filter switch.
This is probably the easiest way…
I have tried a lot of stabilization algorithms; strangely they all fail in such simple situations.
Nobody has ever noticed it (except me).
I've noticed that sometimes. I just thought it was a gust of wind.
The more you deal with the subject, the more you pay attention.
I tried the zoom method with this time lapse video from last Wednesday. I ended up cropping out 4 pixels horizontal, and 3 vertical from the clip with the filter in (4K video). I did it in the rendering progam since it's hard to crop accurately with Lightroom (I'll keep working on it).

Anyway, it seems to have worked pretty well. The ND filter goes out at 40 seconds into the video:
It's hard to see anything happening. If you watch closely, you'll see a slight brightness glitch in the sky.

The video has a lot of brightness fluttering with the Sun in the frame. This could be my 4 million exposures shutter wearing out. But I also mistakenly saved the photos as jpg instead of raw, so it could relate to the camera creating jpgs with blown pixels in the frame.

One thing I've noticed is that the ND filter density needed varies with the brightness you set for the filter to switch in or out. On one of my G1X cameras, the measured density is around 18 ev96 greater when switching in than when switching out.

To deal with this, I save the brightness before the switch, and measure the brightness in the first photo after the switch. I adjust the next photo so its brightness matches the saved brightness before the switch. What this means is that I have a one photo "flash" after a switch, which I can correct for in Lightroom. I can then correct the ND filter density parameter for the next time lapse if necessary.
EOS-M3_120f / SX50_100b / SX260_101a / G1X_100g / D20_100b
https://www.youtube.com/user/DrLapser/videos

Re: Improving CHDK ND filter support
« Reply #35 on: 29 / September / 2017, 14:33:48 »
I tried the zoom method with this time lapse video from last Wednesday. I ended up cropping out 4 pixels horizontal, and 3 vertical from the clip with the filter in (4K video). I did it in the rendering progam since it's hard to crop accurately with Lightroom (I'll keep working on it).
Yes, I know, unfortunately in Lightroom you can’t crop in pixel.
Anyway, it seems to have worked pretty well.
It works great…
One thing I've noticed is that the ND filter density needed varies with the brightness you set for the filter to switch in or out. On one of my G1X cameras, the measured density is around 18 ev96 greater when switching in than when switching out.
That’s interesting….
To deal with this, I save the brightness before the switch, and measure the brightness in the first photo after the switch. I adjust the next photo so its brightness matches the saved brightness before the switch. What this means is that I have a one photo "flash" after a switch, which I can correct for in Lightroom. I can then correct the ND filter density parameter for the next time lapse if necessary.
Maybe I would do this in postprocessing…
My plan is to write a tool which does the metering on RAW data files, like rawoplib but only on the CR2 data. One advantage about this, I can select an area where I do the metering. Then I would modify the ‘Exposure2012’ in the Lightroom XMP’s similar as I descript here:
https://chdk.setepontos.com/index.php?topic=12790.0

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Offline reyalp

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Re: Improving CHDK ND filter support
« Reply #36 on: 29 / September / 2017, 16:11:09 »
One thing I've noticed is that the ND filter density needed varies with the brightness you set for the filter to switch in or out. On one of my G1X cameras, the measured density is around 18 ev96 greater when switching in than when switching out.
This is strange. There's no way the actual ND value can with brightness, so I'd guess there's a bug somewhere or a hardware side effect like the aperture moving when the ND state changes.
Don't forget what the H stands for.

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Offline lapser

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Re: Improving CHDK ND filter support
« Reply #37 on: 29 / September / 2017, 16:52:54 »
One thing I've noticed is that the ND filter density needed varies with the brightness you set for the filter to switch in or out. On one of my G1X cameras, the measured density is around 18 ev96 greater when switching in than when switching out.
This is strange. There's no way the actual ND value can with brightness, so I'd guess there's a bug somewhere or a hardware side effect like the aperture moving when the ND state changes.
The 18 ev96 difference only happens on the camera I sent in to Canon to be refurbished. They replaced the entire lens assembly. I suspect it's a small calibration error. The focus in the refurbished camera is also a little off compared to my other G1X.

The ND switch out occurs at 1 ev darker than the switch in (what you call hysterisis I think). So it sounds like the conversion from ev96 to shutter speed may be a little off at different shutter speeds. I've also found that the measured ev96 of an ND switch is a little different at different switching brightness, in both cameras.

"In theory, theory and practice are the same. In practice, they're not!" _ Anonymous
"Reality is the murder of a beautiful theory by a gang of ugly facts." _ JohnClonts
EOS-M3_120f / SX50_100b / SX260_101a / G1X_100g / D20_100b
https://www.youtube.com/user/DrLapser/videos


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Offline reyalp

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Re: Improving CHDK ND filter support
« Reply #38 on: 24 / December / 2017, 01:16:15 »
I thought sx710 had a "hidden" ND, because PutInNdFilter made a noise and a big difference in exposure.

However, running ndtest.lua, I happened to notice the DOF was a lot deeper for the ND-in shots. So I tried using Av mode with aperture set to F/8 (rather than max Av), and ndtest only reported an ND value of ~117 instead of ~305 as in the previous runs.  When I tested Av overrides, there was detectable change up to around F/11, which would roughly match the F/8 + "ND" value.

Looking at the ROM code, sx710hs PutInNdFilter appears to be roughly
MoveIrisToAv(GetUsableMinAv())
:o :haha :lol

My impression is sx260hs (another "hidden" ND camera) code is the same. The code on G7x (which has an ND in the Canon UI) is totally different.

I would be interested if anyone can confirm the DOF changing significantly with the ND "in" on sx260hs or other supposed "hidden" cameras. If the "hidden" ND is not actually a thing, ND support in CHDK will be simplified considerably...

edit:
Additional data point: The non-hidden ND cameras have asserts for "NdActuator.c" and an ND task. These do not appear to be present in supposed "hidden" ND cams like SX260, SX50 and SX710

edit:
I mixed up Min and Max a couple times 
GetUsableMinAv returns the smallest aperture (e.g. F/11), GetUsableMaxAv returns the largest (e.g F/3.2)
The propcase we call PROPCASE_AV_MIN returns a value like "max"  :-[
« Last Edit: 25 / December / 2017, 22:28:55 by reyalp »
Don't forget what the H stands for.

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Offline srsa_4c

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Re: Improving CHDK ND filter support
« Reply #39 on: 24 / December / 2017, 10:17:18 »
I would be interested if anyone can confirm the DOF changing significantly with the ND "in" on sx260hs or other supposed "hidden" cameras.
I can, I made such an experiment some years ago, with my sx280.
This year, however, I noticed dirt on my "ND in" test shots (and even during half shoot with ND in), which made me believe that the ND does exist in some form...
... until I applied curves on my non-ND test images.
See attached pictures, most spots are there on both shots (F8, full zoom, focus on infinite, "ND" in & out).

 

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