Lowest aperture on highest zoom?

srsa_4c

4451

Re: Lowest aperture on highest zoom?

« Reply #20 on: 21 / March / 2015, 17:41:19 »

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Quote from: waterwingz on 21 / March / 2015, 17:31:27

So if you get a darker picture on the second shot, it seems an ND filter must exist?

I tried the script and I tried it without the script, using just the ND control in the CHDK menu.
The photo with ND forced "out" is overexposed.

If any of you have a camera that supposedly has an *unofficial* ND filter, can you repeat the test?
Av mode, F8.0, CHDK ND override, dim scene...

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TMHKR

77
Canon PowerShot SX170 IS (1.01a firmware)

Re: Lowest aperture on highest zoom?

« Reply #21 on: 21 / March / 2015, 17:56:16 »

Quote from: srsa_4c on 21 / March / 2015, 17:41:19

If any of you have a camera that supposedly has an *unofficial* ND filter, can you repeat the test?
Av mode, F8.0, CHDK ND override, dim scene...

SX170, dim scene, f/8.0, Av mode, camera used 1" speed

ND in = very dark shot
ND out = correctly exposed shot, not overexposed

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srsa_4c

4451

Re: Lowest aperture on highest zoom?

« Reply #22 on: 21 / March / 2015, 18:03:42 »

I'm not sure what would be the best method to reliably test this...
Another test:
M mode, native Av at F8.0, CHDK Av override @ F16. Setting ND in/out has no influence on the photo's brightness (sx280, sx100).

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waterwingz

12132

Re: Lowest aperture on highest zoom?

« Reply #23 on: 21 / March / 2015, 18:16:07 »

Quote from: srsa_4c on 21 / March / 2015, 18:03:42

M mode, native Av at F8.0, CHDK Av override @ F16. Setting ND in/out has no influence on the photo's brightness

So that would tend to suggest that when you override the Av setting with an aperture setting smaller than the minimum iris, Canon inserts the ND filter automatically.

If that action is made after the CHDK set_nd_filter() executes then it would explain what you are seeing?

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Ported : A1200 SD940 G10 Powershot N G16

srsa_4c

4451

Re: Lowest aperture on highest zoom?

« Reply #24 on: 21 / March / 2015, 18:25:01 »

Quote from: waterwingz on 21 / March / 2015, 18:16:07

So that would tend to suggest that when you override the Av setting with an aperture setting smaller than the minimum iris, Canon inserts the ND filter automatically.

If that action is made after the CHDK set_nd_filter() executes then it would explain what you are seeing?

Do you have a suggestion for a test that proves the presence of an actual ND filter? I still tend to think that there is no ND hardware in my 2 mentioned cameras, the ND event procedures influence the iris instead (when they can).

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waterwingz

12132

Re: Lowest aperture on highest zoom?

« Reply #25 on: 21 / March / 2015, 18:31:06 »

Quote from: srsa_4c on 21 / March / 2015, 18:25:01

Do you have a suggestion for a test that proves the presence of an actual ND filter? I still tend to think that there is no ND hardware in my 2 mentioned cameras, the ND event procedures influence the iris instead (when they can).

It seems very unlikely the camera can get to f16 just with its adjustable iris.

So take two shots - one with Av overridden by CHDK to f16 and the other at f5.6 (3 f-stop difference). Hold the Sv value constant and change the shutter speed by 3x to compensate.

So if the two resulting images have essentially the same exposure, it would seem there must have been an ND filter inserted.

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Ported : A1200 SD940 G10 Powershot N G16

srsa_4c

4451

Re: Lowest aperture on highest zoom?

« Reply #26 on: 21 / March / 2015, 18:38:26 »

Quote from: waterwingz on 21 / March / 2015, 18:31:06

It seems very unlikely the camera can get to f16 just with its adjustable iris.

It can't (@ wide angle), F11 is the limit (this is the sx100). I'll see if I can do that exposure test...

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TMHKR

77
Canon PowerShot SX170 IS (1.01a firmware)

Re: Lowest aperture on highest zoom?

« Reply #27 on: 21 / March / 2015, 18:38:59 »

Quote from: srsa_4c on 21 / March / 2015, 18:25:01

Do you have a suggestion for a test that proves the presence of an actual ND filter?

Ask Canon engineers? Disassemble the camera?

In my case (SX170), I look into the lens and then turn it towards a bright scene. Like I said before, I noticed something that gets in the way of the lens elements, with a clicking sound. I believe it's ND filter, I doubt it's the aperture.

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srsa_4c

4451

Re: Lowest aperture on highest zoom?

« Reply #28 on: 21 / March / 2015, 19:43:21 »

Quote from: TMHKR on 21 / March / 2015, 18:38:59

Ask Canon engineers? Disassemble the camera?

That would be the sure thing, but I'd like to get away without that.

Quote

In my case (SX170), I look into the lens and then turn it towards a bright scene. Like I said before, I noticed something that gets in the way of the lens elements, with a clicking sound. I believe it's ND filter, I doubt it's the aperture.

If you're actually seeing something other than the iris, then your cam may have the ND. I don't see anything in front of the iris on my 2 mentioned cameras (the ND could still be behind the iris...?).

edit:
The ND filter is located in front of the iris on the g10, it appears bigger than the biggest iris opening.

« Last Edit: 21 / March / 2015, 19:58:47 by srsa_4c »

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TMHKR

77
Canon PowerShot SX170 IS (1.01a firmware)

Re: Lowest aperture on highest zoom?

« Reply #29 on: 22 / March / 2015, 06:04:05 »

Quote

I don't see anything in front of the iris on my 2 mentioned cameras (the ND could still be behind the iris...?).

edit:
The ND filter is located in front of the iris on the g10, it appears bigger than the biggest iris opening.

Yes, it might be located behind the iris. The bottom line is that something small moves inside the lens, and that I can clearly see it.

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