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Lowest aperture on highest zoom?

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Offline TMHKR

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Re: Lowest aperture on highest zoom?
« Reply #10 on: 21 / March / 2015, 16:09:07 »
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This says that there is an ND filter and it adds the equivalent of 3 stops ( 96- (-192) = 288 which in APEX96 units = 3 f-stops)

Does it make any difference if I used some other setting in the script? I left it at default 3 f-stops.

Re: Lowest aperture on highest zoom?
« Reply #11 on: 21 / March / 2015, 16:26:54 »
Does it make any difference if I used some other setting in the script? I left it at default 3 f-stops.
Actually,  that script I posted was intended for calibrating the ND filter.  Not the easiest thing to actually use when I look at it a year later.  You are supposed to adjust the f-stop parameter setting until the reported exp values match as closely as possible between the two shots.  I just tested it on a couple of my cameras and it doesn't work on cameras that have Canon built-in ND filter options in their menus (like my G10).   I know why, but its really not worth fixing.

Attached is something simple.  It takes one shot,  reads back the Tv, Av, & Sv values, and then takes a second shot using those same values but with the ND filter inserted.  If you use this script,  you should get two images with a significant shift in exposure between them if the ND filter in your camera is actually working.
« Last Edit: 21 / March / 2015, 16:38:02 by waterwingz »
Ported :   A1200    SD940   G10    Powershot N    G16

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Offline TMHKR

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Re: Lowest aperture on highest zoom?
« Reply #12 on: 21 / March / 2015, 16:42:41 »
Attached is something simple.  It takes one shot,  reads back the Tv, Av, & Sv values, and then takes a second shot using those same values but with the ND filter inserted.  If you use this script,  you should get two images with a significant shift in exposure between them if the ND filter in your camera is actually working.

Results at default setting (0):

*** STARTED ***
ND HDR started...
shoot half
start tv= 33 av= 352 sv= 411 offset= 0
shot 1 .. ND filter out
shot 2.. ND filter in
...done
*** FINISHED ***

Resulting photos: Big difference in brightness between the two photos.

Re: Lowest aperture on highest zoom?
« Reply #13 on: 21 / March / 2015, 16:43:45 »
Resulting photos: Big difference in brightness between the two photos.

The second photo should have been a lot darker.  Correct?
Ported :   A1200    SD940   G10    Powershot N    G16


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Offline TMHKR

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  • Canon PowerShot SX170 IS (1.01a firmware)
Re: Lowest aperture on highest zoom?
« Reply #14 on: 21 / March / 2015, 16:46:28 »
The second photo should have been a lot darker.  Correct?

Yes, it's considerably darker.

Re: Lowest aperture on highest zoom?
« Reply #15 on: 21 / March / 2015, 17:02:22 »
The second photo should have been a lot darker.  Correct?
Yes, it's considerably darker.
About 3 f-stops I'd guess  8)
Ported :   A1200    SD940   G10    Powershot N    G16

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Offline TMHKR

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  • Canon PowerShot SX170 IS (1.01a firmware)
Re: Lowest aperture on highest zoom?
« Reply #16 on: 21 / March / 2015, 17:10:23 »
You see, the main reason why I asked about low apertures is because I wanted more shallow DOF while doing portraits. With a camera like mine, which has a small sensor and variable aperture, the only way is to fully zoom in and separate subject from background. Shallow DOF looks best if the background is over a couple hundred meters away, but if it was a constant aperture across enitire zoom (which you explained is impossible), background would be immensely blurred, similar to f/1.8 lenses or less.

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Offline srsa_4c

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Re: Lowest aperture on highest zoom?
« Reply #17 on: 21 / March / 2015, 17:16:24 »
I get confusing results.
I tried 2 cams:
- sx100, has no ND according to CHDK (I have overridden that #define for this test)
- sx280, I assumed it does have an ND (based on its predecessor sx260)
If I set them to Av mode, F8.0, I get a brighter than expected picture when I set ND "out", and darker when I set it "in". Since the scene in question is rather dim... well, does that ND exist or not? The firmware could be just simulating one...

but if it was a constant aperture across enitire zoom
To my knowledge, Canon has never ever produced any PowerShots with a constant aperture zoom lens. The closest "super"zoom models are: S1IS (10x, F2.8 .. 3.1), S2IS - S3IS - S5IS (12x, F2.7 .. 3.5).


Re: Lowest aperture on highest zoom?
« Reply #18 on: 21 / March / 2015, 17:31:27 »
If I set them to Av mode, F8.0, I get a brighter than expected picture when I set ND "out", and darker when I set it "in". Since the scene in question is rather dim... well, does that ND exist or not? The firmware could be just simulating one...
The second script I posted takes two shots and it forces the Tv, Av, & Sv settings for the second shot to be the same as the first shot (taken in Auto mode).  Then it inserts the ND filter.   So if you get a darker picture on the second shot,  it seems an ND filter must exist?
Ported :   A1200    SD940   G10    Powershot N    G16

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Offline TMHKR

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  • Canon PowerShot SX170 IS (1.01a firmware)
Re: Lowest aperture on highest zoom?
« Reply #19 on: 21 / March / 2015, 17:33:50 »
does that ND exist or not? The firmware could be just simulating one...

I wouldn't know for sure, but I know that I do hear a click inside the lens while pointing at the bright scene (as stated before), and using waterwingz's script I do get much darker photo with ND swung in.

 

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