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SX 10 - Extended AV!!!

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Re: SX 10 - Extended AV!!!
« Reply #20 on: 14 / November / 2009, 19:54:14 »
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Excuse me but i'm italian and my english is terrible...it was a sort of question...if the minimun av at max zoom is software limited maybe  because if we open further the iris we can have a lot of purple fringing but today i found the answer by myself...No...the iris is fully open at wide f:2.8 and at max zoom at f:5.7 so we can not open further the iris...

Re: SX 10 - Extended AV!!!
« Reply #21 on: 14 / November / 2009, 20:04:57 »

How did you bypass the lower limit? The area I've been modifying seems to be as close as I can get to setting the aperture without getting actuall access to the aperture mechanism code.
I've tried doing it directly, but my results are the same results as 2.8 giving me the impression that F2.8 is the limit and represents true aperture full open (can't physically get larger). 

Yes...we can't physically get larger openings...

Re: SX 10 - Extended AV!!!
« Reply #22 on: 14 / November / 2009, 22:46:52 »
Yes...we can't physically get larger openings...

Yes, you've got it now.  F2.8 at wide & F5.6 at zoom have the same aerture openign size, which seems to be full open.
However, the flip side of this is that since I can get F2.8-F16.0 at wide, correspondingly I can actually get F5.6-F32.2 at zoom.  See my discussion here: http://chdk.setepontos.com/index.php/topic,4498.0.html.  I have implemented and tested this seemingly successfully (diffraction issues aside).  Some further alterations to the code need to be done to get this to work which I will post for others to test once I'm satified with my own current testing of it.

Re: SX 10 - Extended AV!!!
« Reply #23 on: 15 / November / 2009, 05:17:08 »
Yes, you've got it now.  F2.8 at wide & F5.6 at zoom have the same aerture openign size, which seems to be full open.

I don't understand this. Having the same aperture opening size (area), means that f/N remains constant (with f the focal length and N the f-number). See e.g. Wikipedia
Therefore at full wide, f=5mm and N=F2.8. At full zoom f=100mm, so with the same area, you would have N=F56, not N=F5.6.
To get F5.6 at 100mm your area has to be sqrt(10) larger than at F2.8, 5mm.


Re: SX 10 - Extended AV!!!
« Reply #24 on: 15 / November / 2009, 05:38:04 »
Having the same aperture opening size (area), means that f/N remains constant

No it does not.

It depends on the diameter of the entrance-pupil.
That is the image of the real aperture formed by the lenses in front of it.
That image size changes as you zoom because those lenses move.

Re: SX 10 - Extended AV!!!
« Reply #25 on: 16 / November / 2009, 14:18:28 »
I don't understand this. Having the same aperture opening size (area), means that f/N remains constant (with f the focal length and N the f-number). See e.g. Wikipedia
Therefore at full wide, f=5mm and N=F2.8. At full zoom f=100mm, so with the same area, you would have N=F56, not N=F5.6.
To get F5.6 at 100mm your area has to be sqrt(10) larger than at F2.8, 5mm.
Yes, this was confucing me for a bit as well as the math didn't seem to work (and through my FW disassembly, I can be almost certain that the physical aperture size is the same for f2.8-wide and f5.6-zoom).  What is missing and overlooked in a lot of explainations is that it isn't actual aperture size, but apparent aperture size (i.e. how big it looks, not how big it is).  (http://www.lavideofilmmaker.com/cinematography/f-stops-focal-length-lens-aperture.html).

So, when zooming, even though the actual aperture is the same, the magnification of the lenses in front of it change its apparent size.  So assuming the av96=194 offset between wide and zoom, and the focal length change of 5mm-100mm, the magnification of the aperture is approximately 10x (actually 9.928X based on 194  offset), meaning that, to the camera, the aperture looks about 10X bigger than it is due to lens magnification.

Re: SX 10 - Extended AV!!!
« Reply #26 on: 16 / November / 2009, 21:41:00 »
Idon not know if this can help but if you look at the av96 values and subtract 256 from each the av values vary from a minimum of 32 to 512 in step of value=32...if 32 is f2.8 and the f value vary of about 0,1 between 2 steps than maybe 0 would be 2.7?in other words may be that the iris is not fully opened?

Re: SX 10 - Extended AV!!!
« Reply #27 on: 16 / November / 2009, 23:03:06 »
OK, I've started some verification tests so keep watching this space if interested!

Test #1:

Zoom: Full Wide
Shutter speed=0.6s
ISO=80
Aperture: f4.00 to f16.00

Results:

Quote
Aperture     Ave Pix     Ratio     
f4.000.6629-
f5.660.350752.90%
f8.000.178650.93%
f11.310.091451.18%
f16.000.045149.34%

The exposure ratios are fairly close to 1/2 as expected.

The normal camera operation limits aperture to F8.0, this test has gone 2 full stops beyond to F16.0 successfully.

I have not exceeded f16.00 as that appeared to be the limit I hit in previous tests.  I will test some aperture increments beyond f16.00 at a later time to try to pinpoint the limit.

For this test, the images I've included are the JPGs so they have the incorrect colour space for checking exposure difference (not going to bother posting 19MB TIFs...)


Re: SX 10 - Extended AV!!!
« Reply #28 on: 16 / November / 2009, 23:24:10 »
Test #2:
The purpose of this test is to test the limit of the aperture at full zoom as I have discussed previously in this thread

Zoom: Full Zoom
Shutter speed=2.0s
ISO=80
Aperture: f8.00 to f32.00

Results:

Quote
Aperture     Ave Pix     Ratio     
f8.000.5988-
f11.310.323153.96%
f16.000.170852.86%
f22.630.082248.13%
f32.000.039948.54%

The exposure ratios are fairly close to 1/2 as expected.

The normal camera operation limits aperture to F8.0, this test has gone 4 full stops beyond to F32.0 successfully!

I will test some aperture increments beyond f32.00 at a later time to try to pinpoint the limit.

You can also note that if you compare the the same f stop exposures in this test with those from test 1:
Quote
Aperture    Test 1     Test 2     Ratio     
f8.000.17860.598829.83%
f11.310.09140.323128.29%
f16.000.04510.170826.41%

In Test 1, the actual shutter speed is registered as 0.59s in the exif
In Test 2, the actual shutter speed is registered as 2.00s in the exif
The difference is 1.76 stops -> 1/2^(1.76)=0.295, which is pretty close to the ratios calculated.  I will have to do check this more thoroughly later using the same shutter speed.


Again, for this test, the images I've included are the JPGs so they have the incorrect colour space for checking exposure difference (not going to bother posting 19MB TIFs...)

Re: SX 10 - Extended AV!!!
« Reply #29 on: 20 / November / 2009, 20:31:36 »
Ok!...and now??I'll like to have a try with this mods and if all is working fine it's possible to add it to next build..

 

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