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Min focus distance

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Offline pigeonhill

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Min focus distance
« on: 07 / February / 2019, 11:42:08 »
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Does anyone know if there is anyway to extract the minimum focus distance associated with a given cam? Some hidden metadata.


Or do I just drive the lens to the macro end and stop when the focus distance doesn’t change?


Cheers


Garry
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Offline waterwingz

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Re: Min focus distance
« Reply #1 on: 07 / February / 2019, 11:49:55 »
Quote from: pigeonhill on 07 / February / 2019, 11:42:08
Does anyone know if there is anyway to extract the minimum focus distance associated with a given cam? Some hidden metadata.
Given the fact that we've only been partially successful at getting cameras to accurately even focus at infinity, I'd be surprised if there was an accurate minimum focus distance stored anywhere.

Quote
Or do I just drive the lens to the macro end and stop when the focus distance doesn’t change?
I'm thinking that's about all you can do.
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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline pigeonhill

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Re: Min focus distance
« Reply #2 on: 07 / February / 2019, 11:54:24 »
@waterwingz

Thanks: that's what I thought for the macro end.

As for infinity focus; I've found that, as long as the distance reporting is reasonable, ie I've verified it, focusing to, say, an infinity defocus blur of 2 sensor pixels is a pretty good optical infinity. That is, well short of 'zero infinity'.

Cheers
Garry
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Offline waterwingz

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Re: Min focus distance
« Reply #3 on: 07 / February / 2019, 12:00:28 »
Quote from: pigeonhill on 07 / February / 2019, 11:54:24
As for infinity focus; I've found that, as long as the distance reporting is reasonable, ie I've verified it, focusing to, say, an infinity defocus blur of 2 sensor pixels is a pretty good optical infinity. That is, well short of 'zero infinity'.
When I worked on "focus at infinity" as couple of years ago, I found that different cameras of the same model would work differently.  Not a supported feature from Canon - even when the cameras (S100 for example) offered native Canon MF.
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Offline pigeonhill

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Re: Min focus distance
« Reply #4 on: 07 / February / 2019, 12:04:16 »
@waterwingz

Yes, I agree: it's not a religion with me: but it helps inform my photography, which is why I wrote the DoF Bar script over in ML: http://photography.grayheron.net/2018/12/dof-bar-simple-focus-bracketing.html
« Last Edit: 07 / February / 2019, 13:03:16 by pigeonhill »
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Offline c_joerg

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Re: Min focus distance
« Reply #5 on: 08 / February / 2019, 06:18:25 »
The values for the smallest and largest focal length can be found in the manual. But I never checked the values for how accurate they are.

IXUS160   28 (5.0)   1cm       224 (40)   1,3m
SX230   28 (5.0)   5cm       392 (70)   1m
SX50           24 (4.3)   0cm       1200 (215)    1,3m
S110          24 (5.2)   3cm       120 (26)   30cm
G1x           28 (15.1)   20cm        112 (60.4)   85cm
G7x         24 (8.8 )   5cm        100 (36.8 )   40cm
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M100 100a, M3 121a, G9x II (1.00c), 2*G1x (101a,100e), S110 (103a), SX50 (100c), SX230 (101a), S45,
Flickr https://www.flickr.com/photos/136329431@N06/albums
YouTube https://www.youtube.com/channel/UCrTH0tHy9OYTVDzWIvXEMlw/videos?shelf_id=0&view=0&sort=dd
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Offline pigeonhill

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Re: Min focus distance
« Reply #6 on: 08 / February / 2019, 07:15:23 »
@c_joerg

Thanks for the info, however, I was trying to not use look up tables ;-)

BTW is was I intruiged by the SX50 at 0cm.

Cheers

Garry
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Offline c_joerg

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Re: Min focus distance
« Reply #7 on: 08 / February / 2019, 07:21:04 »
Quote from: pigeonhill on 08 / February / 2019, 07:15:23
BTW is was I intruiged by the SX50 at 0cm.

I have never tried it but you can already run pretty tight...
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M100 100a, M3 121a, G9x II (1.00c), 2*G1x (101a,100e), S110 (103a), SX50 (100c), SX230 (101a), S45,
Flickr https://www.flickr.com/photos/136329431@N06/albums
YouTube https://www.youtube.com/channel/UCrTH0tHy9OYTVDzWIvXEMlw/videos?shelf_id=0&view=0&sort=dd
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Offline waterwingz

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Min focus distance
« Reply #8 on: 08 / February / 2019, 07:37:08 »
Quote from: pigeonhill on 08 / February / 2019, 07:15:23
I was trying to not use look up tables.
I assume you are trying to make a script generic for any camera? One option is to make the value a user entered parameter.

Otherwise you'll need to create huge lookup table of constants to cover every camera (you can get the camera model or ID to index into the table in a script).
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Offline pigeonhill

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Re: Min focus distance
« Reply #9 on: 08 / February / 2019, 10:42:43 »
@waterwingz

Yes, generic.

Added a little feature to allow the user to manually set the starting focus or have the cam carry out a full focus stack, eg from min focus to the blur defined infinity focus.

Here's the code I'm using to set the min focus:
Code: [Select]
if u == 1 then
    local dis = 0
    set_focus(0)
    repeat
        dis = get_focus()
        sleep(100) -- seems to work on G7X & G1X, may need changing on other cams
    until dis == get_focus()
    x = dis
    x_start = x
    h = base_h
end
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