Keeping focus through zoom.

Started by Critical Point, July 22, 2013, 09:20:39 PM

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Critical Point

I was thinking, won't it be possible to have a feature that would keep the image focused in case of zooming ? If for instance you are now at 17mm focused right on, and you zoom to 50mm, the image is no longer focused right, but won't it be possible somehow for magic lantern to maintain the right focus all the way through zoom ? You can calculate the amount of focus correction necessary for a given x mm, like when you go from 18 to 50mm, you can calculate how much focus correction is needed between 18 and 50mm, that way magic lantern could maintain the focus.
600D & GH2 / PC.

mk11174

Quote from: Critical Point on July 22, 2013, 09:20:39 PM
I was thinking, won't it be possible to have a feature that would keep the image focused in case of zooming ? If for instance you are now at 17mm focused right on, and you zoom to 50mm, the image is no longer focused right, but won't it be possible somehow for magic lantern to maintain the right focus all the way through zoom ? You can calculate the amount of focus correction necessary for a given x mm, like when you go from 18 to 50mm, you can calculate how much focus correction is needed between 18 and 50mm, that way magic lantern could maintain the focus.
Maybe your lens is like mine, mine is the kit lens, try focusing first of coarse, switch to MF and the big thing that is a bug in my lens is any time you turn lens in the zoom direction, when you zoom to the point you want, just always nudge back in the wide direction, that will give you your focus back. On my other lens I dont have this issue, once you focus, if you zoom in and out it dont get messed up. But this kit lens is kinda flimsy it seems. So my rule is always nudge back to wide any time I zoom.
500D/T1i  550D/T2i  600D/T3i  700D/T5i

brapodam

Quote from: mk11174 on July 22, 2013, 11:17:31 PM
Maybe your lens is like mine, mine is the kit lens, try focusing first of coarse, switch to MF and the big thing that is a bug in my lens is any time you turn lens in the zoom direction, when you zoom to the point you want, just always nudge back in the wide direction, that will give you your focus back. On my other lens I dont have this issue, once you focus, if you zoom in and out it dont get messed up. But this kit lens is kinda flimsy it seems. So my rule is always nudge back to wide any time I zoom.
I don't see how your post is relevant to his question. He has a problem where the lens does not retain focus after zooming; some lenses have this problem. He wants some sort of feature that re-focuses after zoom to the same focus distance as before the zoom.

I think it might not be possible, because some lenses do not report focus information accurately (they report focus distance in large steps). Focusing to infinity (not to be confused with hyperfocal) is possible though; I see a script on this forum that does that.

mk11174

Quote from: brapodam on July 23, 2013, 02:40:50 AM
I don't see how your post is relevant to his question. He has a problem where the lens does not retain focus after zooming; some lenses have this problem. He wants some sort of feature that re-focuses after zoom to the same focus distance as before the zoom.

I think it might not be possible, because some lenses do not report focus information accurately (they report focus distance in large steps). Focusing to infinity (not to be confused with hyperfocal) is possible though; I see a script on this forum that does that.
I don't see why it matters, I am just trying to be helpful, I really don't see why you have to point out it might not be relevant, can't people just help people without all this attitude, I don't see why it always comes to this in these boards!  ???
500D/T1i  550D/T2i  600D/T3i  700D/T5i

brapodam

Quote from: mk11174 on July 23, 2013, 02:49:05 AM
I don't see why it matters, I am just trying to be helpful, I really don't see why you have to point out it might not be relevant, can't people just help people without all this attitude, I don't see why it always comes to this in these boards!  ???
I don't know, but your post does not seem to help him very much. It might be your English but what I got from your post is that after zooming to 50mm, zoom out to a wider focal length to regain focus. However there is a problem with this: the purpose of zooming in to 50mm is to shoot at 50mm, not something else. This might not be what you meant; if it isn't, then I'm sorry for the misunderstanding.

mk11174

Quote from: brapodam on July 23, 2013, 03:13:55 AM
I don't know, but your post does not seem to help him very much. It might be your English but what I got from your post is that after zooming to 50mm, zoom out to a wider focal length to regain focus. However there is a problem with this: the purpose of zooming in to 50mm is to shoot at 50mm, not something else. This might not be what you meant; if it isn't, then I'm sorry for the misunderstanding.
I was just thinking maybe he is only asking for this feature because he was having the same issue with his lens  losing focus while zooming as I have, so I was letting him know my fix just in case this is why he asked for the feature.

Apology accepted, I really like helping people but when you see people nit pick other peoples responses, it kind of ruins the mood too. It does not matter what help people give, it is just a place for people to brainstorm ideas, should not have to have people commenting in bad ways about other peoples help, especially when they are just trying to be nice and help and that is all I want to do is help as I can.
500D/T1i  550D/T2i  600D/T3i  700D/T5i

Critical Point

Well, even if the lens doesn't give accurate data, it still can be done. Lets say the lens gives x mm, and at the next step y mm.

If we could program in a menu how the focus should react when the lens gives y mm, problem solved.

When ML reads 24mm change focus to +2, when it reads 35mm change focus +3, something like that. All that is needed is just a menu for programing how the focus should react to a given number of mm that the lens reports. It doesn't matter if the lens reports 24mm instead of 27mm, since we can program the focus at a given mm number reported by the lens (even wrong), we program the focus by eye.

We should have in a menu something like this:

17mm - a value
18mm - b value
19mm - c value
20mm - user inserts +/- focus correction in rapport to c value (or inserted by the user in rapport to what value)
.
.
50mm -
.
.
600D & GH2 / PC.

mk11174

Quote from: Critical Point on July 24, 2013, 03:33:19 AM
Well, even if the lens doesn't give accurate data, it still can be done. Lets say the lens gives x mm, and at the next step y mm.

If we could program in a menu how the focus should react when the lens gives y mm, problem solved.

When ML reads 24mm change focus to +2, when it reads 35mm change focus +3, something like that. All that is needed is just a menu for programing how the focus should react to a given number of mm that the lens reports. It doesn't matter if the lens reports 24mm instead of 27mm, since we can program the focus at a given mm number reported by the lens (even wrong), we program the focus by eye.

We should have in a menu something like this:

17mm - a value
18mm - b value
19mm - c value
20mm - user inserts +/- focus correction in rapport to c value (or inserted by the user in rapport to what value)
.
.
50mm -
.
.
Actually I have already done this, check out the module I made.
http://www.magiclantern.fm/forum/index.php?topic=7189.0
500D/T1i  550D/T2i  600D/T3i  700D/T5i