Rack Focus

[russellsnr]

Hi, Don't no if you have ever looked at the MagicLantern firmware for Canon cameras Sebastian but it allows RACK FOCUS ie you focus at one point and set start and another point for stop so in movie mode you get a very smooth transition from A to B when filming from near to far. This also works with the FOCUS STACKING for single images within MagicLantern it allows the setting that are set for RACK FOCUS to be transfered across to the FOCUS STACK so it tells you how many steps from back to front and sets it automatically for the stack. Could this option be added to the QDSLR?
Yes I obviously have MagicLantern but the down side is you can only view on the back of the camera and not a 7" pad screen and that makes it awkward to get low to the ground (especially when you get past the 60 mark )
Thank You
Russ

[GonzoG]

And why focus stacking isn't enough ?? It has setting 2 AF points, setting number of steps or step size and automatically takes photos.

[russellsnr]

And why focus stacking isn't enough ?
Because with QDSLR you have to try and work out how many steps you need in front and behind and the size of each step depending on the size of the object to be photographed with MagicLantern you choose point A and point B in the rack Focus option and transfer that for Stack focus no matter if it be a small watch face or a landscape scene and works out the correct amount of steps and size of each.
Thanks
Russ

[GonzoG]

Well, so it's Canon's limitation not qDD.
With Nikon I set 2 points, size of single step or number of photos to be taken and press shutter button. All calculations are done by qDD.

Mind that ML has access to camera CPU, qDD only to data that can be read from camera with factory firmware. So if there are no command to get data from camera no calculations can be done.

[shotframers]

And how do you diced how many photos are needed or what step size you should chose. Helicon remote gives you a suggestion depending on the aperture and the focus distance.
If the camera/lens linfo of those points were linked with the dof calculator it could make you a suggestion

[GonzoG]

Numer of photos or step size cannot be calculated. Every lens has different minimal step.
You have to determine that yourself.

[shotframers]

So what is the DOF calculation doing?
The following variables are given:
aperture
focal length
sensor size
focus distance 1
and focus distance 2

the calculated dof should fit x times in between distance 1 and 2 and this should lead to a guidance how many photos are needed. Do you have a diffrent opinion?

[GonzoG]

You cannot use DoF calculations because those are based on size of final print, enlargement factor (sensor size, how much photo was cropped) and real focal length of lens.
In focus stacking the size of print doesn't matter at all and enlargement factor isn't fixed.
Also a sensor resolution is important which isn't in a factor in DoF.

Also lens focal length changes with changing focusing distance. The value that is in specifications is accurate only when lens is focused at infinity.

And what's most important - there is no way of knowing on what distance lens is focused.
Those data can be read only from EXIF from photo. So you would have to take 2 photos first (start and end of range), read distances from then and than you might calculate something.

[shotframers]

Hmm so how does helicon remote make there suggestions? Or how do I know how much pictures are enough?

[shotframers]

Here you can find a simple explanation ho helicon is doing it
http://www.heliconsoft.com/heliconsoft- ... rt-davies/