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#apertus IRC Channel Logs

2013/09/03

Timezone: UTC


06:33
se6astian
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ApertusWeb8
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sasha-w
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sasha-w
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13:06
Bertl
morning everyone!
13:30
se6astian
hello!
13:31
se6astian
I played around a little with the spherical joint idea
13:32
se6astian
and came up with an assembly that does not rely purely on material friction
13:32
se6astian
here is an animation
13:32
se6astian
http://www.youtube.com/watch?v=f3Fw4lJ-Jl4
14:02
se6astian
OK gotta go, let me know what you think of this
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se6astian
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aombk
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16:58
se6astian
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16:59
se6astian
Hello, I am back
17:34
Bertl
se6astian: looks really interesting
17:35
Bertl
what I still do not understand, in which range will those adjustments be?
17:35
se6astian
hi, great
17:35
se6astian
the animation shows 3° in 4 directions
17:35
se6astian
what range we really need... no idea
17:36
Bertl
the thing is, yesterday we talked about 0.01mm precision
17:36
Bertl
so that would be 5um
17:36
Bertl
now, if you assume an M2 screw
17:38
Bertl
the pitch is 0.4mm and 0.25mm for the fine spacing
17:38
Bertl
i.e. a turn of the screw will change the center by at least 100um
17:40
Bertl
and the other interesting question would be, how much should the total/maximum adjustment be?
17:40
Bertl
because if we want to adjust within let's say 150um total, there are simpler designs
17:41
se6astian
maybe we can talk to other camera makers at IBC to investigate these ranges
17:41
se6astian
All I know is that Elphel started with a non calibrateable/non tiltable sensor frontend
17:41
se6astian
then did a simple tilt correction one with 3 setscrews
17:42
Bertl
okay, and final question: how do you access the screws?
17:42
se6astian
then a full featured one with rather complex mechanics with springs and moving parts
17:42
Bertl
I mean, where are the screws and where is the sensor?
17:42
se6astian
and then after that one another redesign to compensate for material expansion due to heat
17:42
se6astian
so they definitely underestimated the problem in the beginning, something I want to avoid
17:43
Bertl
interesting
17:44
Bertl
btw, you can easily make that adjustable from outside, with a few simple tricks
17:44
se6astian
the screws would be access from inside the camera (holes in sensor frontend pcb?) by the engineer calibrating the camera, should no be required to be recalibrated by the customer
17:44
se6astian
oh, what kind of tricks?
17:45
Bertl
you remember my .stl with the slits for fastening the joint?
17:46
Bertl
make them six (if you like) and let them go to the base of the mount instead i.e. extend the thin sperical part to match the 4/6 corners of the base
17:47
Bertl
i.e. basically you screw system but screwed on from the outside into the base
17:47
se6astian
http://blog.elphel.com/2010/06/elphel-eyesis-camera-optics-and-lens-focus-adjustment/
17:48
se6astian
hmm, difficult for me to imagine, could you do a quick drawing? ;)
17:49
se6astian
Elphel: "focus/tilt adjustment module is capable of compensating for ±0.15 mm"
17:49
se6astian
this was not enough and they had to redesign the parts completely
17:49
se6astian
they use small sensors and small lenses
17:49
se6astian
we use big sensors and big lenses
17:50
se6astian
http://blog.elphel.com/2011/02/eyesis-4pi/
17:50
se6astian
"Insufficient range of the sensor board tilt adjustment to the lens optical axis. It needed to be just about twice larger to be able to compensate for most sensor chip misalignments"
17:51
se6astian
another redesign lead to this: http://blog.elphel.com/wp-content/uploads/2012/10/393-m12.png
17:52
se6astian
Model NC393 CAD rendering with M12 (S-mount) lens and thermally compensated sensor front end
18:02
Bertl
http://vserver.13thfloor.at/Stuff/AXIOM/lens_mount_tilt2.stl
18:02
Bertl
haven't modeled the screws or done any animation, but I hope you get the idea
18:04
Bertl
basically 3 screws would be more than enough to perfectly define the position
18:05
Bertl
but there is no harm in having six, only for adjustment you should remove 3 of them first, then do the adjustments and after that, screw the other 3 back in
18:07
Bertl
but as I said, for 10um adjustments that won't do the trick, because you will not be able to get that right
18:08
Bertl
(because screw pitches are at lest 100um but likely more around 300-500um to have at least some stability
18:10
Bertl
if you need um precision, you need to use some kind of lever or gear construct
18:15
Bertl
hmm, you can probably get away with a dual pitch screw system for small adjustments :)
18:16
se6astian
ok looking at your stl now, I am not sure I understand it right yet... wouldnt the tilt of the front part make the screw holes move away from the holes on the base so the screws wouldnt fit anymore?
18:17
Bertl
yes, but that would be the same as in your design
18:17
Bertl
i.e. you need to have flexible counterparts or slits or moving nuts, etc
18:19
se6astian
in my design the moving part has no holes for the screws, they just push the flat surface in place
18:21
Bertl
okay, I obviously missed that
18:24
Bertl
but in that case, you can simply turn it around and have the screws on the outside
18:24
Bertl
doesn't really matter, does it?
18:25
se6astian
true, yes
18:26
Bertl
unfortunately the dual pitch trick won't work with this
18:28
se6astian
dual pitch?
18:29
Bertl
well, you can make a cylinder with let's say a 0.5mm pitch on the outside and a 0.4mm pitch on the inside and you get a virtual screw with 0.1mm pitch
18:30
Bertl
this is used for microadjustments, but obviously requires a fixed counterpart
18:32
se6astian
ah I see
18:34
Bertl
but I'm still not sure I completely understand the problem
18:35
se6astian
me neither :)
18:35
Bertl
do the sensors have different glass thickness across the sensor?
18:35
se6astian
cause in the concept so far we have shift as well as tilt when moving the mount which is not good
18:36
Bertl
with shift you mean distance changes?
18:36
se6astian
I think the problem is that the sensor socket will not be 100% plain and the pins not pushed in 100% the same distance
18:36
Bertl
because the spherical design will definitely keep the distance constant
18:37
se6astian
and then again the image sensor pushed into the socket will not be 100% pushed in on all sides
18:37
se6astian
and the PCB itself might not be 100% plain either
18:37
Bertl
that doesn't matter
18:37
Bertl
assuming that we keep the/a socket, the pcb and socket is of no relevance
18:38
se6astian
I dont mean the FFD, I mean the center of the lens being pushed out of the center of the sensor when we tilt it
18:38
Bertl
the sensor should be tightly screwed to the lens mount
18:39
Bertl
that should give a fit within 10um or less
18:39
Bertl
and the sensor socket/pcb doesn't change that in any way
18:40
se6astian
if we maintain this design with the sensor being attached to the lens mount that problem should be radically minimized yes
18:40
se6astian
you had some concerns about that design though if I remember correctly
18:41
se6astian
also it would mean we need to redesign the lens mounf if we change the sensor
18:41
se6astian
or we make the lens mount a 2 part assembly
18:41
Bertl
yes, but they are mainly about pressing the sensor glass agains the metal mount
18:42
Bertl
i.e. I'd introduce a plastic foil or something similar between sensor glass and lens mount
18:42
Bertl
to absorb shocks and protect the glass
18:43
Bertl
(or ceramic in our case)
18:43
se6astian
ok
18:43
Bertl
assuming that we do the stacked design
18:44
Bertl
I'd screw the sensor pcb from the back to the lensmount (with spacers)
18:44
Bertl
after the sensor was screwed into the lensmount (with foil)
18:44
Bertl
so basically foil goes into the lens mount, sensor ontop of foil
18:45
Bertl
screws fix the sensor, pcb is placed onto the sensor pins (with spacers on the sides)
18:45
Bertl
and finally pcb is screwed against the lens mount
18:45
Bertl
where I'd make the lens mount cover the entire front of the camera
18:46
se6astian
sounds good, we just need to take foil thickness into account when we create the lens mount, but that should do it
18:46
Bertl
so the lens mount is sensor specific, yes, but it conencts to the rest of the camer block electrically and mechanically
18:46
Bertl
*camera*
18:47
se6astian
I d say we see with the prototype how plain the sensor alignment will be
18:47
se6astian
and then we decide if we need to take further steps
18:48
Bertl
probably
18:50
Bertl
let me ask, in what way would a constant shift of, let's say 0.2mm affect the lens mount?
18:51
Bertl
(regarding the comment about the foil thickness)
18:53
se6astian
the foil moves the sensor 0.2mm further away from the lens right?
18:56
Bertl
yes, for example
18:57
se6astian
so if the lens mount is designed for FFD of an nikon f mount (46.50 mm) it will actually be 46.52mm
18:58
Bertl
okay, and what will be the effect?
18:58
se6astian
your lens will be slightly out of focus
18:58
Bertl
you won't be able to precisely focus on infinity, I guess
18:59
Bertl
but everything else should work just fine, only with different focus settings, no?
18:59
se6astian
for slight deviation it could mean that when you turn the focus ring to 1m the focus will actually be at 1.5m, in worst cases it would mean as you say that you either cant focus on infinite, cant focus on near objects or cant get anything in focus at all
19:00
se6astian
everything else will work fine
19:01
se6astian
a fun thing with the Elphel cameras ( I might show you soon) is that the c mount thread can be used to change the FFD of the lens by just unscrewing the lens
19:01
Bertl
and how much effect has a single turn?
19:01
Bertl
(which will probably be about 0.5mm)
19:01
se6astian
this means you can basically shift the focus plane to the glass of the lens or even to the innards of the lens glass
19:02
se6astian
you then see tiny hairs and dust that are stuck inside the lens :)
19:02
se6astian
we can try it then how much one turn does
19:05
Bertl
okay
19:08
se6astian
I can take it with us to Brussels
19:08
se6astian
or we do it when I visit to bake the PCB
19:16
Bertl
both is fine for me
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aombk_
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aombk
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aombk
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20:40
se6astian
ok time for bed for me, gnight!
20:40
se6astian
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