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"Bill Pragnell" <bil### [at] hotmail com> wrote:
> "Edouard" <pov### [at] edouardinfo> wrote:
> > One of my shots - to give you an idea of the source material I'm getting with a
> > 1 inch ball.
>
> That's great - much clearer than I've managed so far even with my bigger ball. I
> really need to polish it and investigate that focus override... :)
Thank-you. It took a long time before I could control everything enough to get
good results. The in-focus plane is very narrow, and that was the biggest
problem I was facing.
The CHDK grid I used to help me (you'll have to adjust the circle to you zoom
and ball size):
@title LProbe
@elps 180, 120, 46, 41, 0x01
@line 179, 0, 179, 239, 0x07
@line 0, 119, 359, 119, 0x07
Cheers,
Edouard.
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clipka wrote:
> The more zoom you use, the less prominent these distortions should be.
I wonder if anyone ever tried to do an outdoor mirror ball shot
using a backyard telescope with ccd from really long distances ;)
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"Bill Pragnell" <bil### [at] hotmailcom> wrote:
> "Trevor G Quayle" <Tin### [at] hotmailcom> wrote:
> > > > Maybe post some details of your difficulties, or if you'd like you can email
> > > > me directly.
>
> Here's a pair of angular maps that demonstrate my issue (scaled down to 512x512,
> but it's still evident). I've marked corresponding pixel locations with red
> crosses.
>
> http://www.infradead.org/~wmp/angular_eg.png
>
> It's interesting, now I come to actually look at this in detail, it seems to be
> most pronounced on the horizontal. This suggests to me that keeping the ball
> more central will definitely help...
>
> Bill
Actually, by the looks of it, I think that the technique I described may help
for this as there does appear to be lopsided distortion in the rotated image,
as I would expect from perspective distortion. Give it a try, let me know if
you need any help getting it to work.
What is your ball size to distance ratio?
-tgq
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Christian Froeschlin wrote:
> clipka wrote:
>
>> The more zoom you use, the less prominent these distortions should be.
>
> I wonder if anyone ever tried to do an outdoor mirror ball shot
> using a backyard telescope with ccd from really long distances ;)
If you're going for long distance then why not use Hubble? :)
--
Ger
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"Trevor G Quayle" <Tin### [at] hotmailcom> wrote:
> "Bill Pragnell" <bil### [at] hotmailcom> wrote:
> > "Trevor G Quayle" <Tin### [at] hotmailcom> wrote:
> > > > > Maybe post some details of your difficulties, or if you'd like you can email
> > > > > me directly.
> >
> > Here's a pair of angular maps that demonstrate my issue (scaled down to 512x512,
> > but it's still evident). I've marked corresponding pixel locations with red
> > crosses.
> >
> > http://www.infradead.org/~wmp/angular_eg.png
> >
> > It's interesting, now I come to actually look at this in detail, it seems to be
> > most pronounced on the horizontal. This suggests to me that keeping the ball
> > more central will definitely help...
> >
> > Bill
>
> Actually, by the looks of it, I think that the technique I described may help
> for this as there does appear to be lopsided distortion in the rotated image,
> as I would expect from perspective distortion. Give it a try, let me know if
> you need any help getting it to work.
> What is your ball size to distance ratio?
>
> -tgq
Have a look. I attempted to deconstruct, unwrap, unrotate your images and apply
the technique I mentioned. Its not perfect (and I didn't have the original
unrotated image to work with) but the distortion is far less noticeable. I
added about ~4% to the angular map (+20 pixels to each side of a 1024X1024
image)
-tgq
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Attachments:
Download 'newprobe.png' (689 KB)
Preview of image 'newprobe.png'
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Just to beat the topic to death...
This is another instance where Lat/Long mapping is helpful. If you look at the
original and corrected lat/long versions below, you can clearly see in the
original one how everything 'pinches' in to the point. This basically
indicates that it wasn't a true 360 mapping. In the corrected version, the
pinching is far less noticeable (however there still is a little bit if you'll
notice the doorframe behind, which tells me I didn't add quite enough to the
map, maybe I should've done 25 each side instead of 20)
-tgq
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Attachments:
Download 'lb1.png' (1422 KB)
Preview of image 'lb1.png'
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"Trevor G Quayle" <Tin### [at] hotmailcom> wrote:
> Just to beat the topic to death...
Wow, that really makes a big difference. I'll try this on the images I've taken
so far from scratch. Thanks for taking the time over this, it will be a massive
help! I was aware the ball is a few degrees short of a full 360, but knowing for
certain that this is the cause of my problem is most of the work.
(haha, looks like I have no legs from the knees down - relax folks, I'm kneeling
;-)
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