Author Topic: Combining Images of Different Focal Length  (Read 4999 times)

Offline Starmangmh

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Combining Images of Different Focal Length
« on: 2010 April 10 01:12:23 »
Hello,
As a newbie I'm still in the basic stages of learning but have what may be a more advanced question.  Is it possible to combine images of different focal lengths using PI?  If so, is there a tutorial somewhere about this?  If not, how would I go about doing this?  What program WOULD allow two different focal length images to be combined into one image?

Thanks!
Gary
Thaxton, VA 

Offline vicent_peris

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Re: Combining Images of Different Focal Length
« Reply #1 on: 2010 April 10 02:00:18 »
Hi Gary, welcome!

Of course, you can do that. The only thing you must do is to register all the images. This can be done with StarAlignment (automatic) or with Dynamic Alignment (manual, for special cases).

What do you want to do? It's the classical case of M42 with images for the core? At the time of combining all the data you can go through different ways, depending on what you want.



V.

Offline Starmangmh

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Re: Combining Images of Different Focal Length
« Reply #2 on: 2010 April 10 11:39:23 »
Hi Vincent,
You can call me a dinosaur but I'm still using "film" for imaging.  There is a guy in my club with an unmodified Canon Rebel that wants to try combining his Ha-poor images with my film images.  I primarily use Kodak Elite Chrome 200 slide film and the newer Kodak Ultra Max 400 print film which both have good Ha response.  Unfortunately we don't have any lenses or scopes that are the same focal length so hence my question.  As I have only scratched the surface of the capabilities of PI, I was not aware your program was capable of combining images of different focal length.  I will check out the StarAlignment tutorials to see how this is done.

Thanks!!
Gary

Offline Nocturnal

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Re: Combining Images of Different Focal Length
« Reply #3 on: 2010 April 10 13:38:55 »
Gary,

in general PI can register images taken at different image scales. Image scale defined as angle per pixel. I'm just clarifying because focal length is not the only determining factor. Pixel size is too and in your case scan resolution would also affect image scale.

Let us know how it works out!
Best,

    Sander
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Offline Starmangmh

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Re: Combining Images of Different Focal Length
« Reply #4 on: 2010 April 10 16:19:54 »
Thanks Sander!  I'll start playing with to see how it works. 

Gary

Offline Juan Conejero

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Re: Combining Images of Different Focal Length
« Reply #5 on: 2010 April 11 02:52:39 »
Hi Gary,

Just a few points to add to what Vicent and Sander already have said. StarAlignment can deal with arbitrary scale variations if the images are similar. In general, the problem is not in the scale differences, but in the representation of stars on images acquired with different equipment and media. Don't be surprised if SA is unable to register film and CCD images if the scales differ by a 25% or so, especially in presence of dense star fields. Varying deformations of the focal plane can be also a serious problem, as SA is based on triangle similarity. SA can tolerate a moderate amount of varying local deformations, but not large-scale variations due to dissimilar wide-field optics.

DynamicAlignment is the tool of choice if you have to face such a difficult problem. With DA you can align any two images regardless of media, scale variations or varying optical aberrations. You just have to select a few stars manually on both images to achieve an accurate result in a few minutes.

By the way, I remember you from the good old days of APML :)
Juan Conejero
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Offline Starmangmh

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Re: Combining Images of Different Focal Length
« Reply #6 on: 2010 April 20 23:19:27 »
Hi Juan,

Thanks for the additional info.  By what you have said I may have to go with DA instead of SA.  The shots we plan on combining initially will probably be some widefield piggyback shots just to test the waters and get our bearings.  I'll try SA to start and if it doesn't work out I'll give DA a try.  We're hoping to get together in the next couple of months which will give me some time to play with both SA and DA a bit.

Yes, your memory serves you well.  You registered and worked on a widefield shot of Orion for me.  I'm still on APML but there's not alot of activity on it any more, especially not in film!  Ahh, the good old days!!

Gary