Focal differences

[gloicq]

Hi everybody,

I'd like to know what is the maximum focal lenght difference between 2 instruments that PI is able to process ?
I just formed a 10 persons group (and still recruiting) to accumulate pics on a same object and some  but people have different focal lenghts so you see the point...

Thank you for your answers !
Clear skies !

Geoffrey

[pfile]

i don't know if there is a strict answer to this question. i have never had a problem registering images from different OTAs. if the scales are wildly different, you can define a preview on the wider-field image to restrict the star matching. if you have any problem with registration, using a preview in that manner should solve the problem.


rob

[msmythers]

Geoffrey

I had to try. I took a wide 45mm linear image with M20 in the shot and registered it to my m20 shot done at 1370mm. Granted the 45mm image is not that good it still registered with changes to the StarAlignment parameters. Like rob was saying this works best when you define a preview in the wide shot around the area of interest.


Mike

[msmythers]

And it works the other direction also.


Mike

[chris.bailey]

Geoffrey

I have done a couple of collaborative efforts with up to 15 data sets taken at different image scales (the is the important issue rather than strict focal length) and PI took them in its stride.

There are a couple of options -

1) If you have all the data subs you can pick a single sub and register them all to it and integrate.
2) If you only have the integrations you can register them all to one of them and integrate.

I found 1 yielded better results as you can play around with the weightings in sub-frame selector

IF some of the data sets are wildly different (and are plentiful and dithered) you can drizzle up the wide field ones to better match image scales prior to integration.

You will probably want to turn on distortion correction as the data sets will have varying degrees of field curvature.

Its fun to do but expect to have to do some work on the stars due to differing FWHM's in the data sets.

Chris