Magnification between filters??

[johnnyt123]

HI.

Was doing some RGB imaging a few months ago and just getting around to processing the subs.

noticed that i had to increase the size of some of the subs by about 0.25% to get good alignment.

Is this normal??

I have astronomic 1.25 inch unmounted LRGB Ha SII OIII

thanks

John

[Shiraz]

The Atronomiks are parfocal, so if you had to refocus between filters, the image scale will vary slightly (your scope has residual CA and the focal length is slightly different with different colours). I think that 0.25% (particularly Ha) would be quite normal for a good quality refractor.

[johnnyt123]

Hi Ray.

you are right.

there was significant focusing adjustment that was needed when i which from the LRGB to the NB filters. (something in the order of 1500 steps where the stepper motor is on the fine focus knob) the LRGB filters seem to be fairly close to one another and the NB filters are are also close to one another.
I have the WO 110 Megrez doublet which i was using for image acquisition.

The image scaling of 0.25% was needed when i was overlaying the Ha channel onto the red channel.

Your answer makes complete sense.

[Shiraz]

Glad that made sense - cheers :thumbsup: