question about LRGB

[BABOafrica]

I have been using ST 1.4 for many years -- always with *.fits files from a DSLR, stacked using DSS.

I have now have two identical DSLRs -- except that one is modded for Ha and one is not.

I was wondering if I could use two separate *.fts files (let's say for the Helix Nebula) -- one file for each camera.

I tried doing this the other day using ST 1.4 in the LRGB mode.

I noticed that the two images got combined counter to my expectations. I was expecting the ST software to "align" or "stack" the two images so that the stars would coincide. But that does not happen.

Now it is, perhaps, worth noting that the two images were taken on opposite sides of the meridian. So one looks "upside down" compared to the other. And it was quite obvious, looking at the stars, that the two files were being combined in that orientation -- one "right-side up" and one "upside down".

It was just an experiment. All the same, I would like to do further experimenting with combining images from the two cameras, if that is possible when using StarTools.

Thanks,
Joe

[admin]

I have been using ST 1.4 for many years -- always with *.fits files from a DSLR, stacked using DSS.

I have now have two identical DSLRs -- except that one is modded for Ha and one is not.

I was wondering if I could use two separate *.fts files (let's say for the Helix Nebula) -- one file for each camera.

I tried doing this the other day using ST 1.4 in the LRGB mode.

I noticed that the two images got combined counter to my expectations. I was expecting the ST software to "align" or "stack" the two images so that the stars would coincide. But that does not happen.

Now it is, perhaps, worth noting that the two images were taken on opposite sides of the meridian. So one looks "upside down" compared to the other. And it was quite obvious, looking at the stars, that the two files were being combined in that orientation -- one "right-side up" and one "upside down".

It was just an experiment. All the same, I would like to do further experimenting with combining images from the two cameras, if that is possible when using StarTools.

Thanks,
Joe

Hi Joe,

StarTools does not align images, as this is (highly!) preferably done during stacking. E.g. when stacking, use one stack as a reference for creating the other(s) in DSS, APP, ASTAP or whichever solution you wish to use.

The reason why ST does not do this, is that aligning two finished stacks will yield much less precise results. As a result you would experience slight color shifts and local difference in Point Spread Functions (making something like deconvolution much less feasible). The stacker, on the other hand, can take into account any lens distortions and sub-pixel accuracy.

Once stacked in this manner, you should be able to import the datasets without problems.

Any trouble, let me know!

[BABOafrica]

Thanks, IVO, for the answer. Makes perfect sense.

However, excuse my ignorance.

How do I use the "first stack" as a "guide" for stacking the second set of light frames ???

I use DSS for stacking.

Is there a YouTube that describes that ???

Joe // BABO

[almcl]

Not sure about YouTube videos, but to get DSS to stack two separate nights so that they can be used together in StarTools, you stack the first night as usual and make a note of the reference frame. This (if you don't intervene) is usually the one with highest score and the one with 0 offset values.

ref frame.jpg (51.6 KiB) Viewed 2643 times

To stack the second night's frames, once all the subs are loaded in DSS, add the reference frame from the first night and, taking care that it is unchecked, right click on it and select 'use as reference frame'.

unchecked.jpg (33.6 KiB) Viewed 2643 times

Then go ahead and stack. Your second stack will now be aligned with the first and can be added in StarTools with either compose or the layer module.

This technique won't work if you use intersection or mosaic modes, so select 'Standard Mode' in the result tab of the stacking parameters box.

[BABOafrica]

That's great, IVO. Let me try it out.

Joe // BABO