Combining OSC and Mono with different focal lengths?

[900SL]

Hi Brains Trust

I've been toying with the idea of getting a mono set up to run alongside my OSC for emission nebula targets. 

I currently have a 533MC Pro with a 90mm f6 APO 0.8x reducer focal length 430mm.

I also have a GT71 f6 420 mm fl

I'm thinking of getting a 533MM Pro and Antlia Edge 4.5 Nm SHO filters and running a parallel set up as follows:

533MC Pro OSC on the GT71 with 1.0 field flattener and L2 filter to capture RGB, Pixel scale 1.85"/px (using ASI Air Pro for imaging capture)

533MM Pro Mono on the 90mm to capture Ha, Oiii and Sii, pixel scale 1.8"/px (using Mele PC and Nina)

Question is: can the images be scaled to match in software, and channels combined OSC / Ha /Oiii / Sii in pixel math using Siril?

 

I like a challenge, evidently given where I have chosen to live

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Elp]

Yes. I do it often, but integrate them manually. You have to do what you can with this terrible weather.

[900SL]

3 minutes ago, Elp said:

Yes. I do it often, but integrate them manually. You have to do what you can with this terrible weather.

That's good to hear. I assumed that I would need separate calibration frames for each rig, and separate lights for each NB filter, then pre-process the OSC, and pre-process the Ha, Oiii and Sii mono.

Do you do any initial stretch or exposure balance type of thingy before combining, or use pixel math to get a combined data set then process?     

[Elp]

I treat each session as it's own run because I setup and breakdown each time so my flats have to match the lights, so they all need calibration frames, each session is stacked then if they're from the same setup, each final stack can be stacked whilst they're still linear to give a total integrated time stack.

If they're not from the same setup, I calibrate and stack and pre process as normal each session, do a bit of stretching then copy each result into a master file and align, scale etc until they're all matching. Doing it manually you have more hands on real time control over the blending of the layers. I sometimes use HA as a luminence for example, or I'd use a long focal length stack as a luminence as it will have more resolution. My current project is a mixture of three different setups so it is a challenge, you have to choose how you'll mix them together because of the different imaging scales and the detail each image shows.

Once I'm happy with them all together, I'll adjust each layer slightly, then flatten them into one and treat it as one colour image with the usual adjustments thereafter.

Not sure if it will work with automated software, Siril for example struggles to stack stacks if they've been altered or stretched too much, cropped etc as it can't match the images up as they usually need to be the same.

 

Edited March 6, 2023 by Elp

[ONIKKINEN]

Siril will stack your different pixel scales together just fine in "normal" operation, choose one reference frame from either setup and stack everything to that (doesn't matter which filter, just choose one with a lot of stars). No need to do pixel math for the resolution matching or something like that although you may want to do that for the RGB composition phase if you are adding Ha to R or something similar.

Dont know where the limit for scale difference is but i have stacked 1.8'' and 1.5''/p frames together and it all integrated just fine.

[900SL]

Thanks O.

Mounting this might be a challenge. I have a long WO dovetail plate which I could use sideways with a dovetail clamp each end (I have a TS optics HD clamp I could repurpose for one side with a 20kg capacity so that will take the TS CF 90mm APO)

Like this:

 

 

For this to work I would need some sort of adjustable clamp at the other end capable of carrying around 5 kg (GT71 + flattener + camera) to allow alignment of scope. Once aligned I'd set and forget

Is there any quick and simple fix for this? Vixen show a similar set up with an XY adjuster one end but the cost is rapidly mounting, plus the holes don't match the WO plate

 

 

 

[ollypenrice]

I also did a lot of this at one time. I used Registar to resize and align one data set to the other, essentially a 2 click operation.

What I don't think would work would be Luminance +OSC(RGB). I think the luminance would wash out the OSC colour very easily. However, adding NB to OSC works perfectly.

I feel that the ideal stretch on NB data for combining with colour is not the same as the ideal stretch for a standalone NB image. For combining with colour I prefer harder contrasts from a much more aggressive stretch. This will be toned down once the NB is blended with the appropriate colour channel. I prepare all the images first, therefore - the OSC and each NB separately.

Olly

[ollypenrice]

Regarding alignment, FLO do a decent alignemnt device. I used a Cassady T-Gad which, even second hand, cost a fortune. It is a beast of a gadget, though.

Olly

Edited March 7, 2023 by ollypenrice

[gajjer]

43 minutes ago, ollypenrice said:

I used Registar to resize and align one data set to the other, essentially a 2 click operation.

Could you expand on that please. I'd like to give that a try.

cheers

Gaj

 

[ollypenrice]

3 minutes ago, gajjer said:

Could you expand on that please. I'd like to give that a try.

cheers

Gaj

 

Making one image 'fit' another is the main purpose of Registar. You can use it to make mosaics, to combine data from different scopes, to get a perfect colour channel alignment, and so on. I may have a widefield from a short FL rig which contains a feature of interest which I also have at higher resolution n a long FL instrument. Registar will in 1 click, align and resize the high res image to to the widefield and, in a second click 'crop and pad' it so it will sit on the widefield in just the right place. It will also combine them but that really needs to be done with a little craftsmanship in Photoshop to get a natural blend.

To align your NB data to your RGB in Registar you just pen both and ask it to register Ha (say) to OSC and then 'crop and pad' and that's it. You can go into whatever processing software you use to blend Ha into RGB and the Ha will be a perfect fit.

At one time only Registar could do this. I think other programs can now do it and, for mosaics, APP is better.

Olly

Edited March 7, 2023 by ollypenrice
False click.

[wavydavy]

Also astro art does a similar thing called "coregister"..............

[gajjer]

Thanks for that Olly.

cheers

gaj

[tomato]

I think you can get reasonable colour combining Lum with OSC data. This is 212 x 2 mins with the Esprit 150/QHY268mono and 193 x 2 mins with the Esprit 150/QHY268OSC. I saved the Lum stack as an RGB file and stacked this with the OSC file, it seemed to give a better result than combining them as LRGB.

[Elp]

2 hours ago, 900SL said:

Is there any quick and simple fix for this?

You can try and source a photo panoramic head to mount the second saddle onto which allows horizontal adjustment, I think that's all you need if the two scopes central axis are in line. I did this for my samyang twin setup and had to get some aluminium to act as risers for the first lens to match the height of the second lens which has the left/right adjustment so they both look at the same target.

[900SL]

4 hours ago, Elp said:

You can try and source a photo panoramic head to mount the second saddle onto which allows horizontal adjustment, I think that's all you need if the two scopes central axis are in line. I did this for my samyang twin setup and had to get some aluminium to act as risers for the first lens to match the height of the second lens which has the left/right adjustment so they both look at the same target.

I found a Vixen XY mount on clearance and my finger inadvertently twitched and pressed the button..

 

[900SL]

Did a quick tester this morning to see how practical this is. Used some ADM clamps to mount the 90mm and I'll move the GT71 closer to reduce the polar moment of intertia when I get the Vixen XY mount. 

Up to 9kg and I don't want to go beyond 12kg so I'll be counting the grams and removing any excess flab. I'll mount the guidescope between the main scopes 

 

Good thing about the SXD2 and the offset head design, doesn't need as much counterweight. This balances with 3.7kg and not fully extended.