PIER-14 LET'S DISCUSS MOSAICS

Hi Manuel,

Thanks for the feedback, and I'm in agreement.

I now attach a couple of  mosaic simulations of the North American nebula region.. It has been necessary to rotate an existing image for the simulation. The image with the white rectangular outline is a 2 panel vertical mosaic, and the one with the red, a [3 x 2] 6 panel horizontal mosaic. The final image is an indication of what a single panel, non-mosaic will accommodate, outlined in white.

Best regards,

Ray

To follow up on this conversation, I would like to suggest the following two mosaics for the Cepheus region. I hope this works for everyone.

Cheers

Manuel

A: To cover the mu Cep region:

1x2 Mosaic	Pane	RA	DEC	Overlap
mu Cep / IC1396 (1x2 mosaic)	Pane 1	21 40 38	56 48 16	20%
mu Cep / IC1396 (1x2 mosaic)	Pane 2	21 40 38	58 38 40	20%

B: To cover the broader Messier 52 region:

2x2 Mosaic	Pane	RA	DEC	Overlap
Bubble nebula / 7538 / M 52	Pane 1	23 17 39	62 03 28	20%
Cave nebula / LBN 521	Pane 2	22 53 53	62 03 28	20%
Lobster Claw / Bubble nebula	Pane 3	23 16 59	60 13 10	20%
NGC 7429 / NGC 7419	Pane 4	22 54 33	60 13 10	20%

They both look good.

When making mosaics you have to trim back the edges of each panel a bit. Either to cope with stacking errors or to make the PhotometricMosaic script in Pixinsight work. I go for slightly more overlap to be on the safe side (25%), but that was with the 6200 MM Pro camera with its distorted edge stars. YOu are probably OK with the new setup, but if you have space around the target, you can increase the overlap a little.

Will this be RGB or narrowband?

Hi Manuel,

Thanks for the feedback, and I'm in agreement.

I now attach a couple of  mosaic simulations of the North American nebula region.. It has been necessary to rotate an existing image for the simulation. The image with the white rectangular outline is a 2 panel vertical mosaic, and the one with the red, a [3 x 2] 6 panel horizontal mosaic. The final image is an indication of what a single panel, non-mosaic will accommodate, outlined in white.

Best regards,

Ray

 Ray,

I think the white outlined 2-panel mosaic is a nice framing. The 6-panel version I am more doubtful about as you remember the struggle we had previously where SH2-119 is so weak compared to the NA and Pelican that it was extremely difficult to create a balanced image. I got better results when I treated SH2-119 separately.

Most of SH2-119 fits into a single frame, but you need a vertical 2-pane mosaic to capture it all. It still might be worth doing that as a separate job as doing the full mosaic pushes SH2-119 a bit low in its panels. You would get a better framing doing a separate job, and if we end up processing SH2-119 individually, you have not lost anything.

ANyway, it's your call how you want to do it.

NB, LRGB or both?

 

Steve has just notified us that all uncompleted jobs have been resubmitted in preparation for when the pier is back up and running 

I recently submitted such a target and would be grateful for any feedback before reconfirming the job. The target is diffuse nebula sh2-115 and was originally entered as 2 jobs, O3 and Ha. This is just starting to rise and therefore will initially keep the pier busy at the end of the imaging window. There is the option to alter this into a mosaic, so please indicate if you would prefer to stay with a single panel, or, one of the mosaic options.

Cheers,

Ray 

Ray,

My sky atlas says that you capture all of the key SH2-115 structures in one frame. However, it is all embedded in some juicy nebulosity, so going wider could create a really nice image. The slight problem will be getting a nice framing whilst keeping Deneb out of the picture.

The 2x2 mosaic has more interest, and you can just about set the framing so that SH2-115 fills one panel (see attached), so you can start with a single frame and add the rest of the mosaic if you wish.

Your call I think.

I will check the framing of all my submitted jobs and see if I want to adjust for the new camera. Do we know the camera angle yet?

It is certainly a heroic exercise, but not one I am attracted to.

My key question is why devote so much shared pier time to one project? If I have my calculations correct, with a 15% overlap the final image is about 24,000 pixels wide. At typical high-quality photo printing resolutions of 300 dpi, that is about 2 metres across.

Yes, it would make a great zoomable image on a computer, but to what purpose? To admire it you would want to look at the whole thing, so zoomed out. Zoom in on details and you might as well have single images or small mosaics.

If we want to get the whole sweep of that area, it would be better to use a short focal length lens (Pier 4) or even find someone with a Canon f2 50mm. We can then blend in higher resolution sub-image, e.g. Robert Gendler's technique described in his chapter Hybrid Images: A Strategy for Optimising the Impact of Astronomical Images in the book Lessons from the Masters: Current Concepts in Astronomical Image Processing.

I am also doubtful that you could complete the project in the time allocated. I can't see any allowance for Moon interference (I may have missed it), very important in LRGB imaging. To me, that makes the 50% successful imaging hours assumption doubtful. Allowing for periods of bad weather, defective frames, instrument maintenance and faults, and moon up, I think we would be attempting something very difficult. There are so many ways it could go wrong.

I am personally uncomfortable with committing that much time to providing a high resolution backdrop to a smaller number of interesting targets.

When I started on this pier I was all for massive mosaics. My experiences have made me much more cautious. The struggle to get a 4-panel mosaic to work and produce a pleasing result has pushed me towards 1- and 2-panel imaging.

As you have pointed out, we can use elements of the total mosaic to image specific targets. However, when I look at the map you have provided, it appears that many of the nebula targets require more panels to capture the entire object in a reasonable framing than you would if you were focused on the nebula. For example, the Elephant's Trunk complex would need 4-6 panels.

Obviously, I will take the majority vote, but it is a no from me.

old_eyes

 

 

Good morning,

thank you for sharing your experience, thoughts and perspective. Integrating images of different resolutions is indeed something I'll try. 

Looking at the targets in this area, only two would require a 1x2 mosaic, which (if i understand you well) is feasible in your experience.

CS
Manuel 

Manuel,

I don't want to put you off mosaics, it is just that they get more work as they have more panels, and there is more chance of something going wrong. The work required is some sort of exponential function of the number of panels.

I have done 2, 3 and 4-panel mosaics on this pier. This was on the 6200MM Pro camera and we had real troubles with star shapes at the edges because of field flatness issues, so probably harder than it will be with the new camera. 4-panel was quite a lot of work and struggling with the overlapping edges and the centre section (where all four frames overlap). Much, much harder than 2-panel.

I have also talked to people who have made big mosaics, and they all talk about the time and frustration involved in capturing and processing the data into an acceptable image. I have taken the personal decision not to go for really big mosaics, as I lack both the skills, the time and the compute power for such a big project. I will exhaust the targets that can be fitted into a maximum of 4-panels before I try anything bigger (and buy myself a new computer!).

Hi Manuel and Richard, 

Thanks for the suggestions. Btw I have gone for just 15% mosaic panel overlaps. I have it on good authority that the new setup will be awesome in terms of flatness. I trust my source.

Anyway, I agree we can start with a single panel for Sh2-115, and depending on what the pier load is then add to it. My preference will always be narrowband, but a separate short duration job for RGB stars is fine.

I also prefer the 2 panel North American together with a separate 2 panel for the Clamshell on the left hand side of the 6 panel mosaic simulation.

The 2 mosaics suggested by Manuel taken from the mega-mosaic I'm happy to do, plenty of nice targets, and crops of individual targets might be achievable quite easily. Do be aware that a certain person might be very keen on a 6 panel one incorporating the efelant and squidy. :)  That may well be a job for the 200mm Canon lens pier though. 

Thanks for all the great feedback. 

Cheers,

Ray 

To follow up on this conversation, I would like to suggest the following two mosaics for the Cepheus region. I hope this works for everyone.

Cheers

Manuel

A: To cover the mu Cep region:

1x2 Mosaic	Pane	RA	DEC	Overlap
mu Cep / IC1396 (1x2 mosaic)	Pane 1	21 40 38	56 48 16	20%
mu Cep / IC1396 (1x2 mosaic)	Pane 2	21 40 38	58 38 40	20%

B: To cover the broader Messier 52 region:

2x2 Mosaic	Pane	RA	DEC	Overlap
Bubble nebula / 7538 / M 52	Pane 1	23 17 39	62 03 28	20%
Cave nebula / LBN 521	Pane 2	22 53 53	62 03 28	20%
Lobster Claw / Bubble nebula	Pane 3	23 16 59	60 13 10	20%
NGC 7429 / NGC 7419	Pane 4	22 54 33	60 13 10	20%

They both look good.

When making mosaics you have to trim back the edges of each panel a bit. Either to cope with stacking errors or to make the PhotometricMosaic script in Pixinsight work. I go for slightly more overlap to be on the safe side (25%), but that was with the 6200 MM Pro camera with its distorted edge stars. YOu are probably OK with the new setup, but if you have space around the target, you can increase the overlap a little.

Will this be RGB or narrowband?

Thanks.

Regarding framing:

1. 1x2 mosaic: there is a lot of space north and south and certainly a couple of hundred pixels East and West ... at least from my reading of the framing (attached). Does this look fine from your perspective?

2. 2x2 mosaic seems of in all directions for cropping.

3. Regarding overlap: I can indeed increase to 25%. That would not affect the East-West cropping of the 1x2 mosaic, ad the 2x2 has enough space anyway. Both overlap views are attached.

4. Regarding NB vs BB: This is where I am seeking input from everyone. From my perspective, I would focus on narrow band for both. But of course, I am happy to add LRGB if you think this is good/necessary. 

A. My current thinking for NB: H,S,O each at 42x300s requiring 3.5 hrs per filter/pane or a total of 63 hrs for all 6 panes in both mosaics (21 hrs for 1x2 mosaic and 42 hrs for 2x2 mosaic).

B. If we were to add LRGB, we could consider 30x180s requiring 1.5 hrs per filter/pane or a total of 36 hrs for all 6 panes in both mosaics (12 hrs for 1x2 mosaic and 24 hrs for 2x2 mosaic).

Cheers

Manuel

The new coordinates are:

1x2 mosaic.

2x2 mosaic.

Erratum :: Error in 1x2 mosaic coordinates !

!! WRONG !! 1x2 mosaic.

Pane 1	21 40 27	58 30 25	25%
Pane 2	21 40 27	56 40 01	25%

Correct :: 1x2 mosaic.

Pane 1	21 40 27	56 43 28	25%
Pane 2	21 40 27	58 26 58	25%

 

Hi,

Another target, which I find fascinating, is the Bat and his Squid. I know it is a rather difficult target and needs a lot of OIII data to yield a beautiful image, but I think it is worth discussing here and see whether others are interested in this as well.

With the new setup, we can capture almost the complete Bat, and the complete squid in a single frame centered on 21 07 59 +60 05 39. We could then add the Seahorse to the West, and include NGC 6946 in a frame centered on 20 47 02 +60 05 39. There two panes would give a 2x1 mosaic with a 25% overlap.

Regarding imaging plan:

1. The Bat would require mainly Ha, while the Squid would require a lot of OIII. reading up on this, I think that 42x300s Ha would be sufficient to have a nice Bat, while it would probably take 120x300s OIII to achieve a nice and bright Squid.

2. The Seahorse could be imaged in LRGB, and it may be sufficient to collect 42x180s with each filter. To link up the Western side of the Bat with the Seahorse pane, we may need to add a bit of Ha as well.

Is this something you are interested in?

What are your views/suggestions regarding subs? Should we also collect some LRGB on the Bat to create a smooth transition between the the panes? 

All the best

Manuel

Manuel, 

That's scary. :) I started my message a short while ago and after a brief interruption only just now sent it. Upon exiting I find a notification that someone has posted something on here. :)

Cheers

Ray