Quest for a wider FOV.

[alan potts]

I am strongly considering a new WO 73mm which has a F/L of 430mm. Now this is no issue with my 183MC but on my 071 does give a Pix/sec figure of 2.29 which is a bit more than recommended, something around 500-520mm F/L would be ideal but I see nothing.

If I go ahead with the purchase what are the down sides of this?

Alan 

[Laurin Dave]

Hi Alan..  I believe you’ll need a flattener with that scope, but I shouldn’t worry about that pixel scale being too much, there’s plenty of APODs out there at 3”/pp..  ie Tak106/kaf11000 images, just don’t zoom in too much..  if you want 500-550 mm then you won’t go wrong with an Esprit100, plenty of excellent Esprit100/ASI071 images around..  if you wanted to go shorter still maybe the GT71 at 350mm or so would work well with your ASI183.  Also be aware that WO have 70 and 90mm versions of the RedCat in the pipeline..

so just the usual downsides..   like me, you’ll always want something else as well! 

Dave

[alan potts]

2 hours ago, Laurin Dave said:

Hi Alan..  I believe you’ll need a flattener with that scope, but I shouldn’t worry about that pixel scale being too much, there’s plenty of APODs out there at 3”/pp..  ie Tak106/kaf11000 images, just don’t zoom in too much..  if you want 500-550 mm then you won’t go wrong with an Esprit100, plenty of excellent Esprit100/ASI071 images around..  if you wanted to go shorter still maybe the GT71 at 350mm or so would work well with your ASI183.  Also be aware that WO have 70 and 90mm versions of the RedCat in the pipeline..

so just the usual downsides..   like me, you’ll always want something else as well! 

Dave

Yes the Esprit 100mm, sadly though I don't have that amount of spare cash in my UK, though I could transfer it running the risk of getting stabbed by the wife for spending again. The Esprit is a great scope though. Shorter I already have a Borg 77ll mk2 which I think it 330mm so the 183mc was really only for that. The 071 on the Borg really send the numbers high but maybe I should try it, silly thing is the Borg has been sitting here for over 2 months and so far has not seen a mount.

The only thing that is making me want to move on this now is really only what will be the case after GB leaves the EU, if indeed it ever happens, I like FLO as an outlet and trust them 100%, using them after this could induce customs duties and VAT issues. I guess though Dave on a one off purchase for peace of mind taking a hit is no bad thing.

The only other thing I have against the whole Esprit range is I will be paying for a finder and a diagonal, I have 3 TV 2inch diagonals and WO and 5 different finders, I don't need more. In the event of buying I would ask FLO to remove them and give them as prizes at some event.

Alan

[Laurin Dave]

If you want wide field I'd just try the Borg with the ASI071 and see what you get Alan before spending money,  it'll have essentially the same FOV and "pp (slightly lower in fact) as a Tak106 and kaf11000 camera combination..  

And yes I too have a collection of Skywatcher finders, diagonals and eyepieces

Dave

[alan potts]

1 hour ago, Laurin Dave said:

If you want wide field I'd just try the Borg with the ASI071 and see what you get Alan before spending money,  it'll have essentially the same FOV and "pp (slightly lower in fact) as a Tak106 and kaf11000 camera combination..  

And yes I too have a collection of Skywatcher finders, diagonals and eyepieces

Dave

My word I had no idea the KAF had pixels that large, twice the size of the 071 almost, like the TAK 106 one of the best scopes on the market. I guess doing what you suggest does cost nothing, snowing at the moment which is a bit of a downer.

Alan

[ollypenrice]

On 03/12/2019 at 07:37, alan potts said:

I am strongly considering a new WO 73mm which has a F/L of 430mm. Now this is no issue with my 183MC but on my 071 does give a Pix/sec figure of 2.29 which is a bit more than recommended, something around 500-520mm F/L would be ideal but I see nothing.

If I go ahead with the purchase what are the down sides of this?

Alan 

 

On 03/12/2019 at 08:17, Laurin Dave said:

Hi Alan..  I believe you’ll need a flattener with that scope, but I shouldn’t worry about that pixel scale being too much, there’s plenty of APODs out there at 3”/pp..  ie Tak106/kaf11000 images, just don’t zoom in too much..  if you want 500-550 mm then you won’t go wrong with an Esprit100, plenty of excellent Esprit100/ASI071 images around..  if you wanted to go shorter still maybe the GT71 at 350mm or so would work well with your ASI183.  Also be aware that WO have 70 and 90mm versions of the RedCat in the pipeline..

so just the usual downsides..   like me, you’ll always want something else as well! 

Dave

The Tak 106/Kodak 11 Meg gives 3.5 arcsecs per pixel and, as Dave says, has more APODs than you can shake a stick at. You are welcome to zoom in on mine as much as you like. Fine resolution is lost but there are no screaming artifacts like square stars. This is a tiny crop of the Flaming star from a widefield image so you can see it at full size. This is 3.5"PP so I really don't see what you need to worry about at 2.29.

The full image is here.  https://www.astrobin.com/394025/?nc=user

Olly

 

 

 

 

[fireballxl5]

I've just bought a 071 to use at 255mm and below (maybe with my 100mm camera lens). From experience using similar pixel scales with my DSLR I don't expect any issues 🙂

[alan potts]

1 hour ago, ollypenrice said:

 

The Tak 106/Kodak 11 Meg gives 3.5 arcsecs per pixel and, as Dave says, has more APODs than you can shake a stick at. You are welcome to zoom in on mine as much as you like. Fine resolution is lost but there are no screaming artifacts like square stars. This is a tiny crop of the Flaming star from a widefield image so you can see it at full size. This is 3.5"PP so I really don't see what you need to worry about at 2.29.

The full image is here.  https://www.astrobin.com/394025/?nc=user

Olly

 

 

 

 

Thank you Olly, that is a very nice image a always.

I would concur with your statement, Too many cables, i was looking at a complete case full earlier and have to admit I can't even remember what most are for, only remembered 5 (now) ST4 cables one that works on the AZ EQ 6 and all work on the CEM 60. The cable st4 Moderator Rob sent me has very slightly larger plastic connectors, all things are not created equal, it's only about .15mm but it matters. Maybe the 73mm WO is a decent enough scope for wide field and I should get one whilst i still can.

alan

[Laurin Dave]

And Olly's image is only two hours integration which demonstrates a significant advantage of large pixels... speed at gathering signal... just stick that 071 on your Borg and enjoy the results...after the snow stops of course!

[ollypenrice]

19 hours ago, Laurin Dave said:

And Olly's image is only two hours integration which demonstrates a significant advantage of large pixels... speed at gathering signal... just stick that 071 on your Borg and enjoy the results...after the snow stops of course!

Alas not, Dave. The two hours was just for the comet which we dropped onto an existing 19 hour Flaming Star.

Olly

[Laurin Dave]

5 minutes ago, ollypenrice said:

Alas not, Dave. The two hours was just for the comet which we dropped onto an existing 19 hour Flaming Star.

Olly

So it says..   must pay more attention and read all the way through!

[vlaiv]

@alan potts

What scopes do you have already to image with?

Wider FOV is easily achieved by doing mosaics, so you don't really need to spend money on a new scope if you have one that you are pleased with, but gives narrower field of view than you would like.

It is just a matter of proper acquisition and processing of such data, and although people think that doing mosaics is slower process than going with wider field scope - it is not necessarily so. If you already have fast scope (fast as having fast F/ratio), then doing mosaics is going to be marginally "slower" than using same F/ratio scope capable of wider field with the same sensor (difference being only overlap needed to properly align and stitch mosaic image).

[Adam J]

On 03/12/2019 at 06:37, alan potts said:

I am strongly considering a new WO 73mm which has a F/L of 430mm. Now this is no issue with my 183MC but on my 071 does give a Pix/sec figure of 2.29 which is a bit more than recommended, something around 500-520mm F/L would be ideal but I see nothing.

If I go ahead with the purchase what are the down sides of this?

Alan 

SW ED80DS-Pro is 500mm once reduced. 

A 80mm F6 triplet such as a Starwave 80 EDT will give you 480 

As you want a wider field I am assuming this is to image diffuse nebula, that being the case then 2.29 is perfectly acceptable, you would barely notice any difference between 2.0 and 2.29 if you could detect the difference at all. 

Adam 

[alan potts]

11 hours ago, vlaiv said:

@alan potts

What scopes do you have already to image with?

Wider FOV is easily achieved by doing mosaics, so you don't really need to spend money on a new scope if you have one that you are pleased with, but gives narrower field of view than you would like.

It is just a matter of proper acquisition and processing of such data, and although people think that doing mosaics is slower process than going with wider field scope - it is not necessarily so. If you already have fast scope (fast as having fast F/ratio), then doing mosaics is going to be marginally "slower" than using same F/ratio scope capable of wider field with the same sensor (difference being only overlap needed to properly align and stitch mosaic image).

I have a few scopes Borg 77ED ll F4.3,   a 70mm Ed F6 which has a problem of alignment,  a 115mm APO F7 with reducer .79    and 190mm M/N F5.26.     I guess I could also play with the 180mm Mak and the 12 inch Sc, I have mounting gear for them.

Alan

 

[vlaiv]

5 hours ago, alan potts said:

I have a few scopes Borg 77ED ll F4.3,   a 70mm Ed F6 which has a problem of alignment,  a 115mm APO F7 with reducer .79    and 190mm M/N F5.26.     I guess I could also play with the 180mm Mak and the 12 inch Sc, I have mounting gear for them.

Alan

 

Well, you have quite a selection to choose from.

I would personally go for M/N, but 115mm APO is also an option for wide field.

You would need 9 panels to cover M31 for example.

It would seem that taking 9 panels will take up too much time compare to single panel, but in fact you will get almost same SNR in the same time as using smaller scope that would cover whole FOV in single go (provided that you also have F/5.25 scope). I'll explain why in a minute.

First thing to understand is sampling rate. I've seen that you expressed concerns about going at 2.29"/px. Fact is - when you are after a wide field that is really only sensible option - to go low sampling rate (unless you have very specific optics - fast and sharp, only in that case you can go high resolution wide field). Take for example scope that you were looking at - 73mm aperture. It will have size of airy disk of 3.52 arc seconds - aperture alone is not enough to resolve fine detail - add atmosphere and guiding and you can't really sample at below 2"/px. I mean, you can, but there will be no point.

Another way to look at it is that you want something like at least 3-4 degrees of FOV. That is 4*60*60 = 14400 arc seconds of FOV in width. Most cameras don't have that much pixels in width. ASI071 is 4944 x 3284 camera, meaning you have only about 5000 pixels in width. Divide the two and you will get resolution that it can achieve on wide field that covers 4 degrees - 14400/5000 = 2.88"/px. So even that camera can't sample on less if you are after wide field (not to mention the fact that OSC cameras in reality sample at twice lower rate than mono).

Don't be afraid of blocky stars - that sort of thing does not happen, and with proper processing you will just have a nice image even if you sample on very low resolution.

Now a bit about the speed of taking panels vs single FOV. Take for example above M31 and 9 panels example.

In order to shoot 9 panels you will need to spend 1/9 of time on each panel. That means x9 less subs for each panel than you would be able to do when doing single FOV with small scope. This also means that SNR per panel will be x3 less than single FOV if you use the same scope, but you will not be using same scope. Imagine that you are using small scope that is capable of covering same FOV in single scope - it needs to have 3 times smaller focal length to do that. So it will be 333mm FL scope. Now we said that we need to match F/ratio of two scopes, so you are looking at F/5.25 333mm scope. What sort of aperture will it have? It will be 333/5.25 = ~63.5mm scope.

Let's compare light gathering surface of two scopes - first is 190mm and second is 63.5mm, and their respective surfaces 190^2 : 63.5^2 = ~9. So large scope gathers 9 times more light, which means that it will have x3 better SNR - that cancels with time needed to spend on each panel - you get roughly the same SNR per panel as you will for whole FOV.

You end up with same result with larger scope and doing mosaic in one night as you would with small scope of the same F/ratio that covers same FOV in one night.

There are some challenges when doing mosaic imaging - you need to point your scope at particular place and account for small overlap to be able to stitch your mosaic in the end (capture software like SGP offers mosaic assistant and EQMOD also has small utility program to help you make mosaics). You need to be able to stitch your mosaic properly - APP can do that automatically I believe, not sure about PI, but there are other options out there as well to do it (even free - there is plugin for ImageJ). You might have more issues with gradients if shooting in strong LP because their orientation might not match between panels - but that can be dealt with as well.

Unless you really want small scope, you don't need it to get wide FOV shots - you already have equipment for that, just need to adopt certain workflow to do it.

[alan potts]

2 hours ago, vlaiv said:

Well, you have quite a selection to choose from.

I would personally go for M/N, but 115mm APO is also an option for wide field.

You would need 9 panels to cover M31 for example.

It would seem that taking 9 panels will take up too much time compare to single panel, but in fact you will get almost same SNR in the same time as using smaller scope that would cover whole FOV in single go (provided that you also have F/5.25 scope). I'll explain why in a minute.

First thing to understand is sampling rate. I've seen that you expressed concerns about going at 2.29"/px. Fact is - when you are after a wide field that is really only sensible option - to go low sampling rate (unless you have very specific optics - fast and sharp, only in that case you can go high resolution wide field). Take for example scope that you were looking at - 73mm aperture. It will have size of airy disk of 3.52 arc seconds - aperture alone is not enough to resolve fine detail - add atmosphere and guiding and you can't really sample at below 2"/px. I mean, you can, but there will be no point.

Another way to look at it is that you want something like at least 3-4 degrees of FOV. That is 4*60*60 = 14400 arc seconds of FOV in width. Most cameras don't have that much pixels in width. ASI071 is 4944 x 3284 camera, meaning you have only about 5000 pixels in width. Divide the two and you will get resolution that it can achieve on wide field that covers 4 degrees - 14400/5000 = 2.88"/px. So even that camera can't sample on less if you are after wide field (not to mention the fact that OSC cameras in reality sample at twice lower rate than mono).

Don't be afraid of blocky stars - that sort of thing does not happen, and with proper processing you will just have a nice image even if you sample on very low resolution.

Now a bit about the speed of taking panels vs single FOV. Take for example above M31 and 9 panels example.

In order to shoot 9 panels you will need to spend 1/9 of time on each panel. That means x9 less subs for each panel than you would be able to do when doing single FOV with small scope. This also means that SNR per panel will be x3 less than single FOV if you use the same scope, but you will not be using same scope. Imagine that you are using small scope that is capable of covering same FOV in single scope - it needs to have 3 times smaller focal length to do that. So it will be 333mm FL scope. Now we said that we need to match F/ratio of two scopes, so you are looking at F/5.25 333mm scope. What sort of aperture will it have? It will be 333/5.25 = ~63.5mm scope.

Let's compare light gathering surface of two scopes - first is 190mm and second is 63.5mm, and their respective surfaces 190^2 : 63.5^2 = ~9. So large scope gathers 9 times more light, which means that it will have x3 better SNR - that cancels with time needed to spend on each panel - you get roughly the same SNR per panel as you will for whole FOV.

You end up with same result with larger scope and doing mosaic in one night as you would with small scope of the same F/ratio that covers same FOV in one night.

There are some challenges when doing mosaic imaging - you need to point your scope at particular place and account for small overlap to be able to stitch your mosaic in the end (capture software like SGP offers mosaic assistant and EQMOD also has small utility program to help you make mosaics). You need to be able to stitch your mosaic properly - APP can do that automatically I believe, not sure about PI, but there are other options out there as well to do it (even free - there is plugin for ImageJ). You might have more issues with gradients if shooting in strong LP because their orientation might not match between panels - but that can be dealt with as well.

Unless you really want small scope, you don't need it to get wide FOV shots - you already have equipment for that, just need to adopt certain workflow to do it.

Well thank you for taking the time to type all this, it is something to bookmark and come back to, I need better software than I have at the moment, I am thinking of getting APP as I don't have anything effective for gradients, something I seem to get more of now with the 071 as opposed to the Canon. I also have another camera to mess with a 183mc, not so sure why I bought this now, maybe not my best ever move.

I imagine if I use the Borg which with the 071 will have a massive FOV, of about 4 degrees and I guess this is decent quality in the optics department. I even tried earlier to put the Borg on the mount but despite 2 million bits and pieces could not find screws the correct size to fit the guide scope, why does nothing ever seem to fit together without spending another small fortune on more bits.

Alan

[jimjam11]

On 06/12/2019 at 10:20, vlaiv said:

Well, you have quite a selection to choose from.

I would personally go for M/N, but 115mm APO is also an option for wide field.

You would need 9 panels to cover M31 for example.

It would seem that taking 9 panels will take up too much time compare to single panel, but in fact you will get almost same SNR in the same time as using smaller scope that would cover whole FOV in single go (provided that you also have F/5.25 scope). I'll explain why in a minute.

First thing to understand is sampling rate. I've seen that you expressed concerns about going at 2.29"/px. Fact is - when you are after a wide field that is really only sensible option - to go low sampling rate (unless you have very specific optics - fast and sharp, only in that case you can go high resolution wide field). Take for example scope that you were looking at - 73mm aperture. It will have size of airy disk of 3.52 arc seconds - aperture alone is not enough to resolve fine detail - add atmosphere and guiding and you can't really sample at below 2"/px. I mean, you can, but there will be no point.

Another way to look at it is that you want something like at least 3-4 degrees of FOV. That is 4*60*60 = 14400 arc seconds of FOV in width. Most cameras don't have that much pixels in width. ASI071 is 4944 x 3284 camera, meaning you have only about 5000 pixels in width. Divide the two and you will get resolution that it can achieve on wide field that covers 4 degrees - 14400/5000 = 2.88"/px. So even that camera can't sample on less if you are after wide field (not to mention the fact that OSC cameras in reality sample at twice lower rate than mono).

Don't be afraid of blocky stars - that sort of thing does not happen, and with proper processing you will just have a nice image even if you sample on very low resolution.

Now a bit about the speed of taking panels vs single FOV. Take for example above M31 and 9 panels example.

In order to shoot 9 panels you will need to spend 1/9 of time on each panel. That means x9 less subs for each panel than you would be able to do when doing single FOV with small scope. This also means that SNR per panel will be x3 less than single FOV if you use the same scope, but you will not be using same scope. Imagine that you are using small scope that is capable of covering same FOV in single scope - it needs to have 3 times smaller focal length to do that. So it will be 333mm FL scope. Now we said that we need to match F/ratio of two scopes, so you are looking at F/5.25 333mm scope. What sort of aperture will it have? It will be 333/5.25 = ~63.5mm scope.

Let's compare light gathering surface of two scopes - first is 190mm and second is 63.5mm, and their respective surfaces 190^2 : 63.5^2 = ~9. So large scope gathers 9 times more light, which means that it will have x3 better SNR - that cancels with time needed to spend on each panel - you get roughly the same SNR per panel as you will for whole FOV.

You end up with same result with larger scope and doing mosaic in one night as you would with small scope of the same F/ratio that covers same FOV in one night.

There are some challenges when doing mosaic imaging - you need to point your scope at particular place and account for small overlap to be able to stitch your mosaic in the end (capture software like SGP offers mosaic assistant and EQMOD also has small utility program to help you make mosaics). You need to be able to stitch your mosaic properly - APP can do that automatically I believe, not sure about PI, but there are other options out there as well to do it (even free - there is plugin for ImageJ). You might have more issues with gradients if shooting in strong LP because their orientation might not match between panels - but that can be dealt with as well.

Unless you really want small scope, you don't need it to get wide FOV shots - you already have equipment for that, just need to adopt certain workflow to do it.

The larger scope data could then be binned/resampled which would further increase snr? 

 

Having said that my experience with mosaicing is that matching broadband panels can be very difficult when light pollution and/or the moon is in play. Narrowband mosaics seem relatively easy because background levels are more easily matched.

SGP has a feature requested to allow interlacing of mosaic tiles in an attempt to improve tile matching. 

[vlaiv]

29 minutes ago, jimjam11 said:

The larger scope data could then be binned/resampled which would further increase snr? 

Above is "already binned" although I was probably not clear or forgot to mention it explicitly.

If you need three panels in width to cover target (because focal length of larger scope is three times that of smaller scope) then to get same resulting image in terms of pixel count and sampling rate (same FOV, same number of pixels per width and height and there fore same sampling rate - that is what we would consider same image) you need to bin x3 which raises SNR x3.

In my above example I mentioned that 1/9 of exposure time is compensated by x9 light gathering surface - but that is only if one makes sure that sampling rate is the same.

If you on the other hand do not compensate for sampling rate/resolution then "standard rule" applies - two scopes of same F/ratio will have same "speed". Small scope will gather whole field and larger scope with gather only 1/9 of the field in same time so there is clear benefit of using smaller scope for doing wide field as with large scope and mosaic - you will end up with very large image in terms of mega pixels - but it is going to take x9 more time to get same SNR (or you will have x3 lower SNR in same time - something you can recover by binning x3 and equating sampling rate).

[jimjam11]

7 minutes ago, vlaiv said:

Above is "already binned" although I was probably not clear or forgot to mention it explicitly.

If you need three panels in width to cover target (because focal length of larger scope is three times that of smaller scope) then to get same resulting image in terms of pixel count and sampling rate (same FOV, same number of pixels per width and height and there fore same sampling rate - that is what we would consider same image) you need to bin x3 which raises SNR x3.

In my above example I mentioned that 1/9 of exposure time is compensated by x9 light gathering surface - but that is only if one makes sure that sampling rate is the same.

If you on the other hand do not compensate for sampling rate/resolution then "standard rule" applies - two scopes of same F/ratio will have same "speed". Small scope will gather whole field and larger scope with gather only 1/9 of the field in same time so there is clear benefit of using smaller scope for doing wide field as with large scope and mosaic - you will end up with very large image in terms of mega pixels - but it is going to take x9 more time to get same SNR (or you will have x3 lower SNR in same time - something you can recover by binning x3 and equating sampling rate).

Thanks, that makes much more sense now...

[ollypenrice]

If the infallible fully automated mosaic software exists I have yet to meet it.  Personally I make mosaics by removing gradients in the panels using Pixinsight's DBE and then I build an initial linear mosaic using Registar buit keep the Registar-adjusted individual panels to use as patches in Photoshop if neecessary.

1) Edge crop the linear panels and give them to Registar to build an initial mosaic. Save.

2) Save all the registered/calibrated panels as well for use as 'patches' if necessary.

3) Photshop or similar: give the Registar mosaic an initial stretch, not necessarily going all the way but far enough to show edge defects while recording this stretch as an action.

4) Identify an edge defect and open the 'patch' panel from Registar which will cover it. Apply the Action stretch to it. It should now be nearly identical to the area you want to patch. Slide it into place over the mosaic as a Layer, adjust it slightly in Levels if necessary, and simply use a feathered eraser to remove everything but the part covering the edge defect.

5) Flatten and continue to the final stretch.

Olly

[Adreneline]

I don't know whether APP is infallible or not - so far it's not failed me.

This was assembled in APP:

All the Ha and OIII data for all the sessions was fed into APP in one go and the linear version of the above popped out. No attempt has been made to hide boundaries cos' I couldn't find any (as it is uncropped it is pretty obvious where they ought to be if you want to go looking). I also have the SII data but decided against using it.

Adrian

[jimjam11]

55 minutes ago, ollypenrice said:

If the infallible fully automated mosaic software exists I have yet to meet it.  Personally I make mosaics by removing gradients in the panels using Pixinsight's DBE and then I build an initial linear mosaic using Registar buit keep the Registar-adjusted individual panels to use as patches in Photoshop if neecessary.

1) Edge crop the linear panels and give them to Registar to build an initial mosaic. Save.

2) Save all the registered/calibrated panels as well for use as 'patches' if necessary.

3) Photshop or similar: give the Registar mosaic an initial stretch, not necessarily going all the way but far enough to show edge defects while recording this stretch as an action.

4) Identify an edge defect and open the 'patch' panel from Registar which will cover it. Apply the Action stretch to it. It should now be nearly identical to the area you want to patch. Slide it into place over the mosaic as a Layer, adjust it slightly in Levels if necessary, and simply use a feathered eraser to remove everything but the part covering the edge defect.

5) Flatten and continue to the final stretch.

Olly

I follow the david ault workflow for PI and it works but panel matching can be torture:

http://trappedphotons.com/blog/?p=994

[alan potts]

Interesting read, see I need to look at APP or PI, maybe after Christmas.

Alan