Thinking of C14 Edge vs RC16 ? Choices Choices!!

[Star101]

With Virus Lock Down, so many worries and problems at the moment. I feel, if anything, I am very lucky to have such a hobby as Astronomy and be lucky enough to have my own garden ("sanctuary") ROR Shedservatory.

August, I turn another big milestone in my life and, to celebrate, decided that as my C11 will be a decade old its time to treat myself to something special. 

I have the Mesu 200 with a max payload of 100Kg. So weight is not a problem. 

I image 98% of the time. I am the one asking, whats a nagler?

As I have a TS65EQ Quad, 420mm  and a C11 with Hyperstar. 560mm, 1780mm and 2800mm. And I do love the many smaller, interesting, galaxies out there. So, long FL would be nice.

Two options, C14 Edge or RC16 ?

I'm not afraid of collimation, even if I struggle to spell it 😛 

Anyone have either of these? Or advice as to which would be the most rewarding? ( Or any hidden gotcha's!!  😮 )

Your pro's and con's of the C14 Edge and RC16 please?

 

Thanks in advance.

Dave.

 

 

[Rocket Stars]

Keep the c11 with hyperstar. Giving you very nice field of view! 

RC 16, what focal length? 

[Star101]

2 hours ago, Rocket Stars said:

Keep the c11 with hyperstar. Giving you very nice field of view! 

RC 16, what focal length? 

3250mm

[jaspalchadha]

Go big for sure I own a 14RC on a Mesu Mrk2 and love it

[Rocket Stars]

Well, its a hard, hard decision!  

I would give it a thought of what gives you the best combo of f ratios. Have heard lots of positive things about bigger RC. 

I did chose my edge 8, for the ability of 3 different f ratios. Aka kinder egg, 3 scopes in one.  "Problem" is you ultimately needs at least 2 cameras to get a correct pixel scale. 

Mmm I envy your problem.   

 

[Star101]

Yeah, my C11 is only the XLT and recently I have become very much aware of image quality. Where as before, I was just happy to get images

Looking at some images from the RC are amazing. Round small stars from edge to edge. That's nigh impossible on the C11 XLT.  Not to mention the mirror flop!

 

 

[Star101]

55 minutes ago, Rocket Stars said:

Well, its a hard, hard decision!  

I would give it a thought of what gives you the best combo of f ratios. Have heard lots of positive things about bigger RC. 

I did chose my edge 8, for the ability of 3 different f ratios. Aka kinder egg, 3 scopes in one.  "Problem" is you ultimately needs at least 2 cameras to get a correct pixel scale. 

Mmm I envy your problem.   

 

Yeah, and that will be my next problem...Choosing a larger pixel, probably CCD, camera.....But one step at a time.

[Rocket Stars]

If.. eh when I get a bigger scope. I think a RC would be a strong choise. 

[newbie alert]

For imaging deep sky it has to be the RC surely...

[CraigT82]

I dont know much about DSO imaging, but I assume the RC would be easier to thermally manage? Big SCT with closed tube will need serious thought about how to homogenise the air inside for best quality images. Prob easier with an open ended RC? Though the edge version has vents and aftermarket fans can be fitted. 

I guess if you want to do any kind of science with it, as opposed to 'aesthetic' imaging, you'd be better off with the RC? 

[Star101]

The RC has three fans behind the primary mirror.

It will mostly be for aesthetic imaging. While trying to keep that natural look.

[ollypenrice]

Whoa, the big question is, What will your seeing support?   If your Mesu is anything like the two that I use it will run an RMS under guiding of about O.3-O.4 arcsecs, which will support, at worst, about 0.8 arcsecs per pixel. But what will your seeing support? You'll need a darned stable night to let you work at 0.8"PP. I'm not saying it won't happen but how often will it happen?

Personally I've given up on big reflectors and opted for a focal length of a metre and the simplicity and reliability of refractor optics and a camera with suitably matched pixels to give me a pixel scale of 0.9"PP.

Payload is absolutely not the problem. Seeing is the problem.

Olly

Edit. One more consideration. Pixels are getting smaller. Do you want to end up with a focal length entirely inappropriate to these cameras? I can't read the future but my impression is that it is not going the way of the big amateur reflector.

Edited April 17, 2020 by ollypenrice

[Whirlwind]

15 hours ago, ollypenrice said:

Edit. One more consideration. Pixels are getting smaller. Do you want to end up with a focal length entirely inappropriate to these cameras? I can't read the future but my impression is that it is not going the way of the big amateur reflector.

It don't think big reflectors have had their day.  It is just there has to be a shift in thinking as to how they would be used.  If we go back 10 or so years most CCDs had large pixels and hence you sacrificed resolution for field of view.  With the new CMOS cameras that is no longer correct, and as noted, with smaller pixel sizes even a moderately focal length instrument can get you to high resolution and wide image scales.  The old CCDs also had higher read noise, so each sub-exposure had to be longer requiring a much more hefty mount for the larger telescopes as well as longer guiding, more risk from plane trails and so forth.  In comparison new cameras have lower read noise which means that the sub-exposures can be much shorter even for narrowband, alleviating the need for that perfect mount.

So what is the benefit of a large reflector then?  Well lets consider the situation of a16" 3250mm RC scope paired with a new 6200 mono class CMOS camera.  At native focal length you have 0.24" per pixel (and 62Mpixels which is it's own issue) which you may get the resolution advantage to use once in a lifetime in the UK (assuming no clouds).  But this isn't the only benefit as it is still a larger aperture.  If you binned the camera 3x3, now you have a much more reasonable 0.71" per pixel and down to about 7Mpixel files (which is still fine for almost everything you want to do with the image).  So what is the benefit in doing this.  Well lets compare what type of telescope system you would need to get the same resolution - you would have a 16" 1080mm.  That's equivalent to a F2.7 system using the same camera.  Now lets add 0.8 reducer/flattener to the system.  That takes the native unbinned resolution 0.3"/pixel and 2600mm which is still way too small.  Bin it 3x3 again and we are at a more reasonable 0.9".  Again in comparison the focal length would be 860mm at 16".  That's equivalent to an F2.1 system using the same camera.

So where does this get us? We can't improve on the seeing unfortunately (not until we get real AO systems for amateur market anyway). So the resolution we can achieve is still limited.  So what is the point of the large telescope.. Well it means that low S/N areas of an image can get much more data much quicker because of the larger light collecting area.  As such that faint detail that would be processed out in smaller aperture instruments (because there was too much noise) will be able to be displayed in all its glory.  This would give the impression of higher resolution when in reality all it is allowing is to tease out more detail at the lower resolution (so for smaller galaxies you would be able to pick out faint tidal tails etc).  The only areas where it is unlikely to be of use would be very bright areas such as the core of M42.

As such larger reflectors will return to what visual astronomers see them as....huge light buckets!  However you do sacrifice field of view, extra maintenance, diffraction spikes and so forth.

(*Note I've made some abstraction on read noise etc issues when binning so it won't be quite as good as this but the principles do stand).

- As for the argument as to whether a C14 Edge or RC16 it is going to be same as any argument between the Edge series and RC's at the equivalent sizes.  I'd wonder whether the weight of the mirror might be an issue in the edge and it moving whilst imaging (whereas the RC16 should be more fixed but collimation is more tricky).  From a personal perspective I'd go RC16 but that's because I like to a bit of photometry/spectroscopy with a scope that size and generally lens are only corrected at optical wavelengths whereas a mirror system would also be able to image slightly into the Near Infrared or blue/near UV where lens aren't generally well corrected.

 

[kirkster501]

*Exactly* what Olly and others say.  What will your seeing support?  The Mount Palomar 200" in my back yard would be a waste of time.  My Meade 14" is a borderline waste of time.  The skies are not dark enough and the seeing will not support it.

You must always determine this before buying large and expensive telescopes or else you are just wasting your time and money and setting yourself up for disappointment.  There is a lot more to this than just throwing money at it.

EDIT:  I'd be tempted by the magnificent Astro-Physics Starfire  EDt 130 refractor if I were you  in the For Sale section if you've got money to spend   You'll get a lot more satisfaction with that than a large reflector with 0.35arcsec/pixel which is, at best, once per year seeing for us in Nottingham.  I'm tempted by that scope myself to build a dual refactor system.

Edited April 18, 2020 by kirkster501

[ollypenrice]

59 minutes ago, Whirlwind said:

It don't think big reflectors have had their day.  It is just there has to be a shift in thinking as to how they would be used.  If we go back 10 or so years most CCDs had large pixels and hence you sacrificed resolution for field of view.  With the new CMOS cameras that is no longer correct, and as noted, with smaller pixel sizes even a moderately focal length instrument can get you to high resolution and wide image scales.  The old CCDs also had higher read noise, so each sub-exposure had to be longer requiring a much more hefty mount for the larger telescopes as well as longer guiding, more risk from plane trails and so forth.  In comparison new cameras have lower read noise which means that the sub-exposures can be much shorter even for narrowband, alleviating the need for that perfect mount.

So what is the benefit of a large reflector then?  Well lets consider the situation of a16" 3250mm RC scope paired with a new 6200 mono class CMOS camera.  At native focal length you have 0.24" per pixel (and 62Mpixels which is it's own issue) which you may get the resolution advantage to use once in a lifetime in the UK (assuming no clouds).  But this isn't the only benefit as it is still a larger aperture.  If you binned the camera 3x3, now you have a much more reasonable 0.71" per pixel and down to about 7Mpixel files (which is still fine for almost everything you want to do with the image).  So what is the benefit in doing this.  Well lets compare what type of telescope system you would need to get the same resolution - you would have a 16" 1080mm.  That's equivalent to a F2.7 system using the same camera.  Now lets add 0.8 reducer/flattener to the system.  That takes the native unbinned resolution 0.3"/pixel and 2600mm which is still way too small.  Bin it 3x3 again and we are at a more reasonable 0.9".  Again in comparison the focal length would be 860mm at 16".  That's equivalent to an F2.1 system using the same camera.

So where does this get us? We can't improve on the seeing unfortunately (not until we get real AO systems for amateur market anyway). So the resolution we can achieve is still limited.  So what is the point of the large telescope.. Well it means that low S/N areas of an image can get much more data much quicker because of the larger light collecting area.  As such that faint detail that would be processed out in smaller aperture instruments (because there was too much noise) will be able to be displayed in all its glory.  This would give the impression of higher resolution when in reality all it is allowing is to tease out more detail at the lower resolution (so for smaller galaxies you would be able to pick out faint tidal tails etc).  The only areas where it is unlikely to be of use would be very bright areas such as the core of M42.

As such larger reflectors will return to what visual astronomers see them as....huge light buckets!  However you do sacrifice field of view, extra maintenance, diffraction spikes and so forth.

(*Note I've made some abstraction on read noise etc issues when binning so it won't be quite as good as this but the principles do stand).

- As for the argument as to whether a C14 Edge or RC16 it is going to be same as any argument between the Edge series and RC's at the equivalent sizes.  I'd wonder whether the weight of the mirror might be an issue in the edge and it moving whilst imaging (whereas the RC16 should be more fixed but collimation is more tricky).  From a personal perspective I'd go RC16 but that's because I like to a bit of photometry/spectroscopy with a scope that size and generally lens are only corrected at optical wavelengths whereas a mirror system would also be able to image slightly into the Near Infrared or blue/near UV where lens aren't generally well corrected.

 

These are cogent arguments but are predictated upon using CCD technology. For better or worse CCD chips will probably go out of production to be replaced by CMOS. What are the binning advantages of CMOS compared with CCD?

Olly

[Star101]

16 hours ago, ollypenrice said:

Whoa, the big question is, What will your seeing support?   

Thanks Olly, Yes, my seeing has only been excellent twice this winter. 

My idea was to have something with long enough FL to get closer to all those small galaxies that abound the sky. 

1 hour ago, Whirlwind said:

 

So what is the benefit of a large reflector then? 

 

Thanks Whirlwind, for a great read and more things to think about.

 

54 minutes ago, kirkster501 said:

*Exactly* what Olly and others say.  What will your seeing support?  The Mount Palomar 200" in my back yard would be a waste of time.  My Meade 14" is a borderline waste of time.  The skies are not dark enough and the seeing will not support it.

You must always determine this before buying large and expensive telescopes or else you are just wasting your time and money and setting yourself up for disappointment.  There is a lot more to this than just throwing money at it.

EDIT:  I'd be tempted by the magnificent Astro-Physics Starfire  EDt 130 refractor if I were you  in the For Sale section if you've got money to spend   You'll get a lot more satisfaction with that than a large reflector with 0.35arcsec/pixel which is, at best, once per year seeing for us in Nottingham.  I'm tempted by that scope myself to build a dual refactor system.

Thanks kirkster501, and yes, that scope is looking much more interesting having read Olly's  tuppence worth.

 

Thanks for your thoughts. I can see I need to rethink this. 

 

[kirkster501]

1 hour ago, Star101 said:

Thanks Olly, Yes, my seeing has only been excellent twice this winter. 

My idea was to have something with long enough FL to get closer to all those small galaxies that abound the sky. 

Thanks Whirlwind, for a great read and more things to think about.

 

Thanks kirkster501, and yes, that scope is looking much more interesting having read Olly's  tuppence worth.

 

Thanks for your thoughts. I can see I need to rethink this. 

 

A noble notion Dave, to get closer to those galaxies.  I'm a galaxy man myself and would love to do likewise and have tried to do so. But our seeing where we live simply does not support that mate, we are in English Midlands, under a turbulent confluence of weather systems with Bortle 5 skies.  The art of this activity is to accept limitations and work around them by focusing on the [many] things that we can do.  A large aperture, long FL reflector like you propose is going to disappoint you, I can tell you that from experience.  Many other imagers - Olly included - have converged on using quality refractors for imaging and there is a reason for this.  Please buy that Starfire add remove it from my temptation!  

[Star101]

2 minutes ago, kirkster501 said:

A noble notion Dave, to get closer to those galaxies.  I'm a galaxy man myself and would love to do likewise and have tried to do so. But our seeing where we live simply does not support that mate, we are in English Midlands, under a turbulent confluence of weather systems with Bortle 5 skies.  The art of this activity is to accept limitations and work around them by focusing on the [many] things that we can do.  A large aperture, long FL reflector like you propose is going to disappoint you, I can tell you that from experience.  Many other imagers - Olly included - have converged on using quality refractors for imaging and there is a reason for this.  Please buy that Starfire add remove it from my temptation!  

I am steadily considering my options. 

Even if I did jump in and buy that Starfire, you do realise there are TWO for sale? 😮  Cambridge and Argyll !!

 

Having been to Olly's, I have first hand knowledge of what a great setup he has. with his TEC140 APO on a Mesu. I know my C11 could never compete with that!  So, I may be looking at something around the 130/140mm APO.

I am currently trying to get my head around seeing, FL and Pixels limitations. 

[ollypenrice]

2 hours ago, kirkster501 said:

A noble notion Dave, to get closer to those galaxies.  I'm a galaxy man myself and would love to do likewise and have tried to do so. But our seeing where we live simply does not support that mate, we are in English Midlands, under a turbulent confluence of weather systems with Bortle 5 skies.  The art of this activity is to accept limitations and work around them by focusing on the [many] things that we can do.  A large aperture, long FL reflector like you propose is going to disappoint you, I can tell you that from experience.  Many other imagers - Olly included - have converged on using quality refractors for imaging and there is a reason for this.  Please buy that Starfire add remove it from my temptation!  

A friend down the road has a 175 Starfire. Thank God he isn't selling it!

Olly

[Rocket Stars]

I read all good responses with intrest! 

But if we would image a faint, small object. Same time, same place. Everything optimizied. One rig starfire 175. Other is RC 16. 

We collect one sub. Exactly one houer. Under bortle 6 seeing. 

Who would win with best collected data in the subs? 

 

[pete_l]

A single 1 hour exposure. With both telescopes at F/8. Hmmmm.

The problem could be that you would get a white-out, or very little data. Have a look at Samir's sky fog page

His work suggests that under a Bortle 6 sky, with a DSLR at ISO800, then a 2.8 minute exposure at F/4 would use up half the histogram just with sky brightness. Going to F/8 which is what? 2 F-stops would quadruple that time, about 10 minutes. And who knows what the ISO setting of a cooled astro cam would be.

Edited April 18, 2020 by pete_l

[kirkster501]

Quality refractors on a Mesu mount.  I'm not sure there is anything to beat that combination. 

I have observed The Moon through my TEC140 many times. Sure it may "only" be a 5.25 inch aperture.  But it is spectacular.  The Starfire will be even better.  It will be fabulous on imaging as well.

[ollypenrice]

1 hour ago, Rocket Stars said:

I read all good responses with intrest! 

But if we would image a faint, small object. Same time, same place. Everything optimizied. One rig starfire 175. Other is RC 16. 

We collect one sub. Exactly one houer. Under bortle 6 seeing. 

Who would win with best collected data in the subs? 

 

You'll get answers from theory but what you need is answers with the subs...

Olly

[Star101]

Am I correct in thinking the 16"RC needs a camera with something like a 9um pixel size, KAF-16803 chip? 

From http://astronomy.tools/calculators/field_of_view/

 

 

The FOV changes to make it, as you say, not enviable, from the UK. Matching camera as close as possible to scope. Yes, one gets excellent images but the subject is far away. Use a smaller pixel and unless seeing is excellent, the image wont win any awards as the pixel ratio will be too small.!

 

Edited April 18, 2020 by Star101

[Rocket Stars]

35 minutes ago, ollypenrice said:

You'll get answers from theory but what you need is answers with the subs...

Olly

Exactly what I meant! 😊

if processed the same. Who would win?