Newts

[Simon Pepper]

Hi all 

I have been doing AP for over three years now and I have always used refractors which lets be honest are quite forgiving especially the widefield type plug them in and go!  However recently (and this could be the case of equipment envy) I feel I want to make that jump to something different something that comes with other challenges and perhaps some diffraction spikes! I keep seeing images on Astrobin of users with Newts where the stars just look incredible. I cant get stars that good with my refractors there is sometimes something that's not right whether internal reflections from filters, star bloat or some aberration that I just have no idea where its coming from. I have done a bit of research showing newts come with their own challenges. Collimation, light leaks, focuser sag the requirement for flocking etc. Anyone with experience in this field please give it to me straight how difficult is all of this bearing in mind I have never collimated a scope in my life am I mad to be wanting to do this with just three years experience or is the time right? I have also not ruled out hyperstar or rasa, but for the price of say a SW quattro at F3.45 will be fast enough I believe. Any advice and recommendations on scopes will be very much appreciated.

 

Thanks Simon 

[Mandy D]

@Simon Pepper Not to attempt to put you off moving over to the dark side, but you can get nice diffraction spikes with a refractor by string a pair of crossed wires across the objective.

I'm not exactly experienced in collimating Newts, but today I needed to check mine and found the Astrobaby guide helpful She says it's a simple guide, but to be honest I think it is probably one of the most comprehensive and I found it quite difficult to follow. I persevered with it only because I suspected my secondary was in need of alignment and found it was a long way out, despite having had some pretty good photographic results from the scope. It took me about an hour to wade through it and complete the task, but if it is onl the primary, which is usually the case, then it is a few minutes to do with a Cheshire eyepiece.

I don't think you are mad in wanting to try things with a Newt, but they do come with their own set of quirks. I've never worried about these issues. I don't know about the light leaks, but I'm sure someone will come along and help you with that. Here is the link to Astrobaby:

https://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

[Simon Pepper]

1 hour ago, Mandy D said:

@Simon Pepper Not to attempt to put you off moving over to the dark side, but you can get nice diffraction spikes with a refractor by string a pair of crossed wires across the objective.

I'm not exactly experienced in collimating Newts, but today I needed to check mine and found the Astrobaby guide helpful She says it's a simple guide, but to be honest I think it is probably one of the most comprehensive and I found it quite difficult to follow. I persevered with it only because I suspected my secondary was in need of alignment and found it was a long way out, despite having had some pretty good photographic results from the scope. It took me about an hour to wade through it and complete the task, but if it is onl the primary, which is usually the case, then it is a few minutes to do with a Cheshire eyepiece.

I don't think you are mad in wanting to try things with a Newt, but they do come with their own set of quirks. I've never worried about these issues. I don't know about the light leaks, but I'm sure someone will come along and help you with that. Here is the link to Astrobaby:

https://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

Thanks Mandy and you do make a good point but I was under the impression the fishing line trick over the refractor would t give the diffraction results I would expect with a proper Newt. If someone can prove me wrong though I am all ears 😄

[Captain Scarlet]

I can’t really answer the “size of the stars” query except to say that, everything else being good, the Airy Disc of a small refractor will be significantly bigger than that of, say, an 8” newt.

As for the diffraction spikes, yes fishing line will certainly produce spikes, but fishing line itself might be too thin. Diffraction spikes get shorter and brighter, the thicker the obstruction. As the obstruction gets thinner, the spikes get dimmer and longer, eventually becoming non-existent at infinitesimally small thickness. It would be a case of tuning the spikes you want by trial and error. An experiment to test this out: using a metal rule or equivalent, take a picture with the rule across the aperture at full thickness, and another with the rule “side on” and compare the spikes.

Cheers, Magnus

Edited August 26, 2023 by Captain Scarlet

[Clarkey]

On 25/08/2023 at 18:01, Simon Pepper said:

but for the price of say a SW quattro at F3.45 will be fast enough I believe.

I can't comment on the Quattro specifically, but I did get a 6" f4 TS Photon - mainly for the speed. However, by the time I had brought a new focuser and decent coma corrector it ended up costing me near to £1000. Also, I got horrendous reflections from the OIII and Ha filter and which were a nightmare to remove. See below for the worse version - this is Ha only. (I could have brought new filters but this would have added another £1000). I ended up selling the extra's and now have a redundant f4 scope. I guess the buy cheap, buy twice is correct in this case. For now, I have gone back to refractors and the RC8. I would like a RASA when funds permit (or possibly the F2.8 Sharpstar) - but that may be a while. 

 

[Dan_Paris]

On 25/08/2023 at 19:01, Simon Pepper said:

Collimation, light leaks, focuser sag the requirement for flocking etc. Anyone with experience in this field please give it to me straight how difficult is all of this bearing in mind I have never collimated a scope in my life am I mad to be wanting to do this with just three years experience or is the time right?

I started imaging with a 200/800 Newtonian, in my experience collimation is not really a challenge. After three years of experience it won't be an issue. This is especially true is you use the right tools. I found that the Catseye tools are the best (but a bit expensive). It really just takes two minutes and can be done comfortably indoors just before taking the setup outside.

What's nice with Newtonians is that everything can be upgraded easily to improve the performance: stronger springs for steadied collimation, flocking as you mentioned, new focuser, etc.  At the end you can  turn a modest mass-produced instrument into a truly premium astrograph.

In my opinion Newtonians are the most suitable telescopes for general imaging with the current small pixel cameras. Their focal length in the 800/1200mm range are the perfect balance between FOV and resolution (you are seeing limited under most conditions while keeping a large field) and their speed allow to achieve a good SNR in a rather short time.  But if you are really not into tinkering this may not be the right type of telescope for you (for me it is part of the fun). Or buy an already upgraded OTA like an ONTC from Teleskop Service or a Lacerta Fotonewton from Teleskop Austria.

 

A RASA 8 is not suitable for monochrome cameras and I doubt it can achieve the same resolution than a 8" newt. Mine gives 1.3" stars across the field when the seeing cooperates.

 

Edited August 28, 2023 by Dan_Paris

[Simon Pepper]

Some interesting opinions here. The reflection @Clarkey has there is one of the worst I have seen. It must be painful starting a new OTA only to have those issues. I have been there and that's why AP is a rabbit hole! I guess to simply things a little a colour camera maybe a better option that way its a just a UV IR cut, but I guess one could get a halo from there also! I think my take away from this is yes a newt can produce awesome images and a cheaper option, however to get really decent results the scope will have to be upgraded and cared for which will cost more money in the long run and perhaps some frustration. Maybe I will give it a little longer then till I can afford the scope and all the upgrades required to get great results! 

[Dan_Paris]

1 hour ago, Simon Pepper said:

The reflection @Clarkey has there is one of the worst I have seen.

It is the Newton fault, but rather the filter fault, or a a shared responsibility between the filter and the corrector.  According to the size of the reflection, it occurred approximately 50mm away from the focal plane. No mirror there.

 

Here's a deep exposure with my newt including mag. 2.4 Phecda in the field, there's only a faint reflection in the upper-left corner :

 

Edited August 28, 2023 by Dan_Paris

[Clarkey]

21 minutes ago, Dan_Paris said:

It is the Newton fault, but rather the filter fault, or a a shared responsibility between the filter and the corrector

I was not really suggesting it was down to the newtonian (other than the fast optics). The reflection was between the coma corrector and the filter as far as I could tell. It was just another reason why I gave up on the scope - ever mounting costs. I think a newtonian design that is intended for imaging is not a bad proposition - hence my comment about looking at the Sharpstar hyperbolics. I actually got some good images from it - and pretty quickly. However, I spent a lot of time in processing removing halos. Eventually, I just decided it was too much work and I would look at other options. If I had the OSC camera at the time it may have changed my mind, as the filter reflections would no longer be a problem.

[Simon Pepper]

49 minutes ago, Dan_Paris said:

It is the Newton fault, but rather the filter fault, or a a shared responsibility between the filter and the corrector.  According to the size of the reflection, it occurred approximately 50mm away from the focal plane. No mirror there.

 

Here's a deep exposure with my newt including mag. 2.4 Phecda in the field, there's only a faint reflection in the upper-left corner :

 

This is the kind of stars I am after. When imaged like this the composition just works. I wouldn't look the same if was just a refractor and a bloated stat here lol! What scope did you use for this? Thanks 

[Space Hopper]

Not sure why anyone would want star spikes everywhere (just my opinion) but another scope worth considering,

just for its sheer astrograph performance is the SW Mak Newt 190.

We have a imager on our astro forum (EMS) who uses one and it produces some stunning results.  It ticks alot of boxes. 

[Dan_Paris]

1 hour ago, Simon Pepper said:

What scope did you use for this?

A heavily modded 200/800 newt, more details here

 

 

 

2 hours ago, Clarkey said:

The reflection was between the coma corrector and the filter as far as I could tell.

Out of curiosity, you never had the same problem with this filter and the corrector of one of your refractor? It may be a faulty design of your coma corrector then.

 

1 hour ago, Space Hopper said:

Not sure why anyone would want star spikes everywhere (just my opinion) but another scope worth considering,

 

If you don't like spikes I agree that a newt is not a good option !

The mak-newt is an interesting proposition. A theoretical analysis of the SW 190 MN design can be found there :

https://www.telescope-optics.net/commercial_telescopes.htm#most

It seems well-corrected for moderate sized sensors (and spike-free !)

 

Edited August 28, 2023 by Dan_Paris

[Clarkey]

9 hours ago, Dan_Paris said:

Out of curiosity, you never had the same problem with this filter and the corrector of one of your refractor? It may be a faulty design of your coma corrector then.

I have had occasional issues with the OIII filter and halos - but not like this. I had halos on every bright star which made it such a pain. I use the same filters with a multitude of other scopes without any serious issues. I doubt the issue was with the CC itself as it was a SW aplanatic which generally has a good write up. I actually bought it because the Baader MPCC did not give me good enough stars.

By the way - that is a cracking looking scope you have 'made'. If I had the time, it would be something along those lines I would be looking at. 

[ollypenrice]

Diffraction spikes are an artifact but, if you must have them, they can be created by cluttering your aperture with string or by using Noel's Actions in post processing. But why? Grrr!  

To be honest, modern post processing possibilities make star control so simple that it strikes me as being more sensible to concentrate on a system which gets the best object signal. I'm using a RASA 8 and a Samyang 135 at the moment. Native stars are not great in either, but does it matter? Star Xterminator gives me almost total control over them.

How does StarX work with Newt spikes? I don't know, but if it doesn't work with them I would would ditch the Newt straight away because star removal-replacement has revolutionized imaging.

Olly

[Elp]

You know, as like above, you could just add them in however large and the way you like them to look:

I quite like the crispness my 130pds gave me both visual and imaging. But they're quite large and cumbersome especially as you go up in aperture, and if you can't shield the setup from breezes and your mount + tripod isn't imbedded into the earth a slight sniff of a breeze will hit your guiding. If you can get them to work they perform well.

[Dan_Paris]

14 hours ago, ollypenrice said:

How does StarX work with Newt spikes? I don't know, but if it doesn't work with them I would would ditch the Newt straight away because star removal-replacement has revolutionized imaging.

Quite well actually, significantly better than Starnet v2 which leaves behind some faint spike remnants.

An example with StarX :

 

Btw refractors are not free from diffraction artefacts, I've seen many FSQ106 images with diffraction patterns from lenses spacers around bright stars...

 

Edited August 30, 2023 by Dan_Paris

[ollypenrice]

1 hour ago, Dan_Paris said:

Quite well actually, significantly better than Starnet v2 which leaves behind some faint spike remnants.

An example with StarX :

 

Btw refractors are not free from diffraction artefacts, I've seen many FSQ106 images with diffraction patterns from lenses spacers around bright stars...

 

Very true.

Olly