59 replies to this topic

[Mike I. Jones]

Check out this link:

 

http://www.loptics.c...kietex2023.html

[dustyc]

Mike mentions a "corrector". For F2, I guess he's talking about a "super Paracor"? 

Or a spherical primary with correction (like a Schmidt plate) done at the eyepiece?

Looks interesting!  

[sixela]

He specifically mentions that the primary isn't parabolic nor spherical somewhere I read.

 

So my guess is that it's a catadioptric system with something else than a mere coma corrector that is otherwise "neutral" (i.e. it likely corrects spherical, coma and possibly flattens the field but wants a primary with a certain conic that isn't what we usually associate with Newtonians). Looks like a subaperture corrector, though (so not a Schmidt or Maksutov corrector), so yes, probably Paracorr-like and in what we'd normally call the focuser (but he mentions focusing by moving the primary, so it's more a "corrector, filter wheel and NVD holder" than a focuser.)

 

We can safely rule out a spherical primary (alas):

 

 

Given the speed and asphericity of the optics

 

But he's not spilling all the beans. He *has* indicated a willingness to manufacture similar systems for others, though.

 

I like it; it's the "who needs an afocal stack to get to good speeds for H-alpha" scope for prime focus NVD on nebulae (or of course non-nebulae if you don't filter, but then speed is not as important).

Edited by sixela, 10 November 2023 - 03:31 PM.

[a__l]

 

I like it; 

sixela, how do you like 5" secondary in relation to 12.5" primary?

Do you like this too?
For some reason, people in such cases only make astrographs with a camera in direct focus, without a secondary one.
That probably makes sense, doesn't it?

 

Actually, I welcome that the author eventually moved to the mod3 fan club...

SIPS is not a very good help here.

 

It would be interesting if the price of correctors was announced. Perhaps this would be of interest to users who already have telescopes faster than f/3... If, of course, they work in a parabola design.

Edited by a__l, 10 November 2023 - 04:55 PM.

[sixela]

Secondary obstruction is fairly irrelevant to this application (yeah, it’s not an f/2 unobstructed system, so what?)

Never seen an astrograph with a large obstruction? You must not get out much. Might want to ask RASA or Hyperstar 11” users why they like it despite the 114mm central obstruction.

Doubt it’s a parabolic mirror (see quote).

I see you haven’t shaken that knee-jerk reaction of mentioning the SIPS every time Mike Lockwood comes up no matter how off-topic it is (you sure are breaking a record here).

Edited by sixela, 10 November 2023 - 06:00 PM.

[a__l]

Never seen an astrograph with a large obstruction? You must not get out much. Might want to ask RASA or Hyperstar 11” users why they like it despite the 114mm central obstruction.
 

Celestron never considered the height of perfection. This is mass production. Made in China. Although this is off topic.

You haven’t answered the question why astrographs of such fast's are usually made with camera in direct focus?

There is still a nuance here. A good 5" mirror is quite heavy. Plywood. Not the best material for this. But this may be replaced.

 

 

Doubt it’s a parabolic mirror (see quote).
 

If so, then this is not very good information for those I wrote about above. But let's wait.

 

 

I see you haven’t shaken that knee-jerk reaction of mentioning the SIPS every time Mike Lockwood comes up no matter how off-topic it is (you sure are breaking a record here).

I am writing on the topic, namely about the changed author's attitude towards mod3. Why it was different before, the reason is clear, this is SIPS and it was taboo. Actually mod3 in prime on any telescope will give the best quality of stars. The starting link pays a lot of attention to this.
There is no need to attribute to me something that does not exist.

Edited by a__l, 10 November 2023 - 07:24 PM.

[Mike I. Jones]

For some reason, people in such cases only make astrographs with a camera in direct focus, without a secondary one.

Care to elaborate?  What people or products?  Examples?  Links?

Edited by Mike I. Jones, 10 November 2023 - 07:30 PM.

[a__l]

?

People use products.

Edited by a__l, 10 November 2023 - 07:17 PM.

[a__l]

The Earth also revolves around the Sun. I understand it. I do not understand your question? Robots have not yet learned how to make telescopes. Robots also don't need telescopes.
What do you want to know with this question?

In addition, if the question is about the quality of the stars, clarification is needed. At the edge of the field is it a mod3 eyepiece or something else? To my memory, this is not observed in the best photos of this thread.

[dcweaver]

I wonder if that's a reference to the Celestron RASA series, Hyperstar equipped SCT, or the relatively new Unistellar eQuinox scopes. They all place cameras at prime focus of the primary mirror with no secondary mirror. The RASA and Hyperstar SCTs also having corrective lenses in the path.

[vicuna]

Thank you for sharing the blog post. Great story, great writing, and amazing looking telescope.

[ABQJeff]

All I know is this reiterates my strategy is working: focus on visual while my eyes are good and skies are still Bortle 2 dark…once one or both of those break down, time to observe the universe in Red-Near IR! In the meantime, technology for Red-Near IR observing keep improving!!! So good job Mike Lockwood!!

Edited by ABQJeff, 11 November 2023 - 09:25 AM.

[WheezyGod]

Yea this sounds awesome for night vision! Those high speed filters then aren’t just limited to handheld use which amplifies the already brighter view even further.

Edited by WheezyGod, 11 November 2023 - 08:18 AM.

[Jeff Morgan]

It might be a Hyperbolic Newtonian, like the Takahashi Epsilon. Such an approach would offer a very flat field (remember, the NV device is a flat sensor) and be ideal for prime focus.

 

My best night vision views were with an Epsilon e180.

[Mike Lockwood]

A few points.....

 

1) I have considered a camera-only prime focus version of this telescope, however a filter wheel is needed.  The filter wheel is about 4" across, however it is off-center, and sticks out about 3.25" from the filter in use, so there would be a significantly off center obstruction no matter what.  I'm not going to re-engineer filter wheels, and I prefer the direct visual experience, so a secondary is needed.

 

2) The primary is aspheric, and the corrector is specific to this design and the passband of nightvision.  It is not intended for straight visual use.

 

3) The design(s) will remain proprietary.

 

 

A Mod3c has a particular type of use, and that is prime focus, with fixed power unless a zoom camera lens is used (which tends to be optically slower and produces dimmer images).  For this telescope, I decided to use it for simplicity, and this gave me the opportunity to try a supergain tube (which I purchased from TNVC).  Simplicity is the advantage, the disadvantage is that the power cannot change.  The 12.5" f/2 yields better image quality over the field, but at lower power.  It maximizes throughput into the NV device, and yields brighter images because it is f/2.  This was the goal.

 

My original SIPS is in my 20" f/3.0, built in 2008, and it functions perfectly.  For visual use, stars are pinpoints to the edge, and no more can be asked.  I have hundreds of clients that use it and it saves them lots of observing time and frustration.  Therefore, the afocal use case for NV is strong due to equipment already owned.  For a very fast Newtonian with eyepieces that were never intended for visual use due to the huge exit pupil size, the SIPS or Paracorr 2 works remarkably well, particularly with the 41mm Panoptic.  The 55/67mm Plossl works fairly well.  The 20" f/3.0 yields larger image scale than the 12.5" f/2, and more small detail in objects because of that.

 

When my 20" f/3.0 gets a new 5" secondary to replace the original 4.5" (from back when NV was not even dreamed of) and fresh coatings on both, I'll do some comparisons.

 

After adding some more baffling to the 12.5" f/2 and updating my 20" f/3.0, my next telescope project will likely be to build a 24" f/2 NVT.

[sanbai]

About 250 years ago some observers complained about the secondary mirror. Some tried to avoid their use, but complained that the new method created an even bigger obstruction. Then, some French gentlemen claimed the had found the solution to the new problem, and applied it. However, users did not report back. Some said they were having a more intimate experience of the heavens. I try to spend more time using my telescopes to admire the wonders of the universe than to complain about their construction and the size of the secondary mirrors.

 

Back to the topic, I'm happy to see new innovations and look forward for its further development. My congratulations to Mike and the other people involved. Hopefully one day I will catch up with that technology; now I can't justify the cost (other hobby priorities). It doesn't help not being a US citizen, although I'm aware of french-ware that I could use. Maybe better wen returning to the EU (which will be sooner than later). And maybe the new concept is further developed once I can justify the expense of NV.

 

I wonder why not a f/3 telescope, which allows use of a Paracorr, which in turn can be used for eyepieces. I guess this configuration cannot reach the focus point for prime focus NV (I have very little knowledge of the field). And of course, f/2 provides higher brightness and field of view, pushing the envelope. Also, it's a more compact design, and that matches NV... where one can reach more with less (except for the $$).

[sixela]

Because f/3 is a lot slower if you want to use the device in prime focus for nebulae. I have an f/3.45, and that basically forces you to go to an afocal setup again for really faint nebulae or more field of view (and the latter is limited by the vignetting from the secondary, corrector, eyrepiece and NVD objective, something Mike’s solution is not concerned with as much.)

There is indeed more than one way to skin that cat. Mike’s is a solution “from scratch” tuned to a prime focus NVD, not one cobbled up from existing parts. Even though it’s undoubtedly not cheaper either (except for Mike if he doesn’t bill himself the time spent on the optics).

Edited by sixela, 13 November 2023 - 03:22 AM.

[Deadlake]

The sole point of this scope with the esoteric corrector is simply due to SIPS or Pareacor not being able to function with a focal length less then F2.8.

 

If TeleVue produced such a corrector then no need for this Lockwood special?

 

F 2.8 mirrors are a availiable in Europe for a price, and can be fitted to a TS ONTC however no point in making the mirrors  faster without a functioning corrector..

[Mike Lockwood]

The sole point of this scope with the esoteric corrector is simply due to SIPS or Pareacor not being able to function with a focal length less then F2.8.

No, you should read the article.  That is one of the points, but not the sole point.  (Also I'd call the corrector elegant, not esoteric.)

 

The second point is to avoid the losses and aberrations from ~12-16 pieces of glass, and the coatings that are not optimized for NV.

 

The third and fourth points, which I had not mentioned, are to allow the focal plane to be closer to the tube to avoid an even larger secondary, and to avoid the 1.15x barlow factor.

 

I guess the fifth point is to do something that no one has done before, do it "from scratch" as Sixela put it, and do it properly.

Edited by Mike Lockwood, 13 November 2023 - 06:08 PM.

[sanbai]

I see the point of the NVT and skipping the use of a Paracorr/ SIPS. Some notes I made:

A f/2 telescope isn't adequate for a "pure" visual observer (no use of NV). The math on eyepieces (exit pupils, AFOVs, focal length, exit pupils) shows f/2 isn't a good choice for such application. There's no point for a Paracorr for such (demanding) focal ratio. Ethos call for a ~ f/2.8 or slower. the smaller the eyepiece's AFOV, the larger the minimal focal ratio one should choose. Televue won't market a f/ 2 Paracorr. It isn't logic, and it won't have enough demand.

However, NV doesn't have such restriction. A f/2 offers a clear advantage. F/2 provides twice the light than a f/2.8. Also, the whole NVT system, including the NV device, isn't cheap at all. If you buy into that, you don't care much about the price of the corrector, but sure, you want it optimized.

Mike got the point with his invention/ development.

I just wonder now if one could design a system where the sensitive part of the NV device could be placed at prime focus directly (no regular secondary mirror, but corrector needed at that place), then use a smaller secondary mirror to reflect the intensified image toward the NV eyepiece on the side of the OTA. This is a question out of my total ignorance.
The issue I see is that a filter wheel would not work well, and that collimation could be more difficult unless the mirror was spherical.

That would be basically a celestron RASA + NV with a periscope...

[Thierry Legault]

I was thinking about the RASA 11 too! 

 

It would be easy to adapt a NVD (without lens) after the corrector at F/2.2, and there should be no optical problem, the RASA covering a full frame sensor with very good field flatness and sharpness. The field with a 18mm NVD would be 1.6°. The problem, of course, being the head of the observer causing a quite large obstruction (plus thermal problems) 

 

There may be a possibility to design a specific relay lens, to shift the image to an eyepiece at the edge of the OTA, like a Newtonian telescope. A tube may cause a bit of obstruction (like a very thick spider vane), but IMO nothing critical for visual observation. I will contact an optical designer I know.

Edited by Thierry Legault, 14 November 2023 - 04:32 AM.

[Mike Lockwood]

An update on this telescope......

 

Here's a comparison that I did between regular Gen 3 and supergain, as well as lots of images taken with the 12.5" f/2 NVT.

 

http://www.loptics.c...ghtvision2.html

[WheezyGod]

An update on this telescope......

Here's a comparison that I did between regular Gen 3 and supergain, as well as lots of images taken with the 12.5" f/2 NVT.

http://www.loptics.c...ghtvision2.html

Wow this is great! The Crescent is the best example since it’s the only one that you have photos of across a normal Gen3 tube, supergain, and your f/2 setup.

[Mike Lockwood]

All the images there are taken with the 12.5" f/2.

 

The Crescent is not the only comparison - there are four objects/areas (Gamma Cygni region, Veil 1, Veil 2, and Crescent) that are compared with normal/supergain.  The very first image shows that comparison, top row is normal, bottom row is supergain.

 

All images after that 8-image mosaic are with supergain and the 12.5" f/2 because I sent the other tube back.

[WheezyGod]

All the images there are taken with the 12.5" f/2.

The Crescent is not the only comparison - there are four objects/areas (Gamma Cygni region, Veil 1, Veil 2, and Crescent) that are compared with normal/supergain. The very first image shows that comparison, top row is normal, bottom row is supergain.

All images after that 8-image mosaic are with supergain and the 12.5" f/2 because I sent the other tube back.

Ah sorry I thought you were comparing the views with the 12.5in f/2 vs. another scope to show the difference between that scope’s view vs. a more generic dob of the same/similar size.