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J.T.'s 8" f/10.6 Ed Jones Chiefspiegler build

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#1 jtsenghas

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Posted 27 August 2019 - 08:58 AM

Well, I realized I still had more fingers on one hand than astronomy projects in progress, so I started another!

 

Actually, I very nearly started a project like this nine months ago and came very close to pulling the trigger on buying a Discovery 8" f/8 mirror then.  They had them in stock at the time.  I started an exploratory thread then that ran a few pages and can be found here.  I want to have at least one unobstructed reflector in my stable, and love how Ed Jones has worked out a way with two lenses to make reasonably fast optics perform adequately while completely unobstructed.

 

When I added up the cost of primary, secondary, two lenses from Newport, and a few accessories last year, I decided instead to start building a 12.5" f/4.3 dob that I actually already HAD a mirror for.  That project was 90% complete before this year's June Cherry Springs Star party and is still waiting to be completely done.  I've had a beastly hot summer and haven't been inclined to play in my uninsulated garage after spending at least six days a week in a large plastics factory where indoor temperatures are always at least 10 degrees F hotter than outside. That project will resume shortly in parallel with this new build. Temperatures are getting bearable again after the hottest July on record both locally and worldwide.

 

I decided last year to keep my ear to the ground and continue to watch CN classifieds in the "ATM Parts and Stuff" for reasonably cheap reasonably appropriate components for this project.  Well, about a week ago both an 8" f/10.6 primary that had been tested quite favorably by Mike Spooner and some 2.75" secondaries both were advertised at VERY reasonable prices. What a community! 

 

I now have the mirror, and the secondary is on the way.  Newport reportedly shipped yesterday the two lenses Ed Jones has specified.  This mirror strikes me as almost ideal for this project, except at 1 3/8" thickness it is the thickest I've built with. A cooling fan will definitely be in the design. Being f/10.6 it should do well with the same radii concave and convex lenses I've ordered, according to Mr. Jones. 

 

I've been pestering Ed Jones with questions via PM the past week and he has provided me with rough dimensions to consider in the design. Despite an approximately seven foot focal length, it appears that with a 2.75" secondary (used sideways) I can fold the light path low enough before the lenses to place the eypiece only about four feet from the primary. YEAH! This will have the aperture and approximate focal ratio of a C8 with the eyepiece not much higher than that of an 8" f/6 dob!

 

Anyway, I'm starting this build thread, if for no other reason to motivate me to keep this project moving along at a reasonable pace for a sense of pride.  I've enjoyed looking through Kevin Frederick's 17" chief at Cherry Springs and want to see how well a reasonably priced smaller version will perform.  I have the benefit of both a well appointed woodworking shop at home, and access to water jet robots and CMM equipment at work (both of which I have experience using).  I may make a "top box" that precisely holds the secondary, lens cell, and focuser in their relative positions as Kevin did, and then build the rest like a more traditional dob.  My mechanical design hasn't been envisioned yet.  Ed has warned that if a fixed design doesn't work, "then where are you?". I don't mind taking that risk because I could have a do-over without significant expense because I expect to be my own fabricator.

 

Wish me luck, and come along for the ride!


Edited by jtsenghas, 27 August 2019 - 11:10 AM.

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#2 jtsenghas

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Posted 27 August 2019 - 10:19 AM

So, here's a design question that I'd appreciate input regarding:

 

Might it make sense for the end of the optical train be built similarly to that of  C8 with optional focal reducer?

 

To show my thought process, here's Ed's rough proposed layout.

 

msg-3008-0-21178400-1566663895_thumb.jpg

 

The direction of the final rays can be at a greater angle for improved baffling, but it will be probably something close to that. A chief can have no secondary, but a star diagonal to get the head out the way, or a secondary before or after the lenses. At about a seven foot focal length I'd want the secondary before the lenses for the greatest height reduction.

 

I don't want awkward neck positions for viewing, particularly for my wife who has neck issues. A quality star diagonal would lose little light and make for much more comfortable viewing, including swiveling as needed.

 

Since the aperture and focal ratio are almost the same as for an 8" Schmidt Cass, why not use an optional f/6.3 focal reducer before a C8 diagonal and visual back?  I'd just have to thread the focuser tube to match that hardware.

 

Are there other focal reducer options that won't vignette significantly or present other new problems?

 

Suggestions? I haven't settled on a focuser for this yet, though I was considering a refractor 1 1/4' focuser and star diagonal. 


Edited by jtsenghas, 27 August 2019 - 03:07 PM.

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#3 jtsenghas

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Posted 27 August 2019 - 11:00 AM

Just to be clear about this optical design, the lenses are required to compensate for the primary tilt, which will be less than three degrees, in any event.

 

The unobstructed newts out there are typically made with a circular SECTION of a parabola that lies outside of the secondary location in line with the center of the parent primary. Optically these are no different than large newts with an off axis aperture mask outside of the secondary. Obviously, mechanically these are a lot smaller than a masked Newt.

 

We owe Ed a world of thanks for designing with the aid of Zemax a way to correct the astigmatism adequately with a couple of lenses those images that are produced by slightly tilted parabolic primaries. Bigger and faster versions are possible, as evidenced by Kevin Frederick's 17" and 20" Chiefs.  Faster versions, just like newts, benefit from the addition of a coma corrector.

 

These scopes are quite different from the extremely long focus "Schiefspieglers" designed by Anton Kutter. Those have long primaries to begin with, f/15 or more, made still longer with convex secondaries. I'd rather not observe, however, at f/27 or f/30.

 

Since William Herschel is credited with a number of the original off axis designs, and the addition of lenses make these scopes catadioptric, Ed coined the name Chiefspiegler for Catadioptric Herschelian Schiefspiegler, or simply "Chief". 

 

From Ed"s spot diagrams it appears that on axis performance of these Chiefs can be extraordinary, and modestly off axis still quite good. 

 

I recognize that a bit more care has to be taken for construction than for a Newt, but I think I'm up to the task. I wouldn't go so far as Kevin Frederick has, with his provocative 2015 statement that "The Newt is dead!", however.

 

I think it's great that an 8" chief can be built for about the price of a 10" dob, considering that the lenses cost about the typical difference between the costs of those sized primaries. 

 

My lenses will be uncoated, so will lose about 4% of light per surface, or about 15% overall compared to good anti-reflective coated optics. They shouldn't produce any ghost images because of the tilt, though.

 

Considering the loss through lenses and reflections I expect the light through this 8" aperture to be similar to that of a 7" f/12 apo in brightness and quality. Doesn't that sound like a worthwhile DIY project to aspire to with a mere few hundred dollars worth of parts? 


Edited by jtsenghas, 27 August 2019 - 03:19 PM.

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#4 Jeff Morgan

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Posted 27 August 2019 - 08:36 PM

I'll be interested to see how you tackle the corrector lens holders.

 

Ed gave the the prescription for my old 8" f/9 mirror, but that end of the project seemed pretty difficult to me. The rest of the project is basic Dob.



#5 jtsenghas

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Posted 27 August 2019 - 10:01 PM

I'll be interested to see how you tackle the corrector lens holders.

 

Ed gave the the prescription for my old 8" f/9 mirror, but that end of the project seemed pretty difficult to me. The rest of the project is basic Dob.

I'm completely undecided on this one. I might make a wedge donut from my red urethane tooling board on my wood lathe, or I might draw it in Solid works and print it with a 3D printer we've recently gotten at work. I'm more inclined to machine this at home if I do in fact make a holder for both lenses.

 

I have the very same model digital angle gauge that Ed demonstrated in his YouTube video, so I could make a precisely tapered face plate for my lathe from wood, even if I had to sneak up on the angle with hand sanding.

 

I could first turn the lens cell parallel and make one face, then screw it to the tapered wedge and turn the opposite face.

 

Finally, I could bore shallow 2" diameter holes in each side to house the lenses at the correct distance and centration. I could use that same tapered faceplate as a riser in my drill press for each side for that operation, and use calipers and shims for positioning X and Y relative to each other on opposite faces. 

 

With the angle and centration of the lenses locked in, I would only have to set up some tilt adjustment for overall tilt of the pair for tune in. Once set, I would likely lock it in using epoxy at the pivot.

 

Having just thought that all through, making a fixed box for the secondary, lenses, and focuser has a bit more appeal now. By that I mean I'd dispense with the lens cell and water jet a box with locking tabs and rectangular holes for individual lens holders and the secondary holder as Kevin did on his Chief, mounting each lens on its Plano side, which face outward from each other. If I was off a little, I'd rework the first attempt with files and tape components into position until I had good images, and then cut another box with corresponding adjustments to my robot program. I have some good 3 mm thick carbon fiber plate left over from some materials protyping I did at work a few years ago in the water jet that would make a dandy secondary, lens, and focuser box.

 

I have lots of options. I'm a modern day robotic water jet programmer by day and an old fashioned woodworker at home.  On the one hand I might develop a method that more people can duplicate at home, or I might simply use the high tech tools at my disposal. We have a new engineering technician at work who needs some water jet training... 



#6 Oberon

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Posted 28 August 2019 - 03:27 AM

Excellent! Will follow with interest.



#7 jtsenghas

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Posted 28 August 2019 - 11:51 PM

Excellent! Will follow with interest.

Thanks. Hexapod adjustment is not out of the question! 



#8 jtsenghas

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Posted 30 August 2019 - 09:12 PM

Primary BEFORE recoating brightly backlit:

 

20190830_211847_compress98.jpg

 

The coating on this mirror is definitely thin and a little mottled in several places, and looks decidedly dull in spots. That scratch at the top appears to be through the coating only, but I'll have to see if there are any remnants of it after it is cleaned and recoated.  The seller made the condition of the coating known, and that was a factor contributing to the low price he put on this mirror. 

 

Not much is known about the origins of this particular mirror. It is 1 3/8" thick, which is about 1/2" thicker than I'd consider ideal. I'll definitely have a cooling fan at its back to keep up with falling night temperatures. 

 

The seller had bought it from someone who had apparently discovered that an eight inch scope with a seven foot focal length was too big for his shed. He bought it last year planning to make a planet killer with it, but his plans changed as well. I can relate to that and his re-decision is my gain. 

 

Last December he had Mike Spooner evaluate it and provide observations and Ronchi images inside and outside of focus of it. Those reports were forwarded to me before the sale. Mike reported favorably on it. I'll inquire with him and the seller and, if neither has any objections, I'll share Mike's report in this thread. 

 

I've made inquires to five coaters requesting quotes for stripping, cleaning, and recoating this mirror. I choose them from CN discussions on this topic. I'm pleased to learn that a couple well established vendors still offer very good prices with overcoat for such small mirrors. The range of prices varied with the highest being nearly three times the lowest for aluminum with SiO overcoat. Since this isn't a premium job, I'm not terribly concerned with sending it to one of the lower, but not lowest bidders. 

 

I'll let everyone know how it turns out. 

 


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#9 jtsenghas

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Posted 01 September 2019 - 12:21 PM

Well Mike Spooner and the seller of this mirror both gave me the okay to share the mirror test reports.  I know they hardly were likely confidential, but one must be courteous and abide by the TOS, eh?

 

Last December, Mike wrote:

 

"Set the mirror up in autocollimation tonight. Looks very well corrected with a slight turned up edge. Yes there are some cosmetic issues but IMHO this mirror should provide superb views. Re-coating would be beneficial in the future but it has a nice, smooth surface and the figure is really good. The planets and moon in solid seeing should be exquisite. I haven't checked the secondary yet. I'm attaching some test photos (ideal is straight lines inside and outside focus). The null looks slightly rough but that's mostly air currents and maybe a bit from the coatings on both my test flat and the mirror. The photo make it look worse as it doesn't integrate."

 

and also:

 

"All are 100 LPI Ronchi in DPAC. The hole in the test flat is 1.5 or 1.75" (don't recall at the moment.)"

 

Here are the inside focus checks:

 

Inside1.JPG Inside2.JPG Inside3.JPG

 

 

Here are the outside focus checks:

 

Outside1.JPG Outside2.JPG Outside3.JPG

 

I appears to me from scaling the images that the central hole in the flat is in fact 1 3/4".  If that is double pass with 100 lpi, that appears to me to be a phenomenal mirror!  Does anyone else want to offer observations or opinions?  Though Mike says it has a "slight turned up edge" that appears to me to be a very critical assessment.  I see no need to mask the edge at all!  Opinions on that, too?

 

The mirror has been boxed up for recoating, going out USPS Tuesday.


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#10 jtsenghas

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Posted 02 September 2019 - 12:25 PM

Well, I've decided I'm willing to spend a bit of money on a quality diagonal for this build, to permanently reside in the focuser. I am really grateful for the extraordinary amount of information I'm finding on Cloudy Nights comparing diagonals critically. I can see how for for refractor and SCT users the choice of a diagonal can be an important one.

 

I've had only a couple of refractors with basic mirror diagonals, including an approximately forty year old Tasco 60 mm. I know neither are particularly special as the views are noticeably better without the diagonal in place. I certainly understand, however, that for a rear mounted focuser it really helps ergonomics to turn the light path.

 

This Chief would require the user to look upwards if the diagonal were not used because I'll be folding the light path rearward as much as tilt and baffling allow to reduce the eyepiece height as much as possible. Although I'd probably be willing to suffer such a viewing angle, I know many that I plan to share views with wouldn't. They would include my wife who had neck surgery a few years ago and can't tilt her head significantly upwards.

 

By far the best discussion I've found on Cloudy Nights on diagonals has been this article.

 

I considered using an SCT threaded diagonal and optional f/6.3 focal reducer on this setup by attaching that hardware to a 2" OD tube threaded with 24 threads per inch to go into a standard reflector focuser. The reason for this consideration was that such reducers and field flatteners are optimized for such long focal ratios and would yield fields of view similar to those of the dobs I am far more familiar with as an option, anyway. 

 

I then decided that I was falling into the trap of trying to make this scope "do it all" and, particularly since I won't be imaging and have larger aperture dobs available in even shorter ratios, I should focus on making this scope just a high magnification planetary scope. At 8" f/10.6 that was the mirror maker's intent, I'm sure. 

 

So, I'll likely get a decent quality focuser and diagonal in just a 1 1/4" size to keep weight and cost down. The eyepieces I'd use then, would be my 1 1/4" ES 82 degree ones with that barrel size, the 4.4 through 11 mm, plus my newly acquired Nagler type 2 12 mm. That last has a double barrel that should fit a 1 1/4" diagonal. I've only used that Nagler once, under stable but not extremely transparent skies. It definitely has slightly less eye relief than my ES 82s, and no doubt coatings aren't quite as good considering the age.

 

I'm well aware that the Nagler type 4 and Type 6 are an improvement over the Type 2 for both coatings and eye relief. I'm curious if any of you have had the chance to critically compare the Type 2s to similar focal ratio ES82s. I'm undecided right now if I'll be keeping my sole 12 mm Nagler.

 

With the plan to make this a dedicated high magnification unobstructed scope, I may splurge for a Delite or two, even if that means possibly surrendering my sole T2. 


Edited by jtsenghas, 02 September 2019 - 02:57 PM.

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#11 jtsenghas

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Posted 03 September 2019 - 07:29 PM

Well, to get input on an appropriate diagonal, mirror or prism, I started a thread on the Classics forum today.

 

The readers of that forum seem to have a lot of experience with various diagonals, especially the vintage and used ones I'm considering choosing among. If any of you have any interest or advice on this area of my project, I'd appreciate your input on that thread.

 

At f/10.6 I don't presently see why a prism diagonal would be a worse choice than a mirror, as DAVIDG insists it would be. If any of you think you could be useful to me in that discussion, I'd appreciate it if you joined that sidebar discussion. Thanks. 



#12 BGRE

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Posted 03 September 2019 - 11:23 PM

The wavefront error of a prism diagonal is sensitive to refractive index inhomogeneities as well as to inaccuracies in the figures of the input, output and reflecting surfaces. With an F/10.6 beam the SA wavefront error will be reasonably small (< 16nm for a 50mm glass path length in NBK7):

 

W040 = -(1/128)*(T/F#^4)*((n^2-1)/(n^3))

 

where

T is the axial length of the glass path 

n is the refractive index

F# is the beam F/No.

 

The wavefront error can be reduced by a factor of 4 by balancing the residual SA  with appropriate amounts of defocus and piston.


Edited by BGRE, 03 September 2019 - 11:38 PM.


#13 Jeff Morgan

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Posted 04 September 2019 - 12:21 AM

The issues (and math) of a prism diagonal are covered in Ingalls Amateur Telescope Making Book One, section A8. 

 

While there is a lot of fretting about it, very little is said about the drawbacks of a mirror diagonal. They are not without issues either.

 

At your focal ratio, the prism may be a very good option. And if it is not to your liking, it is certainly a reversible decision.



#14 BGRE

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Posted 04 September 2019 - 12:53 AM

The longitudinal chromatic aberration (486.1nm - 656.3nm) is

 

T*(n-1)/(V*n^2)

 

n = 1.517 for NBK7

V = 64 for NBK7

For T = 50mm the longitudinal chromatic aberration is about 175 microns.



#15 jtsenghas

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Posted 04 September 2019 - 05:26 AM

The issues (and math) of a prism diagonal are covered in Ingalls Amateur Telescope Making Book One, section A8. 

 

While there is a lot of fretting about it, very little is said about the drawbacks of a mirror diagonal. They are not without issues either.

 

At your focal ratio, the prism may be a very good option. And if it is not to your liking, it is certainly a reversible decision.

That's a practical point if I don't invest a lot in a prism diagonal. At worst I'll have have an upgrade available for my antique ATM f/15 refractor when/if I switch to a quality mirror diagonal. 



#16 jtsenghas

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Posted 04 September 2019 - 05:49 AM

After a day of rumination I've decided to go with a quality vintage 1 1/4" prism diagonal unless someone offers me an extraordinary mirror diagonal today. 

 

My main reasons for this decision are :

 

1) Scatter should be less for high magnifications than a mirror

2) At f/10.6 the focal ratio is already longer than most SCTs that do well with prism diagonals, or well enough.

3) At a 1 1/4" diagonal size chromatic effects will be much less than for 2" diagonal prisms, which are commonly used on SCTs

4) Light loss should be negligible with good AR coatings on both glass to air surfaces.

5) As Jeff said, this is reversible. I'll have an excellent diagonal for my sole refractor (f/15) if I change my mind. As long as my last reflection is after the focuser the scope itself will remain unchanged. 



#17 Ed Jones

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Posted 04 September 2019 - 08:00 PM

J.T.

  Here is what you get with a 1.5 inch Bk7 prism on axis.  The left is without, the center is with the prism.  It adds a little more CA than the lenses themselves add (due to equal radii). A little blue light is falling outside the Airy disk.  However you can tweak the concave curve to get a nice tight axis. (right)

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#18 jtsenghas

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Posted 04 September 2019 - 08:41 PM

Thanks , Ed. I have no experience with grinding lenses, so I don't think I'll be tweaking that concave curve.

 

After receiving several offers to sell me quality 1.25" prism diagonals at decent prices, and after stating above that I would go that route, a dielectric mirror 1.25" diagonal popped up in the classifieds, and I've ordered that. (Note that I said "unless" in post 16 above.)

 

I'm aware that, despite 99% reflectivity, that the quality of a dielectric mirror depends as much on the uniformity of the multiple coatings as the underlying smoothness and error, and that scatter may be slightly greater than for a quality prism, but my first pass will be with a mirrored tertiary after all.

 

If for no other reason, a choice of a mirror will mean that any color is due to the lenses and my positioning of them. If I discover that views are noticeably sharper without the mirrored diagonal than with, I could move this mirror to a faster refractor and get a prism after all.

 

As Jeff pointed out, such decisions are reversible. 

 

Thanks for the spot diagrams. I'll try to get some design dimensions to you soon. They may depend in the end on which secondary I end up using, though. 


Edited by jtsenghas, 05 September 2019 - 08:38 AM.


#19 jtsenghas

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Posted 05 September 2019 - 08:03 AM

I'm aware, as DAVIDG pointed out in my thread on diagonals that the other elements in the optical train will all contribute to scatter and their own errors will add to the system error. 

 

I'm also aware that some cheap diagonals such as I have can be surprisingly good...... or not. 

 

To that end I'm going to take Ed Jones up on his generous offer to check a few of my diagonals for quality. This will only cost me postage both ways.

 

If none of them are decent enough I am prepared to invest in a more expensive Antares or similar secondary. Since this flat will be reflecting the light back at a severe angle, a round secondary would in fact be better than a 45 degree ellipse. If I use an elliptical mirror I'll turn it sideways and use a nearly round portion of it with its major axis at right angles to that of the mirror.

 

If any of you have a quality round flat in the 2.5"-3.5" range I may be interested in buying it. My cheap secondaries would be relegated then to such whimsical projects as a fast folded folding "frac-in-a-box" I expect to make eventually with a 5" achro objective I have.  There's never enough time with the work hours I put in...

 

The larger the secondary the shorter I can make this scope, at the cost of only slightly increased tilt. 


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#20 Ed Jones

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Posted 05 September 2019 - 09:18 AM

It likely still better than most refractors. These plots are for C,F and D lines but the deep purple is going to be much worse. Visually it might not be a problem but for AP it might. I can understand the hesitancy to regrind a lens curve so here is another idea I had. I found that if you put a very weak curve on the prism first surface it will correct this CA. You could regrind the prism face but more simply glue on a very weak (1 meter) focal length plano-lens on the prism face. Both flats would need to be uncoated (removing the prism’s coating) and grinding it square to fit. These are available commercially. Makers of prism diagonals might want to do this too. This would correct the CA the same as the right side.

#21 jtsenghas

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Posted 05 September 2019 - 10:37 AM

Very clever, Ed, very clever. Too late for me in this build as I'm expecting a mirror diagonal, though. 

 

Being so close to focus I wouldn't expect such a lens to change focal distance very much either.

 

Everything is a compromise though. The improvements in CA come at the expense of transmission if the coating is removed. Sure it's just 4%, but these factors of 0.96 multiplied several times with several surfaces do make a difference with visual observing.



#22 MKV

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Posted 05 September 2019 - 10:45 AM

That was initiated in the 1950's and is knwon as the Weinstein SA-corrected beamsplitter cube. In this case the beamsplitter is simply a cube considting of two right-angle prisms cemented at their hypotenose.  diverging or converging light signal passing through such bemasplitters or prisms will result in SA, which can be corrected by a simple PCX lens of a   correct radius of curvature cemented to a prism face. I imagine a PCX lens of a different glass index could maybe correct for CA as well. 

 

Mladen

 

Weinstein BS.jpg



#23 jtsenghas

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Posted 05 September 2019 - 10:48 AM

DAVIDG just reminded me by PM that for the reflection angles of the version of Chief I'm planning that a poorer secondary would do better than if used as a 45 degree diagonal. 

 

I'd prefer it if these discussions actually be held in this thread for the benefit of others.

 

I'm aware, for example, that power in a secondary causes astigmatism due to the tilt, so less tilt means less astigmatism for the same amount of power. I'm not sure how much a few rings of power would show in this version of a chief. 

 

Ed pointed out to me in a previous PM (again, I'd prefer these discussions to be out here for the benefit of more people) that astigmatism from a secondary can be tweaked in A Chief with lens tilt angle, which is for adjusting out astigmatism anyway.

 

All neat stuff! 


  • PrestonE likes this

#24 jtsenghas

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Posted 07 September 2019 - 08:34 AM

Does anyone want to venture an estimate of the surface error of my primary based on Mike Spooner's images in post 9 above? Remember, that's 100 lines per inch in double pass collimation. 



#25 MKV

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Posted 07 September 2019 - 10:56 AM

Does anyone want to venture an estimate of the surface error of my primary based on Mike Spooner's images in post 9 above? Remember, that's 100 lines per inch in double pass collimation. 

Given that it's a 200 mm f/10.6, and a 100 lpi the autocollimation Ronchi test with three visible bands shows no measurable curvature of the bands, the mirror is at least 80% parabola with a residual rms OPD of λ/32 pv on the wavevfront -- if, as in this case, the outer (turned) edge of the mirror is masked off to about 175 mm (6.9") clear diameter. 

 

It's difficult to tell how much light scatter will occur, and the degree of loss of contrast resultign form that from that, will result due to the turned-up edge. Generally speaking, a turned-up edge is better then a turned-down edge, but the overall wavefront quality of the mirror at the exit pupil would have to be determined by interferometry and a resolution/contrast chart.

 

Mladen

 

200 mm f_10.6 AC_100_lpi_out .jpg

 

______

 

Edit

 

The estimate is based on the limit of the Ronchi test's sensitivity for a given screen frequency and focal ratio in an autocollimation test setup for the test optic, and is not a measured wavefront deviation. At a conic of -0.8 the test yields no visible curvature using 100 lpi in AC configuration, so the mirror is in the range anywhere from 80% parabola (with an rms residual wavefront error of λ/32) all the way up to a theoretically perfect mirror. An autocollimation knife-edge test wold reveal more due to its higher sensitivity.


Edited by MKV, 07 September 2019 - 11:29 AM.



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