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Post your Optical Design! (This is a no-discussion thread!)

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#51 Mike I. Jones

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Posted 05 June 2020 - 07:03 PM

Nice sharp 220mm f/3, 673.64mm EFL astrograph to cover a 24mm x 36mm full-frame sensor format over the 0.42-0.74µm spectrum.  Total corner-to-corner FOV is 3.6º.  Primary is paraboloidal, corrector lenses are good glass (N-ZK7 and N-FK5).

 

Attached File  220mm f3 DSLR astrograph.len   1.31KB   12 downloads

 

220mm f3 DSLR astrograph prescription.jpg

 

220mm f3 DSLR astrograph layout.jpg

 

220mm f3 DSLR astrograph spots.jpg


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#52 Tony Owens

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Posted 06 June 2020 - 08:06 PM

Here is an evolution of a 10" F4.9 all-spherical Maksutov-Newtonian photo-visual instrument into a F4.6 flatfield, corrected astrograph. The EFL is 1,067mm and the wavelength range is 435 - 851nm. Diffraction-limited 1.8 degree field for a 44mm dia. flat focal plane.

No 'touchup' of the spherical primary or corrector is required to achieve this performance.

Be warned - the design is a bit of a hack. It uses a 2-element corrector to kill the coma, SA and astigmatism residuals. But the corrector design needs detailing to assure freedom from ghosting and good environmental durability. Apply the precautionary principle!

Here is the layout:

 

Corrected_10in_MN-F4.6_1.jpg

 

Here is more detail in the performance with two different diagonal sizes:

 

Corrected_10in_MN-F4.6_2.jpg

 

...and here is the lens design file in OSLO format. Right on the 10-surfaces limit for the EDU version:

Attached File  MN10_F4.6_astrograph.len   1.55KB   16 downloads

 

Food for thought, I hope!

 

Tony Owens


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#53 RajG

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Posted 07 June 2020 - 11:28 AM

Here's by 60mm f/15 flatfield anastigmat quad apo aka poor man's FOA 60Q

 

Steinheil doublet f/7.5 450mm fl objective, with a 2X extender placed approximately halfway from the objective's focus. 0.96 Poly Strehl over 435nm-707nm, flat anastigmat field over a full frame sensor (47mm dia/3 degree full field).

 

See also this thread: https://www.cloudyni...or-mans-foa60q/

 

gallery_326571_13467_77414.jpg

 

gallery_326571_13467_85878.jpg

gallery_326571_13467_4255.jpg

gallery_326571_13467_57442.jpg

Attached Files


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#54 Aljr

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Posted 14 June 2020 - 05:13 PM

* STRELA: Apochromatic Converter for achromatic refracting telescopes 150mm in diameter and 1200mm focal length. It is possible to build them both for apertures larger than 150mm in diameter and / or smaller apertures. I would like to make it clear that this Converter only corrects the RGB primary colors (but does not correct the 435A violet color). This Converter greatly improves the secondary spectrum of the achromatic refractor, see the drawing!
It should be placed close to the telescope's focus. It has two lenses of BK7 or B270 material. The first lens, which is the heart of the converter, this lens introduces a lateral chromatic aberration (LCA), which until then was non-existent, to be corrected later ... it will be corrected by the second lens, the thick lens. Note: the thick lens can be replaced by two other optical elements: a flat "thick" window and a simple flat convex lens.
In a telescope with 150mm aperture and 1200mm (F / D = 8) focal length, close to the focus (+/- 1095mm) two lenses are placed. The first is a field lens and the second is a thick(20mm) converging lens. Note that the focus is formed right after the first field lens, and the "Tolles" lens is placed right on the first focus. Then we will "ALWAYS" have a final image with a constant increase, around 20x.
The final image formed is virtual. And how to access this image? A small telescope (5 to 20x magnification, or as many as you wish ...) with the focus adjusted to infinity, will recover this virtual image. The final number of magnifications will be the constant magnification offered by the telescope multiplied by the number of magnifications on the small telescope. Example: 20x (Telescope magnification) X Small telescope magnification (20x) = 400x total. Note: The eyepiece of this small telescope can be replaced by a planetary camera or webcam (without the lens).

 

In the second drawing, we have another version of the *Strela converter. Now we no longer have the virtual image, but an image formed approximately 10mm from the last lens. This converter will be more efficient as the refractive index is higher, a very dense flint glass. This time, three lenses are used to make the converter.

Attached Thumbnails

  • Strela.JPG
  • Strela2.JPG


#55 RajG

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Posted 14 June 2020 - 06:24 PM

Here is a fast 90mm f/5.6 (500mm fl) apo objective. It is a 4-element 2-group design, basically 2 doublets back-to-back.

 

It is very well corrected from 435nm-707nm, with an equal-weighted polychromatic strehl of 0.94. It would be a great grab-and-go visual scope, and with a suitable flattener, it would make an excellent fast astrograph.

 

gallery_326571_13519_82416.jpg

 

gallery_326571_13519_1446.jpg

gallery_326571_13519_610.jpg

Attached Files


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#56 Aljr

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Posted 15 June 2020 - 12:53 PM

Hello! It's me again. I am the one who proposes to turn an achromatic telescope into an APOchromatic telescope, to introduce a Lateral Chromatic Aberration(LCA) into a Fraunhofer type lens close to the Focus, to correct this aberration immediately afterwards [(with other lens(es)]. This Objective lens has 90mm aperture and 800mm focal length.

 

That optimization is the furthest I can go: now the Violet 435 is corrected, but there is now a failure in the Blue 486. Scotopic vision is ON too. Instead of seeing a violet halo in large magnifications, we will now see a blue color. The "intrusive" color remains irritating!

 

Yes, I am trying to clone the CHROMACOR II device. Its secret remains a mystery. But I can conclude that I would have been successful if yours had an exotic glass with a refractive index greater than 2.0 or greater than that.

Attached Thumbnails

  • Strela90.JPG
  • Strela90b.JPG

Edited by Aljr, 15 June 2020 - 01:47 PM.


#57 Get Sirius

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Posted 15 June 2020 - 02:49 PM

    This is a 4 inch f/10 super-apochromat triplet design with one expensive glass and two very cheap ones.  It is well-corrected from .4000u through .7000u The front lens is Schott BK7 glass, the middle lens is Ohara FPL51 glass and the last lens is Schott SK5 glass. Ohara equivalents to BK7 and SK5 also work well. There is a small airspace between the first lens and the cemented doublet. On a curved image it is diffraction-limited over a 1.0 degree diameter field.  On a flat image it is slightly worse at the edge of the field.  By going to two different cheap glasses it is possible to get a cemented triplet design that is almost as good.  Then the first lens is Schott BK10, the middle lens is Ohara FPL51 and the last lens is Schott K7.  In addition the middle lens then has the same radius on both sides.  The simplicity of this last cemented triplet design has a definite appeal compared to a 4 lens design or an airspaced 3 lens design - fewer surfaces to coat, a very simple lens cell, and low cost except for that middle lens.  The OSLO file for both designs is attached.  A 6 inch f/12 design file is also included. Everything is in mm.   

Attached Thumbnails

  • schief.jpg.png
  • schief4.jpg

Attached Files


Edited by Get Sirius, 15 June 2020 - 05:50 PM.

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#58 Get Sirius

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Posted 16 June 2020 - 04:11 PM

     Here is an unusual design - a super apochromatic lens with only two separate radii.  The first lens is Schott BK7, the middle lens is Ohara FPL51 and has the same radius on both sides, and the last lens is Schott SK5.  The OSLO file for a 4 inch f/10 design is included here.  The two outer Schott glasses have Ohara glass equivalents and then it would be an all Ohara design.  By playing around with those two outer glasses it is possible to get almost the same performance with the last two lenses cemented and still only have two separate radii..  . 

    The 4 inch f/10 design is diffraction-limited on-axis from .4100u to .7100u.  The key to the great color correction is having all the glasses be low index and low dispersion.  The broader the spectrum being corrected for with apochromatic correction, the more you want to avoid the normal flint glasses and stay in the crown glasses end of the chart. 

Attached Thumbnails

  • common3.png

Attached Files


Edited by Get Sirius, 16 June 2020 - 04:28 PM.

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#59 RajG

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Posted 16 June 2020 - 05:22 PM

Here's a 100mm f/10 Steinheil doublet. I had previously posted this solution as an example on a separate thread on an Excel calculator for designing doublets:

 

https://www.cloudyni...gning-doublets/

 

This is an air-spaced contact doublet (not cemented or oiled). Polychromatic strehl of 0.95 over 435-707nm.

 

gallery_326571_13459_48412.jpg

 

gallery_326571_13459_186816.jpg

gallery_326571_13459_51324.jpg

Attached Files


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#60 Get Sirius

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Posted 16 June 2020 - 06:49 PM

That is a  nice doublet design.  I avoid using FPL53 glass and use FPL51 instead because 1) FPL53 costs 18X as much as BK7 while FP51 costs 11X as much.  Probably that difference between them increases for large diameter pieces. 2) both are soft glasses but FPL53 is the softer one, and 3) FPL53 has substantially worse chemical properties with respect to staining and other aspects of making a lens from it.  The last two factors may matter for someone who is not an experienced optical shop worker.  But if you are not deterred by this then FPL53 definitely allows for simpler designs such as that doublet versus a triplet. 

   For my 4 inch f/10 cemented triplet design with FPL51 glass that I posted recently here is a better performance version where the middle lens does not have the same radius on both sides.

 

.  

Attached Files


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#61 Get Sirius

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Posted 18 June 2020 - 07:27 PM

    Here is an interesting attempt to get an apochromat using the least possible expensive glass types.  It is kind of an academic exercise since the actual cost of an objective depends on several different factors, not just the cost of the glasses.  Almost all telescope objective designs with enhanced color correction use one or more lenses with very low dispersion with anomalous dispersion behavior.  And those ED glasses are very expensive.  Ohara FPL53 glass costs 18X the cost of BK7 glass while FPL51 glass costs 11X as much as BK7.  Those glasses have a very low index and are not just expensive, they are also soft and not chemically robust.
      The design shown here uses as its most expensive glass Schott LAK8, which is 5X the cost of BK7 glass.  It a high index glass and is a hard glass with good chemical properties.   It has anomalous dispersion and is the basis of an apochromatic design here, where it is paired with two Ohara glasses (BSM15 and BSM16) that are 2.5X the cost of BK7 glass and one very high index Ohara glass that is 4X the cost of BK7 glass and has anomalous dispersion.   Because the dispersion differences are smaller with these glasses than  with the very low dispersion ED glasses, the lens powers are higher and the tolerances would be tighter. 
      There are probably glass choices on both sides of the LAK8 positive lens that would allow the first two lenses to be cemented without any performance loss, since there is such a near match now of the 2nd and 3rd radii.  I have not tried to do that.  Then there would be a cemented triplet followed by the last single lens.

     The OSLO file is included here. The color correction is very good and it is diffraction-limited over a field about 1/2 degree in diameter from .4358u to .7000u for a 4 inch aperture f/10 design.  This is, again, kind of an academic exercise since glass cost is only one factor in the total system cost. 

    It looks like Schott and Ohara glasses that are described as being equivalent, such as the BK7 glass of Schott and the Ohara equivalent are actually almost identical and can be switched in a design with no effect.  But anomalous dispersion glasses that are billed as being equivalent are actually slightly different and they differ slightly in their anomalous aspect.  A very small difference but significant.  Schott LAK8 glass, the key to this design here, has an Ohara equivalent but it is just different enough so that the design needs to be changed to get back apochromatic correction.  Good to be aware of this.

Attached Thumbnails

  • lak8.png

Attached Files


Edited by Get Sirius, 18 June 2020 - 07:41 PM.

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#62 RajG

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Posted 20 June 2020 - 08:07 AM

Here's a fast 250mm f/3.8 (EFL 946mm) Mak Newt. I was trying to get a system that was well corrected for coma, but the meniscus became very thick (115mm!). So I split the corrector in two, plano-concave and plano-convex, which should be easier to fabricate than a Mak's meniscus corrector. This resembles a Houghton except for the fact that the concave lens is in front (unlike a typical Houghton); also the air gap is fairly large.

 

It is very well corrected on axis. Coma and astigmatism are also very low; the radius of the best image surface is approximately 1200mm.  Unfortunately there is some lateral color, a consequence of the large separation between the lenses.

 

I'm showing the spots and the ray analysis over the best curved surface below.

 

Perhaps someone can design a sub-aperture corrector that would fix the lateral color and flatten the field at the same time? I know that a simple plano-convex lens (roc 400mm) placed very close to the final image can flatten the field, but it doesn't fix the lateral color.

 

You can reply/comment on this thread:

 

https://www.cloudyni...-it-a-houghton/

 

gallery_326571_13570_40418.jpg

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Attached Files


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#63 Ed Jones

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Posted 20 June 2020 - 02:49 PM

A meniscus lens would work:

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  • Mak.jpg

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#64 Ed Jones

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Posted 05 July 2020 - 03:34 PM

Here's what could be done with a C11 primary.   The flat image is internal but now days they make small diam. cameras.

Attached Thumbnails

  • Jones ASC for C11 primary.jpg
  • Jones ASC for C11 primary b.jpg

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#65 Ed Jones

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Posted 21 July 2020 - 11:43 AM

Here's an idea: a telecompressor/coma corrector for newtonians. This shows a 10 inch F/4 parabolic primary and brings it down to F/2.6 and fixes the coma as well.  BFL is only 8 mm so it wouldn't work with DSLRs, at least those with a flip mirror (not sure about the mirrorless ones).  It corrects a 1 degree field (+/- .5 degrees) but no larger and has about 2% distortion.   Not exactly an easy project for ATMs however.

Attached Thumbnails

  • telecom6.jpg
  • spots.JPG

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#66 RajG

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Posted 23 July 2020 - 09:07 PM

100mm f/8 Steinheil doublet using fluorite and Schott N-KZFS2, a lead-free eco-glass. It is a contact doublet (i.e., not oiled or cemented).

 

Strehl ratio exceeds 0.9 for all wavelengths in the 435nm-670nm range.

 

By comparison, Takahashi's FC-100DZ (also f/8) has Strehl greater than 0.9 between ~460nm-670nm, but is below 0.8 at the g-line (435nm).

 

sml_gallery_326571_13893_12745.png  sml_gallery_326571_13893_11577.png

 

 

See also my post at:

 

https://www.cloudyni.../#entry10362069

 

Attached Files


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#67 RajG

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Posted 30 July 2020 - 10:12 PM

Here is a 92 mm f/6.7 (618mm fl) apo triplet using S-FPL53 and N-BK7 glass. It is diffraction limited (>0.8 Strehl) from 435nm-710nm, and Strehl exceeds 0.9 from 460nm-660nm. Peak Strehl is 0.9998 at 511nm. Spots are shown for 435-656nm range.

 

sml_gallery_326571_13965_2818.pngsml_gallery_326571_13965_2096.pngsml_gallery_326571_13965_41526.png

 

Post your comments and feedback on this thread: https://www.cloudyni...f67-apo-design/

 

Attached File  TripletFPL53NBK792mmf6.7.len   1.39KB   4 downloads


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#68 RajG

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Posted 31 July 2020 - 02:11 PM

Paul Peleuba pointed out on the refractor forum that Roland Christen uses FCD100. So here's a re-worked version. FL increased by 1mm. System performance, spots etc are virtually identical, so I'll only post the specs and OLSO file.

 

sml_gallery_326571_13965_11088.png

 

Attached File  TripletFCD100NBK792mmf6.7.len   1.45KB   5 downloads



#69 Get Sirius

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Posted 01 August 2020 - 11:27 AM

It is possible to have some common radii in that design with no loss in performance.

 

 

*LENS DATA

SRF      RADIUS      THICKNESS   APERTURE RADIUS       GLASS  

 

OBJ       --        1.0000e+20    4.3634e+17             AIR  

  

  1     271.633190     9.000000     46.000000 A         N-BK7 C  
  2    138.456715     2.691446    46.000000             AIR    

  3    138.456715    17.000000     46.000000          S-FPL53 C  
  4   -226.247543     2.845085    46.000000             AIR    

  5   -226.247543     9.000000     46.000000           N-BK7 C  
  6   -863.721718   593.722000     46.000000             AIR     

 

IMS       --            --        

 

- Dave               


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#70 Mark Harry

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Posted 02 August 2020 - 05:09 AM

I know this is a non-discussion thread, but to me, this is an example of the very best that Cloudy Nights could have for a thread.
Utterly fascinating! (my 2¢ !)


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#71 RajG

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Posted 02 August 2020 - 07:01 AM

Here is a cool example of the design tradeoffs in my previous post. Take the lens from my previous post but reduce the air gaps slightly, to 0.7mm. The peak Strehl of 0.9998 is now at 546nm (e-line). It is no longer diffraction limited at 435nm (strehl 0.665), but is diffraction limited from ~460-710nm. It is unlikely that you'd be able to notice the difference between these two versions visually.

 

sml_gallery_326571_13965_3032.png

 

Attached File  TripletFPL53NBK792mmf6.7E.len   1.38KB   5 downloads



#72 RajG

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Posted 02 August 2020 - 10:35 AM

The Herzberger-Hoadley  f/5 patent design from 1949, at the original 100mm focal length & scaled up to 250mm. This is an awesome lens. The 250mm with a suitable field flattener would be a cool alternative to the WO Redcat. Spots shown from 435-707nm.

 

100mm version:

 

sml_gallery_326571_13982_6509.pngsml_gallery_326571_13982_37755.png

 

 

 

250mm version:

 

sml_gallery_326571_13982_28755.pngsml_gallery_326571_13982_24319.png

 

Attached File  Herzberger Hoadley 100 f5.len   831bytes   3 downloads

 

Attached File  Herzberger Hoadley 250 f5.len   653bytes   3 downloads


Edited by RajG, 02 August 2020 - 10:49 AM.


#73 RajG

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Posted 02 August 2020 - 06:23 PM

Two fast f/5.6 triplets, SFPL-53 & BK-7, 100mm & 92mm aperture.

 

https://www.cloudyni...triplet-design/

 

92mm:

 

 

sml_gallery_326571_13985_21440.pngsml_gallery_326571_13985_69446.png

 

100mm: 

 

sml_gallery_326571_13985_4662.pngsml_gallery_326571_13985_370.png

 

Attached File  TripletFPL53NBK792mmf5_6.len   1.44KB   4 downloads

 

Attached File  TripletFPL53NBK7100mmf5_6.len   1.44KB   5 downloads



#74 RajG

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Posted 03 August 2020 - 09:59 AM

Improved version of the 92mm triplet, now fully diffraction limited (>0.8 Strehl) from 435nm-656nm. Peak Strehl of .99 at 510nm.

 

sml_gallery_326571_13985_12035.png

 

Attached File  TripletFPL53NBK792mmf5_6Improved.len   1.5KB   4 downloads


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#75 RajG

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Posted 03 August 2020 - 10:04 AM

Benach requested an 80mm f/5 design, so here it is. Basically diffraction limited from 404nm-707nm, spots shown over that range.

 

 

sml_gallery_326571_13985_9088.pngsml_gallery_326571_13985_18535.png

 

Attached File  TripletFPL53NBK780mmf5.len   1.46KB   4 downloads


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