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Equipment Discussions >> ATM, Optics and DIY Forum

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ken hubal
Pooh-Bah

Reged: 05/01/07

Re: The Wall Hypochromatic Refractor works! new

[Re: Ed Holland]
#4365482 - 02/05/11 02:44 PM

I couldn't disagree with you more, Bill.

You obviously didn't grasp the context of what I was saying as well as its relation to experimenting with different optical designs(seems to be the norm on the refractor forum

), so I will repeat it agian. Part of the Scientific Method is experimentation, it is the "aperture" to finding out what works and what doesn't.

This applies to telescope critique in the strictest sense of engineering design as well.

Cheers!

Post Extras:

Starhawk
Post Laureate

Reged: 09/16/08

Loc: Tucson, Arizona

Re: The Wall Hypochromatic Refractor works! new

[Re: ken hubal]
#4365958 - 02/05/11 05:57 PM

There's no magic to this. What you are really doing is using the refractor as a focal reducer for whatever objective lens you have come up with. Beware on your f/# and focal length counts- you must calculate based on the actual objective, which is the front lens. Putting a 6" element in front doesn't turn a 70mm scope into an f/3. You have a 6" f/18 to f/24, depending on if you had an f/30 to f/40 objective and that's why it's low color. Not quite miraculous, but definitely possible.

-Rich

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Crayfordjon
Vendor - Zerochromat

Reged: 06/17/09

Loc: UK

Re: The Wall Hypochromatic Refractor works! new

[Re: Starhawk]
#4366850 - 02/06/11 03:16 AM

Ed if you use a singlet for the reduction lens you would get colour in the final image, It seems that the reduction is there, but the unaffected natural dispersion of the singlet would be added to that of the lower dispersion from the OG. No it would not work, I have tried it. A note: the quality of the image in a Hypo is highly dependant on the quality of the Achro reduction lens. I have not tried an APO yet.

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Crayfordjon
Vendor - Zerochromat

Reged: 06/17/09

Loc: UK

Re: The Wall Hypochromatic Refractor works! new

[Re: Crayfordjon]
#4366857 - 02/06/11 03:33 AM

Starhawk, yes, exactly, why do that to an F:15 refractor, you reduce the F ratio to a smaller number and it would be less than F:15 of course.It works well for bino OG,s of say 7 inches focal length by two inches aperture, typically corrected for and working at F:3.5. The f ratio is dropped still further for7X50,s to around F:2.5, with little field distortion, but the effective focal length of the bino OG is increased, adding to the overall power of the system. The axiom is, the longer the focal length of the reduction lens, the larger the final RtoB separation is, and colour will start show significantly.

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Ed Holland
Pooh-Bah

Reged: 06/16/10

Loc: San Jose, CA and Oxford, UK

Re: The Wall Hypochromatic Refractor works! new

[Re: Crayfordjon]
#4367465 - 02/06/11 01:10 PM

Thanks for your reply John. The results seem to be what I'd expect based on intuition.
The fact there is a small amount of lateral colour (Spherochromatism by another name, no?) is possibly a clue to the design's success.
Thanks for an interesting discussion.

Ed

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Crayfordjon
Vendor - Zerochromat

Reged: 06/17/09

Loc: UK

Re: The Wall Hypochromatic Refractor works! new

[Re: Ed Holland]
#4369059 - 02/07/11 03:03 AM

Ed a final word, most of the lateral colour is due to the prismatic effect at the periphery of the OG lens. I found that LCA can be reduced by making the focal ratio about F: 40, this will give a very small included angle to the edge prism effect.

Post Extras:

Starhawk
Post Laureate

Reged: 09/16/08

Loc: Tucson, Arizona

Re: The Wall Hypochromatic Refractor works! new

[Re: Crayfordjon]
#4369338 - 02/07/11 08:55 AM

Long focal ratio refractors always had good color correction. As it is, the main push of the past 50 years of optical development has been on controlling aberrations to get to shorter focal ratios.

-Rich

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Crayfordjon
Vendor - Zerochromat

Reged: 06/17/09

Loc: UK

Re: The Wall Hypochromatic Refractor works! new

[Re: Starhawk]
#4380823 - 02/12/11 11:17 AM Attachment (110 downloads)

Using this design configuration, " the duplex" I got these images. The chromatic aberration has been reduced from 40mm RtoB for the OG to 1mm at the final focus, a reduction of 40:1

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Crayfordjon
Vendor - Zerochromat

Reged: 06/17/09

Loc: UK

Re: The Wall Hypochromatic Refractor works! new

[Re: Crayfordjon]
#4380825 - 02/12/11 11:18 AM Attachment (113 downloads)

and

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Crayfordjon
Vendor - Zerochromat

Reged: 06/17/09

Loc: UK

Re: The Wall Hypochromatic Refractor works! new

[Re: Crayfordjon]
#4380846 - 02/12/11 11:28 AM

The pic is a TV antenna at a distance of 55m,at apower of X20

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Crayfordjon
Vendor - Zerochromat

Reged: 06/17/09

Loc: UK

Re: The Wall Hypochromatic Refractor works! *DELETED* new

[Re: Crayfordjon]
#4380848 - 02/12/11 11:29 AM

Post deleted by Crayfordjon

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Crayfordjon
Vendor - Zerochromat

Reged: 06/17/09

Loc: UK

Re: The Wall Hypochromatic Refractor works! new

[Re: Crayfordjon]
#4380852 - 02/12/11 11:32 AM Attachment (101 downloads)

more images

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Crayfordjon
Vendor - Zerochromat

Reged: 06/17/09

Loc: UK

Re: The Wall Hypochromatic Refractor works! new

[Re: Crayfordjon]
#4380872 - 02/12/11 11:39 AM Attachment (98 downloads)

building colour shows on verticals.

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highfnum
Carpal Tunnel

Reged: 09/06/06

Loc: NE USA

Re: The Wall Hypochromatic Refractor works! new

[Re: Crayfordjon]
#4382735 - 02/13/11 07:48 AM

interesting
any fpl type glass involved?

Edited by highfnum (02/13/11 07:49 AM)

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Andy Taylor
Twisted, but in a Good Way

Reged: 09/24/08

Loc: The Pub. UK

Re: The Wall Hypochromatic Refractor works! new

[Re: highfnum]
#4382792 - 02/13/11 08:25 AM

John,

I have to hand at work a 150mm diameter F15 singlet coated lens and a 80mm diameter achro about F5.6.

Any way to work this up into a working scope? I've bench tested the two together but the results are poor.

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Alan French
Night Owl

Reged: 01/28/05

Loc: Upstate NY

Re: The Wall Hypochromatic Refractor works! new

[Re: Crayfordjon]
#4383443 - 02/13/11 01:28 PM

Quote:

Here is some data on the development of the Hypo to date, the best so far, here is the recipe, the LCA is nearly non existant, and is less than the secondary colours seen in an Acromatic.

I guess I don't understand the point here. A 50mm C-F corrected doublet of 330mm focal length has a focal variation (from C to F) of 0.19mm. A 71mm doublet of 420mm focal length would have a focal variation of 0.23mm.

Your "virtual" objective shows a variation of 0.76mm, which is more than three times a vanilla 71mm achromat of 420mm focal length.

Am I missing something?

Clear skies, Alan

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highfnum
Carpal Tunnel

Reged: 09/06/06

Loc: NE USA

Re: The Wall Hypochromatic Refractor works! new

[Re: Ed Holland]
#4383881 - 02/13/11 04:41 PM

i just tried this on ground targets
seems to work but im not sure what it means

is it just a big focal reducer or a weak corrector lens
i dunno

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Alan French
Night Owl

Reged: 01/28/05

Loc: Upstate NY

Re: The Wall Hypochromatic Refractor works! new

[Re: highfnum]
#4383947 - 02/13/11 05:09 PM

The color correction differs from a standard achromat. A typical achromat brings C (red) and F (blue) to the same focus, and the colors in between focus closer to the lens. In the case of the Wall instrument, it focuses like a singlet, with blue closest to the lens and red farthest away.

I played with the Duplex version in ATMOS, and got a focal variation of 1.13mm. A bigger problem is spherical aberration. Following the design and spacings shown, with all spherical surfaces it had three waves of spherical aberration in green light.

Here's what I did.
1) Designed a BK7 PCX singlet of 150mm aperture, 2557mm focal length.
2) Designed a C-F corrected 80mm doublet of 640mm focal length.
3) Designed a C-F corrected 50mm doublet of 300mm focal length.
4) Entered them into a final design with the spacings specified for the "Duplex."

Clear skies, Alan

Edited by Alan French (02/13/11 05:19 PM)

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gatorengineer
Carpal Tunnel

Reged: 02/28/05

Loc: Hellertown, PA

Re: The Wall Hypochromatic Refractor works! [Re: Alan French]
#4384208 - 02/13/11 07:15 PM

Interesting concept, a 20mm plossl can take if I am reading it right an F2.24 light cone......But other than that very very interesting.

The issue will be is it just an academic issue or does the design scale?

I would be very interested in seeing a spot diagram for a 150mm F 4 to 5 scope, compared to an Achro and an APO....

Design is very Chinese manufacturing and materal (no fancy glass) friendly as well , so maybe soon we will have Wall-John-Astrotech $1200 6" refractor.... Sign me up for one..... This is the engineer talking......

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Crayfordjon
Vendor - Zerochromat

Reged: 06/17/09

Loc: UK

Re: The Wall Hypochromatic Refractor works! [Re: gatorengineer]
#4385046 - 02/14/11 04:37 AM

Andy, your bench test shows that the F number is too small, it should be at least F: 35 to 40. You will get LCA dominating.

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