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Mike Loffland
Web Guru (Astronomics)
Reged: 09/03/04
Posts: 2080
Loc: Norman, Oklahoma
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A New Refractor Concept: "The Wall Hypochromatic Refractor"
By: John Wall
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sludlinger
journeyman
Reged: 05/29/08
Posts: 5
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This is an old idea that didn't work 150 years ago and will not work today. Foolishly, I actually tried to ray trace it - nothing. Try it on a star and you will be very disappointed.
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GJJim
scholastic sledgehammer
Reged: 09/09/06
Posts: 907
Loc: Western CO
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It does offer performance slightly better than Galileo's refractor. 
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gatorengineer
scholastic sledgehammer
Reged: 02/28/05
Posts: 880
Loc: Hellertown, PA
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Work is a relative term I guess. It appears to be a variant of a Petzval with a radically longer focus front lens. If the color correction is reasonable, it could prove a very affordable alternative to an achromat...... I think it bears further looking into before bashing, especially if the second set of lenses could be commercially available.... I smell possibilities of an 8" achromat for under a $1000.....
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20" F5 Dob
16" Dob in pieces
Comet Catcher
MN71
12" Doc Clay Sky Patrol MEADE SCT
12.5" F4 Newt under construction
Siebert 45mm Binoviewers
Lots of binos---
Optics Past - 8" Stf Mak, 4" B&W triplet, 6"Schmidt newt, 12"LX200, C8, Meade LX10-10", 10" MEADE ACF, SN8, TAL150K, Orion 150MC, Jason 60mm refractor, ATM 6" F8, WO 110FLT, 92mm Off Axis Newt, Televue Genesis, Nikon 20x120 bino's, 15x110 Boarderguards, Kuhne Flaks
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 370
Loc: UK
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Horses for courses, try making one! you might change your mind, I am fully aware of it's short comings, but it is definitely better than a Galileo, in fact it is as good as some achros now on the market, I have made comparisons, A large 100mm binocular showed about the same degree of colour at the edge of the field. The OSLO thing again, but reductionism does not tell you what it is like to look through it. Star images now, you are wrong, I have star tested it, and was completly surprised to see that star images were free of colour exhibiting very tiny pin pricks of white light, bright stars look like sparkling diamonds, and are also very tiny, I expected to see disappointing star images as you predicted, not so amigo. I am interested in a reference of the system you made mention of , that it was tried 150 years ago, could you oblige source refs please. The merit of the Hypo is that it will make a very cheap and useful refractor that ATM's can make to get a feel for refractor construction. Finally, I have one hypo that is a 'grab and go' for looking at trhe moon or some interesting object tha is worth looking, including terrestrial.
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 370
Loc: UK
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Gatorengineer, hi,someone with a positive attitude at last. Take care, the long focus OG must be at least F:40, I recommend that you do not go above 5 inches. I have made a 5 inch Hypo, and fitted the optics into a case about 30 inches long, the folding flats need not be high precision, also don't go above X40 mag, this scope in definatelyn in the low power wide field intermediate aperture range.
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 370
Loc: UK
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Sludlinger, the Hypo is not a Petzval dialyte as you suggest. it has not flint lens in the system, and works by suppressing colour not correcting it. The sysrem comprises a singlet OG and a bino OG doublet, the doublet does not correct for colour it suppresses it, the Hypo is a newv idea.
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 370
Loc: UK
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It seems that reviewers of the article are taking one glance at it and then jumping to the conclusion that I have dug up a design by Alexander Rogers circa 1828. The similarity is such that one can jump to that conclusion, so I stress, read the article carefully and take notice of what I am saying, take a careful look at the diagram that compares the magnitudes of longitudinal chromatic aberration for a simple OG, the Hypo, and a control lens having a similar EFL as the Hypo. Nowhere is there a correcting flint lens near the reduction lens, there isn't one! so it is not a dialye , a Petzval or an Alexander Rogers. The similarity is purely coincidental. Color correction as such, is achieved by reducing the distance between the red and blue focus by use of a reduction lens, the fact that the amount of reduction is smaller than common sense would have it is exceptional, and this "effect" is the mainstay of the design.
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GJJim
scholastic sledgehammer
Reged: 09/09/06
Posts: 907
Loc: Western CO
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What exactly is an 8" f/40 refractor suited for?
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arpruss
scholastic sledgehammer
Reged: 05/23/08
Posts: 853
Loc: Waco, TX
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Quote:
What exactly is an 8" f/40 refractor suited for?
It wouldn't be F/40. The objective lens would be F/40, but the EFL would be much lower.
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Coulter Odyssey 13.1" split-tube
Coulter Odyssey 8"
Home-made 7.8" F/4 dobsonian travel scope
Home-made 68mm F/5.3 achro (typically used as finder on 13.1")
Skymaster 15x70
BPTs4 8x30
32mm Plossl, 30mm Rini, 27mm Kellner, 13mm Hyperion, 6mm TMB/BO Planetary, Owl 2X Barlow
Palm TX with AstroInfo and RescoViewer
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davide
member
Reged: 06/17/08
Posts: 11
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In my opinion it was not fair to compare the new system with a single lens at F:3. I think it would be more interesting to see if the Wall Hypochromatic Refractor has a color correction better or similar to a standard achromatic doublet with the same diameter and focal length (127/380 in the article).
If it is the case, the advantage of the Wall Hypochromatic Refractor would be the lower cost (hopefully) and the disadvantage the larger dimensions.
Is it correct?
Is the large lens at F:30 or F:40 available commercially?
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Jim Rosenstock
Post Laureate
Reged: 07/14/05
Posts: 3709
Loc: MD, south of the DC Nebula
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IMO, davide is asking the right questions.
Personally, my knowledge of optics and optical theory is rudimetary at best, and my ATMing skills don't go much beyond building a simple Dob, so I'm not the one to evaluate this design, or to execute a prototype. I hope one or two such folks are reading this thread, though. 
To me, the $64,000 question is "What will this do better and/or cheaper than anything that's currently available?"
Awwww Heck. It's pretty tough to observe anything through a *theory*. Who's gonna *build* one??
Jim
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 370
Loc: UK
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Jim Rosenstock, Hi. I have built three prototypes,all of them give surprisingly good results, otherwise I would not have published the idea in the first place. Star images are tiny pinpricks of white light, larger stars sparkle like Sirius on the horizon, but are still very small dots, that is how serious the color is in this scope. Now, let us get the point straight, the hypo is not a rival to the apo, or even well corrected achro, it is a scope that has a little color left in the image towards the edge of the field, it is a cheap and cheerful scope that gives good results, after all it is made up of one weak lens and a bino OG! it is a fun scope, like a low power dob, ATM's can make them and get a feel for refractor work. The hypo is a low power wide field scope and it fits into the intermediate aperture range, from 3inches up to six, no more at the present, how many of you have a six inch refractor costing about $50! As for the OG, it has such a shallow curve that that it can be made easily, and you can use float crown glass, you need two folding flats to reduce the length of the tube, these need not be 20th wave but several waves in fact I make the flats by grindind and polishind two peices of glass and leave it at that, I have found no degradation. After all ,you accept spectacles without complaint, have you seen the colour at the edge of the lenses, and an OSLO analysis...well!    
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 370
Loc: UK
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I think it only fair that you guys see some evidence of the performance of the Hypo. So here are some pics, one is a shot of a window 55m away at a power of X25, the scope is a 5inch F:3 with an EFL of 381mm, also the scope is the instrument that I used,it is 36 inches long. The moon shot was taken with a 76.2mm aperture Hypo, F: 5.1 EFL 388MM at a power of around X50. The moon shot is blurred due to the camera being hand held with a prevailing wind, but the visual image is extremly good, note that there is only a slight colour fringe around the limb of the moon.
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 370
Loc: UK
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and
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 370
Loc: UK
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finally
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 370
Loc: UK
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A final note. I was for some years night assistant on the 28 inch refractor at Greenwich, and the moon image in this scope had more colour than the moon shot I have submitted.
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davide
member
Reged: 06/17/08
Posts: 11
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I did few analysis with OSLO: indeed a large lens few meters in front of an achromat increases the chromatic shift just a bit.
If I have well understood, the purpose is to upgrade a 60 or 80 mm achromat using a low power 120 or 150 mm lens (and a couple of flat mirrors).
What about placing only one mirror in front of the OG and keep the telescope fixed? Like here:
http://home.isoc.net/%7Eejones/A%2010%20Inch%20Window%20Scope3.htm
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 370
Loc: UK
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I disagree with you about shifting the CA just a bit, a typical Hypo will decrease the CA at about a 60 times reduction, one scope I set up on the optical bench has an aperture of 100mm at F:40, and will have a RtoB shift of 63.7mm as calculated, the reduction lens placed at 50% focus has a focal length of 330 mm, this will produce a back focus of 288mm giving a focal ratio to the system of F: 5.78, and an EFL of 578mm, the red to blue shift at the back focus is 1.5mm, this is a reduction of 51 times.I am constantly getting results of OSLO analysis which is just not right!! I set up the optics on an an optical bench and measure the parameters of the system, for instance the Rto B shift of the OG agrees with calculation, and so does the Rto B shift at the back focus, furthermore, I will say again that the image quality is very good, but OSLO seems to say otherwise, who is right?, the numbers crunchers or the experimental evidence, I know what I would rather believe. Take another look at my pictures of objects photographed through the 100mm Hypo, and ask youself is this bad? 
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GJJim
scholastic sledgehammer
Reged: 09/09/06
Posts: 907
Loc: Western CO
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Here is a design that will produce a useful, large aperture refractor without exotic/expensive glasses. Unlike the Wall design, it does not have a soda-straw FOV and it could be used for astrophotography. Any amateur can build one of these from scratch, or if they're lucky, by using the right combination of surplus optics. The only drawback is length, and that could be addressed by folding the optical path.
http://astro.umsystem.edu/atm/ARCHIVES/APR00/msg00167.html
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