351 replies to this topic

[Aljr]

Yes, this telescope works. Grab your telescope 60mm, 70mm or 80mm. Place a large lens 5" or 6" OG PCX Lens F:15 to F:40 in front of him and see what happens. Put your telescope that is about half the focal length of OG lens. Do not worry, the focus appears when you zoom in or out the lens telescope. I suggest that you use a simple PCX lens as eyepiece. For low / medium power the Telescope Hypochromatic Wall that has a contrast unique! I say it works. See for yourself.

My name is Aldevio C JR. I am 39 years old.
I am an Brazilian Amateur Astronomer.

Regards to all!!

OG PCX LENS

[Aljr]

The Wall Hypochromatic Refractor. The Wall Hypochromatic Refractor.

[ken hubal]

Hi Aldevio:

I've successfully used this design for spectrographic work and have continued to experiment with the design on the optical bench with good results. Other projects and poor weather conditions here in Northern Ohio have prevented further use for the time being.

Wishing you continued success!
Ken

[TonyF]

I had a spyglass from the 70's I mail ordered as a kid that had a similar lens arrangement.. It was hella long! A Comical Capt Jack!

TonyF

[Cotts]

I wish to understand this type of telescope. I put the single, very inexpensive 6-inch lens from Surplus Shed in front of my 80mm William Optics FD refractor (f/6) and I have a color-free 6-inch refractor? With all the light gathering and resolving power of a 'normal' 6-inch refractor?

Is that approximately correct?

Simply amazing!

Dave

[Aljr]

Hi Mr. Cotts.

I believe these questions are best answered by the John Wall. But He is very busy. He works all the time! I can say that the amount of light that reaches the eyepiece, is equal to a refractor 6". As for the colors is a touchy subject. I believe that until now, this Hypochromatic Wall gets to have higher contrast than a refractor 6" for low power (50X or 100X). But if we have (200X or 300X), I believe that is an issue that should be further investigated. On the other hand, John Wall said that this Hypocromatic Refractor=low cost but good quality would be an alternative, another side, another way. A Refractor 6" can cost up to here in Brazil, between US$1,000 and US2,500 (+ tax + shipping + fees). By other hand, the focal length of your William Optics 80mm F / 6 will be smaller than 80mm x F6 = 480mm. The focus of the system will go inside the tube of the telescope. It is necessary to improvise a short tube.

Thanks.

[Crayfordjon]

WOW folks, I thought the Hypo was dead in the water, especially after the roasting I got from some of the critics of my paper< see "A new refractor concept"> in the articles forum. I have refined the design so that very little colour remains from the LCA, the main points are that the singlet should be a low dispersion glass, BK7 or lower,the focal ratio of the singlet should not be less than F:40, F:30 is the absolute minimum, the achromatic reduction lens must be of good quality, this doublet is placed at half the focal distance of the singlet, it can work even better if placed nearer to the singlet, and the focal length of the reduction lens is no greater than 400mm. The folding flats if you need them, ( not for 75mm aperture ),need only be 1/2 wave, I made my flats by just grinding and polishing then testing with helium wavelength against a master flat, I was satisfied with six of more waves to commercial standard, it made no difference to the image, also the singlet needs no special treatment. The Hypo is a very user friendly scope to make and all tolerances are very forgiving.

[Ed Holland]

Interesting. I read the original thread and felt it received a rough ride for such a novel idea...

My hand-waving argument for how it works is that the reduction achromat is used in a position where the incident rays are converging. Of course it's design parameters, (assuming an off the shelf well corrected design), will assume parallel rays from the object i.e. it is corrected for infinity. In its hypochromat application it is able to behave as if over-corrected, which counteracts the CA introduced by the large slow singlet at the front of the 'scope.

Does that make sense?

Ed

[BillP]

WOW folks, I thought the Hypo was dead in the water, especially after the roasting I got from some of the critics of my paper< see "A new refractor concept"> in the articles forum.

There are always critics. Remember that critics don't innovate, they just criticize, so they aren't do-ers. So pay little attention. Remember all the critics of the round Earth idea?! Remember all the movie critics that are film makers? Zero? What you are working on is a great concept.

[ken hubal]

Critiquing a particular design doesn't necessarily indicate a lack of innovation. It DOES indicate a willingness to constantly improve and refine a particular design or design concept by accepting or discarding certain functional principles. This is part of the Scientific Method. It is the "aperture" to finding out what is correct and what works most efficiently based on the optical properties employed in a given telescope design.

The statement that "critics aren't innovators or do-ers" is quite shortsighted and simply incorrect.

Comparing an optician who likes to experiment based on what I have mentioned to a movie critic is also an invalid, if not unscientific analogy!

[Ocram]

I have written an email to Mr Wall today, but here the gist of my mail. I belive the power of the hypochromat lies in the fact that it can serve as a telecompressor/amplifier for a small refractor. As such using an 130mm f40 lens with an 70mm f5 achromat midway between the focus of the f40 lens would work out to give the effect of an 70mm f3 albeit with approx 3,5 times the lightgatheringpower.

Doing the math using said contraption with a 21 ethos would give a TFOV of abt 10 degrees at 10x.

Can you say rich-field telescope??
An ideal comet-hunter or scope for low power variable star observing/nova-hunting.

Maybe I got all the maths wrong but I hope to get a mail from Mr Wall soon with his feedback and numbers.

[johnnyha]

Sounds great but I think the real challenge is folding it all up into a usable package. Or maybe it would be just cool to have a looong achro refractor that is f/3 with virtually no color? Hmmmm...

[timwetherell]

especially after the roasting I got from some of the critics of my paper

long, long ago when I was a professional scientist I learned that generally speaking the more "out side the box" an idea was the more it got roasted regardless of what evidence there was to support it. Mediocraty on the other hand, was always warmly welcomed!

all the best

Tim

[Crayfordjon]

Hi Ed, how the hypo works is this, We have a long focus weak OG, ther converging uncorrected ray cone is intercepted about halfway along the focal length by an achromatic doublet, such as an ex bino OG. The uncorrected ray cone is condensed into a short focal length typically about F:5 or F:3 depending on the f/l of the doublet. The R to B focii are usually reduced from around 68 mm to 1.0mm or even 0.5mm , the scope is not corrected , all that happens is that the CA is so small that it can be used at low powers without noticable colour, say, at X25 to X30. The down side is that lateral chromatic aberration is not suppressed, and the only way to do this is make the focal length of the OG long, I found that F:40 did this well.

[Crayfordjon]

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.

Attached Thumbnails

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[Crayfordjon]

One of my Hypo's, the tube is 38 inches long.

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[BillP]

The statement that "critics aren't innovators or do-ers" is quite shortsighted and simply incorrect.

Comparing an optician who likes to experiment based on what I have mentioned to a movie critic is also an invalid, if not unscientific analogy!

I would disagree on both points On first point there are as you know constructive critisisms and simply critisisms (like movie critics). Those whose purpose is not to improve but simply provide nay-say critisism are never a good thing. In the context of my response thought it would be evident as such...espeically with things being said like "doesn't work". So not short sighted and not incorrect within the context of the poster I replied to.

On your second point not sure what you are referring to since nothing in this thread relative to your comment. Seems you think I'm talking about the engineer who experimented and came up with this novel design. Not so. To him I Again, the proper context is to those making non-constructive critisisms about things new. So think you are missing the context of my message as not related to experimenting opticians.

As a side note, dismissing something because it does not or did not follow a scientific approach has no bearing on truth or correctness. The scientific method is simply a tool that both gets us to an answer and sometimes leads us away from the answer depending on the circumstance. So it is not a be all and end all...unless we make it into scientism (i.e., a belief structure). But this is a topic for another thread

[Ed Holland]

Thanks John, for your reply.

I read the details in the original postings, and other links found on the 'net., so have a grasp of the concept... perhaps not complets. I'd just wondered that the bino OG was able, incidentally, to reduce the CA introduced by the large objective as a result of its intercepting converging rays from the large objective, rather than the parallel object rays for which it was designed.

Now I think I see what you are saying - the R & B ray focal points are reduced in distance by the focusing action of the bino OG - or put another way, because of the effective reduction in f number at that point - Do I have it right now?

Cheers,

Ed

[Crayfordjon]

The entering ray cone into the reducion lens is converging, and this has, incidentally the effect of shortening the focal length of the reducing lens, But back to the point, we have a bit of a conumdrum here, the high reduction of the B to R ratio is not related to the ratio of the focal ratios of both the OG and the reduction lens, this being 24:1, also it is not related to the ratio of the focal lengths of the OG and reduction lens, which is, 12.25:1, yet the ratio of the B to R dispersions are 75:1 ! There is some higher order operating here, and I have not any idea at the moment why this is, it can be resolved by analysis no doubt, and I shall spend a quiet time getting into this problem. Calculation, and bench experiment show that the high reduction happens.

[Ed Holland]

This is an interesting discussion - thanks again for your reply.

May I pose a thought experiment for you.... or indeed one for the optical bench: what is the performance if the reduction lens is a simple singlet? Is there still a reduction in B - R focal spacing?

Ed

[ken hubal]

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!

[Starhawk]

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

[Crayfordjon]

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.

[Crayfordjon]

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.

[Ed Holland]

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