133 replies to this topic

[Crayfordjon]

There is a new experimental refractor concept, it uses a very weak objective lens which is a single plano convex 100mm aperture imager of around F:40, this is not corrected for color, but if a small achromatic 7X50 binocular objective is placed half way along the focal length, the resultant F:6 image is very free of colour, the difference between the red and blue focus is only about 1mm, the color reduction is many more times than it should be, it can be reduced to 0.4mm by addition of a second lens. It is known as a "Wall Hypochromat", it is not a dialyte or a schup' as there is no flint lens in the system, the color is suppressed not corrected for. There is a little color left in the system and this can be ignored if you are not too fussy, it will make a superb RGB filter scope. The main thing it is very cheap, I have made a 5inch version.The system is in it's infancy and needs to be developed, how about it you ATM's out there. Ref to the Journal of The British Astronomical Association June 2009 vol :jump:119 No3. Wanna know more, discuss it with me.

[John Kemp]

Hi Crayfordjon - I was just about to email you to say that I think your suggestion of hypochromat is a better one than my arcane suggestion of elakhistochromat. You will no doubt have spotted that hypochromat(ic) already exists with another technical meaning, but this does not matter! Best wishes, John

[Crayfordjon]

Hi John, I am sorry not to use your beautiful description of the new system, but I felt that it would,be a bit of a mouthful,so after much brain damaging cogitation the option of Hypochromat seemed fairly apt, the 'Hypo' means below, "hence Below color" You have no doubt heard of Hyper chromatic effect where "hyper" means above, this is found in some systems where over correction happens, I found this on my research into dialyte systems where the blue and red foci are reversed.

[Crayfordjon]

Post deleted by Crayfordjon

[Crayfordjon]

The system was called a Parachromat, the name has been changed

[robboski2004]

There is a new experimental refractor concept, it uses a very weak objective lens which is a single plano convex 100mm aperture imager of around F:40, this is not corrected for color, but if a small achromatic 7X50 binocular objective is placed half way along the focal length, the resultant F:6 image is very free of colour, the difference between the red and blue focus is only about 1mm, the color reduction is many more times than it should be, it can be reduced to 0.4mm by addition of a second lens. It is known as a "Wall Hypochromat", it is not a dialyte or a schup' as there is no flint lens in the system, the color is suppressed not corrected for. There is a little color left in the system and this can be ignored if you are not too fussy, it will make a superb RGB filter scope. The main thing it is very cheap, I have made a 5inch version.The system is in it's infancy and needs to be developed, how about it you ATM's out there. Ref to the Journal of The British Astronomical Association June 2009 vol :jump:119 No3. Wanna know more, discuss it with me.

Hello John,

could you supply the perscription for you lens design ?
when you mention there is no flint in the system.......
what type of glas makes up the second part of the bino
objective ??
also if the final focal ratio of you system is F6 then
colour error has to be less than 0.4mm to even be as good as
a standard achromat.

look forward to further details.

all the best
Ian Robinson.

[Crayfordjon]

Diagrams of the hypochromat principle

[Crayfordjon]

Yes Ian. The objective lens is BK7 but a low dispersion glass would be better. It is plano convex and need only be ground and polished, figuring is unescessary. It is F:40 for reduction of lateral chomatic aberration The bino achromat is just that, no special features 7X50 binos are OK but higher powers are obtained with focal length of 330mm Coliour is not so bad as calculation would predict, the images are brilliant lit and the resolution is that for the objective not the bino lens as so is the resolution. there is some edge color due to lateral CA, so the weak lens must be just that.I have seem worse secondary residual color in a commercial grade 5inch refractor! Make one and try it, you will be surprised.. easy! I fold my Hypos down to one third of half the focal length of the weak og. My current Hypo is only 32 inches long in spite of a focal length of 6000mm.

[Crayfordjon]

Further info Ian, The scope is unique in that it has an enormous depth of focus ranging from infinity to a spot of tape tacked to the front of the Objective, it will even focus on anything inside the objective lens, in this case the ob lens is out of play and only the reduction lens is doing the focusing, however there is a serious loss of aperture if the focus is on an object less than the focal length of the ob lens away. I fold the optics in three by using two flats, but the flats do not have to be high precision, within one wave is quite adequate, easy to make.

[GJJim]

Amazing - the objective doesn't have to be figured, and the EFL is 6 meters!

[tim53]

I can't find anything on the internet about this design. Any pointers?

-Tim.

[George Kiger]

"it will even focus on anything inside the objective lens, in this case the ob lens is out of play and only the reduction lens is doing the focusing, however there is a serious loss of aperture if the focus is on an object less than the focal length of the ob lens away..."


I assume that focus can also be achieved past both the primary objective and the intermediate lenses, but in this case the aperture is reduced even further to the diameter of the observer's pupil!

[DAVIDG]

I played around with OSLO EDU and setup the design as described, that being a 100mm x 4000mm plano convex lens as an objective and achromat place 2000mm from the objective. I used an Edmund A32-886 50mm achromat which has 150mm focal length. This is a typical binocular achromat. I found the color correction to be fairly good but the effective focal length of the system is only 278mm which is not close to 6 meters. I also found that the 50mm diameter lens would be too small in diameter when placed at 2000mm away from the objective. Maybe I'm not understanding the design correctly ?
- Dave

Attached Thumbnails

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[DAVIDG]

Here is the performance graphs.

- Dave

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[rwiederrich]

Further info Ian, The scope is unique in that it has an enormous depth of focus ranging from infinity to a spot of tape tacked to the front of the Objective, it will even focus on anything inside the objective lens, in this case the ob lens is out of play and only the reduction lens is doing the focusing, however there is a serious loss of aperture if the focus is on an object less than the focal length of the ob lens away. I fold the optics in three by using two flats, but the flats do not have to be high precision, within one wave is quite adequate, easy to make.

Very interesting for sure. What if you wished to use a bit stronger plano convexed lens...and its focal length was shorter...will the system still work accoring to your descriptions?

Rob

[nytecam]

Hi CrayfordJon - your new scope got a mention a few weeks ago on this forum but thread got hijacked by a Schupmann fan You're the best to describe - hope to see you maybe this Saturday at Greenwich for annual BAA ExMet

[Crayfordjon]

Hi Tim 53, you will not find anything on the net because it is a brand new conception, and was published in the Journal of the British Astronomical association this year. I discovered the principle about two years ago and have been researching it since, this is it's first exposure to the ATM community.

[Crayfordjon]

Hi GJJJim, The objective lens is so weak that there would be difficulty figuring it, the Hypo system is very insensitive to errors of figure, but the upside is that only a very shallow sagitta is required on the front surface, easy peasy to make.

[Crayfordjon]

Hi George Kiger, yes you have hit the nail on the head, the aperture becomes very small when the system is focussed on any object a meter or so away.

[John Carruthers]

Hmm, I started a 150mm x 4m heliostat lens a couple of years ago, maybe I'll finish it and try your idea.

[Crayfordjon]

Hi DavidG, your understanding is OK, yes the red lens must be larger than 50mm to accomodate for the diameter of the field. The red lens does reduce the focal length from 6000mm to around the figure you have computed for, and the system is has a fast F: number, around F:2 to F:6 or so, depending which red lens you use: a note, you can put the reduction lens anywhere you want, the one half focal length of the OG is an optimum position, but I have placed the red lens at only one third the dist inside the prime focus, and conversely one third the distance away from the OG, it is a very loose system. Thanks for the analysis, I have only had one other ATM do one for me on OSLO.

[Crayfordjon]

Hi Rob, The F:40 option was arrived at because of the lateral chromatic aberration caused by the wedge effect of the periphial edge of the OG, acting as a prism, if you shorten the focus to say F:16, the CA will still be well suppressed, but the LCA will give unacceptable colour fringes to the edges of the images, the solution I arrived at was to make the OG very weak and at F:40 the LCA is hardly noticable. Now! if the Hypo is used as a filter refractor where images in only discreet wavelengths are required, eg, red blue green, He line,O111 etc, then the OG need only be F:16

[Crayfordjon]

Hi Nytecam, I am afraid I now live in Coventry, and going all the way down to Greenwich is not an option, I have been down twice since I moved up here, and did a nostalgiasville tour of the ORO where I worked for seven years and I have used the 28 inch refractor many times.I was the optical engineer there, and built equipment for the planetarium and 28 inch. About Crayfordjon. very very dedicated ATM or 'TN' I have been making telescopes since 1953. lost count on how many I have built. I worked on retrofocal dialytes ( Schup deriviative)using all refracting optics, this enabled me to make the thirty inch refractor dialyte which is at the Hanwell Community Observatory near Oxford. I am also the English amateur so described who invented the Crayford focuser, go into the website of the Crayford Manor House Astronomical Society for further details; telescope making? is there anything else in this universe?

[GJJim]

Hi GJJJim, The objective lens is so weak that there would be difficulty figuring it, the Hypo system is very insensitive to errors of figure, but the upside is that only a very shallow sagitta is required on the front surface, easy peasy to make.

Just curious, have you ever ground, polished and figured a mirror or a lens?

[Ed Jones]

How about a prescription for the skeptics?