81 replies to this topic

[meade4ever]

I have just received a 4" hypochromat today made by John Wall himself.

 

It is not a coincidence if the topic title looks like the one used for the Zerochromat.

John Wall is a brillant UK optician, inventor of the crayford focuser and the retrofocal dialyte system that Peter Wise used to make the Zerochromat refractor.

 

If the Zerochromat is in the upper level of the refractor family, the Hypochromat is on the other side.

It can be seen like a RFT telescope,  used for the same targets as the fast achro refractors (comet finder) but much cheaper (thousand of $ for an 250mm achro vs  a few hundred $ for my 250mm hypo, see atm forum).

The Hypo's philosophy is to make a very cheap, fun and easy to build refractor.

 

Like the Zerochromat, the Hypo use a thin single lens made from ordinary crown glass followed by a reduction less assembly made with one or two smaller achro objective (50mm binocular glass).

Typical powers are X20 to X50, depends of the OG focal lens.

 

 

 

More to come

Louis

 

 

 

Edited by meade4ever, 02 October 2014 - 11:16 PM.

[Mark Harry]

Very educational type to get aquainted with. A lot can be learned about basic optics as well as abberations present with simpler lens systems. Hope this thread stays up.
Mark

[meade4ever]

Thanks Mark.

 

Here is a sketch of the Hypo on an alt az GOTO mount.

The observer is looking downward when the telescope points at zenith.

Edited by meade4ever, 02 October 2014 - 11:16 PM.

[meade4ever]

The tube is a lightweight wood tube that can be splitted in the middle into 2 equal lengths of around 700mm each for ease of transporting.

A flat mirror is used to reduce the overall length of the OTA and can be adjusted for collimation.

 

 

Edited by meade4ever, 02 October 2014 - 11:16 PM.

[Psion]

THERE is older topic with more information.

[hottr6]

I have just received a 4" hypochromat today made by John Wall himself.

 

And all we get to see are rough drawings on napkins???? 

[meade4ever]

The OG lens cell is 130mm diameter, machined from high impact industrial polythene block :

Edited by meade4ever, 02 October 2014 - 11:17 PM.

[meade4ever]

The tube made with wood is open for lightness, below one of the two parts that support the focuser and mirror :

Edited by meade4ever, 02 October 2014 - 11:17 PM.

[Starhawk]

Huh?

 

-Rich

[GlennLeDrew]

A telescope restricted by its color aberrations to only the lowest powers is awfully inefficient when so long/bulky. One half of a 25X100 bino is pretty much the equivalent of the 100mm Hypo, and can fit into some deep overcoat pockets. If a telescope must be long, it had better be able to operate at higher magnification.

[meade4ever]

May be Glenn, but how much would you pay, if you can find one, for a 100mm binocular objective ?

The cost for a 4" hypo (lenses) do not exceed  $30 (only $25 for a 6" lens at surplusshed) and can provide fun for those who will build one.

 

There was a thread a few weeks ago about a member who wanted to buy a 8" f6 achromatic refractor at thousands dollars.

I don't think that a such refractor can be used at high powers.

My 250mm hypo cost me 10% of this price, even if I'm not saying it performs as well.

At least that shows that some members may be interested by a low power refractor.

[meade4ever]

So here the parts before assembly, you can note the beautiful grey color that reminds me the Zeiss APQ :-)

 

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[meade4ever]

Here assembled, note the sticker !

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[meade4ever]

... and the crayford focuser made and signed by John

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[meade4ever]

finally the dewshield with the cap.

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[Psion]

It is pretty nice! I love solution like this. In these days almost everybody wanted clear APO and quite often forget for older nice optic designs.

[Mark Harry]

A singlet type Galilean is extremely long, and a HYPO not as much. For experimental purposes, I don't think the telescope's length has much to do with having fun. I built one out of scraps for less than $40. The bino achromat cost $35 of that!
   And I'm using it as a stepping stone by adding a negative crown element just past the reduction achro to make a dialyte- cost nearly nothing, save for making a couple tool castings to grind the added element. But it will be a DIALYTE instead of a HYPO. Big deal. I can leave it at my dark observing site, and if anything happens to it, I won't have remorse!
  Mine is 4.5" and about 60" long.
*********
  I'm also working on a self-designed 6.5" triplet, which will likely be around the same length when done. Though cost is minimal compared to an apo, it's up to almost $200 in scrounged documented glass already. With a 5" aperture mask, it should be as good as any apo out there. But I used singlets and hypos first to get a knack of designing before I even thought of starting this latest project. I imagine when done, the OTA should cost less than $1000. Better than having to buy a ready-made commercial one! Go ahead, and have fun. I fully encourage you to do so, and enjoy reading about your scope project.
M.

[starcanoe]

How well do these things work at low power?

 

Like 6mm exit pupil low power.

[meade4ever]

I have not yet tested this telescope, I have no mount here until next month.

However John has tested it before sending to me, he got great results (low CA) with a 20mm Plossl eyepiece which gives x17 (5.8mm exit pupil).

At an higher power x30, a little colour appears and it is better to use a yellow or orange filter.

 

I have used the 250mm a few times, the CA is well controlled at low powers, but the lateral chromatic aberation can clearly be seen w/o filter.

But the 250mm OG I have has a focal ratio of only F17. To get better result the OG should be F30 to F40.

 

Even with some CA and LCA the image is very crisp, that is what surprised me.

The other particularity is the huge depth of focus from infinity to the surface of the OG.

You can put a tape on the OG and get a clear image !
 

The final focal ratio of a hypo refractor is very low F/D=3.5 for the 98mm hypo, so it is better to use eyepieces made for fast telescopes.

[Aljr]

Would be interesting now, do astrophotography, we could see the true quality of the telescope. We know that the telescope is F/D=3.5 The time exposoure will be shorter for shooting DSO objects. I also agree, the telescope is a comet hunter.

[Balok]

I remember folded refractor from childhood, they are quite rare I think.

 

Great score.

 

Regards,

Balok

[meade4ever]

and no diagonal is needed.

 

I have just tried on the moon w/o mount so it was not easy to center the target.

 

I tried the 20mm eyepiece John made for me, the image was very clear, so I switched for a Meade OR 12.5mm eyepiece (x28) and I could see more craters.

So, I forgot John's advices to not use the hypo with powers exceeding x25 and I used the Meade 9mm (x40) and got even better results.

With the OR 6mm  eyepiece (x58) the image became softer because of the CA.

 

What I can say is that the CA is well controlled, but the LCA is very intrusive and degrades the image out of the center for a bright and extended object like the moon.

That being said, I have not tried to collimate the hypo, used OR eyepieces that are not well suited for a hypo refractor and no filter, with "high" powers.

[Mark Harry]

The lateral color can me minimized or perhaps eliminated by using a positive singlet either in front of, or just after the eyepiece.. This aspect can make a dialyte type scope just as good as any expensive apo or semi apo sold.  One trouble, the eyepiece so modified is limited to be used with just that scope.
M.

[meade4ever]

Mark,

 

Could you please give more details, what kind of singlet (focal length) ?

Any drawing ?

 

Thanks

Louis

[Crayfordjon]

Fixed eyepieces are not a bad idea, all binoculars have them,as do many telescopes.  Placing a small positive lens in front or behind the eyepiece does not compllcate a design that uses second hand lenses.