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Equipment Discussions >> ATM, Optics and DIY Forum

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Mark Harry
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Reged: 09/05/05

Loc: Northeast USA
Re: Hypo/Dialyte testing discovery new [Re: Crayfordjon]
      #5553514 - 12/04/12 08:13 AM Attachment (49 downloads)

I'm using a positive meniscus crown BK7, 8" diameter. It has a 40"(~) ROC convex on the front, and a concave 120" on the rear. About 3/4" thick.
*******
Hey, lightning--- so far, I've made this thing by using just a grind/polish stand, a hunk of glass, and some grits. You could likely use a good piece of plate glass instead of BK7. The achro, I think I got hold of it for about $15 US; very cheap. Probably scavenge a binocular objective somewhere. So far, that's all I have in it. I did however, spend something on the BK7 chunk. If this thing -DOES- work well, I'd just as soon have a water-clear objective to keep the detractors at bay, and the rep intact!
I'll try to include the basic OSLO file:- using the 'zero power' dedicated achro.
M.

Edited by Mark Harry (12/04/12 08:15 AM)


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Mark Harry
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Reged: 09/05/05

Loc: Northeast USA
Re: Hypo/Dialyte testing discovery new [Re: Mark Harry]
      #5553533 - 12/04/12 08:30 AM

The file above should show the particulars of focal length, spacings, and radii. It could be folded with a flat for shortening up the finished scope.
*****
Jonesey sent me a file on a Ramsden eyepiece a while back. I have another file using a single achro from a Plossl, and one singlet, which maxed out the EDU's surface limit. Done afocally, it -APPEARS- to be correct, but I'm not 100% sure. But experiments with a std refractor, and low power eyepiece/positive singlet shows blue focusing first, or closer in across the field of view when using this singlet type eyepiece arrangement.
I sized the spotplots for both eyepiece and this scope using the same scale, and ran them thru the printer on the same sheet. Just quick and dirty, they overlapped nicely, and -should- compensate each other's lateral color problem.
As I said before, the singlet's distance from the eyepiece can adjust the degree of "compensation".
M.


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Mark Harry
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Reged: 09/05/05

Loc: Northeast USA
Re: Hypo/Dialyte testing discovery new [Re: Mark Harry]
      #5553546 - 12/04/12 08:37 AM

One provision:
The back side of the objective has hyperboloidal correction on it. IIRC, it's around -3.75 or so... shouldn't be a problem, similar to putting overcorrection on an 8" F.7.5: probably like correcting an F/4-4.5 which is quite achieveable. This makes the LSA's green and red-blue lines stand up nice and straight, as they should be. The delta, btw, is around .050"; quite respectable for even a std achro!
M.


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Mark Harry
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Reged: 09/05/05

Loc: Northeast USA
Re: Hypo/Dialyte testing discovery new [Re: Mark Harry]
      #5553616 - 12/04/12 09:24 AM

On further thought, I'm going to clean up the back side to a sphere, and perhaps experiment with a standard achro, and a piece of negative flint and see what happens. I can always aspherize the back side later if necessary. At least I can get the back side cleaned up, and reasonably accurate.
M.


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glennnnnnn
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Reged: 10/20/09

Loc: San Diego, CA
Re: Hypo/Dialyte testing discovery new [Re: Crayfordjon]
      #5553673 - 12/04/12 10:08 AM Attachment (28 downloads)

I had that image of the large single front lens stuck in my head, because it reminded me of the Angenieux retrofocus. The difference being that the large objective is a negative lens producing a wide-angle short-focuser. Rich field when applied to a telescope?

Edited by glennnnnnn (12/04/12 10:52 AM)


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Crayfordjon
Vendor - Zerochromat
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Reged: 06/17/09

Loc: UK
Re: Hypo/Dialyte testing discovery new [Re: Crayfordjon]
      #5553734 - 12/04/12 10:46 AM Attachment (37 downloads)

I have said this on another thread. I have developed the Hypo as an imaging scope, optical system comprises a 12 inch F:7 singlet OG in made from BK7, and another short focus 6 inch BK7 singlet half way along the focal length. The digital highly chromatic image was processed in the computer to produce the image shewn. I used alternate optical tricks to do this, to illustrate that there are alternate ways to skin a cat.

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tim53
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Reged: 12/17/04

Loc: Highland Park, CA
Re: Hypo/Dialyte testing discovery new [Re: Crayfordjon]
      #5553795 - 12/04/12 11:25 AM

That would be impressive if it were an RGB image.

-Tim.


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Mark Harry
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Reged: 09/05/05

Loc: Northeast USA
Re: Hypo/Dialyte testing discovery new [Re: tim53]
      #5554018 - 12/04/12 01:41 PM

I smoothed the back side with a polisher slightly less than 6" diameter; which made the central 5+ inches fairly spherical, with the area out to the edge with an increasing radius, about .125" or so on the ROC. At least it's good and smooth, and a faint diffraction line is on the same side as the KE blade. Reasonable.
Placing it in the stand and setting up the achro/eyepiece end of things, It looks even better than before. A bit better contrast.
I also used the achro by itself on the target. Of course it has far less color issue, but detail was just a smidge less than with the meniscus objective. The target made this fairly straightforward to accomplish.
Lateral color (with meniscus) is still a problem- more so than the longitudinal color at present. The meniscus appeared to be distinctly brighter- not sure the exact reason; I wouldn't think it'd matter. Hmm.
Every once in a while when I have everything fairly well aligned, the small area in the central fov has very little/no lateral color.Looks nice there at low powers using 40+25mm eyepieces.
M.


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Crayfordjon
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Reged: 06/17/09

Loc: UK
Re: Hypo/Dialyte testing discovery new [Re: Mark Harry]
      #5554031 - 12/04/12 01:46 PM Attachment (31 downloads)

I did but not in the way it is normally done. I took three images in red green blue using narrow passband interference filters. Here is the green image

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Crayfordjon
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Reged: 06/17/09

Loc: UK
Re: Hypo/Dialyte testing discovery new [Re: Crayfordjon]
      #5554039 - 12/04/12 01:49 PM Attachment (32 downloads)

Just for illustration, an image in white light shewing the degree of CA in the system

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Gary Fuchs
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Reged: 05/22/06

Loc: Easton, PA, USA
Re: Hypo/Dialyte testing discovery new [Re: Crayfordjon]
      #5554057 - 12/04/12 02:04 PM

Quote:

There are a couple things that should be noted about the pics- both pertaining to edges. If you look close, you'll see an edge issue on the -LEFT- of the lens, right at the bevel. None can be seen on the -RIGHT-. A good way to make a quick test for gross edges without any testing.




Maybe I'm the only one that's missing the problem...could you be more specific? And what is the "quick test"?

Quote:

Obviously, this shows the edge problem is on the concave back side of the lens, which is only pad polished. The convex front has been pitch polished for a couple hours, and no such artifact can be seen on the right; nor is it in a position to be affected by the TDE of the back side. Cool, huh?




Do you mean the photo from the previous post, or the screen shot?

Quote:

Maybe if someone has doubts about the color correction in a refractor they have, this test could be used to make a rough check.




How do you mean "doubts about the color correction in a refractor"? Would your setup show something we wouldn't see just using the scope on say the moon or a bright planet?

Quote:

But I think this is falling on deaf ears.




Not at all. I enjoy reading about good new (or old) designs; especially ones I might be able to make myself; and especially if they're inexpensive.

But the designs have to be for scopes that have the potential to be really good performers and offer real advantages.
I've looked at most or all of John Wall's pictures and only a very few show even reasonable performance; and none look to be anything remotely better than what could be achieved by making a mirror out of that objective glass instead of a lens.

Is your design going to offer superior performance? Is it easier/cheaper to get a 12" or larger piece of BK7 than a suitable mirror substrate that size and the secondary, spider, and coating? And then maybe try to figure it to a hyperbola? Never mind mounting a 12"+ refractor.

I don't mean to be a wet blanket, and maybe if I understood more of the jargon I'd see the clear advantages...but so far I'm missing it.

Gary


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Mark Harry
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Reged: 09/05/05

Loc: Northeast USA
Re: Hypo/Dialyte testing discovery new [Re: Gary Fuchs]
      #5554250 - 12/04/12 04:34 PM

Your first 2 quotes of mine pertain to the pic of the 8" meniscus lens. I guess you just don't see it. In a private communication with someone else recently, who is very knowledgeable about testing and paying attention to what they can see when using their eyes correctly, plainly understood full well with what I'm referring to. If you saw it for yourself instead of just the jpeg picture, perhaps you would not be 'missing it'. Or, perhaps not. It's better if you had tested quite a few pieces of glass, and looked at a lot of lenses and paid close attention to the edges. It would certainly help to have this experience.
Your 3rd quote of mine referrs to the dot matrix that's set up about 35 yards away. I related how I made it. Try it for yourself, perhaps; and with a refractor or lens to reveal what I explained.
******
Now the reply to your 4th quote, first sentence is fine. That's precisely the purpose of this scope. But I and I think others would appreciate you refraining from singling anyone out, and posting something that can be construed as criticism.
*****
There is -NO- refractor that has absolutely -NO- color. In light of that you have discounted the main competitor for reflecting scopes. But there seems to be a -LOT- of folks in the refractor forum that says they are just fine, and they spend a lot of money on them. In essence you're telling them they made the wrong decision???

" for scopes that have the potential to be really good performers and offer real advantages"

Yes, if money is no concern to you; that may be a legitimate statement. But you also said "...especially if they're inexpensive."

So which is it? You get what you pay for. The best color correction in a refractor is gonna cost you!
This is intended for low to medium powers, and hopefully bridge the gap between John's Hypo and a good achro, for a relatively modest outlay. Evolve the concept, so to speak. It might work just by making a smallish piece of PCV flint to go with a standard achro reduction lens, and to make a crown positive meniscus of full size.
And just my 2 cents, I wouldn't make a mirrored telescope with a piece of BK7 lens substrate. Can be done, but there are better choices.
Regards,
M.


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Mark Harry
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Reged: 09/05/05

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Re: Hypo/Dialyte testing discovery new [Re: Mark Harry]
      #5554288 - 12/04/12 05:05 PM

I should add a bit more...
The achro reduction lens can be obtained from S/S for something like $20 or so,(80mm F/4~; to provide longitudinal color correction) and they also have a lot of various lenses- in various precision, and even coated. Maybe more than a dozen or so, in the area of $5-15 each to be used to compensate the lateral color at the eyepiece of both the Hypo and Dialyte as referred earlier in this thread. This should satisfy the inexpensive "advantage" and also address the color issues. (pays to keep -ALL- aspects in mind that have been posted...)
M.


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Gary Fuchs
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Reged: 05/22/06

Loc: Easton, PA, USA
Re: Hypo/Dialyte testing discovery new [Re: Mark Harry]
      #5554602 - 12/04/12 08:31 PM

Quote:

Your first 2 quotes of mine pertain to the pic of the 8" meniscus lens. I guess you just don't see it. In a private communication with someone else recently, who is very knowledgeable about testing and paying attention to what they can see when using their eyes correctly, plainly understood full well with what I'm referring to




I wouldn't call myself "very knowledgeable about testing"...but then this is an amateur telescope making forum and I'm pretty sure a number of us hope to learn here. I know I've learned plenty. Oh just for example that Texereau was wrong when he called the polishing tool we polish mirrors with a "pitch lap". ("For the past fifty years the polishing tool used almost exclusively by professionals and amateurs alike has been the pitch lap.")

I agree, I "just don't see it". That's why I asked.

Looking through a partially polished lens, through a window pane (or two?) at overexposed snow(?) on the ground at a very finite distance at what looks like a significant angle to the lens (which is supposed to be used at as close to infinity as we're likely to see) sounds to me like a questionable way to evaluate a lens. But then I'm not "very knowledgeable about testing", hence my asking. What I can see is the bottom of the window and through the lens that looks pretty straight. Same for the upright on the right side--which I understand was not in question. But what I see through the left side seems pretty ambiguous.

Quote:

If you saw it for yourself instead of just the jpeg picture




If the picture doesn't show it to an untrained eye (see above about the nature of this forum) then maybe it needs more explanation--which I don't think you provided.

Quote:

paying attention to what they can see when using their eyes correctly




Exactly why I asked for the explanation--so I can learn to use my eyes correctly and pay attention.

Quote:

Your 3rd quote of mine referrs to the dot matrix that's set up about 35 yards away. I related how I made it. Try it for yourself, perhaps; and with a refractor or lens to reveal what I explained.




Thank you. I actually read the entire thread twice, as carefully as possible for me, and the parts about the testing more. Now I see what you set up. I'll suggest using a printed sheet for an easier to make and cheaper target. Well, assuming you have a printer.

Quote:

Now the reply to your 4th quote, first sentence is fine.




Whew! Finally! Thanks!

Quote:

That's precisely the purpose of this scope. But I and I think others would appreciate you refraining from singling anyone out, and posting something that can be construed as criticism.




Understood. Will try to keep that in mind. But I think it was you that introduced someone into the thread at an earlier stage with what could be construed as if not criticism then certainly a disparaging remark:

Quote:

I am not to be credited for the basic idea of this design. John Wall (CRAYFORDJON) was the originator of it, and I'm simply trying to carry it to a next step, as it were; with a little improvement that could make it a legitimate acceptable adaptation of a refractor of largish aperture.




From my reading of many of John Wall's posts regarding his design, I got the impression--correct me if I'm wrong--that he thought the design was already an "acceptable adaptation of a refractor of largish aperture".

Quote:

There is -NO- refractor that has absolutely -NO- color.




Understood. Some can come pretty close though; and probably so close that human eyes can't detect the color.

Quote:

But there seems to be a -LOT- of folks in the refractor forum that says they are just fine, and they spend a lot of money on them. In essence you're telling them they made the wrong decision???




Oh no. Not my intention at all. I own a little refractor myself. Do any of those folks say their dialyte refractors are just fine? And if so, compared to what? Oranges?

Quote:

This is intended for low to medium powers, and hopefully bridge the gap between John's Hypo and a good achro, for a relatively modest outlay.




Would the outlay be significantly less than for a reflector of same or even smaller aperture? Because I'd rather have a fine performing 4" than a color-laden fairly sharp in the center 12" any day--costs being roughly equal.

Quote:

It might work just by making a smallish piece of PCV flint to go with a standard achro reduction lens, and to make a crown positive meniscus of full size.




May I have a show of hands for how many people here have made or feel confident in their ability to make a "crown positive meniscus of full size" versus say a decent 8" f8 mirror?

Quote:

And just my 2 cents, I wouldn't make a mirrored telescope with a piece of BK7 lens substrate. Can be done, but there are better choices.




Actually, I meant that for the cost of the BK7 an ATM ought to be able to find a "suitable mirror substrate" of a more usual glass: Pyrex, plate, whatever.

Cheers,

Gary


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Mark Harry
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Reged: 09/05/05

Loc: Northeast USA
Re: Hypo/Dialyte testing discovery new [Re: Gary Fuchs]
      #5554815 - 12/04/12 11:05 PM

That's just about enough, Gary. Thank you for your contribution to this thread.
M.


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Crayfordjon
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Reged: 06/17/09

Loc: UK
Re: Hypo/Dialyte testing discovery new [Re: Mark Harry]
      #5555043 - 12/05/12 03:22 AM

May I butt in here, it is no more difficult to make a singlet lens than a mirror, the downside is that for a lens you have to make two surfaces, and you can correct it by placing a flat in front and do the usual Knife edge or rhochi test, in this case the lens will be tested at infinity focus. A red filter will give reasonable one colour light for testing. You test for a flat figure.I usually figure the back or flat surface it is easier. The upside is that lenses are very forgiving, as errors are four times less damaging than those for a mirror, that is why a lens always looks good after viewing a distant object with an eyepiece before figuring. Mirrors on the other hand have to be well figured before they even perform reasonably well, and they are very unforgiving.

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David PavlichAdministrator
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Reged: 05/18/05

Loc: Mandeville, LA USA
Re: Hypo/Dialyte testing discovery new [Re: Crayfordjon]
      #5555281 - 12/05/12 08:40 AM

This is a good thread. Let's leave the snark at the door, please.

David


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Crayfordjon
Vendor - Zerochromat
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Reged: 06/17/09

Loc: UK
Re: Hypo/Dialyte testing discovery new [Re: David Pavlich]
      #5555413 - 12/05/12 10:20 AM

Er sorry I wasnt aware I was snarking, only giving advice.

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Mark Harry
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Reged: 09/05/05

Loc: Northeast USA
Re: Hypo/Dialyte testing discovery new [Re: Crayfordjon]
      #5555889 - 12/05/12 03:50 PM

I have a plaster tool curing for the F2 flint that will go with the reducing achro. Might be a few days before I report anything more. I anticipate it will have to be switched to a short, or heavy high index flint before done. John, I wouldn't worry!
M.


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Dave O
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Loc: Sri Lanka
Re: Hypo/Dialyte testing discovery new [Re: Mark Harry]
      #5556677 - 12/05/12 11:41 PM

Hey Mark -- I enjoy and follow threads such as this one and several by John as I find the 'Hypo' design both innovative and interesting. Obviously building a 'largish' refractor using only one large piece of glass, which is easily obtained is something worth pursuing.

I do wonder though, what advantages the 'hypo' has over say a Shupmann?


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