161 replies to this topic

[stanislas-jean]

 

 

a portable dialysis machine

The idea has crossed my mind a few times...

 

 

Clear skies!
Thomas, Denmark

 

The data given by Vla are interresting to note.

The residual CA evaluated compared to those performed by apo and superapo  is at final not disturbing in visual observations for a 200mm aperture.

However expensing 5000usd in comparison to a 200mm newtonian or Cassegrain with very good optics can be a subject of discussion. This is not enough decisive for the selection buying this dyalit design.

We have to think that the absence of obstruction is a major concern that is not in fact with such aperture and observational experience.

For 5000 we can access to a 300-350mm near perfect in newtonians with access to more finer data on planets.

For a 200mm we can access to Cassegrain of near perfect optical level in blue, green and red portions of the light Spectrum.

What I see with refractor is the low air currents disturbance Inside the tube as an avantage: not enough with 200mm for selection.

Stanislas-Jean

[stanislas-jean]

 

 

a portable dialysis machine

The idea has crossed my mind a few times...

 

 

Clear skies!
Thomas, Denmark

 

The data given by Vla are interresting to note.

The residual CA evaluated compared to those performed by apo and superapo  is at final not disturbing in visual observations for a 200mm aperture.

However expensing 5000usd in comparison to a 200mm newtonian or Cassegrain with very good optics can be a subject of discussion. This is not enough decisive for the selection buying this dyalit design.

We have to think that the absence of obstruction is a major concern that is not in fact with such aperture and observational experience.

For 5000 we can access to a 300-350mm near perfect in newtonians with access to more finer data on planets.

For a 200mm we can access to Cassegrain of near perfect optical level in blue, green and red portions of the light Spectrum.

What I see with refractor is the low air currents disturbance Inside the tube as an avantage: not enough with 200mm for selection.

Stanislas-Jean

[wiseone]

One important point is that refractors have the objective lens at the top of a long tube, which gives better seeing than equivalent sized instruments with a mirror near the ground. There is also a reduced effect of heat from the observer upsetting seeing.

[Psion]

Second important point is that reflector 300-500mm needs excellent seeing and in our country is normal seeing 1.5"-2.5" and big diameter didn't reach better resolution from 200mm refractor (tested on TMB 8" F9 refractor and RC 500 ASA). Anyway, TMB is for 30 000 EUR and ASA 44 000 EUR. Zerochromat is for 4 300 EUR now.

[stanislas-jean]

Knows the seeing instrumental and local lower mostly with refractor.

Over a year on a 6" I noted a benefit of one step in danjon scaling.

But this can be improved with reflectors and compacts scopes by designing.

A Cassegrain 250mm costs around 4000 and the 300mm DK 7800 with carbon tube and very good optics (see toscano optics and orion UK), CO around 25%.

Stanislas-Jean

[nicknacknock]

Stanislas,

 

I have a 300mm Dob from Orion Optics UK and whereas a large refractor is never a "value proposition", sometimes it's all about the views.

 

I love my dob and the mirrors are absolutely fantastic, but I do yearn for the purity of views from a refractor. Call me sentimental but I am probably going to bite the bullet and order a 123mm APO refractor which costs more than twice my 300mm reflector...

[Psion]

Knows the seeing instrumental and local lower mostly with refractor.

Over a year on a 6" I noted a benefit of one step in danjon scaling.

But this can be improved with reflectors and compacts scopes by designing.

A Cassegrain 250mm costs around 4000 and the 300mm DK 7800 with carbon tube and very good optics (see toscano optics and orion UK), CO around 25%.

Stanislas-Jean

 

Yes, ASA has excellent optics but didn't beat TMB 8" most of the year!!

[stanislas-jean]

The refractor may have (because depending on the optical acuracy) higher contrasts for coarse size détails on planets, but for very fine size détails, no more avantages.

Stanislas-Jean

[TG]

There are a couple of things not entirely clear to me:

 

1. Dialyte designs have been known for well over a hundred years, but their main drawback has been lateral color. What makes this one different? Are there any details on this? Perhaps Vla can comment here.

 

2. The Strehl ratio is very high in green, nice. But what's the design's polychromatic Strehl ratio? I recently came across Roland's triplet prescription in Telescope Making #28. In OSLO it gives a very high Strelh ratio (0.99 or so) in green but plugging in the other weighted wavelengths shows 0.93. From the spot diagrams, I'd expect a worse polychromatic Strehl ratio for the Zerochromat.

 

3. OK, I said 'couple' but I really have 3 questions: what about performance in the violet? This is the bugaboo of the early 1980-90 short-flint based A-P apos.It's not important for visual but is so for imaging. For a refractor claiming apochromatic performance, comparison with today's apos is only natural.

 

I'm not dissing this scope. Rather, I think it's a very promising design but I feel it'll be in the interest of this design if facts are made clear up front and not slowly 'discovered' which could harm its credibility in the long term.

 

Tanveer.

[wiseone]

Various dialyte designs have been around for well over 100 years, it's true. However, this is a very modern take on the concept, and is completely original.

 

The quoted Strehl ratio is polychromatic for the visual range. 490nm, 560nm and 620nm. It's on the web site.

 

The performance in the violet is not as good as for the visual range, but you can't have everything. For imaging, I have always said that you need to use filters - again it's all on the web site. Nothing is hidden, and there are no 'bugaboos' to be found.

 

This design is not intended to replace 3 and 4 element apos, and the price is not the same, either.

[TG]

Various dialyte designs have been around for well over 100 years, it's true. However, this is a very modern take on the concept, and is completely original.

 

The quoted Strehl ratio is polychromatic for the visual range. 490nm, 560nm and 620nm. It's on the web site.

 

The performance in the violet is not as good as for the visual range, but you can't have everything. For imaging, I have always said that you need to use filters - again it's all on the web site. Nothing is hidden, and there are no 'bugaboos' to be found.

 

This design is not intended to replace 3 and 4 element apos, and the price is not the same, either.

 

Wiseone, thank you for the quick reply. Unfortunately, I can't find the polychromatic Strehl on the web site. I see the OSLO screenshots on this page:

 

http://www.zerochrom...t/features.html

 

which shows the wavefront analysis only for "0.56μ" which is green. Perhaps I'm not looking in the right place? Also, looking at the analysis graphic, the red and blue are foci are separated by almost 0.5mm from green, where they cross over, and by a similar amount from each other in other zones. While this is certainly better than an 8" f/12 achro, perhaps this doesn't actually meet the definition of apochromatic performance since R/G/B don't actually come to a common focus?

 

Regardless, I think many people would be happy to have an 8" refractor with this performance for visual use.

 

Tanveer.

[Psion]

I measure shift between R/G/B and it looks not bigger than 0.2mm. 

[wiseone]

Thanks, Psion.

 

Tanveer, if you look at the wavefront error, there is a coloured bar on the right-hand-side. This shows the various wavelengths being employed. The error is polychromatic, but only the prime wavelength is shown.

[Derek Wong]

 

 

a portable dialysis machine

The idea has crossed my mind a few times...

 

 

It is no coincidence that dialyte is the name of the compound lens in the Zerochromat and a solution for dialysis patients...

 

Derek

[Astrojensen]

 

It is no coincidence that dialyte is the name of the compound lens in the Zerochromat and a solution for dialysis patients...

   

 

 

Clear skies!
Thomas, Denmark

[Psion]

I agree, an astronomer is kind of patient... 

[Niklo]

Hi,

it really seems to be an interesting design. What I'm wondering is how the performance of the Zerochromat is compared to an achromat with Chromacorr. Has anybody tested that? The next question is why the dialyte refractors haven't been popular for such a long time.

Clear sky,

  Roland

[Psion]

The achromat with Chromacorr has a very small FOV and is not ease to adjust. Small a photography test is HERE

[SandyHouTex]

Thanks, Psion.

 

Tanveer, if you look at the wavefront error, there is a coloured bar on the right-hand-side. This shows the various wavelengths being employed. The error is polychromatic, but only the prime wavelength is shown.

 

I don't have an axe to grind here, and I may eventually purchase this scope.  What I do want to say is congratulations on bringing to market an idea that may really "stir the pot" in the APO world.  It looks to be a beautiful concept and scope with excellent optical characteristics.

 

I wish you the best.

[TG]

Thanks, Psion.

 

Tanveer, if you look at the wavefront error, there is a coloured bar on the right-hand-side. This shows the various wavelengths being employed. The error is polychromatic, but only the prime wavelength is shown.

 

We must not be looking at the same diagram. The one I'm looking at shows wavefront maps for 0.56 microns and a color key representing deviations in microns from the ideal wavefront, red coding for large deviations and violet for small. The correction does indeed look excellent in green even at the edge of a 0.6 degree field.

 

Tanveer.

[Psion]

I observe the Moon today and I can't see any CA in magnification 550x (Zeiss MARK V bino-head, Nagler).

[jrbarnett]

Various dialyte designs have been around for well over 100 years, it's true. However, this is a very modern take on the concept, and is completely original.

 

The quoted Strehl ratio is polychromatic for the visual range. 490nm, 560nm and 620nm. It's on the web site.

 

The performance in the violet is not as good as for the visual range, but you can't have everything. For imaging, I have always said that you need to use filters - again it's all on the web site. Nothing is hidden, and there are no 'bugaboos' to be found.

 

This design is not intended to replace 3 and 4 element apos, and the price is not the same, either.

Essentially what you've done is to "thread the needle."  You have delivered a high quality unobstructed visual instrument with excellent color correction, eclipsing the big achros, at a lower per inch cost than big APOs.  Sounds like a smart product positioning move.

 

- Jim

[Crayfordjon]

What I like is humility?? in ones accomplishments, when my name was mentioned to Einstein, he said,"Who"?

[Crayfordjon]

Dialytes have been a concept that goes back to Dollond who is credited with inventing the achromat, he wanted to produce larger OGs but was limited by the quality of flint glass,which could not be made in large pieces at that time, although,much larger pieces could be made from crown glass. He conceived the idea of placing small flint lenses about half way down the focal length,producing the first ideas about dialytes. However he could not find a method of calculating the radius of curvature of the flint element.

[Benoit]

I observe the Moon today and I can't see any CA in magnification 550x (Zeiss MARK V bino-head, Nagler).

 

I agree. chromatic correction is beautiful. the Contrast for mid range size feature is also amazing, even compared to a good C14

 

-- benoit