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Zerochromat - vapourware??


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Performance wise it is more like such a scope because it has no central obstruction.

The old central obstruction myth again ... the corrector lens package is going to do more to reduce contrast (by scattering from the surfaces and in the glass) than a moderate CO would.

The Zerochromat is nothing like a long focus refractor. It's a compound instrument that just happens to have a lens as the light gathering element.

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Like the Vincent motorcycle it might be described as a solution in search of a problem. Unlike the Vincent motorcycle it has not convinced may people of its virtues. Save yourself a shedload of money and buy a TEC140/Tak/AP which might have all sorts of theoretical shortcomings... but somehow they just ain't there when you step up top take a peek. Ah, but the makers will be there when you have a problem. Cape Newise, hello?

Olly

Edited by ollypenrice
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Cape Newise, hello?

Well, I've met the guy that runs the company ... more than I can say for the top execs of the large corporations that the "well known" brands are.

I sort of know what you mean, and I wouldn't buy stuff from him without the safeguards of working through a credit card company ... as I said, the design is clever, the workmanship is good, but as you say, it's certainly no better than a conventional apo of similar aperture. And neither is it cheaper.

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The old central obstruction myth again ... the corrector lens package is going to do more to reduce contrast (by scattering from the surfaces and in the glass) than a moderate CO would.

The Zerochromat is nothing like a long focus refractor. It's a compound instrument that just happens to have a lens as the light gathering element.

Not quite right. Central obstruction is not a myth. The central obstruction has a very distinct effect on the point-spread function (PSF) of the optics, because it suppresses a very particular set of spatial frequencies is the Fourier plane of the optics. This tends to narrow the central peak of the PSF, and increase the intensity of the first few fringes in the diffraction pattern. Central obstruction is not the bugbear many people think, it is, but it does have an effect on contrast, less so on resolution.

This particular effect on the PSF is not seen in the Zerochromat, though it may have other problems. In fact the Zerochromat resembles certain apochromatic telephotos and some Russian design 5 lens APO telescope (if you forget the mirrors, which I gather are plane, and therefore only act to fold the optical path, just like the old Zeiss design). The 5 lens Russian design also has a single element front lens, errors of which are corrected by lenses further back in the optical pathway. There is no physical reason that the correction this gives is worse than having a closely spaced triplet right up front. If anything, the extra degrees of freedom in the design could lead to better correction for a reduced weight, because fewer lenses need to have a size dictated by the full aperture. That said, thermal expansion can be more of a headache in this type of design. The mirrors will also add weight.

In summary, it should be possible to make a good scope with this design, and until I see a test proving the contrary, I will give this design the benefit of the doubt.

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Well, I've met the guy that runs the company ... more than I can say for the top execs of the large corporations that the "well known" brands are.

I sort of know what you mean, and I wouldn't buy stuff from him without the safeguards of working through a credit card company ... as I said, the design is clever, the workmanship is good, but as you say, it's certainly no better than a conventional apo of similar aperture. And neither is it cheaper.

The only advantage I see is its compact size, compared to an unfolded APO design. If you want compact size, you could get a significantly bigger (and cheaper) ACF, Edge-HD or RC for the same price.

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Well, I've met the guy that runs the company ... more than I can say for the top execs of the large corporations that the "well known" brands are.

I sort of know what you mean, and I wouldn't buy stuff from him without the safeguards of working through a credit card company ... as I said, the design is clever, the workmanship is good, but as you say, it's certainly no better than a conventional apo of similar aperture. And neither is it cheaper.

Yuri Petrunin at TEC does reply to Emails very quickly. TeleVue will have you talking to an optician in about thirty seconds. From previous threads on the forum this is not a universal situation, shall we say?

Olly

Edited by ollypenrice
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Central obstruction is not the bugbear many people think, it is, but it does have an effect on contrast

Agreed ... but in practice the effect on contrast is hardly noticeable even with a large (33%) CO when the seeing is really good. The CO seems to have more of an effect in poor seeing, possibly because of inaccuracies in focusing (accurate focusing being much more difficult when the atmosphere is lumpy).

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Agreed ... but in practice the effect on contrast is hardly noticeable even with a large (33%) CO when the seeing is really good. The CO seems to have more of an effect in poor seeing, possibly because of inaccuracies in focusing (accurate focusing being much more difficult when the atmosphere is lumpy).

It is also a matter of getting used to the contrast of your instrument. As you gain experience, you tease out more detail by careful observation. The 80mm APO I recently acquired does have stunning contrast, but the 8" SCT beats it at planetary and lunar views every time, simply because it resolves more.

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  • 2 weeks later...

Hi everyone, the 'Newise' design is actually an extremely good one, as evidenced by those who own and use one. Sadly, it was killed off by poor quality control of Chinese optics - we ordered 100 sets of optics, paid up front, and had to reject 96 of the front widows due to astigmatism. Having nothing to sell, and no funds to sort out the window nightmare, I had no choice but to wind the company up. The patent is still in effect, so maybe one day it will be resurrected.

The Zerochromat is not 'vapourware', but may take a little more time before it sees the light of day commercially. Collimation is much much easier than you would think. Dave Tyler has had access to an early version, as has Martin Taylor. If you watch this space, an upgraded (prettier!) prototype will be appearing in March this year. The theoretical Strehl ratio is 0.995 across the visual range, so stars look textbook perfect. One reviewer even complained that the diffraction rings at high powers are very weak compared to the Airy disc, and thought that that reflected some sort of optical defect. 'Nuff said......

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Hi everyone, the 'Newise' design is actually an extremely good one, as evidenced by those who own and use one. Sadly, it was killed off by poor quality control of Chinese optics - we ordered 100 sets of optics, paid up front, and had to reject 96 of the front widows due to astigmatism. Having nothing to sell, and no funds to sort out the window nightmare, I had no choice but to wind the company up. The patent is still in effect, so maybe one day it will be resurrected.

The Zerochromat is not 'vapourware', but may take a little more time before it sees the light of day commercially. Collimation is much much easier than you would think. Dave Tyler has had access to an early version, as has Martin Taylor. If you watch this space, an upgraded (prettier!) prototype will be appearing in March this year. The theoretical Strehl ratio is 0.995 across the visual range, so stars look textbook perfect. One reviewer even complained that the diffraction rings at high powers are very weak compared to the Airy disc, and thought that that reflected some sort of optical defect. 'Nuff said......

OK, but a question. Why was this new instrument advertized so far ahead of its being even remotely ready and tested? If you have already had your fingers burned by problems arising from the realities of a production run, why go there again?

Olly

Edited by ollypenrice
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One reviewer even complained that the diffraction rings at high powers are very weak compared to the Airy disc, and thought that that reflected some sort of optical defect. 'Nuff said......

Rule of D/ro<=1: if you can see clean diffraction rings your scope is too small anyway :).

I'm half joking, of course: many people do take pleasure in viewing the largest stable image the seeing allows; I'm just not one of them and tend to prefer D = ro * 3, or even more (and lots of patience in that case), which means I see more detail but no clean diffraction rings.

Edited by sixela
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Not quite right - the Zerochromat had been tested by Dave Tyler, plus my own testing showed that the optics are very good. I have not followed the design up for quite a while because of other projects, but now have the time to do so. It is quite common for designers to put products on the market at an early stage - even large concerns such as car makers etc have put products on the market which are not really ready for sale. Early Sierra cars were awful! Also the early Celestron telescopes had all sorts of problems, which took a while to sort out.

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Not quite right - the Zerochromat had been tested by Dave Tyler, plus my own testing showed that the optics are very good. I have not followed the design up for quite a while because of other projects, but now have the time to do so. It is quite common for designers to put products on the market at an early stage - even large concerns such as car makers etc have put products on the market which are not really ready for sale. Early Sierra cars were awful! Also the early Celestron telescopes had all sorts of problems, which took a while to sort out.

So what is the point here? If Ford and Celestron can get it wrong it is okay for us to get it wrong?

Olly

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Not the point. The plain fact is that the precise point at which a product is ready for market cannot be known with any degree of certainty. Until several have been made, you cannot do an analysis. Why do you think that car makers have to do recalls? None of us wants to get it wrong, but even multi-million pound enterprises make mistakes.

For those people that have never invented anything, it is only too easy to criticise. There are very few people with the foresight, sheer guts and persistence to attempt something completely new, but a huge number just waiting to pick fault.

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I am mostly curious what makes the zerochromat fundamentally different from a folded apo design previously made by Zeiss, combined perhaps with the newer Russian apo designs with only a single front lens at full diameter, and correction lenses further down the tube. I could of course read the patent, but have not found the time for that yet, and patents are notoriously long-winded in their explanations (I know, I have one to my name (with others):().

I can understand that a design like this, if properly collimated, could have excellent performance, but at the same time I know that a good optical design should not just have a good performance when executed perfectly, but also have some degree of tolerance to errors. I remember a fellow student at the Kapteyn Institute drawing up a design for a Cassegrain system, which was very compact, worked perfectly, but was so terribly sensitive to thermal expansion, that it would need a focussing system capable of shifting instruments at secondary focus by several meters :). The trick is not just to find an optimal design, but also to find an optimum which is comparatively wide with respect to design parameters. This would prevent too many rejects.

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Not the point. The plain fact is that the precise point at which a product is ready for market cannot be known with any degree of certainty. Until several have been made, you cannot do an analysis. Why do you think that car makers have to do recalls? None of us wants to get it wrong, but even multi-million pound enterprises make mistakes.

For those people that have never invented anything, it is only too easy to criticise. There are very few people with the foresight, sheer guts and persistence to attempt something completely new, but a huge number just waiting to pick fault.

I run a business in astronomy, too. I am very conservative (not a natural mental state for me) when it comes to promising what I can offer. If you sell a duff product, it won't do to ask your customers to forgive you because you were bravely trying to innovate. Try bravely to innovate, make sure your innovation works, then put it on the market.

I do have a question about this instrument though. What is its intended purpose? Is it primarily a planetary scope, maybe visual or for imaging? The focal ratio is unfashionably slow, not that I present that as a criticism. I wonder who would want to buy it. I stress, this is not a criticism, or a coded criticism, but just a question.

Olly

Edited by ollypenrice
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The design has been made to be very tolerant of mis-collimation. It is true that the corrector lenses need to be carefully aligned with regard to each other, but that is a fairly trivial mechanical exercise. As long as the corrector array is then aligned with the focuser tube, the rest is easy. The large fold flat takes care of any small inequalities, and can even take out atmospheric refraction.

The main idea is to make a superb planetary/lunar telescope that can take in the smaller DSO's. Although it was designed for visual use, it can also be used for imaging. It is also very lightweight at 10kg, and is the length of an 8 inch f6.5. The price is a moot point, as it depends so much on the numbers! The system has virtually no expansion - I set one up in the Arizona desert on distant mountains during the day, and at night, it needed no focus adjustment on stars.

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I do not see how the fold flats take care of atmospheric refraction. Mirrors can neither introduce nor correct for chromatic errors. If the flats refract, correcting the chromatic errors introduced by atmospheric refraction requires adaptive refraction depending on the pointing altitude (and atmospheric conditions to a lesser extent). On an EQ mount, such a correction would be quite a nightmare.

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That is simple - by adjusting the fold flat, errors are introduced to counter atmospheric refraction (as long as you tweak the correct knob!). It is an easy job to then re-adjust for stars or planets higher up. Of course, what you get is not perfect, but a distinct improvement on a bad situation. The result is surprisingly good.

The Russian apo system using a single lens is not retro-focal, so is different from the Zerochromat. It also can only be used in small telescopes, as the errors multiply very quickly past 100mm in aperture.

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