Zerochromat - vapourware??

[michael.h.f.wilkinson]

Retrofocal as I know it is a term used for wide angle lenses in which the distance from the rear element to the focal plane is longer than the focal length (as needed in SLRs, to accommodate the mirror). This leads to all kinds of problems such as barrel distortion. The long focal length Russian designs do not fall into this category. Rather, it seems they use a system more akin to Petzval optics, to correct both field curvature and chromatic errors. I do not doubt such systems have limitations, but retrofocal they are not.

The tilt you need to introduce to correct for atmospheric refraction must have a horizontal axis of rotation (I guess), which again in an EQ mounted system would be problematic.

[wisepeter]

Only a small amount of adjustment is needed, at worst about a quarter turn of one of the knobs. Even with an equatorial mount, the adjustment is simple, and if you turn the wrong knob, it is easy to return it to its previous position, and then try a different one. When you turn the correct one, the chromatic aberration magically disappears. Of course, observing near to the horizon is not going to give a very good image anyway, but it is good for demonstrating planets to newcomers when you have no choice as to planetary position.

[brianb]

Only a small amount of adjustment is needed, at worst about a quarter turn of one of the knobs. Even with an equatorial mount, the adjustment is simple, and if you turn the wrong knob, it is easy to return it to its previous position, and then try a different one. When you turn the correct one, the chromatic aberration magically disappears. Of course, observing near to the horizon is not going to give a very good image anyway, but it is good for demonstrating planets to newcomers when you have no choice as to planetary position.

Sounds like the old idea of using a badly achromatised eyepiece (Ramsden) & putting the planet off centre in the field so the radial CA in the eyepiece cancels the atmospheric dispersion ....

[wisepeter]

Exactly the same principle! There was also the Risley prism which worked in the same way.

[AlexB]

I find this design interesting, I was thinking about having a custom Yolo design made as I am not comfortable with having large diameter SCT and Maks with massive obstructions in the way, it just seems 'wrong' to me.

Your design is looking like an advanced Yolo.

It seems there is a lot of doubt and question over the design and the readiness to supply. I would think a smart move would be to hand a model / prototype over to an esteemed astro figure for a public test and review.

It's a lot of money, but then so are Edge HD's etc so understanding how this compares in usability, image/obs quality, construction etc. would definitely be of benefit to potential customers willing to wait 3 months for their hard earned to be realised into a practical high-powered scope.

Just my two penneth.

EDIT: One other thing is that the gallery on the site doesn't have many images, this is not good for promoting your product and also, it seems there is an Etalon filtered Ha shot of the sun, was that taken with this scope and with what extra equipment?

[wisepeter]

I am going to hand over the scope I am currently finishing off to a recognised astro imager, as this not an area that I am anywhere near expert in! Though I am going to take some images myself before doing that. Please form an orderly queue.............!

[michael.h.f.wilkinson]

Edge HDs are a lot less than the quote for an 8" Zerochromat. A 14" Edge HD OTA is listed around EUR 7000, vs EUR 10000 for an 8" Zerochromat. Regarding central obstruction: All the big boys have it (Yerkes is the biggest refractor at 40"). Hubble has it, and I cannot say it has ruined its optical performance. A 14" Edge HD should run rings around an 8" APO, if my comparison on the moon between my 80mm APO and 8" SCT are anything to go by. Do not forget, many if not all of the best planetary images posted in this forum are taken with big SCTs and Newts.

Central obstruction is not nearly the bug-bear people make it out to be, even though we are still better off without.

[AlexB]

Central obstruction is not nearly the bug-bear people make it out to be, even though we are still better off without.

Fully appreciate that but if you're trying to get some of the smaller DSO's, light gathering is surely an increasingly important factor for both imaging and observation. No obstruction means a percentage more light (what are we talking in general 30% more light?)

Forgive me, I'm not an expert, I've been doing a lot of reading and learning but still need to find my way on the technicalities.

[michael.h.f.wilkinson]

Fully appreciate that but if you're trying to get some of the smaller DSO's, light gathering is surely an increasingly important factor for both imaging and observation. No obstruction means a percentage more light (what are we talking in general 30% more light?)

Forgive me, I'm not an expert, I've been doing a lot of reading and learning but still need to find my way on the technicalities.

Twice the aperture means 4x more light! The oft quoted 30% central obstruction is by diameter, not surface area. This means that the secondary to primary surface area ratio is around 0.09 (0.3 squared). So a 14" HD collects 2.78x as much light as an unobstructed 8" scope.

[AlexB]

Twice the aperture means 4x more light! The oft quoted 30% central obstruction is by diameter, not surface area. This means that the secondary to primary surface area ratio is around 0.09 (0.3 squared). So a 14" HD collects 2.78x as much light as an unobstructed 8" scope.

So a 30% obstruction removed would give how much extra light on a 14" diameter?

My point being, if there was a 14" Zerochromat/Yolo, then this would give more light then the Edge HD. Sorry if that wasn't clear, and this is my problem with the SCT etc. design.

Anyhow, it's not a major thing, as you say, the images given by these optical assemblies are extremely good anyway. I guess the pursuit of large diameter obstruction-less optics is one of pedanticalness!

On this point, I'm wondering, I see the quoted f numbers for the SCT style scopes and this is calculated on focal length over the aperture, however, if some of that aperture is obstructed then this would surely mean the aperture is effectively less in 'area' and thus the 'f' number is not right as the amount of light moving through the optical system is less? Have I got that wrong and sorry a bit off topic.

[wisepeter]

The price of a Zerochromat 8 inch could be around 8,000 Euros or less, depending on numbers.

I have designed the Zerochromat in much larger apertures, and a 12 inch version is not impossible, maybe even a 16 inch. I would probably make it f10, and shorter in relative terms than the 8 inch. However, the 8 inch needs to be established first.

[michael.h.f.wilkinson]

So a 30% obstruction removed would give how much extra light on a 14" diameter?

My point being, if there was a 14" Zerochromat/Yolo, then this would give more light then the Edge HD. Sorry if that wasn't clear, and this is my problem with the SCT etc. design.

Anyhow, it's not a major thing, as you say, the images given by these optical assemblies are extremely good anyway. I guess the pursuit of large diameter obstruction-less optics is one of pedanticalness!

On this point, I'm wondering, I see the quoted f numbers for the SCT style scopes and this is calculated on focal length over the aperture, however, if some of that aperture is obstructed then this would surely mean the aperture is effectively less in 'area' and thus the 'f' number is not right as the amount of light moving through the optical system is less? Have I got that wrong and sorry a bit off topic.

The 30% C.O. removes just 9 percent of the light (about the same as that of 1cm of glass traversed in a lens system). The Yolo design is very difficult to correct for astigmatism. Either you have to shape the secondary very carefully, or you need to introduce a lens in the optical pathway (which also cuts down the light).

My main point is that the Zerochromat design at 8" is more expensive than the (more compact, but heavier) 14" Edge HD. Of course a 14" unobstructed system is going to be a bit faster IF the other losses (reflectance losses, absorption losses, etc) are smaller than 9%. Given the number of optical surfaces in the Zerochromat design, I doubt that any difference in image brightness would be noticeable (at the same magnification and aperture).

[michael.h.f.wilkinson]

I should add that there may be a distinct difference in contrast (APOs tend to have a distinct edge over SCTs in that respect)

[AlexB]

Thanks Michael.

Only 9% surprises me, they look massive on so many scopes!

[michael.h.f.wilkinson]

Thanks Michael.

Only 9% surprises me, they look massive on so many scopes!

The human mind can sort-of compare linear measures, but not surfaces. Compare these two square "apertures":

XXX

XXX

XXX

XXX

X X

XXX

The lower has a 33% CO by diameter, but retains 89% of the light (8 Xs vs 9)

[AlexB]

Optics ... fun fun fun!

[syd_malicious]

Interesting replies that have gone a bit away from my original point.

I am glad the Zerochromat manufacturer has taken the trouble to reply but I was also getting at a credibility issue. I (and virtually everyone else) am not in a position to judge everything but the real point was this is an unproven innovative design that has had little progress (looking at the Zerochromat website) in a long time by a manufacturer that could not deliver another unproven innovative design from a previous company that had rather poor feedback overall.

Sorry, just calling it how I see it.

As mentioned the only way to pursuade people is to get a reasonable number out with positive reviews (both about support and the product). I think you will have an uphill struggle but good luck.

Paul

[na508120@eclipse.co.uk]

Defending Peter Wise is why I've joined. His Cape Newise 8" modulated Newtonian and the Zerochromat will be appreciated by those who think ahead or by experience of dislocated knees, slipped discs or hip replacement prevention. He rejected 50% of his Chinese made front glass supplies-a credit. Most customers could not get the performance expected owing to the hike up in collimating which no manufacturer would know about beforehand. 'Get on with it, this must be normal' was my attitude with the well thought out 2nd Newtonian that came with no collimating instructions.
There are 8 correction moves compared to 4 of a classic Newtonian and it took me 6 years, 3 if I'd been steered towards a Cheshire Eyepiece instead of an accurate Laser collimator. In this time Peter had a living to make, I've had a pension. It's not more difficult, but you must be chronological. Nice if you can work them out. This recent Mars apparition got me checking with a website recent image that the snow detail I was seeing wasn't a fault at all! When it returns plan for a 3 year apprenticeship. Peter Clark:hello2:

[ollypenrice]

Sorry, I don't follow what you mean by the 'hike up in collimating which no manufacturer would know about beforehand.' (To be clear, I mean literally that I don't understand.) Could you expand?

Olly

[rl]

As someone who has spent a career in various sectors of the UK manufacturing industry I feel the need to point out it is incredibly difficult to manufacture any sort of precision item reliably and consistently. As a one- or two- man band you  can't make it all yourself and therefore you are always at the mercy of suppliers; quality, distributor's incompetence, the fickleness of banks....there is always something to throw a spanner in the works. It's just not possible in this country for some small one-man outfit to produce Takahashi quality at Meade prices. There is a long list of failed telescope manufacturers and angry customers as testamant to this sad reality.  Even if you buy from OrionOptics (I have several of theirs) there is always a small amount of fettlling to be done before it all comes right, and they could  turn out some real dogs before they had the good sense to invest in the Zygo tester. I speak as someone who has been very disappointed in the past...I had an early OMC140 which was rubbish before they got the testing sorted out ok. They changed..they sorted the issue and I've bought OO since.

If you want guaranteed perfection then save up for a Tak or an AstroPhysics, be happy. But  personally I hope there will always be a place for the very small home-grown people prepared to innovate provided the final product eventually meets reasonable customer expectations.

Regards to all

RL

[Dude_with_the_tube]

I understand where you are coming from and I agree with everything you said RL,however,returning to this particular instrument.

1.Despite numerous requests by many posters here in SGL and also in CN (cloudy Nights) owner of this instrument actually never responded with willingness to give this instrument to any known astronomer for a test purpose and review purpose.This has been highlighted to him many times in both forums here in UK and also in USA.

I have been following both threads as i find the concept quite interesting and as mainly planetary observer i am always on a look out for that magical "better" instrument.

2.Answers on few questions raised by people where answered in quite a negative tone what did turn a lot of people off and only caused opposite reaction.You have to understand that as a newcomer with new instrument to already crowded market place,despite instrument being "unique" you have to be prepared to all sorts of questions and handle the "heat" the right way,what in some cases wasnt done.

what leads to last point.

3.Price. I can see currently this instrument is being advertised for £3600 what by all means is not  £3.60 or £36 or even £360. It is a lot of money being asked for instrument what no one knows,no one has seen and there have not been any reviews either.Correct me if i am wrong but for £3600 i can buy a heck of a lot of telescopes and still have change left over for a pint!And on top of that, that amount of money does indeed bring in a lot of other very high quality scopes into play including Takahashi and Astro Physics what are known for they quality of build and quality of optics.

Not trying to be negative here,but i am the one who also reads reviews,hears the word of mouth before i go out and splash that amount of money for something.

As such,if there are people who actually have one of these instruments or the actual manufacturer reads this.Give us good reason and convince us that we should actually save up or trade up our instruments for this one.Give me a good reason why for example myself should sell a 6" vixen ED what doesnt cost 3600 and buy one of these? Aperture maybe rules but not in planetary observation.What are the pros of this scope over my one? I dont need to colimate my scope and it has been perfectly fine for over 10 years now,zerochromat will need colimation.( not that it is an issue).What are the cooling times? how does the scope performs under UK skies taking into consideration our wet and far from ideal conditions? Who is the manufacturer of the optics?What coatings are used? Accuracy of the mirrors?Any supportive tests on optics? There are quite a few people even here in SGL who will gladly assist the manufacturer to perform a review based test as soon as the manufacturer itself is willing to cooperate.I am up for it of needs to be.(not that i am famous of any sort,but darn,i am more than happy to do it to promote a UK based manufacturer and i dont want anything in return),but you cant expect people queue at your door with bundles of cash by not doing the ground work.

Wishing all the best.

[rl]

iF the manufacturer is really not prepared to give you any details then that tells you all you need to know...caveat emptor.

RL

[Dude_with_the_tube]

it definitely does that so far.And as such,how the Dragons Den people say:I AM OUT!

[Moonshane]

I'd sooner have an 8" (apochromatic) dob and a decent holiday.

[John]

I'm going to move this to the Scopes and setups section as it's about a scope.

FWIW a member of the Cloudynights forum has recently taken delivery of a Zerochromat:

http://www.cloudynights.com/topic/484508-zerochromat-impressions/