Largest refractor

[OneCosmos]

Hi,

Just throwing this question out there. Does anyone know what the largest non-professional refractor is in Australia -by which I mean owned by an individual? Perhaps the question should be split into the largest achromatic and the largest APO.

I have a 6" APO and there are a few of those around for sure and someone may have a Tec 180 but I do wonder if anyone seriously owns larger but they might. Anyone know?

Anyone ever looked through a refractor larger than 6"? Not buying one but really interested to know if there is a point at which the views change significantly.

Chris

[Atmos]

I know Peter has a TEC 180, that's about all I've it off hand :)

[The Mekon]

I have observed through a private 8"F12 achro. Heaps of colour, and to put it plainly, it could did not compare well to my 130 APO which was in every way superior.

[OneCosmos]

Yeah, I reckon an achromat would be pretty disappointing. An 8" APO however would be great to look through. Anyone near Brisbane got one?

[gregbradley]

I had a TEC180 fluorite for several years. A lovely scope. Views though, whilst really good were not as memorable as from a Tak FS152 I had. But then I had a wider collection of eyepieces and spent more time using it visually. The TEC180 was only a few times and not for long. M42 though started to show some colour (a greenish colour in the neb).

I suspect there is a less improvement with size factor which is the seeing.
6 inch is often regarded as the sweet spot for APOs.

TEC used to make a 200 APO using FPL53 glass. They come up occasionally. They make a 250mm APO now as well. I see also APM make large APOs. 200mm is probably max for amateur as the scope ends up too long and too hard to handle. The TEC180 was close to my physical limit for length and handleability. Also simple aspects like how do you fit a long 200mm APO in the back of an SUV. The 180 took up most of the room in the back of a Prado with a little to spare.

Moment arm momentum means APOs will require a more sturdy mount faster than a mirrored compound scope for the same weight.
A Tak NJP mount handled AP140, BRC250, Tak FS152 but was really overloaded by the TE180. Everything had to be spot on for round stars. PMX would be the minimum in my opinion.

Greg.

[OneCosmos]

Hi Greg,

Of course mine is an APM 152mm so well aware of what is available from them, but interestingly whilst mine today is Euro 11000 the 180mm, just 28mm bigger is an EXTRA Euro 15000 making each millimeter staggeringly expensive.

Markus also told me that the glass LZOZ use is now rationed due to demand from the military and anything 8" or more involves significant wait time.

Chris

[OneCosmos]

I must say I'd like to look through a larger refractor just to see if there is much difference. If anyone in Brisbane has an APO larger than 152mm please do let me come and look😀 If you have a 10" I'll even fly to any Australian location to look 😀😀

[UniPol]

My 1958 6" (157mm) F15 achromat Polarex/Unitron photo equatorial telescope still undergoing restoration. I have all the bits, pieces and accessories to complete the restoration and hopefully it will look something like the second pic when completed.

[Jon_hm]

That is a thing of beauty Steve :thumbsup:

I am in the process of putting together a homage to the 6" Unitron model of refractor which Unipol is restoring. Mine is based around an f17.5 D&G lens and weighs enough that I have put a Ute crane in my back yard so I can get it mounted. Even though 6" f17.5 is some way from the Sedgwick achromat limit it doesn't have that much colour. I am struggling to get it to track properly (when viewing the zenith the dew shield is nearly three meters off the ground) but still managed to snap the attached

Cheers and happy friday

Jon

[OneCosmos]

@Steve that will be a beautiful scope and Saturn would be a sight to behold. Where are you based? I wouldn't mind seeing that! My more recent APO was primarily for imaging but I have done great deal of usual if late, especially with my new denkmeir binos. Love it!

@Jon before posting this reply I did a quick search for thesedgwuck achromatic limited but couldn't find anything explicit but assume there is a point T which an achromat doesn't display false colour? Usually that would imply visual only as the f speed would be just too slow but your shot of the moo and Saturn looks great. I'll also reply to your email but if you ever get that 10" I'm coming to look wherever you live😀

Thanks to both and all for replies. What I'm getting at the moment that the 7" may be the largest amateur refractor in Australia -that can't be!

[anj026]

Nice photos Jon. I am pleased to see another D&G owner in Australia. Is that the telescope that used to belong to Ziggy's daughter?

Steve your Polarex/Unitron is a great project.

I have an old Parks mount that I bought with the intention of restoring for use with my 6" f15 D&G but it is just so much easier to use it alt/az for the kind of casual observing I do.

Tim Wetherell used to have a TEC 200 mm apo but I understand it has been sold to America. http://www.wetherellart.co.uk/pages/astronomy.html

[OneCosmos]

Firstly I should correct my earlier post referring to 7" as the largest it thought Jon had said he had one in an email but it was a 7" makcass and yes I've have always heard reports that they are planetary killers. That means still the largest I currently know of is 6".

Andy, I know Tec made a few 250mm ones in the US and I was told there is even one available for $50k. To be honest that seems really cheap compared to smaller APOs today! Of course the EQ8 won't wuite do it 😉 you would need the mother of all mounts in fact. I don't want to own one. I want to know someone who owns one 😀😀😀

[OneCosmos]

Oh, and not stray too far from my own thread exactly why are longer refractors e.g.f15 considered planetary killers?

Yes you'll get more magnification with the same eyepiece than on a shorter scope but the atmosphere prevents going too high anyway and you can always use a shorter eyepiece with the faster refractor to achieve the same. Is there something else about the views through a long slow refractor?

[OneCosmos]

I've only just seen this. Stunning scope and if it comes with the girl I'll find the money😀

[OneCosmos]

Thoughts?

http://www.zerochromat.net/buying-a-zerochromat-apochromatic-refractor.html

[anj026]

For professional achromats 100-150 years ago it is traditional for them to be f15 or thereabouts. I think there is a benefit in the long focal ratios in terms of depth of focus. For a more detailed analysis please have a look at this link to Neil English's article.

http://www.cloudynights.com/page/articles/cat/articles/stranger-than-fiction-r2452

[anj026]

Here is a link to an interesting chart that shows the relationship between aperture and focal ratio for achromats.

http://www.cityastronomy.com/CA-ratio-chart-achro.jpg

[glend]

My 127mm iStar Anastigmatic R30 f12 is very clean with no detectable (to me) CA but it does require a fair amount of swing room in the observatory. Unfortunately iStar does not make R30 objectives in long focal length sizes anymore, the longest being a 250mm f11 which has a focal length of 2712mm and weighs a wopping 14kg for the objective cell. I wish they would stay in the market but low demand from people willing to take on building a large acrho seems to have closed that line down, however i am hearing that they will build custom R30 objectives in your chosen focal length as special orders. A 250mm R30 f11 objective cost $5995 USD these days, still its reasonable for a refractor of that apeture.

Btw, iStar are running out their production 150mm f10 achromat scopes, with a 2.5" Moonlight focuser for $1750 USD - seems like a bargain to me!

[gary]

Hi Chris,

I had the opportunity to spend a couple of nights observing with
a privately-owned 15" F12 D&G achromat housed in a magnificent
28' Ash-Dome observatory in the north of Texas.

At the same site there was also a 30" Obsession reflector in a roll-off
roof observatory which I also spent time on.

The 15" refractor was breathtaking to look at, but as expected, the 30"
reflector delivered far more impressive views of everything.

You think a 30" Dob is big until you see the size of a 15" F12 refractor.
In terms of real-estate occupied by the two, certainly the 30" Dob was the
more economical. :lol:

[Jon_hm]

I have been drooling over the IStar objectives for a while. Unfortunately they are gradually reducing their range. D&G still offer large achromats at long focal lengths but the waiting time is getting longer and longer.

Like Chris I was quite interested in Zerochromat. Their main "big gun" is an 8" but they were also talking about going 10 inches and larger. The plus to this design was that the folded light path reduced the scope's length. Sadly its a bit of a downside for me too because I want something that I can leave set up in an observatory and not have to worry about mirror coatings. Also their prices skyrocket with aperture and a little voice is whispering in my ear that I cold do just as well with a chromacor and nice Istar or D&G lens for a quarter of the price.

Andy - that is indeed Ziggy's old scope, or at least its lens and focuser. The price of getting the whole thing shipped was more than I paid for the entire OTA so he just boxed up the objective and some other bits and pieces and sent me that.

Thanks for the comments on the planetary snaps. I hope to do better once I get a mount I am working on at the moment in action - its that monster ATM thing that was for sale in Frankston last year.

Clear skies everyone.

Jon

[MattT]

My take....expensive and doesn't look like a long FL refractor. Better off with a large Cass.

All I can bring to this discussion is I'm waiting on an email from Ales over at Istar on getting an 8" f12 R30 Lens. Nearly finished a 2" Pillow Block that will take an 8" with ease.

As a kid at school I got to use the 9" f15 Oddie Refractor on Mt Stromlo every clear Wednesday night for a year....sealed my fate. That and the Astro Optical Supplies catalogue....photos of Unitron's, like Steve's 6" :cool3:

Matt

[anj026]

I have had good experience with Istar. I made a telescope with a 5" f12 R30 which is a great lens. An 8" f12 sounds wonderful Matt. I hope it comes together for you.

Back in the 90's I was fortunate enough to visit Mt Stromlo. I can only imagine what it would be like to observe through a large classic refractor like that.

[OneCosmos]

I am sorely tempted to exchange my APM 152 for the new f7 180mm from APM. Markus has agreed but we're talking another $17k-more than $500 per mm😫

[glend]

Do you realise that for $2300 (current price) you could have a wonderful Skywatcher MN190 Mak-Newt f5.3, 1000mm fl, . Fully corrected -no detectable coma, heavily baffled, amazing contrast, very small secondary mounted on the corrector - so no diffraction spikes. Reviewers suggest large APO performance at 1/3 the price. It is both a astrograph and a powerful visual scope. Yes i have one of these.

I have nothing against large refractors, i have a 152mm achro, and my iStar, but from a value for money perspective, true colour rendition, and apeture, it is hard to make a case for the investment required (for me) just to have an exclusive brand name on a scope. These are simply devices to enable our grasp of night sky, imho. However, i understand that for many people they become "objects d'art" and therefore the experience of having one, for them, is a reward in itself.

[Satchmo]

While this is probably a thread for refractor fanboys ;), I have to back up Glens comments in that I used one of these at SPSP and it is indeed a very nice solution and fantastic bang for buck in having many of the similar qualities to an APO refractor of aperture which would be nominally unaffordable , but with far less elements and you still get to have a big chunk of glass at the top end to catch dew and dust :).

I saw a very refractor like high contrast image of Saturn that held up under high power. The only down side was the weight and it was up high on an HEQ6 and was swaying a bit in the wind.

[UniPol]

As an aside to my 6" Polarex refractor, I have a project underway for my A E Jaegers 6" F15 achromat lens bought before the 1980's fire which destroyed their factory. I had a spare lens/dew shield assembly from a 6" Unitron so I machined up a lens cell for the Jaegers lens and it screws into the cradle just like the Polarex 6" lens. About all I need now is a tube around 6 1/2' diameter and about 7 feet long! It will be interesting to see how it compares to the 6" Polarex lens.

[anj026]

Very nice! I used to own a nice 6" f5 Jaegers.

When I made my D&G scopes I found it difficult to source light weight metal tubing. So I made the tubes from thin ply. That has worked out very well however I would consider rebuilding them if decent metal tube was available at reasonable expense.

[anj026]

There is a used TMB 175 f8 available here for a good price. ($9750 USD). :)

http://www.astromart.com/classifieds/details.asp?classified_id=926145

[OneCosmos]

Yeah, that is a good price but it wouldn't fit in my observatory. The new APM 180 is f7 and thus only 60mm longer than my existing scope.

Probably I won't pay to go to 7" though but I'd love to look through a 8": plus refractor one day. If I come in to serious money I'll get a 10" :lol:

[phomer]

Well it appears that everyone has an opportunity to have the largest refractor in Australia for a bargain basement price.

http://www.iceinspace.com.au/forum/showthread.php?t=148496

Regards

Paul

[glend]

Your hexagonal ply tube, even at a seven foot length, would probably be stiffer than a thin walled steel or aluminium tube and they would require wide spaced tube rings and bars to support them. I always wondered how people baffle and paint the inside of those long metal tubes. Laying up a ply tube, at least the way you did it, seems very sensible. The test would be to check the collimation sag on the mount.

[OneCosmos]

Quite funny!

[anj026]

The thin ply tube is very stiff and light with no sag at all. The 6" OTA is 14kg and the 5" is less than 9kg including tube rings, finder, diagonal and eyepiece.

They just don't look like classic telescopes, not that that really matters. They perform like the real thing and at night I still enjoy using them very much.

There are a few techniques for fitting baffles to metal tubes. One way is to make a skeleton frame with the baffles at their correct spacing and then slide the frame into the tube. Painting the inside can be done with a brush on a stick or even a spray can on a stick with an extended trigger for the nozzle.

[MattT]

Have heard back from Ales at Istar. Here is his reply on a thread I started at ISC

http://istarscopeclub.proboards.com/thread/704/wanted-buy-f12-35-objective

So this 8" f12 R35 might happen....specially if anyone else wants to do the big Refractor thing. Istar would build a few lenses if they had a couple of interested buyers. I know its nuts...I don't care. At current exchange rates it'll be $3-3500K for the objective in a cell....anyone interested send Ales an email at Istar optical.

If it doesn't happen thats OK I still have my 6" f12 Istar Achro.

Matt

[Satchmo]

An Istar 8" F8 ( ?) Achro lens went cheap here on IIS Trade not too long ago for well under $1000 - the glass was substandard and showed veins of inhomogeneity that could be seen in the extra focal star test, so you would have to be vigilant. The cost of optical glass skyrockets as you go larger as the cost of finding glass and value of pieces free of inclusions and veins goes up exponentially .

I'm interested in doing some more lens work sometime, and would like to do a large achromat ( F12) - I was thinking about something in 10" league . But something like that would have to go into a very large dome or use at least one folding flat to cut the tube down to something manageable and then you would have to look down from the top.

I think such a configuration would not tick the 'romance' box which I think is the great appeal of achro refractors which are basically visual instruments.

[anj026]

I have considered an 8" f12 for the backyard. I think it might be do-able if the weight can be kept down.

My experience with the 5" f12 R30 Istar lens proved it to be very heavy for it's aperture. An 8" R35 would need to be permanently mounted for me as I think it would just be too heavy. I would prefer a standard achromat 8" f12 for that reason alone.

Mark if you ever offer an 8" f12 coated achromat lens in cell I would be interested. D&G offer them for the price of $2395 USD plus $275 USD for simple coatings on all four surfaces. That would be over $4000 AUD and who knows how long you would have to wait for it, maybe years.

I don't know if it would be commercially viable for you to make a run of them in Australia. What do you think? :)

[MattT]

Good point on the weight of an 8" f12 amnstigmat. Ales did say in an email that he could do an 8" f12 achro FMC in a cell for USD 2,250 plus post and a wait of two months.Would likely be cheaper for two? Lots of time to work it out. Zane sold a 180 f8 recently. The only Istar lens that I have heard of that wasn't perfect.

[Satchmo]

Andy : Probably wouldn't be viable - I would expect a hefty expense on the AR coatings , USA sourced glass and adjustable mirror cells. Probably a fast track to working for $10 an hour committing to a production run on something like that !.

I suspect what D nd G would be batch polish production runs of elements getting radii of surfaces more or less right but not worrying to do much surface figuring . They would then mix and match lenses to find pairs producing the best wavefront , then do some quick localised polishing on the rear element surface to achieve an optical null and decent star test . Just my guess for that price , but I may be wrong .

As I said I am interested in making a large achromat for fun at some stage with a view to making a large oiled triplet down the track . Oiled triplets have always appealed to me as the two oil mated surfaces have next to no surface quality tolerance and don't have to have AR coatings. So after mating there are no more complications beyond that of mounting and aligning a doublet. I have no idea why they aren't more common, but it is probably to do with less design freedom in that the mated curves of the oiled elements have to be more or less matched in radii.

[anj026]

No worries Mark. I understand there are risks involved in AR coating and that would naturally complicate any commercial endeavour.

The oiled triplet does make a lot of sense for one off production. Even more so if it allows you to shorten the f ratio and make the tube length more user friendly.

D&G must have ways of reducing their costs somehow. I have heard that Barry Greiner the owner of D&G makes his main income through other optical contracts and that is also why lens production can be sporadic and lead to long wait times.

R Royce advertises an oiled doublet that sounds interesting but it would be f15 and very long.

For me if I am honest with myself and considering the cost and the convenience, I am probably better off with a Mewlon Cassegrain.

[bratislav]

That would be Barry Adcock's 10" APO triplet (FPL53 based). Barry has made more than a dozen refractors, APOs and achros, doublets and triplets and this recently completed APO has now replaced his 14" Schiefspiegler as his planetary instrument of choice.
His 8" f/30 Coelostat refractor (fixed eyepiece, inside the house) is probably among the largest achromats too, if not the longest, but certainly most comfortable.

[troypiggo]

Recollecting our chat about this up at Astrofest.
Understand that aperture is king, but is the cost/benefit ratio there?
Other question is do you find the 152mm is limiting you in any way?
Keep the 152 I reckon, and just get out and enjoy/use it more ;)

[Satchmo]

They are bargain basement price achromats priced to compete with USA made D and G lenses - it would be not unreasonable to assume that less than perfect glass gets through occasionally and the lack of experience of the owners will often give them a bit of lattitude . If not they simply couldn't sell them so cheaply ( I am making assumptions there as I haven't had any direct experience with them )

[strongmanmike]

Well I only have two things to say in this thread :)

1) I spent many nights observing through the 9" Oddie refractor (http://www.pbase.com/strongmanmike2002/image/110766126/original) at Mt Stromlo over several years, before it was tragically lost in the 2003 Canberra bushfire :sadeyes:, including having my 12" LX200GPS setup outside for direct comparison one night... and the views were definitely grander with better separation of close stars and planetary features, globular cores and kinda more meaty through the Oddie.. overall image brightness and visibilty of galaxies and faint nebs etc was fairly comparible.

2) See 6" of Astrophyiscs genius HERE (http://www.pbase.com/strongmanmike2002/image/109399708/original) :D

Mike

[Hodur]

The Neil English article resolves many questions re: Classic Achro's. Great thread, great article. Cheers

[OneCosmos]

Yeah Troy that sounds sensible enough and anyway, right now my outgoings vs income preclude such indulgence. The thread was mainly started to find out how many refractors larger than 152mm are extant in Australia. I'd still love to look through something larger.

[Kunama]

I looked through the Oddie II yesterday......
albeit only at a wall at Mt Stromlo, this is a 220mm F15 achromatic doublet refractor built by Tim Wetherell. It is housed at the new Mt Stromlo Visitor Centre and may eventually be moved into the Oddie Dome for public outreach. The objective was made my iStar Optics.

It is a big and beautiful recreation of the original which now is also displayed at Mt Stromlo.

[dannat]

Melb obs 8" f13 is obstructed by inner city light pollution, it would be good to get it out to dk skies. has quite small amounts of colour on the gas planets but a fir bit around bright stars, venus & the moon depending on ep & axis

[Kunama]

220mm F15 iStar lensed Oddie II awaiting its mount to be restored..... one day...

[Satchmo]

Looks very `steam-punk' with all those riveted steel panels !

[Kunama]

I am very tempted to make a 1:3 scale version of this scope, I have the right objective in heavy brass cell. Might need to quiz Mr Mitchell to see if he can roll tapered tubes.......... :question: