Largest refractor

[OneCosmos (Chris)]

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 (Colin)]

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

[The Mekon (John Briggs)]

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 (Chris)]

Originally Posted by 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.

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 (Chris)]

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

Originally Posted by 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 (Chris)]

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 (Jonathan)]

That is a thing of beauty Steve

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 (Chris)]

@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 (Chris)]

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 (Chris)]

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 (Chris)]

Originally Posted by anj026;1268

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

http://www.wetherellart.co.uk/pages/astronomy.html[/URL]

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

[OneCosmos (Chris)]

Thoughts?

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

[anj026]

Originally Posted by 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?

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/art...-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 (Glen)]

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]

Originally Posted by OneCosmos

Anyone ever looked through a refractor larger than 6"?

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.

[Jon_hm (Jonathan)]

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