New SDM 20" Scope arrives: Pictures

[Rodstar (Rod)]

Thanks everyone for some great suggestions for names.

I like one or two of the names suggested so far, but I might just wait for a few more suggestions before settling on a name. The scope isn't actually red/burgundy, so you might steer away from that theme!! Maybe my purple house has played colour tricks on peoples' minds??

Some ideas that I have also had for names:

*"Lord Rosse", being the third Earl of Parsonstown in Ireland, who built the Leviathan, the largest telescope of the 19th century on his estate (183cm mirror), and who famously gave the "Crab Nebula" its name. My maternal family's name is, co-incidentally, Ross. (NB: the Leviathan is name that has been used for many other scopes and is therefore a tad old-hat).
*Bill Parsons, the regular name (well, at least it is "William Parsons") of Lord Rosse.
*Desiree, the very tall, fat, gold-wearing black character from the BBC series "Little Britain" who gets into naked rumbles in health spas.
*Pyxi, being rather like the constellation Pyxis, and conjuring images of Pixi Skase.
*Carina, being my favourite constellation, and bringing back fond memories of real people by that name whom I have met.
*Jacob Sladder (for the biblically literate, the patriarch Jacob dreamt of a ladder taking him all of the way to heaven)
*B.F.T. (Big Friendly Telescope, based on Roald Dahl's "The B.F.G"." – The Big Friendly Giant, a favourite of my three kids)
*Gough (as in Whitlam, being tall, larger than life, representing idealism – in this case astronomical, but ultimately bad for the family economy)
*Anastasia (Russian royal, seductress)
*Kamal (tall, dark, deep – sky, bedecked with glittering jewellery)

Any other suggestions??!!

[AstroJunk (Jonathan)]

Well mine has become "the Mistress".

as in 'Just popping out with the mistress dear, don't wait up...'

[g__day (Matthew)]

Beautiful!

[Rodstar (Rod)]

Well, I am pleased to report that I have finally seen some star images in my scope!

I got up at 3am today, the eastern sky was clear, thick clouds to the west, but I decided to chance it, and set up. By the time I was set up at about 3.20am, the clouds were covering the entire skyline. Damn!

Anyway, having hauled myself out of bed, and having gone to the trouble of setting up and collimating, I was determined to see something. So, I ranged the skies, trying to see through little gaps in the clouds.

Quite unexpectedly, suddenly out of the grey flashed Rigel Kent. Quick as a jack rabbit, I was onto it. Beautiful, but transitory....it disappeared behind the Grey Shroud never to be seen again. I also chanced a view at Jupiter through the clouds....boy, will it be bright when I see it without clouds! I also glimpsed some star fields momentarily. So folks, I can report that the mirror works, and I have seen first light.

Hopefully I can achieve some more serious work later this week. IN the meantime, my apologies to the astronomical community of south-eastern Australia for destroying your observing for the past week.

[GTB_an_Owl (Geoff)]

Rod

have you seen the weather forcast for the following week on "d-weather" - cloud and more cloud right up to NEXT friday - yes not THIS Friday - NEXT FRIDAY


geoff

[ving (David)]

call it ving...



jupiter is gunna be almost too bright for the scope me thinks

[matt]

A few very choice filters will help that brightness problem, should it indeed prove to be a prob

[Satchmo]

Congratulations on your new arrival Rod.

The hole in the data set is due to the hole in the autocollimating flat, not to do with the interferometer.

Rememeber to allow some artistic licence in the Strehl number on a large thinner mirror as the astigmatism co-efficient is subtracted from the data. As the vertical mirror bend with horizontal axis alone, would lower the Strehl into the 0.70's without adding the complexities of momentary air movement and mirror seating and any real astig present. As always it comes down to the experience and skill of the optician for a good optic, there are no simple solutions to proving how good a mirror is on paper, just eyeball at the telescope in the end.

Enjoy, and look forward to seeing your SDM at SPSP.

[Rodstar (Rod)]

Originally Posted by Mark Suchting

Congratulations on your new arrival Rod.

The hole in the data set is due to the hole in the autocollimating flat, not to do with the interferometer.

Rememeber to allow some artistic licence in the Strehl number on a large thinner mirror as the astigmatism co-efficient is subtracted from the data. As the vertical mirror bend with horizontal axis alone, would lower the Strehl into the 0.70's without adding the complexities of momentary air movement and mirror seating and any real astig present. As always it comes down to the experience and skill of the optician for a good optic, there are no simple solutions to proving how good a mirror is on paper, just eyeball at the telescope in the end.

Enjoy, and look forward to seeing your SDM at SPSP.

Mark,

The mirror is two inches thick. What thickness of mirrors do you use? I am surprised that you would think there might be vertical mirror bend on the horizontal axis from such a thick mirror, or that this could so significantly affect the Strehl. Can you clarify??

I am aware that Strehl is only one measure of the quality of a mirror, and does not disclose other potential failings in the mirror, such as astigmatism or a turned edge. I'll let you know how the mirror performs in real life when I have a decent night's observing under my belt. In the meantime, I am not going to anticipate any negatives unless they become apparent.

I have received some emails from Paul Haese about his new 18" SDM, with OMI mirror. He reckons that at the recent star party he attended (Snake Valley) those he observed with made the comment that the mirror performed as well as any they had ever seen. I am expecting mine to perform likewise. I am extremely happy to have ordered my mirror from OMI.

[ausastronomer (John Bambury)]

Hi Rod,

Just reporting in from downtown Coonabarabran where we are keeping the 40 Texans amused, by giving them glimpses of southern skies targets, through sucker holes. We got lucky on Monday night with an excellent nights observing, where we did an "allnighter", otherwise it has been pretty cloudy. Peter Read arrived in Coona on Sunday arvo with John Trudgen and his new 20"/F5 (SDM #11). It is a lovely scope. Peter parked it next to my 18" Obsession and Andrew Murrell's 25" Obsession. While we didn't get to use it too much on Sunday Night, several of us gave it a good "shakedown" on Monday night. Our good friend from Texas, Van Robinson, who owns several Starmasters up to 22" fitted with a variety of mirrors from John Hall (Pegasus Optics) and Carl Zambuto, was also highly impressed with SDM #11. Both, in terms of looking at and through it. SDM #11's OMI mirror is outstanding. As Mark Suchting indicated, don't worry about the Strehl numbers, just go and enjoy the views. The 4 3RF 18" Obsessions and the 20" of John Trudgens all have OMI mirrors and they are all excellent. I wouldn't be too worried about any astigmatism in the mirror, your problem is going to be convincing Nina to let you play with your toy as and when required

CS-John B

[Rodstar (Rod)]

Originally Posted by GTB_an_Owl

Rod

have you seen the weather forcast for the following week on "d-weather" - cloud and more cloud right up to NEXT friday - yes not THIS Friday - NEXT FRIDAY


geoff

Bugger!

Geoff, the BoM websites is currently describing the forecast for this Friday as "mainly fine and sunny". I remain resolutely optimistic about a Kulnura session on Friday night!

[Rodstar (Rod)]

Originally Posted by ausastronomer

Hi Rod,

Just reporting in from downtown Coonabarabran where we are keeping the 40 Texans amused, by giving them glimpses of southern skies targets, through sucker holes. We got lucky on Monday night with an excellent nights observing, where we did an "allnighter", otherwise it has been pretty cloudy. Peter Read arrived in Coona on Sunday arvo with John Trudgen and his new 20"/F5 (SDM #11). It is a lovely scope. Peter parked it next to my 18" Obsession and Andrew Murrell's 25" Obsession. While we didn't get to use it too much on Sunday Night, several of us gave it a good "shakedown" on Monday night. Our good friend from Texas, Van Robinson, who owns several Starmasters up to 22" fitted with a variety of mirrors from John Hall (Pegasus Optics) and Carl Zambuto, was also highly impressed with SDM #11. Both, in terms of looking at and through it. SDM #11's OMI mirror is outstanding. As Mark Suchting indicated, don't worry about the Strehl numbers, just go and enjoy the views. The 4 3RF 18" Obsessions and the 20" of John Trudgens all have OMI mirrors and they are all excellent. I wouldn't be too worried about any astigmatism in the mirror, your problem is going to be convincing Nina to let you play with your toy as and when required

CS-John B

Great to hear from you John! I am glad you have had at least one night's good observing. What do 40 Texans do in Coona when the weather is foul??

Glad to hear that Peter Read's handiwork (in concert with OMI) has made an impression. I wonder how many orders have been placed for SDM scopes? I dare say Peter would have a captive audience with money to spend!

Hope you get some decent weather before the week is over. And drive home safely, buddy.

[Satchmo]

Originally Posted by Rodstar

Mark,

The mirror is two inches thick. What thickness of mirrors do you use? I am surprised that you would think there might be vertical mirror bend on the horizontal axis from such a thick mirror, or that this could so significantly affect the Strehl. Can you clarify??

I am aware that Strehl is only one measure of the quality of a mirror, and does not disclose other potential failings in the mirror, such as astigmatism or a turned edge. I'll let you know how the mirror performs in real life when I have a decent night's observing under my belt. In the meantime, I am not going to anticipate any negatives unless they become apparent.

Hi Rod ,

I wasn't intending to cast any doubt on the quality of your mirror. 20" mirrors regardless of thickness bend about 1/2 wave with axis *horizontal* regardless of whether being 1.6" or 3" thick. ( In answer to your question I use 1.6" as they perform perfectly on an 18 point cell and cool faster than 2" ). This mirror bend is almost gone by the time you are pointed 15 degrees above the horizen. It is with axis *vertical* that thicker mirrors need less float points. But ( horizontal ) thats not how you use your scope, and the wavefront quality from the sky near the horizen would be many waves anyway.

I responded in an 'educational' sense when I saw you make a comparison about your mirror not being 'quite as good as Mike Sidoneo's 12" , by comparing the Strehl ratio's. From memory Mikes mirror being a lot more rigid, allowed the opticians to leave the Astigmatism component 'switched on' in the output. Makers of large mirrors usually subtract it out to show a high Strehl number and more indicative of the good spherical aberration correction) and use judgement and experience to make that call. That is the sense that I meant there was artistic licence involved. A proper analysis of a large mirror to extract the true astigmatism component would probably cost more than the mirror. So to keep mirrors affordable you have to trust the optician and their reputation.

Strehl is probably a bit too mis-understood as a `golden bullet' and it is just not possible to make comparisons of different size mirrors on the basis of Strehl alone, as it is usually derived in basic interferometry by fitting polynomals, and doesn't really cope or take account with small period zoning, roughness , astigmatism , and turned edges. Phase shifting interferometry is better at those things but I'm not aware of any opticians to the amatuer industry using it.

OMI certainly know what they are doing, it wouldn't really matter what documentation they supplied, they have a great reputation. I've only looked through John Bambury's 18" but there were certainly no isssues there and yours won't be any different I'm sure .

Hope this clarifies your questions and proved educational.

[Ambermile]

Originally Posted by ving

jupiter is gunna be almost too bright for the scope me thinks

Certainly is in mine - if I want to peek it's better at dawn when the skies are a bit lighter atm. Better that than drilling a hole through my eye. Even the Moon with a 7mm nagler (680x) needs an ND to tone it down a bit!

You're going to love this scope Rod

Arthur

[AstroJunk (Jonathan)]

Originally Posted by Ambermile

with a 7mm nagler (680x)

that makes your scope F8+! Thats a big Ladder, or a tiny miscalculation

In answer to an earlier point about left/righthanded dobs - I don't think there is a true reason. Obsession started the trend and it has kind of stuck. It actually makes more sense in Australia, as much of the time is spent looking North, so the scope tracks away from the ladder making it safer.

It took me while to get used to initially, but now it feels more comfortable than t'other way.

[Ambermile]

f/4.8... yup, 380x not 680x, sorry! FL is 2700mm

Ah - you are also right on the track away bit. Still means you can fall off the ladder though, but you just hit the ground rather than the ladder on the way down

Arthur

[Rodstar (Rod)]

Mark, thanks for clarifying your comments. I note we agree that Mike Sidonio's mirror stats are better than mine, which is actually all I said!!!

[acropolite (Phil)]

Congratulations Rod, looks like a beastie. The weather here in Tas is clear at the moment, so load up the car and drive on down. I'm curious as to how long the mirror will take to cool.

[GTB_an_Owl (Geoff)]

save some of that clear sky to-nite for us to-morrow nite Rod

Pleeeeeeeeeeeeeeeeeeeeeeeeease

should be out there myself - but too much to do if i gunna take to-morrow nite off for kulnura

geoff

[MortonH]

Since you referred to the scope as "her", why not name it Stella?

Morton