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Posts Made By: Phil Barker

September 8, 2002 08:04 PM Forum: Telescope Making

getting a flat coated

Posted By Phil Barker

Am about to embark on folded newtonian scope. I have the secondary and primary both extremely fine optics.

The flat is better than 1/10th wave the primary purchased thru astromart for $900 a 20 inch f-6.05 is 1/14th wave on the wavefront and zone free according to my foucault tester.

I still can't believe what a bargain that primary is. 2 inch fine annealed pyrex to boot!

I wish to get the flat enhanced coated or if possible the new 98% coatings we all hear about.

Is this possible?

Any help appreciated.

The design if your're interested has the primary 92.5 inches from the 6 inch secondary with a tertiary then diverting the light to the focuser which is low profile.

Full illumination over 1.2 inches results which will do nicely.

The primary can be coated locally for peanuts(about $75US) but only standard 89% coat available and I'm not paying to send it overseas.

I live south of Australia in New Zealand.

September 10, 2002 02:20 AM Forum: Equipment Talk

coating a flat

Posted By Phil Barker

thanks Herb.

From what I understand enhanced coatings are not available in australia. In any event Australia is a long way from NZ and pricewise the US is usually a better for astro gear etc.

I will contact your friend and see if he can help.

February 8, 2003 12:25 PM Forum: Equipment Talk

Meade 8 inch f-10 sct optics

Posted By Phil Barker

I've owned a 2000 lx200 8 inch f-10 for over a year now. purshased for a song on astromart.

Standard coatings etc etc.

Finally got the chance to use it is superb seeing on Jupiter and compare it to a host of other scopes including a parks optics 8 inch f-6 newt plus an ap6 inch f-9 from the early 90's.

This was at the South island (NZ) stardate on Friday night. 100 astronomers and superb conditions.

Also a 6 inch f-12 D&G.

The D&G was the best planetary scope there a whisker sharper in than the AP which surprised me. Colour correction better in the AP but on Jupiter the D&G was showing slightly more. The AP isn't the current model.

The SCT was behind the other 3 less contrast but a respectable performance. On Jupiter virtually everything was visible in the sct but slightly lower in contrast as expected.

I finally got to startest at 300 times in perfect seeing condition on a bright star overhead and the Meade showed a very fine optical figure. Slight undercorrection only just apparent close to 1/8th wave I suspect.

For the price they pack a punch. On DSO's the meade was also doing very well. A 10 inch meade sct from about 1990 with mediocre optics was also present and the 8 was clearly better on jupiter and Saturn.

Looks like meade are getting it right with the optics.

February 11, 2003 12:40 AM Forum: Equipment Talk

Meade standard coatings

Posted By Phil Barker

Are these the same as the emc multi-coatings. I see an add with the seller saying they aren't.

Whats the story in a reference to the mirrors in my lx200 manuel it states the reflectence is around 94% which would mean more thruput than the standard coatings shown in the ads or its wrong?

Interested in opinions

February 24, 2003 05:40 PM Forum: Solar System Observing

Mars 22.2.2003

Posted By Phil Barker

Viewed from 43 south with 5 inch f-15 D&G
8mm televue plossl 254 X 6 mm zeiss orth 312 X

Planet 5.8 arc seconds approx.
Polar cap visible and noticeably gibbous disc.

Not a lot of surface detail apparent still very small. Didn't bother with a sketch will wait til she's bigger.

This opposition will seriously favout the south and on Aug 27 she's 25.12 arc seconds I can't wait!

March 4, 2003 10:12 AM Forum: Solar System Observing

C/2002 V1 (NEAT) looks great

Posted By Phil Barker

I saw this comet visually from my light poluted backyard 2 days ago and last night went to a dark site to see it easily with about 3-4 degrees of tail and quite a bit of detail in the tail.

Took 14 135mm 9f-2.8)telephoto shots with 400asa slide film and looked at comet through my 8 inch lx200 very nice.

Small bright coma possibly 3.5 but tail very bright total magnitude probually 3 or so. I'm not expert on comet magnitude estimates it was nice nowhere near halebop obviously but a nice naked eye spectacle to the south west.

The site was at west melton christchurch. I'll post pitcures I want another crack at this comet tonight may try a 300mm shot for a closeup.

March 27, 2003 08:44 PM Forum: Telescope Making

polishing with a sub diameter lap

Posted By Phil Barker

A question

If you have a 13 inch mirror and a 10 inch lap to polish it with what stroke do you use ie is the stroke length 1/3rd of 13 inches? ie would take the 10 inch lap if working on top to just over 2 inches above and below the 13 inch.

Or is the stroke simply just over 2 inches forward and back of the 10 inch tool?

Very interested to see which one applies?

May 25, 2003 04:51 PM Forum: Telescope Making

bvc glass my experience with it

Posted By Phil Barker

I thought I would briefly share my experience of this glass v plate and pyrex.

i just completed a 13.25 inch f-5.6 mirror with the glass and I'm reasonably happy with the scopes performance.

However I ran into a number of interesting problems with the glass in terms of polishing and especially the figuring stage.

The glass was very difficult to get a really smooth polish and i went for softish pitch in the end and finished the figuring with a full tool used along with a 4 inch starlap type tool.

I ended up over correcting and coming back with accentuated pressure full tool on top.

Found this smoothed the surface but I struggled to get repeatable measurements when i rotated the mirror. Pyrex is far more predictable and overall was easier to use.

I did a 13 inch f-6 with pyrex for a friend first and it was a walk in the park when compared to the BVC.

It is soft and prone to sleeking. i never got rid of all the sleeking on the surface. I am however happy with the views and appear to have got close with the figure.

It polishes fast but is prone also to astigmatism if not careful. I had varations in the order of 15-20 % in terms of the caustic zone from centre to edge after intial figuring. I got this much closer with patience and care but I have never experienced anything like this variance with Pyrex or plate.

I would not use this glass again because of the figuring problems it took a long time to get a reasonable even figure. The more experienced amongst you may be able to tame it better but I know one very serious atmer who has done work including wright schmidt scopes who had the same problem.

One positive is the very quick cooldown when out in the field it does what itr says and is clearly at least as stable re temperature than pyrex.

One last thing the glass is slumped to form a shape and should never be ordered and then ground as it consists of 1/4 inch sheets baked together.

May 31, 2003 03:30 PM Forum: Telescope Making

Why f-5.5 is better than f-4.5

Posted By Phil Barker

I was running my 13.25 inch f-5.6 scope up against a very fine 12.5 inch f-4.5 at low power.

At f-5.6 the ammount of coma visible is minimal its hard to notice at all the number of people who have commented on this amazed me. All are use to our fine 12.5 inch f-4.5 newt. With a 40mm pentax xl (65 degree field) I get near the best poss deep sky exit pupil at 7mm!!

granted the tube or trusses are longer and a ladder is the order of the day for the vertically challenged like myself at 5 foot 9.

The f-4.5 is a fine mirror and works well at high power but the coma really detracts from the image at lower powers. Even with a paracorr it does'nt match the uncorrected f-5.6 images.

Then there's the figuring even a slight mistake in an f-4.5 is far more devistating than an f-5.6.

the 12.5 inch f-4.5 as a sphere has over 3 waves of spherical aberration to remove and the 13.25 inch at 5.6 its 1.6 waves.

If the respective parabolas are 10% undercorrected they read for the 12.5 inch approx .3 wave

and for the 13.25 inch at f-5.6 .16 wave well under diffraction limited.

I struggle to see reasons to go for a fast parabola in fact the idea scares me.

I have to admit I have the upmost respect for those of you out there that pull it off and make a good deep parabola. It still needs a paracorr or similar to give the good edge definition.

I will be using a ladder on the 16 inch f-5.5.

Convince me I'm wrong I'm interested to see what people think on this one.

July 2, 2003 11:59 AM Forum: Equipment Talk

European Maks standard v delux

Posted By Phil Barker

I'm in the market for a european Maksutov.

The standard versions of a lot of russian Maks are pyrex mirrored and typically of a lesser strehl ratio wavefront error than the delux which have
-ceramic mirrors
-better coatings.

Is the extra money worth it??

Has anyone owned both and in a position to comment?

Phil B