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Posts Made By: Kevin Barker

September 2, 2012 12:01 AM Forum: Telescope Making

Another Wooden Refractor... Barkonian!!!!

Posted By Kevin Barker
Or is it a Hiltsonian!! After Dan Hilts superbly designed 5 inch f4.8 scope.

This is a wooden scope made for a niece and nephew as a Christmas present. It has a surplus shed 100/600 lens and a 50 mm elliptical secondary.
It is supposed to be like an Astroscan on legs, hence the red. It is a bit more user friendly than my earlier prototype( a 127/830)

The lens is OK but not spectacular, however in the 20-100 power range it is fine. CA seems more obvious than in my version with an 127/830 lens.


Kevin Barker

June 22, 2002 07:11 AM Forum: Zeiss

Posted By Kevin Barker
Congrats on getting this superb mount.

It is rock solid for a refractor up to about 10 kg or so.

Maybe an inverter could be made to turn a 12 volt source up to a 220-240 V. NZ has 240 volt power so it tracks perfectly.

I got such an inverter made. A friend who is an electronics expert made it for me. It is even rechargeable and works well in the field.

My Ib had a damaged RA slow adjustment.
The mount however is so well made I find releasing the course adjustment works fine. Otherwise I use the seting circles after carefully polar aligning.

It is a beautiful mount.

Kevin B

June 23, 2002 04:06 AM Forum: Refractors

Question for the Optical Police: Am I nuts?

Posted By Kevin Barker
Bob
Is the false colour you see off axis in the TV102?? By this I mean not in the centre of the field of view.

Another issue is how high in altitude was the moon when you were viewing it?? And another is it possible the eyepiece is introducing the false colour on or off axis??

I am sure it makes no difference whatsoever to the quality/contrast of the view.

Chromatic aberration is very subjective some folks seem to see it easily. I recall my 6 inch f-12 D&G had practically no false colour on the moon's limb, just a fleeting violet flash that seemed worse when atmosphere was turbulent. On Jupiter it was easier to see but still not a problem.

I have two Zeiss apo's and neither has any false colour seen in focus. The larger (a 130 mm) shows slightly green out of focus images with Canopus and Sirius one side and possibly purple the other side.

Bloody good really.

The limb of the moon is a tough test.

Kevin B

July 19, 2002 03:57 PM Forum: Equipment Talk

7 x 50's or 10 x 50's

Posted By Kevin Barker
Chris
I personally would opt for the 7 X 50. I have owned both 7 and 10 X 50's and prefer 7's to use.

I find at night it is more difficult to steady the binoculars and effectively the 7 X 50's show as much.

If mounted the 10 X 50's resolve a little more and produce a smaller exit pupil but they will also have less eye relief and a narrower actual field of view. I often lie on an old bit of carpet on the lawn to get a steadier hand held view.( No snakes here in NZ!!!!)

I am in my mid 30's and still have a decent exit pupil so use 7 X 50's by hand and a pair of 10 X 70's on a sturdy mount. When under a dark sky I feel the exit pupil really comes to the fore. If i want to get in closer still I prefer to use a telescope.

Another option might be 8 X 42's?? My partner has a pair and they are a good compromise. Just about perfect for day use as well.

Best wishes

Kevin B

July 29, 2002 06:28 PM Forum: Refractors

% light loss due to chromatic aberration?

Posted By Kevin Barker
Paul
Our eyes visual response (Response versus wavelength)looks similar to the colour correction plot for an achromat which is why they work so well.

Our eyes response to unfocused blue and red light is not as good as green light. So I would qualitatively guess that an achromat will be close to an apochromat of similar aperture.

Especially if it is longer in focus.

My experiences using long focus achromats's bears this out. The differences are slight.

Kevin Barker

August 25, 2002 08:49 AM Forum: Deep Sky Observing

The effect of seeing

Posted By Kevin Barker
Ron
I enjoyed reading this link. I write whilst outside terrible{V} seeing is evident with a cold Southerly wind.

Certainly one gets the steady airy disc a lot easier with smaller apertures.

I have noticed quite a difference with my 100 and 130 mm refractors.

On one of the few occasions I have put both up on the same night the seeing was near perfect for the 100 mm (I)but clearly a {II} or {III} with the 130 mm. Both scopes star test in excellent seeing as perfectly as I can ascertain.

The airy disc sizes gives clues to the seeing in arc seconds on that night.

Also my smaller 63 mm refractor is almost always a {I} or {II}, unless it is a {V}.

Only on two(out of 40 odd) occasions have I had the 130 mm show perfect airy discs.

Perhaps this helps explain why around 80 -100 mm is an optimum size for a high quality refractor.

An interesting aside I read off a link on this forum (Todd Gross quoting others)that many believe that unobstructed refractors handle seeing better compared to obstructed apertures of the same size.

bset wishes

Kevin B




August 26, 2002 10:37 PM Forum: Deep Sky Observing

Unusual star image

Posted By Kevin Barker
Ryan
get scope collimated. Then re startest.

If the images reappear I would guess that it is astigmatism caused by the mirror cooling. Perhaps the mirror is thin and not annealed??

It could also be astigmatism in your eye with the large exit pupil.

Kevin B

September 2, 2002 08:03 PM Forum: Equipment Talk

4" instrument, a serious planetary scope it is!

Posted By Kevin Barker
Ron
I was able to do some excellent drawings with a 100 mm f 10 Zeiss refractor the last three oppositions.

The colour balance and contrast in these scopes is excellent for Mars. Contrast per image brightness is as goos as it gets and I guess Zeiss made the best objectives available ib their day.

They certainly deliver the goods as good as one can expect for a modest aperture. I've yet to see C 8's and homemade dobsonians do as well but I will admit I have'nt spent all that long at their eyepieces. Too busy enjoying the Zeiss views.

And while the 100 mm size will do well with an excellent objective(like your TV102) a 5 inch refractor aperture if made well will do even better.

Kevin Barker

Kevin




September 14, 2002 12:00 AM Forum: Deep Sky Observing

spokes

Posted By Kevin Barker
Kim
You seem to be having excellent time of viewing saturn etc with the steady air. I have just checked my log book and see that it was November 1998 that I saw the markings on Saturn's rings. I was using only 100 mm of aperture.
It was not discernible with a C8(too much brightness per contrast??)Although on the same night a suspected division in the A ring was apparent in the C8.

It was not all that hard to make out when seeing was still. It appeared on one side and looked like a V that started from the C/B ring boundary. I saw it three or four times around 14th Nov 1998. I called them Tores at the time. The crepe ring was also plainly visible on both Ansae.

I have not seen the feature since but will put the 130 into action tomorrow morning to take a peek if the weather settles a little.

Have you sketched your observations??

best wishes

Kevin B

The rings were not as open back in 1998 so maybe the brightness makes these features more difficult to see??

September 19, 2002 08:45 AM Forum: Deep Sky Observing

Saturn's Moons

Posted By Kevin Barker
edz
Good stuff. you sound like you have had good seeing.

Did you see the C ring /B ring boundary was not clear cut. (Read some of the recent saturn posts)

Also did you notice any white spots????

the stripes?? Did you see hints od other ring divisions in the A ring???

Best wishes, weather has hampered any viewing from my neck of the woods.

Kevin B


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