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Posts Made By: Kevin Barker

August 4, 2002 04:13 AM Forum: Deep Sky Observing

Venus

Posted By Kevin Barker

I was rewarded today with a view to die for of Venus.

I am observing from approximately 37 degrees South in the late afternoon with my 5.1 inch apochromat.

I could make out terminator variations in brightness. Subtle cloud bands curving upwards and away from the terminator. It was rock steady at 166 X and I even tried 250 X at one stage. I used a variety of coloured filters but preferred the unfiltered image best.

It is well worth a peak. Especially when the planet is high up in the sky as it is to Southern observers at present in the afternoon.

Give it a whirl. It is just above a first quarter type phase.

Kevin Barker

August 7, 2002 03:30 AM Forum: Film Astrophotography - Imaging and Processing

ADVICE SOUGHT RE FILTER PROBLEM

Posted By Kevin Barker

Hi,
I have a wee problem that some of you folks may be able to help me with.

I am attempting to take some 35 mm slide photographs of Southern celestial targets from my back yard in a light polluted city. I am using an excellent clock drive that allows exposures of up to 8 minutes or more with perfect tracking.
I am using 800 ASA slide film.

Results so far have been very encouraging. I would however like to introduce a broadband filter to reduce sodium vapour light pollution.

The scope I am using is a 130 mm f7.7 refractor. The scope's photographic accesories use a Zeiss M44 thread.

I have a M44 to T adapter and use Olympus cameras for prime focus. Does anyone know where T threaded broadband filters are found??

Also what other alternatives are there for filtering. Perhaps a female T thread to male 2 inch adapter and a female 2 inch to male t threaded adapter are possible??

Also are two inch filters like say Lumicon's deep sky filter male and female threaded???

Thankyou for looking.

Kevin Barker

August 11, 2002 11:40 AM Forum: Equipment Talk

Re: 20x80 binocs or 7x50 or what???

Posted By Kevin Barker

Rob
I too read Alan Adler's article and agree he made some good points.

I am not totally convinced with his index system. I personally prefer a wider exit pupil and higher quality construction and optics.

I use the 10 X 70 Fujinon's under a dark sky held by a solid wooden mount. All objects are viewed well and the improved optics mean resolution is still great. The 16 X 70's would work well too if you insist on more power.
My 10 X 70's show brighter or larger galaxies superbly.
The Lagoon nebula with the 10 X 70's is amazing.

These binoculars are more expensive but i think in the long run they pay for themselves.

Repeatedly using binoculars and removing and placing on a mount eventually weakens cheaper construction and collimation suffers.
Kevin B


August 22, 2002 04:58 PM Forum: Deep Sky Observing

PLATO

Posted By Kevin Barker

I have asked questions about Plato before. Here is another.

Two nights ago(between showers) I observed Plato a couple of days before full moon. I find a full moon is also a good time to view plato and the surrounding areas.

I viewed 4 craterlets including the double craterlet.
Telescope was a 130 mm apochromat. Power used 166 X.
Seeing was OK perhaps 7/10. Antares was split OK at 166 X. Nu scorpio's double double was just discernible at 125X.

I was not able to discern the 5 th craterlet that is closer to the triangular wall feature(See Rukl's map)3 or 4??

What aperture do others find necessary to view these craterlet?? Especially the 5 th. I have viewed these 4 in a 100 mm apo too and the central crater in a 63 mm refractor??

Your experiences on this fascinating crater are rrequested??

Best wishes

Kevin Barker

August 30, 2002 03:27 PM Forum: Deep Sky Observing

ASHEN LIGHT!!!!!!!

Posted By Kevin Barker

Well last evening my good friend and fellow astronomer (Larry Field)and I were observing Venus in very good seeing.
It was about 6 pm and Venus was high in the West perhaps 50 degrees altiude and decreasing.

We were viewing through thin cloud that was intermittent and extremely slow moving. Telescope was my Zeiss APQ 130/1000.
We were using a 6 mm Zeiss orthoscopic(166 X) with and without Schott glass filters Blue, yellow green, neutral density and green. We both saw subtle shadings and terminator intensity variations.

We decided to record and compare what each was seeing. Independently this was done. While I was finishing my sketch I was damned if I could make out the unlit edge of the planet continuing around 50 % of the unlit limb at the top and slightly less at the bottom.

It was unmistakable and best seen with the yellow green filter. I muttered this to Larry and he replied" I did not dare mention it but i could make out the faint outline of the rest of the disc"
We were trying not to interfere with each other's independence while sketching.

We swapped back and tried to see it in white light and when the disc was bright it did not show. But it was there when cloud partially obscured and acted as a filter.

Cloud then proceeded to blanket out our viewing.

Later we compared sketches and our sketches of dusky markings correlated well.

This is the fourth occasion I have observed the Ashen light.
It was barely perceptible this time. Other times I have observed with a C8 and my APQ 100/1000 and seen "The Ashen light".

Kevin Barker

October 28, 2002 12:09 PM Forum: Equipment Talk

CLEANING SOLUTIONS FOR COATED LENSES

Posted By Kevin Barker

Hi folks

I had a discussion with a friend recently and we discussed whether or not alcohol based solutions were usable with coated lenses.

Because of the alcohol dissolving the MgF2.

With modern hard coated lenses is this still a concern?

I know with my prescription eyewear(plastic lenses) it is best to use a detergent/water based cleaner. I presume this is because the coatings(MgF2) can not be hard coated (this requires high temperatures)

I would be interested in hearing your thoughts on cleaning modern eyepieces and objectives. I realise that objectives should only ever be cleaned rarely.

Also what techniques/solutions do you folks use.

Thankyou
Kevin B

November 14, 2002 07:19 PM Forum: Equipment Talk

Re: p.t.v. error on Discovery mirrors?

Posted By Kevin Barker

Rob
If you are happy with your telescopes optics perhaps do not worry about the mirror figure. The secondary mirror will also add to the errors in the images as may also your eyepieces.

It must be a reasonably good figure if the views are nice and sharp. To get a near perfect figure will cost a lot more and may not improve images by all that much more.

P-V,etc is quite a complex subject. Also how much of the wavefront is in error and measures of overall average error e.g.(rms)need to be considered when judging an mirror or optics. The main P-V error of part of the mirror may be quite small or the mirror may have a small P-V but quite a bit of surface roughness.

Quoted figures of manufacturers are often the surface accuracy of the main mirror rather than the overall wavefront error leaving the optical system.

Star testing is one way of assessing the optics of a telescope. Suiter's book "Star testing Astronomical Telescopes"is useful here but it is not an easy read. The physics is rather complex. Star testing is not easy to master.

Best wishes

Kevin B

December 2, 2002 05:46 PM Forum: Refractors

Restoring a Cooke

Posted By Kevin Barker

I have attached a picture of a restored 5 inch Cooke refractor that is soon going to be up and running for public viewing and also solar viewing at the CAS(Canterbury Astronomical Society)observatory at West Melton, New Zealand.

The Cooke dates back to the 1870's and has had several illustrious owners one who discovered several comets with it.

My brother Phil led a group of refractor nuts that have completed a soon to be added copper dome made from an old beer vat which i helped with on a recent holiday.

I thought you refractor fans might enjoy this sight.
The f15.66 telescope performs similarly to Phil's excellent 5 inch D&G f 15 refractor. A review comparing the two can be found at cloudynights.com.

Best wishes

Kevin Barker


February 11, 2003 12:42 PM Forum: Deep Sky Observing

Re: Transit of GRS

Posted By Kevin Barker

I enjoyed thw same spectacle at about 1200 UT on Tuesday.

From 37 degres South and warmer climate. instrument a 5.1 inch apo. Seeing was 6-7/10 only alas!!

The swirling in the GRS and preceding turbulence you spoke of was easily evident as was the equatorial belt.

I was too damn tired to try and photograph or sketch the spectacle.

Best wishes

Kevin B

March 18, 2003 02:45 PM Forum: Zeiss

Zeiss 15X60 versus Fujinon 16X70

Posted By Kevin Barker

I read with interest the claim that the Zeiss 15x is brighter than the Fuji binoculars.

This really surprises me considering the high levels of transmission for Fuji's fabled EMC coatings of over 95%.

Simple physics would suggest the 16X should be brighter.
The exit pupil is slightly larger and also the Adler index and twilight factor is also higher.

I own the 10x70 FMTSX. They are really well coated certainly better than my Zeiss Classic 10X40T*P's.

I am considering buying the 16X70's for the extra magnification.

Is it extra contrast because of exotic glass used in the Zeiss. Does excess chromatic aberration in the 16X70's play a part?? or is it possible the extra brightness claim is conjecture not supported by reality????

Surely the 16x70 will show a faint extended object as brighter and also show fainter stars??

Your thoughts??

I know Zeiss gear is great I own 5 Zeiss refractors/objectives and 3 zeiss binoculars but heh physics is physics!!!!

Kevin B