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Posts Made By: Vahe Sahakian

October 7, 2009 10:41 AM Forum: ASTRONOMY

Star Party at The White House

Posted By Vahe Sahakian

Wonder if secret service will allow the White House exterior lights to be turned off if they hope to see anything at all.

Vahe

January 6, 2010 08:46 AM Forum: APM

Mak-Cass Image Circle

Posted By Vahe Sahakian

Generally speaking all Mak Cassegrains that are optimized for best visual performance by implementing smallish co. and narrower center baffles have a very restricted fully illuminated fields, that is the main tradeoff with this design. Reducers can not perform miracles as the restrictions to the illuminated field occurs at the front end.

Take a high contrast image of cloudy sky with a digital camera, preferably with a full frame sensor, and see how much visible light fall off there is at corners of the field and decide what would be the optimum CCD chip size, or acceptable image circle, that clears most of the corner fall offs.

The fully illuminated image circle of my TEC 250/20 is roughly 1mm in diameter or about the size of Jupiter at the focal plane, visually the light fall off is not at all visible at moderate to high powers, the co is 22%, yours being 25% is fairly close to mine.

Vahe

January 15, 2010 04:19 AM Forum: Refractors

Can anyone fix my Unitron?

Posted By Vahe Sahakian

$50,000 is a bit excessive, but if you are prepared to spend about $600 to $700 I would recommend getting a used Takahashi FC or FS60, this little grab & go scope is the best 60mm refractor out there, it is an apo, and , if for any reason you did not like it you can sell it for what you paid for the little thing fairly quickly.

Vahe

February 5, 2010 07:43 PM Forum: CCD Imaging and Processing/Solar System

Mars on APOD

Posted By Vahe Sahakian

Amazing image, I wonder if HST has taken any images of Mars lately, would be interesting to compare the two images.

vahe

February 7, 2010 03:57 PM Forum: APM

Optimal moving primary position

Posted By Vahe Sahakian

Only the designer of the optics has the info that you are looking for.

Generally speaking the optimum design location for the moving primary Maks is somewhere between the two extreme primary positions and that is also where you get the F/12.5, beyond that point the F ratio will also change and depending on the amount of movement allowed the F ratio will probably go approximately from F/11 to F/14 on your scope.

Vahe

August 23, 2010 04:04 PM Forum: Eyepieces

Televue Plossl

Posted By Vahe Sahakian

Are the older TV plossls better then the current line available.

It all depends.

I bought a pair of TV20 Plossl’s a while back after giving up the hope of finding a high end Ortho in that focal length, none of the big boys offer an Ortho in 20mm.
Although there is absolutely nothing wrong with the TV20 I was not impressed very much by its overall quality, it is a decent eyepiece but lacks that wow factor that one can expect from 18mm Pentax Ortho or even the 18mm Tak LE.

I had to have a 20mm planetary eyepiece as it produced 250x, the optimum power for Jupiter with one of my long focus Maksutovs.

Somewhat disappointed with the TV20 I went on a search mission for TV 21mm Plossl, this one was discontinued a while back. The 21 seldom shows up in the classifieds, after two years I came across two, one on CN and another on AM.
I bought both, one was “circle NJ” and the other “R” version, both in like new condition.

Long story short, it is hard to believe that the TV20 and the TV21 are produced by the same company, the TV21 is simply superior to TV20 on all counts, fit and finish, ergonomics, eye relief, performance, you name it, no contest.
I can say the same about my other TV Plossl’s, 17mm and the 26mm, I have a pair of both and they are superb.

Vahe

December 28, 2011 01:32 PM Forum: Eyepieces

Best ones

Posted By Vahe Sahakian

In pairs, 34 ZAO, 25 ZAO, 24 Brandon, 18 Pentax Ortho.

Vahe

January 23, 2013 08:02 AM Forum: APM

world biggest triplet Apo Binocular 12"

Posted By Vahe Sahakian

In these days of everything optimized for CCD astronomy it is refreshing to see someone spending over half a million on a strictly visual setup, good job.

Vahe

September 5, 2013 06:59 PM Forum: Astro-Physics

Re: Yahoo NEO

Posted By Vahe Sahakian

My home computer is iMac and with that computer I get the old look, our office computers are Windows PC and with that one I get the new look, do not understand what is going on, can someone explain.

Vahe