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Posts Made By: Lorne Johnson

April 24, 2009 03:28 PM Forum: Deep Sky Observing

Optimum exit pupil for galaxy details?

Posted By Lorne Johnson
Mike Alexander said:

In your opinion, what is the optimum exit pupil range for viewing details in galaxies? I have a Meade 12 inch LX90, f/10.

I am 61 years old...retired and lovin' it.

Thanks for any feedback.

Clear skies.....Mike

This isn't scientific, although it is empirical. The ideal exit pupil is often presented as 2mm. In your scope that would be a 20mm eyepiece.

In my personal experience with an f 5.7 8" dob, I have seen the most detail on galaxies with a 9mm eyepiece, as opposed to the 13 mm eyepiece (which ain't bad). I was surprised by this result, and it seemed to hold up using some different eyepieces of similar focal lengths. So it may be that 1.5 mm works better for me. Obviously it does with that scope.

I would suggest trying out some different options at star parties.

April 24, 2009 08:29 PM Forum: Refractors

Opinions? TV60 vrs Tak FS-60C vrs SV70ED

Posted By Lorne Johnson
Jackie Pritchard said:

Has anyone used 2 or more of these and can compare them? I know the TV and Tak are excellent quality, but can they overcome the disadvantage of having 10mm less aperture? My quandary: the TV and Tak are expensive for their size. If they would only give me a small advantage - say 10 or 15% - over a less expensive Stellarvue SV70, then I would opt for the Stellarvue. If they would give me a significantly better image - say 40%-50% - then I would consider biting the bullet and paying more for a TV or Tak. Now, I know one can't put exact percentages on this sort of thing. So basically, I am asking if spending significantly more money for a TV/Tak will equate with a significantly better view, or it will be a relatively small difference because the Stellarvue has more aperture and is a fine telescope itself? I have larger telescopes (80mm triplet apo & 4" fluorite refractor), so I am not interesting in opinions about the advantages of going to an 80mm or 90mm telescope. I want one of these 3 telescopes for travel and quick looks. I don't want to spend more than necessary, but I am willing to pay a premium IF WARRANTED. I can get the Stellarvue for hundreds less that the TV or Tak.

I think that you are selling Vick Maris and Stellarvue short. The 70 mm is a new design, and the optical quality should be right in line with the TV and Tak, although the f ratio at 6 is pretty fast. I've used a Tak FC 50, and while it was a very good 50 the TV Ranger with a relatively crude ED Doublet killed it. On top of that my daughters Stellarvue 80 9D (a mere achromat) smacks the TV Ranger. So, I think that you are likely to be very happy with the SV 70 as a travel scope.

April 28, 2009 01:42 AM Forum: Refractors

SV105 or TSA 102

Posted By Lorne Johnson
Rich Camarda said:

Which one would you get, and why? (not considering price as a factor.


I am a visual observer, so I would question the value of either scope (for me), although the quality of the optics in either scope are superb (quality of the machining is comparable). They are both 4 inch objectives. For imaging the Stellarvue has a slightly wider field of view. Tak is something of a proprietary brand which might annoy some folks.

So, do you own a Holland and Holland or a Purdy?

May 1, 2009 05:48 PM Forum: Telescope Making

Flocking inside of upper cage

Posted By Lorne Johnson
David Tarshis said:

What have you used, what works well? I looked at Protostar's flocking paper, which would be awsome. But being as cheap as I am, what would work from say a fabric store? 5.00 to ship a piece of paper is a bit pricey for me. Thanks


I believe there is a comparison review of materials on cloudynights.com that would be a good starting point. They really liked something from JoAnn fabrics.

May 29, 2009 01:49 PM Forum: Telescope Making

Any thoughts on the best dob kits?

Posted By Lorne Johnson
Jack Bruneau said:

I'm thinking of making a nice dob, but by the time I spend the money on the power tools, I might as well buy a nice Obsession. What are the best kits out there? Thanks for your input.

Be sure to check up carefully on the company's ability to perform on an order. I am having a terrible experience with ED Taychert at TScopes--as in three years and nothing happening.

June 10, 2009 04:03 PM Forum: Beginning Astronomy?

. Dobson 8 or 10 " Meade or SkyWatcher

Posted By Lorne Johnson
Jon has it right (not surprisingly). They are both good scopes, so you won't really go wrong.

A lot depends on how you will use it:
If it's opemn the garage door and carry it out 20 feet, I would go for the 10" on the appeture rules theory.

If it's carry it down two flights of stairs from your apt., put it in the VW bug, along with you wife and 8 year-old, drive 20 miles and move the whole thing 150 yards to the observing sight, I would definitely go with the more collapsible 8" truss.

If the 10 inch is within a reasonable drive, see how it fits in your car, and follow the theory for shoes.

Note that I have said almost nothing about the scope, and a lot (okay--too much) about where and how you observe, or image you will observe.

June 22, 2009 01:05 PM Forum: Refractors

Help with pinched optics

Posted By Lorne Johnson
Brian Coltrane said:

My Vixen 80SS I got last winter has always shown signs of "pinched optics". I had read that it's not uncommon for factories to overtighten lenses, and that colder weather can make it worse due to the aluminum housing contracting; but it hasn't gotten any better in the warmer months. I took out the lens cell to see if there were some screws I could adjust, but the lenses are held in place by a large (+/- 80mm) threaded ring with two tiny slots for a very special tool to grab. I'm afraid to go much further with trying it myself, but I'm having difficulty finding anyone who will work on it? Any suggestions?
P.S. I did call a nearby astronomy dealer who sells Vixen scopes, but since I didn't buy it there, they won't help me.

Martin has some good advice below. I would simply add that the "very special tool" used to be fairly common at larger full service photo shops. At 80mm on the objective, you are likely to be able to find one, or find a camera repair place with one that could unfreeze that retaining ring for you.

July 26, 2009 01:53 AM Forum: Eyepieces

best Planetary Ortho or radian for my 12" Dob?

Posted By Lorne Johnson
Those are all good eyepieces.

In a 12 inch f5, some are better corrected thatn others, the Televue plossls, the Super Monos are good at that f ratio. The taks may well be, but I can't confirm it.

The orthos are slightly correection limited beginning about f6, but it is not really a big deal at f 5.

Other factors become rather more important, such as field of view, especially if you have a a 12 inch dob and rely on the object drifting across the field. Nagler type 6's are very good for this application.

In the Maks at f 10 plus, "all ist klar."

Paulo Mesquita said:

For my 12" f5 Dob and my 127mm and 180mm Maks which of these EP's is the best for planetary views? With ther most AFOV?

TMB Super Monocentric,
Zeiss or UO Abbe Orthoscopic,
Brandon Orthoscopic,
Clave or TeleVue Plossl,
Takahashi HI LE Ortho.

Expert opinions needed. Anticipated thanks for any tips.

Cheers

August 9, 2009 05:54 PM Forum: Equipment Talk

Truss Dobs

Posted By Lorne Johnson
This may be unnecessary since no one has mentioned the name. But, T Scopes owned by Ed Taychert, appears to keep taking orders and has had really serious problems with delivery.

There have been a number of law suits. (Yes, I lost some money, probably less than many others.) It's too bad, because his design is significantly lighter than others.

October 27, 2009 12:59 AM Forum: Beginning Astronomy?

difference in telescopes.....

Posted By Lorne Johnson
Todd Smith said:

Other than length of the OTA, what is the difference between an 8" mirror (newtonian) and an 8" SCT. I understand the physical difference in the scopes themselves, but what is the visual or photographic advantage to one over the other? Can anyone help me with this? Is one better for photography? or for visual observing?

They all work and they all have their quirks.

Most Newtonians are dobsonians and better for visual than photography. They are typically f6 and have a central obstruction of about 20% (of diameter). All else being equal, this should give the Newtonian a wider maximum field of view, and higher "planetary contrast", a real but subtle characteristic.

SCT, being shorter, fit on a GEM more easily and are therefore more suitable for imaging (in this way). they are typically f10 (almost any eyepiece will work well) and are more compact for transportation. Their central obstruction runs about 35%.

For simple visual use the dob 6 to about 15 inch has a lot of "bang for the buck," to use Eisenhower's classic phrase.

Taste has a lot to do with it, and star parties are a great way to discover one's own taste.

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