Posts Made By: Alan French

Very nice. I still have to stop myself from saying Myrtle warbler.

Clear skies, Alan

About the only thing that would pique my interest is a computerized telescope that responds to "get back in the car" (and it doesn't have to have any other computerized features). My wife has wanted one with this feature for years.

Clear skies, Alan

THUD! Past redemption now.

Clear skies, Alan

UO sold a kit to make a 80mm refractor of 500mm focal length. For a time I think there were implications that the glasses were something special, but it was simply an achromat using SF2 and FK5, and had a very typical color error from C to F a bit better than 1 part in 2000.

I had one here for a few weeks, and it was a very nice achromat.

You can use a green laser to identify fluorite (the beam is visible in any glass, but not in fluorite), but there is no simple test for ED glass.

Clear skies, Alan

Wes,

The Feathertouch is a fine focuser, and I find myself wondering why you want an electric focuser. I have used some scopes with motorized focusers. I think they are horrid, with one exception that I'll cover after my rant .

Focussing usually involves going toward best focus, passing it a bit, and then going back a hair. With the electric focussers I've tried, I found it much more difficult to "back up" that tiny bit to the best focus. They just didn't stop the motion as easily or reliably as I can do myself, and it took a lot of button pushing to get the focus where I wanted it. I'll stick with my Feathertouch.

At WSP two or three years ago TEC had a Mak-Cass - I hope I have these details right - with a very nice electric focuser. There was a hand control with a pot (potentiometer) you turned, with the position of the focuser corresponding exactly to the positon of the pot. You could very easily back up just the right amount. Far, far superior to those with a button for each direction, IMHO.

Clear skies, Alan

The folks selling binoculars give exit pupil because it is supposed to imply something about the abilities of the binoculars. During the day, at least when it is reasonably sunny, our eye is open to 2 to 3mm. If you use an instrument with an exit pupil larger than this, you are stopping down the objective diameter. You are, however, still getting all the light and all the resolution you could possilby get at that power.

During deep twilight, your eye's pupil opens up to 5 to 7mm, depending loosely on age, and a larger binocular will deliver more light to the eye.

For astronomy, at least, the exit pupil does not seem as useful. Binocular users have found that increasing either objective diameter or magnification increases your ability to see celestial objects. In spite of its smaller exit pupil, a pair of 12x36 binoculars will show more than a pair of 7x35s will.

The blackouts are generally because your eye is not correctly posistioned at the exit pupil. With 7x42s I almost never have this happen, but with my 12x36s I have to be careful positioning my eye. Incorrect eye position caused by incorrect IPD can also produce added chromatic aberration.

Clear skies, Alan

Jeff Thomas said:

Just a quick poll. Given equal quality and prices and assuming a mix of deep sky and planetary observing, would you prefer a 3 inch APO or a 4 inch acromat?

To my mind, the big advantage of an APO is the ability to get good correction in a short focal length. A 3" APO is generally short enough to provide nice wide, low power views, yet is able to handle high power planetary viewing and yield about as much as any 3" can show.

You can get a reasonably fast 4" achromat that will also give low power wide field views, and secondary color is not much of an issue at low powers. Things will get pretty nasty for high power planetary viewing, however.

A quality 4" f/15 is going to be a nice planetary scopes, and it will give fine views of deep sky objects, but will be incapable of low power, wide field views.

Properly mounting a 4" f/15 OTA is not trivial, especially compared to a short 3" APO, and even a 4" f/15 shows some color (an f/20 would be essentially color free).

I was able to use a 4" f/15 Clark for a while, and I really enjoyed it. Although I'd love to own such an instrument, I'd consider a 4" f/6 APO a better and more versatile choice.

Clear skies, Ala

I have used the 10x30s and own the 12x36 IIs. They are quite light, and the IS system works very well. The 15x50s or 18x50s would certainly show you more, at the expense of field of view and extra weight. Since I use mine also for birding, I did not want the weight. You will also find the larger sizes are considerably more expensive.

You can compare bincoular performance on the night sky by simply multiplying the magnification by the aperture, giving Bishop's "Visibility Factor." Adler thinks magnification should be given more weight, and multiplies magnification by the square root of the aperture. In either case, increasing aperture or increasing magnification increases what you can see in the night sky.

In some cases, you might want to give some weight to true field of view. A 7 or 8 degree field is not something you can get with a telescope.

Clear skies, Alan

David Wasch said:

Ok, I’m starting to come to the end of my rope with a mirror vendor.
{SNIP]
Flash forward 10 months, and I start to become concerned because Mars is coming and I want to have the scope finished. The vendor and I decide to pull the plug on the order, and he says he will get a refund out to me ‘shortly.’

Since that time (two months ago), the vendor has refused to answer three e-mails over the past six weeks asking for the status of the refund. I know the vendor is actively receiving e-mail, because he posts on these forums.

I have run out of the friendly options for the refund and I need my money back to finish building my telescope. I figure I can go to the Better Business Bureau, but don’t know what other steps will shake a few coins out of this guy’s pockets. Any advice would be appreciated (yes, I know I should not have gone with a vendor with a bad rep).

-David

David,

Do you have a phone number for the vendor? If so, have you tried calling. Personally, I've never thought e-mail was a good way to try resolving such problems. For one thing, even through you see posts by the person here, it is no guarantee he actually got your e-mails.

Good luck - I hope you get your refund. If not, I don't think you should be shy about mentioning the person by name. It is hard for a company to complain if you say "I ordered a mirror on mm/dd/yy, I have asked x times for a refund over y weeks, and I have neither a mirror nor my money," as long as your report is accurate.

Clear skies, Alan

IMHO, a cork or flock lined unpainted aluminum tube is the best choice for a Newt.

Sonotube does work well, but really needs a good set of stiff end rings. They protect the ends of the cardboard and add greatly to the stiffness of the tube. Alas, most commercial scopes have mere cosmetic end rings, and they do little to protect the ends and nothing to add stiffness.

If John has a Meade Starfinder Dob, with the closed back and the steel ring to move the balance down-tube, it would benefit greatly from opening up the back to allow good airflow, and removing the heat storing steel ring.

Clear skies, Alan