Posts Made By: Renato Alessio

September 30, 2002 07:34 AM Forum: Equipment Talk

A question to Experts

Posted By Renato Alessio

I doubt it'll work properly if you take the lens cell out, as those other lenses may well do more than just reduce the focal length.

University Optics used to sell a right angled, erect image, 3X Barlowed gadget that one attached a camera lens and eyepiece to - and you had a telescope. Mine worked as advertised, except that it showed how poor the quality of my lenses were.

Various big photography stores used to sell gadgets that fit on the back of your lens. But those gadgets didn't enable you to change eyepieces. But for 50 or 60 dollars, you'd have a nice low power telescope.

What you may wish to try, is to get a spare rear plastic cap of your lens and some 1.25" internal diameter tube, and see if you can make an eyepiece holder that fits into the plastic cap. You would then have a working telescope.
Renato

October 1, 2002 05:17 AM Forum: Equipment Talk

8" or 10" Dobsonian

Posted By Renato Alessio

The portability issue has been well addressed by the other respondees.

A 10" catches 56% more light than an 8".

If you are going to do most of your viewing from a relatively dark site, then the 10" is definitely the way to go.

If you're going to be doing a lot of viewing from a relatively light polluted backyard, the image in the 10" may be a bit less pleasing than in the 8". You'll still see more with the 10", but the brighter background can be annoying. To get to the background level of an 8", you'd have to bump up the magnification - which may then make the 10" dob a bit harder to use than an 8".
Renato


October 1, 2002 07:59 AM Forum: Equipment Talk

Solar Filter Safety

Posted By Renato Alessio

The important thing isn't the filter, it's the finderscope. One can get so used to using one's telescope, that it becomes automatic - taking off the finder's cap before going outside, regardless of whether it's day or night, and looking into the finder.

Though I'd observed the sun dozens of times, one day I had a solar filter on the scope, hadn't yet found the sun, and looked through the finder for a split second before all alarms went off with a "What the hell are you doing!!!??? Why is the cover off the finder? Why are you looking into it???"

I consider myself lucky that the finder wasn't pointed directly at the sun, just in its general direction. If it came close to happening to me, it could happen to others.

I now tend to stick to using my 80mm refractor on the sun -which only has a Telrad on it.
Renato

October 7, 2002 06:02 AM Forum: Equipment Talk

Quality image erecting prism?

Posted By Renato Alessio

I've got three 90 degree erect image diagonals, two I got from University Optics and one from Pocono Mt. All three are much superior to my 45 degree Celestron erect image diagonal. But all are inferior to any of my prism and mirror diagonals.

Bright planets and the bright stars exhibit a diffraction spike either side of them. So they're suitable for moderate power viewing of DSOs. The images at high power seem okay - you still see bands on Jupiter -until you do a side by side comparison with a standard diagonal.

If you're into eagle spotting, you'd presumably be doing it at lowish power, and would find them okay. For an afocal digital image, you'd probably be better off using a standard diagonal, and using the mirror image function in your picture processing software to get the correct image orientation.
Renato

October 7, 2002 06:17 AM Forum: Equipment Talk

Filter question

Posted By Renato Alessio

I've seen some writings that filters are useless and a waste of money. Yet when I'm lying down at the beach looking up at clouds through various filters (aka sunglasses) I get clear improvement in visibility of many cloud features. Why the clouds on other planets should not be similarly affected, I don't understand.

That said, I mainly use a red filter on Mars to see the ice caps well, Neutral Density filters on Jupiter and Saturn, and yellow filters when using a non-APO refractor.

Most filters do degrade high power views. This may not be obvious when you only use one filter. But stack it with another filter, and the deterioration is impossible to miss. Hence, don't bother with stacked polarising filters for varying brightness.
Renato

October 15, 2002 07:36 AM Forum: Equipment Talk

wideband nebular filters

Posted By Renato Alessio

The Orion SkyGlow and particularly the Lumicon Deep Sky don't dim the view that much. The views on non nebula objects are somewhat aesthetically more pleasing, but without any real additional detail.

I tend to use my wideband ones more at dark sky sites, preferring the narrower, wideband Celestron LPR or the Ultrablock for nebula in my light polluted backyard.
Renato

November 20, 2002 05:55 AM Forum: Equipment Talk

southern hemisphere guide book

Posted By Renato Alessio

Hartung's "Astronomical Objects for Southern Telescopes" 2nd Ed, is the current definitive guide book. The Reidy and Wallace book is more a beginner's guide.

But if you're on a short trip, and don't want anything too bulky, the listings of DSO's plotted in Tirion's Bright Star Atlas is a good guide to the best and brightest must see objects.
Renato

November 20, 2002 06:09 AM Forum: Equipment Talk

Question on Planetary Magnification Increments

Posted By Renato Alessio

I can't see that you'd need the 225X.

That said, if you're achieving 200X with an eyepiece/barlow combination you can get higher power easily - just don't push the eyepiece all the way into the Barlow. Or use an extension tube in the Barlow (if you have a filter adapter, you're in luck, as it's an extension tube).

The further the eyepiece from the Barlows lens, the greater the magnification.
Renato
P.S. - But then again, an eyepiece giving 225X AND a Wideangle may be nice.

November 26, 2002 05:00 AM Forum: Equipment Talk

SCT or Refractor?

Posted By Renato Alessio

Aperture is everything on Deep Sky Objects. The only draw back of SCTs is that you always see big blobby stars, and often don't get good views on planets.

I have a C8 and a 4" APO refractor. The C8 kills the refractor on DSOs. The refractor kills the C8 on the brighter double stars. The refractor is somewhat better than the C8 on planets.

I also have an old University Optics 80mm f/6.25 short refractor. I recollect elderly beginners looking through the various telescopes at a club viewing night. They were being shown all sorts of nebulas and galaxies in 8 and 10" telescopes. Toward the end of the night, they looked at a few big open clusters in Scorpius through my little telescope. They later quitely told me that the best views of the sky they'd had all night were those through my little refractor. There's certainly something aesthetically appealing about refractors.
Renato



December 5, 2002 06:39 AM Forum: Equipment Talk

What makes for a good Cheshire eyepiece?

Posted By Renato Alessio

My Cheshire doesn't have the crosshairs, and it works well - in fact, I can't see how it couldn't work well. (See the article in JAN 2003 issue of S&T, regarding it's accuracy versus a Laser Collimator's).

The cross hairs are certainly handy when aligning the secondary mirror, and saves you having to make up a cross hair sighting tube on the one or two times you need one.

But the cross hairs aren't needed for collimating the primary mirror in normal field usage. All you need to do is put the dark dot into the middle of the annulus, that's been stuck in the exact centre of the mirror.
Renato