Posts Made By: Jeff Quinn

I first began really seeing detail in Jupiter when I purchased a 6" refractor. You would be very happy with an Orion XT8, as it gives all the detail my refractor does at a fraction of the cost. 6" f/5 is not a planetary reflector, as it will have a large central obstruction and most likely will always be slightly miscollimated, which will hurt the fine details in Jupiter. Aperture really isn't everything, contrary to some peoples' opinions. A good quality scope is really what matters, and sadly, many commercial "budget" range scopes don't show Jupiter very well. But the Orion XT8 I looked through gave a great image of Jupiter after I collimated it for its owner.

Forget the whining of these fools, you are not choking Astromart to death!!! I have seen you refer to yourself this way twice now, either sarcastically or in fun, but I sure hope you are just being humorous! The silent majority regards you as a pillar of the astro community for providing us with this venue.

I think the most basic MgF coatings pass 96% of incoming light on average per surface, depending on index of refraction of the glass. Multicoatings can get up to 99% or better. Then you lose a tad to glass absorption, but normally a refractor should pass about 95% before reaching your diaganol. The oilspaced Astro Physics triplets are very good because the oil seems to suppress reflections all the more, removing what would have been 4 more air to glass surfaces within the triplet lens group. Yep, that's why refractors seem to perform better on deep sky than like aperture reflectors or catadioptrics, plus not losing a small percent of light to the central obstruction.

Where's the FSQ? I see an AP 155EDT on it instead!

If it is of any significance, my older styled University Optics 16mm Konig on my 2x Ultima barlow equalled an 8mm Radian on Jupiter in my 6" ED refractor last weekend. I almost thought I saw a reflection in the Radian that was not there in the Konig, perhaps due to the Radian's concave eye lens vx. the Konig's convex one. Contrast, sharpness, sky blackness around the planet, all the same.

Hi, I have a 12" LX200 and it takes it a couple of hours before I don't see an upward spike in my focused or defocused star images. It might be a current of rising air off the primary mirror, collecting in the top of the tube and refracting the incoming light rays enough to show up as a spike when viewing focused or defocused star images. BTW when I collimate my scope, I do it with the star image in focus. It seems to be much more accurate than trying to center the defocused diffraction rings over the central dark disc of the defocused pattern. I just try to center the airy disc in the surrounding flare (this is done at 200x or above with my scope) and it works very well. I use this same tecnique with my 152ED refractor.

Hope this helps

Clear skies

Jeff Quinn

Here is one little gem which needs Takahashi knobs. This is my new finderscope and quick look scope, which was an Omcon 708 (Sky Instruments) refractor based on a Vixen 80mm f/7 achromat lens and Synta parts. I repainted it, added Protostar flocking to the tube innards, a 2" focuser, stainless steel hardware, and nylon setscrews. A Pentax 40mm XL eyepiece gives a 14.5x straight through view. Just look at how those black plastic focuser knobs clash with the Takahashi aesthetics!

If the 30mm Widescan II worked well at f/4.8 then I think the 31mm Nagler would work well at f/5. Having used both eyepieces, I can certainly say that the 31mm Nagler is a world away from the 30mm Apogee Widescan II for edge of field sharpness. Contrast, I don't know, but I would tentatively guess that the Widescan would be a tad brighter due to less air to glass surfaces and less total glass thickness to absorb light.

I commend you for the choice of the Discovery 15" f/5 dob. Eyepiece height not too high, step stool necessary perhaps but no ladders, and a lot of aperture to satisfy your deep sky endeavors for many years. Just don't get aperture fever! It is a bad, bad disease!

That is great news because the Terminagler is too big!! This one sounds just right.

Jeff Q

My vote is for a Discovery 12.5" truss. If you can afford a 10" equipped with a Zambuto mirror, you can afford a slightly larger Discovery with optics that are certainly very good. Remember Ed Ting's review on this scope?

The larger the aperture, the deeper you can reach into space in terms of brightness and angular resolution. All it takes is perfect seeing and 1/4 wave optics to get perfect images, due to the diffractive nature of light waves. Seeing us normally not perfect, hence the popularity of the premium mirrors which show better images in bad seeing than something a little less expensive. However, judging by the two 14" Discovery dob reflectors I have looked through, you will get pinpoint star images and sharp planet views in "normal" conditions just the same. Discovery optics are quite good.

Jeff Q