Astronomical eyepieces for Pentax PF-80ED?

I have a Pentax PF-80ED angled body scope coming. It is suppose to take any 1.25 astronomical eyepiece. Does anyone have practical experience with this scope or a similar one to tell me the do's and don'ts of buying eyepieces? Can it use barlows? Are some types of eyepieces too powerful (e.g. Pentax XW 3.5)? Will some eyepieces not focus properly because of size? I know I need a very good tripod with good head for astronomy viewing rather than cheap tripod - I have a Bogan with fluid head on the way.

This scope will primarily be used for daytime terrestrial viewing using the 20X60 zoom, but I would like to do a bit of nighttime viewing in the 90X to 105X range. I am unsure of the 4mm eyepiece that would give me 130X (525 divided by 4). Too much? I wanted the Pentax PF-100ED but settled for the 80mm because the larger scope does not come in angled body. I know it would be better for brightness.

I just see lots of eyepieces from Meade, Celestron, Vixen, Televue, etc and I need to know if I can buy and use any reasonably. Since my scope has a 20X60 zoom, I am assuming I mostly need to buy eyepieces in the 4-7 mm range for higher magnification. But would a 10mm or 12mm astronomical eyepiece give me better field of vision or some other quality that I could not get out of the zoom at the same magnification?

Since this is the beginners forum, I am assuming its OK to ask dumb questions like these...

Let me start by saying I have never used such a scope. So what I am about to say is theory.

>>>>>the do's and don'ts of buying eyepieces?

There is lots of advice going on down in the "eyepiece" Forum. But it may be a little too dogmatic for you till you have some experience with your scope and eyepieces. In general you want to buy the best eyepieces you can afford. They will be with you forever, even as you change tubes. I'd say if you have a 20-60 zoom coming with it, you are set for a while.

>>>>Can it use barlows?

Don't know, but if it can use any 1.25 eyepeices, it should be able to, at least optically.

>>>Are some types of eyepieces too powerful (e.g. Pentax XW 3.5)?
Yes, it is possible to overpower a scope. Generally, one can get approximately 50 power per inch of aperture in a quality refractor, so you could expect about 140 or so power in this scope before the image starts to get fuzzier than you like (assuming your tripod can hld it still). There may be a different number daytime users apply because they are dealling with different conditions, but that is the astronomical rule of thumb.

Your scope has a focal length of about 500 mm. If you divide 3.5 into 525, you get that the eyepiece/tube combination is delivering 150 power--just about at the rule of thumb limit. So, yes, this would be overpowering the scope, or close to it. (It depends on a lot of things.)


>>>>>Will some eyepieces not focus properly because of size?
That would have nothing to do with the size as in "focal length" of the eyepiece (i.e., 3.5 mm eyepiece, or 7 mm eyepiece). It would have to a lot to do with the "mechanical size" of the eyepiece. If the eyepiece barrel is particularly long, for instance, the focuser may not be able to get it close enough at infinity to allow it to reach focus. This is not an optical question, but a mechanical one. But before I make a categorical statement here, I would have to look at the focusing mechanism....Just how much travel does it have? The telescope focuses an image at an exct plane, despite where you put your focuser. The location of that plane is entirely dependent on the focal length of the optics (which essentially do not change). "Focusing" is merely moving the eyepiece back and forth until its field stop in where the telescope focuses that image. Whether an eyepiece can focus in a telescope is a mechanical question of whether the focusing tube can move it to the proper place.

>>>>>I just see lots of eyepieces from Meade, Celestron, Vixen, Televue, etc and I need to know if I can buy and use any reasonably.

You also said "It is suppose to take any 1.25 astronomical eyepiece." If that is true, than theoretically, you can. (Again, I have never seen your scope.)

>>>20X60 zoom, I am assuming I mostly need to buy eyepieces in the 4-7 mm range for higher magnification.

Your eyepiece would have an effective focal length of about 8.75 yo about 25 mm. So, yes, if you plan to buy more eyepieces, you would tend to the shorter lengths than 8.75.

>>>>But would a 10mm or 12mm astronomical eyepiece give me better field of vision or some other quality that I could not get out of the zoom at the same magnification?

Zooms are famous for having a narrowed field of vision than the equivalent dedicated eyepiece. I would have to look up what the "Apparent Field Of View" is for your zoom, but I would suspect that with a good set of plossl's wyou would get wider fields. This is not only aesthetically more pleasing, but makes it easier to find and follow things.

Most important advice I would give is to use your scope for a while, and especially to show up at a star party near you and try out some other people's eyepieces. See what you like.
(Oh, and wait for an answer from somebody who knows what he or she is talking about!)
Alex

Thanks Alex, Warren, Peter and Alexis! I feel like I have just stayed at a Holiday Inn Express!