# Orion SpaceProbe 130 EQ question

by AnTiFreeze3
Tags: orion, spaceprobe
HW Helper
PF Gold
P: 3,724
 Quote by AnTiFreeze3 EDIT #2: So I figured out that using the Barlow on the 20mm Night Owl with a 68 degree FOV will decrease its FOV. My new question is how that decreased FOV would compare to a 52 degree FOV of a Meade Super Plossl 10mm, seeing as how I'm not sure how to do the math behind this.
I don't think so. I think you are confusing actual FOV with apparent FOV. Apparent FOV remains unchanged but whenever you magnifiy the image you lose actual FOV. You will be looking at a slightly smaller piece of the sky (actual FOV) but the apparent FOV will remain at 68 degrees. Some report that the barlow can vignette the view a bit but it shouldn't be that noticeable.

edit: Jimmy beat me to it.
P: 251
 Quote by chemisttree ... If you don't want to invest much, you might consider an inexpensive extension to get your 2X barlow up to about 3X. A barlow lens is like a projector lens in that the farther away you place your eyepiece, the larger the magnification. This would definitely not be overkill and would represent a significant increase in magnification vs. the 2X barlow + 25mm (96X).
As for the 32mm with 68 degree AFOV or larger, I was mistaken... I don't know of any. If there are any, I'm assuming that they would be incredibly expensive.

That extension piece actually seems interesting. It doesn't explicitly state that it increases the the magnification of a Barlow lens, but if they work as you claim they do, then I would be all for it.

"The power of an adjustable Barlow lens is changed by adding an extension tube between the Barlow and the eyepiece to increase the magnification." - Wikipedia.

They do mention an "adjustable" Barlow lens, but would a regular, Shorty Barlow 2x lens be acceptable as well?

And from what I've gathered, if I were to increase the distance between the eyepiece and the Barlow lens by the length of the Barlow lens one time, then I would bump up its magnification from 2x to 3x. If I were to increase the distance by the length of the Barlow lens again, it would go from 3x to 4x.

So the Shorty Barlow 2x lens is 3" long, whereas the eyepiece extension tube can increase the distance between the EP and the Barlow by 2", so I should be increasing the magnification of my Barlow from 2x to ~2.67x magnification. That would give me potentially 160x magnification with my 20mm lens (with my scope having a 1200mm focal length), which is, I think, as much as I'll be getting out of my scope, aside from any crystal clear viewing conditions.

That actually seems like the perfect solution, thanks for the idea!

EDIT:

About the corrections, thanks for clearing that up. I think I was a little confused about the difference between the AFOV and FOV. I should've known that zooming in on something obviously doesn't allow me to see as much of it....
 P: 251 So I'm done with all of my purchases now. In the instance that someone else seems to be in a situation similar to mine, with a budget similar to mine, with interests similar to mine, I'll list what I've purchased, from where, and how much the total cost was for it all: - This telescope (Costs $349.99, but note that I was able to snag a Cyber Monday deal and ultimately got it for$299.99). - This 20mm eyepiece (costs $33.95). - This Variable Density Eyepiece Moon Filter Set (was$19.95 at the time; you'll have to scroll down a bit to see it). - This eyepiece extension tube (costs $19.99). The telescope also included a 2x shorty barlow, so take that into account with it all as well. The total price comes out to$373.88 (with the deals that were present at my time of purchase). Considering the fact that I'm getting the telescope and the accessories that come with it for Christmas, I spent well under $100 of my own money, got some very nice equipment, and am very pleased with my purchases. Once again, thanks for all the help that everyone has provided me; I probably won't need to stop by here again until it's time to unwrap presents  Sci Advisor PF Gold P: 9,488 AFOV is the apparent field of view. When you increase magnification, your AFOV is unchanged, but, true field of view [TFOV] decreases commensurately. Your choices look reasonable. The extension tube is probably a waste of money, but, I've wasted a lot more money than that on dubious purchases.  Sci Advisor HW Helper PF Gold P: 3,724 Believe me, the extension tube works as described with the shorty barlow. I've been using mine now for 6 years and it works fine. Eye relief at short focal length is very tight but use a longer FL EP with a barlow and it's nice and comfortable. You can take your time and really concentrate on what you see. You will note that a barlow is built in to every Nagler eyepiece ever made for just that reason. Use the variable polarizer filter on the end of the barlow, equip it with the extension tube and view comfortably through the 20 or 25 mm EP on the Moon. I can't imagine a better way to spend an evening in the back yard. PF Gold P: 7,363  Quote by chemisttree Believe me, the extension tube works as described with the shorty barlow. I've been using mine now for 6 years and it works fine. Eye relief at short focal length is very tight but use a longer FL EP with a barlow and it's nice and comfortable. You can take your time and really concentrate on what you see. You will note that a barlow is built in to every Nagler eyepiece ever made for just that reason. Use the variable polarizer filter on the end of the barlow, equip it with the extension tube and view comfortably through the 20 or 25 mm EP on the Moon. I can't imagine a better way to spend an evening in the back yard. Some good advice here. I have some very short FL eyepieces and eye-relief can be tight. I found out that I have "just" enough astigmatism to make observing fine detail problematic, so using a Barlow and a longer EP works out well, since I can leave my eyeglasses on. That short Nagler stays in the case most of the time. A longer EP with a Barlow is more comfortable to use.  P: 251 So after a quick google search, I found a pretty legitimate, professional, and interesting local astronomy club. There's a membership fee ($20), but they have their own observatory with a 20" telescope, with its own location in a park. Most of the members seem to be older guys, but I'm still applying. It should be fun.

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