# Planning to buy a first telescope?

by turbo
Tags: planning, telescope
P: 245
 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: 245 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: 9,180 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: 3,725 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: 7,367  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: 245 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.
 P: 245 How useful are collimation eyepieces? I wouldn't shell out the money for a laser collimator, but some of the eyepieces (like this one) are as cheap as $30, and appear to work very well. My scope came with a collimation cap, but even after trying to collimate my telescope, I'm still not sure if it's properly collimated. PF Gold P: 11,021  Quote by AnTiFreeze3 How useful are collimation eyepieces? I wouldn't shell out the money for a laser collimator, but some of the eyepieces (like this one) are as cheap as$30, and appear to work very well. My scope came with a collimation cap, but even after trying to collimate my telescope, I'm still not sure if it's properly collimated.
Welcome to my world. My Newt is...terrible. Flimsy design REALLY brings it down. My collimation on it falls apart just by slewing from one part of the sky to another. Couple that with the fact that I am TERRIBLE at collimation. I found the laser collimator to be the most useful for me, while the collimator eyepiece was decent also.
 Mentor P: 21,999 It would be better to learn star collimation, but it will be tough on a Dob since it requires high magnification. (and calm skies)
 Sci Advisor PF Gold P: 9,180 For a practical collimation guide see http://www.skyandtelescope.com/howto/diy/3306876.html.
 Quote by AnTiFreeze3 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. thats great :) Its us "older guys" (like me) that learned how to get around the sky without digital setting circles and "goto" telescopes. LEARN and I say it again LEARN how to starhop you way around the sky to find objects yes it takes a little longer but the huge advantage is you will really get to know your way around the stars :) And that nite you are at some friends place and the only thing they have is a pair of binoculars, you wont be lost in showing them a few objects of interest Dave P: 245  Quote by davenn thats great :) Its us "older guys" (like me) that learned how to get around the sky without digital setting circles and "goto" telescopes. LEARN and I say it again LEARN how to starhop you way around the sky to find objects yes it takes a little longer but the huge advantage is you will really get to know your way around the stars :) And that nite you are at some friends place and the only thing they have is a pair of binoculars, you wont be lost in showing them a few objects of interest Dave Luckily, I'm almost forced to learn the skies, since I have a simple dobsonian mount. And I actually just got back from the meeting. It's very official, in that they are allotted a decent amount of money from grants, and are building a new observatory (there are on-going debates as to what type of telescope should go in it), but everyone there was very welcoming and relaxed. They were all at least 35 years or older, but this will only benefit me, because they all seem very experienced. Apparently, one guy got bored and built his own 32" dobsonian; I feel like I will have a lot to learn from them.  Sci Advisor PF Gold P: 9,180 My first scope had setting circles that proved utterly useless. Of course I had no clue how to polar align my scope [6" f8 newt], which was a contributing factor. The setting circles had like 5 degree increments which further exacerbated an already hopeless situation. My favorite eyepiece offered less than about 1 degree tfov, which was also unhelpful. Goto was a pipe dream back in those days, so, star hopping was the only option. I hated star hopping, and still do. Albeit, I admit, it was instructive. Mentor P: 21,999  Quote by davenn Its us "older guys" (like me) that learned how to get around the sky without digital setting circles and "goto" telescopes. LEARN and I say it again LEARN how to starhop you way around the sky to find objects yes it takes a little longer but the huge advantage is you will really get to know your way around the stars :) While I have respect for the skill required to look for things without GOTO, IMO, this was largely a barrier that got in the way of the primary goal of looking at things. I'm not sorry to see that skill die. Sci Advisor PF Gold P: 2,242  Quote by AnTiFreeze3 Luckily, I'm almost forced to learn the skies, since I have a simple dobsonian mount. And I actually just got back from the meeting. It's very official, in that they are allotted a decent amount of money from grants, and are building a new observatory (there are on-going debates as to what type of telescope should go in it), but everyone there was very welcoming and relaxed. They were all at least 35 years or older, but this will only benefit me, because they all seem very experienced. Apparently, one guy got bored and built his own 32" dobsonian; I feel like I will have a lot to learn from them. in many ways you should be thankful that you have a "Dobo" mount, you really will never regret learning to move around the sky the old way. Goto scopes are great, only just got one myself at the beginning of the year after 40+ yrs in astronomy. But one has to be consious of not becoming too lazy and forgetting the basics by letting the scope find everything for them. There is nothing wrong with goto scopes, for some one who really likes to get around many objects quickly say... those that supernova hunt in a mass of galaxies regularly or if you are trying to find new faint objects, whatever they are... comets, asteroids, or deep sky objects then having the scope get you into the right area of the sky helps lots :) Dave  Sci Advisor PF Gold P: 9,180 You still need some basic star hopping skills, even with goto. I feel insecure until I can match the field of view to a star chart, but, goto is a huge time saver when it puts you close enough not to deal with the tediousness of leaping star to star from several degrees away to reach the target area. I've been a variable star observer for 40 years and finding those target fields are incredibly difficult compared to something distinctive, like a galaxy or planetary nebula. I still use my 40+ year old all sky charts.  P: 245 Long story short, OwlAstronomy had to cancel my orders and fully reimbursed me for my purchases: the 20mm eyepiece (33) and the variable polarizing filter (\$20). So, I'm still stuck with my 25mm, standard-issued Plossl, the shorty 2x Barlow, and the extension tube that I bought (which has worked well thus far). So I've searched around a bit, and found this. So here are my options.... tell me if they're feasible or not: 1.) I don't buy the case. I would consider making individual purchases based on what I need at any given time. That leaves me with the following magnifications: KEY: 2xB = 2x Barlow ... ET = Extension Tube 25mm Plossl: 48x 25mm Plossl + 2xB: 96x *25mm Plossl + 2xB + ET: 128x 2.) [a.] I buy the case, selling what I don't need, keeping what I need. I would sell the 4mm and 6mm eyepieces (4mm gives too high of a magnification, 6mm would be redundant w/ 12.5 and Barlow) so that I could use them to finance a nice 5mm planetary eyepiece. I would compare the Zhumell Barlow with my Orion Shorty Barlow, and sell the lesser of the two. In this option, I would debate selling the 25mm Plossl or not; I primarily use it as a finder, and feel as if the 32mm would take over this role. That leaves me with the following magnifications: 32mm Plossl: 37.5x (about as low as my telescope should go... or so the internet tells me) 32mm Plossl + 2xB: 75x *32mm Plossl + 2xB + ET: 100x 25mm Plossl [Refer to above for magnifications] 12.5mm Plossl: 96x 12.5mm Plossl + 2xB: 192x *12.5mm Plossl + 2xB + ET: 256x (And assuming I purchase a 5mm planetary eyepiece) 5mm: 240x ... I wouldn't use the Barlow/ET for obvious reasons. [b.] I would be the scrooge of this Christmas, and follow suit as in Part A, but would skimp out on purchasing a 5mm planetary eyepiece (I am still in consideration of selling the 25mm Plossl that came with my telescope because there's an overlap in magnification when using 25mm with the Barlow and the 12.5mm by itself). I would do this because, when using EP + 2xB + ET with the 12.5mm, I can get up to 256x magnification, whereas with the 5mm eyepiece, I would be limited to 240x. _ _ _ _ I know this seems ridiculous, but I am almost always incredibly careful when spending my own money. It also seems as if I should just altogether skip out on the case, since I would sell two of the four eyepieces, but the filters and Barlow would be very beneficial, and I haven't seen a package like this anywhere else. *Assuming I did my math correctly. The extension tube is 2" long, and the shorty barlow lense is 3" long. If I were to have a 3" ET, then my shorty barlow would bump up from a 2x to 3x, so I made my calculations under the assumption that, when using a 2" extension tube, it would essentially make a 2x Barlow into a 2.666...x Barlow lens.