Here is the place to talk about all those equipment(Telescope, Mounts, Eyepieces, etc...) you have. Not sure which scope/eyepiece is best for you? Trash it out here!
Ok so this article suggest us to Buy a 100° televue eyepiece because both are important for dsoer . So what is the suitable magnification for deepsky object
rlow wrote:Excellent scope! I wished I had that buying power when I was your age...
What's your budget for eyepieces? Here's my suggestion based on your criteria:
A. Big budget: Nagler 31mm, Ethos 8mm, Powermate 2x
B. Small budget: TV Plossl 32mm, TV Plossl 8mm, TV 2x barlow
Anyway, rlow give very good recommendation for the Tak TSA-102. Or may be:
C. Somewhere in between budget: Baader Planetarium Hyperion 68° Modular Eyepieces: 24mm, 17mm, 8mm, 5mm and 3.5mm.
Have a nice day.
Yang Weixing "The universe is composed mainly of hydrogen and ignorance."
Gary wrote: So what is the suitable magnification for deepsky object
No simple answer to that because different DSO have different apparent size and brightness. You also have to consider the framing of the DSO you prefer in your FOV.
But generally, the idea is to start low power on a DSO and keep increasing it gradually until you find one that *you* like for that particular DSO. Repeat the process for other DSOs.
Agastro has plenty of nice eyepieces so be patient and take your time to find out the answers for yourself via observation before plonking some serious moolahs for your own eyepieces.
"The importance of a telescope is not how big it is, how well made it is.
It is how many people, less fortunate than you, got to look through it."
-- John Dobson.
Junming-jm wrote:Err I changed my mind . Since the weight of the ota is 5kg and the uti 8 inch truss dod with f/4.5 weight 6kg. Btw powermate works like a barlow ?
Powermate act like a barlow, but will not increase the eye relief of the eyepiece and the magnification is quite constant. If your eyepiece had short eye relief, a barlow might be better. Also, a short barlow increase the eye relief more than a long barlow.
Anyway, most deep sky object are usually observe in the magnification around from 60x to 160x.
Have a nice day.
Yang Weixing "The universe is composed mainly of hydrogen and ignorance."
I'd go with the UTI 8 if I had the moolah to blow...
There is no substitute for aperture, an 8" will always show lots and lots more than a 4". Now the TSA102 is a very fine 4" and will perform at the maximum of what a 4" can do.
An average/indifferent 8" will still show more than a perfect 4" but it may not be as sharp etc. etc. The UTI8 however is a near-perfect 8" (very good mirror, plus it's very light). Best of both worlds.
I personally feel that eyepiece purchase should be solely based on focal ratio and exit pupil and not anything else. As such i propose the following exit pupils as guidelines to getting a decent set of eyepieces.
2-2.5mm exit pupil for general deep sky observation since an exit pupil around this size gives a gd match of magnification and control of abberation (astig of your own eyes, floaters, astig of scope, coma of scope, sky glow, etc etc). I would recommend getting an eyepiece that has a large fov and decent eye relief. Ethos, naglers, radians, panoptics Pentax XL/XW, hyperions fall into this category.
0.5mm exit pupil for high power planetary observation as this matches the 50x per inch rule. I tend to lean towards simple eyepieces with lesser elements over here. Most of the orthos and plossl based eyepiece fall into this category. If 0.5mm exit pupil exceeds 300x, keep 2 separate planetary eyepiece, one that is roughly 300x and the other one at the limit of your scope. Not all scopes are built equal and thus not all scopes are capable of performing at 50x per inch. Do consider slightly lower magnification if that happens to be the case.
Your generally purpose low magnification eyepiece should not exceed 7mm exit pupil, infact anything more than 5mm may not be the optinum for viewing. Reasons are as follow, actual pupil size is smaller than exit pupil, thus light is lost/wasted, coma of scope, astig of eye, sky glow, shadow of secondary mirror, astig of eyepiece, etc etc etc.
As such, the focal ratio of the scope determines what would be your most commonly used eyepieces. For a F/8 scope, the following may be gd options. Pano 19/XL21/NaglerT4-17/22/Ethos17/Hyperion17/21, XO5/UO4/XP3.8/TakHiOrtho4/Mono4, NaglerT5-26/31, Pano35/27, XW30. Feel free to add your recommendations to the list.
~MooEy~
Last edited by MooEy on Tue Oct 05, 2010 9:16 am, edited 3 times in total.
I would be a bit more conservative and say for DSO you can aim for a 4mm exit pupil: which on an 8" Royce f/4.5 UTI would mean 51X, or an 18mm eyepiece (there's a Nagler 16 which would come pretty close... giving a 1.6-degree field).
The advantage of the 2.5mm exit pupil is that your eye centering over the eye lens isn't so critical, but of course 2.5mm exit pupil means 81X mag (11mm eyepiece and only 1-degree field if a Nagler.. would be even less for eyepieces with smaller AFOV).
IMHO if you're stuck with a 1-degree field, better get an SCT and 30mm Plossl. It will give you 1-degree, be more compact and cheaper.
For the high power, I think 0.5mm exit pupil is too prone to floaters already and the 50X/inch rule works out fine for premium optics. By sticking with 1mm exit pupil (which would be 200X on the UTI8, or a 4mm eyepiece) you're not straining your optical train as much.
So -- mooey says 2.5mm and 0.5mm exit pupil (factor of 5 between the low-power and high power EP) and I say 4mm and 1mm (pretty much the same).
Either choice would be good (although 200X IMHO is more usable than 400X moreso the UTI8 is an undriven scope; the seeing would also be a big factor at 400X).
Based on my usage and testing of the UTI vs. other 8" Newtonians, I would say that unless you really really need a ultra-light 8" travel scope for widefield low power views and do not mind its relative compromise on sturdiness, smoothness and balance, otherwise a standard dob will be a better choice. And much cheaper too. It's not that UTI is bad (it's a premium scope after all), but one has to understand its constraints and limitations, not just its strength. So I would not necessarily recommend it as the first choice for a newbie.
"The universe is composed mainly of hydrogen and ignorance." 
