Star Clusters and the like
Posted 18 February 2004 - 09:34 AM
I have a 4.5 Helios Skyhawk(now Skywatcher) short tube reflector, and I am looking to upgrade. Everything I have read leads me to a 8" Newton/Dob, (even the owner of my scope shop), but I want some portability, and I am only short myself.
Is a maksutov ok for clusters?
Is the etx Meade 90 ok, or is it two 90mm too small?
Is a short tube reflector really only good for Planets?
I accept that a F9 1000m Reflector is perhaps the best, but can you let me know how you all find your Maks/Refectors for Star Clusters.
I am talking about UK £500 max.
Posted 18 February 2004 - 11:09 AM
To address your various comments....
1. Yes, an 8" Newt (equatorial mounted) is, in my opinion, a great general purpose scope...big enough for nice deep-sky work, good on planets if you keep well-collimated (with tracking being a real plus), not exactly "grab'n'go" on portability, but still pretty easy to setup and break down and transport wherever you want in a vehicle. A nice balance between aperture and portability, and a nice balance between working on planets and DSOs.
2. Yes, a Mak is good on clusters and everything else. There are really only 2 negatives to a Mak...long cooldown time (no big deal if you just remember to put it outside awhile before use), and narrow FOV (just something you have to work with I guess). But as for image quality, a Mak is probably going to give you a better view of just about anything except an APO refractor...for a given aperture of course. However, if you already have a 4.5" scope, why do you want a 4-5" Mak? To me, an upgrade means "bigger". Sure, there are quality/design issues, but I think you'll find the difference between your scope and a Mak won't be THAT different, except maybe on planets (or unless you're talking about a 6-7" Mak).
3. In my opinion, 90mm will be pretty small for deep sky work. If you're interested in star clusters, you'll be better off with your 4.5".
4. You've got it backwards on the Short-tube reflector. Reflectors are better for deep sky than planets. What's the f-ratio on your short-tube? If it has the corrector plate that makes it a f9 or f10, it would, in theory, be better on planets than if it was f5. But, I understand these Barlow-added "short-tube" designs aren't very great in terms of giving them long f-ratio capabilities (e.g., being good for planets). So, an f10 SCT or f12 Mak will be better on planets than your short-tube. Your short-tube will still be better on star clusters than it is on planets.
Posted 18 February 2004 - 11:19 AM
Posted 18 February 2004 - 12:13 PM
jmoore, I forgot to say my 4.5" is F8.9
Your comments are interesting, suggesting that my scope is ok for what I want.
The reason of thinking of changing is because it is a cheap Synta scope, and I am having trouble resolving the Moon with my 9mm e.p.. I bought 3 Super plossls 9mm/25mm and 40mm. The two larger I like alot, especially the 40mm. M45 looked good.
My scope shop, who are very good, suggested that the mirrors might need moving. It is Collumated ok. They said "bring it in next tme you try it on the Moon with the 9mm e.p." I will of course do that.
The only problem is that in NW England I have only seen the sky twice since Christmas, and the Moon once. But that is life here.
Thanks again for your help.
Posted 18 February 2004 - 12:15 PM
90mm is really way too small for much enjoyment. And the 90mm Mak will seem even smaller due to a narrow FOV and a fairly restrictive power range.
The other thing about Maks is that it totally depends on where you live and observe as to how much of an issue long cool down times are to you. For instance, lots of folks erroneously assume that cooldown is primarily a winter issue, and that all that is required is an unheated storage space. What I found here in NC, is that it was as much or more of an issue in Summer. If you leave the scope in an unairconditioned space, then it starts out lots higher temp than ambient, and takes all night to cool down. If you leave the scope in an air conditioned house, then it becomes a dew magnet the very instant you take it out into the humid summer air. Either way, I found the cooldown times on the M603 to be such a major issue that I reluctantly traded it. The smaller Maks were sold off with much less reluctance, and frankly I was glad to be rid of them.
If you're in England, you probably are familar with very humid air. The problem with any of the Maks or SCTs is going to be that the front corrector plate tends to collect humidity very quickly, and that totally wrecks the views. You can get heaters to solve for that, but be aware that adds a whole separate layer of complexity in terms of batteries, cables, heater bands, etc.
I would echo others that suggest you consider a 200mm reflector.
Posted 18 February 2004 - 12:18 PM
You ought to be getting better performance than that out of your 4.5" Definitely, have it checked out before buying anything else.
Posted 18 February 2004 - 02:42 PM
I know what you mean about the dearth of clear skies lately.....I live just south of the Humber.
Now on to telescopes.As you can see from my signature, I have a 4" f9.8 refractor and an 8" f6 newt.The 8" started life as a dob but I removed the altitude bearings and mounted it on a EQ5 gem.I am going to also make a removable box for the tube assembly so I can also use it as a dob.This way I've got the option of a quick set up dob and a more leasurly equatorial.The 8" is a very good telescope both for deep sky and the planets.Saturn is fantastic in this 'scope and Jupiter takes your breath away.
If I'm honest, I have to say the 4" hardly gets used as the views are very disappointing compared to the reflector.
The refractor is a Helios ( synta )and the reflector is a Skywatcher.I would recommend the reflector as your main 'scope and if you really need a quick set up 'scope either do as I have or get yourself something like a short tube 80mm skywatcher.My view is ( and no doubt some will dissagree )Skywatcher makes great reflectors but only mediocre refractors.
Posted 18 February 2004 - 03:06 PM
Mike, your post was very helpful giving all those points. I will get mine checked out again.
John, your "two mounts" sounds interesting.
Posted 18 February 2004 - 03:34 PM
I am going to also make a removable box for the tube assembly so I can also use it as a dob.This way I've got the option of a quick set up dob and a more leasurly equatorial.
John, would you mind posting this in the ATM forum so we can discuss this further. I have an 8" Hardin Dob that I will be converting to my GEM (using a variation of your pier design!), but I want to retain the ability to use the dob base as well.
Posted 18 February 2004 - 05:16 PM
So the answer is, get the biggest reflector you can afford. You're not getting any younger and you better enjoy those 16 cloudless nights a year. You might want a dobsonian not only for price reasons but also because large GEMs for large scopes are really bulky.
Suggesting a newtonian reflector does not mean that other designs are bad for clusters, but as you go towards large apertures they become the only affordable instruments. SCTs are ok up to the 10" range, then become prohibitively expensive.
So my vote is an 8-10" dobsonian.
A gentleman in England was selling on ukastroads.co.uk a 14" Dob for 400£... you might give it a try!
Posted 18 February 2004 - 08:13 PM
Posted 19 February 2004 - 03:19 AM
Thank you very much for your help. It looks like the 8" Reflector. Will try the mounts in my shop, but will have my 4.5" checked first. Bit of a fag, as first I will have to wait until the moon is visible, and then hope I get some clear skies as well.
Posted 20 February 2004 - 03:18 PM
Turn of events!
After all your help etc, I went to my scope shop (I am lucky) it is only 6 miles away, and the biggest supplier in NW England)I was going to buy a Magazine and talk about fixing my scope. However, they had just got a second hand Dob, which they had built a few years ago. (T & L Optics). I t has a David Hinds made Mirror. 6.25"(158mm) F7.6 and a 47.85"(1215mm Tube).
The base is all wood, and I could lift the scope complete
So I part ex'd mine. They had checked it over etc. and used a laser to coll.
What was nice, was they showed me how to coll, whilst there, and they had put a coll dot. on to help me.
I tried it for an hour tonight. Great, I could see stars that were not there before, and the views looked good -despite next doors upstairs windows. What a difference between the two scopes? Carn't wait to use it on a dark site. Found it easy to scan with the 40mm and 25mm e.p's The other scope was like Roy Hudd and the Emu (that's for the UK readers)
Off to my Ast.Soc. obs. now, but might have another looke after midnight.
Might take a photo, if I can work out how to post it
Posted 20 February 2004 - 04:11 PM
Posted 20 February 2004 - 07:06 PM
Posted 20 February 2004 - 07:27 PM
Posted 20 February 2004 - 07:33 PM
Posted 21 February 2004 - 03:19 AM
Will think about it and try again?
Posted 21 February 2004 - 03:25 AM
Posted 21 February 2004 - 05:25 AM
Here is the link to my "down the road scope shop"
It might be down the road, but the uk is small compared to accross the pond, and in rush hour it is nearly quicker to walk accross the tops of the cars!!
Went to my Ast. Soc. Obs. last night again only 13 miles away - They have a 14" fixed EQ Reflector. My first view through anything other than my old scope. Wow!! Could see space between the four stars in the Orion Trap. Jupiter was amazing with the four moons like jewels.
Regards to you all
Posted 21 February 2004 - 08:45 AM
Ah well. I need the exercise anyway.
You must live near our daughter....she lives about 15 minutes away from SBTC. (Chorelton )
Posted 21 February 2004 - 09:15 AM
Yes, I am about the same distance South of SBTC as your daughter is in the opposite direction ; just about on the edge of the Peak District, but "attached" to Gtr. Manchester on the other.