which scope

[thommo10]

I am considering buying a refracter OTA purely for visual use I have 2 in mind, the TAL 100 and the SW Evo 102, But I cannot make my mind up.

[perrin6]

Is there an astro shop in Purley near south croydon?

[CGolder]

Can you buy the evo 102 without a mount? pretty sure its only available as a package.

[thommo10]

Sorry, thanks for pointing out my spelling mistake Alan have edited my post now, I have been looking around the web and I think you may be right CGolder although I have found the SW Startravel 102 OTA. How would this compare to the TAL ?

[CGolder]

It wouldn't, the star travel would give some nice wide field views but due to the fast optics would have way more false colour on bright objects.

The etx125 will probably outperform them both on planets

[thommo10]

Thanks CGolder, I don't know what to do now may be a big aperture Newt ?

[CGolder]

What are you trying to view and that extra performance?

[RikM]

Have a think about what type of objects you intend to look at, then plan your new scope around that. If you are wanting to view planets then perhaps an APO refractor or 8" SCT, if your interest is faint fuzzy DSO's then maybe a mid-large dob.

Rik

Edit: hahaha typing at the same time as CGolder.

[thommo10]

I live close to Birmingham so Light Pollution is a issue, I think faint fuzzys are out, so basically the planets and the brighter DSO's ie Orion Nebula etc. as far as performance is conserned somthing that will show more detail than my etx.

[CGolder]

Your ETX 125 is optically a very good scope and performs above its weight on planets and bright DSO's. (well at least mine did)

Do you not find it performing very well?

[RikM]

I have a Skymax-127 and a 5" refractor and the Skymax is the better scope on both planets and brighter DSO's. Globular clusters are a dream in this scope and I would imagine it to be similar to your ETX 125. I live on the outskirts of Gloucester so light pollution is an issue for me too.

My next tough decision is

a. 10" dob

b. PST

or

c. 1/2 an HEQ5 pro

choices choices...

Rik

[thommo10]

May be I need better eyepieces, at the moment I use the one that came with it 28mm Plossl 4000 series and a barlow 2x (when I can due to seeing} and may be I'm being a bit fussy, but the planets such as jupiter don't seem as sharp as when I look through my 150mm Newt using the same ep.

[CGolder]

jupiter in a 2x14mm in your 150 is only 54x mag(providing its F5), in the ETX is 136x mag.

the view will look sharper at lower mags, but i have pushed the etx to 238x on good nights and it still performs very well. are you giving the scope time too cool down?

[RikM]

That's down to the focal length of the scopes. The ETX 125 will give a higher magnification than the Newt with the same eyepiece. You also need to make sure the Newt is well collimated. That has a big effect on sharpness and the detail visible on planets.

If you want more detail on planets, generally, a bigger aperture will give you the possibility of resolving finer detail. If the scope is working to it's potential. (Big can of worms here and a few of them are starting to poke their heads out).

Rik

[thommo10]

I keep it in a shed so I thought it would be pretty cool anyway how long do you I should leave it

[thommo10]

yes I can see were this is going Rik. Complicated !!!

[RikM]

Collimation is making sure the mirrors are all correctly aligned with each other so they can bring the light to focus in the right place and produce a sharp image.

That is not the same thing as cool down time, but that is also important to resolving planetary detail. I get the best views of planets after the scopes have been outside at least an hour. Maybe a bit less for my refractor and a bit longer for my MAK. I also find observing better after midnight because the local council dim all the street lights round me by 25% after midnight. It doesn't make much differences just walking about, but the sky background in through the eyepiece is definitely better.

Rik

[CGolder]

there is a chance the collimation is out of the etx too. its a lot harder to diagnose and resolve.

[thommo10]

Thats what I was starting to think, how can I check ?

[RikM]

I've no idea how to collimate a MAK. I can see little allen bolts on the back plate of the Skymax and every fibre of my being screams LEAVE THEM ALONE.

I've done a basic star test and I get nice concentric rings both inside and outside of focus and I'll leave it at that.

Rik

[CGolder]

I have only seen 1 mak that was out on collimation, if you stand around 2m from the tube and look down it with one eye closed. look at it center on and you should see a series of rings and they should all be central. you can also star test by being out of focus and checking the rings.

if its not right, it will require some skill to correct.

[RikM]

Make sure the meniscus isn't all dewed up as well. Sometimes that creeps in and smudges everything up. I use a dew shield, but even that is not enough sometimes.

Rik

[thommo10]

Right ok, I do use a dew shield, but what do you do if the meniscus is dewed up ? I will try a star test, and I have learnt a lot tonight thanks guys.

[RikM]

Some people suggest a little 12V camping hair-drier on low or cold setting and gently dry it off from a foot or so away. I haven't got one of those yet so when my MAK gets dewed up I generally admit defeat and pack up for night muttering expletives as I go...

Rik

[thommo10]

I have looked at my etx as you suggested CGolder everything looks fine as far as I can tell, will do a star test as soon as poss, it may be just a case of dew on the meniscus as you suggested Rik. Thanks again for the advice.