Alkaid

58 minutes ago, Ben the Ignorant said:

 

And someone from an older thread here has this to say:

Spherical mirrors will work if the focal length is high enough (and has a theoretical Strehl of 0.80 or higher).

A 130 900 will not have 0.80;

100*e^-(2*pi*( (130/2)^4/(2*900)^3/16/0.00056)/3.5)^2 = 68.65

And this is not factoring in obstruction, roughness of the mirror, bad edges and other errors, but it purely the theoreticly possible.

 

 

I don't think that's quite right?  A diffraction limited optic must have a minimum strehl of 0.8  (80%) and this is the minimum benchmark for the manufacturer.  A scope delivering 68% or 0.68 would not come to focus??  The 130/900 clearly does actually work and delivers good images, so it definitely has a strehl of at least 0.80.

I wouldn’t get too hung up on spherical vs parabolic....the small TAL-1 uses a spherical mirror and produces excellent images. 

I wouldn't class the '102 as a telescope for imaging though.....however for widefield visual it is a great little scope with the power level at around x20.

Depends how sensitive to chromatic abberation you are, but all achromats exhibit the fringing. Some worse than others, the lower the F ratio then the worse it is. My little 102 at F5 is quite objectionable on the moon....but at low power on star fields it’s very pleasing.

I had a 6” f5 newt, it was a very nice scope but I missed sitting down behind the scope like you do with a frac. 

That looks great!  I've no experience of these, please let us know how the view compares with your Mak?  (When the clouds go away anyway!  🙂 )

The AZ4 suits the 102 beautifully.  Here’s a pic.

19 hours ago, JamesF said:

You have been seriously unlucky.  I'm only a few miles on the Somerset side of the Devon border (close to the edge of Exmoor) and I've had several nights outside in the last week.  A couple with exceptionally good seeing.

James

This year we were in Galloway Forest Park, Scotland.  Lovely place. Sounds like I should have headed south for Astro though...

I get maybe 2-3 deep sky trips per year. One of these opportunities is an annual summer camping trip, either to Scotland or down to Devon / Cornwall.  We just returned from this trip and I got just one night out of seven....same last year too.  I recently downgraded the size of my ‘camping’ scope as I couldn’t justify the space taken up for just one clear night!

Great write up, I went through quite a few scopes and always thought I’d end up with one of these until a C8 came up beforehand.  8” aperture really is a  sweet spot and the ease of use and storage of your 200P must really hit the spot.  Thanks for sharing your experiences!

Looks alright, not bang on, but not out enough to warrant adjustment.  Get a bright star in a high power eyepiece. Rack the focuser in a bit, then back out. Does the star evenly expand and does it contract back down to a nice point? If it does, collimation is ‘in’.  For ‘out’ look for the star expanding & contracting unevenly, on one side. 

It’s easy to get hung up on this.  If you’re targeting small lunar features or planetary, then yes it’s important, especially in an F5 scope. But if you’re using your 250 for DSO’s and sky sweeping, it’ll be absolutely fine at low power, even if it’s a little bit out.

Have fun!

Unfortunately....no.  The vibration would render the set-up completely un-useable.  I’m afraid that the EQ5 would be the absolute minimum in your case.  Not the news you wanted to hear, but will save you frustration in the long run.  EQ5’s come up quite often 2nd hand, as it’s the summer time right now you could hold out until one comes up?

Practicality is the most important aspect for me.  Due to my somewhat hectic life, if I owned one, a really big scope just wouldn't get the attention it deserves.  It would find itself sitting there woefully, waiting.  I used to think that this hobby was all about aperture - granted that is extremely important, but you have to balance that with observing opportunities, lifestyle and storage space.  For me, it's these that actually win!

Portability is key for someone like me.  I used to have five scopes, but now whittled down to just two that actually get used.  I find my C8 wonderfully practical, it is just so short but still packs in enough aperture to satisfy me personally at a dark site.  When I am at home in the city, it's very good on moon / planets too.

I often take the smaller C6N on camping trips - a mere 6" at a dark sky site can deliver some pretty good views.

Provided you have the time and storage space for using a large aperture regularly, by all means go for it though!

On 19/01/2019 at 13:57, Prador said:

I really like the look of this f11. For me, it does resurrect the question of the f11 102ED or a f12 SW Skymax 150.

Does anybody here have any experience of viewing through comparable telescopes? It would only be for planetary viewing.

Many thanks for any insight as it will inform what will probably be my final scope purchase.

If you happen to suffer with floaters (like me), the bigger aperture will help with that and also provide a brighter image.

21 hours ago, Rick_It said:

Yes, but a C8 is not a rich-field scope, so it's not universal. For example, you can't frame the Pleiades. With a 200/1200 you get up to 2.26° FOV.

Does it count if I use the F6.3 reducer?  (I don't have it yet, but will soon).

?

I haven't had it that long, so perhaps unjustified, but I'm really liking my C8.  It performs really well for me on the Moon and surpassed my expectations in terms of image quality (for this unit anyway).   It did confirm double the resolution of my 4" frac (expected with aperture, but I equally wanted a sharp image too and I got it).  I'm yet to really give it the deep sky test, but initial visual on M42 was rather good.  It's a compact tube, easy to carry around and out of the house and far easier to manoeuvre than the frac.    I like it.

Nice scope!

On 02/05/2017 at 19:16, spaceboy said:

I guess this may also be why John considered your wavering in the hobby and not the ED120 itself. I know you said at SGLXII that your very much into drone flying now...

Sorry to re-open the thread after such time, but well said.  It's very important to have other hobbies and interests, otherwise one can loose a bit of enthusiasm.  

I think that by taking time out from a hobby, two things happen.  1) You stop worrying about all the crap that comes with that particular hobby (e.g. poor weather and clouds).   And 2) when you do re-visit after a couple of months, you sort of re-kindle the hobby with double the enthusiasm.

In Jules defence, I think that if he was to take a break (won't happen LOL!) - he'd be very happy with whatever  scope was in the current line up.  It's simply brilliant to look through any telescope when you haven't done it for a while.  Brilliant.

PS - Jules, I quite like the fact that you are constantly changing scopes for evaluation - please don't let anyone stop you!

Been mentioned a couple of times in the thread, here's mine - taken on a phone and the pics could be better (should've used the DSLR)...

For transport....with a fetching orange cap from Screwfix(!) which reduces the length to around 900mm...

When up and running...

I used a Baader finder shoe and a dual finder attachment from FLO....simple red dot to get me in the area, RA finder to hone in...simples!

Stock TAL finder is very nice, but I can't get on with straight finders myself.  I've kept the TAL finder and shoe in a box for safe keeping.

Humble 4" achromatic glass.   Very well figured though!  It's a great scope.  Perhaps one day they'll make them again...

Excellent. I have astigmatism so found this very interesting. Thanks for sharing.

Nice, I've also got my eye on a 102 mak for travel.

What a nice idea, good for you. Just sorry I don't live near your friend...but I'm sure someone on here will. I love showing new people the night sky, sorta reminds me of how impressed I was when I first saw Saturn.

Jupiter was in full glory last night, a fitting tribute to Sir Patrick. Jupiter was one of his favourites. I remember seeing his Jupiter sketch book on S.A.N. Lovely drawings, and all with a 3" frac if I remember rightly.

How fitting that it was a lovely clear night to mark the end of such an accomplished lifetime.