16" of aperture for £1,172

[Chris]

Since I added more eyepieces I suffered form revere aperture fever. The 5 inch is getting as much use as ever. Couple of nights ago was perfect example, it was clear but looked like it might not have remained that way, as it happened it did, and had a good long session with it, doubles, planets, lovely for high mag views in a scope that is well cooled in 20 - 25 mins and well settled/optimised for the high power in a short time. Amazing how clean the splits were on that night in the dinky little heritage, good seeing helping out.

These little gaps in the clouds  session have happened quite a bit recently and the 5 inch is perfect for that when I am not sure how it will pan out and sneak in a nice session 

I must suffer from the rare reverse aperture fever condition and  just be weird  

I wonder how often I would use such a big beast, not that much I feel over a year, aside from the fact it would split my car in half fitting it in   Plenty life in the 10 inch to gather enough photons for my liking for time to come.  I'll see if I still sing the same tune a year from now  but clearly aperture fever strikes some a lot more than others, it would be a boring world  if we all the same   

Your not alone, see my avatar I'm doing plenty of observing with my 100mm f/4 Dob and my cheap bins now days. Can't seem to find time for anything other than the odd 10-20 minutes with a busy family life. My imaging with my obsy setup seems to have gone right out the window recently, too tired alot of the time, I'm just happy to have 20 minutes piece staring into space at the eyepiece, its good therapy!

[Ptarmigan]

Exactly as AlexB67 says ! (edit : and Starfox)

My story is that I plan to buy a small portable job, and for 'tween the clouds use instead of my binos, ( I was about to press the button on an 8SE when the Evolutions were announced ! That threw a spanner in the works ! )

and something larger, perhaps a 12" dob, for at home use and group sessions with my wife (we do that sometimes )

That was all till John flagged up this'un, which is a case of what if , , , or even WOW! What if

which is why I am asking all these damn-fool questions, to be ready to jump on the next discount weekend :)

[John]

My personal take on coma is that I can't see the point of shelling out for wide field, well corrected eyepieces if the outer parts of the field of view are going to comprise of comet shaped stars. In my case the answer was to move from F/4.8 to F/5.3 where coma is all but absent (to my eyes at least) from even 100 degree apparent fields. If I was contemplating a scope faster than F/5 I'd either budget for a good coma corrector or I'd sacrifice the FoV.

The degree to which coma and astigmatism are bothersome is highly personal (you can tell that from the varied reactions in posts on the forum about them) but I'm someone who likes, as far as possible, pinpoint stars across the whole field of view.

Al Nagler shares this I suspect as one of his mottos is "show no field unless it's sharp". 

It can be a costly "taste" though, if you don't own your own eyepiece company  

[Dreadz]

.............How about me asking a similar question but from the opposite end :

What would be the next step up from the supplied eyepieces, ie. "you would need at least a .... "

to make this scope work ?

In otherwords instead of peering down the supplied eyepieces and thinking "oh what a lemon" on the basis of the reviews

If you see what I mean.

As has been stated what is acceptable to one person is far from acceptable to another when it comes to coma, astigmatism and aberration.

Buy a fast scope but be prepared for the possibility you may need to also purchase a coma corrector to get the most out of it. Equally be prepared to posibly have to spend a little more on eyepieces than you would with a slower scope.

As it stands I use a f4.7 scope with BST starguiders and no coma corrector.

Is the field of view pinpoint sharp from edge to edge, no.

Is it still giving me fantastic and enjoyable views, yes.

Sent from my GT-I9300 using Tapatalk

[crashtestdummy]

Al nagler has wasted his time as his beloved ethos will still show coma in a fast scope.

With fast scope you also have to be prepared for some awesome deep sky views so it balances itself out

[AlexB67]

Al nagler has wasted his time as his beloved ethos will still show coma in a fast scope.

Did he ? sounds a lucrative business to me he has. He invented the paracorr to answer that so as not to waste your time and maintain his motto of delivering on the Don't show the stars unless they are sharp to the edge, the paracorr should just do that.

Buy a fast scope, buy an ethos, buy a paracorr, and you are bust, but you'll have a nice coma free field.  

How much are you prepared to pay is the only question 

[Chris]

Al nagler has wasted his time as his beloved ethos will still show coma in a fast scope.

With fast scope you also have to be prepared for some awesome deep sky views so it balances itself out

agreed, depsite the difficulties with fast scopes they give nice bright widefield views, my little mini dob only has 100mm aperture but seems to show quite a bit, I'm guessing this is down to it being f/4?

[Mike73]

Blimey this thread just about covers all of SGL in five pages! 

So far we've had Johns dislike of GSO mirrors, coma correctors (needed or not!) and eyepieces....all we need now is for Emad to chine in with a rant about the council and the evil streetlights and I think that covers most of it! 

Its been an interesting read though.

[estwing]

No problems here at F3.9..big mirrors,ethos and paracorr2 doesn't leave you skint, I make plenty by selling the big issue!

[John]

Al nagler has wasted his time as his beloved ethos will still show coma in a fast scope.

With fast scope you also have to be prepared for some awesome deep sky views so it balances itself out

Do we really still need to clarify the difference between coma and astigmatism ???

    Coma - scope produced so Al designed the Paracorr to correct the scope optics.

    Astigmatism - often eyepiece produced so Al designed eyepieces that were free of it down to F/4.

[crashtestdummy]

but doesn't that mean he should have advertised his eyepieces with a disclaimer of  **all eyepieces will show coma in fast scopes regarless how much we over charge for them**???? 

[John]

but doesn't that mean he should have advertised his eyepieces with a disclaimer of  **all eyepieces will show coma in fast scopes regarless how much we over charge for them**???? 

I suspect we are not going to find much common ground on this

[crashtestdummy]

agree to disagree fella

[Joves]

Wondering, did anybody end up taking advantage of this offer in the end?

Also curious as to how the optics in this scope might compare to something like the Orion XX16g? Their website states it has a 94% reflectivity parabolic mirror but, to be honest, I really have no idea on these things. Is this considered half decent, I wonder??

Not that I really have anywhere to store a 16" dob, the idea of such aperture with full go-to keeps pressing at my temptation button!

[AlexB67]

94% seems to be the normal value for the coating used on these, syntax and GSO are similar in that regard AFAIK when new. It is only the Hilux  used in OO optics for example that reach 97%.

Just like eyepiece coatings there can be some  variation depending on coating materials used as well. What vendors say ( to make it look good are likely peak performance values ) but AFAIK they are fairly flat performance in the visible range anyway form what I recall. I do remember seeing some plots at one point and a study of lifetimes showing that for the standard coatings that value will drop to about 88% after around two years of use if well looked after and clean.  The Hilux ones will last much longer and degrade more slowly with time.    You get what you pay for I suppose

[Joves]

Well explained, thanks Alex. I wonder what the reflectivity is on something like my LX90. I'd imagine mirror coatings hold up for a lot longer (probably forever) in the SCT design.