6" Refractor vs 10-12" Dobsonian

[Deadlake]

5 hours ago, Louis D said:

Speak for yourself.  My TS-Optics (Sharpstar) 90mm FPL-53 triplet APO takes at least 30 minutes to acclimate just 15 degrees F (7 degrees C ?) before stars quit having spikes.  My 8" Dob acclimates in about the same time, but to get rid of blurriness associated with tube currents.  If I put fans behind the primary, I'd probably be ready to go in under 10 minutes.  Low power views are fine in the Dob while waiting.  Not so much with the APO.  Those spikes are still plainly visible on bright open clusters like the Pleiades.

There are numerous threads on these forums about glass or mirror quality. However little reports on how thermal stable or how quickly a scope acclimates.
I find during winter months my Vixen SD103S is ready to go in around 10 minutes with a temperate delta of around 10 oC.
I suspect other manufactures like LZOS and Stellarvue with steel lens cells can keep the same performance but with larger apertures, in the winter I'll find out.  

[PeterW]

1 hour ago, niallk said:

The 2" mirror does need time to cool though, and the views show it of course. 

… 2”, you needs a bigger scope 😉

 

Peter

[faulksy]

14 hours ago, Stu said:

So long as you have enough in focus with it fitted, isn’t that why the paracorr has the built in barlow effect?

or just add S.I.P.S. fit and forget then stu

[faulksy]

3 hours ago, niallk said:

I'm thinking small fans, on bendable metal brackets in the 4 corners angled downwards on to the front of the mirror.  I won't attempt to achieve "laminar flow"... just keeping the air moving to aid cool down.  With a speed control, I could possibly leave on while observing. 

Otherwise, I'm thinking to just have a bigger fan on frame I can just place over the front of the mirror box during cool down, removing when observing. 

i use a 16" pedestal fan from b and q pointing down the uta towards the primary. but worry about what it might throw in my tube

[niallk]

7 hours ago, PeterW said:

… 2”, you needs a bigger scope 😉

 

Peter

🤣🤣 yes, I'm not cooling a 2" mirror for 2-3 hrs looking for 1/100 ~ perfection!

That sentence of course omitted the all important word 'thick'...

[Tiny Clanger]

I don't understand the title of this thread ... unless ... should it actually read ,

"6" Refractor vs 10-12" Dobsonian, which should I buy first " ?

Heather

[Stu]

1 minute ago, Tiny Clanger said:

I don't understand the title of this thread ... unless ... should it actually read ,

"6" Refractor vs 10-12" Dobsonian, which should I buy first " ?

Heather

Absolutely! You can always make use of both!

[Deadlake]

5 minutes ago, Stu said:

Absolutely! You can always make use of both!

Or should I buy a Dob when I have a refactor and I'll use the Dob three times a year before selling it?
 
I want a reflector for more aperture but I'm concerned I will not use it enough to justify its purchase.

Might just be a summer scope.

[Stu]

12 minutes ago, Deadlake said:

Or should I buy a Dob when I have a refactor and I'll use the Dob three times a year before selling it?
 
I want a reflector for more aperture but I'm concerned I will not use it enough to justify its purchase.

Might just be a summer scope.

I have an 8” dob which gets fairly regular use, it’s lightweight and f8 so more Lunar/ planetary orientated. Larger dobs have never got regular use as there is often not so much benefit due to the light pollution. They are good for globs free here though. The ones I’ve used most have been truss dobs which can be taken somewhere dark easily.

[John]

My 12 inch dob gets just as much use as my refractors and is no more hassle to setup. Possibly a bit less hassle than the 130mm frac.

Circumstances are a key part of how often larger scopes get used though.

 

 

 

[Stu]

6 minutes ago, John said:

Circumstances are a key part of how often larger scopes get used though.

That’s very true John. If I had your negotiating skills and was allowed to keep my dob in the house, with an easy lift outside the door and with dark skies available then a 12” Dob would be top of my list! 👍

[Stu]

Just to add..... I’m hoping to move down your way soon @John so should be able to benefit from darker skies at last! Hurrah! Time to finish that 12” truss dob project at last. I still don’t think my powers of persuasion are up to keeping the scope in the house though! 🤣

[JeremyS]

12 minutes ago, Stu said:

Just to add..... I’m hoping to move down your way soon @John so should be able to benefit from darker skies at last! Hurrah! Time to finish that 12” truss dob project at last. I still don’t think my powers of persuasion are up to keeping the scope in the house though! 🤣

Sounds like a plan being hatched 👍🏻

[John]

18 minutes ago, Stu said:

Just to add..... I’m hoping to move down your way soon @John so should be able to benefit from darker skies at last! Hurrah! Time to finish that 12” truss dob project at last. I still don’t think my powers of persuasion are up to keeping the scope in the house though! 🤣

Get down here before the house prices catch up with the home counties

 

 

[PeterW]

I can only store scopes in the house, but I have run out of places to put them that won’t be noticed and cause an issue. Maybe my scope aspirations need to get smaller.. or wait for the kids to leave home?!
Peter

[Captain Scarlet]

12 hours ago, Deadlake said:

I suspect other manufactures like LZOS and Stellarvue with steel lens cells can keep the same performance but with larger apertures, in the winter I'll find out.  

I’ve found that my LZOS 105 takes a fair while to cool down such that the extra-focal spikes disappear. Obviously dependent on temp difference but 40 minutes at least is a rough guess.

[John]

2 minutes ago, Captain Magenta said:

I’ve found that my LZOS 105 takes a fair while to cool down such that the extra-focal spikes disappear. Obviously dependent on temp difference but 40 minutes at least is a rough guess.

My LZOS 130 F/9.2 takes about 30-40 minutes to fully cool.

 

 

[Louis D]

Glad to know I'm not losing my mind when so many keep claiming APOs are good to go right out of the case, and yet that has not been my experience.

My AT72ED is a small ED doublet, and it is ready to observe in almost no time at all.

[Stu]

1 hour ago, John said:

Get down here before the house prices catch up with the home counties

 

 

We are doing! Trying to complete before end of June, but so is half the country so it may not happen by then.

[Stu]

4 minutes ago, Louis D said:

Glad to know I'm not losing my mind when so many keep claiming APOs are good to go right out of the case, and yet that has not been my experience.

My AT72ED is a small ED doublet, and it is ready to observe in almost no time at all.

Big difference between a doublet and a triplet. The FC100DC cools very quickly but a faster triplet with thicker glass inevitably takes longer.

[niallk]

1 hour ago, Stu said:

 I still don’t think my powers of persuasion are up to keeping the scope in the house though! 🤣

I keep a 15" dob ... assembled ... in our bedroom! 😂

[JeremyS]

5 minutes ago, niallk said:

I keep a 15" dob ... assembled ... in our bedroom! 😂

Where is it?

[Stu]

7 minutes ago, niallk said:

I keep a 15" dob ... assembled ... in our bedroom! 😂

I think if I tried that, Mrs Stu would, well, disassemble me! 😱🤣

[John]

"Medical news - surgeons laboured to remove a 2 metre truss pole from a Surrey man today. His condition is described as stable but possibly uncollimated"

 

Edited May 18, 2021 by John

[PeterW]

I’m surprised you’ve not at least tried to hide it, You could drape a towel, hang some clothes on it….

Peter