Refractor 102/7 FPL51 vs. 80/7.5 FPL53

[Ratlet]

I love globs in dobs, but there is something so tantalising about them in a smaller scope.  It's hard to describe.  Some clusters (open and glob) it's almost like one of those pictures where if you move right up it's just dots, but if you stand back you can see the picture.

I want to say Caroline's rose does something like that, but I could be wrong.

[John]

After my eye has adjusted, I usually get a faint halo of resolved stars around the brighter globular clusters and the unresolved portions have a sparkling texture when using my 100mm - 120mm refractors. 

With a 150mm - 200mm scope they start to look a bit more like their images and with 250mm-300mm they can be quite stunning. 

It does depend on the globular though - some are more condensed than others.

After many years observing I find these days that I can usually see most of what larger apertures show with a smaller aperture but I have to work that much harder to tease it out. Sometimes it's right on the edge of visibility. 

I have sometimes thought that using a large aperture scope vs a smaller one is a bit like the difference between 1.1 litre car and 2.5 litre (we had these for a while). The small engined car could certainly push along at 70 mph on the motorway but the larger one did it with a lot more ease and the engine was barely turning over (or at least gave that impression).

I'll probably regret that analogy - car comparisons usually backfire when used on astro forums 🙄

 

 

Edited October 20, 2023 by John

[Zermelo]

34 minutes ago, Ratlet said:

I love globs in dobs, but there is something so tantalising about them in a smaller scope.  It's hard to describe.  Some clusters (open and glob) it's almost like one of those pictures where if you move right up it's just dots, but if you stand back you can see the picture.

I want to say Caroline's rose does something like that, but I could be wrong.

I agree.

I would say there are two effects I see in globulars when they are on the limit of resolution. The first is the scintillation that @John describes. The second is a graIniness, a grey area with a texture that just fails to show individual stars. Personally, I find these effects to be as pleasant as a resolved cluster.

I don't see the same effects with open clusters, with the exception of one or two that are small and dense (such as the Wild Duck).

[Louis D]

27 minutes ago, John said:

I have sometimes thought that using a large aperture scope vs a smaller one is a bit like the difference between 1.1 litre car and 2.5 litre (we had these for a while). The small engined car could certainly push along at 70 mph on the motorway but the larger one did it with a lot more ease and the engine was barely turning over (or at least gave that impression).

Right there with you.  Moving up to a 3.6 liter V6 is a nice boost as well, but going to a 6.0 liter V8 really puts a smile on your face.  I just got done running errands in my 2009 Pontiac G8 GT, and the big engine is really fun until you pull up to the gas (petrol) pump (which I also did today).

If my back was up to it, I'd take my old Tectron 15" Dob (Nova mirror) out for a spin under the stars.  If you buy these older, big custom Dobs used, they can be quite a bargain.  I doubt if I could get even $1500 for mine nowadays.  Everyone wants a scope from a current maker with a currently known premium mirror.

[paulastro]

2 hours ago, mikeDnight said:

That's true! Many but not all, and suggesting using a blackout blanket to achieve good dark adaption could help some to get far more out of their telescopes.  Having said that, years at the eyepiece is no guarantee of observing skill. I recently recieved the Web Societies latest journal in which the editor immediately begins by mocking the deep sky observing skill of some Cloudy Nights sketching contributors who use small telescopes, implying they're seeing too much detail. When I first read it I had to check that I hadn't joined the BAA by 

 I would have thought most people would have heard about it (using a dark cloth) as its hardly a new idea - though of course, there's a difference between knowing and doing.

 

Edited October 20, 2023 by paulastro

[John]

3 hours ago, mikeDnight said:

.... Having said that, years at the eyepiece is no guarantee of observing skill. I recently recieved the Web Societies latest journal in which the editor immediately begins by mocking the deep sky observing skill of some Cloudy Nights sketching contributors who use small telescopes, implying they're seeing too much detail. When I first read it I had to check that I hadn't joined the BAA by mistake. 

I believe the same source was rather sceptical a while back about reports (on SGL I recall) of seeing Sirius B with modest instruments. 

 

[Louis D]

52 minutes ago, paulastro said:

 I would have thought most people would have heard about it (using a dark cloth) as its hardly a new idea - though of course, there's a difference between knowing and doing.

 

It would be one more thing to make me sweat profusely here during a sweltering Texas summer night.  It would probably be okay from fall through spring, though.

[Mr Spock]

3 hours ago, John said:

I'll probably regret that analogy - car comparisons usually backfire when used on astro forums

Indeed. Reminds me of youths who believe their home tuned Astra is as fast as a Ferrari. You hear a loud exhaust behind you, turn round expecting to see something spectacular, instead there's this clapped out rust-bucket pootling along