83 replies to this topic

[Brent Campbell]

NO this is incorrect information.

I'm surprised at this statement Jay. I had thought you had looked through a supreme Strehl optic.

On DSO globs and maybe even most nebulae but an 4inch apo with a divine figure will eat an 8inch Dob for lunch on planetary fine scale contrast.

Nature of the beast mirror SCATTER jeesh.


There is a very good reason a good apo is two or three times the cost of a 8inch Dob.


CSS
Lance

The reason a 4 inch apo is 2x the price of a dob is that they cost twice as much to make.  Per inch of aperture my refractor outperforms every other scope I have but the other scopes more than make up for it because they  have many more inches.  My 4 inch apo shines in convenance it’s just so much easier to tote around and set up.  Also when conditions don’t allow larger instruments to reach their full potential the 4 inch apo is really the best instrument for those nights.  I also use the apo for moon observations simply because the moon has so much light that the apo can reach stupid high magnifications.  On other objects the dimming of the object as magnification goes up becomes your limit.

 

For planetary observations I believe the apo is about 70 percent the capability of my c8 on most nights.  My 10 inch dob actually does better ( smaller central obstruction than the c8 and more aperture).  Again the APO tries harder but aperture still rules.  For DSOs that are much dimmer aperture is king.

[WillR]

The reason a 4 inch apo is 2x the price of a dob is that they cost twice as much to make.  Per inch of aperture my refractor outperforms every other scope I have but the other scopes more than make up for it because they  have many more inches.  My 4 inch apo shines in convenance it’s just so much easier to tote around and set up.  Also when conditions don’t allow larger instruments to reach their full potential the 4 inch apo is really the best instrument for those nights.  I also use the apo for moon observations simply because the moon has so much light that the apo can reach stupid high magnifications.  On other objects the dimming of the object as magnification goes up becomes your limit.

 

For planetary observations I believe the apo is about 70 percent the capability of my c8 on most nights.  My 10 inch dob actually does better ( smaller central obstruction than the c8 and more aperture).  Again the APO tries harder but aperture still rules.  For DSOs that are much dimmer aperture is king.

You are completely right of course, but we don’t want to get Lance wound up again.

 

I think the fact that an apo is so much more expensive than a dob, and “looks” like a telescope, maybe gives them a certain mystique, maybe unjustified by their actual performance. I have a very good 100mm Televue Genesis and an off-the-shelf 10” dob, and 9 times out of 10, I prefer the dob.

[Jay_Reynolds_Freeman]

For planetary observations I believe the apo is about 70 percent the capability of my c8 on most nights.  My 10 inch dob actually does better ( smaller central obstruction than the c8 and more aperture).  Again the APO tries harder but aperture still rules.  For DSOs that are much dimmer aperture is king.

It might be worth restating that Strehl-ratio plots show that given perfect optics and perfect seeing -- neither of which being something anyone can count on -- a telescope with a 33-percent-of-diameter central obstruction will show as much or more detail of any size or contrast level as an unobstructed telescope with 70 percent as much aperture. The larger telescope will also have a stellar limiting magnitude at least half a magnitude fainter. In the context of the topic-starter's original question, that suggests that for visual use, an excellent eight-inch Dobson in excellent seeing has a substantial advantage over every 120 mm telescope ever made. Complications arise from storage requirements, difficulty of transportation and setup, et many ceteras.

 

 

Clear sky ...

[dnrmilspec]

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[Patrick]

I've watched Ed Ting rate the 8inch dob as his "if i could only have 1 scope", even more than the 10 inch due to size,awkwardness etc.

I have never looked through one before.
Biggest Ive used is a 5inch dob and I found my 80mm ed apo more contrasty and sharper on planets and moon.

Does anyone have any stories or comparisons between an 8 inch dob and smaller apos. Was it a wow moment viewing the moon, planets or dso after using a smaller scope (which scope)

I had no idea or may have forgot a 8inch dob is only £370. Going to keep my 80mm apo and get a dob as opposed to 120mm skywatcher ed ( would have cost over £2000 incl a mount).

It all depends on how deep you want to go.  High power planetary observing requires aperture regardless of the type of scope.  Your 80mm APO will only get you to around 160x or so before it runs out of steam.  An 8" scope will easily exceed 300x.

 

The absolute best views I've ever had of Jupiter was with a well cooled 11" SCT late in the evening with very good seeing conditions.  I was observing well above 300x. 

 

For small, faint DSO's, aperture still rules.  For the brighter, brighter, spectacular wide field objects, small aperture APO's will through up some wonderful images.  I'm not knocking small scopes as I have several, but my 8" SCT will still out preform the smaller scopes.

 

Patrick

Edited by Patrick, 30 March 2025 - 10:34 PM.

[TheChosen]

The 10" DOB is a nice telescope, my friend with whom we observe together has it.

 

Personally I never warmed up to it, the 8" seemed like the best option to start with, easily transport and use with budget eyepieces. Those same eyepieces which were OK in my 8" f/6 were really starting to fall apart in my friend's 10" f/4.7 

 

My thinking was always if I am going to get something bigger/heavier/ and faster than the 8" f/6, requiring more expensive eyepieces, I might as well get the 12", which I did and have been very happy with.

 

Make sure to do a lot of research on the best eyepieces.

 

Low power is usually not recommended enough. A nice 2" , something like the APM UFF 30mm (SkyRover 30mm) works really really well in the 10".

 

As for the difference between an APO 80mm and a 10" DOB. It is literally universes apart. Basis physics says nothing beats aperture. We can at most discuss differences between an 80mm APO and a 100mm DOB because of the central obstruction.. but that's about it. A 80mm vs 250mm difference is HUGE by all means.

Edited by TheChosen, 31 March 2025 - 04:47 AM.

[Arkade]

The 10" DOB is a nice telescope, my friend with whom we observe together has it.

Personally I never warmed up to it, the 8" seemed like the best option to start with, easily transport and use with budget eyepieces. Those same eyepieces which were OK in my 8" f/6 were really starting to fall apart in my friend's 10" f/4.7

My thinking was always if I am going to get something bigger/heavier/ and faster than the 8" f/6, requiring more expensive eyepieces, I might as well get the 12", which I did and have been very happy with.

Make sure to do a lot of research on the best eyepieces.

Low power is usually not recommended enough. A nice 2" , something like the APM UFF 30mm (SkyRover 30mm) works really really well in the 10".

As for the difference between an APO 80mm and a 10" DOB. It is literally universes apart. Basis physics says nothing beats aperture. We can at most discuss differences between an 80mm APO and a 100mm DOB because of the central obstruction.. but that's about it. A 80mm vs 250mm difference is HUGE by all means.

Thanks for advice. A company called stellalyra, they make really nice 10 inch dobs. It has a fan, handle to carry the tube. Their 10 inch is slightly more, not much more than skywatcher dob. Also, you said about the 2 inch eyepiece, stellalyra seem to have thought the same as yourself as they have 2 regular eyepieces, 15mm , 9mm and a 30mm 2" 68º (in reviews, they have said this is a good eyepiece,not a throw away sort one usually gets with ones telescope)

[TheChosen]

Yes, the Stella Lyra's offering is a LOT better and these days I recommend them over Sky-Watcher. I upgraded myself from an 8" Sky-Watcher to a 12" GSO (Same as Stella Lyra).

 

I am not sure they offer the 15mm with the telescope. Do they? The 30mm is GSO SuperView , pretty good for the 10" and will last you a long time before you decide for an upgrade. The 9mm is a basic Plossl.. I am not very picky about eyepieces, but Plossls below 20mm go straight to the trash as far as I am concerned (I sell them immediately on the second hand market actually for $10)

[Arkade]

Yes, the Stella Lyra's offering is a LOT better and these days I recommend them over Sky-Watcher. I upgraded myself from an 8" Sky-Watcher to a 12" GSO (Same as Stella Lyra).

I am not sure they offer the 15mm with the telescope. Do they? The 30mm is GSO SuperView , pretty good for the 10" and will last you a long time before you decide for an upgrade. The 9mm is a basic Plossl.. I am not very picky about eyepieces, but Plossls below 20mm go straight to the trash as far as I am concerned (I sell them immediately on the second hand market actually for $10)

Yes, a 9mm ,15mm plossl.
Also, Ursa major have a 8 inch with the gap mirror, looks similar to the Orion ones ed ting has on his channel. It is at a reasonable price at UK £369, comes with a fan,2 inch plastic crayford focuser, 8x50 finderscope, 9mm ,25mm plossl. For that price, it seems really good, so far the best bang for your buck 8 inch dob I've found this far...but since I'm getting a 10, doesn't matter to me ,incase anyone else is looking for a 8 inch in the UK