6" Refractor vs 10-12" Dobsonian

[jetstream]

3 minutes ago, vlaiv said:

Just a thought - seeing does have impact on resolution.

In poor seeing / not optimal conditions - detail in globular cluster can suffer as much as planetary detail.

6" refractor in good seeing will outperform 12" dob in poor seeing, although 12" will have both more light grasp and better resolving power.

 

Seeing has to be pretty bad to affect at this level- and the low/med power views are still much better in the 12" vs the 6" at high power.

[vlaiv]

1 minute ago, jetstream said:

Seeing has to be pretty bad to affect at this level- and the low/med power views are still much better in the 12" vs the 6" at high power.

Does it?

I think that to start resolving M13 for example - you need x100+ magnification. I think that at these magnifications - seeing effects start to show already.

I might be wrong though - I haven't observed M13 in quite a long time. Last time I did it was in 4" scopes  .

[jetstream]

1 minute ago, vlaiv said:

Last time I did it was in 4" scopes  .

Seriously I dont find seeing to be an issue for me- unless I look over the wood stove chimney in the winter

When living in town, larger dob always won, from mag 20 skies and observing around other houses.

Vlaiv- eagerly waiting your report on M13 with a 200mm dob vs a, lets say 150mmish frac from a nicely dark location!

[Rusted]

I found my 10" f/8 Newtonian provided instant gratification on Plato craterlets.
Whereas my 7" f/12 refractor showed them, but not quite so willingly.

However, the two instruments were not being used, side my side, on the same night.
Lunar lighting, seeing conditions and personal equation could all have affected the outcome.

I insisted on using both OTAs on an equatorial. So lifting either onto the mounting was a real struggle.
I ALWAYS wear thin, but grippy, industrial gloves to aid handling without the need for excessive strength.
Handles on my main tubes further aid carrying and handling long and heavy OTAs.

Had I not had cool storage close to the observing site I would have chosen the 7" as only slightly more manageable.
Had I had to carry either OTA from indoors, or down some stairs, I would not have chosen either instrument.
Choose your weapons carefully according to your age, fitness, wealth and accommodation.

There is clear logic to choosing an APO for its shorter focal length without suffering the "LSD trip" of false colours.
A shorter Newtonian is not quite so compromised by coma as is a short refractor by its rainbow hues.
Now what was the question again?

[faulksy]

there will always be refractor v,s reflector wars. refractors are better for photos. but i realy dont think these apo ish people have looked through a decent sized reflector. if they did they would buy one.

[ollypenrice]

3 hours ago, Mr Spock said:

I've viewed a 0.7" separation double with my C9.25. Two airy disks clearly separated by space.

0.7" is smaller than the airy disk of a 150mm refractor. Just thought I'd mention it 

That's fine, and perfectly correct, but, to be fair, it's not not what the OP was asking about.

Olly

[ollypenrice]

11 minutes ago, faulksy said:

there will always be refractor v,s reflector wars. refractors are better for photos. but i realy dont think these apo ish people have looked through a decent sized reflector. if they did they would buy one.

I have owned an assortment of premium apos from 70 to 140mm and reflectors of 20", 14," 10", 8" and 4.5". I am also trying to answer the OP's question, not regurgitate the tired old refractor-reflector debate! And I think that he would be better served by a 12 inch reflector (make it 12, not 10) for the purpose he describes.

As an imager I don't think refractors are better than reflectors, I simply think that they are usually easier. That's why I use them.

Olly

[neil phillips]

22 minutes ago, faulksy said:

there will always be refractor v,s reflector wars. refractors are better for photos. but i realy dont think these apo ish people have looked through a decent sized reflector. if they did they would buy one.

Get your point. But it should never be a war of words or beliefs. Both have merits with advantages and disadvantages obviously. The idea refractors are better for photos, is a bit misleading, especially cost per performance criteria. Would like to see a refractor do this for anything less than many many thousands of pounds. Skywatcher 300p new price £900 

I got mine for £100 secondhand. Would like to see the cost of a refractor, any refractor match this for resolution. Either new or secondhand. 

 

 

Edited May 14, 2021 by neil phillips

[Stu]

31 minutes ago, faulksy said:

there will always be refractor v,s reflector wars. refractors are better for photos. but i realy dont think these apo ish people have looked through a decent sized reflector. if they did they would buy one.

I’ll respectfully disagree with that Mike 😉. 

I’ve owned a 16” dob and used it under some pretty reasonable skies, so know what it is capable of. I sold it because it got used about once a year, same with my 14”.

I choose refractors to observe with (amongst others) because of their convenience, flexibility and quality of views. My scope ‘which must not be mentioned’ is highly portable, will show me excellent lunar, planetary, white light solar, double star and widefield DSO views. With my current personal situation I simply wouldn’t use a large Dob, so the views are pretty irrelevant. Refractors aren’t just better for imaging, they serve a very valid purpose and would not still be so popular for visual if they didn’t.

I confess I don’t get this ‘aperture is everything’ argument, there is so much more to it than that. I fully understand what you get from owning and using your scope, the views are fabulous I’m sure and I would enjoy viewing through it, and even owning one if my circumstances allowed me to regularly use it. I struggle with being told that I’m missing out on something, or using the wrong scope constantly when my refractors fulfill my needs very well, and have kept my enjoyment of the hobby going for years despite living under some fairly horrendous skies.

If it helps, despite being a refractor nut, I would choose a 12” dob over a 6” refractor in the case of the OP 👍

[faulksy]

13 minutes ago, ollypenrice said:

I have owned an assortment of premium apos from 70 to 140mm and reflectors of 20", 14," 10", 8" and 4.5". I am also trying to answer the OP's question, not regurgitate the tired old refractor-reflector debate! And I think that he would be better served by a 12 inch reflector (make it 12, not 10) for the purpose he describes.

As an imager I don't think refractors are better than reflectors, I simply think that they are usually easier. That's why I use them.

Olly

good point olly

[mikeDnight]

10 hours ago, scotty38 said:

@mikeDnight and @ollypenrice I stand by my comment that that's how M13 looks through my 6". Just to reiterate though:

1. It's an achromat (Altair Starwave 152 f5.9)

2. On the occasions I've had to use it it's not been what we'd call dark (I've only had it a couple of weeks)

2. I know my low light vision isn't the best

I made the point of mentioning these things for all the obvious reasons but given your comments can you give examples of what constitutes a good 6" refractor please?

I would say the Starwave is an excellent achromat that should give wonderful views of a target like M13. Dark adaption is important though,  especially with scopes of limited light grasp. I'll often observe using a blackout blanket over my head and eyepiece, which greatly improves the view when observing from town. Of course local seeing and sky transparency can make a big difference for the good or bad, but the beauty of a refractor should really become evident on stellar targets such as open and globular clusters when observing from a reasonably dark site. Even the Skywatcher 6" F8 & F5 achromats can put on quite a show, and the Starwave is almost certainly significantly better corrected for spherical abberation than those. No need for an apo on deep sky in my view. I'd love a 6" Starwave. Perhaps one day!

Edited May 14, 2021 by mikeDnight

[neil phillips]

42 minutes ago, Stu said:

I’ll respectfully disagree with that Mike 😉. 

I’ve owned a 16” dob and used it under some pretty reasonable skies, so know what it is capable of. I sold it because it got used about once a year, same with my 14”.

I choose refractors to observe with (amongst others) because of their convenience, flexibility and quality of views. My scope ‘which must not be mentioned’ is highly portable, will show me excellent lunar, planetary, white light solar, double star and widefield DSO views. With my current personal situation I simply wouldn’t use a large Dob, so the views are pretty irrelevant. Refractors aren’t just better for imaging, they serve a very valid purpose and would not still be so popular for visual if they didn’t.

I confess I don’t get this ‘aperture is everything’ argument, there is so much more to it than that. I fully understand what you get from owning and using your scope, the views are fabulous I’m sure and I would enjoy viewing through it, and even owning one if my circumstances allowed me to regularly use it. I struggle with being told that I’m missing out on something, or using the wrong scope constantly when my refractors fulfill my needs very well, and have kept my enjoyment of the hobby going for years despite living under some fairly horrendous skies.

If it helps, despite being a refractor nut, I would choose a 12” dob over a 6” refractor in the case of the OP 👍

Great points there Stu, and it runs central to the debate of reasons why someone may own a refractor. Recently got a bog standard Evo 120 achro and enjoying both the views and images it produces a lot, Whats the debate here ? we know the science of resolution. We know why people enjoy refractors. I am glad we have both in the world. It makes astronomy much more interesting and varied. Different flavors  always enrich life.

[Stu]

Just now, neil phillips said:

Great points there Stu, and it runs central to the debate of reasons why someone may own a refractor. Recently got a bog standard Evo 120 achro and enjoying both the views and images it produces a lot, Whats the debate here ? we know the science of resolution. We know why people enjoy refractors. I am glad we have both in the world. It makes astronomy much more interesting and varied. Different flavors  always enrich life.

👍👍👍

[jetstream]

On 12/05/2021 at 16:06, chrispj said:

But, I'm finding one thing I'd like to see is galaxies and other DSOs, which I've had quite limited success so far

Heres one of the OP's questions- and I dont think there can be much debate over what it takes to see galaxies and DSO- its aperture. Or we can tell the member to drive to very dark skies with his 100mm, or better yet drive to very dark skies with a 10"-12" dob.

[John]

4 minutes ago, jetstream said:

Heres one of the OP's questions- and I dont think there can be much debate over what it takes to see galaxies and DSO- its aperture. Or we can tell the member to drive to very dark skies with his 100mm, or better yet drive to very dark skies with a 10"-12" dob.

Good idea to re-visit the original questions Gerry

 

[Stu]

1 hour ago, Stu said:

If it helps, despite being a refractor nut, I would choose a 12” dob over a 6” refractor in the case of the OP 👍

I repeat 😉😉

[faulksy]

1 hour ago, Stu said:

I’ll respectfully disagree with that Mike 😉. 

I’ve owned a 16” dob and used it under some pretty reasonable skies, so know what it is capable of. I sold it because it got used about once a year, same with my 14”.

I choose refractors to observe with (amongst others) because of their convenience, flexibility and quality of views. My scope ‘which must not be mentioned’ is highly portable, will show me excellent lunar, planetary, white light solar, double star and widefield DSO views. With my current personal situation I simply wouldn’t use a large Dob, so the views are pretty irrelevant. Refractors aren’t just better for imaging, they serve a very valid purpose and would not still be so popular for visual if they didn’t.

I confess I don’t get this ‘aperture is everything’ argument, there is so much more to it than that. I fully understand what you get from owning and using your scope, the views are fabulous I’m sure and I would enjoy viewing through it, and even owning one if my circumstances allowed me to regularly use it. I struggle with being told that I’m missing out on something, or using the wrong scope constantly when my refractors fulfill my needs very well, and have kept my enjoyment of the hobby going for years despite living under some fairly horrendous skies.

If it helps, despite being a refractor nut, I would choose a 12” dob over a 6” refractor in the case of the OP 👍

fair comment stu 😃

[reezeh]

On 13/05/2021 at 12:19, Mr Spock said:

I just went through the same choice process. I have a 250mm Goto Dob on order

It doesn't matter how good a refractor is, or what some claim they can see, as has already been said, ye canna change the laws of physics.

I used to have a 250mm Newt on an EQ6 before it came too unwieldy. I switched to a C9.25 which was a drop in contrast and quality.

The C9.25 also too a long time to cool down despite being stored in a cool porch. The new Dob is going in a shed so should cool really quick when put outside.

I thought being at the science station on the USS Enterprise would be all you need! 

[Deadlake]

11 hours ago, jetstream said:

Heres one of the OP's questions- and I dont think there can be much debate over what it takes to see galaxies and DSO- its aperture. Or we can tell the member to drive to very dark skies with his 100mm, or better yet drive to very dark skies with a 10"-12" dob.

You forgot contrast, which also means smooth mirrors or something else without an obstruction .. 😀

On balance a really smooth reflector is best value approach to finding and observing DSO.

[Piero]

My 16" F4, but also my 12" F6, regularly show far more details than my 4" Tak DF.

The refractor "wins" on wide field (3" Deg Vs 1 Deg fov) and solar observing (only possible with the refractor). 

 

Side note..

comparing top notch refractors like Tak, TEC, TV against low-end commercial dobsons is unfair. The optical quality is a major component, but there are other critical aspects in a newtonian telescope which must be considered to make it really fly.. at least the following: collimation (process+telescope mechanics for retaining it), mirror cell supports (back+side), mirror cooling, focuser quality, baffling, thermal currents, and (drum sound..) boundary layer above the primary. 

Whilst working on most of the list above reduces imperfections to a level in which these can be invisible to the eye, the last one can play like a "turbo" for magnification. After testing this, I really agree with the statement that a lot of the reported atmospheric seeing issues are actually 1-2" above the primary mirror surface.

As an example, the mirror box of my 16" is 11" deep and open at the back (Kriege design). Observing the moon, ~300x seemed the highest I could go before the image started softening. After pulling up the light shroud for 5-6" (this is enough to move the boundary layer away, as the mirror box is shallow) from the mirror box and defocusing the image intentionally, I could see substantial air turbulence going towards one direction (the warm air was blown away and moved up). Note that, this air flow only affects the air above the mirror surface, not the mirror side wall! An air flow directed at the mirror wall can impair the temperature across the mirror causing astigmatism and spherical aberration (tested on the other dob). After refocusing back, the image was getting better and better as the air flow stabilised.. the limit of 300x was pushed forward to about 650x (crisp). The images was still acceptable at around 800x (yeah.. viewing craters and details like from an Apollo spacecraft). What about stars? Thin diffraction cross on the bright stars, otherwise stars were pin points. Globulars? M13 or M3 at 300x were bright, with pin point stars all over and kind of star dust (not a diffuse cloud) near the core.

 

 

 

Edited May 15, 2021 by Piero

[faulksy]

48 minutes ago, Piero said:

My 16" F4, but also my 12" F6, regularly show far more details than my 4" Tak DF.

The refractor "wins" on wide field (3" Deg Vs 1 Deg fov) and solar observing (only possible with the refractor). 

 

Side note..

comparing top notch refractors like Tak, TEC, TV against low-end commercial dobsons is unfair. The optical quality is a major component, but there are other critical aspects in a newtonian telescope which must be considered to make it really fly.. at least the following: collimation (process+telescope mechanics for retaining it), mirror cell supports (back+side), mirror cooling, focuser quality, baffling, thermal currents, and (drum sound..) boundary layer above the primary. 

Whilst working on most of the list above reduces imperfections to a level in which these can be invisible to the eye, the last one can play like a "turbo" for magnification. After testing this, I really agree with the statement that a lot of the reported atmospheric seeing issues are actually 1-2" above the primary mirror surface.

As an example, the mirror box of my 16" is 11" deep and open at the back (Kriege design). Observing the moon, ~300x seemed the highest I could go before the image started softening. After pulling up the light shroud for 5-6" (this is enough to move the boundary layer away, as the mirror box is shallow) from the mirror box and defocusing the image intentionally, I could see substantial air turbulence going towards one direction (the warm air was blown away and moved up). Note that, this air flow only affects the air above the mirror surface, not the mirror side wall! An air flow directed at the mirror wall can impair the temperature across the mirror causing astigmatism and spherical aberration (tested on the other dob). After refocusing back, the image was getting better and better as the air flow stabilised.. the limit of 300x was pushed forward to about 650x (crisp). The images was still acceptable at around 800x (yeah.. viewing craters and details like from an Apollo spacecraft). What about stars? Thin diffraction cross on the bright stars, otherwise stars were pin points. Globulars? M13 or M3 at 300x were bright, with pin point stars all over and kind of star dust (not a diffuse cloud) near the core.

 

 

 

nice one piero

[Stardaze]

44 minutes ago, Piero said:

My 16" F4, but also my 12" F6, regularly show far more details than my 4" Tak DF.

The refractor "wins" on wide field (3" Deg Vs 1 Deg fov) and solar observing (only possible with the refractor). 

 

Side note..

comparing top notch refractors like Tak, TEC, TV against low-end commercial dobsons is unfair. The optical quality is a major component, but there are other critical aspects in a newtonian telescope which must be considered to make it really fly.. at least the following: collimation (process+telescope mechanics for retaining it), mirror cell supports (back+side), mirror cooling, focuser quality, baffling, thermal currents, and (drum sound..) boundary layer above the primary. 

Whilst working on most of the list above reduces imperfections to a level in which these can be invisible to the eye, the last one can play like a "turbo" for magnification. After testing this, I really agree with the statement that a lot of the reported atmospheric seeing issues are actually 1-2" above the primary mirror surface.

As an example, the mirror box of my 16" is 11" deep and open at the back (Kriege design). Observing the moon, ~300x seemed the highest I could go before the image started softening. After pulling up the light shroud for 5-6" (this is enough to move the boundary layer away, as the mirror box is shallow) from the mirror box and defocusing the image intentionally, I could see substantial air turbulence going towards one direction (the warm air was blown away and moved up). Note that, this air flow only affects the air above the mirror surface, not the mirror side wall! An air flow directed at the mirror wall can impair the temperature across the mirror causing astigmatism and spherical aberration (tested on the other dob). After refocusing back, the image was getting better and better as the air flow stabilised.. the limit of 300x was pushed forward to about 650x (crisp). The images was still acceptable at around 800x (yeah.. viewing craters and details like from an Apollo spacecraft). What about stars? Thin diffraction cross on the bright stars, otherwise stars were pin points. Globulars? M13 or M3 at 300x were bright, with pin point stars all over and kind of star dust (not a diffuse cloud) near the core.

 

 

 

The element that I’ve not had issues with my 10” is cooling, but I’ve never really rushed it. Half an hour seems to be ample for mine. I did consider knocking together a fan, more for the hell of it, but I haven’t really felt the need for one. The point regarding the dob is that with cooling, collimation and the bulk to move, it is a longer drawn out process than a small grab and go frac. I’ve resisted the temptation of a frac just now, but the simple form for those opportunist nights will inevitably mean I’ll add one at some point. But, the views from the dob can be spectacular, M13 in my bortle 5 garden was beyond what I could have hoped for last year.

[Piero]

6 hours ago, Stardaze said:

The point regarding the dob is that with cooling, collimation and the bulk to move, it is a longer drawn out process than a small grab and go frac. 

 

My mirror is 1.5" thick. I start the fan at the highest speed when the telescope is still inside. So, I "wheel" it out, then go back inside to get better clothes, then go back outside with eyepiece case, collimate the telescope, and start observing. At this point I reduce the speed of the fan by half - the views are already acceptable (that's about 1/2 h fan on). Within another half an hour I might switch it off or just leave it at low speed, depending on how the night temperature goes.

 

 

 

P.S.

grip material on wheelbarrow handles is now yellow (black looks cool, but invisible at night time). Wood blocks for making that step ramp were a very temporary solution. I now use the following:

 

Next step is to make a good adjustable chair to be used with both the refractor and the dobson.

Edited May 15, 2021 by Piero

[Deadlake]

5 minutes ago, Piero said:

 

My mirror is 1.5" thick. I start the fan at the highest speed when the telescope is still inside. So, I "wheel" it out, then go back inside to get better dressed, then go back outside with eyepiece case, collimate it, and start observing. At this point I reduce the speed of the fan by half - the views are already acceptable (that's about 1/2 h fan on). Within another half an hour I might switch it off or just leave it at low speed, depending on how the night temperature goes.

 

 

 

P.S.

grip material on wheelbarrow handles is now yellow (black looks cool, but invisible at night time). Wood blocks for making that step ramp were a very temporary solution. I now use the following:

 

Next step is to make a good adjustable chair to be used with both the refractor and the dobson.

Amazing home build!!!! 😀 How high is the eye piece off the ground, do you need to use a step to use it?
It's the one thing thing that puts me off Dobs.

[Stardaze]

12 minutes ago, Piero said:

 

My mirror is 1.5" thick. I start the fan at the highest speed when the telescope is still inside. So, I "wheel" it out, then go back inside to get better clothes, then go back outside with eyepiece case, collimate the telescope, and start observing. At this point I reduce the speed of the fan by half - the views are already acceptable (that's about 1/2 h fan on). Within another half an hour I might switch it off or just leave it at low speed, depending on how the night temperature goes.

 

 

 

P.S.

grip material on wheelbarrow handles is now yellow (black looks cool, but invisible at night time). Wood blocks for making that step ramp were a very temporary solution. I now use the following:

 

Next step is to make a good adjustable chair to be used with both the refractor and the dobson.

Love that!! I need to knock some ramps up too. I’m thinking of getting a little truck so that I can do it all in one go instead of breaking down the base and OTA, but certainly need to negotiate the door step. Hopefully save my back which I occasionally suffer with.