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60mm f15 for lunar: setting expectations, fair return criteria, & vs 70mm f5

EQ Moon Observing Refractor
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#1 marh

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Posted 21 September 2021 - 11:54 AM

I will take delivery first week of October of a factory new achromatic 60mm f15 refractor that comes with a simple equatorial mount and aluminum tripod.

So before it arrives I'd like to get some advice on what to expect as far as visual viewing of lunar features as compared to the slightly larger but much faster refractor (70mm f5) we're currently using.

For now here are some things that I could use some feedback on:

1) Our ETX 70 tracks the moon stably enough that we've used a maximum of 175x magnification with a 3x Barlowed 6mm eyepiece for crater viewing. Can we expect to stably track the moon with a simple equatorial mount with magnifications of 150x, and to a maximum of possibly 225x?
2) The manufacturer is supplying accessories to reach 338x magnification, but this would give an exit pupil of only 0.177 mm - is it really possible to view lunar features with such a tiny exit pupil?
3) The Conrady criteria for the f15 scope is well over 5 so my understanding is that chromatic aberrations should be essentially zero. Is this lack of CA true even at magnifications of 225x? The fast f5 achromat we now have is less than 2 on Conrady's scale - our expectation is that details on the moon should be more visible with the slower refractor. On the other hand the objective lens is 10mm smaller with the slower scope. Is it reasonable to expect to see more and sharper details with the 60mm f15?
4) The kit includes a 90º mirror diagonal which may degrade the image quality so if possible I'll try to evaluate this by using the scope without the diagonal.  On the other hand I've read that a 90º prism may actually be a better alternative than a 90º mirror for refractors slower than f8. If we end up keeping the kit, would a prism be a good accessory to have?
5) The ETX 70 included a 45º erecting prism that we can hopefully attach to the new scope, does anyone know if this will in theory help or not? Of course, I realize that depends on the quality of the erecting prism we now have but it would be nice to understand what the physics says about this.

My hope is that this 60mm f15 kit will perform better for lunar observing than the 70mm fast f5 refractor that we now use from under the light dome of several large cities that surround us that give us Bortle 8 skies.  (We do have access to a quite large park without city or housing lights that is not accessible by car where we first saw comet Neowise two weeks after peak viewing days - cloudy skies were the culprit - through 7x35 binoculars. So we are looking for portability also, for us – over 60 years young - that means being able to hand carry for a 3km walk, half of which is dirt paths, to a site that is locally dark but still under a huge metropolis light dome that never shows the Milky Way.)

Though, in closing, I understand that the manufacturer is probably playing a numbers game (sort of 'the dilemma of the marketer' when having to compete with unscrupulous producers that exaggerate the capabilities of their products) by advertising stable views at 338x with this small, slow refractor with a lightweight German equatorial mount and aluminum tripod.

To be honest, I do not expect this kit to perform as the marketing specs promise - though in all fairness I do expect it to manually track well at least at 150x along with giving nice sharp views of the moon's details, or is this asking too much? Or have I been royally duped into buying the infamous department store ripoff?

In any case I'll have 30 days to test the complete package with a full refund and no additional cost for either shipping on delivery or return if we decide to not keep it.

Comes what may, with your advice/suggestions I will gladly send it back if it does not meet some reasonable minimums for performance in real life conditions - hopefully a return would in some measure contribute to holding telescope kit suppliers to some minimal standards for marketing claims that exaggerate performance specifications.

 


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#2 Brian Carter

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Posted 21 September 2021 - 01:59 PM

Congratulations on finding a new scope!  A lot of folks here have a soft spot for long-focus refractors, there's something special about them.  The answers to a lot of your questions would be specific to the exact scope you've chosen, can you provide a link to it?  But without knowing the exact scope, here are my thoughts.

 

1.  Tracking.  Typically polar-aligned mounts track quite well.  But you will have to do a good polar alignment.  This isn't terribly difficult, but it is counterintuitive at first.  Watch some YouTube videos and give it a try, it's a handy skill to know.  But assuming the mount is adequate for the scope, it should track fine.  Equatorial mounts have the advantage of only needing to track in one axis because they are aligned to the earth's tilt.  Your ETX has to track in two axes, and that's actually a more difficult job.

 

2.  Magnification - No, I think 338x is a little ambitious for that little scope.  A nice rule of thumb is 50x per inch of aperture is your expected max, that would be about 120x for a 60mm.  The moon is special though because it is very bright, so you'll likely be able to go higher.  But not 300x.  I'd expect you can push it about as high as your ETX.  So if you are happy with the ETX at 170x, you might expect something similar with the 60mm, give or take a bit.

 

3.  A 60mm F/15 should be free of false color.  It will be a major improvement over the ETX.  An ETX 70 was actually my first scope!  My dad bought me one when I was in college and I used it for a few months before I bought a large dob.  A fast achromat like that though, it has a lot of false color.  I'm sure you've seen it on the moon.  The 60mm f/15 won't look like that, I think you'll be surprised.

 

4/5 diagonals.... Meh, there's not much difference between a cheap mirror diagonal and a cheap prism diagonal.  There isn't a huge difference between an expensive mirror/prism diagonal.  But there is a difference between cheap diagonals and expensive diagonals.  So don't worry too much about prism vs mirrors.  You can do a simple test though:  look at the moon with both diagonals you have, and then remove them and put the eyepiece straight into the focuser.  You might get a stiff neck, but the straight through method will show you the best you can get.  Ask yourself if you see a difference with/without the diagonal.  You'll have your answer then.

 

Post some pictures of your new scope when it arrives.  Looking forward to how you think the moon looks without that purple haze!


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#3 vtornado

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Posted 21 September 2021 - 02:25 PM

I will take delivery first week of October of a factory new achromatic 60mm f15 refractor that comes with a simple equatorial mount and aluminum tripod.

So before it arrives I'd like to get some advice on what to expect as far as visual viewing of lunar features as compared to the slightly larger but much faster refractor (70mm f5) we're currently using.

For now here are some things that I could use some feedback on:

1) Our ETX 70 tracks the moon stably enough that we've used a maximum of 175x Can we expect to stably track the moon with a simple equatorial mount with magnifications of 150x, and to a maximum of possibly 225x?

-- probably not.   A 900mm fl telescope will probably over stress a spindly eq mount.  If I am surprised

and the acoompanying mount is strong and sturdy then yes.

 

Something else is that many 3x barlows are not well made.  I would check this.

2) The manufacturer is supplying accessories to reach 338x magnification, but this would give an exit pupil of only 0.177 mm - is it really possible to view lunar features with such a tiny exit pupil?

 

Seriously??? the marketing department didn't say 1001x???  At most I view the moon with an exit pupil of .5mm.

120x with a 60mm refractor.

 

 

3) The Conrady criteria for the f15 scope is well over 5 so my understanding is that chromatic aberrations 

 

Yes over a CA ratio of 5, CA is well controlled and will not interfere with the image.

 

4) The kit includes a 90º mirror diagonal which may degrade the image quality so if possible 

 

Many bundled diagonals with low cost kits are trash.  You will have to evaluate it when you get it.   An equal quality mirror diagonal will not introduce additional CA to a fast telesecope.  But for a slow telescope, both are about equal.

 

5) The ETX 70 included a 45º erecting prism that we can hopefully attach to the new scope, 

 

A typical Amici prism will introduce a "spike" to bright high contrast objects.   Typically they have reduced aperture.

They are fine for daytime terrestrial but detract from high power, high contrast astro viewing.

 

My hope is that this 60mm f15 kit will perform better for lunar observing than the 70mm fast f5 

 

If the optics of the two scopes are the same  quality, the two scopes will perform about the same on the moon. However, fast achromats are harder to make well than slow achromats, so you may have less spherical abberation and field curvature for the slow scope.   The slow scope will have less chromatic abberation.  (This is more likely

to help on Jupiter and Mars than the moon).  The 70mm will be a touch brighter so it will allow a higher magnification with a larger exit pupil, (but only by a little). 70 mm will have slightly higher resolution.  Fast scopes can be difficult to focus at high power with

a low cost focuser.

 

As an anecdote, I had an 80mm f/15 scope that was just beautiful on the moon.  It was a Japanese made

Towa scope from the 80's.  CA was very well controlled, and I believe it was the lack of field curvature,

spherical abberations, and lens polish that made it work so well.  


Edited by vtornado, 21 September 2021 - 08:06 PM.


#4 EJN

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Posted 21 September 2021 - 02:26 PM

Where did you get the 60mm f/15, and who makes it? I didn't know anyone still makes them.


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#5 desertlens

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Posted 21 September 2021 - 05:24 PM

While not a doublet, the Takahashi FOA-60Q is ƒ15. I've had superb solar system results with this instrument.

 

FOA60Qmd.jpg


Edited by desertlens, 21 September 2021 - 05:29 PM.

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#6 marh

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Posted 21 September 2021 - 07:42 PM

Where did you get the 60mm f/15, and who makes it? I didn't know anyone still makes them.

https://www.astrosho...b_bar_1_select 

 

https://www.bresser....-Telescope.html

 

Bresser branded, though I'm not sure who makes them or even more relevant for the image quality who actually makes the crown and flint objective achromat pair and to what quality standards.


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#7 marh

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Posted 21 September 2021 - 07:59 PM

Congratulations on finding a new scope!  A lot of folks here have a soft spot for long-focus refractors, there's something special about them.  The answers to a lot of your questions would be specific to the exact scope you've chosen, can you provide a link to it?  But without knowing the exact scope, here are my thoughts.

 

https://www.astrosho...b_bar_1_select 

https://www.bresser....-Telescope.html

 

1.  Tracking.  Typically polar-aligned mounts track quite well.  But you will have to do a good polar alignment.  This isn't terribly difficult, but it is counterintuitive at first.  Watch some YouTube videos and give it a try, it's a handy skill to know.  But assuming the mount is adequate for the scope, it should track fine.  Equatorial mounts have the advantage of only needing to track in one axis because they are aligned to the earth's tilt.  Your ETX has to track in two axes, and that's actually a more difficult job.

 

Supposedly being sold as a kit hopefully means that the mount and tripod should handle the supplied 4mm eyepiece, 225x magnification, adequately.

 

2.  Magnification - No, I think 338x is a little ambitious for that little scope.  A nice rule of thumb is 50x per inch of aperture is your expected max, that would be about 120x for a 60mm.  The moon is special though because it is very bright, so you'll likely be able to go higher.  But not 300x.  I'd expect you can push it about as high as your ETX.  So if you are happy with the ETX at 170x, you might expect something similar with the 60mm, give or take a bit.

 

Agreed, but f15 has me hoping for 225x.

 

3.  A 60mm F/15 should be free of false color.  It will be a major improvement over the ETX.  An ETX 70 was actually my first scope!  My dad bought me one when I was in college and I used it for a few months before I bought a large dob.  A fast achromat like that though, it has a lot of false color.  I'm sure you've seen it on the moon.  The 60mm f/15 won't look like that, I think you'll be surprised.

 

Yes, I hope to see an improvement - though false color from the ETX wasn't too noticeable.

 

 

4/5 diagonals.... Meh, there's not much difference between a cheap mirror diagonal and a cheap prism diagonal.  There isn't a huge difference between an expensive mirror/prism diagonal.  But there is a difference between cheap diagonals and expensive diagonals.  So don't worry too much about prism vs mirrors.  You can do a simple test though:  look at the moon with both diagonals you have, and then remove them and put the eyepiece straight into the focuser.  You might get a stiff neck, but the straight through method will show you the best you can get.  Ask yourself if you see a difference with/without the diagonal.  You'll have your answer then.

 

Right, only by testing will the open questions be answered.

 

Post some pictures of your new scope when it arrives.  Looking forward to how you think the moon looks without that purple haze!

 

Will definitely post a quick review, though for the pics you can click on the links above. Thanks for the feedback!

 

 



#8 marh

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Posted 21 September 2021 - 08:27 PM

I will take delivery first week of October of a factory new achromatic 60mm f15 refractor that comes with a simple equatorial mount and aluminum tripod.

So before it arrives I'd like to get some advice on what to expect as far as visual viewing of lunar features as compared to the slightly larger but much faster refractor (70mm f5) we're currently using.

For now here are some things that I could use some feedback on:

1) Our ETX 70 tracks the moon stably enough that we've used a maximum of 175x Can we expect to stably track the moon with a simple equatorial mount with magnifications of 150x, and to a maximum of possibly 225x?

-- probably not.   A 900mm fl telescope will probably over stress a spindly eq mount.  If I am surprised

and the acoompanying mount is strong and sturdy then yes.

 

Yes, field testing will be the only way to know for sure - though the kit does come with a 4mm eyepiece giving 225x so without going to the advertised 338x I`m hoping it will be stable enough.

 

Something else is that many 3x barlows are not well made.  I would check this.

 

The ETX came with the 3x barlow and we've used it with a 6mm eyepiece with no problems. This new kit should get us to 225x with no barlow and using the supplied 4mm eyepiece.

 

2) The manufacturer is supplying accessories to reach 338x magnification, but this would give an exit pupil of only 0.177 mm - is it really possible to view lunar features with such a tiny exit pupil?

 

Seriously??? the marketing department didn't say 1001x???  At most I view the moon with an exit pupil of .5mm.

120x with a 60mm refractor.

 

We've gotten down to an exit pupil of 0.35mm on the moon with images still being bright, so I'll try to get to 0.28mm with this new kit. 

 

3) The Conrady criteria for the f15 scope is well over 5 so my understanding is that chromatic aberrations 

 

Yes over a CA ratio of 5, CA is well controlled and will not interfere with the image.

 

That confirms what Conrady recommends, though I have doubts about CA at high, ie 225x, magnification.

 

4) The kit includes a 90º mirror diagonal which may degrade the image quality so if possible 

 

Many bundled diagonals with low cost kits are trash.  You will have to evaluate it when you get it.   An equal quality mirror diagonal will not introduce additional CA to a fast telesecope.  But for a slow telescope, both are about equal.

 

5) The ETX 70 included a 45º erecting prism that we can hopefully attach to the new scope, 

 

A typical Amici prism will introduce a "spike" to bright high contrast objects.   Typically they have reduced aperture.

They are fine for daytime terrestrial but detract from high power, high contrast astro viewing.

 

My hope is that this 60mm f15 kit will perform better for lunar observing than the 70mm fast f5 

 

If the optics of the two scopes are the same  quality, the two scopes will perform about the same on the moon. However, fast achromats are harder to make well than slow achromats, so you may have less spherical abberation and field curvature for the slow scope.   The slow scope will have less chromatic abberation.  (This is more likely

to help on Jupiter and Mars than the moon).  The 70mm will be a touch brighter so it will allow a higher magnification with a larger exit pupil, (but only by a little). 70 mm will have slightly higher resolution.

 

As an anecdote, I had an 80mm f/15 scope that was just beautiful on the moon.  It was a Japanese made

Towa scope from the 80's.  CA was very well controlled, and I believe it was the lack of field curvature,

spherical abberations, and lens polish that made it work so well.  

 

Thanks for the inputs  - the major downside is the 60mm diameter for this refractor. Looks like testing will be the only way to find out if f15 can compensate for it!

1



#9 vtornado

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Posted 21 September 2021 - 08:54 PM

We've gotten down to an exit pupil of 0.35mm on the moon with images still being bright.

 

Try observing with a light on nearby.  That should keep your eye stopped down,

and the moon should not be so bright.  I only have a problem with the moon when

full an in a large scope, because driving down the exit pupil small enough

is too much power for what the atmosphere will allow.  At sub 1mm exit

pupils I don't have a problem with lunar brightness.   I am in a grey

light pollution zone so my eyes never fully dark adapt outside.



#10 Anony

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Posted 22 September 2021 - 02:10 AM

I will take delivery first week of October of a factory new achromatic 60mm f15 refractor that comes with a simple equatorial mount and aluminum tripod.

So before it arrives I'd like to get some advice on what to expect as far as visual viewing of lunar features as compared to the slightly larger but much faster refractor (70mm f5) we're currently using.

For now here are some things that I could use some feedback on:

1) Our ETX 70 tracks the moon stably enough that we've used a maximum of 175x magnification with a 3x Barlowed 6mm eyepiece for crater viewing. Can we expect to stably track the moon with a simple equatorial mount with magnifications of 150x, and to a maximum of possibly 225x?

You've done better with your ETX 70 than I have. Mine doesn't play so nice with my barlow... typically 6mm or so is the best I can get with it. And there tends to be a ton of CA. The moon is okay, but false color is certainly noticeable.

 

As for your 60mm scope, I wouldn't expect you to get much or any CA. If you are okay with the CA from the ETX 70, you'll certainly find the f/15 scope better in that regard.

 

Although I'd say if you have a used market (craigslist) where you are, you'd probably be better off just hunting for a 70mm-80mm refractor there. In my area they almost give them away. My celestron 80mm f/11 cost me a mighty $25.



#11 Bonco2

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Posted 22 September 2021 - 03:46 PM

I have full confidence that if the 60mm comes with good optics it will provide better lunar views than the 70mm ETX Why? Almost every 60mm f/15 I've used provides stunning views of the moon up to about 140X. However I can't predict how your mount will perform. If it's of low quality, high power views could be difficult even if it tracks. Mount/tripod steadiness and smooth slomo controls are essential to use a 60mm f/15 to max potential. 

Let us know how it works out.

Bill


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#12 marh

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Posted 22 September 2021 - 04:50 PM

We've gotten down to an exit pupil of 0.35mm on the moon with images still being bright.

 

Try observing with a light on nearby.  That should keep your eye stopped down,

and the moon should not be so bright.  I only have a problem with the moon when

full an in a large scope, because driving down the exit pupil small enough

is too much power for what the atmosphere will allow.  At sub 1mm exit

pupils I don't have a problem with lunar brightness.   I am in a grey

light pollution zone so my eyes never fully dark adapt outside.

I have to admit that I'm still trying to understand the eye's response to telescope exit pupil and the dilated or not so dilated pupil size.

I've read some posts that mention the importance of our physiological vision system - pupil size, density of rods/cones in the retina, and the processing in our visual cerebral system, etc - and now recognize that I just assumed that the best viewing conditions meant that our eyes should be fully dilated. Now I see that this may possibly be true only for trying to view very low contrast deep sky objects.

By the way, with a 70mm refractor I've never felt that the moon was too bright - maybe because I would be using a minimum of 80x magnification, and just like you I never had a problem with sub 1mm exit pupils.


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#13 marh

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Posted 22 September 2021 - 05:19 PM

You've done better with your ETX 70 than I have. Mine doesn't play so nice with my barlow... typically 6mm or so is the best I can get with it. And there tends to be a ton of CA. The moon is okay, but false color is certainly noticeable.

 

As for your 60mm scope, I wouldn't expect you to get much or any CA. If you are okay with the CA from the ETX 70, you'll certainly find the f/15 scope better in that regard.

 

Although I'd say if you have a used market (craigslist) where you are, you'd probably be better off just hunting for a 70mm-80mm refractor there. In my area they almost give them away. My celestron 80mm f/11 cost me a mighty $25.

The 3x barlow that came with the ETX 70 works really nice with a 6mm Plossl that didn't come with the ETX kit. And this is the combination that gives 175x magnification. 

I guess that I didn't notice the CA because at this high power I concentrated on the details on the moon's surface and really never bothered to look for the false color.

But yes, the CA is there because when I did some daylight testing of distant tree branches against a gray bright sky the false color was definitely there with the kit's 4mm eyepiece.

What I don't quite have clear is whether a 3x barlow changes the effective focal length of a refractor, because of it does the ETX would then have a Conrady ratio of over 5 (essentially free of CA) instead of something less than 2.

Well I might just end up looking for something used if the 60mm f15 doesn't give me good moon views with the supplied eyepieces. I'm not expecting them to work with the included barlow because they give some ridiculously high magnifications when in combination.

So as long as the mount and tripod and 4mm supplied eyepiece give nice detailed lunar views and smooth tracking and scanning of the moon's surface I will consider it a good purchase.

Though on the theoretical side I wonder if the resolution of a 60mm lens is too low to show detail at 225x.



#14 vtornado

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Posted 22 September 2021 - 05:19 PM

Viewing the moon is a  tricky business.

 

It is very dependent upon a person's eyes and brain.   The abiltily to see dim images, small details and contrast.

And these variables are at odds with one another.  Small details can be made larger with more magnification,

but that dims the image and lowers contrast.

 

For Lunar I normally wind up with my best views around .75 - .5 mm exit pupil, this is when I am looking for

objects like tiny craterlets or seeing the most detail on crater walls, or tracing an ejecta pattern.

 

For Jupiter/Mars .75 seems to be the best.

 

Saturn because it is so dimmer than Jupiter 1mm seems best , shading is very low contrast.

 

In a large scope like 12 inches 1 mm exit pupil is 300x and near me the atmosphere will not allow that.

At the atmospheric limit of 200x, that same scope is at 1.5mm EP and that is too bright for me.

That is when I am tempted to go to a variable polarizer.



#15 vtornado

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Posted 22 September 2021 - 05:34 PM

What I don't quite have clear is whether a 3x barlow changes the effective focal length of a refractor, because of it does the ETX would then have a Conrady ratio of over 5 (essentially free of CA) instead of something less than 2.

 

No it will not.  Picture the light cone of your telescope, actually there are 3 light cones*. (Red, Green, Blue)

Each cone has a slightly different focal length and each cone strikes the barlow at different widths.  Each

cone is extended the same amount, by the barlow so CA is actually worse with the barlow.  The tip

of each cone is now farther from the others.

 

The moon is not a great subject to see the effects of CA.  It will blur certain low contrast features, but

there are so many high contrast items that there is lots of eye candy there even with CA.

CA is much more damaging on Jupiter because there are not many high contrast details (main belts).

But all the swirling, the GRS, the barges etc are really blurred.

 

In a reflector Jupiter has many pure white areas between the bands.  When I use my achro refractor

the entire disk of jupiter is kind of a light grey/brown from the CA.

 

*actually there are a thousands cones for the entire visible spectrum but that complicates the concept.


Edited by vtornado, 22 September 2021 - 05:35 PM.

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#16 marh

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Posted 22 September 2021 - 05:34 PM

I have full confidence that if the 60mm comes with good optics it will provide better lunar views than the 70mm ETX Why? Almost every 60mm f/15 I've used provides stunning views of the moon up to about 140X. However I can't predict how your mount will perform. If it's of low quality, high power views could be difficult even if it tracks. Mount/tripod steadiness and smooth slomo controls are essential to use a 60mm f/15 to max potential. 

Let us know how it works out.

Bill

Well I'm now getting good 175x views with the ETX while it tracks smoothly the moon, while also letting me scan the surface with the slow slew speeds.

The 60mm f15 comes with a 4mm eyepiece so I'm hoping that the manufacturer knows that lunar viewing is a fair expectation of mine - this means 225x and with the equatorial mount and slomo controls they are definitely leading me to believe the kit should be capable of allowing exploration of the moon's surface and terminator.

Though on the theoretical side I wonder if the resolution of a 60mm lens is too low to show additional detail at 225x as compared to the 70mm.



#17 marh

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Posted 22 September 2021 - 06:00 PM

What I don't quite have clear is whether a 3x barlow changes the effective focal length of a refractor, because of it does the ETX would then have a Conrady ratio of over 5 (essentially free of CA) instead of something less than 2.

 

No it will not.  Picture the light cone of your telescope, actually there are 3 light cones*. (Red, Green, Blue)

Each cone has a slightly different focal length and each cone strikes the barlow at different widths.  Each

cone is extended the same amount, by the barlow so CA is actually worse with the barlow.  The tip

of each cone is now farther from the others.

 

The moon is not a great subject to see the effects of CA.  It will blur certain low contrast features, but

there are so many high contrast items that there is lots of eye candy there even with CA.

CA is much more damaging on Jupiter because there are not many high contrast details (main belts).

But all the swirling, the GRS, the barges etc are really blurred.

 

In a reflector Jupiter has many pure white areas between the bands.  When I use my achro refractor

the entire disk of jupiter is kind of a light grey/brown from the CA.

 

*actually there are a thousands cones for the entire visible spectrum but that complicates the concept.

Got your last 2 messages, so I'll respond to both here.

Thanks for clearing up the 3x barlow/CA  question - looks like I need to understand better the principles at work in a barlow lens.

The upside is that the 60mm f15 has at least the potential to bring out some low contrast features on the moon that just aren't visible in the 70mm f5 -  plus details on Jupiter and Saturn too washed out at f5.

Though on the theoretical side I wonder if the resolution of a 60mm lens is too low to show additional detail at 225x as compared to the 70mm on the moon or J&S.

Or as you mention maybe seeing will be the limiting factor.



#18 vtornado

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Posted 22 September 2021 - 08:47 PM

And one more thing.

 

Post back here and let us know how it is going.

 

I'm always curious.

 

VT



#19 Redbetter

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Posted 24 September 2021 - 01:45 AM

I have Celestron's version of the 60 f/15 with the little EQ mount (circa late 2018.)  To answer one of the original questions:  I considered the lightweight mount unusable for this long tube.  The first objective had some problems with the spacers being unevenly positioned and a lot of lateral color. Bright spurious disks were 3:2 elongated oval shapes but with uneven lateral color separation (bent pattern.)  I RMA'ed it.  I picked up some inexpensive Canon rings to attach to a small dovetail so that I could use the OTA on a real mount.

 

The replacement is sort of Dr. Jeckyll and Mr. Hyde.  In warm weather it has only a tiny amount of trefoil and the planetary images are decent.  But in cooler weather the trefoil gets worse, and is quite noticeable when it is cold.  It isn't due to classic pinch, because I can effectively remove the retainer and it still has the problem.  It yields disappointing images when the trefoil is strong.  So let's call it a fair weather scope.  Hopefully, yours won't have this sort of problem.

 

To answer another of the questions.  In warm weather, there is only a little CA visible at focus.   

 

For planetary or lunar with a small refractor I prefer exit pupils of around 0.5mm if the scopes are well corrected.  Somewhat larger pupil (lower mag) if the objective is not as well figured or CA is a little greater.   I used this scope primarily with 7mm eyepiece.  It can support a 6mm but that is typically not the optimum, depends on the seeing.    

 

I use an RDF with the scope.  The supplied accessories didn't have any value to me.  I use good 1.25" diagonals, not the "comes with box" type or 45's.  Cheap mirror diagonals are often misaligned, and RACI's introduce some artifacts that make them unsuitable for high power.  

 

I have no idea how it will work for you.  The magnifications you use with a 70 f/5 achro are well beyond what I would find useful with such a short achro, so I can't extrapolate how this one might compare.



#20 Paul Sweeney

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Posted 24 September 2021 - 02:45 PM

Interesting comparison. I just sold a 70/500 and kept the 60/700.

A good 60/900 will show you a lot if it is solidly mounted. The scope you showed is a mass produced scope of questionable quality. The optics are hit and miss. You may get a poor performer, or a great performer. The mount is way too light and will wobble a lot. That will have a negative effect on your ability to pick out fine details.

If you want a good 60/900, go over to the Classics forum. There is a thread for ebay and other internet market places. The classic scopes will have (mostly) far better optics, better mounts and eyepieces made of high quality glass.

Unless you are fixed on a 60/900, you might want to look at an 80/1200. Mine, a Vixen, is incredibly sharp and can handle high powers easily. It came with a NP mount and a massive wood tripod. Very stable.

If there is a club near you, contact them and look through some of their scopes. Someone might have a 60mm scope that you can acquire a a low price. It pays to look around before buying.

Edited by Paul Sweeney, 24 September 2021 - 02:59 PM.

  • Bonco2 likes this

#21 Bonco2

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Posted 24 September 2021 - 03:45 PM

Good advice by Mr. Sweeney. The Classics forum is the BEST forum on CN. Lot's of posts there using 60mm classics and other small refractors. BTW I have a very lightweight Classic 60mm f/12 Lafayette on a fine quality equitorial mount. It's a superb lunar telescope and planetary scope. Classic Telescopes like these can be found from between $75 to $200 depending on model, condition, and completeness.

Bill



#22 teashea

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Posted 24 September 2021 - 10:08 PM

You need a better mount.  The mount is as important as the telescope.



#23 marh

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Posted 25 September 2021 - 01:53 PM

I have Celestron's version of the 60 f/15 with the little EQ mount (circa late 2018.)  To answer one of the original questions:  I considered the lightweight mount unusable for this long tube.  The first objective had some problems with the spacers being unevenly positioned and a lot of lateral color. Bright spurious disks were 3:2 elongated oval shapes but with uneven lateral color separation (bent pattern.)  I RMA'ed it.  I picked up some inexpensive Canon rings to attach to a small dovetail so that I could use the OTA on a real mount.

 

The replacement is sort of Dr. Jeckyll and Mr. Hyde.  In warm weather it has only a tiny amount of trefoil and the planetary images are decent.  But in cooler weather the trefoil gets worse, and is quite noticeable when it is cold.  It isn't due to classic pinch, because I can effectively remove the retainer and it still has the problem.  It yields disappointing images when the trefoil is strong.  So let's call it a fair weather scope.  Hopefully, yours won't have this sort of problem.

 

To answer another of the questions.  In warm weather, there is only a little CA visible at focus.   

 

For planetary or lunar with a small refractor I prefer exit pupils of around 0.5mm if the scopes are well corrected.  Somewhat larger pupil (lower mag) if the objective is not as well figured or CA is a little greater.   I used this scope primarily with 7mm eyepiece.  It can support a 6mm but that is typically not the optimum, depends on the seeing.    

 

I use an RDF with the scope.  The supplied accessories didn't have any value to me.  I use good 1.25" diagonals, not the "comes with box" type or 45's.  Cheap mirror diagonals are often misaligned, and RACI's introduce some artifacts that make them unsuitable for high power.  

 

I have no idea how it will work for you.  The magnifications you use with a 70 f/5 achro are well beyond what I would find useful with such a short achro, so I can't extrapolate how this one might compare.

Sort of a lottery but if the CA is bad or the optics give disappointing images the kit will be sent back.

The mount is a big question mark too - the ETX 70 even at 175x tracked steadily with no vibration problems but such a fast refractor at f5 doesn't give any details on Jupiter or Saturn that other people observe fairly easy with 60mm f15 OTAs.

This topic https://www.cloudyni...netary-viewing/ has me expecting to use 180x with the 60mm f15. This means a 5mm eyepiece but the closest the kit supplies is a 4mm.



#24 Anony

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Posted 25 September 2021 - 04:47 PM

Sort of a lottery but if the CA is bad or the optics give disappointing images the kit will be sent back.

The mount is a big question mark too - the ETX 70 even at 175x tracked steadily with no vibration problems but such a fast refractor at f5 doesn't give any details on Jupiter or Saturn that other people observe fairly easy with 60mm f15 OTAs.

This topic https://www.cloudyni...netary-viewing/ has me expecting to use 180x with the 60mm f15. This means a 5mm eyepiece but the closest the kit supplies is a 4mm.

I've found a polarizer helps a bit with Jupiter and CA. And I know some folks use color filters, but I kind of find them annoying -- it's like the cure to fix some false color is add a ton of really really false color all over the place.

 

Still amazed you can crank that ETX 70 as high as you can. I managed to use a half barlow with my 6mm to get around 4.5mmish, but that's the best I could do. Somehow you are getting it to play nice with the equivalent of a 2mm eyepiece. And you should get some Jupiter details (a couple of bands, albeit rather a small view).



#25 marh

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Posted 25 September 2021 - 04:51 PM

Interesting comparison. I just sold a 70/500 and kept the 60/700.

A good 60/900 will show you a lot if it is solidly mounted. The scope you showed is a mass produced scope of questionable quality. The optics are hit and miss. You may get a poor performer, or a great performer. The mount is way too light and will wobble a lot. That will have a negative effect on your ability to pick out fine details.

If you want a good 60/900, go over to the Classics forum. There is a thread for ebay and other internet market places. The classic scopes will have (mostly) far better optics, better mounts and eyepieces made of high quality glass.

Unless you are fixed on a 60/900, you might want to look at an 80/1200. Mine, a Vixen, is incredibly sharp and can handle high powers easily. It came with a NP mount and a massive wood tripod. Very stable.

If there is a club near you, contact them and look through some of their scopes. Someone might have a 60mm scope that you can acquire a a low price. It pays to look around before buying.

I see you have a Bresser too - they know the astronomy world so when they offer a kit with OTA and mount I can only expect that they have tested and specified adequately the complete package.

 

This means for me that if they include a 4mm eyepiece, then the mount and 60mm/f15 OTA will satisfactorily work for planetary viewing at 225x - otherwise why include this particular eyepiece? They could just as easily included a 5mm/180x or 6mm/150x eyepiece instead.

 

Now if this is just deceptive marketing they will get a bad review from me and a returned product and a lost sale - and I made sure to buy it from a good reputable retailer that stands by their customers with very good service that includes me not having to pay any shipping fees. Neither delivery nor, if the case may be, return shipping costs.

 

Not sure how transportable an 80mm/f15 and adequate mount is - probably a bit too much to hand carry 30-35min/3 km. But it is just at Conrady's limit so it is probably free of CA and should make a fine planetary scope for those with car access to good viewing sites or better yet from their homes.




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