Considering an upsize, but is it worth it?

[Paul Manuell]

Is a 120mm refractor upsize from a 90mm one of the same focal length worth it? I understand the 120 will be much brighter, but would there really be that much of a noticeable difference in planetary detail, considering that the eyepieces used will give the same magnification in both telescopes?

Edited September 2 by Paul Manuell
To correct the punctuation

[NGC 1502]

It would help if you can say which 120mm and 90mm you mean?

The larger aperture should show fainter stars.  If both are achromatic refractors the same focal length then the larger will have greater issues with brighter objects like planets. 

[licho52]

When it comes to aperture bigger is always better.

[Stu]

7 hours ago, licho52 said:

When it comes to aperture bigger is always better.

Not necessarily true with refractors as it depends on their type eg achro vs Apo, focal length, degree of SA etc. As mentioned above, knowing which 90mm and 120mm are involved would help us to give better advice. 

[Mr Spock]

As above. A 90mm apo will give much more satisfying planetary views than a 120mm achro, though the 120mm will still bring in more light.

[jjohnson3803]

Don't know your mount situation, but consider OTA weight and also length if you intend to travel.  I've downsized scopes for convenience.

[niallk]

22 hours ago, Paul Manuell said:

Is a 120mm refractor upsize from a 90mm one of the same focal length worth it? I understand the 120 will be much brighter, but would there really be that much of a noticeable difference in planetary detail, considering that the eyepieces used will give the same magnification in both telescopes?

You could go to 254mm aperture for less money with a 10" dob: 8x light gathering plus ~2.8x the resolution.

Very good for planetary; but also for DSOs.

[Paul Manuell]

3 hours ago, niallk said:

You could go to 254mm aperture for less money with a 10" dob: 8x light gathering plus ~2.8x the resolution.

Very good for planetary; but also for DSOs.

Except I don't want a Dob, which is why I based my question on refractors

[Paul Manuell]

On 02/09/2024 at 23:03, NGC 1502 said:

It would help if you can say which 120mm and 90mm you mean?

The larger aperture should show fainter stars.  If both are achromatic refractors the same focal length then the larger will have greater issues with brighter objects like planets. 

The 90mm is a Celestron Astromaster, the 120mm will be a Skywatcher Evostar. Both 1000mm fl and achromats. What issues will the larger one have with planets?

[Paul Manuell]

15 hours ago, Stu said:

Not necessarily true with refractors as it depends on their type eg achro vs Apo, focal length, degree of SA etc. As mentioned above, knowing which 90mm and 120mm are involved would help us to give better advice. 

90mm Celestron Astromaster, 120mm Skywatcher Evostar. Both 1000mm fl and achromats

[Paul Manuell]

5 hours ago, jjohnson3803 said:

Don't know your mount situation, but consider OTA weight and also length if you intend to travel.  I've downsized scopes for convenience.

Will be getting a mount and tripod capable of supporting the larger telescope if I buy it, so that won't be an issue

[Mr Spock]

I have a 120mm - it's a Helios, basically the same as the Skywatcher. There is false colour on all bright objects. The moon has good detail, so does Jupiter. I'd suggest a 5mm eyepiece for the moon (x200), and a 6mm for Jupiter (x167). It's also very good on doubles; Izar looked brilliant at x250. I'd suggest a Svbony 3-8mm as a good match for high power viewing. It's very capable on deep sky. I've had a lovely view of M42 with it at x26.
However, a 100mm apo spanks it totally on planets (at a price, obviously).

Where it is good is on solar. With a Baader Coolwedge and Continuum filter, it's bitingly sharp. The green of the filter removes all aberrations. That's how I use it these days - it's my main solar scope.

It's useable on my EQ5, though can shake a bit in the wind. It balances nicely with a single weight at the end of the shaft.

I'm happy with mine. Definitely recommended. I'd prefer it over the 90mm.

It used to be black - I painted it white...

 

[NGC 1502]

7 hours ago, Paul Manuell said:

The 90mm is a Celestron Astromaster, the 120mm will be a Skywatcher Evostar. Both 1000mm fl and achromats. What issues will the larger one have with planets?

 

I have a Skywatcher 120/600 achromat.  It’s best as a low to medium power telescope. That’s not to say it’s unusable at higher powers, but that’s not where it excels, especially on bright objects.

 

For instance Jupiter at above 100x, disc details are there, but the planet is enveloped in a haze of purple. Your 1000mm focal length should have somewhat less purple haze. Some will find that acceptable, others may not.

Your 90/1000 should suffer less than the 120/1000 from purple haze (false colour/chromatic aberration).

Opinions are all over the place as to what’s acceptable and what is not. Only you can decide what’s ok for you.

 

 

 

 

 

Edited September 4 by NGC 1502

[Stu]

7 hours ago, Paul Manuell said:

90mm Celestron Astromaster, 120mm Skywatcher Evostar. Both 1000mm fl and achromats

Sounds like a decent upgrade. Both relatively slow achros so CA will be there but better controlled than a faster scope, and spherical aberration should also be better. SA is in many ways worse than CA in terms of robbing an image of detail at higher powers.

You should certainly notice an improvement in resolution. CA tends to worsen with aperture so the 120 will show a little more but still manageable I should think. You can use certain filters to cut down the effects of CA for me planetary and lunar observing if it’s an issue for you.

[Paul Manuell]

On 04/09/2024 at 02:03, Mr Spock said:

I have a 120mm - it's a Helios, basically the same as the Skywatcher. There is false colour on all bright objects. The moon has good detail, so does Jupiter. I'd suggest a 5mm eyepiece for the moon (x200), and a 6mm for Jupiter (x167). It's also very good on doubles; Izar looked brilliant at x250. I'd suggest a Svbony 3-8mm as a good match for high power viewing. It's very capable on deep sky. I've had a lovely view of M42 with it at x26.
However, a 100mm apo spanks it totally on planets (at a price, obviously).

Where it is good is on solar. With a Baader Coolwedge and Continuum filter, it's bitingly sharp. The green of the filter removes all aberrations. That's how I use it these days - it's my main solar scope.

It's useable on my EQ5, though can shake a bit in the wind. It balances nicely with a single weight at the end of the shaft.

I'm happy with mine. Definitely recommended. I'd prefer it over the 90mm.

It used to be black - I painted it white...

 

I've got a 6.5mm eyepiece already (153x magnification), but I'm hoping planets (well, Jupiter really)  will be more detailed using that eyepiece on a 120 than it currently is with my 90

[Paul Manuell]

20 hours ago, NGC 1502 said:

 

I have a Skywatcher 120/600 achromat.  It’s best as a low to medium power telescope. That’s not to say it’s unusable at higher powers, but that’s not where it excels, especially on bright objects.

 

For instance Jupiter at above 100x, disc details are there, but the planet is enveloped in a haze of purple. Your 1000mm focal length should have somewhat less purple haze. Some will find that acceptable, others may not.

Your 90/1000 should suffer less than the 120/1000 from purple haze (false colour/chromatic aberration).

Opinions are all over the place as to what’s acceptable and what is not. Only you can decide what’s ok for you.

 

 

 

 

 

I'm just wondering whether the 120 will be THAT much brighter and show more planetary detail than a 90 at any given magnification. For instance, with my current 90 and using my 6.5mm (153× magnification) eyepiece, all I can see on Jupiter are 2 distinct bands. I can't see the GRS, though I have seen the shadow of one of the planet's moons on its disc once. Will the GRS be visible at that same magnification with the larger/brighter 120 aperture?

[Roy Challen]

59 minutes ago, Paul Manuell said:

I'm just wondering whether the 120 will be THAT much brighter and show more planetary detail than a 90 at any given magnification. For instance, with my current 90 and using my 6.5mm (153× magnification) eyepiece, all I can see on Jupiter are 2 distinct bands. I can't see the GRS, though I have seen the shadow of one of the planet's moons on its disc once. Will the GRS be visible at that same magnification with the larger/brighter 120 aperture?

You should be able to see the GRS easily with 90mm aperture. I can see it with 60mm, no problem. Bear in mind, the seeing conditions will also affect how much detail you'll see on any given night. And timing - if the GRS is on the side facing away...

More magnification doesn't necessarily mean more detail. I find that I can see everything that my telescopes are capable of resolving at between x100 and x125 or so.

Edited September 5 by Roy Challen

[NGC 1502]

6 hours ago, Roy Challen said:

 

More magnification doesn't necessarily mean more detail. I find that I can see everything that my telescopes are capable of resolving at between x100 and x125 or so.

 

Definitely agree with that……..smaller and sharper beats bigger and fuzzier.  It comes with practice to “learn how to see”.   That’s relevant to planetary and deep sky.  Having said that, double star observation can take higher mags than most other types of objects.  A good Barlow in your kit is handy to have, just use it with discretion.

[NGC 1502]

7 hours ago, Paul Manuell said:

I'm just wondering whether the 120 will be THAT much brighter and show more planetary detail than a 90 at any given magnification. For instance, with my current 90 and using my 6.5mm (153× magnification) eyepiece, all I can see on Jupiter are 2 distinct bands. I can't see the GRS, though I have seen the shadow of one of the planet's moons on its disc once. Will the GRS be visible at that same magnification with the larger/brighter 120 aperture?

 

In good conditions my 70mm TeleVue Pronto shows the GRS no problem.  And some regard the Pronto as “just an achromat”.

[Cosmic Geoff]

Depends on your aspirations and how determined you are to stick to refractors.  I found that with catadroptics, bigger was better, and imaging blew the socks off visual observation.  I found it very hard to see the Great Red Spot with my 127mm Mak, but could image it no problem.  Imaging Jupiter with a 200mm SCT reveals a mass of detail.

[Gonariu]

On 9/3/2024 at 12:03 AM, NGC 1502 said:

It would help if you can say which 120mm and 90mm you mean?

The larger aperture should show fainter stars.  If both are achromatic refractors the same focal length then the larger will have greater issues with brighter objects like planets. 

For chromatic aberration (or other optical aberrations) there is always the diaphragm technique. I had to diaphragm a 120/1000 achromatic (the Konusuper 120) to 90 mm due to a lateral chipping of the achromatic doublet that I don't know how it occurred. By doing so I obtained good results on Jupiter with which I previously saw only the two main bands (the Konusuper, being one of the first Chinese refractors with a short focal length, had a performance that varied from example to example and mine has some problems; certainly today in the former Celestial Empire they produce 120/1000 achromatics that are on average better than 25-30 years ago). I share with you a sketch of Jupiter made with the Konusuper diaphragmed to 90 mm.

[Gonariu]

Sorry, I forgot the sketch of Jupiter that I attach now.
Telescope: Konusuper 120 diaphragmed at 90 mm;
Magnifications: X167, X200, X250;
Use of the 90o mirror star diagonal, the sketch was photographed and the right and left were exchanged (to compensate for the diagonal);
Date: July 29, 2021;
Time: 1.45 UT.

[Paul Manuell]

On 05/09/2024 at 05:27, Roy Challen said:

You should be able to see the GRS easily with 90mm aperture. I can see it with 60mm, no problem. Bear in mind, the seeing conditions will also affect how much detail you'll see on any given night. And timing - if the GRS is on the side facing away...

[More magnification doesn't necessarily mean more detail. I find that I can see everything that my telescopes are capable of resolving at between x100 and x125 or so.

The magnification in my current 90mm will be the same as the 120mm I'm considering cos they're both 1000fl, I was just wondering if the extra brightness would make much difference in resolution

Edited September 7 by Paul Manuell
Tried to highlight some of the quoted post but it didn't work

[Roy Challen]

24 minutes ago, Paul Manuell said:

The magnification in my current 90mm will be the same as the 120mm I'm considering cos they're both 1000fl, I was just wondering if the extra brightness would make much difference in resolution

More aperture = more resolution. So, yes, you will see more.

[bosun21]

On 04/09/2024 at 00:58, Paul Manuell said:

The 90mm is a Celestron Astromaster, the 120mm will be a Skywatcher Evostar. Both 1000mm fl and achromats. What issues will the larger one have with planets?

None apart from some CA on the brighter planets which will also be present on the smaller 90mm. This can be countered by the addition of a filter. The 120 will definitely be better for showing planetary details. If everything else is equal then bigger is better always.