56 replies to this topic

[Dave96]

Hello everyone. I am new to amateur astronomy and would like to know if there is a big difference in the view between a 90mm refractor and a 127mm or a 130mm refractor? I keep hearing that aperture is one of the key factors for telescopes. I currently own a 90mm refractor on an altazimuth mount since July 2020 and I have enjoyed it, but would like to know if a larger refractor makes a big difference or not. I am considering a second telescope (more aperture), preferably another refractor because I like the simplicity, size, and the durability. I do not have a specific model in mind, but my budget is about $800.00.

 

My viewing conditions are the suburbs (Bortle 6 sky) and I view planets, the moon, star clusters, double stars, M45, M42, M31 (was actually able to see M31 as a small grey-colored faint fuzzy), and any other brighter DSOs that my 90mm scope can handle. Will a 127mm or 130mm refractor show a considerable difference and more details of these objects compared to my 90mm? Also, is a 127mm Mak-Cass a good option for an overall telescope to view the same objects? I am only interested in viewing, no photography. I typically view at home in my yard or back deck. The details of my current 90mm refractor are below in my signature block.

 

I appreciate any advice from those with personal experience with various refractors and/or Mak-Cass telescopes. Thanks.

[Supernova74]

Aperture can be a little confusing at times and I will explain why for exsample the 90mm you mentioned firstly give or take micro measurements comes in at 3.5” and generally in scopes like refractors that’s the true (clear aperture of the scope) however tho on some other manufactures ie 100,102,105mm is basically the same aperture even tho it states on the lens cell of a refractor so basically you still getting there abouts a 4” refractor even when it states ever so slightly different measurements with different brands.

 

some manufactures like Meade do oversize there primary mirrors this is on there sct cassagrain optical design telescopes and the reason thay do this is actually try and compensate the secondary mirror which is behind the correcter plate of the scope,this because the mirror is obstructed some what for the actual true aperture of the scope so effectively you are not getting a full let’s say 10” scope,that’s just the design of the scope,also the maksutovs act in a similer way however not quite as bad I believe.

[DAG792]

Hello everyone. I am new to amateur astronomy and would like to know if there is a big difference in the view between a 90mm refractor and a 127mm or a 130mm refractor? I keep hearing that aperture is one of the key factors for telescopes. I currently own a 90mm refractor on an altazimuth mount since July 2020 and I have enjoyed it, but would like to know if a larger refractor makes a big difference or not. I am considering a second telescope (more aperture), preferably another refractor because I like the simplicity, size, and the durability. I do not have a specific model in mind, but my budget is about $800.00.

 

My viewing conditions are the suburbs (Bortle 6 sky) and I view planets, the moon, star clusters, double stars, M45, M42, M31 (was actually able to see M31 as a small grey-colored faint fuzzy), and any other brighter DSOs that my 90mm scope can handle. Will a 127mm or 130mm refractor show a considerable difference and more details of these objects compared to my 90mm? Also, is a 127mm Mak-Cass a good option for an overall telescope to view the same objects? I am only interested in viewing, no photography. I typically view at home in my yard or back deck. The details of my current 90mm refractor are below in my signature block.

 

I appreciate any advice from those with personal experience with various refractors and/or Mak-Cass telescopes. Thanks.

Personally, I would see substantial difference between a 130 mm and a 90 mm refractor. 

You state your main requirements are DSOs and a wide field? If that is the case, a Mak-Cass would be a poor choice. It will have a narrow FOV, and would frame objects like M31 and M45 poorly. 

Even though this is the refractor forum, I'll ask, why aren't you considering a Dobsonian? Refractors- great as they may be- cannot satisfy the need for more aperture. All of your needs would be better fulfilled by a 150 mm or 200 mm Dobsonian with a 2 inch focuser. DSOs would be better, planets would be better. In a $800 budget, you can even afford a 10 inch dob, which is (except portability) a much better scope for DSOs than any 130 mm refractor.

[Barlowbill]

I have been viewing with a 90mm Mak-Cass for a few years now.  I like it alot for its size as a grab and go.  However, the field of view is small.  Would I rather have an ETX 125?  Sure.  More power is better.  would I get another similar scope for such a miniscule improvement?  No!  Would I go from an 8" Dob to a 10" Dob?  No!  Twelve inch?  Yes!.  Get a Dob.  An 8" is fairly easily moved.

[sg6]

Aperture collects more light, in a way that is all you can say.

Chromatic aberration and spherical aberration generally get worse with bigger objectives, that is where the focal ratio is a good indicator.

 

A 90mm f/10 will I expect show less CA then a 120 f/6 - I have a 102 f/6 and the CA is a real PAIN. A 120 or 130 f/6 or f/7 will be worse. So as said all aperture says is how much light it can collect. Nothing more.

 

If you want reduced CA then it is ED or triplet and they are just costly.

 

Which 90mm have you? There are a few generally f/10 but some are f/5.5 now.

I have a 90mm, William Optics Megrez 90 doublet with FPL-53. It's good.

 

Also have a Mak, field of view too narrow and just not easy to set up. Because of the lack of ease it rarely gets used. Mine has a strange habit of suddenly thinking it is equitorally mounted and tries to ram the OTA into the base unit. That also doesn't help make for "ease". Sure it hates me!!!

Edited by sg6, 23 February 2021 - 12:49 PM.

[scadvice]

How dark are your skies where you live? That can effect the abilities gained quite a bit of a larger aperture scope.

 

From what you described of you needs I would suggest a 12 inch Dobsonian for DSO and the 90mm for planetary and double stars. Though it can be fun to compare what you see of the same object with both the refractor and the reflector at the same time. I find it interesting to see different details when doing that.

 

I no longer have just viewing gear now that I'm into AP.  But I do belong to a club where there are people who bring out Dob's up to an amazing 32". I find it much more enjoyable setting my rig up  to image and while it's doing it's thing walking over to these big Dob's viewing and visiting with their owners. I get the benefit of viewing through the big apertures without the cost and work of setting them up!

Edited by scadvice, 23 February 2021 - 01:07 PM.

[jeffreym]

welcome to Cloudy Nights!

 

I think the 90mm refractor you have hits a good spot in terms of size/weight for the aperture.  Going bigger 127+ will likely require a much better mount which by itself would used your budget.

 

If you want aperture, there is substitute for a dob in terms of cost to aperture.  The 10 or 12" dobs are just an incredible value if you can adjust to the overall size.

 

What's in the middle? I think the 8" SCT is popular because it fits in between the other two.  A compact package with significant aperture.  The C8 by itself is 12lbs.  The Meade units are a couple lbs more.  This might also need a mount upgrade.

 

Have fun,

Jeff

[JMW]

I have  90, 115 and 140mm refractors. I have a 130mm refractor on order. 

 

I like my SVR90T on a FTQ mount/Gitzo 5541LS tripod because it is a one handed out the door and pickup and move to another location to avoid a tree or house in the way setup. It also has a very wide true field of view compared to my longer focal length scopes.

 

My SV115T20 can certainly show more detail, show objects that are dimmer and still be reasonable size. It requires that I use my FTX mount on a TPOD 130 which is now 2 trips because I can't move the scope easily while going through the door when it is attached to the mount and tripod. It is still light enough that I can pick up both scope and mount to move to another part of the yard.

 

My TEC 140 is used on a DM6 mount/Planet tripod setup. It is a 3 trip out the door setup. Tripod first, DM6 mount 2nd and scope last. I can't move scope/mount/tripod together after setting up. I mostly use it at dark sky location version short sessions at home. My TEC 140 and the SVX130T that I have on order are very close in weight. I am ordering the SVX130T for imaging because the TEC 140 is almost always in use by my wife for visual. The 130 and 140 will be able to go deeper and show more details. The tradeoff is the great weight and hassle of needing a heavier tripod and mount. It also is not as great as wide field scope as my SVR90T.

 

When we travel we usually bring a 8 inch f/6 custom dob along with the TEC 140. If we are going to a multi night start party where we can stay set up and secure for many nights we will bring the 14.5 inch dob plus other scopes for imaging, solar, etc...

 

I feel the best experience is to have a decent size and affordable refractor setup next to a larger Dob.

[LDW47]

Hello everyone. I am new to amateur astronomy and would like to know if there is a big difference in the view between a 90mm refractor and a 127mm or a 130mm refractor? I keep hearing that aperture is one of the key factors for telescopes. I currently own a 90mm refractor on an altazimuth mount since July 2020 and I have enjoyed it, but would like to know if a larger refractor makes a big difference or not. I am considering a second telescope (more aperture), preferably another refractor because I like the simplicity, size, and the durability. I do not have a specific model in mind, but my budget is about $800.00.

 

My viewing conditions are the suburbs (Bortle 6 sky) and I view planets, the moon, star clusters, double stars, M45, M42, M31 (was actually able to see M31 as a small grey-colored faint fuzzy), and any other brighter DSOs that my 90mm scope can handle. Will a 127mm or 130mm refractor show a considerable difference and more details of these objects compared to my 90mm? Also, is a 127mm Mak-Cass a good option for an overall telescope to view the same objects? I am only interested in viewing, no photography. I typically view at home in my yard or back deck. The details of my current 90mm refractor are below in my signature block.

 

I appreciate any advice from those with personal experience with various refractors and/or Mak-Cass telescopes. Thanks.

I assume you are using some 2” eps as well as 1.25” ? That is a big factor in your low power, wide field viewing pleasures.

[clearwaterdave]

Hello.,Yes there will be a noticeable difference. A bigger mount may be needed as well.,I built a mount that holds all my refractors from 80mm to 127mm.,Good luck.,

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[bobhen]

If you want to stay in the refractor family consider the…

 

Celestron 120mm Omni XLT refractor. You can purchase the refractor with a mount for around $640.  

 

However, you can purchase the Celestron 120mm Omni XLT Refractor as an OTA (Optical Tube Assembly) for $400 from High Point Scientific. HERE is a link.

 

You can then purchase a more robust mount from Orion Telescopes & Binoculars like the Sky View Pro for around $300. HERE is a link.

 

The Omni is a pretty good size refractor so I would recommend the Sky View Pro mount.

 

Other telescopes to consider within your budget might be an Orion 8" Dobsonian or a Celestron Nexstar 6SE on a computerized mount. Each telescope has advantage and disadvantages so do some research regarding weight, size, collimation and acclimation of the optics to the cold and then select one. All will deliver the goods.

 

Bob

[Allan Wade]

There is a difference in observing between the 90mm and 130mm class refractors, but it is not a major upgrade. I had 76, 85 , 101 and 130 size refractors at the same time. There’s incremental improvement with each step up, but it’s just a little more of the same.

 

Observing with a larger mirrored scope is like a different hobby by comparison. My advice to get the most enjoyment from observing is to own a smaller refractor around that 4” class combined with a larger dob around the 10” to 12” class. Those two scopes could keep an observer going for a lifetime. A 90mm/130mm combination wouldn’t get close to achieving that.

[LDW47]

There is a difference in observing between the 90mm and 130mm class refractors, but it is not a major upgrade. I had 76, 85 , 101 and 130 size refractors at the same time. There’s incremental improvement with each step up, but it’s just a little more of the same.

 

Observing with a larger mirrored scope is like a different hobby by comparison. My advice to get the most enjoyment from observing is to own a smaller refractor around that 4” class combined with a larger dob around the 10” to 12” class. Those two scopes could keep an observer going for a lifetime. A 90mm/130mm combination wouldn’t get close to achieving that.

I have a 4”, I have a 130mm but if I was younger I sure as ...... would have me a 12” dob to go with them, instead I have a 6” dob, lol !

[JMW]

The advantage of the smaller setups is the ease of bringing it to dark skies. I would rather have my SVR90T under very dark skies than my 14.5 inch Zambuto mirror at my light polluted home. Wide field is it's best when there is no light pollution. Some times we only bring one scope and it's usually the TEC 140.

Edited by JMW, 23 February 2021 - 07:52 PM.

[Echolight]

A used C6 SCT with reducer on a Porta II mount would pair good with the 90. You no doubt will see a difference in light gathering and resolution.

 

I see a huge difference between my 6 inch f/8 achromat and 80mm f/7.5 apo. The big scope wins in a landslide, but needs an especially tall mount.

 

Then again.... for widefield.... the ST120 seems to always be calling my name.

Edited by Echolight, 23 February 2021 - 08:53 PM.

[GSBass]

The answer is a dual mount with two scopes, a small refractor for duties below 100x and a cass of some sort for over 100x, you will see 100s of post of people trying to find gadgets to make one scope the Jack of all trades, they can do it but it’s not ideal, every design has its strengths and weaknesses. So two on the same mount is nirvana..... and for those nights of true dedication and good seeing, have a 3rd 20” dob ready to roll out of the garage

[clearwaterdave]

Two for one is nice.,I used the 127 as a finder for the 80mm.,.lol.,This helps to really compare the differences between your scopes.,

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[GSBass]

Twice the fun .... I seriously could never make the mistake of giving up my mak cass again, but that does not mean you have to be stubborn and miss out on the joys of a small refractor, neither can match the other, both great

Two for one is nice.,I used the 127 as a finder for the 80mm.,.lol.,This helps to really compare the differences between your scopes.,

[Dave96]

Thank you everyone for replying to this post. I appreciate all of your different opinions and facts about the various telescopes that you use. Thanks for describing your telescopes, setup configurations, and the comparisons between the different views regarding what you have seen with the different apertures. This information helps and I am glad I joined Cloudy Nights. It is nice to hear from real people to receive great information on multiple telescopes. Vendor websites are okay to get information about telescopes, mounts, etc., but it doesn't compare to the valuable experiences coming from people who have actually used the different types of equipment. Your replies to this post will make it easier for me to decide on what my next telescope will be. I'll let everyone know what I decide to get when the time comes. Thanks again!   

[Dave96]

Personally, I would see substantial difference between a 130 mm and a 90 mm refractor. 

You state your main requirements are DSOs and a wide field? If that is the case, a Mak-Cass would be a poor choice. It will have a narrow FOV, and would frame objects like M31 and M45 poorly. 

Even though this is the refractor forum, I'll ask, why aren't you considering a Dobsonian? Refractors- great as they may be- cannot satisfy the need for more aperture. All of your needs would be better fulfilled by a 150 mm or 200 mm Dobsonian with a 2 inch focuser. DSOs would be better, planets would be better. In a $800 budget, you can even afford a 10 inch dob, which is (except portability) a much better scope for DSOs than any 130 mm refractor.

DAG792,

Thank you for your reply; I appreciate the info on the Mak-Cass, I didn't realize it has such a narrow FOV. I am becoming more interested in DSOs, mainly because there are so many objects to see. I like to view the planets and the moon, but they are not always in the night sky to be seen. A Dob is definitely something for me to consider after reading your reply and many others have suggested a Dob also.   

[Dave96]

I have been viewing with a 90mm Mak-Cass for a few years now.  I like it alot for its size as a grab and go.  However, the field of view is small.  Would I rather have an ETX 125?  Sure.  More power is better.  would I get another similar scope for such a miniscule improvement?  No!  Would I go from an 8" Dob to a 10" Dob?  No!  Twelve inch?  Yes!.  Get a Dob.  An 8" is fairly easily moved.

Barlowbill,

Thanks for the information. Others have said the same thing about a Mak-Cass having a small FOV. Sounds like a Mak-Cass is very good for planets. I can also see where the Mak-Cass is good for portability. 

[Dave96]

Aperture collects more light, in a way that is all you can say.

Chromatic aberration and spherical aberration generally get worse with bigger objectives, that is where the focal ratio is a good indicator.

 

A 90mm f/10 will I expect show less CA then a 120 f/6 - I have a 102 f/6 and the CA is a real PAIN. A 120 or 130 f/6 or f/7 will be worse. So as said all aperture says is how much light it can collect. Nothing more.

 

If you want reduced CA then it is ED or triplet and they are just costly.

 

Which 90mm have you? There are a few generally f/10 but some are f/5.5 now.

I have a 90mm, William Optics Megrez 90 doublet with FPL-53. It's good.

 

Also have a Mak, field of view too narrow and just not easy to set up. Because of the lack of ease it rarely gets used. Mine has a strange habit of suddenly thinking it is equitorally mounted and tries to ram the OTA into the base unit. That also doesn't help make for "ease". Sure it hates me!!!

sg6,

I appreciate the info on aberration and focal ratios. Yes, a Triplet would be too expensive for me. I have an Orion VersaGo E-Series 90mm, which is considered an entry-level telescope, but I am happy with it. It has a 600mm focal length and is f/6.7. The CA is not too bad and is hardly visible; doesn't bother me. I also have an Orion eyepiece kit, which I believed really helped in improving the views with the telescope. I have multiple EPs to choose from. I also have a 90-degree star diagonal and I do not use the 45-degree diagonal that came with the scope. Thanks again for the information.

[Dave96]

How dark are your skies where you live? That can effect the abilities gained quite a bit of a larger aperture scope.

 

From what you described of you needs I would suggest a 12 inch Dobsonian for DSO and the 90mm for planetary and double stars. Though it can be fun to compare what you see of the same object with both the refractor and the reflector at the same time. I find it interesting to see different details when doing that.

 

I no longer have just viewing gear now that I'm into AP.  But I do belong to a club where there are people who bring out Dob's up to an amazing 32". I find it much more enjoyable setting my rig up  to image and while it's doing it's thing walking over to these big Dob's viewing and visiting with their owners. I get the benefit of viewing through the big apertures without the cost and work of setting them up!

scadvice,

My skies are about a Bortle 6 (suburbs). Once my eyes are dark-adapted, I can see most stars and can easily identify constellations. I have not yet used my 90mm at a darker sky, but hopefully that will happen soon. I don't think I know my telescope's full potential yet because I have only used it at home. It does sound fun to compare the same objects using different telescopes side by side.

 

A 32" Dob must be amazing! I can only imagine the view from such a large aperture. Thanks for your reply.  

[dan_h]

some manufactures like Meade do oversize there primary mirrors this is on there sct cassagrain optical design telescopes and the reason thay do this is actually try and compensate the secondary mirror which is behind the correcter plate of the scope,this because the mirror is obstructed some what for the actual true aperture of the scope so effectively you are not getting a full let’s say 10” scope,that’s just the design of the scope,also the maksutovs act in a similer way however not quite as bad I believe.

 No.  The corrector is a slightly negative element that causes the light cone to diverge.  As a result, the light cone is bigger than the aperture when it gets to the primary mirror.  A slightly larger primary is used to prevent the loss of light at the edges.

 

dan

 

PS.   Your posts would be much more interesting and far more readable if you would include some basic punctuation. It is much easier for you to add a period here and there to separate your sentences than it is for every reader to read and reread your post several times to try and get the meaning of of it. 

[Dave96]

I have  90, 115 and 140mm refractors. I have a 130mm refractor on order. 

 

I like my SVR90T on a FTQ mount/Gitzo 5541LS tripod because it is a one handed out the door and pickup and move to another location to avoid a tree or house in the way setup. It also has a very wide true field of view compared to my longer focal length scopes.

 

My SV115T20 can certainly show more detail, show objects that are dimmer and still be reasonable size. It requires that I use my FTX mount on a TPOD 130 which is now 2 trips because I can't move the scope easily while going through the door when it is attached to the mount and tripod. It is still light enough that I can pick up both scope and mount to move to another part of the yard.

 

My TEC 140 is used on a DM6 mount/Planet tripod setup. It is a 3 trip out the door setup. Tripod first, DM6 mount 2nd and scope last. I can't move scope/mount/tripod together after setting up. I mostly use it at dark sky location version short sessions at home. My TEC 140 and the SVX130T that I have on order are very close in weight. I am ordering the SVX130T for imaging because the TEC 140 is almost always in use by my wife for visual. The 130 and 140 will be able to go deeper and show more details. The tradeoff is the great weight and hassle of needing a heavier tripod and mount. It also is not as great as wide field scope as my SVR90T.

 

When we travel we usually bring a 8 inch f/6 custom dob along with the TEC 140. If we are going to a multi night start party where we can stay set up and secure for many nights we will bring the 14.5 inch dob plus other scopes for imaging, solar, etc...

 

I feel the best experience is to have a decent size and affordable refractor setup next to a larger Dob.

JMW,

Thanks for the details on your multiple telescopes. Portability and setup time are things I need to consider. Many others have suggested a Dob also.