help me to choose the correct telescope

[vlnikolic]

hello everybody,

 

i would like to use a telescope for observation of landscape and observation of celestial objects. i have several scopes on my mind and i would like to have your opinion - because i would like to have one telescope for all my needs (i am not so demanding user, so i think it is possible).

i was thinking about these two refractors:

1) BRESSER Taurus 90/900 NG

https://www.bresser.de/en/Astronomy/Telescopes/BRESSER-Taurus-90-900-NG-Refractor-with-Smartphone-Camera-Adapter.html

i like this scope, because it is all-in-one package, the only downside i found is that objective is 9 cm.

2) Meade Infinity 102mm AZ Refractor

https://www.meade.com/infinitytm-102mm-refracting-telescope.html

this one i found interesting because of it's objective lens (10cm), and its length - allowing me larger field of view for landscape observations

i was thinking about this reflector as well:

3) BRESSER Telescope Spica 130/650 EQ3

https://www.bresser.de/en/Astronomy/Telescopes/BRESSER-Telescope-Spica-130-650-EQ3-parabolic-Reflector-with-Smartphone-Camera-Adapter.html

i am aware that this one is on eq mount, and that it's not for landscape observations - but i could buy eyepiece that will modify the image for landscape use, and this eq mount could be very useful for gazing into the sky. for this one i would by collimator, and this eyepiece, and i would have the complete amateur package, and for any of the refractors i could by maybe some better 6mm eyepiece, and solar / moon filter.

 

thanks for your time and interest, any suggestion is welcome

: )

vlad

 

[Gonariu]

To start with, there are three telescopes that are fine. I see poorly the red dot finder to use the telescope to see the landscape as the red dot is visible only at night and not during the day, here you need a classic finder. Keep the following things in mind:
1) I have seen from the links you put that propose these telescopes at exaggerated magnifications using a Barlow 3X, in particular 675X for the 90/900 refractor and 487.5X for the Newton 130/650 that are absolutely useless. The resolving power of a telescope is given by the formula P = =120/D (the formula comes from wave optics), with D diameter of the objective in mm and P in seconds of arc. For example, the 90/900 will therefore have a resolving power of 1.3 "which are the closest details that the optics will be able to resolve, a double star whose components are 0.8" apart, the 90/900 will not be able to separate it whatever magnification you put and the same is for two details of the lunar surface; therefore to see more you have to increase the diameter of the objective (lens or mirror). The maximum magnification that a telescope can exploit is 20 - 25 times the diameter of the objective in cm, therefore 180X - 225X in the case of the 90/900;
2) the refractor 102/660 is beautiful for landscapes and deep sky objects, it is less or less good for the observation of the Moon and planets at high resolution (and therefore at high magnification) due to the fact that the chromatic aberration is not well corrected as the focal length is too short. To be negligible the chromatism the focal length f must satisfy the relation f> = D^2 (with f and D in cm) otherwise it makes itself felt with a decrease in resolution. Here at least in part it can be remedied with a light yellow W8 filter or some other special filter (contrast booster, fringe killer, the Baader semi-opener). Another problem could be spherical aberration as it is less easy to work well with lenses with such a short focal length. Here I can tell you that I have two short focus achromatic refractors, a 70/400 and an 80/400. The first on the planets is like this, on Jupiter you just distinguish the two main bands at 100X, the second is much better, on Mars last year I distinguished Syrtis Maior and the south polar cap at 160X - 200X, on the Moon it did not mind and the vision was more contrasted with the W8 filter or the semi-opaque one of the Baader Planetarium. The problem is that these optics are all Chinese and do not control them in a maniacal way as Astrophysics does, so the successful model or that can happen.
3) Make sure that for the Newton 130/650 that the mirror is really parabolic as it says in the link, usually for these entry - level instruments they put a spherical mirror that to work well must have at least a certain focal length, 650 mm are few. In an Italian forum one said that he had taken a Newton 130/650 (I think from Skywatcher) that beyond 100X could not go due to the non-negligible spherical aberration due to the spherical primary mirror. So if you find out that the mirror is spherical, forget it. Also consider that a Newtonian is not ideal for panoramas due to the blind spot due to the secondary.

Edited August 1, 2021 by Gonariu

[vlnikolic]

Gonariu, thank you for your detail reply, i found it very useful.

ofcourse - magnifications are exaggerated with bresser, and should be max around 180 for refractor, and in real life much less, since light pollution and atmosphere in gereral..

if you have any other scope on mind, please post

thanks

[vlaiv]

Hi and welcome to SGL.

If you want to do both terrestrial and celestial observations, then two telescope types are good option:

1. refractor

2. catadiotric telescope

Newtonian design is not very well suited for both of these roles.

Thing to keep in mind is that for terrestrial observations you need special type of diagonal mirror - one that properly inverts image back to "normal". For celestial observations you don't need that as there is no really "up" or "down" in space and it does not matter which way you observe, but if you observe nature - then you want things to be oriented properly - the same way you see it without telescope.

Some scopes come with 45° amici prism diagonal that gives properly oriented image, while others come with 90° diagonal mirror. Amici prism is usually not very well suited for celestial observations since it introduces some artifacts to the image - like single spike on bright stars and similar.

It would be best to get both - 90° mirror for night time use, and 45° amici prism for day time use.

You did not give much in terms of requirements (budget, transportation and storage and so on), so I'll go by scopes you listed, and recommend this one:

https://www.firstlightoptics.com/evostar/sky-watcher-evostar-90-660-az-pronto.html

It is very similar to Meade 102mm you listed, but it probably has better mount. Meade looks like it is using AZ3 type of mount and while that is well suited for terrestrial viewing - it is not as good for celestial. Slow motion controls have very limited range of motion and pointing scope near zenith (best place to observe as there is least atmosphere and light pollution) is not convenient.

If you provide a bit more detail on your requirements, maybe better recommendation can be given (storage, transportation, budget - what do you intend to observe - do you need higher magnifications or will low to medium do and so on).

[vlnikolic]

hello and thank you all once again for your time and energy.

i would like to have something up to 500 eur

i have idea to use it on a balcony of my house - and i have view on the hills and a factory in the front.

since i am in a town, light pollution i would categorize as medium (side lights / street lights i have to deal with as well)

i have no particular intention of moving the thing to better watching spots (at least i think like that for now). i've used to watch the land and the sky from the same balcony using the monocular 8x42 for a long time.

i would not categorize myself as a star/sky gazer, rather somebody who would like to enjoy the place he lives by observation.

vlad

[vlaiv]

Size of telescope / aperture is important for several reasons:

1. Amount of light it gathers.

This part is not really that important for terrestrial viewing, but it is very important for celestial observations. It helps see fainter stars and fainter objects. Given your requirements of both type of viewing and budget - you are really limited to 4" to 5" scope depending on type (4" refractor or 5" Maksutov). That is plenty of aperture to see all sorts of things from dark location. City lights really ruin the night sky as far as faint objects go - nebulae, clusters and galaxies.

2. Resolved detail at high magnification.

Larger telescopes have potential to resolve more detail - but that potential is often limited by atmosphere for night time viewing of the sky. In any case, maximum useful magnification will depend on your eyesight (people with sharp eyesight don't need as much magnification as people that don't see that good). General magnification is in range of x1 (excellent sharpness of vision) to x2 (medium sharpness of vision) per millimeter of aperture.

With 100-125mm telescopes (4" - 5") that turns out to be between x100 and up to x250 with larger scope. For planetary / lunar observation atmosphere often limits magnification to max x200.

You can figure out how much magnification you'll get at say x100 on terrestrial target in following way:

Eyepieces that come with telescope are often 50° of apparent field of view (a bit larger field of view than that monocular). With x100 magnification that turns into 50° / 100 = 0.5°. That is about 5mm held at arms length. Take for example Aspirin pill and hold it at arms length - everything that is covered with that Aspirin will be "in front of you" when looking thru a telescope at x100 magnification.

Lowest magnification will depend on type of telescope that you get / focal length. If you are used to x8 provided by monocular - this will be new experience as even lowest magnification will be at least x2 that if not more.

Back to telescope choice - you really have two choices - refractor and maksutov type telescope. I'd recommend getting AltAz type of mount for your telescope as EQ mount is very unsuited for your use (daytime and balcony, especially if you can't see Polaris to do polar alignment).

Maksutov will have very high magnification range as it has long focal length. There are really two choices 4" model or Mak102 - 102mm or aperture (from different vendors - like Skywatcher, Orion or Bresser for example) or Mak127 - 127mm of aperture (again from different vendors and most have both models as they are scaled versions).

They have focal lengths of 1300mm and 1500mm respectively. Magnification is calculated by dividing telescope focal length with eyepiece focal length. Eyepieces start at about 32mm and can go down to just few mm - like 3mm. This means that Maksutov scopes will have lowest magnification at x40-x45. That is rather high magnification compared to your x8 monocular.

These scopes are very good if you want to have high magnification capability. Good for planets, the Moon and double stars. Their weak side is that they are somewhat slower to cool down - larger the model - it takes more for it to cool down properly so that view is steady (at those magnifications every little thing is magnified and so are thermal currents in the air and scope itself). They also can't provide low magnifications / wide field of view.

Refractor telescopes come in two different types (this is very arbitrary division aimed at explaining your options - not general rule).

Long refractors and short refractors. With refractors, you'll be limited to 4" or 100mm (or smaller models) due to price. They will be achromatic refractors (no exotic expensive glass so chromatic aberration will be present).

90 / 900 and 100/1000 refractor models are considered long refractors. They are slightly shorter focal length than Maksutov telescopes - but still quite long. Minimum magnification is about x30 on this scopes (so four times what you are used to). Long refractors tend to be sharper scopes with less chromatic aberrations.

They require little to no maintenance (this is true for both short and long refractors) and their cool down is very quick - you can be observing in matter of minutes (in winter time it does take 10-15 minutes for scope to properly cool for high power views).

Their drawback is that they are physically long telescopes - like 1m in length so space for use and storing is consideration. They look like "proper" telescopes - something people like as they can be kept in living space as decoration when not in use.

Short refractors are telescopes for wide views and lower magnifications. They have focal length of about 500-600mm. This means that you can have as low magnification as ~ x20 (even x15 which is only twice what you are used to). They don't cope well with high magnifications, so it is best to keep them up to say x80 or possibly x100 and not above as they tend to show much chromatic aberration (purple fringing around bright objects and high contrast edges). They are light, don't shake as much as longer tubes when in use.

The telescope that I recommended above 90/660 is somewhere between the two refractors. It is short enough to enable you up to 2.5° of true field of view with right eyepiece and x20 magnification, yet is long enough to comfortably enable magnifications up to say x120-140. It is light / manageable for use and storage.

 

[vlnikolic]

vlaiv,

thank you for a detailed explanation (hvala lepo). i've just seen that you are from novi sad, and that provides me with opportunity to ask you for even more recommendation about purchasing this thing.. and i can buy you a drink without any problem, since i am from kragujevac. since we both live in serbia - we know that availability of equipment to buy is also a limit..

makutsov is a great idea really - but i am not sure about maintenance and general robustness of these devices / is there need for collimation with this type of scopes.

: )

Edited August 1, 2021 by vlnikolic

[vlaiv]

Yes, maintenance can be issue with systems that have mirrors.

Newtonian scopes require collimation and in principle, Maksutov telescopes also do.

I own couple of reflector telescopes - 8" newtonian telescope on dobsonian mount and 8" RC type reflector. I also have Mak102mm.

8" dob holds collimation very well. Much better than I first thought it will. I drove with it couple of times to Fruska Gora and it keeps collimation. I probably need to touch up on it once or twice a year. RC is photographic instrument and it also holds collimation well. In fact - I did collimation only once when I got it and will have to do it now again - but because I messed with collimation screws and not because it came out of collimation itself.

These are larger and heavier mirrors than Maksutov telescope. More weight there is in mirror - more likely it will go out of collimation. I don't think you really need to worry about collimation that much. You might need to tweak it once when you get your scope - and maybe not even then - mine came in perfect collimation. Other than that - maybe once in few years.

New Maksutov 102 telescopes from SkyWatcher even come without collimation screws. This is probably due to weight saving, but also because most people never needed to touch up collimation on their small scope (I still decided to get version with collimation screws just in case).

Other than that - you'll need dew shield for night time. This can be DIY thing - piece of PVC pipe of right diameter with some felt lining or similar.

I think that these small Maks are virtually maintenance free most of the time.

As far as robustness - well, it is delicate piece of kit. It has front corrector lens and back mirror, but it is very light weight (at least 102mm model is). You should handle it with a bit more care than your monocular - but nothing special.

When transporting or storing it - use some sort of padded bag for example and make sure you don't put anything heavy on it.

I think that you will get instant feel for what can and should be done - once you take it in your hands. You'll see that scope optical tube walls are not quite thick and with right kind of pressure it will bend. It feels like it can be easily scratched by keys or screwdriver or similar. Other than that - thing feels quite solid in hand and nothing will fall out or fall apart even if you shake it

All in all - I don't think that you need to worry much about these things - it certainly should not put you off from having that scope if you feel is right for the type of observing you are interested in.

As far as getting the gear in Serbia - I have experience with three different retailers. Our local retailer deals exclusively with SkyWatcher gear and is often cheapest option due to import and shipping fees. I ordered from Teleskop Service in Germany and from FLO (sponsor here on SGL).

FLO has very competitive prices but main problem is very steep shipping charges for larger items. On smaller items it is quite affordable (for eyepieces or similar it will cost something like £8-10 for shipping, but for items the size of telescope it can be couple hundred of pounds).

Teleskop Service has somewhat steeper prices now and also raised their shipping fees - but can sometimes be the best option (large items get shipped for ~30euro - which is quite ok).

P.S. If you signed up for our local forum (Astronomski Forum) - but did not get confirmation e-mail there, that is because you mistyped your e-mail address - as yahoo.con instead of yahoo.com . Your account has been approved and you should be able to access it now (I'm moderator there fighting spam bots and approving new members manually ).

[vlnikolic]

vlaiv, thanks for a detailed reply. i think that i've leared a lot in the meantime (a lot compared to my starting position hehe)

i was thinking about yet another possibility:

SkyWatcher Startravel 120T AZ3

why?

* it's 120

* short focal length means that even less potent is for planets however, but i do presume that is somewhat in the class of meade102inf

* it has 45* amici prism, and in conjunction with az3 land observations should be very pleasant

* as far as i understand it supports 2" eyepieces, thus in perspective i could acquire 90* diagonal, barlow, and some good eyepieces for nice skygazing

0: )

btw i tried my luck  with "astronomski forum" again and hope the best

hehe

 

[vlaiv]

7 hours ago, vlnikolic said:

vlaiv, thanks for a detailed reply. i think that i've leared a lot in the meantime (a lot compared to my starting position hehe)

i was thinking about yet another possibility:

SkyWatcher Startravel 120T AZ3

why?

* it's 120

* short focal length means that even less potent is for planets however, but i do presume that is somewhat in the class of meade102inf

* it has 45* amici prism, and in conjunction with az3 land observations should be very pleasant

* as far as i understand it supports 2" eyepieces, thus in perspective i could acquire 90* diagonal, barlow, and some good eyepieces for nice skygazing

0: )

btw i tried my luck  with "astronomski forum" again and hope the best

hehe

 

ST120 is interesting scope, and although ST102 has 2" focuser as well - ST120 simply has more aperture and can quickly be turned into sharper scope - by using aperture mask.

You can make mask that goes over the front of objective lens that has smaller aperture than the scope itself. Say you want to lower chromatic aberration and get sharper higher magnification view. Your scope is 120mm F/5 and thus 600mm of focal length. You can easily make 90mm aperture mask that will turn your scope into 90mm / 600mm - F/6.66 scope that is better suited for high power viewing and lowers chromatic aberration.

I used to do that with my ST102 by using simple PVC water sewer pipe plug like this:

Here ready to be drilled.

You can say choose to make 100mm mask and at F/6 that will give you better planetary performance than ST102 that is F/5.

It is good choice - but do be aware of the size of that scope, and also - if you can, get it on AZ4 rather than AZ3. I had both of these mounts - and AZ3 is really very basic mount and not very good. I don't recommend it.

Your new account at Astronomski Forum is also approved and you should be able to login to it now (although it is experiencing some technical difficulties - beyond my control, admins should be dealing with it).

[jetstream]

On 01/08/2021 at 17:13, vlaiv said:

P.S. If you signed up for our local forum (Astronomski Forum)

You guys take old crippled up Canucks?

[vlnikolic]

hello again

 

i would like to know your opinion on these two different eyepieces configurations for st120

(diagonal mirror would be 2" 99% with adapter for 1.25 ep)

 

configuration1:

ep: 4mm 12mm 20mm (decent quality fov ~65) + decent barlow 2x, thus giving:

4mm+B (300x), 4mm (150x), 12mm+B (100x), 20mm+B (60x), 12mm (50x), 20mm (30x)

 

configuration2:

ep: 4mm 8mm 12mm 20mm (decent quality fov ~65) + decent barlow 2x, thus giving:

4mm (150x), 8mm (75x), 12mm (50x), 20mm (30x)

 

both configurations in conjunction with fringe-killer 1.25 (for eyepieces, and not 2" that could be attached to diag.mirr, as far as i understand)

 

thanks..

: )

[vlnikolic]

p.s. idea behind high zoom variants are that i could rely more on the optic, than on my eyes that are not as they used to be..

[jetstream]

I'll mention something- I use my 90mm frac over a 120mm because for terrestrial viewing the smaller scope is less sensitive to local seeing, I couldn't believe it actually. I do view over water though which is nasty. But, the 90mm, straight through will show insects flying over the water 800 meters away (as measured on a Zeiss rangefinder, near island).

Not sure how an aperture mask will perform, in theory it should work but Id want to try it before giving an answer on this one. @vlaiv is helping me with lunar imaging, once I'm ready, and preliminary views through the camera suggest that 120mm scope is sensitive to that local seeing, big time- for various reasons.

[vlaiv]

17 minutes ago, vlnikolic said:

hello again

 

i would like to know your opinion on these two different eyepieces configurations for st120

(diagonal mirror would be 2" 99% with adapter for 1.25 ep)

 

configuration1:

ep: 4mm 12mm 20mm (decent quality fov ~65) + decent barlow 2x, thus giving:

4mm+B (300x), 4mm (150x), 12mm+B (100x), 20mm+B (60x), 12mm (50x), 20mm (30x)

 

configuration2:

ep: 4mm 8mm 12mm 20mm (decent quality fov ~65) + decent barlow 2x, thus giving:

4mm (150x), 8mm (75x), 12mm (50x), 20mm (30x)

 

both configurations in conjunction with fringe-killer 1.25 (for eyepieces, and not 2" that could be attached to diag.mirr, as far as i understand)

 

thanks..

: )

I would not bother with barlow lens.

x300 is way too much magnification for a scope like that. If it was perfect optics scope - I would not recommend going beyond x240 in magnification. As it is fast achromatic refractor - it won't do well over say x100-120 - maybe x150 with fringe killer. Alternative would be to stop it down to 80 or 90 mm and again go with say x150 max.

Instead of barlow lens - maybe look into getting one really wide field eyepiece like this one:

https://www.teleskop-express.de/shop/product_info.php/info/p2334_TS-Optics-35-mm-2--UFL-Eyepiece---69--Field-of-View---6-Element-Design.html

As far as eyepieces go, maybe best option would be to get BST starguiders:

https://www.firstlightoptics.com/bst-starguider-eyepieces.html

These are very decent quality affordable 60° AFOV eyepieces that have enough Eye relief and work ok with fast scopes like F/5

12 minutes ago, jetstream said:

Not sure how an aperture mask will perform, in theory it should work but Id want to try it before giving an answer on this one.

Aperture mask works wonders on fast achromats. I tried it both for imaging and visually. With ST102 if you just take cap of the middle of the scope cover - it leaves hole that is 2" in diameter and you get 2" F/10 achromat. If you observe Jupiter say at x70 or so (500mm FL and 7mm EP) and then switch to this view - you instantly get sharp image free of chromatic aberration.

 

[jetstream]

31 minutes ago, vlaiv said:

Aperture mask works wonders on fast achromats.

Vg to know. With respect to seeing, including local- do you see a big difference between masked and unmasked? I played around with newt masks but thats a whole different ball game.

[Gonariu]

On 4/8/2021 at 17:34, vlnikolic said:

vlaiv, grazie per una risposta dettagliata. Penso di aver imparato molto nel frattempo (molto rispetto alla mia posizione di partenza eheh)

stavo pensando ad un'altra possibilità:

SkyWatcher Startravel 120T AZ3

I have a Ziel 120/600 achromatic refractor (the Ziel GEM 60) that I bought in 2011 and that I keep in Cagliari at my mother's house (I bought it so as not to be starved of astronomical observations when I go there for the holidays) . I use it to see the Moon at 150X (with a 4mm Vixen Lanthanum eyepiece) and last year also to see Mars at 200X - 3000X (high magnification for a short focus achromat, personally I find it better not to exceed 200X ), I will tell you that the Moon can be seen well despite the chromatism (the lunar edge has a beautiful blue halo ....) and on Mars last year, mounting the telescope on an equatorial EQ5 and tracking by hand I made some beautiful observations . I put my drawings that I made of Mars in an Italian forum of which this is the link: https://astro.forumfree.it/, to see them just click when a short blue refractor appears on the variable screen. in Italian “Osservando Marte con un 120/600” ( = "Observing Mars with a 120/600" in english). In these drawings I write in Italian and often in italics, if you need to ask me something about it no problem. I also bought the semi-opaque filter from Baader Planetarium which reduces chromatic aberration (but does not cancel it) looking at the Moon and Venus, but on the Moon I preferred to remove it because I liked a brighter image. I have been wondering for some time if the fringe killer filter or the contrast booster is better than the half-op. 

[vlaiv]

38 minutes ago, jetstream said:

Vg to know. With respect to seeing, including local- do you see a big difference between masked and unmasked? I played around with newt masks but thats a whole different ball game.

Never really compared the seeing mask on / off.

People say that smaller aperture fares better in poor seeing, and there is some merit to that in theory, but I don't have any hands on experience in that field.

[jetstream]

2 hours ago, vlaiv said:

Never really compared the seeing mask on / off.

People say that smaller aperture fares better in poor seeing, and there is some merit to that in theory, but I don't have any hands on experience in that field.

Yes I must try it, the SW120ED has a mask built into the lens cover. It will be interesting to see the tradeoff between seeing effects and resolution changes between all this.

[vlnikolic]

hello everybody,

i'll need a few weeks to complete everything i plan concerning this telescope setup.

i'll not speak aloud now about the exact components - but soon you'll find out if i was a good pupil of yours.

thank you!

: )

[vlnikolic]

hello everybody,

 

since this morning i am owner of beautiful st120.

i have not bought all the equipment yet, but i am very happy.

i have star diagonal 2", 12mm Magellan, 30 mm lacerta ed, and barlow 2x

i am not sure if this lacerta 30 mm is maybe damaged - thus i'll start another formum thread..

 

thank you very much for your help

vlad