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Skywatcher 102 advise on lenses


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20 minutes ago, Alysha said:

 Would a 32mm eye piece be better than a 25mm for wide viewing? (I know this probably sounds like a dumb question) 

The 32mm will give you the widest fov in a 1.25" focuser and slightly less magnification. You would see a greater area of the sky. Not much greater I may add. There are some very wide eyepiece designs but they are also very expensive.  

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2 hours ago, Franklin said:

What's that Vlaiv? 

Is it a Frankenstein scope?

That is just an image I found online that shows aperture mask use, but telescope is Bresser AR102s Comet Seeker.

Scope is no longer produced, but here is link with specs:

https://www.bhphotovideo.com/c/product/1124708-REG/bresser_br_ar102s_00_rich_field_ar_102mm_for.html

(btw Bresser still has F/4.5 fast 4" achromat but it looks different and uses some kind of ED glass - although CA is still very strong)

 

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38 minutes ago, Alysha said:

Would a 32mm eye piece be better than a 25mm for wide viewing? (I know this probably sounds like a dumb question) 

32mm Plossl is probably best "beginner" wide field eyepiece. I highly recommend it to everyone as cheap and good EP for low power views.

 

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That's a handy toy to mess with isn't it 🙂

Do be aware, though that the strengths of your 'scope , which is 500mm focal length, are in wide field rather than high magnification use. Achromat refractors do not bring all colours of light to the same precise focus causing Chromatic Abberration (that's why they are a lot cheaper than the apochromatic refractors astro  photo enthusiasts spend  big money on, which correct that fault) and this C.A. can be intrusive . It annoys different people at different levels, and it shows more at higher magnifications, and on brighter objects ... you may have noticed a neat coloured line around the Moon ? That's CA.

You've got a great 'scope for wide field , and a decent mount by the sound of it, get the hang of using it for visual observing before diving into the money pit that is astro photography :evil4:.

For some targets  I can guarantee can be seen from the edge of the city , the Loughton list is a very handy resource , try the 'bronze' level targets first (there are coloured bars on the object's pages bronze/silver/gold) https://las-astro.org.uk/docs/Loughton_List_v2_0.pdf

 

 

 

 

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I'm sure that many people already saw this table, but its worth reiterating:

post-134792-0-99138700-1535427968.jpg

I currently have SkyWatcher 102mm f/10 achromat that replaced ST102 that I used to own. SW 102 F/10 is rather good planetary instrument. Yes it shows chromatic aberration, but it shows good detail on planets.

According to above table - it has ratio of 2.54.

Making aperture mask of 65mm will give you Chromatic index of 3 - as 65mm is 2.56" and F/ratio will be ~7.7. Those two divided give CA index of 3 - which means Minimal or no CA.

65mm will be able to provide one with x100 - x130 views without much of a problem, that means use of 4-5mm Eyepiece. It won't be killer planetary scope - but will shot some detail and image will be nice.

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@Tiny Clanger Thankyou for all your support, it is appreciated. I am not quite ready for my full pay cheque to be going into new camera etc.. yet but it is certainly a future hobby to try. I will give the Loughton list a browse and have a look :) 

@vlaiv I will be giving the aperture mask a try this evening. I have ordered the eyepiece you have recommended previously and I am looking forward to giving it a try. Thankyou! 

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1 hour ago, vlaiv said:

Bresser AR102s Comet Seeker.

Wow, I've never seen that before. It must have an in-built mirror/prism. I thought you had made it by putting a spider and secondary into the back of Bresser 102.😀

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The ST102 was my first scope. Scopes have come and gone... But I still have it! 🙂
I've "jazzed up" the OTA with Carbon Fibre "Sticky"... "Found" a better focusser...
I seem to remember it showed (me) Jupiter had Band(s) and Polar Darkening? 🙃

Personally SOME of it's "lack of capabilities" were with my lack of "good eyes"...
or rather observing patience? I suspect the latter could have been cured, but... 😁


 

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I finally got myself a 1.25" star dielectric-mirror diagonal...

1783138560_starmirror.jpg.77ab83c48457417b19550a5eeadf3114.jpg

https://www.amazon.co.uk/Dielectric-Diagonal-Reflectivity-Coatings-Compression/dp/B08QRY4V97/ref=sr_1_1?dchild=1&keywords=svbony+sv188p&qid=1634233841&s=electronics&sr=1-1

I've tried it out once thus far.  I pitted that one against this star-mirror diagonal, from an ES/Bresser kit, not a dielectric of course, and I did not notice any improvement whatsoever...

1787133030_star-mirrordiagonal3.jpg.001191895ba5d5046672076135776844.jpg

As a matter of fact, the ES diagonal was seemingly better than the SVBONY dielectric, but only by a slight margin.  But I will have to test them further in future, and before a definite conclusion.  I tested the diagonals with this 80mm f/6 achromat...

1733083736_Test-100821.jpg.9251dd88597d8d771d52b1c2d4896ef9.jpg

Therefore, at this point, I would not select a dielectric-mirror diagonal.  For now, select one with a standard mirror rather, for example...

https://www.amazon.co.uk/Diagonal-Adapter-Refracting-Telescope-Eyepiece/dp/B07GPMX7BN/ref=sr_1_22?dchild=1&keywords=astromania%2Bstar%2Bmirror%2Bdiagonal&qid=1634234686&sr=8-22&th=1

There are those cheaper, so consider those as well.

Edited by Alan64
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8 hours ago, Alan64 said:

I finally got myself a 1.25" star dielectric-mirror diagonal...

1783138560_starmirror.jpg.77ab83c48457417b19550a5eeadf3114.jpg

https://www.amazon.co.uk/Dielectric-Diagonal-Reflectivity-Coatings-Compression/dp/B08QRY4V97/ref=sr_1_1?dchild=1&keywords=svbony+sv188p&qid=1634233841&s=electronics&sr=1-1

I've tried it out once thus far.  I pitted that one against this star-mirror diagonal, from an ES/Bresser kit, not a dielectric of course, and I did not notice any improvement whatsoever...

1787133030_star-mirrordiagonal3.jpg.001191895ba5d5046672076135776844.jpg

As a matter of fact, the ES diagonal was seemingly better than the SVBONY dielectric, but only by a slight margin.  But I will have to test them further in future, and before a definite conclusion.  I tested the diagonals with this most difficult and demanding 70mm f/4.3 achromat...

achromat3b.jpg.61258c1fa1afc3de233f7ae64222b89c.jpg

Therefore, at this point, I would not select a dielectric-mirror diagonal.  For now, select one with a standard mirror rather, for example...

https://www.amazon.co.uk/Diagonal-Adapter-Refracting-Telescope-Eyepiece/dp/B07GPMX7BN/ref=sr_1_22?dchild=1&keywords=astromania%2Bstar%2Bmirror%2Bdiagonal&qid=1634234686&sr=8-22&th=1

There are those cheaper, so consider those as well.

What kind of magnification were you using?

I found that at low magnifications diagonals were all pretty similar but it was as I got to higher powers that differences became readily apparent.

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13 minutes ago, Andrew_B said:

What kind of magnification were you using?

I found that at low magnifications diagonals were all pretty similar but it was as I got to higher powers that differences became readily apparent.

My bad; I have since edited my original post.  It was with an 80/480(f/6) achromat, and a Vixen 6mm "NPL" Plossl, at 80x.

My 70/300 is disassembled still, and before the diagonal had arrived.

I will be testing the diagonal further, and then decide if I want to keep it, or chuck it back to SVBONY.

Not surprisingly, my Celestron star-prism diagonal, the third contender, handily beat the two star-mirror diagonals.  Indeed, there was an almost 3D quality with the star-prism, which left the star-mirrors in the star-dust.

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Re. diagonals, I have read comparative surveys which indicate that even the cheap ones will be optically flat enough, and the expensive ones merely have better reflectivity, or longer lasting coatings, or better build quality (or all three).  Since we are discussing a Startravel achromat, I would expect the view to the the same regardless of what star diagonal is fitted.

Apparently prism diagonals are not recommended for short focus instruments below f6 or so (i.e. refractors) as they introduce distortion, but are fine for long focus refractors, Maksutovs and SCTs. And they have no coatings to deteriorate.

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Just to chime in with my experience which the OP is finding too but Celestron are appealing to beginners but the quality isn't amazing and the price is high. 

Like other have said, avoid starter kits and just buy what you find you need. 

Offerings from Skywatcher are usually better value I have found. 

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14 hours ago, Alan64 said:

My bad; I have since edited my original post.  It was with an 80/480(f/6) achromat, and a Vixen 6mm "NPL" Plossl, at 80x.

My 70/300 is disassembled still, and before the diagonal had arrived.

I will be testing the diagonal further, and then decide if I want to keep it, or chuck it back to SVBONY.

Not surprisingly, my Celestron star-prism diagonal, the third contender, handily beat the two star-mirror diagonals.  Indeed, there was an almost 3D quality with the star-prism, which left the star-mirrors in the star-dust.

Interesting point about the prism. I did a comparison between one and a dielectric diagonal and felt like the prism did give a bit more contrast and show fine detail better although the test wasn't ideal for showing the difference.

Prisms have less scatter so I'd guess that's what we were both seeing. 

6 hours ago, Cosmic Geoff said:

Re. diagonals, I have read comparative surveys which indicate that even the cheap ones will be optically flat enough, and the expensive ones merely have better reflectivity, or longer lasting coatings, or better build quality (or all three).  Since we are discussing a Startravel achromat, I would expect the view to the the same regardless of what star diagonal is fitted.

Apparently prism diagonals are not recommended for short focus instruments below f6 or so (i.e. refractors) as they introduce distortion, but are fine for long focus refractors, Maksutovs and SCTs. And they have no coatings to deteriorate.

You see a lot of mirrors advertised with 1/10 wavelength surface figure but apparently with dielectric ones this nearly always refers to the quality of the substrate rather than the finished item. Apparently it only takes a tiny variation in the thickness of each dielectric layer to quickly add up until the end result is several wavelengths off being flat. Like you say though, it might not be an issue if it's being used with a budget achromat at moderate magnifications.

Prisms are supposed to be better suited to longer focal ratio instruments but I use one with my little f/6 refractor and while it may cause a bit more false colour there isn't enough to be a problem for me and I like the contrasty views it gives me.

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  • 1 month later...

Alysha,

I'm thinking of buying a skywatcher 102 telescope with a mount and a tripod. I've never actually seen one, and the nearest retailer doesn't have any in stock.

I'm interested in finding the total weight of the scope, mount and tripod, yet non of the specifications on the net give the weight.

I wonder if you could let me know the total weight of the equipment ? It may be that the printed specification supplied with the equipment gives the total weight?

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Thanks for the question. I thought of buying a small refractor which should be easy to transport. I prefer an Alt Az mount and I don’t want a Go To set up. I got advice on a new scope from this forum in early April but there still seems to be some shortages. 

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14 minutes ago, keora said:

Thanks for the question. I thought of buying a small refractor which should be easy to transport. I prefer an Alt Az mount and I don’t want a Go To set up. I got advice on a new scope from this forum in early April but there still seems to be some shortages. 

The weight for a given telescope or mount can generally be found on the WWW somewhere if you search around a bit. Why do you need the weight? Have you portability in mind? Note that if you are buying a bundle, the manufacturers often include the lightest and most wobbly mount they can get away with.  If it's for back garden use, you would be happier with a sturdy mount like an AZ4-2 with steel legs.

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19 hours ago, johninderby said:

Yes, that’s the one I was thinking of. At 7.5 kg it’s a bit on the heavy side. I can’t  inspect it in the nearest scope retailer because it’s not in stock and I don’t fancy driving to FLO Devon. I’ll have to wait until they are in stock up here.

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3 hours ago, keora said:

Yes, that’s the one I was thinking of. At 7.5 kg it’s a bit on the heavy side. I can’t  inspect it in the nearest scope retailer because it’s not in stock and I don’t fancy driving to FLO Devon. I’ll have to wait until they are in stock up here.

You're not going to find refractor & mount combination much lighter than that unless you're willing to spend a great deal more, or considerably downsize to a very cheap travel scope package. Even then, you will only shave off a couple of kilos.

The mount, tripod and telescope individually are easily manageable assuming an able bodied person is carrying them. Unless you intend to travel with the kit along with other gear?

 

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I have the same scope on an AZ GTI mount. I have a cheap 90 deg erecting prism to replace the 45 degree that came with it. Might upgrade this at some point.

I bought BST Starguider eyepieces giving a good range of magnifications :-

3.2 156
5 100
8 63
15 33
25 20

 

I did have a 32mm but found I wasn't using it as I also have a upgraded finder scope that gives me x9 magnification and the 25mm BST gave me 20x.

If you want to limit the number of lenses I would keep your 25mm, and get an 8mm BST with your barlow initially

Happy with the BSTs and have used the 3.2 recently for Jupiter. As has been said it was low in the sky and seeing was not ideal but I was reasonably happy with what I saw.

I have spent way too much upgrading my scope and probably should have bought something better from the start but I have enjoyed the process :-).

Edited by Richard_B
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On 24/11/2021 at 22:04, ScouseSpaceCadet said:

You're not going to find refractor & mount combination much lighter than that unless you're willing to spend a great deal more, or considerably downsize to a very cheap travel scope package. Even then, you will only shave off a couple of kilos.

The mount, tripod and telescope individually are easily manageable assuming an able bodied person is carrying them. Unless you intend to travel with the kit along with other gear?

 

Thank you for the advice. I was thinking about getting a lightweight telescope. I’ll start looking for one weighing up to about 7kg.  
 

I’ve got a basic beginners telescope, it weighs just under 5kgs. I must admit it’s awkward to drag it from the bedroom, down the stairs and thro the rooms on the ground floor and into the garden. It’ll be worse if if I get a large one at say 10kg. As a beginner, the downside to astronomy is all the faffing about, setting things up, taking them down, waiting weeks for a night when there’s a clear sky. But somebody’s got to do it.

I think this forum is excellent, I can get plenty of good advice from members. 

 

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