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Refractor For Purely Visual Astronomy?


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7 hours ago, Louis D said:

Have you looked into getting an observing hood to block local stray light?  Even a black towel covering your head would help.

Right now I'm using a baseball cap and a regular hooded shirt (which I peel off cause it's still warm here some nights). Thanks for turning me on to that though, I may try it. Last night wasn't pleasant, nor is anything really that's not a planet, lunar or the sun. No matter what I'm inevitably holding a hand over an eye and trying to crowd the other eye with the eyepiece.

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  • 3 weeks later...
On 06/10/2021 at 17:43, johninderby said:

Would recommend buying from Astrograph as they are a UK dealer so no customs or high shipping costs to bother about. Plus top class service and the owner Rupert is an expert that can answer any questions you might have.

https://astrograph.net/epages/www_astrograph_net.sf/en_GB/?ObjectPath=/Shops/www_astrograph_net/Products/AGTEC125F78

https://astrograph.net/epages/www_astrograph_net.sf/en_GB/?ObjectPath=/Shops/www_astrograph_net/Categories/Shop/"Telescopes %26 Binoculars"/Apochromatic_Refractor_Telescopes

322986C8-F14E-4CA5-AEE7-162AE5592ADC.jpeg

It looks very much like my Starwave 102 ED-R - and also the offering from Teleskop Express: https://www.teleskop-express.de/shop/product_info.php/info/p4964_TS-Optics-ED-APO-102-mm-f-7-Refraktor-mit-2-5--R-P-Okularauszug.html

Are they all made by the same manufacturer, do you know?

(P.S. I absolutely love my Starwave :))

 

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16 hours ago, Nicola Fletcher said:

It looks very much like my Starwave 102 ED-R - and also the offering from Teleskop Express: https://www.teleskop-express.de/shop/product_info.php/info/p4964_TS-Optics-ED-APO-102-mm-f-7-Refraktor-mit-2-5--R-P-Okularauszug.html

Are they all made by the same manufacturer, do you know?

(P.S. I absolutely love my Starwave :))

 

The pic is of my Tecnosky 125 but yes they are made by the same manufacturer although specs may vary a bit depending on what the particular brand chooses. I like the Tecnosky as they test the scopes and Astrograph also tests the scopes again when they arrive in the UK so you know you will get a perfect one.

Edited by johninderby
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I think I might have a useful perspective as I’m not Uber experienced and recently bought my first proper refractor. 
 

snagged the stellamira 80 f10 off the classifieds. 
 

I’ve got a 10” SW dob and an Orion starblast on an EQ1. 
 

Starblast is great by the way, super wide field of view and surprisingly good light capture but a newt on an EQ is a truly horrible combination. 
 

Get a 4” refractor…. I’d like to upgrade my dob at some point too but it’d be for limited gain in performance in truth. 
 

My next scope will almost certainly be a 125ed like @johninderby to give me a refractor with more aperture. 
 

Yesssss the dob beats everything else I’ve got. When the seeing is good it beats them by a LOT. Lugging that god awful mount out into the garden though and then bear hugging the tube out after it puts me off using it 80% of the time. If I’m not having a big session I won’t get it out, and I’m relatively young, have no injuries, good eyes. Prime candidate for using a large reflector, and I still can’t be bothered usually. 
 

The refractor just feels right to use. It’s nice to look through rather than into. The contrast on the refractor is better than the reflectors. Sharpness is better. The image may not have as much detail but it’s more pleasing and easier to pick out the detail that is there. Stars have much better shapes, especially the bright ones. It’s almost strange to see vega as a disk floating in the blackness compared to a big cross sat on dark grey. The moon looks especially good through the refractor. 

no worries about collimation. Fast cool down on a doublet. 
 

If I was going to have only one refractor (which I’ve already decided isn’t enough personally) I think 4” apo doublet is probably the one to have which covers the most ground while still being grab and go sized. 
 

look for a used mount, don’t bother with goto IMO. The eq1 if that’s what you’re planning on using will struggle with anything but the very smallest and lightest scopes. 

 

imo blow the entire budget on a tecnosky 102 f7 or Altair 102ed-r and worry about a mount diagonal etc later or just go over budget by a couple of hundred quid. I suspect the above options will be good enough to scratch the itch without leaving you with a what if thought that you might get going for something on the very budget end. 

 

 

Edited by Sargares
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15 hours ago, johninderby said:

The pic is of my Tecnosky 125 but yes they are made by the same manufacturer although specs may vary a bit depending on what the particular brand chooses. I like the Tecnosky as they test the scopes and Astrograph also tests the scopes again when they arrive in the UK so you know you will get a perfect one.

Apologies- I can see now it’s bigger! You must get some great views through it. I agree, knowing that it’s tested is a huge bonus.

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  • 3 weeks later...
On 28/09/2021 at 06:40, dweller25 said:


if the 8” Dob in your avatar is yours then you will have to spend a lot of money on a refractor to beat it’s visual performance on both deep sky objects and the planets.

I picked up a used Sky-Watcher  Evostar 120 Achro recently, you're observation (no pun intended) is absolutely spot on.

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On 29/09/2021 at 14:14, Louis D said:

For low power views they would probably be fine.  You could always add a Baader Contrast Booster to suppress all purple and deep blue light if the color fringing bothers you.

At high powers, their chromatic and spherical aberrations would detract from the view.  It really depends on what you want out of a refractor.

Whilst I was forewarned about CA with achromats, I picked up a used SW Evostar 120 recently.  I can easily detect the purple fringing and it's more obvious than I thought it was going to be.  I guess having used a 8" Dob for over 18 months has spoiled me...🙄

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In 2011 I bought a Ziel 120/600 achromatic refractor, the Gem 60 which I love. I had taken it as a second telescope when I went down to my parents in Cagliari so as not to "fast" from astronomical observations. On the Sun for projection it was fine, the Moon at 150X is very beautiful even if it has a nice blue halo, on Mars in the autumn of last year for the opposition of October I put from 200X to 300X making some beautiful observations, i drawings I made I put them in a forum in Italian of which I post the link: https://astro.forumfree.it/?t=78404004
(unfortunately I wrote the annotations in Italian, being Italian-speaking). I think both the Skywatcher 120/600 and my 120/600 from Ziel are always made by Synta as they are both made in China. On the deep sky I tried it a little, I can say that I don't mind.

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1 hour ago, Ian McCallum said:

Whilst I was forewarned about CA with achromats, I picked up a used SW Evostar 120 recently.  I can easily detect the purple fringing and it's more obvious than I thought it was going to be.  I guess having used a 8" Dob for over 18 months has spoiled me...🙄

You could try a Baader Semi-Apo or something, I found it helped with my 90 short tube (though it wasn't horrendous to start with) but your mileage may vary. I think a wratten 8 might also assist for considerably less. Both types give a yellowish cast to the view though I dont recall it being to awful :)

Edited by wibblefish
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1 hour ago, Ian McCallum said:

Whilst I was forewarned about CA with achromats, I picked up a used SW Evostar 120 recently.  I can easily detect the purple fringing and it's more obvious than I thought it was going to be.  I guess having used a 8" Dob for over 18 months has spoiled me...🙄

Here's a photographic comparison from Rohr of various fringe filters through an achromat:

Fringe-Filters-Comparison.jpg.aec2c1c4e7526c07acfcb2efcae38d7c.jpg

ohne Filter is without any filter.  The Contrast Booster does the best at completely eliminating fringe.

Here's the what the various spectrums look like through each filter:

Fringe-Filters-Spectrum.jpg.ee4b32c91ee17f6a476eba6ad6acfa2b.jpg

It's clear that the CB filter is the most aggressive at cutting violet and blue.

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36 minutes ago, wibblefish said:

I think a wratten 8 might also assist for considerably less

I use a Wratten #8 to deal with atmospheric dispersion with some success, so I think it would work quite well for CA.

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So recapping, I'm back to looking at the Scopetech 80mm offers from Aunty @FLO.  Will I notice the difference between the F15 and F12.5 versions?  What difference will the single verses multi coating make?

The reason for the renewed interest is, I've got a SW EQ5 Deluxe mount coming.  Also, @FLO has a price drop on a ex-display model of the F12.5 version.

https://www.firstlightoptics.com/offers/offer_scopetech-stl80a-l-80mm-f125-classical-refractor_155968.html

Edited by Ian McCallum
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Not a big difference between the two versions.Yes the f/15 will have a small edge optically but the shorter focal length will still be excellent and have hardly any noticeable CA. Given the price difference for the demo scope I’m sure you would be happy with the f/12.5. 

You should ask Stu as he has both versions on test for FLO.

I went with the f/15 as it wasn’t a lot more than the f/12.5.

And you might want to get the Vixen to T2 adaptor and a Baader Ultrashort T2 to 1.25” adaptor to replace the single screw clamp on the drawtube.

Edited by johninderby
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This chart sets out the levels of CA that you can expect from achromat refractors. The relative differences between different spec scopes are reasonably accurate from my experience:

CA-ratio-chart-achro.jpg.61ef14bb53a4880ca5ded84bca7cacc3.jpg

Quality achromat refractors such as the Scopetechs should also have minimal amounts of spherical aberration (SA) which means sharper views and better handling of high magnifications.

 

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25 minutes ago, Ian McCallum said:

So recapping, I'm back to looking at the Scopetech 80mm offers from Aunty @FLO.

Did I get this right, you have Evostar 120 with you right now?

Why don't you use that one to get the sense of 80mm F/12.5 scope?

If you make 80mm aperture mask for that scope - you'll get 80mm with 1000mm FL - which gives F/12.5.

Btw, that is effective way to get planetary scope out of larger achromat. You can try different size masks to see which one gives you best view as aperture too stopped down will impact level of detail, and not stopped enough will leave some CA. Depending on how sensitive you are - you can hit balance between the two for the best views.

You can even combine aperture masks with filters (say Baader Contrast Booster).

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24 minutes ago, vlaiv said:

Did I get this right, you have Evostar 120 with you right now?

Why don't you use that one to get the sense of 80mm F/12.5 scope?

If you make 80mm aperture mask for that scope - you'll get 80mm with 1000mm FL - which gives F/12.5.

Btw, that is effective way to get planetary scope out of larger achromat. You can try different size masks to see which one gives you best view as aperture too stopped down will impact level of detail, and not stopped enough will leave some CA. Depending on how sensitive you are - you can hit balance between the two for the best views.

You can even combine aperture masks with filters (say Baader Contrast Booster).

I was thinking of using the Evostar 120 with the dust cap on, but with the small hole in it to stop it down.

post-296016-0-43318200-1570310611.jpg

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That will work and will reduce the CA visible considerably. It will also reduce the effective aperture of the scope to the diameter of the hole in the dust cap and therefore the resolution and light grasp will reduce as well.

 

 

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1 minute ago, Ian McCallum said:

I was thinking of using the Evostar 120 with the dust cap on, but with the small hole in it to stop it down.

It is better to make your own, it can be as simple as cardboard cutout or fancy like 3d printed part. If you make one - you'll control diameter of opening (say go for 80mm or 100mm) - and it is best if opening is in the center of the lens rather than to one side.

Newtonian scopes often use off axis aperture mask due to central obstruction, but for refractors - it is better to go on axis.

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12 minutes ago, vlaiv said:

It is better to make your own, it can be as simple as cardboard cutout or fancy like 3d printed part. If you make one - you'll control diameter of opening (say go for 80mm or 100mm) - and it is best if opening is in the center of the lens rather than to one side.

Newtonian scopes often use off axis aperture mask due to central obstruction, but for refractors - it is better to go on axis.

That photo was taken from another website, it was just to use as an example.  My refractor has a centre hole in the dust cap.  Agreed about making my own...

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3 minutes ago, Ian McCallum said:

That photo was taken from another website, it was just to use as an example.  My refractor has a centre hole in the dust cap.  Agreed about making my own...

I always wanted iris style aperture mask - but no one is making them (at least not affordable to mortals :D ). Such mask could be "dialed in" on the fly depending on target.

Maybe 3d printed version of DIY iris - like this one:

https://www.instructables.com/How-to-make-a-12-leaves-Mechanical-Irirs/

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I've tried my Skywatcher ED120 stopped down using the central hole in the dust cap which turns it into a 52mm F/17.3 ED doublet refractor.

I was doing this for fun really, just to see what could be seen with such a small aperture :icon_biggrin:

I've also done it using a cardboard mask with an off axis aperture with my 12 inch dobsonian and I can get a 110mm unobstructed aperture with an effective focal ratio of F/14.4. The performance of that seemed just as an apochromatic refractor of 110mm would perform, perhaps unsurprisingly.

 

 

Edited by John
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3 minutes ago, John said:

I've tried my Skywatcher ED120 stopped down using the central hole in the dust cap which turns it into a 52mm F/17.3 ED doublet refractor.

That is going to be one killer full disk lunar scope :D

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I have to correct myself - there seems to be very cheap version of iris that can be adopted for achromat use.

https://www.amazon.com/Aluminum-Template-Adjustable-Measurement-Measuring/dp/B08N6CH24H/ref=psdc_12896671_t1_B08QMKNH5N

Only issue is that max aperture is ~70mm. Ideally we would like something like 50-100 range or maybe 50-120mm

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