What scope to buy next

[GalaticBoba]

I'm probably not going to buy just yet, but I do like looking. 

I have an 8" SCT and a 10" dob. So my next scope has to be a refractor, I would want to use this one for DSO AP, I've also been looking at dedicated ZWO cooled mono cameras that I will attach to it. I'll worry about the mount once I've decided on scope.

From what I've read the "faster" the scope the better at collecting light with scopes between F/1.4 and F/2.8 being ideal. But even something at F/4 will be better then what I've currently got. 

Here's my issue, I can't find any fast refractors, although I've only been looking on FLO. 

Anyone know of a good one? I have seen some but these are in the multiple thousands, I don't mind spending £2k or £3k on the OTA. But as a beginner scope I'd prefer to spend less than a grand. And I really can't justify spending £5k or £6k. 

[dweller25]

I don’t think you will find anything at those camera lens F ratios in your budget.

The Skywatcher ED80 seems to be a very popular choice for astro imagers…..

https://www.firstlightoptics.com/pro-series/skywatcher-evostar-80ed-ds-pro-ota.html

You can get down to F/6.37 with the reducer.

Edited September 2, 2021 by dweller25

[DaveS]

Mount, mount, mount.

The 'scope is the last thing to worry about. Does your SCT already have a good EQ mount? If not then budget for a mount first. HEQ5 level *minimum" unless you want to spent all your time fettling it.

Then worry about what you're going to put on it.

You talk about f/1.4 or 2.8. Have you budgeted for the ultra-high-speed NB filters to work at that ratio?

At that speed you'll be looking at camera lenses, and not very long unless you're prepared to pay serious money, possibly into 5 figures.

Fast 'fracs are seriously expensive as they get down to f/4. The Vixen VSD100 is f/3.8 from memory, and getting on for £6k. A Tak FSQ106 plus reducer will get into similar territory, for similar money. This is especially true if you want stars to look like points, and not seagulls.

If you start thinking f/4.5- f/5 then you'll have a better chance of finding something affordable, that will give reasonable quality.

[DaveS]

If you want fast, for something less than bankrupting money, then a Celestron RASA8 might be worth looking at,

[GalaticBoba]

34 minutes ago, dweller25 said:

I don’t think you will find anything at those camera lens F ratios in your budget.

The Skywatcher ED80 seems to be a very popular choice for astro imagers…..

https://www.firstlightoptics.com/pro-series/skywatcher-evostar-80ed-ds-pro-ota.html

You can get down to F/6.37 with the reducer.

I might just go for a budget sky-watcher refractor similar to this one and keep it for visuals that is also easy for traveling. 

 

33 minutes ago, DaveS said:

Mount, mount, mount.

The 'scope is the last thing to worry about. Does your SCT already have a good EQ mount? If not then budget for a mount first. HEQ5 level *minimum" unless you want to spent all your time fettling it.

Then worry about what you're going to put on it.

You talk about f/1.4 or 2.8. Have you budgeted for the ultra-high-speed NB filters to work at that ratio?

At that speed you'll be looking at camera lenses, and not very long unless you're prepared to pay serious money, possibly into 5 figures.

Fast 'fracs are seriously expensive as they get down to f/4. The Vixen VSD100 is f/3.8 from memory, and getting on for £6k. A Tak FSQ106 plus reducer will get into similar territory, for similar money. This is especially true if you want stars to look like points, and not seagulls.

If you start thinking f/4.5- f/5 then you'll have a better chance of finding something affordable, that will give reasonable quality.

I've looked at lots of mounts and there are a few I like, probably end up going for something like the EQ6. 

But for now, I was going to get the refractor and use it on my SCT mount for visuals, then get an EQ mount and figure out how that works, whilst still doing visuals. Then lastly get a camera and the relevant accessories, I'll spread it out over a few months. It's a lot to learn in one go. 

 

30 minutes ago, DaveS said:

If you want fast, for something less than bankrupting money, then a Celestron RASA8 might be worth looking at,

I like the Celestron SCT I've got now and so maybe I will get another one later for AP, as mine is an F/10. My dob is F/5 so I could get some tube rings and an EQ mount and have a go with AP on that one. 

 

But... 

I still want a refractor!!!

I guess it won't be for AP after hearing all your comments. 

[GalaticBoba]

How about this?

https://www.astroshop.eu/telescopes/opt-apochromatic-refractor-radian-ap-61-275-raptor-ota/p,68993?utm_medium=cpc&utm_term=68993&utm_campaign=2109&utm_source=froogle&utm_content=

[DaveS]

I will add, if you haven't already get it, buy This book and read it through at least twice before spending anything more on AP kit.

[GalaticBoba]

4 minutes ago, DaveS said:

I will add, if you haven't already get it, buy This book and read it through at least twice before spending anything more on AP kit.

That book is on my wish list

[Planitair]

This hobby is very subjective when it comes to equipment advice, read up, look at what other folk are getting & using , think about what you eventually want from this game, dont rush into buying anything, you can throw a lot of cash at this and then find you need the other.

ew

[Clarkey]

22 hours ago, GalaticBoba said:

I might just go for a budget sky-watcher refractor similar to this one and keep it for visuals that is also easy for traveling.

With your suggested budget you could also get a triplet which would be great for AP and visual. (If you can find one of course). The Evostar is still good for the money though - I use one for AP.

[GalaticBoba]

I've now got my eye on this one, with a reducer gets down to F4.4, even if I don't use it for AP right away, it will still be good for visuals on Nebulae and Galaxies, I think?! 

https://www.365astronomy.com/sharpstar-94edph-ed-triplet-apochromatic-refractor-telescope

[doublevodka]

If you just want to dip your toe into the world of refractors to see if you like it this maybe worth a look below? 

Your 10 inch dob will be better visually on nebulae and galaxies though, more aperture, more light

 

Also as above, mount, mount, mount  if you want any decent AP performance it doesn't matter how fancy the glass is, the mount is key

 

[GalaticBoba]

Alright, alright, alright... if you're all going to force me to pick a mount, then I'm currently undecided between the following 3 ;)

 

https://www.firstlightoptics.com/skywatcher-mounts/skywatcher-az-eq6-mount.html

Pros

Looks cool in Altaz mode with two scopes

Cheap

Can buy it now and use in altaz mode whilst I read "Making every photon count"

 

https://www.365astronomy.com/celestron-cgx-equatorial-computerised-goto-telescope-mount-and-tripod

Pros

Can use my existing Celestron Starsense and wifi sky portal

Excellent payload capacity

Don't have to buy it now, I can just use my current mount until I've read "Making every photon count"

 

https://www.firstlightoptics.com/ioptron-mounts/ioptron-gem45-geq-goto-mount-with-iguider-literoc-tripod-case.html

Pros

Good payload capacity

Built in guide scope

Comes with case for easier transport 

Don't have to buy it now, I can just use my current mount until I've read "Making every photon count"

[doublevodka]

On 03/09/2021 at 17:32, GalaticBoba said:

Alright, alright, alright... if you're all going to force me to pick a mount, then I'm currently undecided between the following 3

 

https://www.firstlightoptics.com/skywatcher-mounts/skywatcher-az-eq6-mount.html

Pros

Looks cool in Altaz mode with two scopes

Cheap

Can buy it now and use in altaz mode whilst I read "Making every photon count"

 

https://www.365astronomy.com/celestron-cgx-equatorial-computerised-goto-telescope-mount-and-tripod

Pros

Can use my existing Celestron Starsense and wifi sky portal

Excellent payload capacity

Don't have to buy it now, I can just use my current mount until I've read "Making every photon count"

 

https://www.firstlightoptics.com/ioptron-mounts/ioptron-gem45-geq-goto-mount-with-iguider-literoc-tripod-case.html

Pros

Good payload capacity

Built in guide scope

Comes with case for easier transport 

Don't have to buy it now, I can just use my current mount until I've read "Making every photon count"

All decent choices, in your shoes I'd probably be swung by the celestron as you have some useful accessories although the guys in my local astro club swear by the ioptron stuff

[vlaiv]

On 02/09/2021 at 17:05, GalaticBoba said:

From what I've read the "faster" the scope the better at collecting light with scopes between F/1.4 and F/2.8 being ideal. But even something at F/4 will be better then what I've currently got. 

Well, no.

Faster isn't always better - and for that matter, it is not always faster either.

You won't be able to find any decent telescope at below F/2. Such speed simply requires complex lens arrangements and can only be found in lenses. Camera lens and fast scopes are not diffraction limited either and will not be good in travel scope role.

Photographic speed is determined by aperture size and working resolution. That means combination of telescope, corrective element and camera.

Say you want to work at 1.8"/px. In that case - I'd say get largest aperture that will give you 1.8"/px with chosen camera. This is with regards to imaging alone, but if you want to take that telescope on vacations - that adds constraints on your choice.

Here are couple of examples:

1. Take ASI6200 with 3.76µm pixel size and 10" OOUK ODK 10" with focal length of 1700mm. Bin data x4 and you'll get working resolution of ~1.8"/px (1.82"/px to be precise). That is 10" of aperture providing you with 1.8"/px resolution

This scope has 50mm imaging field and can easily illuminate full frame sensor

Effective F/ratio - F/6.8

2. Take 6" f/5 newtonian and add best coma corrector - like TV VIP-2010 Paracorr and pair that with ASI2600 camera. Bin pixels x2 this time and you get again 1.8"/px

Effective F/ratio - F/5.75

3. Take 80mm F/7 and pair it with ASI1600 and TS x0.79 reducer flattener. Again you have ~1.8"/px

Effective F/ratio - F/5.53

In terms of F ratio - third option is "fastest", followed by second option and first option comes in last.

However, in term of real speed - first option is clearly the fastest as it uses 10" of aperture vs 6" of aperture vs 3.15" of aperture - but they will all produce the same sampling rate image - target will be covered by same amount of pixels. More light divided by same number of pixels - means more light per pixel - higher signal - better SNR.

Now, I would recommend you to think in terms of 1.8"/px - 2"/px imaging resolution and to get yourself nice affordable triplet refractor and pair it with nice camera and flattener reducer to get to your target sampling rate.

iOptron mount you linked above should handle such scope and resolution with ease.

Here is scope for you:

https://www.altairastro.com/altair-wave-series-102mm-f7-super-ed-triplet-apo-102715-452-p.asp

Add this reducer flattener:

https://www.teleskop-express.de/shop/product_info.php/info/p11122_Riccardi-0-75x-APO-Reducer-and-Flattener-with-M63x1-Thread.html

And this camera:

https://astronomy-imaging-camera.com/product/asi294mm-pro

(comes in both mono or OSC version - so you have choice there).

That combination will give you 1.78"/px working resolution.

Alternatively, if you want a bit more oomph for your travels - look at this scope:

https://www.altairastro.com/altair-starwave-115-f7-ed-triplet-refractor-9198-p.asp

But due to focal length, your working resolution will be a bit lower with above FF/FR and camera - 1.58"/px

[GalaticBoba]

44 minutes ago, vlaiv said:

Well, no.

Faster isn't always better - and for that matter, it is not always faster either.

You won't be able to find any decent telescope at below F/2. Such speed simply requires complex lens arrangements and can only be found in lenses. Camera lens and fast scopes are not diffraction limited either and will not be good in travel scope role.

Photographic speed is determined by aperture size and working resolution. That means combination of telescope, corrective element and camera.

Say you want to work at 1.8"/px. In that case - I'd say get largest aperture that will give you 1.8"/px with chosen camera. This is with regards to imaging alone, but if you want to take that telescope on vacations - that adds constraints on your choice.

Here are couple of examples:

1. Take ASI6200 with 3.76µm pixel size and 10" OOUK ODK 10" with focal length of 1700mm. Bin data x4 and you'll get working resolution of ~1.8"/px (1.82"/px to be precise). That is 10" of aperture providing you with 1.8"/px resolution

This scope has 50mm imaging field and can easily illuminate full frame sensor

Effective F/ratio - F/6.8

2. Take 6" f/5 newtonian and add best coma corrector - like TV VIP-2010 Paracorr and pair that with ASI2600 camera. Bin pixels x2 this time and you get again 1.8"/px

Effective F/ratio - F/5.75

3. Take 80mm F/7 and pair it with ASI1600 and TS x0.79 reducer flattener. Again you have ~1.8"/px

Effective F/ratio - F/5.53

In terms of F ratio - third option is "fastest", followed by second option and first option comes in last.

However, in term of real speed - first option is clearly the fastest as it uses 10" of aperture vs 6" of aperture vs 3.15" of aperture - but they will all produce the same sampling rate image - target will be covered by same amount of pixels. More light divided by same number of pixels - means more light per pixel - higher signal - better SNR.

Now, I would recommend you to think in terms of 1.8"/px - 2"/px imaging resolution and to get yourself nice affordable triplet refractor and pair it with nice camera and flattener reducer to get to your target sampling rate.

iOptron mount you linked above should handle such scope and resolution with ease.

Here is scope for you:

https://www.altairastro.com/altair-wave-series-102mm-f7-super-ed-triplet-apo-102715-452-p.asp

Add this reducer flattener:

https://www.teleskop-express.de/shop/product_info.php/info/p11122_Riccardi-0-75x-APO-Reducer-and-Flattener-with-M63x1-Thread.html

And this camera:

https://astronomy-imaging-camera.com/product/asi294mm-pro

(comes in both mono or OSC version - so you have choice there).

That combination will give you 1.78"/px working resolution.

Alternatively, if you want a bit more oomph for your travels - look at this scope:

https://www.altairastro.com/altair-starwave-115-f7-ed-triplet-refractor-9198-p.asp

But due to focal length, your working resolution will be a bit lower with above FF/FR and camera - 1.58"/px

Thanks for the info. It's apparent, that I need to do more reading before getting into AP. I've ordered the linked book above. 

 

I have been looking at similar tubes to the one you mentioned, I'm less concerned with the f number now, although the more I look and research the more I want to spend. Currently the Askar FRA600 takes my fancy. No one has it in stock yet, so I might wait until after Christmas before I get myself a refractor. 

https://www.firstlightoptics.com/askar-telescopes/askar-fra600-f56-108mm-quintuplet-apo-astrograph.html

 

I think for now a mount has to be my next purchase. I received my baader zoom EP yesterday, and had so much wobble on my nexstar 8SE looking at Jupiter last night on highest power. Too much weight with all the accessories. I'm now debating between the CGX and CGX-L.