What’s the refractor sweet spot ?

[Newforestgimp]

Hi All,

I have a Small refractor for wide field AP, just wondering what the next step might be in terms flexibility. An 80, 90 or 100 ?

I know the prices increase considerably with refractors so where is the sweet spot for AP, which should I be looking out for at the bring n buy sales ?

regards

Andy H

[JeremyS]

Not sure about sweet spot, but I’ve definitely got an itchy spot so far as refractors are concerned 😊

[Ags]

Definitely 66 mm.

And 72 mm.

Also 80 mm.

100 mm hits the spot.

120 mm too.

Don't forget 150 mm!

[Stu]

22 minutes ago, Newforestgimp said:

Hi All,

I have a Small refractor for wide field AP, just wondering what the next step might be in terms flexibility. An 80, 90 or 100 ?

I know the prices increase considerably with refractors so where is the sweet spot for AP, which should I be looking out for at the bring n buy sales ?

regards

Andy H

I think a lot depends on the types of target you want to image and the camera you are using. Small refractors with short focal lengths are ideal for large targets, as the targets get smaller such as for smaller galaxies and globs etc you need a longer focal length, and to keep the focal ratio reasonably fast, the aperture inevitably goes up too.

[Alien 13]

As refractor objective increases so does the f/ratio required to get decent colour correction so the "sweet spot" might be sub 130mm, larger refactors get unwieldy too requiring very expensive mounts. In my view the cutoff point is around 130mm where even a SW 130PDS or better still a Tac Epsilon 130mm will not only be faster but easier to mount, at 200mm and above it has to be a mirrored scope.

Alan 

[callisto]

I don't think you can go wrong with this one 😁

 

[Floater]

2 minutes ago, Alien 13 said:

As refractor objective increases so does the f/ratio required to get decent colour correction so the "sweet spot" might be sub 130mm, larger refactors get unwieldy too requiring very expensive mounts. In my view the cutoff point is around 130mm where even a SW 130PDS or better still a Tac Epsilon 130mm will not only be faster but easier to mount, at 200mm and above it has to be a mirrored scope.

Alan 

Now this is wisdom on a stick.

Well put, Alan.

[Space Hopper]

Make that 140mm......😉

[Earl]

Its sweet spot is where your wallet says enough

 

[Newforestgimp]

26 minutes ago, callisto said:

I don't think you can go wrong with this one 😁

 

I’m sure I saw that in the WMD dossier !!

[Ags]

Is that a 1.25" drawtube on the back?

[Ags]

Spotted this today. Totally convinced it is my sweet spot. Next step is to analyze it to death for three years, then buy something else... 🤣

https://www.teleskop-express.de/shop/product_info.php/info/p13519_TS-Optics-ED-Apo-96-mm-f-6-with-2-5-Inchl-RAP-Focuser---ED-Objective-from-Japan.html

[johninderby]

FLO did mention the possibility of a couple of new StellaMra refractors. Will be interested to see what they turn out to be. 🤔

[vlaiv]

If we consider "capability vs budget" sweet spot for APO refractor, then I'd say this one is in pretty sweet spot:

https://www.teleskop-express.de/shop/product_info.php/info/p3041_TS-Optics-PHOTOLINE-115-mm-f-7-Triplet-Apo---2-5--RAP-focuser.html

add in this flattener / reducer:

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

You'll be hard pressed to find such aperture, color correction and field flatness at that price point.

 

[Newforestgimp]

12 hours ago, Ags said:

Spotted this today. Totally convinced it is my sweet spot. Next step is to analyze it to death for three years, then buy something else... 🤣

https://www.teleskop-express.de/shop/product_info.php/info/p13519_TS-Optics-ED-Apo-96-mm-f-6-with-2-5-Inchl-RAP-Focuser---ED-Objective-from-Japan.html

Ooh now that looks promising !! 96mm, good bang for buck.

[vlaiv]

54 minutes ago, Newforestgimp said:

Ooh now that looks promising !! 96mm, good bang for buck.

Do keep in mind that said scope will be good for visual or EEVA but not for astrophotography.

It uses FCD1 glass and it is larger aperture fast doublet scope. It will have significant color fringing in astrophotography applications if you shoot broad band. For narrowband only it will probably be good choice.

[Newforestgimp]

24 minutes ago, vlaiv said:

Do keep in mind that said scope will be good for visual or EEVA but not for astrophotography.

It uses FCD1 glass and it is larger aperture fast doublet scope. It will have significant color fringing in astrophotography applications if you shoot broad band. For narrowband only it will probably be good choice.

Invaluable detail again Vlaiv, I think to be honest if I go too much beyond a 90 I’ll be into buying another mount too to cope with the payload demands.

[Ags]

51 minutes ago, vlaiv said:

Do keep in mind that said scope will be good for visual or EEVA but not for astrophotography.

It uses FCD1 glass and it is larger aperture fast doublet scope. It will have significant color fringing in astrophotography applications if you shoot broad band. For narrowband only it will probably be good choice.

Indeed I am concerned only with visual performance, small size and low weight - just 3 kg.

[johninderby]

If it weren’t for the cost this would be a great choice. Dream scope category. 😁

https://www.baader-planetarium.com/en/telescopes/baader-planetarium/baader-apo-95-580-caf2-travel-companion.html

Edited July 20, 2021 by johninderby

[vlaiv]

32 minutes ago, Newforestgimp said:

Invaluable detail again Vlaiv, I think to be honest if I go too much beyond a 90 I’ll be into buying another mount too to cope with the payload demands.

That is true, I was going to suggest this scope:

https://www.teleskop-express.de/shop/product_info.php/info/p3881_TS-Optics-PHOTOLINE-80mm-f-6-FPL53-Triplet-APO---2-5--RAP-Focuser.html

I have it and it is really excellent little scope, however, I fear it won't be as much difference to your WO61. Both are wide field scopes AP scopes.

If you want to get into medium resolutions with refractor, you really need to go 100mm+ and that will get you below 2"/px down to say 1.6-1.8"/px range. However, that would require something like Heq5.

[Rustang]

I nearly brought one of these second hand which I would still consider to upgrade from my SW 80 ED DS Pro. How much better it would be though... 

https://www.teleskop-spezialisten.de/shop/Telescope/ED-APO/80-90mm/TSAPO906-TS-Photoline-90mm-f6-6-triplet-FPL-53-SuperApo-2-5-CNC-OAZ-tube-length-adjustable::1055.html?language=en

[Newforestgimp]

7 hours ago, vlaiv said:

That is true, I was going to suggest this scope:

https://www.teleskop-express.de/shop/product_info.php/info/p3881_TS-Optics-PHOTOLINE-80mm-f-6-FPL53-Triplet-APO---2-5--RAP-Focuser.html

I have it and it is really excellent little scope, however, I fear it won't be as much difference to your WO61. Both are wide field scopes AP scopes.

If you want to get into medium resolutions with refractor, you really need to go 100mm+ and that will get you below 2"/px down to say 1.6-1.8"/px range. However, that would require something like Heq5.

My eqm35 has had the Darkframe Ltd Stella drive treatment so sub arc sec guiding should be no issue and I’m assured by Darkframe I can use the full 11kg payload for AP now. Even so I wouldn’t like to run it at its new upper limits for AP.

[Deadlake]

8 hours ago, johninderby said:

If it weren’t for the cost this would be a great choice. Dream scope category. 😁

https://www.baader-planetarium.com/en/telescopes/baader-planetarium/baader-apo-95-580-caf2-travel-companion.html

Not reportedly as good as a stowaway 92….

[mauzito]

On 20/07/2021 at 22:05, Deadlake said:

Not reportedly as good as a stowaway 92….

Interesting.

I wonder what is your source?

[Deadlake]

9 minutes ago, mauzito said:

Interesting.

I wonder what is your source?

Someone who owns both, he sold the Baader. Mind hair’s breadth between them. He also had specialist application of NV. For visual very close.