Short(er) tube Newt?

[raadoo]

I've googled long enough to confidently resort to your collective knowledge in helping me track down a bit of unicorn.

We all have some personal limitations when looking at OTAs and quite often they refer to size. In my case, I'm limited by my long, but narrow, balcony - specifically 90cm. This 90cm limit includes image train and possible dew shield.

As I'm looking to dip my toes into some short exposure DSO imaging, aperture and speed are my main priority for any OTA, so a fast Newt seems like the most cost effective way to get there*. The obvious go-to would be a 10" f/4 but a quick bit of math puts any Newt of that configuration at about 100cm long.

An 8" would fit, but I doubt that's enough aperture for the intended purpose. Anything over 10" would be too heavy for my mount and certainly longer than my 90cm limit.

To cut a long story short:

Does anyone know of a 10" Newt with a native f ratio of between 2.8 and 3.5?

*RASA / Hyperstar setups fit the bill but cost is beyond what I'd be comfortable with.

[Alkaid]

I would also consider the mount / tripod when the feet are 'splayed', my EQ5 is well over 90cm across the floor when the legs are out so wouldn't fit....   What will you mount the scope on?

[doublevodka]

1 hour ago, raadoo said:

I've googled long enough to confidently resort to your collective knowledge in helping me track down a bit of unicorn.

We all have some personal limitations when looking at OTAs and quite often they refer to size. In my case, I'm limited by my long, but narrow, balcony - specifically 90cm. This 90cm limit includes image train and possible dew shield.

As I'm looking to dip my toes into some short exposure DSO imaging, aperture and speed are my main priority for any OTA, so a fast Newt seems like the most cost effective way to get there*. The obvious go-to would be a 10" f/4 but a quick bit of math puts any Newt of that configuration at about 100cm long.

An 8" would fit, but I doubt that's enough aperture for the intended purpose. Anything over 10" would be too heavy for my mount and certainly longer than my 90cm limit.

To cut a long story short:

Does anyone know of a 10" Newt with a native f ratio of between 2.8 and 3.5?

*RASA / Hyperstar setups fit the bill but cost is beyond what I'd be comfortable with.

2.8 to 3.5 seems to be quite exotic, had a quick search myself and no results in the size range so far, but I suspect they would be very expensive and niggly to collimate to say the least

An 8 inch Quattro would fit the length limit though - https://www.firstlightoptics.com/skywatcher-quattro-f4/skywatcher-quattro-f4-imaging-newtonian.html and there are dedicated coma correctors

Alternatively the StellarLyra - https://www.firstlightoptics.com/stellalyra-telescopes/stellalyra-8-f-4-m-lrn-newtonian-reflector-with-2-focuser.html (slightly cheaper on the coma corrector side too)

I know you ruled them out, but with a bit of digging on the used market, you may be able to get a hyperstar based setup in the same ballpark, they do occasionally come on the market

Even an 8 inch F/3.2 is £3,199 - https://www.firstlightoptics.com/sharpstar-telescopes/sharpstar-2032pnt-f3-2-paraboloid-newtonian-reflecting-astrograph-telescope.html, can't imagine what a 10 inch would be, an 8 inch RASA is cheaper for referrence - https://www.rothervalleyoptics.co.uk/celestron-8-rowe-ackermann-schmidt-astrograph-rasa-ota.html

[raadoo]

29 minutes ago, Alkaid said:

I would also consider the mount / tripod when the feet are 'splayed', my EQ5 is well over 90cm across the floor when the legs are out so wouldn't fit....   What will you mount the scope on?

I'm using an RST-135, and having had a Mewlon-180c in full imaging garb on it with good results (measured at 80cm from front to camera), I'm quite confident in its ability to handle a similarly sized Newt.

[raadoo]

4 minutes ago, doublevodka said:

2.8 to 3.5 seems to be quite exotic, had a quick search myself and no results in the size range so far, but I suspect they would be very expensive and niggly to collimate to say the least

An 8 inch Quattro would fit the length limit though - https://www.firstlightoptics.com/skywatcher-quattro-f4/skywatcher-quattro-f4-imaging-newtonian.html and there are dedicated coma correctors

Alternatively the StellarLyra - https://www.firstlightoptics.com/stellalyra-telescopes/stellalyra-8-f-4-m-lrn-newtonian-reflector-with-2-focuser.html (slightly cheaper on the coma corrector side too)

I know you ruled them out, but with a bit of digging on the used market, you may be able to get a hyperstar based setup in the same ballpark, they do occasionally come on the market

Even an 8 inch F/3.2 is £3,199 - https://www.firstlightoptics.com/sharpstar-telescopes/sharpstar-2032pnt-f3-2-paraboloid-newtonian-reflecting-astrograph-telescope.html, can't imagine what a 10 inch would be, an 8 inch RASA is cheaper for referrence - https://www.rothervalleyoptics.co.uk/celestron-8-rowe-ackermann-schmidt-astrograph-rasa-ota.html

There does seem to be a very steep increase in price when you move from f/4 to anything faster, when it comes to Newts. I'd expect them to be more expensive but for a wee bit faster aperture you seem to be paying out of every orifice.

Good shout about looking for a used hyperstar; maybe pairing it with a standard 9.25 to keep cost down.

RASAs are the fastest option by far - my only concern is that they're a bit of a one-trick-pony. You can always un-hyperstar an SCT and use it for planetary work. And you can always chuck a 1.5x Düring Barlow on a Newt. But a RASA is a RASA is a RASA.

[doublevodka]

53 minutes ago, raadoo said:

RASAs are the fastest option by far - my only concern is that they're a bit of a one-trick-pony. You can always un-hyperstar an SCT and use it for planetary work. And you can always chuck a 1.5x Düring Barlow on a Newt. But a RASA is a RASA is a RASA.

They are a bit of a one-trick pony, but they do that trick very, very well! A member of my local astro club has a RASA 11 and the pictures are really something else

A 9.25 though, f/10 standard, f/2.2 hyperstar, 0.7 reducer for f/7, 2x barlow for f/20 on planets really can be a bit of a Swiss army knife, albeit an expensive one once you add all those accessories, but there are lots of them around so the used market is ok and well supported with accessories etc. so maybe a little easier overall than an exotic newt?

[raadoo]

23 minutes ago, doublevodka said:

They are a bit of a one-trick pony, but they do that trick very, very well! A member of my local astro club has a RASA 11 and the pictures are really something else

A 9.25 though, f/10 standard, f/2.2 hyperstar, 0.7 reducer for f/7, 2x barlow for f/20 on planets really can be a bit of a Swiss army knife, albeit an expensive one once you add all those accessories, but there are lots of them around so the used market is ok and well supported with accessories etc. so maybe a little easier overall than an exotic newt?

Food for thought, indeed.

Alternatively, I could reconsider the 8" f/4 and try and pair it with the minuscule pixels of my 183.

Definitely have to do some back-of-the-napkin math for this one.

[doublevodka]

28 minutes ago, raadoo said:

Food for thought, indeed.

Alternatively, I could reconsider the 8" f/4 and try and pair it with the minuscule pixels of my 183.

Definitely have to do some back-of-the-napkin math for this one.

Save yourself the brain ache - http://astronomy.tools/calculators/field_of_view/