Options - scopes with flat fields out of the box (300-400mm)

[rnobleeddy]

I didn't realise that getting a larger camera would just lead to a greater battle to optimise flattener spacing/tilt! I'm very much hoping this weeks efforts can be cropped or fixed it post processing, as it's otherwise been a great week.

Which got me thinking - I've been trying to reduce the barrier to doing astrophotography, because I want to keep going, but don't have as much free time as I did during COVID. One obvious way to do that would be to use an OTA that doesn't need a flattener or reducer, especially as I share a camera/filters/spacers between >1 scope, and swapping the kit tends to lead to needing to reset spacing.

I'd like something in the range 300mm-400mm, so was wondering what people recommend?

So far, I've got:

Askar FRA300

Askar FRA400

Redcat 71

 

Is there anything else I should consider? Are there any unforeseen downsides to using this type of scope?

As it stands, the Redcat costs more and appears to need an adapter to fit a ZWO EAF, so I'd need to see a marked benefit in terms of image quality to choose the Redcat over one of the Askars.

 

 

Edited January 19, 2023 by rnobleeddy

[fwm891]

@rnobleeddyTake a look at the Altair astro refractors 

Edited January 19, 2023 by fwm891

[Lee_P]

Askar FRA400 is great, I've used one extensively. Review here and most of the photos in my gallery were taken using it.

[Louis D]

14 minutes ago, fwm891 said:

Take a look at the Altair astro refractors 

Are you referring to these offerings?

Altair 70 EDQ-R F5 Quad APO Astrograph

TS-Optics 70 mm f/5 Quadruplet Flatfield Apo with 3-Element FPL53 Objective

TS-Optics 61EDPH - 6-Element Flatfield Apo 61 mm Aperture F/4.5

TS-Optics 5-Element Flatfield Photo Apo Refractor - ED61PHD

[GalaxyGael]

For very widefield (depending on sensor size) the FRA300 is nice and easy to use. Good color correction for imaging, flat field and wide (300 mm) at f/5.

Light and a well thought out long dovetail and handle/guide scope placement if you need it. I enjoyed using it for a few months and got a good sample. Off to the classifieds for a new camera.

I found adding an astrozap dew shield removed the need for heated options, improved spurious light cover too. the Askar focusers are solid, no sag.

Edited January 19, 2023 by GalaxyGael

[rnobleeddy]

4 hours ago, Louis D said:

Are you referring to these offerings?

Altair 70 EDQ-R F5 Quad APO Astrograph

TS-Optics 70 mm f/5 Quadruplet Flatfield Apo with 3-Element FPL53 Objective

TS-Optics 61EDPH - 6-Element Flatfield Apo 61 mm Aperture F/4.5

TS-Optics 5-Element Flatfield Photo Apo Refractor - ED61PHD

 

4 hours ago, fwm891 said:

@rnobleeddyTake a look at the Altair astro refractors 

Thanks both - didn't realise there was so many to choose from!

[CCD-Freak]

The Sharpstar 15028HNT at 420mm and the 13028HNT at 364mm could be added to the list though you will still have to get the 55mm spacing set right.

 

Edited January 19, 2023 by CCD-Freak

[rnobleeddy]

1 hour ago, CCD-Freak said:

The Sharpstar 15028HNT at 420mm and the 13028HNT at 364mm could be added to the list though you will still have to get the 55mm spacing set right.

 

Was entirely unaware that these existed! I guess the main advantage over a refractor is the fact they're so fast? How do you find collimation? I also imagine I would a new dual band filter, which adds extra £.

[rnobleeddy]

5 hours ago, GalaxyGael said:

For very widefield (depending on sensor size) the FRA300 is nice and easy to use. Good color correction for imaging, flat field and wide (300 mm) at f/5.

Light and a well thought out long dovetail and handle/guide scope placement if you need it. I enjoyed using it for a few months and got a good sample. Off to the classifieds for a new camera.

I found adding an astrozap dew shield removed the need for heated options, improved spurious light cover too. the Askar focusers are solid, no sag.

My camera is APS-C sized and I'm currently using a 290mm scope for widefield imaging. So this would be the same, but wouldn't cause as much frustration in the corners. I'd probably opt for this over the 400, but I'll probably spend some time assessing what does/doesn't fit amongst the objects I enjoy imaging.

[Adam J]

8 hours ago, rnobleeddy said:

I didn't realise that getting a larger camera would just lead to a greater battle to optimise flattener spacing/tilt! I'm very much hoping this weeks efforts can be cropped or fixed it post processing, as it's otherwise been a great week.

Which got me thinking - I've been trying to reduce the barrier to doing astrophotography, because I want to keep going, but don't have as much free time as I did during COVID. One obvious way to do that would be to use an OTA that doesn't need a flattener or reducer, especially as I share a camera/filters/spacers between >1 scope, and swapping the kit tends to lead to needing to reset spacing.

I'd like something in the range 300mm-400mm, so was wondering what people recommend?

So far, I've got:

Askar FRA300

Askar FRA400

Redcat 71

 

Is there anything else I should consider? Are there any unforeseen downsides to using this type of scope?

As it stands, the Redcat costs more and appears to need an adapter to fit a ZWO EAF, so I'd need to see a marked benefit in terms of image quality to choose the Redcat over one of the Askars.

 

 

 

The FRA300 would be my choise the redcat 71 in my view is a little weird having a helical focuser on such a large scope.

Adam

[CCD-Freak]

2 hours ago, rnobleeddy said:

Was entirely unaware that these existed! I guess the main advantage over a refractor is the fact they're so fast? How do you find collimation? I also imagine I would a new dual band filter, which adds extra £.

I don't find the SS Hyper Newts to be too hard to collimate but I have been working with reflectors for many years.  Hyper Newts are more "fiddly" than a refractor and it helps if you are not "mechanically challenged".  Once my SS15028HNT is dialed in it holds colimation quite well.   For me collimation is a tradeoff for imaging at F2.8.  I have been imaging with an ASI-533MCp and a recently acquired ASI-2600MCp.