Biggest differences between newtonian Telescope and Astrograph Generic equipment discussions · Jens · 11/13/2023 · 7 · 594 · 0

The biggest difference between a cheap and a high quality imaging newt is going to be build quality. Cheap newts have thin steel tube, weak focuser, and weak mirror holders. All of these things result in a telescope that does not hold collimation well. A high quality newt will have a thick tube (often carbon fiber) that will remain rigid, strong focuser that is less likely to tilt with heavy image trains and will accommodate a coma corrector, a larger secondary mirror to illuminate larger camera sensors, strong mirror holders to prevent lose of collimation during operation.

Even with high quality newts you can have mechanical issues though. There is a 16" DREAM in my observatory that had to have its focuser shimmed to fix the tilt. I've read many horror stories of OOUK newts. So it is not a guarantee that just because a scope is advertised as high quality or an astrograph you wont have at least some minor issues. I have been very fortunate with my ONTC. It has given me zero problems since day 1.

Many make projects out of taking cheap newts and modifying them to be in good condition for imaging. Some succeed some don't. I tried with 2 GSO newts and the weak point ended up being the primary mirror cell so collimation would not survive the scopes initial slew. Some have had better luck.

I have experience with both "cheaper" Newtonians and so-called "Astrograph"-Newtonians. The main difference is the mechanical quality of the Tube, most importantly the mirror cells and support structures. In theory, your are able to get great images of similar quality with a modified cheap Newtonian as well, in practice it takes disproportionally more effort and is often not possible. When I used the cheaper Newtonian, careful collimation had to be done multiple times per night and the focussing was not too precise, resulting in tilt issues and frequent refocus. One of the most important telescope parts for astrophotography is the focusser, the one delivered with these Newtonians really struggles and causes issues like mentioned above. When modifiying, I would start with replacing the focusser and maybe invest in a motorfocus. Getting an aperture ring for the primary and beter screws/springs for the mirrors is a cheap upgrade.
Putting all this aside, it really depends on what your expectations and requirements are. If you just want to have fun taking images, why not modify the telescope? If you want get high-resolution images down to the seeing-limit with round stars all over the field and so on I wouldn't invest my money that way.
If your looking for a high-quality Newtonian that works reliably without problems and yields very sharp images (while not beeing as expensive as other options), I would look into the ONTC Series from TS-Optics.

The "astrograph" tag is not a quality tag unfortunately, it is just associated with some characteristics:  lower f-ratio (f/4 instead of f/5), bigger secondary and focal plane further away from the tube. 

If by "astrograph" we would like to mean suitable for high quality astrophotography, unfortunately few commercial offerings deserve this tag. TS ONTC were mentionned, other models to consider are Lacerta Fotonewtons, or Skyvision at the upper end of the market.

Fortunately it is not hard to either improvre an existing mass-produced one by changing key components or to assemble one from scratch.

Definition: An astrograph is a telescope designed for the sole purpose of astrophotography. Thus a Newtonian is a subset, design specific, of astrographs when is is used for the sole purpose of astrophotography. This definition is a bit restrictive.

Consider: A Newtonian is a reflective primary with a fold mirror inside focus reflecting the image outside the tube. And: Your Newtonian is an astrograph when with are doing imaging...