200p dob vs 180 pro Mak

[Beardy30]

Just wondering if anyone has ever used a 200p dob for imaging and if it was any good compared to the 180 Mak on a Heq5 mount ? Be good to know if the dob is as sharp on planets and moon ? 

[Nik271]

A well-collimated 200mm Newtonian can be amazing at high magnification. I'm sure many owners will happily confirm that. I have a 180 Mak and I'm very happy with it, it beats my 150mm F5 Newt at high magnification easily.

You would need  2x or 3x barlow on the Dob to image at the same image scale as the Mak but the bigger problem I foresee is tracking the planet at this high magnification, especially on a small sensor (which is most planetary cameras). Usually you record a 2-3 minute video which is then stacked, so you would need to be able to keep the object in view for this time which on a Dob may not be so easy.

In a perfect optical system aperture rules so a perfect 200mm Dob will just outperform a perfect 180mm Mak but in practice it depends on so many other factors that its impossible to generalise. 

Edited January 20, 2021 by Nik271

[vlaiv]

Indeed, as a design - 8" F/6 Newtonian will beat 180mm Maksutov on planetary if everything else is equal - but it rarely is.

Newtonian has slightly smaller secondary obstruction and slightly bigger aperture. It has only one complex surface as opposed to at least three on Maksutov (two on corrector plate and one on primary - SW mak is Gregory Maksutov - meaning secondary is simply aluminized spot on meniscus corrector and not separate mirror - so same curve) - less complex curves - less surfaces that can "go wrong".

Problem is that mass produced dobs are not going to be optically perfect. I have 8" Dob and have mounted it on Heq5 - mount can just barely hold such large tube for imaging (works better for planetary than for long exposure). Main problem are "ears" that SW dob has on tube - that I did not want to remove - it limits OTA rotation in rings - not very good for visual - but we are talking imaging here.

Mine tested about 0.8 system Strehl - so really on edge of being diffraction limited. Regardless of that - it gives me excellent views of planets that are 99% of time limited by seeing conditions.

I often recommend 8" F/6 Newtonian as planetary scope - but for best performance, one should get mirror with good figure. Maybe Orion Optics UK. They sell 1/10 PV mirrors in their scopes. There are conflicting reports about this company online (most regarding their customer support - but few in regards to their large "research grade" mirrors that were not even diffraction limited) - but others are very happy with their OO scopes. I have not used their scopes so I can't tell from first hand experience - only what I've read online.

[Beardy30]

Thanks- so what I’m reading here I think 🤔 is ...planet imaging - use the Mak , dso visual use choose the Dob

no one scope does all so maybe have both in an ideal world ! 

[vlaiv]

10 minutes ago, Beardy30 said:

Thanks- so what I’m reading here I think 🤔 is ...planet imaging - use the Mak , dso visual use choose the Dob

no one scope does all so maybe have both in an ideal world ! 

If you have budget for only one - then go with 8" F/6 Newtonian - but consider getting one with better optics.

[KP82]

I actually contemplated getting an OOUK VX8L 1/10 when I was shopping for my dob. In the end the mixed reports on the web regarding OOUK made me decide to go with the far cheaper but more popular SW 200P dob.

If you have an existing dob which you can replace its mirror or have the skill to make your own tube, you could order one of the Zambuto newtonian mirrors which are truely high quality.

[Beardy30]

No I do t have a dob I was just curious about the comparison 👍🏼

[vlaiv]

There is another "contender" to consider.

https://www.firstlightoptics.com/stellalyra-telescopes/stellalyra-8-f12-m-lrs-classical-cassegrain-telescope-ota.html

It is said to outperform Mak180 with contrast and does not have as much issues with dew as there is no front corrector plate.

Price is comparable (or used to be before price increase not long ago).