8” comparison

[Kram]

Can anyone advise me on these two? There’s a big difference on price. But both are 8”. Sky-Watcher Explorer 200P vs StellaLyra 8" f/12 M-LRS Classical Cassegrain 

[vlaiv]

There is a reason why there is such a price difference, and these are two very different instruments.

It really depends what you plan on doing with your scope.

200P is general purpose visual instrument. That is its strong side. It can do different types of astrophotography - but there are better models of the same scope that are meant for that - like 200PDS (dual speed focuser and optimized secondary size).

8" CC is very specific instrument - it is suited to planetary and lunar visual, but much more for photographic applications. It comes with decent dual speed focuser and has massive focal length of 2.4m. It has quite large corrected field - up to APS-C size so you don't need any sort of corrector - which is good for certain applications like IR part of spectrum that works best with purely mirrored systems (no refraction in glass).

What will you be using the scope for?

[Kram]

Thanks for replying. I’m using a 127mm sct at the minute. But I’d like to see the planets more clearly. Mars is barely visible. Jupiter and Saturn are nice but very small. And I’d like to take some photos

[johninderby]

I love my 8” Classical Cassegrain. Indeed it is a great lunar and planetary scope. Great for visual and if fitted to an EQ mount the eyepiece will allways be in the right place. The problem with using newts on an EQ mount is that the eyepiece can end up in some very awkward positions. Not a problem for AP though

I’ve found that the CC is sharper on axis than a mak or SCT..

Edited July 26, 2021 by johninderby

[johninderby]

TS 8” Classical Cassegrain and Tecnosky 125. 🙂🙂🙂

Edited July 26, 2021 by johninderby

[vlaiv]

2 minutes ago, Kram said:

Thanks for replying. I’m using a 127mm sct at the minute. But I’d like to see the planets more clearly. Mars is barely visible. Jupiter and Saturn are nice but very small. And I’d like to take some photos

8" CC is very good instrument for planetary and for imaging.

Do bear in mind that for best images you need to use special technique that requires dedicated camera - planetary type camera and special processing. It is so called "Lucky" type planetary imaging.

Mounting such instrument on EQ class mount is a bonus for observing as it will track the target and you won't need to nudge the scope every so often. Just keep in mind that you'll need larger mount than for Mak127 as this scope is heavier.

Low cost alternative that will give you very good planetary views would be 8" F/6 dob mounted newtonian. Drawback is that it is manual tracking and you can't really do photography on it.

[Kram]

Would this mount be good enough?

[johninderby]

For visual you would just about get away with that mount if it’s an EQ5 for the 8” CC but just not strong enough for AP.

Edited July 26, 2021 by johninderby

[Kram]

If I add some more weight would it help?

[Kram]

Will this do everything I’m looking for? I think that might be my final question 

[vlaiv]

22 minutes ago, Kram said:

Would this mount be good enough?

I can't be completely sure but that looks like EQ3 class mount. I think you need something with more payload capacity to carry 8" CC

19 minutes ago, Kram said:

If I add some more weight would it help?

No. Adding more weight will help balance the scope - but it won't improve mount stability. Views will be shaky and overall experience not so good. You really want something in EQ5 or higher class for scope that is alone something like 8.5Kg and with accessories can easily get up to 10kg.

22 minutes ago, Kram said:

Will this do everything I’m looking for? I think that might be my final question 

Probably yes, but I'd like to advise you to check few things again before you decide on purchase (just to avoid being dissatisfied by new scope).

1. Did you check collimation on your old scope?

2. Did you let it cool before observing planets?

3. Did you optimize your observing session - did things like - avoid viewing over large bodies of water, houses or anything that absorbs heat during the day

4. Do you know how to spot poor seeing and recognize good seeing?

5. Did you optimize exit pupil / use right eyepieces for the job?

There are a lot of things that go into having a good planetary session. If everything is done properly, then yes, larger and better scope will give you better views, but not all the time as much depends on conditions.

You really need to manage your expectations. It is very easy to find very large and detailed images of Jupiter, Saturn, Mars online these days, but that is not what you'll be able to see thru the telescope. Jupiter will be about the size of pea held in hand in front of you. Not larger than that. You can make it somewhat larger - but it will be blurrier and that is not necessarily what you want.

In ideal conditions - difference between 127mm and 200mm scopes on planetary will be less than twice, but most of the time - both scopes will be limited by atmosphere and will show roughly the same view.

If you understand all of the above - then yes, 8" CC will give you very good planetary views and be very good platform for planetary imaging with appropriate gear (dedicated planetary camera, tracking mount, laptop, etc ...).

 

[johninderby]

Yes as above you need to think about what it is you want from the scope. While I think the CC is a great scope it is a bit of a specialist but if it is for lunar planetary use and you have a mount that will handle it then yes it could be the right scope for you.

[rl]

It might be worth managing the op's expectations here...Regardless of the scope choice Mars will still be miniscule until the next opposition. For a considerable outlay,  Jupiter and Saturn will be slightly less small and showing a bit more detail. Since both are fairly low at the moment, the seeing may well be the limiting factor rather than the scope. 

Your EQ5 mount would not normally be considered stable enough for general long-exposure photography but you might well have some success doing lucky imaging of the bright planets where slow movement of fast exposures around the frame is less important, and removed on stacking.  Planetary cameras with a high frame rate are not expensive by the standards of this hobby. 

Maybe it's worth going to a local society and having a look through someone else's scope, certainly before committing to a Classical Cassegrain. The Skywatcher 200 PDS is a good choice for a medium-large general purpose Newtonian but it's probably not the easiest way to start photography. Most people start with wide field deep-sky with a small fast refractor. 

If you are thinking of deep-sky photography, the usual advice is to concentrate on the mount and guiding rather than the scope!

[vlaiv]

This is what Jupiter usually looks like in my 8" dob at x200 power when the seeing is decent:

(viewed from about half a meter at 96ppi device).

 

[jetstream]

2 hours ago, Kram said:

And I’d like to take some photos

Research what is needed to do this IMHO, you might end up with 2 scopes, one for visual, one for planetary. There are scopes that will do both. Personally I like low central obstruction dobs for most things.

Thing is your "seeing"- if its typically poor then there are scopes that can deal with it better than others, if you get bursts of good seeing frequently more aperture will give the views you want.

If you compound poor seeing with slight miscollimation in a hard to cool SCT (etc) the views will be horrible.IMHO.

Edited July 26, 2021 by jetstream

[Cosmic Geoff]

I have a 127mm Mak and a 203mm SCT, and I can confirm that the 203mm SCT gives significantly better views and planetary images - but only if the seeing is good.  I have largely dropped visual viewing of the planets in favour of imaging (lucky-imaging) which gives a permanent record of detail one can otherwise only glimpse in moments of good seeing, and in practice the images show more than I could see visually.  I find that the mount is not critical for this, as even the SE mount (adequate for visual, awful for imaging) will deliver good results.

If you are purely interested in visual viewing of the planets, a Dobsonian Newtonian would be the cheapest choice.  For planetary imaging, until recently a SCT would be the tool of choice, but the Classical Cassegrain seems equally suitable, is competitively priced and is getting good reports from early adopters.   Note that the CC is heavier than a SCT of the same aperture, and would require a serious mount, probably costing a serious amount of money.

[Kram]

Well thanks to all of you. Plenty to think about now. I’ve used the sct for a couple of years with a few different lenses and learned early on to let it cool down outside for a bit before using it. Also the later I used it the better the views I got as planets being higher and generally cooler outside. I’ve had some excellent views of Jupiter and Saturn and the moon never disappoints. But I can’t get good photos (I’m using an iPhone with a bracket to hold it in place 🙈 I know). I do have a Sony a6000 and haven’t tried to rig it to the telescope yet. As good as the views are I feel like I just need a little more power. But then if I upgrade will I feel the same?  Maybe I dunno. I’m not sure if there are any clubs near me but I’ll try to find out because I absolutely could do with some guidance and looking through some other scopes would surely be a massive help. Once again thank you all

[jetstream]

4 hours ago, Kram said:

I do have a Sony a6000

I think something like the ASI 224 might be better, @vlaiv can explain.

[Kram]

1 hour ago, jetstream said:

I think something like the ASI 224 might be better, @vlaiv can explain.

As it happens I was looking at those wee cameras today. Definitely more suitable than sticking a dslr on the ts. I was leaning towards that being my first move before I change my telescope. 

[vlaiv]

9 hours ago, Kram said:

As it happens I was looking at those wee cameras today. Definitely more suitable than sticking a dslr on the ts. I was leaning towards that being my first move before I change my telescope. 

If you want to take images of planets than only feasible approach is to use so called Lucky planetary imaging. It consists of shooting a bunch of very short exposures (practically a video) and then selecting sharpest / the least distorted subs and stacking them. With some further processing like sharpening one can obtain decent results.

ASI224 is one of the best cameras for this.

[Stu]

16 hours ago, Kram said:

As good as the views are I feel like I just need a little more power.

What sort of magnification are you using? It’s not always the case that a larger scope will take higher magnification, but it should show you higher resolution/more detail.

I’ve often found that larger scopes can be disappointing on planets because the seeing doesn’t support higher power views in them, so a smaller scope can be better. In good conditions, larger will win but it’s a balance with many factor involved as Vlaiv says.

For example, I’ve had nights where my 4” apo has shown better views than my 8” f8 dob, but that was because the seeing wasn’t great. On great nights, the 8” beat the 4” quite easily and took higher power (x360 vs x300 on Mars).

[Alan White]

@Kram do be aware Mars will be tiny presently its not well placed for observing, you missed its close approach.
But this has been said already.



 

Edited July 27, 2021 by Alan White

[Alan White]

13 minutes ago, Stu said:

I’ve often found that larger scopes can be disappointing on planets because the seeing doesn’t support higher power views in them, so a smaller scope can be better. In good conditions, larger will win but it’s a balance with many factor involved as Vlaiv says.

For example, I’ve had nights where my 4” apo has shown better views than my 8” f8 dob, but that was because the seeing wasn’t great. On great nights, the 8” beat the 4” quite easily and took higher power (x360 vs x300 on Mars).

Stu has hit it on the head, seeing can be the real issue, my 4" scope delivers small sharp images most of the time, when it does not its the seeing.
My 10" shows bigger images, sharp when conditions allow a 10" to shine, which for me is far less often than the 4".

[jetstream]

On 26/07/2021 at 07:26, Kram said:

I’m using a 127mm sct at the minute

You should see @vlaiv lunar images with a small Mac.... excellent.

[Louis D]

You can always use an off axis aperture mask on a larger reflecting scope to see if the image improves.