New Scope for Planetary Observing

[David Smith]

I'm considering a second scope for planetary observation, specifically a 120mm frac (either Celestron omni or Skywatcher Evostar). All I have read on SGl seems to indicate these are good scopes with acceptable levels of chromatic abberation.

My question is how will planetary images with these scopes compare to what I currently see with my 250mm dob? I seek to see further detail in targets such as Jupiter and have been quite dissappointed with my scopes performance on Venus this year.

If this is not going to give me that extra detail then i might have to consider a bigger dob.....350......400 but that will require additional pennies.

Any thoughts comments and especially experience welcomed.

Thanks

[iwatkins]

Have you considered a big Mak or SCT? Longer focal lengths = bigger planets

Cheers

Ian

[David Smith]

Good point, hadn't considered that. How big is a "big Mak or SCT"?

[laser_jock99]

Have you considered a big Mak or SCT? Longer focal lengths = bigger planets

Cheers

Ian

Yeah I'd be thinking along the lines of a C11 for planetary work. Something like 2800mm focal length, lots of resolving power and no chromatic abberation. Put it this way- there's a C11 or C14 on my wish list!!

Celestron Advanced C11 OTA XLT Schmidt-Cassegrain (CG-5 dovetail).

[Dave Dubya]

I would think something like the Skymax 127, or the Celestron equivalent, would have a longer focal length than those refractors, and probably are in the same price bracket.

[Moonshane]

I had a 120mm f8.3 Celestron OMNI refractor. it was nice but the CA on Jupiter in particular bothered me. I bought a 12" dob and the views were completely different and far better. personally, I'd be astonished if you get better views with the refractor. I suspect you'd get better views with a 6" SW dob as this has an f8 focal ratio. My 6" f11 gives really superb views albeit not as good as my 16" masked to 6.7" f11.

[David Smith]

C11 or similar would be fantastic, realistically though out of my price range. 127 mak on the other hand is priced similar to the omni I was looking at. Nothing is out of scope (excuse the pun) here, just want to ensure I get a noticeable improvement in the image.

Probably should also have mentioned that the scope will need to come with a mount.

[hunterknox]

I'm a big refractor fan but honestly: either of those refractors would be a step down from your dob. If your collimation is good and your scope is at ambient temperature it's unlikely that you'd get a better view of Venus throught a smaller scope - it's a tricky planet at the best of times. Save for a bigger dobsonian. You won't regret it.

[David Smith]

Moonshane, hunterknox - That's kind of what i expected people to say.

[Caldwell 14]

I had a 120mm f8.3 Celestron OMNI refractor. it was nice but the CA on Jupiter in particular bothered me. I bought a 12" dob and the views were completely different and far better. personally, I'd be astonished if you get better views with the refractor. .

Any problems with star spikes at all?

[iwatkins]

There is always the 150 or 180 Maks.

I won't be without my 180Mak, 2700mm FL

All depends on your budget really.

Cheers

Ian

[Moonshane]

Any problems with star spikes at all?

they are there (apart from with the 16" f4 masked off) but I look at the planet not the spike.

[Stu]

I get great planetary views with my omc 200, 4000mm focal length

13mm ethos gives x307 which is incredible for those very stable nights with good seeing. Best ever views of Saturn were with this scope. Collimation and cooling are very important to get right. I imagine the 180 is not far off in terms of planetary performance.

I've been getting great views through my 4" apo recently, it is just such a reliable, easy scope to use and gives plenty of detail with no CA.

I agree with the other comments that you won't see a benefit from the two fracs you mention, I would think the 250 should be pretty good if collimated and cooled well?

Finally, I've never found Venus very rewarding, all you can ever really see is the phase, and it often just looks a colourful mess looking through all that turbulent air! Doesn't really matter what scope you use, it's the same.

Stu

[David Smith]

Thanks all for your comments. Think I will hold off and turn a critical eye to my dob's collimation etc.

[catburglar]

I had a 10 inch dob and never got satisfactory planetary views, yet I know that others are very happy with them. For me, even when collimation was spot on it was frustrating:

• Difficult to achieve critical focus at F4.7 with the single speed crayford
  
• Difficult to track smoothly at high magnification
  
• Diffraction spikes were always distracting on brightest objects
  

I had better views of Mars with an 80mm ED, I think simply because it was more user friendly in respect of the above issues.

This week I plumped for a SkyMax150, and first night out was last night. Had the sharpest views of Mars I've had. Obvious surface markings at 120x and even better at 250 in reasonable seeing. The scope is fairly small and sits easily on an AZ4, no diffraction spikes and easier than the dob to get sharp focus.

It's early days, but I'm pretty happy so far.

[A McEwan]

I know it's slightly off-topic, but I find a very small aperture (60mm or 80mm) better for Venus - seems to beat the seeing and atmospheric dispersion a bit better than larger apertures, resulting in a sharper image. For me anyway...

Ant

[David Smith]

I had a 10 inch dob and never got satisfactory planetary views, yet I know that others are very happy with them. For me, even when collimation was spot on it was frustrating:

• Difficult to achieve critical focus at F4.7 with the single speed crayford
  
• Difficult to track smoothly at high magnification
  
• Diffraction spikes were always distracting on brightest objects
  

I had better views of Mars with an 80mm ED, I think simply because it was more user friendly in respect of the above issues.

This week I plumped for a SkyMax150, and first night out was last night. Had the sharpest views of Mars I've had. Obvious surface markings at 120x and even better at 250 in reasonable seeing. The scope is fairly small and sits easily on an AZ4, no diffraction spikes and easier than the dob to get sharp focus.

It's early days, but I'm pretty happy so far.

Interesting, I find diffraction spikes distracting as well and this was part of my reason for considering a refractor specifically for planetary obs.

[catburglar]

I considered a C6 or C8 as well as the Mak 150 and 180. The larger scopes are probably a bit too much for my mount, so went for the Mak150 just because it is ready to take 2 inch EP's and has a better optical finder out of the box.

I'd suspect there's not a lot between either Celestron SCT's or the Skywatcher Maks in optical terms, and from first impressions can certainly confirm there's a lot of planetary detail to be seen with a 6 inch scope.

[A McEwan]

Not that I actually "need" any more scopes, and all mine are already good (or excellent) planetary performers, but I could possibly be tempted one day by one of these: 152mm (6-inch) Maksutov Cassegrain (OTA only) - Astronomica

Ant

[John]

Not that I actually "need" any more scopes, and all mine are already good (or excellent) planetary performers, but I could possibly be tempted one day by one of these: 152mm (6-inch) Maksutov Cassegrain (OTA only) - Astronomica

Ant

As a big refractor fan I was very taken by the performance of the Intes 6" mak-newtonian that I owned for a while before I got my ED120. Cool down time was longer than a frac but the planetary / lunar performance was really superb

If you can handle the cooling and mounting requirements, a 7" mak-newt would give you 6" apo refractor performance for much less cost, I reckon.

[Gina]

I think I'll probably go for the SkyMax 127 later on when my funds have built up enough after buying the other things I want. Meanwhile, I'll see how I do with my ED80 and MS LifeCam webcam. Might get an IS camera for planetary. Not really sure whether another scope or another camera would be the next step in the planetary field. Camera is certainly the easiest.