Jupiter with a Frac & a Mak

[PaulG]

Last night I had the opportunity to view Jupiter with my 70/900 refractor and my 127 Skymax. I was swapping eyepieces from one to another for the limited 30 minutes that Jupiter was in view. Magnification was 90x on the refractor and 75x on the Mak.

The view was slighty brighter in the Mak and I could see both main equatorial belts in both scopes with about the same amount of detail which was twin faint horizontal belts (very subtle).

I have to say the overall detail was spoilt by the Mak because of the increased brightness which caused a bright-ish glow around the circumference of the planet. Slighty better contrast was achieved with the small refractor and did not exhibit the bright-ish glow.

I increased the magnification to 150x on the Mak but this made no real difference to any detail increase.

I then pointed both scopes to Arcturus and defocussed both scopes and found that the refractor gave less distortion (wobbly rings) than the Mak. I would say using the Pickering scale the refractor was "good to excellent" seeing and the Mak "Good" seeing.

I was expecting a little more detail from the Mak, I had left the Mak outside for a good hour and was also suprised how it performed against the refractor when looking at Arcturus.

Can anybody who has both a Mak and refractor comment on "do you find this par for the course" or is there something amiss.

It's my first look through both scopes, I hope the Mak can perform better looking at the Moon.

Paul

[philsail1]

Hello Paul,

Yes, I managed to get a glimpse of Jupiter last night (from up here in North Wales) for about an hour before the clouds rolled in.

Well, I can only compare my Skymax 90mm with the 100mm Tal100RS refractor. The Tal gives me better views of Jupiter than the Mak. Although my Tal does give an ever so tiny yellowish tinge to the planet. My 90mm Mak does seem to give a bright - but less stable view of Jupiter at the same magnification (100x) than the TAL. The Mak is far easier to use than the TAL.

I do get the most satisfyring views through the "Astro Engineering" "binoviewers" though. I find even using two 25mm eyepieces (with a simple skywatcher 2x Barlow) gives me a nice "3D" effect through the 90mm Mak and the TAL. (There's plenty of "in" focus in the Mak to use the binoviewers on their own, but with the TAL, I have to use the Barlow.

I think you will receive more replies soon.

Regards,

philsail1

[PaulG]

Hi Phil

Nice to see your getting clear skies if only for a short while, it's been pretty poor for too long Phil.

That Tal will take some beating Phil, I'm not too surprised it out shines the Mak. It has a solid reputation.

The binoviewer system would be the ultimate Moon killer, I have had a very quick look through one and was amazed at the strain free viewing sensation they provide.

I must admit the 127 Mak is rock solid on the EQ3-2, my refractor does exhibit focus jiggles. It's a must to have a beefy rock solid mount for a refractor.

Cant wait for the Moon to appear to test the Mak further.

Paul

[Woodsey65]

I'm doing a shoot out in my ezine soon between Vixen A70lf, Skymax 102 and WO Megrez 72FD quite soon and will also be published online, so it's interesting to read the comments here.

There will also be a test between the Skymax and the Explorer 130/900.

I nearly bought the 127 but read about cool-down times lasting hours, there's a lot of glass in those baby maksutovs!

Dave

[PaulG]

I'm doing a shoot out in my ezine soon between Vixen A70lf, Skymax 102 and WO Megrez 72FD quite soon and will also be published online, so it's interesting to read the comments here.

There will also be a test between the Skymax and the Explorer 130/900.

I nearly bought the 127 but read about cool-down times lasting hours, there's a lot of glass in those baby maksutovs!

Dave

Not sure what to think of this initial look through both telescopes. I'm just a novice trying to evaluate the performance on a visual basis (probably to justify the extra expense of the Mak).

I thought I left the Mak out for long enough (1 hour) maybe not ?.

It's early days yet, maybe I have a great performing refractor or a poor Mak.

Paul

[Woodsey65]

I don't think there's any problem with the Mak. They are usually reliable.

I do think (and there is much to support this) they can take ages to cool down. My 102 is great, but the light is folded up into a Z so there are three mirrors in a short space inc the diagonal, with a large central obstruction. So in effect a refractor does less with the light. However the engineering of the lenses play a great part in the image quality, and they have the fastest cool-down times.

Maks are the worst for cool-down, even SCTs are better as they use thinner mirrors, Newt's somewhere in between refractors and Maks up to 6", so I have read and experienced IMHO.

Every design is a compromise. Mine took 2 hours to ambient, I measured it with a non-contact temp meter. Left it in the Sun once for a photo shoot in 30 minutes, beeping hot! Won't do that again!

70mm versus 127mm with a central mirror? In theory you should see a big plus, but they both handle light in different ways.

All I can say is, Newton was one clever chap.

[russ]

Don't get too hung up on differing views of Jupiter. Last year (or maybe the year before) myself and Rob compared the views of Jupiter through his Skymax 127 and my ED80. Jupiter was almost as badly placed as it is this year. The view through the ED80 was surprisingly a match for the 127 Mak, perhaps a smidge better. We concluded, despite a 1.5hour cool down, that the Mak had still not cooled sufficently. This was proved correct an hour later when the Mak provided some great views of other objects.

Maks are the worst for cool-down, even SCTs are better as they use thinner mirrors, Newt's somewhere in between refractors and Maks up to 6", so I have read and experienced IMHO.

This is an interesting point but in my own personal experience i always found it the other way round. Using another comparison, again Rob and myself, this time we were using an ED100, Skymax 127 and a Celestron C8. It was a cold night so we expected cool down to be a problem. The ED100 was up to speed within 30mins, providing good views within 15mins and knockout views in 30mins. The 127 took again 2hours before it was providing good views. But we waited 3 hours for the C8 to finally outperform the others, and then it clouded over 15mins later.

All 3 scopes were brought out from a warm house into freezing temps. That C8 just didn't want to cool down. Perhaps a 5" or 6" SCT would cool a lot quicker, faster than the 127 Mak?

One thing is certain, 30mins is not enough time for a closed tube design (SCT or Mak) to cool sufficently and provide good views. Although on a warm summers evening it should be less of an issue.

Russ

[Woodsey65]

Thanks Russ,

Size for size SCT cool quicker than Maks due to thinner mirrors ( from the book Astronomy Hacks... an excellent read). Also different glass, like Pyrex cool quicker so I am led to believe, as this is why it's used on 8" LXD75 Newt's but not on the 6" which I have. My SkyMax 102 takes ages. and my 10" Dob has a fan on it, but I normally leeave it out for an hour before I use it.

Which C8 was it? The SCT?

[russ]

Just a bog standard C8 SCT. I think the key is - big SCT + warm house + cold night = nightmare

A C5 would probably cool faster compared to the 127 Mak but perhaps not too much in it.

I took delivery of a secondhand Skymax 150 Pro today, so i can report back on how a larger Mak fares. I imagine it will need hours and hours unless i stick it in the shed.

Regards

Russ

[philj]

Hi Paul, Im surprised that the Mak didnt give betetr performance. I have had a 127 Mak for years now and still consider it to be my best small lunar and planetary scope. The secret is, as already mentioned, if you plan to use it stick it outside for at least an hour before viewing to cool down. This will stanbilise the image no end. I once did a side by side comparison with my Mak and a Tak Sky 90 on Jupiter and the Mak shot the 90 out of the water, OK the 90 is not a planetary scope but an astrograph but I would have expected more.

Now as far as the circunferentila glow is concerned, this could be because of several factors:

How clean are the optics, both scope and eyepiece? Not just muck but dew. You will get the glow if your objective and or eyepiece are dewing up. Have you got a dew shield on the Mak? If not it will dew up and spoil the view as soon as the meniscus cools down.

If you have a shield but still have problems consider a dew heater.

Phil

[RobH]

Hello Paul,

My first thought when reading your post was the same as Phils', the glow is probably caused by dew....it doesn't take long for scopes to dew up at all, and the amount that would cause the glow you describe may not be easy to see in the dark.

Cheers

Rob

[Whippy]

I took delivery of a secondhand Skymax 150 Pro today, so i can report back on how a larger Mak fares. I imagine it will need hours and hours unless i stick it in the shed.

I hope not Rus, I keep my 6" Intes Mak in my overhang and the longest it's taken to get to equalibrium is about 45 mins. By all accounts those 150's are pretty darn good .

Tony..

[PaulG]

Hi Paul, Im surprised that the Mak didnt give betetr performance.

Snip.......

How clean are the optics, both scope and eyepiece?

Phil

Hi Phil

It suprised me too, I'm going to let the Mak cool down for longer next time round.

The scope and optics are spotless as its almost new.

I not seen any dew yet so I don't know what caused the bright-ish glow around the planet.

In the Mak the sky is not black like the refractor, it's lighter.

Jupiter and it's moons are brighter in the Mak but the detail is about the same in both telescopes.

It may be different when I get to looking at the Moon.

Paul

[russ]

In the Mak the sky is not black like the refractor, it's lighter.

I wouldn't say that was unusual. The refractor, especially at f13, has better contrast than the Mak. The background sky will appear blacker.

Jupiter and it's moons are brighter in the Mak but the detail is about the same in both telescopes.

Dew does sound a problem and it's hard to see without pointing a flashlight at the corrector. The Maks and SCT's only last a couple of minutes if it's a soggy night. I live in a particular bad area and have to use a heater every session. My night is over in 5mins otherwise.

Russ

[russ]

I hope not Rus, I keep my 6" Intes Mak in my overhang and the longest it's taken to get to equalibrium is about 45 mins. By all accounts those 150's are pretty darn good .

I hope not too Tony. We are putting up a new shed next week, was going to be the obs but that plan is scrapped. But i will permanently leave the scope and kit out there. That should drastically reduce the waiting time. Fingers crossed :?

[philj]

Quote

In the Mak the sky is not black like the refractor, it's lighter.

Jupiter and it's moons are brighter in the Mak but the detail is about the same in both telescopes.

It may be different when I get to looking at the Moon.

Unquote

Hi Paul

The Mak is around the F12 mark so should give similar to the refractor.

A cooled Mak should easily out perform the refractor see my Jupiter image below this was with the Mak127 with a Toucam and shows what can be done with them.

When you get chance pick your best eyepiece, give the Mak an hour to acclimatise, but not form dew, then pick a brightish star. Get the star smack in the middle of the FOV and then defocus it. If its correctly collimated you should have a perfect doughnut shape if not the scope may have been dropped and youve lost collimation. All is not lost though because this Mak is one of the few scopes of its type that has collimation screws on the primary mirror.

Phil

[PaulG]

Quote

Hi Paul

The Mak is around the F12 mark so should give similar to the refractor.

A cooled Mak should easily out perform the refractor see my Jupiter image below this was with the Mak127 with a Toucam and shows what can be done with them.

When you get chance pick your best eyepiece, give the Mak an hour to acclimatise, but not form dew, then pick a brightish star. Get the star smack in the middle of the FOV and then defocus it. If its correctly collimated you should have a perfect doughnut shape if not the scope may have been dropped and youve lost collimation. All is not lost though because this Mak is one of the few scopes of its type that has collimation screws on the primary mirror.

Phil

Hi Phil

I did test this with Arcturus in both scopes and had nice doughnuts in each. The seeing conditions in the Mak were not as good which seems to indicate turbulance in the tube. So I will try again and let the tube cool for longer next time.

Cheers

Paul