Mak frustration!

[recceranger]

I had great clear skies last night and gave the Mak a run out.  Report below!

 

Ok, after all my who ha about my new Mak 180 pro I finally got it out tonight for a full first light test. While waiting for the moon and Jupiter to come into my FoV I targeted Rigel, some of M45 and the Orion Neb. 

 

On adjusting focus on Rigel I couldn't get that razor sharp focus that I can with my ED80. In fact no where near. So I tried another few bright stars higher up from horizon including some of M45. Again focus wasn't at all what I expected. I have heard so much about the mak and how it's very near to an APO so I was a little surprised. At the start of the session (and it was very frosty!) for a period of around 10 - 15 mins I realised I had forgotten the dew shield. Perhaps this was the cause for lack of focus.

 

As soon as Jupiter came online I locked on. First impression was disappointing as once again I couldn't quite get that sharp focus and the legendary Mak contrast was nowhere near my ED80. This was on the 24mm Baader Hyperion so I tried my SW Click stop zoom. As soon as I went below 18mm all contrast was lost! Not exactly killing planets!

 

On observing the moon all was well at low mag i.e. 28 - 24mm but on increasing power again contrast left the building.

 

I must say that I was really looking forward to getting the Mak out as the reviews are fantastic but it's not the experience I'm having. My Q is could all this be as a result of initially not using the dew shield? Or would it be an issue with the scope?

 

I have looked long and hard at the primary lens and mirror and can see nothing wrong. However, other Mak users are posting great images using Barlow lens etc. when I tried a Barlow contrast disappeared!

 

Can anyone for a little advice as £700 odd quid doesn't grow on trees!

 

Rick

[Mikea]

Did you allow some time for cool-down?

[F15Rules]

Hi Rick,

Maks are very susceptible to temperature variance and a big scope like your 180mm will need at least 90minutes to cool down if you take if from a warm house to the outdoors (it was very cold last night). Do you keep the scope indoors? If so, it will take probably up to 2 hours to reach thermal equilibrium. That's why a lot of Mak users leave their scopes outside for at least an hour before trying to use them properly.

The dewshield can help prevent dew on the corrector lens, and can improve contrast (the way details "stand out" visually), but won't affect the focus of an object one bit.

I'd say that it's 99% likely to be just an issue of insufficient time to cool down properly. One trick that can help the cooldown a bit is to point the scope down at the ground and lock it in place...then, with the diagonal end pointing up to the zenith, remove the dust plug or eyepiece from the diagonal and the warmer air inside the tube will rise up and escape that bit quicker. Try it, it does help.

Good luck with getting the views you were hoping for!

Dave

[scoobee]

Was the scope cooled down enough?

It’s important that your mirror be at the same temperature as the evening sky. If it’s not, you’ll have difficulty focusing the image because the mirror will be minutely flexed due to thermal differences

[Earl]

The 180 really needs to be well cooled and this can take in excess of 2 hours if going from a warm house to outside, if you can keep it stored in a cool place this will help loads.

[nightfisher]

Gotta be cool down, also you can do a quick daytime collimation check, see this link     http://www.robincasady.com/Astro/myimages/collim.html

[Stu]

I agree with all the above. My Mak can be a fickle beast, wonderful when working well but a pain in the backside when not. Cooling is key, I use the built in fans, and also one in the diagonal to draw the warm air out of the baffle tube for a long time before use.

A dew shield and dew strips are pretty essential most of the time, the corrector plate can fog up both internally and externally if you are not careful.

Stick with it, I'm sure it will reward you with some lovely views.

Cheers,

Stu

[Grotemobile]

Thanks for that link.I have got the C11, & it

takes hours to cool down.The main problem is

dew with this scope.A heated band is a must.

Steve

[Helen]

Looks like we're on this journey together and have both had a bit of a faltering start!  I'm hoping/expecting cooldown and poor seeing was my problem last night.  I had colours and wobbling and unsharpness.  But I was also trying to use too high magnification to start with too - over 350x!!

When I get a bit of time (once this piece of work I should be doing now is finished!!) I'll give the scope a proper once over just to check that nothing has come loose in shipping, check the collimation etc.  (It was well packed and nothing looks or feels immediately wrong.)  But the weather is looking pretty hopeless for another night-time test for a while.  

Helen

[recceranger]

Cheers Helen.

Yes, defiantly share updates.  I had all the same issues.  Another 180 pro user mentioned a link called Earth Wind which stated the jet stream was right over Uk last night.  He is experienced using the mak and said that although at a glance seeing was good, in reality the F15 would play havoc with the image.  He never even attempted to use his as it was futile.  This explains why I had no issues with the ED80 (F7).  As soon as we both pushed our Maks to high mag we lost the war!

Pretty sure I learnt the lesson on the dew shield though!

Rick

[Steve Ward]

Mine was out briefly on Jupiter last night , cooled for a couple of hours first but the jetstream made viewing impossible , and was no better at 11:00am when I nearly aborted my Solar shoot because of it ... 

How it sits at the moment ... !

[Macavity]

The focal length is 2700mm: An eyepiece of f < 18mm is already a magnification of 150+

I know, I know, "it should...",  but I think I am more appreciative of "seeing" limitations now?

Even with my f=1800, Mak 150, I mostly used a Hyperion ASP 31mm (60x) & 17mm (105x).

I'm thinking of getting the 10mm (180x) - I rarely bothered with 8mm (225x) - just too "soft"?

On the other hand, I found the Hyperion's (idem the Zoom?) long ER a bit tricky with small 

"exit pupils". Something to do with all that glass in the eye lens? For higher powers maybe

a dedicated short ER "Planetary Eyepiece" might be easier? I can remove my glasses etc.  

That said, even on nights of lousy seeing, the (boiling!) MOON at "stupid powers" is fun.

[Steve Ward]

I must admit to pushing it even on those 'bad seeing' nights , for those very fleeting moments of clarity it's worth it .... 

[recceranger]

Thanks all,

The image really softened out and lost contrast as I used 20 - 18mm EP or below.   Though I suspect its more to do with seeing conditions and possibly a little dew on the primary.  The scope itself is most probably fine and I certainly can't find any problem.

Rick

[nightfisher]

Very interesting regarding the jet stream

[Steve Ward]

Link to the site here Jules ... 

http://www.netweather.tv/index.cgi?action=jetstream;sess=

[John]

Interestingly, I was out with my ED120 refractor last night and, in between the clouds and even the occasional short shower, I thought the views of Jupiter about as good as I've seen for quite a while. I stuck to 150x and alternated between the Ethos, Astro Hutech and Baader Classic ortho in the 6mm focal length.

Maybe the smaller aperture was better suited to the conditions last night ?

[recceranger]

ED120, a great scope.  Frac's do this business.

[Steve Ward]

Had both the ED80Pro and ST120 on the Sun this morning and the view made me seasick the disc was wobbling that much , so I don't think the Mak was to blame last night ... 

[chiltonstar]

I had my ED80 and my (small) Mak (5") out here last night. Viewing on Jupiter with the Mak and the ED80 was reasonably good (nice GRS transit) but not up to the standards of a week ago.

A problem I have found with my Mak which you may well have as well is hand contact; if I carry the Mak to the mount, it warms the tube enough to give me grief for 30 mins or more. I've tried gloves, but they are too risky, and have instead mounted a separate dovetail rail as a carrying handle to avoid hand contact.

Chris

[John]

A couple of things in favour of refractors are i) that your body heat is well away from the tube and ii) that light has to make just one pass through the tube to reach the eyepiece.

On cold nights I can put my hand on the side of the tube of my dob and, looking at a de-focussed star,  see the warm thermals from my hand percolating through the tube and into the light path. Remove my hand from the tube and it stops straight away. 

[Bobcat918]

Hi John,

This might be a DIY project worth looking into.  Attached is a cooling device built from computer, telephone, plumbing parts and silicone sealer.  The cable and battery are not included in the pictures.  The cable is standard telephone wire that clips into the jack on the side of the device (I hope this points to the pics).

I attach this device to the visual back where the diagonal fits, secure it and then position the scope to point the visual back to azimuth.  The fan is connected to the battery so that it draws air from the OTA not into the OTA to help prevent debris entering into the OTA.  The device is sealed to help draw warm air from the OTA rather than just stir air around itself.  I don’t have data to confirm or deny its effectiveness.  Subjectively the equilibration period seems shortened.  On the other hand, it might be that I’m not watching the scope to equilibrate.  As you know time seems to stand still when waiting for water to boil. 

One more little bit of information that may prove useful.  I read an article on the Cloudy Nights Site regarding the benefits of prism and mirror diagonals.  Slower (high f/#) scopes, like the Mak, may benefit using a prism diagonal.  Some manufactures include the prism diagonals because their design leverages the optical property of the prism to address spherical aberration in the case of the Mak’s and chromatic aberration in the case of refractors (especially the achromatic type).  Mirrors are the preferred diagonal for faster scopes.  Just some information to experiment with.  I’m going to try it when sky’s clear next week to see if there is any perceptual difference.

[ronin]

As you compared what you saw to peoples images I would also suspect that during the processing they are sharpened. You have to consider that any image has been processed and quite likely for some time. Also it is rare that anyone posts the images that didn't come out. If you want a laugh get to one of Nik's talk where he shows the ones that went wrong.

I would advise that any visual and imaged results are not actually a valid comparison.

Optically a Mak has enough bits inside that contrast will suffer, think they are worse then a newtonian reflector for this.

[Bobcat918]

I have a correction to make.  The text 'position the scope to point the visual back to azimuth'  should be  'position the scope to point the visual back to zenith'.  Sorry about that.  It was 2:00 A.M. Central Time (CT) when I made the reply.

[Bobcat918]

I found more pictures of the fan unit.  I hope this gives a more complete concept of the unit.

I agree with White Dwarf and I am skeptical of the claim by retailers that Mak Cassegrains deliver APO like views.  The claim may be true of high-end Maks Cass like Alter, Intres, Quasar, Astro Physics and the one Meade LX200 180 mm Mak Cass, etc.   Mak Newtonians are another subject but some good accomplished armatures swear the Mak Newts deliver APO views.  

This is a bit out of  the scope (pun not intended) of the forum topic, but I am passionate about retailer claims and what is actually delivered.  My apologies in advance.  

I fell for this line because as a refractor user (first scope) it was a key requirement I hoped to achieve with larger aperture on a tight budget.  The claims of retailers regarding the performance of their Mak Cass was a good fit.  I did not know about about the trade-off's (there are always trade-off's).  The scope I purchased was listed at a reputable and popular telescope website with the Konus brand.  When I needed parts, Konus was not able to help.  My research identified the manufacturer as Bosma Optical in China.  Bosma was more interested in exports, no help there.  The scope quality is good  (not APO however), The eyepieces are good, the finder scope was trash, and mount needed overhauling but now performs acceptably.  This always leaves a bad taste in ones mouth on a new purchase.  So, why did I not just return it?  It was not 'bad' enough to return and I was open to the possibility that it was my lack of experience, which in fact did contribute to my frustration.  Time passed and the scope has grown on me.  I overcame the initial disappointment and now I use the scope regularly and enjoy the views and its not bad splitting double stars.