Maxvision 28mm 68degree first light

[Reeny]

Once I had collimated the scope to get rid of some starbursts and astigmation from the 24mm, it was 3-months before I noticed any issues with the view from the MaxVisions.

It was only at the edge, and you really had to look for it.

I have been using the Explore Scientific 82-degree tonight, together with the 16mm MaxVision.

Both of them performed well in the dob.

When Jupiter gets near to the edge I normally nudge it back again anyway, instead of refocusing.

Dew was going to be a bigger problem tonight.

[wolfpaw]

Once I had collimated the scope to get rid of some starbursts and astigmation from the 24mm, it was 3-months before I noticed any issues with the view from the MaxVisions.

It was only at the edge, and you really had to look for it.

I have been using the Explore Scientific 82-degree tonight, together with the 16mm MaxVision.

Both of them performed well in the dob.

When Jupiter gets near to the edge I normally nudge it back again anyway, instead of refocusing.

Dew was going to be a bigger problem tonight.

To be fair I think that's entirely to be expected in a 200P. By almost all accounts the Maxvisions perform very well in a f6 telescope along with many other cheaper eyepieces. But the increase in potential coma between f6 and f4.7 is significant. What only appears "at the edge" in the f6 will rapidly start to move towards the centre of the field of view in an f4.7. It is inevitable which is why I find claims of the Maxvisions being aberration-free, edge-to-edge, in a fast telescope difficult to believe.

I'm not an experienced observer by any definition but in my f4.7 the coma is very apparent in both the MV16 and MV24 (the 16mm is worse in this regard) and not just at the edge of the FoV.

An f6 telescope and an f4.7 telescope are quite different beasts and shouldn't really be compared.

[michael.h.f.wilkinson]

Coma from the parabolic mirror needs a coma corrector, and depends almost entirely on the apparent FOV of the EP. A Nagler will show more coma in a Newtonian than a 68 deg EP. In terms of coma, a MaxVision 24 mm 68 deg EP will show the same amount of coma as a Panoptic 24mm.  Astigmatism introduced by the EP is the main issue that will distinguish those too, and that depends mainly on the focal ratio of the scope. A Nagler will most likely show less astigmatism in a coma-free F/5 scope than the 68 deg MaxVisions.

[wolfpaw]

There's an interesting comparison review here, comparing 24-26mm 68 degree EPs, including Meade 5000 SWAs/Maxvisions.

http://www.cloudynights.com/item.php?item_id=2729#_Toc317169034

One of the scopes used was an Orion XT10 with a focal ratio of f4.7, the subject being NGC869 in Perseus. The reviewer concluded that:
 

without a TeleVue Paracorr in place on the fast optics of the Orion XT10’s f/4.7 mirror, coma obscured the central asterism of NGC869 sufficiently to make it unrecognizable only 50% from center FOV to the field stop in almost all the eyepieces

The use of the Paracorr (not surprisingly) removed the coma almost completely from all of the EPs. The moral of the story is that without a coma corrector aberration will be present in a fast telescope across a significant part of the field of view.

[jetstream]

It must be said that in BillP's test he looked at the object ngc689 off axis and his method was to move 25% from center to field stop,50% etc and then look over to the object.With my f4.8 dob if I center an object and look straight at it with different EP's most look great,with very minimal aberrations.The one I plan to correct is the 21mmEthos-my 17mmEthos,18mmES 82,16mmNagler are all fine.When I look off axis I try to just move my eye to see,not moving my head at all because head movemen't can really cause "flare ups".

My f4.8 dob has never shown aberrations as you describe on Jupiters moons,and seeing as your other EP's show less aberrated stars,moons etc sounds like you just need to get another EP in that FL that is known to be well corrected......after you have confirmed your COLLIMATION is on.What does a star test show with the 16mm MV?Coma,astigmatism,pinched optics...?http://www.telescope-optics.net/diffraction_pattern_and_aberrations.htm

[wolfpaw]

It must be said that in BillP's test he looked at the object ngc689 off axis and his method was to move 25% from center to field stop,50% etc and then look over to the object.With my f4.8 dob if I center an object and look straight at it with different EP's most look great,with very minimal aberrations.The one I plan to correct is the 21mmEthos-my 17mmEthos,18mmES 82,16mmNagler are all fine.When I look off axis I try to just move my eye to see,not moving my head at all because head movemen't can really cause "flare ups".

My f4.8 dob has never shown aberrations as you describe on Jupiters moons,and seeing as your other EP's show less aberrated stars,moons etc sounds like you just need to get another EP in that FL that is known to be well corrected......after you have confirmed your COLLIMATION is on.What does a star test show with the 16mm MV?Coma,astigmatism,pinched optics...?http://www.telescope-optics.net/diffraction_pattern_and_aberrations.htm

Surely if the collimation was off I wouldn't get good views in the centre of the field of view? As it is I can see a white 'marbling' effect in the dark belts of Jupiter's atmosphere, six stars in the Trapezium of M42, the Rigel double, etc.

[jetstream]

Well if other EP's work and the 16mmMV doesn't-get a different eyepiece.If you are just on the "edge" of the coma free "sweet spot" after collimating weird things may show up.The link to the aberration was given to help you track down the source of the problem,might have provided you with some evidence for you to get your money back on the 16mm and also may have shown any problems with your optics.I guess your either gonna live with it,get another EP or get a different scope-me I'd try a different EP.Here is a good article on collimation,read down to the 'what happens if the scope is not collimated" paragraph-even if not your problem it's interesting http://www.cloudynights.com/item.php?item_id=2677,I hope you get the issue resolved.

[AlexB67]

When I look off axis I try to just move my eye to see,not moving my head at all because head movemen't can really cause "flare ups".

That's' very good point.  I wonder wolfpaw  there are some slight issues trying to get used to the eyepiece ? . In the end I don't deny there will be coma, but just find it hard to rationalise, it  seems somewhat extreme what you described in the other thread.

The sketch of the jupiter moon could be flare ups ... possibly.   With that  in mind I did some test again to see if we can help a bit, so I started deliberately rotating my head a bit in various directions, and indeed I could notice the flaring up in my 28mm and made it happen quite easily, it just goes to show once you get used to an eyepiece and position you head in a certain way these things do not become issues, so I had not considered it much as being a potential part of the problem.

I did not really compare to another eyepiece at the time, but  another way to get some iffy results, this can happen quite easily, if you do not tighten the 1.25 inch or 2 inch tube properly in the SW focuser, the eyepiece tilts a bit and the stars deform badly too, it does not take much tilt for that to happen.

Perhaps some little things to play with the MV eyepiece and experiment,  given that you mention you find your basic plossls more satisfactory which I also find a bit hard to understand ( I assume you don't just mean because of the narrower FOV) . 

I would have a play with the twist cup and set it in such a way you can just see the entire field stop just, try taking in the whole view with a good eye point and keeping check on the flaring when you change your positioning.  

Perhaps you have it all covered and these are not the problems, so sorry if I am just stating the obvious you have already checked.

Not doubt a coma corrector is nice and will address coma and that is a good thing, I don't deny that, but once you buy that coma corrector and go that route, you will want to be fairly sure you are addressing the issues to make sure only coma is the problem that really annoys you.   The last thing you'd probably want is to find you are still not happy with the results a CC may give you.  There still may be an issue with the eyepiece of course, perhaps you do have an iffy mirror or something else. 

Hope that eventually you can get it sorted to your satisfaction

[jetstream]

Alex,good point about tightening the "tube" correctly.My own dob with its 1 3/8" extension needs to be checked as the compression rings can "[removed word]" the extension and wreck my secondary colli.My 2" sight tube indicates this as well....I can collimate perfectly,take sight tube out,put back in,re-check...off again!What I found is that to have repeatable collimation is tighten the screws in a certain order that keeps the crosshairs in the dot,and then tighten the extension in the same manner.I should really get a 1.25" sight tube/cheshire to check the extension,but my views are very good,with high resolution.

If this misalignment existed at the same time as being on the edge of the sweet spot in primary collimation who knows the effect?