mak 150 trouble at high power

[theskipper1961]

Please more help required – I have been using my Sywatcher 150mm mak  with a 42mm revelation 2” eye piece which is very good , also my BST  27 mm however my 7mm Axiom lx is not much use and pushing the capabilities of this scope too far possibly  as indeed I was advised here that would happen ,

I do have a nice x 2 Barlow also which gives me 133 x mag but the scope does seem to struggle a little with this too However talking with Telescope house – 365 astronomy they advise me that this scope should be able to cope with the 7mm axiom lx Celestron under perfect sky conditions, something we don’t seem to get very often.

– I have checked comulation and this is bang on , I have also put my eye pieces direct into the scope

And see no improvement  so I am wondering now if its just that  I am strugeling to focus at high power  ? at lower powers the scope is amazing  using the 27 & 42 mm .

Your advice would be much appreciated on the Cray focuser attachments that are available and the pro’s and cons of these and if I choose to go down this route which one to buy.

Many Thanks Steve

[michael.h.f.wilkinson]

I would expect a 12mm EP (150x magnification) to work under decent sky conditions with one of these scopes. A 7mm would be pushing things. In my F/10 scope my 7mm does not see a huge amount of use. In an F/12 instrument, it would be roughly the same as a 6mm (5.8 really) which I can only use on the moon and in very rare cases Mars. Focusing can be an issue, and simply might require some practice.

[damnut]

hi Steve,

I have a 150mm mak also, using a 7mm ep would yield almost 260x. The theoretical linit for the scope is c300x. Even though the Axiom is a great ep ( I have the 10mm) at 7mm it would have to be in great seeing conditions.

Use the links below, plug in your scope data away you go.

http://www.stargazing.net/naa/scopemath.htm

http://www.12dstring.me.uk/fov.htm  (remember to switch to visual view)

[michael.h.f.wilkinson]

Another point might be that some EPs (especially wide angle) do not work that well with some Barlows. What Barlow do you have?

[Stu]

Can you describe the problem you are having in a little more detail?

I wonder if it is an issue with cooling and tube currents rather than anything else.

The scope should be capable of high powers and Maks can be a little picky if you haven't got the cooling right...

[michael.h.f.wilkinson]

+1 for the cooling issue. I keep my SCT OTA stored in a practically unheated garage for that reason. It is generally only 5 degrees above outside temperature in there. That means the scope is fully cooled down quickly when I go outside. You can see the currents in the tube if you look at the donut you get when viewing a defocused star. Tube currents can completely ruin the views

[Grotemobile]

Had a similar sort of problem with the C11.

The Moon looked like a shimmering

wave, sometimes,@ high power. Not cooled

down enough.

Steve

[theskipper1961]

Many thanks for you’re prompt replies.

The Barlow is a good quality 3 element  costing around £50.00 from 365 I believe it is from the same factory that produce the BST eye pieces  , I also leave my scope in its case in an unheated room next to my garage and generally leave the scope out side for at least 30 mins but generally 1 hr , I did at first think it could be the diagonal mirror unit ( unbranded ) causing my issues but the fact that putting the eye piece straight into the back of the scope solves nothing  rules this out I think ,

I have read here that the Revelation quartz diagonal is a good buy but I don’t really want to buy kit that will not improve my viewing experience , I was out last night on Jupiter  not good sky conditions from where I was so using the 27mm  BST gave me a nice image added the Barlow and this was not so good but there was wispy cloud up there I think , I went out last night just to check the comulation really the one thing I haven’t checked  is comulation of the mirror without the eye piece in I’m told you can do this / would this not show up through the eye piece if the diagonal was in some way out of line ??

I do know this diagonal has been stripped and cleaned by the previous owner; I have looked at it and the mirror look clean and in good condition

[Stu]

How does the collimation look?

I believe the best way to quickly check with a Mak is to put the scope horizontal and stand at the focal distance in front of it with your eye central. All the optical elements and reflections should be concentric. This is quite a handy test.

Maks can take longer than an hour to cool, and can have stubborn boundary layers of air internally and within the baffle tube. Do you use fans? How about a fan drawing air through the baffle tube via the visual back?

Again, can you describe what you see with stars when in focus? Tube currents making the stars look fuzzy and dance around, or just a stable image which won't focus?

[ronin]

Your 7mm will be giving 257x which will be a bit high at times. I also note that in general although the manufacturers say 2x dia that many people get nowhere near this when actually looking through a scope.

If the manufacturers all came out tomorrow and said 3x, do you actually think that the performance will change at the time of the announcement? One of the Celestron (I think) scopes is in effect saying 2.6x Dia now.

There a was a post elsewhere asking about eyepieces for planets and one replier listed their eyepieces at the "planetary" end, it was I think:

12mm, 11mm, 10mm, 9mm, 8mm, 7mm, 6mm, 5mm, 4mm, 3.5mm.

Basically your 7mm (257x) may not work, but an 8mm (225x) may, and if that doesn't then a 9mm (200x) better chance still.

You are looking at 1mm differences making a significant change. You may simply have stepped over a performance threshold with the 7mm and an 8mm may be fine.

Concerning the barlow not producing a great deal better the barlow has to work with the scope and with the eyepiece, when you consider it neither scope, barlow or eyepiece were designed to operate specifically with any other item, they are all a bit of a compromise when combined.

Also what do you expect to see?

The instruments do not suddenly change from crisp and sharp to gooey images. At some point it starts to deteriorate, where in that downwards slope do you say "It's poor" ? If someone from TH/365 looked and said that is what I would expect, it's OK, what then?

Why did you get the Mak ?

[michael.h.f.wilkinson]

Can you perhaps borrow a decent 12mm (or similar focal length). It need not be top of the line, because at F/12 the scope should be pretty forgiving. This might rule out any problems with Barlow and BST 27mm.

[Macavity]

I used to have the classic (Fibonnacci!) Hyperion series 5, 8, 13, 21mm... 

(Any visual astronomy is indeed done with my trusty (f=1800) MAK150!)

But frankly, I found the 8mm (225x!) "too optimistic", in most instances.

So, simply I switched to the "alternative" common series: 10, 17, 31mm.

The 10mm (180x) seems more usable - Even for planetary observation?

And, with 2" adaptation, and (usually) DSOs in mind, I frequently leave

things mostly to the (60x) 31mm Aspheric plus occasional (100x) 17mm.

Just over a degree of field seems a good match for most DSO sizes too.

[Moonshane]

quite often the seeing conditions restrict you to 120-150x let alone 200x or 250x, especially on Jupiter. I'd agree that a 12mm (or your 25mm barlowed) should give a decent view most nights with the 7mm usable occasionally but more often on doubles and the moon. this can be the case even with a 12" dob. any more than this and you get fuzzier and bigger rather than sharper and smaller.

[theskipper1961]

Ok Thank you.

There is a lot of good info here for me, bearing in mind I don’t know much about telescopes, one of the questions I meant to ask was indeed would 1 or 2 mm difference in the focal length of an eye piece make a big difference, I have got my hands on an Orion 10 mm eye piece so this is the next step, Why did I buy a MAK  well I had a short tube Orion (1^st scope ) which I was not overly impressed with , then I picked up a 80mm sky watcher Mak which I was impressed with so I bought a bigger one !!

So the other two now have new homes, I do not consider this to be a mistake I love it it’s just a case of mastering the beast I think I do have a Dobsonion on my hit list though.

Back to the Mak, I did wonder if the Barlow is causing some issues, as I know from my SLR days that x 2 converters on photographic lenses are a compromise after all it is an extra set of elements in the middle- as for what I actually see I find the image is fuzzy  and very difficult to focus the detail is there I can see the rings on Jupiter as you would expect  I don’t really see shimmering , one thing I do note is very often the image drops off and even when re focused in and out it is difficult to get it back ,I don’t see any moisture inside the tube and I do use a dew shield and don’t use filters , neither am I using a dew heater at the moment , and at what outside temperature do we need to factor one of these in .

A fan I don’t use and I am unsure how this would work / fit to my MAK.

I guess it sounds like I am disappointed with this scope , I actually like it a lot , I have read about other people having issues with these scopes and overcoming them  which I’m sure with the kind help here  I will too – What about the Cray focuser would one of these be worth considering  in the future .

And is it possible the diagonal could give me issues at higher power.