jetstream

27 minutes ago, markse68 said:

BCO 10mm I now kinda regret buying. 

Can I ask why?

3 hours ago, Piero said:

The mirror clips seem to be glued..

Piero, are those top right angle holders thread on to the vertical supports? I see a machined hole in the side I think- is there an allen screw in there or something?

2 hours ago, Piero said:

How much gap is there between the sling cable and wood edge limiters (clamps?) of your mirror cells?

Back soon Piero- but there is about 1/8"-3/16"...

C8

3 minutes ago, Piero said:

This is actually quite important if the ground is not exactly flat.

IME it is really not an issue, a properly adjusted cable holds the mirror centered ie I can wheel my trusses over very uneven ground, and observe with them far from a flat place and no issues. Minor collimation is needed, but my center triangle is never outside the cheshire dot and in fact only the triangle tips will show off center slightly. Even putting the 24"on the trailer, pulling it with the loader, unloading etc didn't throw it way off.

My cells use wood for the edge limiters (soft, no hard contact) and are not far away from the edge, but a gap is always maintained.

I agree rollers CAN be a benefit if tested in a cell, a friend is choosing something similar to the image and the site- Aurora Precsion says Zambuto had input in the cell design

2 hours ago, Piero said:

For now my cable sling is loosened in such a way that it does not touch the mirror.  

Great catch Piero!

I just knew it was this

Yes that will do it but the cable will work- can you widen those clips -or- actually do you have a picture of the cell with the mirror out? are those pads integral with the clips?

ps - you might dump the pads and use velcro.

@Kokatha man ,Mr Malika offers great information and his images speak for themselves.

http://www.momilika.net/WebPages/AstroIntro.htm

14 minutes ago, Piero said:

I think I found the main source of the problem.. 

Oh?!

Your keeping us in suspense?lol!

On great nights I see piles of sharp structure in the area, I'll have a good look to confirm B144 (or not). Dark nebs are a favorite of mine.

1 hour ago, Piero said:

As far as I know secondary mirror can cause astigmatism in the optical system when they are glued to the holder by a large amount of glue or silicon rather than three small points.

Any restraint can cause this -including my holders I read- but I just follow Astrosystems instructions and no issue. I'm not so sure about the 3 dab of silicone method- does  the secondary have an even gap all around?

As far as cells- my 200mm f3.8 OOUK has a nice cell that was maladjusted and the mirror was a bit too thick for it. As received there were used 3 dabs of silicone to "secure" it to the cell and the result was big astigmatism.

All contact points must support equal weight regardless of type.

The beauty of those fiber "button" supports is that they in themselves can offer "self" adjustment by the amount of squish the mirror imparts, ensuring even contact. My OOUK nylon tips were fussy to set up evenly and the mirror was jammed against the clips.

Obviously rotating the primary will show if it is the culprit, but there is always the slim chance that the sec might be an issue at the same time.

I'm puzzled by the transient nature of the issue though? Did the scope maker notice this when he tested it?

Just now, faulksy said:

should be set at the c of g gerry not the centre of the mirror edge 😁

Yes,great point Mike! and I'm very thankful that my mirrors aren't fussy to need the extra precision!

How about OOUK cells that let the mirror rest on the clip (supports!) your former Whiffletree cell is optimum I think, but a well adjusted cable sling works well with thick enough mirrors IMHO.

@Piero I would still try rotating the primary to see if it (astig) rotates with it, just a thought...

Your mirror is thin and should equalize right away so the chance of cooling astig is small unless there is residual strain in the glass, but the chance of this is minute.

What does a very high power view look like that opens up the airy disk?

Stunning images Mo!

A very interesting read is "QED: the strange theory of light and matter" by Feynman. It describes how light behaves and this is what we see in the eyepiece so...

Thanks @andrew s for recommending this great book to me years ago.

6 minutes ago, Angie said:

The main mirror inside telescope is completely off and I don’t know how it goes in. There are three screws with springs around the mirror  and I do not know where that mirror is suppose to be screwed on inside the telescope. 

The three holes in the bottom plate should line up with those three screws or "studs" and there should be some kind of "hollow nuts" possibly that thread on the studs, once through the holes.

Is there more parts?

18 minutes ago, Angie said:

The mirror inside my telescope is  completely loose. Can  someone please help me in installing this telescope. 

Can you send some pictures of it?

5 minutes ago, Piero said:

Do you still use your Catseye tools or just the Glatter's?

I use Glatters laser for secondary alignment on the primary dot and in general the TuBlg. There can be an increase in accuracy with the Catseye cheshire over the Tublug - the cheshire is more consistent. For critical lunar/planetary the cheshire goes in and also the autocollimator at times.

Does the astig rotate with the primary?

What kind of "pads" does the primary sit on in the cell? I had a case of restraint with my 15" causing astig when the mirror froze to the cell pad supports. Any large friction etc here can cause issues. It disappeared when I freed the mirror by moving it.

Uneven cooling can cause astig, my 24" likes the fans off for the final cooling as the 4 fans cool the center faster than the edges but I have never had an issue using a shroud with either truss dob. I normally leave the shroud pulled back at the top a hair to let the rising warm air out, until equalized.

Whats the astig look like- flipping oblongs in and out of focus?

Hot here too, just got back from a walk, not as hot as there though. Time for a nice cooling swim...

1 minute ago, Piero said:

I'm cycling back home. Will reply asap.

Just now, Piero said:

I believe the sling was just too tight, but have to check this better. Possibly it was just air turbulence.

Unless the sling wraps the mirror instead of 1/2 or so cradling it there should be no issues with restraint causing astig. Another possible cause of transient astig can be secondary mirror restraint and as you know astig during cooling. I was told that centering the sling in the center of the mirror edge eliminates potential issues, but this may or may not apply always.

Does your sling "squeeze" the mirror?

10 hours ago, Piero said:

Last night I slightly loosened the glatter sling

Just curious, why loosen? was the mirror pulled up contacting the stops at times?

Do you have velcro on the mirror edge to keep the sling positioned in the center of the edge? If you rack the focuser in and out with the laser installed does the laser dot move ?

Awesome you are getting great views Piero. Man, I just counted my questions...sorry lol!

36 minutes ago, andrew s said:

While not about Maks or visual, have a look at Thierry Legault's site. As well as stunning high resolution images his Technical section has the results of his studies on types of scope, obstruction impact, focus and collimation. He uses a refractor as well as catadioptic telescopes and in my view gives a very balanced perspective. 

www.astrophoto.fr. in English.

Regards Andrew 

 

I like this statement by Thierry

" These results are valid only if the instrument is optically good and properly collimated. If it is not the case, the MTF curve is squashed, the resolution limit is lowered and the loss of resolution affects all the objects, including high contrast objects like the Moon "

It amazes me how it seems so many are intimidated by collimation and it makes me wonder how many newt (SCT too) owners are really missing their scopes performance.

Because the true planetary performance of any telescope, represented by the MTF graph, is absolutely dependent on optical quality we can only compare telescopes of equal optical specs if we want to get a meaningful comparison. A great place to start understanding this is to compare a refractor with 1/4 wave spherical aberration vs a 1/8 wave newt with a 20% obstruction.  My point is real world comparisons need to take individual scopes characteristics into account vs generalizing about telescope "type" ie Mak, refractors etc.

and in all this miscollimation or poor focus destroys everything from start to finish with respect to the quality and amount of detail seen.

There are no magic telescopes but there are ones more suited to given seeing conditions and thermal equalization becomes a big factor. Given equal optics and assuming thermal equalization a larger aperture will show more just as sharp as any scope in excellent seeing.

Off topic a bit but here is Mels sketch with the 150mm f2.8 and shows what I mean about the galaxy growing, but possibly the galaxy ends and IFN starts? but where lol! I can see parts of this but not as extensive as this (yet).

One of the interesting things about M31 is how larger apertures makes it "grow" in size extensively, and conversely smaller in smaller apertures, even from dark skies. I guess the extra mag at enough eye illumination that the right big scope (fast) enables seeing the fainter outer sections. From the best of nights I can see M31 with a core brightening naked eye. The 200mm f3.8 gives a really interesting low mag view of M31 at 2.75 deg or so and 29x and I would love to try one of Mel Bartels fast newts on it. The view is completely different from a low mag refractor view. This 200mm scope also makes it "grow".