jetstream

Off topic, but the sky here tonight might be extremely good... I'm thinking NGC7331 and dissecting Stephans Quintet further with the orthos. After this back to the picturesque Veil, wait until you see those little forked tips at the end of the 2 brighter wisps... What do you have for an OIII?

lol! This is exactly what happened to me using the SQM... I used to drive piles of miles way up in the bush to observe- only to realize our cabin was just as good! I do miss the adventures though, but its sure nice living under dark skies. Your gonna like what you see in this scope....

Your welcome and pursuing dark skies is fun in itself. Reading reports elsewhere I've noticed that when the term "Bortle" is used by some as a static label- I even did when I said I live in Bortle 1 skies. My skies vary as do others and to say that most any location is always "Bortle1" is very misleading. I read a report where the observer described a Bortle 2 sky as 22mag with high 7's NELM.....and then the site was then labelled Bortle 2. What I did in the pursuit of dark skies is to find a few dark sites that I could travel to and avoid cloud etc- it might be in your best interest to find sites such as this. I'll take a super transparent 21.4 sky over a 21.6 sky with lower trans. My best views come near zenith and I try to pick objects up high, like the Veil is now. The other night M81/M82 were nice in the 24" but no where near as good as they will be higher up. As far as the Little Veil, try many times after warming up the eyes but don't waste too much valuable dark sky time on it IMHO- too many better objects to see lol! Normally one challenge object is included in each serious obs session here, thats it.

I live in Bortle 1 skies and was just observing with the 24". Personally I don't like the Bortle scale- it says M33 is visible naked eye under Bortle 4 skies... skies are variable as is darkness levels for a given site depending on time of year etc. These days I judge the sky by the look of the Milky Way- under my best skies it casts its glow, brightly reflecting off the lake and shows sharp jagged structure along its course and will extend from horizon to horizon. Many objects such as the Lagoon neb are brightly lit among the billowing bright clouds in the split. The ability to see M33 naked eye is a superb, tough test of sky conditions and I do see it here. I can't wait to hear your 20" reports from dark skies! Get that sucker on the Veil! ps if you observe in truly dark skies your 20" will chew the Little Veil up no problem.. (Sh2-91), give it a whirl with the OIII.

I meant the metal ones- one on each triangle- is this what you meant?

Looks VG Piero! Question- what function do those screws set up above the triangles serve? Also, here are some numbers relating to mirror cells if anyone is interested. Configuration Description RMS at COG RMS 2.5 mm above COG 180° cable sling cable on half the mirror circonference 1.8 nm 6.6 nm 120° cable sling cable on a third of the mirror circonference 7.6 nm 12.0 nm 90° cable sling cable on a quarter of the mirror circonference 10.7 nm 18.5 nm 90° edge bearings 2 support points at 45° from vertical 4.0 nm 10.7 nm 60° edge bearings 2 support points at 30° from vertical 8.9 nm 14.6 nm 120° edge bearings 2 support points at 60° from vertical 16.7 nm 39.7 nm mirror on edge one support point at bottom of mirror 15.6 nm 28.6 nm 45° whiffletree 4 support points at 22.5° and 67.5° from vertical 2.0 nm 7.0 nm 30°/60° whiffletree 4 support points at 30° and 60° from vertical 2.8 nm 8.4 nm 30° whiffletree 4 support points at 15° and 45° from vertical 8.0 nm 12.8 nm 14°/45° whiffletree 4 support points at 14° and 45° with unequal load (Alois Ortner) 7.1 nm 10.5 nm

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?

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

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

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.

Oh?! Your keeping us in suspense?lol!

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?

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?

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...

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?

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!

Very apt description Mark. With the limited use of my scope I found my self saying "no way!", " are you kidding me?!" etc when viewing objects with the 24", they are that good and startling.

I tested all my newts for focuser sag and the resultant miscollimation- in the OOUK's it wasn't just the focuser, it was the aluminum tube deflecting. Te good news is that this only happened with very heavy eyepieces. I made a weight simulating eyepiece/binoviewers for the tests. If anyone notices image degradation in fast OOUK newts with binoviewers this is the first place I'd look. I really don't know why OOUK pushes the focus out so far requiring an extension adapter. If they ran the focus point closer in they could shrink the size of the secondary and eliminate the tube deflection IMHO.

Yes, thanks. Mine has 2 sets of mounting holes in the cell edges giving flexibility to the focus point. This in combination with adjusting the bolts gives a good range.

😁 🤣🤣

Forward? This confuses me too... These scopes collimate easily- you have a cheshire? I think moving the mirror forward (towards top of tube) pushes the focus point out- wrong direction for you. If you move it back it should suck the focus in the other direction ( which is what you want). Tighten the collimation bolts until they lightly bottom out, back them off 1/2 turn each and collimate. Tightening the bolts shorten the springs, pulling the mirror back,then check your focus. Of course I could be wrong- I'd hate to argue with OOUK...😀

Mine too , there are 2 sets of mounting holes in the cell supports. The OP can also shorten (tighten) collimation bolts to lower a bit more too.