Stub Mandrel

Hmm. Shouldn't depend on where the primary is. Took me a while to find this but I posted this back in December: I've just taken some 'real world' measurements. It looks to me that ZWO have supplied a pretty much optimal set of adaptors, assuming a standard 55mm back focus for the typical field flattener or coma corrector. Without the EFW: ASI1600 ---> 21mm T2 adaptor** ---> female/female adaptor** ---> T2-48mm adaptor** 6.5mm + 21mm + 11mm + 16.5mm = 55mm **supplied with ASI With EFW: ASI1600 ---> EFW ---> T2-T2 male/male adaptor* ---> female/female adaptor** ---> T2-48mm adaptor** 6.5mm + 19.97mm + 1.96 mm + 11mm + 16.5mm = 55.93mm *supplied with EFW **supplied with ASI Allowing for ~0.7mm shortening of the light path by the filter, this is pretty close again at 55.2mm.

Some people have criticism of the SW CC, but it needs no spacers to work with a T-adaptor and DSLR, and if used with the ASI1600 there are two spacers supplied that give the correct spacing; unlike other types it seems to be relatively insensitive to spacing anyway. Some people get reflections of bright stars, but I've found that only Sadr and Alnitak are bright enough to cause a visible 'ghost' image and was easily able to correct it. And here are a couple of works (some in progress) from last night:

Well done, I wish my view would let me get 17 hours on a target! I managed about 30 minutes each for LRGB last night, need more to reduce the noise in the extended disk.

Lots of us! It's a match made in heaven 🤣 I think you will want a CC, the Skywatcher one works well when used with the two spacers that come with the camera.

This is one from Friday night. I was chuffed to get the faint outer spiral. @Whistlin Bob this is indeed a fine target, can't believe I haven't found this gem before!

I've added some Ha:

I'm beginning to get the hang of processing LRGB. This is M51 from last night, with my 150PL, which at 120mm is ideal for galaxies. I lost the guide star a few times during the first half of the night so lost a lot of my L subs (nearly an hour salvaged out of two hours effort), but all the RGB ones (about 30 minutes each) were spot on.

Last night felt more like a 'getting to know you again' session than anything else. Guidescope focus was a bit off so stars aren't perfect, especially in the first image. Iffy transparency meant almost all frames suffered from LP gradients. Some stuff near the cone nebula in Ha (it's actually just poking into the top of the frame...) Gradients are a bit off as it was auto-flat corrected by sharpcap using the wrong flat... The snowman nebula, which is far to faint to image last night as it barely showed above the LP, so very, very noisy. I need a night of almost perfect transparency for this one or lots and lots and lots of data. And my first proper L-RGB DSO image, the Leo Triplet, still showing a bit of gradient.

Originally intended for 'show us your setup at night'... I've stretched this image 🙂 and it shows what I'm hanging off the 130PDS stock focuser.

That's not bad actually, that area isn't very starry the shapes in the galaxy are not points. Ha isn't ideal for galaxies, and for comparison here's a shot of mine and you can see my stars are nowhere near as nice as yours...

It's still possible OK as I just attach the dovetail to the mount near the front ring (best position for me is with about 1" between the stop screws and the cl;amp on the mount) . A small amount of nose-heaviness helps limit dec backlash.

Not on my scope. Depends where you have the tube rings!

Or just flip the focuser spindle assembly 180 degrees, this also puts the focuser nearer the c-of-g of the mount.

The ZWO one is very good and doesn't carry the 'Prima Premium'. It si abit tricky to mount (I had to shorten the mounting bar by 2-3mm)

When you say 'it slips on the spindle' do you mean: The spindle turns but the focuser tube doesn't move. The autofocuser turns but the spindle doesn't rotate and the tube doesn't move. The autofocuser doesn't turn and the stepper 'skips' steps? If the second of these the universal joint between stepper and spindle needs to be tightened up.

Have you seen this document (google found it somewhere on here, I can't find the thread): https://stargazerslounge.com/applications/core/interface/file/attachment.php?id=301468 Near the end it explains how the teflon block adjusting screws, if too tight, can cause slippage when you tighten the pressure screw.

What approaches have you taken to adjusting the focuser? There are many screws and it is easy to adjust the wrong one. As well as screws holding the spindle block in position (with 0-rings to allow for misalignment) tehre are also scres that adjust the alignment of the focuser spindle which must sit level on the focuser tube flat for maximum effectiveness. All conventional crayfords rely on solely on pressure from the screw (or screws) that press the focuser spindle against the bearings OR the lock screw. The lock screw is not central to the bearings and may not hold the tube as accurately. Have you tried tightening the spindle adjusters until it starts to go stiff, then backing off a tiny amount? Also, is it sag or mis-alignment? If the secondary isn't well placed or collimation is off, this can tilt the focal plane. It's also possible the bearings are mis-adjusted - there are two screws opposite the spindle on the focuser body, these should be set so the tube moves freely and doesn't bind or scrape against the tube. It's also possible the focuser isn't aligned straight. Each of the three screws holding the focuser body to the mounting plate has a grub screw next to it. Each pair of screws can be adjusted together (slack off the main screw before adjusting the grub screw) to tilt the whole focuser into accurate adjustment. Most people never need to touch these adjustments, but if your focuser is off, it may be that they need attention. The reason I ask is I have imaged with very heavy rigs hanging of the focuser with no signs of sag, and with something like 16 screws that can potentially affect sag or alignment (not allowing for the 13 involved in collimation which could also be a problem) it is pretty easy to run out of patience or ideas before actually tracking down the source of the problem.

Sorry, I've now had this problem myself and the answer is ridiculously simple: the scope needs collimating. It's a quick and reliable cure.

Managed seven quick snaps a couple of nights ago, had to stack them manually so Venus is a bit odd-shaped...

Not impossible to do, but buying a new nylon or brass gear will be more reliable for such a small, highly stressed part. If you post the outside diameter, measured as accurately as possible, I can point you at a likely source.

Aha! Found it in the end 🙂

Well done for coping with those lights! I use a 30mm long 'dewshield' made from camping mat lined with black flock; I bet if you used something like that you might see improved contrast.

Worth having a try. I use a 50mm x 183mm guide scope which is probably a bit more reliable and on a good day gets ~ 0.60" (someone I know with a similar setup gets 0.40" grr...)

Yes... I read the last page after posting...

Assuming there isn't a single fixed point, try shortening all of the springs by the same number of turns until you can feel they are supporting the bed securely.