Avoiding camera rocking in focuser

[lukebl]

Just wondered how you guys avoid your camera 'rocking' in the focuser. I am using a CCD attached to a Baader Coma Corrector, and I just can't seem to avoid the camera being slightly loose (highly exaggerated in the animation below), which I'm certain is the root of my imaging problems:

Basically, the coma corrector pivots on the two holding screws, resulting in the cam not being 'square' to the optical plane, and also moves as the centre of gravity changes. I have tried using both the standard eyepiece holder (right-hand image below), and a compression type (on the left) which, in theory, should hold the whole thing tight. Yet the problem persists with both holders. Any ideas?

[George]

I had the same problem so I drilled and tapped a third hole for another thumbscrew......problem solved

[lukebl]

I had the same problem so I drilled and tapped a third hole for another thumbscrew......problem solved

Thanks George. Sounds good. Not being very technical myself, how do you get a thread in the new hole?

[yeti monster]

One uses a tap to cut a thread in a hole.

Does your camera adapter have a small shoulder, just where the thumbscrews locate? Mine had such a shoulder and cause my camera to rock, much as in your animation. I turned it down in my lathe and now my camera sits squarely in the focuser.

[nightvision]

I did the as George did but for my guide cam connection, fixed it perfectly.

[earth titan]

Cracking discussion as I suffer with this.

Drill and tap it is then!

Typed by me, using fumms...

[ollypenrice]

Three scews are best. Altair Astro have gone down this route. Pushing the camera in while clamping it goes some way to helping, in the mean time.

Olly

[earth titan]

With nothing better to do this evening due to the clouds (again), I cut up a plastic milk bottle and shimmed my focuser tube.

Works beautifully!

[Bizibilder]

Firstly I would simply file the ends of the locking screws flat - that way you get a better grip and the ends of the screws won't cut little circles into your adapters! But i must admit the three screw method will be the most secure, short of machining a completely new part that actually fits!!!

[martin_h]

I did the 3 screw trick a while back on my ED80 focuser, works a treat

[lukebl]

Thanks, gents. The 3 screw method it is, then. I'm clutching at straws, really, as it's the last option for resolving my imaging problems. Unless, of course, the problem is due to the CCD being misaligned in the camera itself, which is something I have no idea how to fix.

[badgers]

Three screws and shimming should cure that fast. I had exactly the same issues, but caved in and bought a moonlite

It's also worth tightening up the grubs that compress the tube onto the rollers. I found that they actually cause the tube to compress slightly and give me a slightly tighter fit when the tube is racked in. It also helps with removing any focuser tube to focuser slop, and the dreaded focus slip.

I'm now chasing OTA flex, but think I've made some significant progress last night (see my eggy stars thread).

[Sp@ce_d]

Can you get a Baader 2" clicklock for your focusser? I've replaced the ones on my ED80 and ZS66 with them and it's night and day.. a bit pricy but well worth it.

[badgers]

Hotech also do a 2" adapter with t-threads that has 3 compression rings running around it.. That thing would hold like epoxy resin.

[lukebl]

Hi all,

Well I think I'm getting somewhere. I had the extra thumscrew drilled and tapped, and the cam now fits snugly with no rocking:

Having only time for a couple of quick captures last night, I did this single 10 minute exposure of the area around 68 Cygni (no darks or flats), and am quite pleased with the result. There still seems to be some star distortion, particularly towards the bottom right, but it's a whole lot better than before. Guiding seems to be good too. Won't say that my problems are over, but at least that's one variable ruled out. Thanks for all the input.

[nightvision]

Looking good.

[badgers]

Looks like problem solved to me, and you didn't have to fork out £250 for a moonlite either.

[dugpatrick]

It sounds like the problem has been solved, but there might be another way for people that have not drilled holes yet. With my Celestron (Synta) R&P focuser I use the compression adapter from scopestuff: http://www.scopestuff.com/ss_faga.htm

It holds my DSLR camera and MPCC pretty well. (and it holds a cooler around the DSLR too)

Doug

[badgers]

Do you use an off-axis guider Luke ?

That last shot is very impressive, I'm getting close but think I have some flexure remaining.

Anton

[lukebl]

Do you use an off-axis guider Luke ?

That last shot is very impressive, I'm getting close but think I have some flexure remaining.

Anton

Hi. Thanks, Anton. No, I'm not using an off-axis guider, although I'm thinking of getting one. Guiding was with a QHY5 cam and an ST80 scope. I sold off a lot of my gear earlier in the year, including filters and filter wheel (long story), but am now buying stuff again and an OAG is something I'm considering.

Had another quick session last night to check things. here's M57. 12 x 5 minute exposures with the SXVF-H9 cam, UHC-S filter, plus colour added from a DSLR image I took a couple of years ago. Unfortunately, part of the main ring was slightly overexposed, but I'm pleased that you can just make out the fainter outer shell of the ring, which surprised me for such short exposure, and also the faint variation in the central nebulosity. I think the UHC-S filter helped.

Full frame:

And here's a crop:

[badgers]

That's fantastic.

Stars are about as round as you can get them I'd say. I'm amazed at the detail you've pulled out.

Don't change anything with your setup!

I must come back to M57 and try it again with my fixed setup to compare my star roundness to yours.

I did take some test shots the other night, but somehow my focus had slipped.

I'm amazed at the difference one thumbscrew can make.