have had a continuing battle to get consistent results from an f4 GSO Newt. Latest change seems to have yielded significant improvement.
the problem was that moving the scope around yielded obvious movement in a laser collimation spot projected onto the primary. it seemed to have many different stable positions and could move from one to another - with maybe as much as 1cm change in spot position - without warning or apparent reason. Also similar behaviour (bit less dramatic though) with a moolite focuser. Eventually tracked it down to the way that the focuser clamp works - it is based on keeping two cylinders aligned but the clamp only acts at one end. when I put a Barlow tube in the focuser it was easy to move it around by pushing on it from the OTA side. When you think about it, the slot for the brass compression clamp limits the locking surface to the very thin outermost lip of the draw tube - asking for trouble.
solved the problem completely by fitting an additional screw to clamp coma correctors/ Barlows in two places along the focuser as in the image. The screw on the compression ring holds the weight and the inner one is tightened just enough to stop any movement between the two tubes. Works a treat and now the laser spot stays fixed regardless - I even removed the primary, washed it and replaced it to find that the whole system required only a minor tweak on the primary - previously unheard of.
this mod appears to turn the GSO focuser into something usable for imaging with camera weights up to maybe 800g, which will be quite suitable for an OSC on this scope. Will be able to try it out with my QHY8 when the clouds clear. Also want to try the mod on the Moonlite next - very simple mod since there is free space for the screws.
Thanks for posting Ray, I'm tossing up whether ill get a gso or a skywatcher ota for my next setup ... Hmmmm, a focused upgrade will probably be a way off for me, which is leaning me toward the SW.
I always try to watch that everything that goes into the focuser tube (eyepieces, adapters, extension tubes) goes in all the way to the stop, and then clamp it down. That's the only way to make sure everything is square and wobble-free.
From limited personal experience (few samples of each) I much prefer the GSO Dob focuser to the SW one.
I always try to watch that everything that goes into the focuser tube (eyepieces, adapters, extension tubes) goes in all the way to the stop, and then clamp it down. That's the only way to make sure everything is square and wobble-free.
From limited personal experience (few samples of each) I much prefer the GSO Dob focuser to the SW one.
Cheers
Steffen.
thanks for the heads up Steffen, any experience on just the OTA? I have a DSLR and have heard there isn't enough inward focus on the GSO with a coma corrector? I'm not sure if thats correct either though? I know the SW is ok, although i believe there is a bit of inward protrusion in the light path.
I always try to watch that everything that goes into the focuser tube (eyepieces, adapters, extension tubes) goes in all the way to the stop, and then clamp it down. That's the only way to make sure everything is square and wobble-free.
From limited personal experience (few samples of each) I much prefer the GSO Dob focuser to the SW one.
Cheers
Steffen.
Quote:
Originally Posted by rustigsmed
thanks for the heads up Steffen, any experience on just the OTA? I have a DSLR and have heard there isn't enough inward focus on the GSO with a coma corrector? I'm not sure if thats correct either though? I know the SW is ok, although i believe there is a bit of inward protrusion in the light path.
Cheers,
Rusty
thanks for the comments.
Am in the process of testing it- chalk and cheese - the focuser now works well, the coma corrector works pretty well (collimated through it) and everything is nice and square and stable. This mod made a major difference.
not sure about the coma corrector problem - mine focuses with plenty to spare on the QHY8 but the focal plane is only a little way back from the front plate of the camera - not 55mm. You might consider the RCC1 coma corrector, which provides bags of room.
Sorry Rusty, can't help with imaging questions. I believe GSO make a low-profile focuser to deal with in-focus issues. My experience is purely from visual use.
Did you just remove the barrel from the focuser, drill and tap it?
I think removing wobble is Moonlites rationale behind their 'smooth bore to T-thread' adaptors...
I'm awaiting my Glatter collimator to be delivered to collimate mine, may have to look into a mod like this....
Did you just remove the barrel from the focuser, drill and tap it?
I think removing wobble is Moonlites rationale behind their 'smooth bore to T-thread' adaptors...
I'm awaiting my Glatter collimator to be delivered to collimate mine, may have to look into a mod like this....
yes, drill tap new holes and also make a small opening in the outer cover flange to clear the extra screw head. The screws have to be on a part of the barrel that clears the internal bits of the focuser - there is plenty of clear space though. The barrel comes out easily when the main shaft is slid out. I put the inner screw on the inner edge of the solid section of the barrel - not the undercut bit.
Doesn't turn it into a Moonlite by any means, but the scope is now quite effective for imaging with a lightweight camera - it wasn't beforehand
edit: just noticed that Televue use conical mating surfaces in the focusers on the NP scopes - guess that would be an even better solution.
..... I believe GSO make a low-profile focuser to deal with in-focus issues.......
They used to, but ceased some years ago. I know, I've been trying to get one, but without any success. One view stated on Cloudy Nights was that there was something fundamentally wrong with the design of the low profile with respect to its primary aim, holding camera weights rigidly.
