M19 in a break in Sydney's Weather

[David Fitz-Henr]

Well, we had a somewhat clear night last night so I used the time to redo my FocusMax V-Curve runs (necessary because I have changed the spacing between Paracorr and CCD). At around 2:30am I decided I would take some images of a star field to test my new focusing parameters, and I chose M19 (globular cluster) which is also embedded in a rich star field. Unfortunately, clouds started to roll in after only 6 x 2min of luminance, and I also heard some thunder in the distance, so I decided discretion was the better part of valour and packed up.

Anyway, I processed the 6 luminance with some mild deconv and unsharp masking / stretching in PS. The focus is now much superior across the whole field due to the change in spacing; there is some slight distortion in the upper left which I attribute to flex in my focuser. Also, it looks like I need some new flats due to the slight change in configuration.

High Res Image:
http://www.pbase.com/image/125267597

Small Image:
http://www.pbase.com/david_fitz_henr...25267597/large

[Moon (James)]

David
That is so good it's not funny -you really nailed it.
I've got a paracorr-stl on order - I'll let you know how it goes.
James

[multiweb (Marc)]

Very sharp. Beautiful flat field. Looks like your spacers tweaking paid off. Nice.

[David Fitz-Henr]

Originally Posted by Moon

David
That is so good it's not funny -you really nailed it.
I've got a paracorr-stl on order - I'll let you know how it goes.
James

Thanks James, I'm very pleased with the result. I think it shows that you don't have to spend a fortune to own a good astrographic telescope. The most expensive item was the focuser / controller, but actually it needs a more solid focuser to support the weight of the STL. What focuser do you plan on using?

Originally Posted by multiweb

Very sharp. Beautiful flat field. Looks like your spacers tweaking paid off. Nice.

Thanks Marc - yes, it appears to have paid off nicely!

[Moon (James)]

I'll use the stock GSO focuser to start with and see how it goes. It should arrive here next week. If you have any suggestions for an upgrade, let me know.
James

[David Fitz-Henr]

Originally Posted by Moon

I'll use the stock GSO focuser to start with and see how it goes. It should arrive here next week. If you have any suggestions for an upgrade, let me know.
James

A Newtonian puts greater demands on a focuser than a refractor or Cassegrain because the greatest torque is exerted on the focuser when pointed at the zenith - remember that you have a heavy camera (~4.5 lbs) + Paracorr held near right angles to the tube and several inches out, and that exerts a fair bit of lateral force to be held by bearings that are just one inch apart. I've also found with the STL that this is exacerbated if you have the offset part of the camera positioned above the level of the focuser due to added leverage. You can't rely on the load lift capacity of the focuser to determine the maximum rating for acceptable usage, especially for a Newtonian. The focuser that I have (with stepper motor) is rated at 7lbs lift capacity, yet I have a lot of flex when pointed near the meridian with my STL / Paracorr. I have improved this by tightening the tensioning screws though and I need to test this out a bit more. If I had my time over, I would probably buy an Optec 2" or Moonlite 2.5" focuser for my 200mm - expensive I know, but if I had to nominate one aspect of a Newtonian that can act as its Achilles heel this would be it.

[Hagar (Doug)]

Very nice David, looks like the parracore has worked well and focus is good also.

Well done.