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LXD55 6-inch refractor

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#1 Clumpybug

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Posted 18 July 2013 - 05:03 PM

I have an opportunity to buy a LXD55 5-inch refractor from someone on craigslist. It comes with the mount, the controller, and some eyepieces. I want to use it for DSLR astrophotography. Thoughts? Good idea? Bad idea? Would this be a good scope for that purpose?

#2 jgraham

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Posted 18 July 2013 - 06:00 PM

I have an LXD55 AR-6 on an LXD75 mount. It is a wonderful visual scope and you can use it for basic imaging, but that is not its strength. Its size makes good tracking a challenge and the chromic aberration has to be dealt with using filters and careful processing. I dearly love my AR-6 and I enjoy the challenge of imaging with it, but there are better choices for an imaging scope.

#3 Falcon-

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Posted 18 July 2013 - 06:55 PM

I would say it depends on just how good of a deal you are looking at. the LXD55 should be a reasonable mount for wide-FOV imaging using camera lenses, but I side with John on the suitability (or lack of) for AP.

Still if it is a REALLY good deal then the worst case is some wide-field AP and a nice visual scope.

#4 avarakin

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Posted 18 July 2013 - 09:43 PM

I use LXD55 for imaging from home observatory. If all planets are properly aligned, I can image with 8" F5 reflector.
I think it all depends on what kind of deal you are getting. I got my LXD55 + SN6 for $200. I am not complaining!
If you are getting this setup for less than $500 then I think it is a good deal and you should go for it. Mount itself is ~$500 new.

Alex

#5 Clumpybug

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Posted 19 July 2013 - 10:45 AM

Oh yeah, sorry, "5-inch" was a typo. It's the 6-inch. It's being offered for $700 o.b.o. I already have a LXD75 8-inch Newtonian that I use for astrophotography (with a good degree of success). I just didn't know if a refractor with about a 50% longer focal length would give me anything I don't already have. To be honest, I don't really understand the point of refractors, given that reflectors are so much cheaper for a given aperture area. Slightly longer focal length, maybe? Or is there another advantage to them?

#6 avarakin

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Posted 19 July 2013 - 10:56 AM

The main reason why you may want to buy this setup is because the mount shares many parts with your LXD75 which is no longer manufactured, so you can swap the parts if needed.
You can use the refractor for visual or sell it.
For imaging it is not too good - too much of CA. You need an APO refractor to get decent images.
I would try to knock off couple of hundreds off the price and get it. LXD55 are going for around $300, have no idea about the refractor though.
Alex

#7 jgraham

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Posted 19 July 2013 - 11:27 AM

The real joy of my AR-6 is visual. It cools down remarkably fast and you can easily max-out the exit pupil without encountering the shadow of the secondary like you would with an obstructed light path. I was really surprised when my AR-6 became my favorite RFT! The clean light path also helped to take my double star observing to the next level. I also lifted my AR-6 up by adding a pier extension to my LXD-75 making it a very comfortable telescope to use.

#8 jgraham

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Posted 19 July 2013 - 12:56 PM

Just for yucks...

M27 – The Dumbbell Nebula in Vulpecula
Telescope: Meade LXD75 AR-6
Camera: Canon Rebel T2i
Filter: Orion Imaging Sky Glow Filter
Guide scope: None
Exposure: 60x20sec, ISO 3200 saved as RAW
Darks: Internal
Flat: Synthetic
Software: Backyard EOS, Digital Photo Professional, Deep Sky Stacker, Photoshop

Attached Files



#9 jgraham

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Posted 19 July 2013 - 12:56 PM

M13 – Globular Cluster in Hercules
Telescope: Meade LXD75 AR-6
Camera: Canon Rebel T2i
Filter: Orion Imaging Sky Glow Filter
Guide scope: None
Exposure: 40x30sec, ISO 3200 saved as RAW
Darks: Internal
Flat: Synthetic

Attached Files



#10 jgraham

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Posted 19 July 2013 - 12:57 PM

M3 – Globular Cluster in Canes Venatici
Telescope: Meade LXD75 AR-6
Camera: Canon Rebel T2i
Filter: Orion Imaging Sky Glow Filter
Guide scope: None
Exposure: 40x20sec, ISO 3200 saved as RAW
Darks: Internal
Flat: Synthetic
Software: Backyard EOS, Digital Photo Professional, Deep Sky Stacker, Photoshop

Attached Files



#11 Falcon-

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Posted 19 July 2013 - 01:34 PM

Oh yeah, sorry, "5-inch" was a typo. It's the 6-inch. It's being offered for $700 o.b.o. I already have a LXD75 8-inch Newtonian that I use for astrophotography (with a good degree of success). I just didn't know if a refractor with about a 50% longer focal length would give me anything I don't already have. To be honest, I don't really understand the point of refractors, given that reflectors are so much cheaper for a given aperture area. Slightly longer focal length, maybe? Or is there another advantage to them?


My thinking is that since you already have an LXD75 and your use includes AP the $700 would be better spent on other gear rather then the LXD55/AR6.

For example - do you have a guiding setup yet? If not a 50mm finder-guider and guide scope can be had for half that total. How about a wider FOV telescope? You 8" newt is probably something on the order of 800mm focal length (guessing an f/4 scope), something like the AT65EDQ would give you a nice 420mm focal length to use on larger targets or groups of targets.

#12 Clumpybug

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Posted 19 July 2013 - 02:52 PM

Yep, my scope has an 800mm focal length. I have a guiding setup on it, too. Problem is a lot of times I have lots of trouble, as the guider doesn't like to track very well in the North/South direction (which I think is declination?). I think it's because there's too much slop in the gears. I'm not exactly sure how to solve the problem, as I'm afraid if I try to take apart the motor to service it, I'll screw something up.

#13 Falcon-

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Posted 20 July 2013 - 01:41 AM

The Dec axis on the LXD75 type mount (very similar to my CG5) can often have "stiction" issues where the axis resists very small movements (the type guiding wants to give it) until it suddenly lets go and jerks to a new location. This is caused by too much grease, sticky old grease, or rough-spots in the axis (or all three). This, naturally, is makes it somewhat difficult to get good long exposures if your mount is doing this. There can also be a problem with backlash (slop in the gears) such that if the guiding changes directions from North to South (or vice versa) seems to not work and then suddenly over-correct as the slop in the gears is taken up.

There are thankfully quite a few things you can do to help with the problem:

1) When your polar alignment is not *perfect* (and really, when is it ever perfect?) watch what direction DEC wants to drift and then change PHD's DEC guide mode to either North Only or South Only (depending on what direction it is drifting). This can avoid the backlash issue.

2) Spend some time doing Drift Alignment to get as good a polar alignment as you can possibly get before you start imaging. With a good enough polar alignment you may be able to simply turn DEC guiding off (this would avoid the sticktion issue). Yes I know this contradicts #1 ;)

3) disassemble the mount (or just the the DEC axis), clean off the grease, re-apply new high-quality grease and re-assemble. Possibly adjusting the worm/worm-wheel mesh as you do so in order to remove some of the backlash (just do not adjust it so that it becomes tight). Doing this improved the guiding of my CG5.

4) Do a Hyper-Tune on the mount. This is basically the same thing as #3 but also involves replacing some bearings and polishing some of the metal surfaces to reduce stiction even further. This set of instructions is for the CG-5 but as far as I understand it applies to the LXD75 as well (both the CG5 and LXD75 are clones of the Vixen Great Polaris mount). If you ignore polishing section you can use this as a guide for #3 as well.

5) Image at shorter focal lengths. If you image with wider Fields of View such as a smaller scope or camera lenses provide you will not be able to see problems that are fairly obvious at 800mm focal length.

and finally.....

6) Get a better mount (possibly selling the LXD75 to fund it). This is what I eventually did to get acceptable performance at 1370mm focal length (and better performance at 900mm and 300mm). I still have my CG5 though for use in easily portable wide-field imaging with camera lenses.


That #6 might be a bit tough to chew on, but if you consider that $700 you where thinking of spending and toss in what the LXD75 might sell for you could probably get a used Orion Atlas EQG (also called the Skywatcher NEQ6 Pro). That is a significantly beefier mount with a proven track recored for AP use.






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