fuadramsey
member
Reged: 06/26/07
Posts: 80
Loc: Orange County, CA
|
|
I am looking at replacing my stock 1.25 focuser on my Celestron Omni XLT 150 6" newtonian relector http://www.celestron.com/c2/product.php?CatID=63&ProdID=433 to the Orion Crayford-type 2" focuser http://www.telescope.com/shopping/product/detailmain.jsp?itemID=228559&itemType=PRODUCT&RS=1&keyword=13039 .
I mainly want to do this to put a filter infront of my DSLR. I looked at other options and this seems to give me the most flexability.
What issues may come up? I know I will have to open up the hole on the OTA, but is there anything else that I would have to modify?
Thanks,
Jamie
--------------------
www.mbsastronomy.com
Astronomy for Real People
|
NewAstronomer
Carpal Tunnel
Reged: 09/03/04
Posts: 2977
Loc: Scranton, PA U.S.A
|
|
I just did a similar upgrade to an Orion 6" f/5 newt , converted to a GSO Crayford 2" focuser. A few things to keep in mind:
1) I'd measure your secondary, I believe mine was 1.83", which was just big enough for all but the biggest 2" eyepieces.
2) In addition to cutting the opening wider, you will need to "shim" the focuser to the tube since they are designed for 8" tubes and bigger. I used old mouse pads, cut out to fit under the focuser inbetween the OTA, got that tip from someone else here, and after a few nights of use I was convinced it worked well (no slop).
3) I needed longer screws since I shimmed the focuser into place, found them at a hardware store, what I wish I did was bring the old ones with me, the ones I got were too long.
Thats about it, good upgrade and well worth it. The stock 1.25" R&P focusert was garbage. A 2" GSO Crayford focuser (never tried Orion's version) was much much better.
Here is a picture:
--------------------
Chris
280mm f/10 C11 SCT
250mm f/4.8 Dob
70mm f/6 SV70ED
Atlas EQ-G
SVP Intelliscope & ST-4 Autoguide Mod
DBK 21AU04
Olympus e-500 DSLR
Meade DSI-C
Edited by NewAstronomer (09/12/07 02:34 PM)
|
fuadramsey
member
Reged: 06/26/07
Posts: 80
Loc: Orange County, CA
|
|
Thanks for the tips. I was wondering about the shim thing.
How what am I looking for when I measure the secondary mirror?
Also the GSO looks like the Zhumell here: http://www.orion.telescopes.com/telescope-accessories/focusers/crayfordfocuser.cfm
Is yours like the Zhumell on this dob which "allows the viewer to acheive a rough focus quickly by pushing or pulling th efocus tube and fine focusing of the image using the focus knobs?"
Also does this hold a camera well?
--------------------
www.mbsastronomy.com
Astronomy for Real People
Edited by fuadramsey (09/12/07 03:47 PM)
|
PJF
professor emeritus
Reged: 05/06/04
Posts: 653
Loc: UK
|
|
Quote:
What issues may come up? I know I will have to open up the hole on the OTA, but is there anything else that I would have to modify?
The spacing of the mounting holes is different on these focusers, so you're looking at drilling new mounting holes in the tube in addition to enlarging the hole for the drawtube.
This work needs to be done carefully to avoid focuser alignment complications. Should be straightforward if you're mechanically competent, but is a potential quagmire if you're a ham-fisted doofus like me. 
I'm hoping Moonlight make an adaptor for 1.25" Vixen focus mount to Moonlight 2" for my 'scope. Am waiting to hear back.
--------------------
Peter
10x50 binocs
ED80 'frac
6" f/6 Newtonian alt/az
10" f/4.3 Newtonian alt/az
Bryce
|
GlenM
Vendor
Reged: 05/20/07
Posts: 1632
Loc: Lancashire UK
|
|
You can't go wrong with the 'Moonlite' They have a 2''focuser with a flip in filter or 4x filter holder which resides in the top cage. Very nice engineering and always willing to help.
Clear Skies,
Glen.
--------------------
Glen
www.lyraoptic.co.uk
|
PJF
professor emeritus
Reged: 05/06/04
Posts: 653
Loc: UK
|
|
Quote:
You can't go wrong with the 'Moonlite'...
Heh, well I don't know how long I've been going wrong with their name  . I'm usually pretty good at remembering these things. It must be the beer.
I'll have one and see. 
--------------------
Peter
10x50 binocs
ED80 'frac
6" f/6 Newtonian alt/az
10" f/4.3 Newtonian alt/az
Bryce
|
GlenM
Vendor
Reged: 05/20/07
Posts: 1632
Loc: Lancashire UK
|
|
Hi Peter,
your memory is probably better than mine. I don't have 'senior moments' now I have moved onto 'craft moments' I can't drink with my 'old man' tablets, that's what the Grandchildren call them.
Clear Skies,
Glen.
--------------------
Glen
www.lyraoptic.co.uk
|
NewAstronomer
Carpal Tunnel
Reged: 09/03/04
Posts: 2977
Loc: Scranton, PA U.S.A
|
|
Quote:
How what am I looking for when I measure the secondary mirror?
Take the secondary out of the OTA and measure it, longest part.
Quote:
Also the GSO looks like the Zhumell here: http://www.orion.telescopes.com/telescope-accessories/focusers/crayfordfocuser.cfm
Is yours like the Zhumell on this dob which "allows the viewer to acheive a rough focus quickly by pushing or pulling th efocus tube and fine focusing of the image using the focus knobs?"
Yes, the GSO Crayford I use is just the the Zhumell one. I bought it used on Astromart, but ScopeStuff.com also sells them as do many others.
Quote:
Also does this hold a camera well?
Much better than the stock 1.25" it replaced, it was a 100% improvement with no slop or focuser tube movement due to camera weight.
--------------------
Chris
280mm f/10 C11 SCT
250mm f/4.8 Dob
70mm f/6 SV70ED
Atlas EQ-G
SVP Intelliscope & ST-4 Autoguide Mod
DBK 21AU04
Olympus e-500 DSLR
Meade DSI-C
|
fuadramsey
member
Reged: 06/26/07
Posts: 80
Loc: Orange County, CA
|
|
Quote:
How and what am I looking for when I measure the secondary mirror?
Take the secondary out of the OTA and measure it, longest part.
Am I measuring the longest part of the mirror? What am I comparing this measurement to? If you have the time please elaborate on this.
Are you using 2 inch eyepieceses on yours? I don't plan on using 2" yet, but maybe down the road.
Thanks for all your help, I just want to be confident before I commit to this.
Edited by fuadramsey (09/13/07 11:50 AM)
|
NewAstronomer
Carpal Tunnel
Reged: 09/03/04
Posts: 2977
Loc: Scranton, PA U.S.A
|
|
Measure longest part of secondary, I used a GSO 2" Superview in mine, worked fine, the secondary size will illuminate the eyepiece, so if your secondary is 1.83" at its widest, and your eypiece field stop is 1.8" you will be fine if your collimation is good.
The largest 2" eyepiece, like a 31mm Nagler, may have a larger field stop (I'm not sure, check eyepiece forum), it will be usable, but you may not fully illuminate the field (lose light gather by primary).
If your goal is to attach a camera, like a DSLR, you will be happy. Trust me.
If your secondary is smaller, like 1.5" your really cutting it close and may want to upgrade it (they are relativly checp).
The hardest part will be cutting the new holes for your screws, and widening the existing focuser hole. Just go slow, allocate much time.
Of course remove all mirrors from the scope before you begim.
--------------------
Chris
280mm f/10 C11 SCT
250mm f/4.8 Dob
70mm f/6 SV70ED
Atlas EQ-G
SVP Intelliscope & ST-4 Autoguide Mod
DBK 21AU04
Olympus e-500 DSLR
Meade DSI-C
|
walt r
Post Laureate
Reged: 02/13/07
Posts: 3351
Loc: Doylestown, PA
|
|
Quote:
Quote:
How what am I looking for when I measure the secondary mirror?
Take the secondary out of the OTA and measure it, longest part.
A secondary mirror is measured across the minor axis (shortest part). That is the dimension that looks like a circle when viewed from the focuser.
walt
--------------------
Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
|
fuadramsey
member
Reged: 06/26/07
Posts: 80
Loc: Orange County, CA
|
|
Quote:
so if your secondary is 1.83" at its widest, and your eypiece field stop is 1.8" you will be fine if your collimation is good.
The largest 2" eyepiece, like a 31mm Nagler, may have a larger field stop (I'm not sure, check eyepiece forum), it will be usable, but you may not fully illuminate the field (lose light gather by primary).
I measured the secondary and I have similar measurements. Even accounting for error it still will be bigger than most large 2" eyepiece field stops.
Okay I think I'm sold. I'll have to take photos. I might order tomorrow! I better clear the work bench!
--------------------
www.mbsastronomy.com
Astronomy for Real People
|
sixela
Postmaster
Reged: 12/23/04
Posts: 10564
Loc: Boechout, Belgium
|
|
Quote:
Measure longest part of secondary, I used a GSO 2" Superview in mine, worked fine, the secondary size will illuminate the eyepiece, so if your secondary is 1.83" at its widest, and your eypiece field stop is 1.8" you will be fine if your collimation is good.
It's not as simple as that. And accurate calculators like that at http://www.bbastrodesigns.com/diagonal.htm , which will tell you what edge of field illumination you still get on the edge of wide field eyepieces, want the secondary's minor axis, i.e. the shorter axis.
You also have to know where the focal plane is (you can play a bit with this through collimation - moving the mirror to the back will improve edge of field illumination, but it moves the focal plane closer to the tube, and you'd better make sure that the focal plane can still be reached by the eyepiece focal planes in the new focuser plus any adapters you need for e.g. 1.25" eyepieces).
By the way, you can pretty much estimate the minor axis without removing the secondary - and the major axis is sqrt(2) larger.
A last word: there is no problem to have only 70% or (for the really wide views) even 40% illumination at the field stop. Newt are routinely designed to deliver only 70% illumination at the edge of the field of a 31mm Nagler.
--------------------
400mm f/4.46 David Lukehurst truss Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
|
fuadramsey
member
Reged: 06/26/07
Posts: 80
Loc: Orange County, CA
|
|
Quote:
2) In addition to cutting the opening wider, you will need to "shim" the focuser to the tube since they are designed for 8" tubes and bigger. I used old mouse pads, cut out to fit under the focuser inbetween the OTA, got that tip from someone else here, and after a few nights of use I was convinced it worked well (no slop).
I got everything, and all mirrors are out of the ota. I have the hole marked out ready to cut.
I'm just looking at the shimming right now. Did you cut one rectangular piece of the mouse pad that is the same size of the focuser base?
It's hard to make out that detail with your photo.
Thanks!
--------------------
www.mbsastronomy.com
Astronomy for Real People
|
fuadramsey
member
Reged: 06/26/07
Posts: 80
Loc: Orange County, CA
|
|
Okay here's the stock focuser.
Celestron Omni XLT 150
--------------------
www.mbsastronomy.com
Astronomy for Real People
|
fuadramsey
member
Reged: 06/26/07
Posts: 80
Loc: Orange County, CA
|
|
Removal of the focuser.
--------------------
www.mbsastronomy.com
Astronomy for Real People
|
fuadramsey
member
Reged: 06/26/07
Posts: 80
Loc: Orange County, CA
|
|
the sad empty hole.
--------------------
www.mbsastronomy.com
Astronomy for Real People
|
fuadramsey
member
Reged: 06/26/07
Posts: 80
Loc: Orange County, CA
|
|
The stock 1.25" versus the 2".
--------------------
www.mbsastronomy.com
Astronomy for Real People
|
fuadramsey
member
Reged: 06/26/07
Posts: 80
Loc: Orange County, CA
|
|
removal of the secondary.
--------------------
www.mbsastronomy.com
Astronomy for Real People
|
fuadramsey
member
Reged: 06/26/07
Posts: 80
Loc: Orange County, CA
|
|
I marked the primary before I removed it just to keep things aligned close to stock.
--------------------
www.mbsastronomy.com
Astronomy for Real People
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
[Re: