Ned Smith
super member
Reged: 04/10/10
Loc: NW Georgia, USA
|
Guiding: OAG vs Guide Scope
#5509947 - 11/08/12 01:08 PM
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
I am building a GEM for my new VRC8. Can someone tell me the pros and cons of OAG vs a separate guiding scope with guiding camera.
TIA
|
Phil Sherman
Pooh-Bah
Reged: 12/07/10
Loc: Cleveland, Ohio
|
Re: Guiding: OAG vs Guide Scope
[Re: Ned Smith]
#5510267 - 11/08/12 05:11 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
OAG:
1. limited FOV to find guide stars
2. Heavier equipment for the focuser to support.
3. Requires camera with two imaging chips or an attachment between the camera & focuser to divert the guide camera light. An attachment will increase back focus.
guide scope:
1. Can use different focal length and f/ ratio than imaging scope
2. Subject to differential flexure - imaging scope & guide scope bend (sag) a little differently.
3. Can be aimed at different stars.
4. 3. above can cause more field rotation because you can image further away from the guide star.
5. More weight for the mount to carry
An 80mm APO makes a great guide scope and, if it's a short focal length compared to your main scope, you can swap the imaging and guide scopes to get a wider FOV.
Phil
Edited by Phil Sherman (11/08/12 05:15 PM)
|
*skyguy*
Pooh-Bah
Reged: 12/31/08
Loc: Western New York
|
Re: Guiding: OAG vs Guide Scope
[Re: Ned Smith]
#5510336 - 11/08/12 05:56 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
 I'm staying out of this one!
|
SMigol
super member
Reged: 07/30/10
|
Re: Guiding: OAG vs Guide Scope
[Re: *skyguy*]
#5510391 - 11/08/12 06:40 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
One con to an OAG that may not be easily tested:
Be sure that your scope has enough in-focus travel to handle the extra length required by the OAG. I recently tried this on a scope of mine and found this problem.
|
TxStars
Pooh-Bah
Reged: 10/01/05
Loc: Lost In Space
|
Re: Guiding: OAG vs Guide Scope
[Re: Ned Smith]
#5511011 - 11/09/12 03:46 AM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
If I'm not mistaken the VRC-8 is the same scope as the AT-8RC from Astro-Tech.
If it is then you have several options open to you including:"OAG" "On axis guiding".
|
agmakr
member
Reged: 12/14/07
Loc: Agrinio, Greece
|
Re: Guiding: OAG vs Guide Scope
[Re: TxStars]
#5511030 - 11/09/12 04:27 AM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Phil made an excellent analysis on the pros and cons.
I used a guidescope for some time and almost always had problems
with differential flexure.So i ended up throwing away about 30% of the fits i got.
I recently changed to an OAG and i managed to get 15,20,30min subs without any trail.
However, it may be a bit tricky to focus the OAG at first.
You may check here:
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5502330/page...
If you choose the guidescope path, make sure you mount it
very compactly with the main scope.
|
Ned Smith
super member
Reged: 04/10/10
Loc: NW Georgia, USA
|
Re: Guiding: OAG vs Guide Scope
[Re: TxStars]
#5511110 - 11/09/12 07:27 AM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Yes, that is the scope.
What are the options?
|
Jared
Post Laureate
Reged: 10/11/05
Loc: Piedmont, California, U.S.
|
Re: Guiding: OAG vs Guide Scope
[Re: Ned Smith]
#5511263 - 11/09/12 09:15 AM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
If you are going to be imaging with a scope greater than about 1,500mm focal length, you will likely find that an OAG provides a noticeably better result since it isn't subject to differential flexure. If you are going to use a scope with a moveable primary mirror, especially one without mirror locks, you will likely need to use an OAG. At shorter focal lengths, guide scopes are easier to use since it is easy to find a guide star in virtually any part of the sky. As mentioned, OAG's will also use up some back focus, so make sure you have enough room.
I think OAG's are the only way to go if you want tight, round stars above (approximately) 1,500mm focal length, despite the drawback of a limited field of view.
Oh, one other possible advantage to guide scopes is that you can guide on the center of the field. If you want to image a comet, this can be critical.
|
JoseBorrero
Carpal Tunnel
Reged: 09/04/09
Loc: MI
|
Re: Guiding: OAG vs Guide Scope
[Re: Jared]
#5511603 - 11/09/12 01:04 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
It seems that if you fail to set an OAG will frustate you and go guide scope
|
TxStars
Pooh-Bah
Reged: 10/01/05
Loc: Lost In Space
|
Re: Guiding: OAG vs Guide Scope
[Re: Ned Smith]
#5512112 - 11/09/12 06:28 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Quote:
Yes, that is the scope.
What are the options?
There are several off-axis guiders that can be used.
One example:
http://www.optcorp.com/product.aspx?pid=17671
You can also use an On-axis guider which makes finding a guidestar easy:
http://www.astromart.com/articles/article.asp?article_id=836
|
guyroch
Vendor (BackyardEOS)
Reged: 01/22/08
Loc: 3rd rock from the sun, Canada
|
Re: Guiding: OAG vs Guide Scope
[Re: TxStars]
#5512135 - 11/09/12 06:44 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Once you get the OAG going you'll never go back to a guide scope imo.
Phil forgot to mention that a OAG takes care of flexure, whereas a guide scope may cause flexure depending on the sturdiness of your gear.
Hope this helps,
Guylain
Edited by guyroch (11/10/12 03:04 PM)
|
Ned Smith
super member
Reged: 04/10/10
Loc: NW Georgia, USA
|
Re: Guiding: OAG vs Guide Scope
[Re: guyroch]
#5513262 - 11/10/12 02:28 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Thanks for your comments.
|
jgraham
Postmaster
Reged: 12/02/04
Loc: Dayton, Ohio
|
Re: Guiding: OAG vs Guide Scope
[Re: Ned Smith]
#5513332 - 11/10/12 03:33 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
I use both; a guide scope on my SN6 and an off-axis guider on my SC8. Personally, I would never use an off-axis guider on a moveable focuser, way too much weight, though for an SCT with its fixed eyepiece tube the weight is far less of an issue. I've also found that an off-axis guider benefits from a guide camera with a large chip (I use a Pro III as my guide camera). Sooooo, a Newtonian or any other scope with a focuser that uses a moving draw tube I'd suggest a guide scope. For telescopes with a fixed draw tube an off-axis guider is worth considering if you also have a nice guide camera.
|
wolfman_4_ever
Pooh-Bah
Reged: 07/15/11
Loc: El Segundo, Ca, So. Cal
|
Re: Guiding: OAG vs Guide Scope
[Re: jgraham]
#5514708 - 11/11/12 04:08 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Is flexure an issue if the guidescope is setup in a side-by-side configuration?
|
TxStars
Pooh-Bah
Reged: 10/01/05
Loc: Lost In Space
|
Re: Guiding: OAG vs Guide Scope
[Re: wolfman_4_ever]
#5514799 - 11/11/12 05:02 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
When using a guidescope there is always a chance for flexure to cause elongated or strange shaped stars.
The longer the focal length you image at the more any flexure will show up.
|
jgraham
Postmaster
Reged: 12/02/04
Loc: Dayton, Ohio
|
Re: Guiding: OAG vs Guide Scope
[Re: TxStars]
#5514818 - 11/11/12 05:19 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
I don't think side-by-side is any more or less susceptible to flexure. I've done it both ways.
|
Patrick
Postmaster
Reged: 05/16/03
Loc: Franklin, Ohio
|
Re: Guiding: OAG vs Guide Scope
[Re: jgraham]
#5589102 - 12/26/12 12:21 AM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
With SCT mirror locks is the flexure issue as much of an issue with a side by side or guide scope arrangement? It seems like it would not be. I do not like off-axis guiders because I've been unable to get mine working to date.
Patrick
|
Footbag
Carpal Tunnel
Reged: 04/13/09
Loc: Scranton, PA
|
Re: Guiding: OAG vs Guide Scope
[Re: Patrick]
#5590008 - 12/26/12 05:12 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Quote:
With SCT mirror locks is the flexure issue as much of an issue with a side by side or guide scope arrangement? It seems like it would not be. I do not like off-axis guiders because I've been unable to get mine working to date.
Patrick
Flexure comes from more places then the mirror. I'm limited to 8m subs due to flexure in my setup despite the mirror locks.
I understand what you are saying about not getting an OAG working. I never got my Celestron Radial Guider working with my SSAG(Needed more inward focus). Then I tried the Older model Celestron OAG(Need more outward focus, but thumbscrew doesn't hold then camera stable enough)
I just purchased a TS9 OAG and will be getting a Lodestar. I'm fairly confident this setup will work, but won't know until it all shows up.
|
hcsceo
super member
Reged: 10/14/09
Loc: Austin, TX
|
Re: Guiding: OAG vs Guide Scope
[Re: Footbag]
#5591276 - 12/27/12 02:30 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
A couple of notes from my OAG experience. First thing is that I love it! Much better with my SCT than a guide scope ever was. However, getting there was not easy and I gave up on it at least once. A sensitive guide camera is a must. The longer the focal length the more important this is. Don't expect to put a webcam on there and be guiding. Dsi pro mono is minimum. A lodestar would be awesome. Next finding focus is where I'm guessing most people fail. It was a horrible experience for me. In the end I measured distances with some calipers from imaging chip to the front of the pick off prism OAG and again from the pick off prism to the guide chip. These need to be the same. I ordered a bunch of spacers from scoffstuff to get this perfect. It seems to find stars a little easier if focus is a little soft. Take it all outside during the day and focus both before trying at night. Watch out for the prism casting a shadow on your imager during this phase. You might need to play with the prism location. On mine it is located on the long side of my imager ccd. One final note is to get the oag as close to the imager as possible to reduce vignetting. Because it is picking off light from the edge of my SCT light cone I have some coma in those stars. This doesn't seem to affect the performance however.
|
jgraham
Postmaster
Reged: 12/02/04
Loc: Dayton, Ohio
|
Re: Guiding: OAG vs Guide Scope
[Re: hcsceo]
#5591606 - 12/27/12 06:47 PM Attachment (12 downloads)
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
I chose to use a guide scope on my SN6 as its tube rings made a natural attachment point for the scope and it's nice to be able to align the field of view of the guide camera with the imaging camera.
|
jgraham
Postmaster
Reged: 12/02/04
Loc: Dayton, Ohio
|
Re: Guiding: OAG vs Guide Scope
[Re: jgraham]
#5591615 - 12/27/12 06:53 PM Attachment (15 downloads)
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
However, for my SC8 I ended up with an off-axis guider. This was a nice option for me as my SC8 doesn't have tube rings and the fixed focuser hardware made an effective attachment point for the combined weight of the imaging and guide cameras. I'm using a DSI Pro III as my guide camera which gives a generous field of view. I was also able to keep this system very compact which helped a lot in making this such a nice system to use. An unexpected bonus is that I don't have to set the focus of the imaging an guide cameras separately. After the initial setup I've never had to fiddle with the focus of the guide camera.
|
wolfman_4_ever
Pooh-Bah
Reged: 07/15/11
Loc: El Segundo, Ca, So. Cal
|
Re: Guiding: OAG vs Guide Scope
[Re: jgraham]
#5591951 - 12/27/12 11:10 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Just do the best of both worlds..
Side-by-Side.. and an OAG with an AO!
|
JoseBorrero
Carpal Tunnel
Reged: 09/04/09
Loc: MI
|
Re: Guiding: OAG vs Guide Scope
[Re: wolfman_4_ever]
#5593187 - 12/28/12 07:28 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
my best guiding is so far with tandem setup shown here: http://www.flickr.com/photos/70224675@N06/7989767360/in/photostream
lately I experiment with 50mm mini guide scope and got same good guiding results as the tandem. http://www.flickr.com/photos/70224675@N06/8273999430/in/photostream
|
CounterWeight
Postmaster
Reged: 10/05/08
Loc: Cloudyopolis, OR.
|
Re: Guiding: OAG vs Guide Scope
[Re: JoseBorrero]
#5593495 - 12/28/12 10:52 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
I've never experienced differential flexure... I use piggyback exclusively. I think any flexure is bad, anywhere, for imaging.
Smeared stars due to mirror movement I don't consider to qualify as the term often defined (by that I mean purely mechanical issues elsewhere)- but it's an obvious reason to use an OAG.
Good rings and saddle plate/DTP are important, focusers and collets as well. OK, everthing is. Using two screws vs. one in ring attachment, making sure and certain all well seated and square to tube and there is no play if your rings have felt or other mat'l to avoid marring scope finish. I often state that IMO other than optics alone, it's a guality focuser assy that makes the difference, this includes the IMO often neglected collet type and being certain CCD is is 'ortho' or seated squarely/securely.
One thing I've been curious about that I see mentioned rarely and that is if you are remote and using a tripod (possibly allpies to porta-piers too)- that adds a world of things IMO as far as the tripod legs, load, tensioning, spreaders, surface type/hardness.
If you are going portable and setting up every time, there is lot to get right. I've been using a permanent setup (or somewhat permanent anyway) and can take my time - but I've had good stars all the way with various piggyback setups using refractors and being very careful about focuser CCD setup and critical focus.
Seems each setup has it's own things to be certain of, and this without considering the portable pier or tripod.
|
hcsceo
super member
Reged: 10/14/09
Loc: Austin, TX
|
Re: Guiding: OAG vs Guide Scope
[Re: CounterWeight]
#5593575 - 12/28/12 11:47 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
My setup is completely portable and setup every time at different locations. It is on the standard CG5 tripod. I leave the OAG, FR, spacers, DSLR, and Meade DSI Pro all together in a camera bag and take them out and screw them on as a complete assembly when ready. This keeps dust and dirt out of the image train and I only have to clean he front of the FR if needed. I've had no issues. I also automate it with CCD commander and have no issues acquiring stars with any target throughout the night.
|
groz
Carpal Tunnel
Reged: 03/14/07
Loc: Campbell River, BC
|
Re: Guiding: OAG vs Guide Scope
[Re: hcsceo]
#5594386 - 12/29/12 01:14 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
I think one thing folks tend to overlook in this discussion of oag vs separate guidescope, is the mount. It is after all, the mount that guiding is intended to make corrections for.
With a long focal length and small field that's typical of most oag setups, you need relatively long exposures to get a star, bright stars are rare in the oag field. If you do 30 second exposures on the guide camera, finding a star will never be a problem. It also means, corrections can only happen once every 30 seconds, a big problem if your mount has an 8 second cycle on the PE that you are trying to correct for.
So, if you are trying to correct a low end mount, with a first order PE cycle on the range of 8 to 12 seconds, you need to get corrections running at roughly 1 second intervals. This is a challenge for many oag setups. On the other hand, if you are correcting a mount that has 4 or 5 arcseconds of PE, over 8 or 10 minute timescales, with no noticeable period on shorter timeframes, using an oag with 15 second exposures is going to provide plenty of opportunity for corrections at the rate needed.
|
hcsceo
super member
Reged: 10/14/09
Loc: Austin, TX
|
Re: Guiding: OAG vs Guide Scope
[Re: groz]
#5594695 - 12/29/12 04:28 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Groz has a very good point here. Part of this is helped with a sensitive guide camera but the combination of focal length and mount is critical. On my CG5 with C8 my max exposure is 4 seconds and my average is around 2 seconds. At 4 seconds I'm getting a lot of drops. Any more than that then there is no point with the PE I'm dealing with. This means that I must use the .63 reducer to be successful. I've been trying it at f10 but haven't had much luck yet with the OAG. The big advantage of the separate guidescope is you can move around the sky a little to find a suitable star. On an SCT you have to decide if losses to mirror shift with a separate guidescope or losses to longer exposures on the OAG due to lack of bright stars is worse for you. Like almost everything in this hobby there is a balance to be found, but everything comes down to the mount.
|
jgraham
Postmaster
Reged: 12/02/04
Loc: Dayton, Ohio
|
Re: Guiding: OAG vs Guide Scope
[Re: hcsceo]
#5594844 - 12/29/12 06:23 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
I can see where some would have problems finding guide stars with an off-axis guider. I'm fortunate to have a very sensitive guide camera with a fairly large chip and so far I haven't had any problems.
|
jgraham
Postmaster
Reged: 12/02/04
Loc: Dayton, Ohio
|
Re: Guiding: OAG vs Guide Scope
[Re: jgraham]
#5595301 - 12/29/12 11:13 PM Attachment (20 downloads)
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
I was cleaning images off of my DSLR's memory card and came across this picture of my SC8 with its off-axis guider. I was really pleased with how this turned out. It is very solid and compact.
|
ChubbyNinja
member
Reged: 12/07/11
|
Re: Guiding: OAG vs Guide Scope
[Re: jgraham]
#5597781 - 12/31/12 11:31 AM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
I tried out my Hutech OAG5 last night for the first time since I received it 3 or 4 weeks ago (it has been so cloudy here!) I use a DSLR for imaging and a QHY5 for the guide camera. I was able to achieve focus on the guide camera by aiming the scope at the moon. Even with the bright moon it took a while to focus so I couldn't imagine doing it on a dark night. Now that it's done I don't have to worry about it later so that's good.
Finding a guide star took some time because of the sensitivity of the QHY5 I think, so I may consider an upgrade to a lodestar or something.
I was able to take a single shot of M42 for 15 minutes and the stars looked great -- even with my fast and sloppy polar alignment. I probably could have taken a lot longer exposure but it was cold and the moon was too bright to make any resulting pics worth it. Plus, I'm not so sure long exposures of that magnitude are really necessary for a DSLR. With my previous setup using the QHY5 and a Celestron 80mm piggyback I was lucky to get 3 minutes before flexure kicked in causing my target to slowly shift out of the frame over the course of the night.
|
CounterWeight
Postmaster
Reged: 10/05/08
Loc: Cloudyopolis, OR.
|
Re: Guiding: OAG vs Guide Scope
[Re: ChubbyNinja]
#5597797 - 12/31/12 11:39 AM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Wayne - just curious what that flexure was from, were you able to isolate the source? Glad to hear the OAG solution worked for you  How long of guide exposures were you using? I'd be interested to see a 15 minute sub from a DSLR - I don't visit that forum.
|
Peter in Reno
Post Laureate
Reged: 07/15/08
Loc: Reno, NV
|
Re: Guiding: OAG vs Guide Scope
[Re: CounterWeight]
#5597871 - 12/31/12 12:18 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Wayne,
I have Hutech OAG-5 with Lodestar and they work great with my C-8 EdgeHD. I have an optional Helical focuser at the guide port and it's very handy to precisely focus a guide star. I parfocal both Lodestar and imaging camera during the day. I aim for a distant object like street light about a mile away. Once parfocaled during the day, it should be very close under the dark sky. You might have to tweak a bit.
I will never go back to guide scope. I typically have to throw out up to 50% of the subs with guide scope. With OAG, I usually never throw out a single sub unless an airplane flew by. I can easily guide up to 30 minutes with OAG.
See my setup and images in "Peter's Galleries" in my signature.
Peter
|
ChubbyNinja
member
Reged: 12/07/11
|
Re: Guiding: OAG vs Guide Scope
[Re: CounterWeight]
#5598133 - 12/31/12 03:02 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Quote:
Wayne - just curious what that flexure was from, were you able to isolate the source? Glad to hear the OAG solution worked for you How long of guide exposures were you using? I'd be interested to see a 15 minute sub from a DSLR - I don't visit that forum.
Hi there,
No I never isolated the problem. I tried tightening everything down as much as possible but no matter what I did, the image would eventually slip out of the frame over the course of the night even when I took short enough exposures to keep the stars tight. (Typically 60 to 120 seconds) It was so frustrating.
Given the moonlight and cold last night I didn't get to perform a similar test but I am going to assume that since the stars stayed round in 15 minutes then the image isn't going to move on me once I start taking lots of subs - fingers crossed.
The picture I took last night was hot with light pollution but the stars looked good. I'll post the image if I get a chance to boot up the laptop later.
|
ChubbyNinja
member
Reged: 12/07/11
|
Re: Guiding: OAG vs Guide Scope
[Re: Peter in Reno]
#5598139 - 12/31/12 03:04 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Quote:
Wayne,
I have Hutech OAG-5 with Lodestar and they work great with my C-8 EdgeHD. ...
Peter
Hi Peter,
So what is your process for finding the guide star? Do you locate your target then rotate the OAG around until you see something on the display? I notice that there are some additional adjustment screws on the OAG but I'm not sure what they may be used for and was wondering if you have to use them at all in your experience?
|
Peter in Reno
Post Laureate
Reged: 07/15/08
Loc: Reno, NV
|
Re: Guiding: OAG vs Guide Scope
[Re: ChubbyNinja]
#5598190 - 12/31/12 03:28 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Hi Wayne,
I have been very fortunate because I have not had to hunt for guide stars after framing an DSO with imager camera. Thanks to Lodestar's high sensitivity, at least one guide star is always in Lodestar's FOV. I highly recommend to get a Lodestar. My scope is C-8 EdgeHD at 2000mm focal length.
I orient my OAG so the guide port is parallel to Dec axis. I first focus on a bright star with imager camera and Bahtinov mask, then move the mount's Dec axis until the same star is in OAG's guide port, focus the star using Helical focuser. The sharper the focus of guide star, the brighter the stars are and the easier to find guide stars. If you are imaging with C-14 (from your signature) which is a very long focal length scope, you might not have as good luck as my C-8 due to much narrower FOV from C-14.
First loosen the two screws at the top of OAG, move around the OAG guide port until you find a guide star and tighten the screws. If you can't find a guide star, then slowly rotate the OAG at the scope side by loosening three screws until a guide star is found and tighten the three screws.
Peter
|
Peter in Reno
Post Laureate
Reged: 07/15/08
Loc: Reno, NV
|
Re: Guiding: OAG vs Guide Scope
[Re: ChubbyNinja]
#5598245 - 12/31/12 03:51 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Quote:
No I never isolated the problem. I tried tightening everything down as much as possible but no matter what I did, the image would eventually slip out of the frame over the course of the night even when I took short enough exposures to keep the stars tight. (Typically 60 to 120 seconds) It was so frustrating.
60 to 120 seconds guiding exposures?!?!?!? No wonder the image drifted off. Typical guide exposures should be less than 5 seconds.
It's usually next to impossible to find the source of the flex between guide and main scopes. If you are trying to guide a C-14 EdgeHD even with mirror locks engaged using guide scope, you will likely to have differential flexure not because of mirror might flop, but the focal length is very long and OAG is usually the the best method.
Peter
|
ChubbyNinja
member
Reged: 12/07/11
|
Re: Guiding: OAG vs Guide Scope
[Re: Peter in Reno]
#5598303 - 12/31/12 04:24 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Quote:
60 to 120 seconds guiding exposures?!?!?!?
Oh sorry I meant my images were 60 to 120 second exposures. The guide camera was set to 2 or 3 second exposures. : )
|
Peter in Reno
Post Laureate
Reged: 07/15/08
Loc: Reno, NV
|
Re: Guiding: OAG vs Guide Scope
[Re: ChubbyNinja]
#5598313 - 12/31/12 04:29 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
That's more like it. 
Peter
|
Peter in Reno
Post Laureate
Reged: 07/15/08
Loc: Reno, NV
|
Re: Guiding: OAG vs Guide Scope
[Re: Peter in Reno]
#5598608 - 12/31/12 07:17 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Hi Wayne,
There is a cool feature in some planetarium software called Field of View Indicator or "FOVI" which allows you to plan ahead for suitable guide stars when using OAG. Take a look at the old CN thread at:
The Sky FOVI
Do a search for "FOVI" in Google and you will find useful information.
Peter
|
mewmartigan
professor emeritus
Reged: 07/02/08
|
Re: Guiding: OAG vs Guide Scope
[Re: Peter in Reno]
#5610198 - 01/07/13 01:00 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
The Lodestar and the SBIG STi seem to be the top guidecameras for sensitivity.
I had switched from piggyback to OAG just to help reduce weight. A side affect was apparently better guiding even though I didn't think I had flexure.
I usually average about 30 10 minutes frames in a night. With the guidescope, my stacking software threw out 5 or 6 frames...first time with the OAG it threw out 1 so I was happy.
I have the SBIG STi and like it....I bought it withe the SBIG OAG for the 8300 cameras. It's a nice package but a much better deal if you buy the bundle with the camera.
|
dickbill
professor emeritus
Reged: 09/30/08
|
Re: Guiding: OAG vs Guide Scope
[Re: mewmartigan]
#5610417 - 01/07/13 03:13 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
I guess it depends of the OAG, but with the Orion one, I say piggyback wins.
I have so many problems with it, i give up. First, my guide camera is a Meade dsi pro1 and it's too heavy to lay on top of the oag without getting loose and rotate freely...in addition to other problems reported by other users of this OAG.
So here, i say there might be some good OAG, but you have to put some $ in it.
|
hcsceo
super member
Reged: 10/14/09
Loc: Austin, TX
|
Re: Guiding: OAG vs Guide Scope
[Re: dickbill]
#5611299 - 01/08/13 01:47 AM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
I read a lot about the Orion OAG issues before I bought my Orion OAG. I'm also using a Meade DSI pro and a Canon T3 with it. I can report it works flawlessly. The only change I made to mine was to use locktite on all the little screws holding it together. I also don't remove my cameras or focal reducer from it ever. I keep it as a unit in a camera bag and screw it on as needed which keeps all the internals nice and clean. The weakest point of the design is how the prism assembly is held to the main body. Keeping things together as a unit reduces stress at this critical location. I'm completely automated as of now and have done as many as 5 automated targets in a night plus Dawn flats while I've slept using it and have had 0 issues. Again, like I said earlier, getting here wasn't easy but it is definitely worth it and my experience has been the Orion OAG is a good value. It's both servicable and usable. I suspect many get thrown out because they dont know how to focus it or because the one screw that holds the prism assembly on gets loose and it starts to wiggle. Both are very easy to fix. Like everything ymmv and more money will by a better OAG. I know I'm in the minority about my good experience with the Orion but it does work for me!
|
Previous
Index
Next
Threaded
