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The end of OAG?

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#51 Raginar

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Posted 20 October 2013 - 04:39 PM

Dave,

That's your opinion of OAG guiding.. I'm just dabbling in it and so far it's been frustrating for me (all user generated I assure you). I guess if I had something like star lock that worked perfectly with my random conglomeration of scopes I have... I'd be stoked and might buy it.

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#52 Peter in Reno

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Posted 20 October 2013 - 05:36 PM

Some people are missing the point about OAG. The reason OAG is mentioned in this thread is the OP mentioned it in the first post and title of this thread as being a P.I.T.A. to operate. If he had left it out and only mentioned SBIG's new flex free guide scope, compared with ordinary guide scopes and nothing else, this thread would not have gone viral.

I was in the same boat as Dave. Long time ago I started imaging with C-11 (2800mm focal length) and guide scope and I had nothing but trouble thanks to mirror flop inside the scope. I threw out the guide scope and replaced it with OAG/Lodestar and viola no more image shifts in between subs. Not only that, at least one guide stars have always been found in OAG guide port and NEVER had to hunt for guide stars by rotating OAG thanks to high sensitivity Lodestar. This is my hard fact and objective words about OAG. I live in extremely high light pollution area and I am very surprised I have not had a single issue with OAG and Lodestar.

I am very sorry that OAG has not worked quite well for Hilmi. Maybe he can start a new thread describing his issues and possibly someone will provide a good solution.

I now own a TEC 140 F/7 APO refractor but will still use OAG since I know how to operate it and why risk using guide scopes when there's a better chance of flexure?

Probably the most common mistake when people could not get OAG working is they use insensitive guiders like Orion SSAG.

Frank is correct about some disadvantages of OAG like it won't work for Hyperstar and some Newts with very short back focus. That's fine for Hyperstar since focal ratio is extremely small (or fast) and sub-exposures are also very short that any small guide scope would very well.

If the OP removes any negative comments about OAG in the original post, then discussions about OAG may stop. Discussions about OAG will never stop here until the OP removes negative comments in his first post and title of the thread.

I agree with Dave that discussions should always be objective.

To OP, if you remove any negative comments about OAG in the first post and title of this thread, I promise not to mention OAG from then on.

Finally, my comments do not in any way bash SBIG's new flexure free guide scopes. In fact I welcome this new technology. I never said that using OAG is easy. Quite the opposite. It takes time for some people to grasp the concept of using OAG. I also admit using guide scope is easier but not necessarily better than OAG. Please understand my reluctance of replacing OAG with guide scope.

Peter

#53 SL63 AMG

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Posted 20 October 2013 - 06:10 PM

I don't just spout off.


Save your money and go with the 5. I don't know to many people using a 3 on SII


Supporting Thread


Here's what Don told me at the Advanced Imaging conference. The greater the light pollution your dealing with the lower the number you want. I'm in the country with 4.5 skies, so I could use the 5nm. Had I been closer to town with more light pollution I would have coughed up the extra for the 3nm. I don't think you can get much better than the AstroDon E2's. I did my research and there's nothing close to para focal as they are. That does come at a price though.



Contradictory Supporting Thread


Would you like me to post a couple dozen more examples just like it?

#54 PGW Steve

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Posted 20 October 2013 - 06:44 PM

Is it possible to just disagree with someone and state your point without turning it into a thread with more information on discrediting them than there are facts about the topic at hand?
I'm glad the OP shared information on a new technology. How that technology is applied, and how good/bad it is remains to be seen. As someone stated, it is unlikely SBIG did this just to waste R&D money, obviously there is a reason for it, AND a demand. Until there are working systems, with tangible results of the pros and cons of this system in real life imaging systems, EVERYONES opinion is just that. Perhaps we can carry on this discussion about Differential Guiding (DG) when there has been a suitable demonstration of its features via youtube, or a reputable imager that isn't an employee of SBIG.

Talk about shooting the messenger, this thread has brought out the bad in some people.

#55 Peter in Reno

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Posted 20 October 2013 - 07:36 PM

The OP made very poor statement in his original post by making poor comparison with other technology like OAG. This is not about bashing or disagreeing with SBIG's new technology of flexure free guide scope. Dave and I actually welcomed this new technology. It's simply the way the OP made comments very poorly in his original and subsequent posts, that's all.

Please carefully read what Dave and I are trying to say. We did not bash or disagreed with SBIG's new technology of flexure free guide scopes. I just wished the OP simply had stated about SBIG's new but untested technology and nothing else.

Peter

#56 Raginar

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Posted 21 October 2013 - 09:46 AM

I don't think he did. He made an opinion, just like you are right now. I'm just learning how to setup an oag, and it's not easy like my finder guider. So, it's a PITA.

Again, you guys are just attacking poor Mike over a very small part of his post. Who cares if mike thinks a OAG is a PITA? The thread is about the new tech.

#57 Peter in Reno

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Posted 21 October 2013 - 10:26 AM

You are correct that the OP made an opinion and I simply rebutted his opinion. For that I am sorry that I didn't presented in a diplomatic manner.

I believe a better comparison would be to compare to typical guide scopes that has difficulty keeping in sync with the main scope since OAG do not have flexure issues. Primarily I believe this is supposed to replaced ordinary guide scopes, secondary for OAG.

Back to original thread. Did the speaker mention anything about software or will it still work with popular guiding software like PHD or MaximDL? What about dithering? After each dithering, will it have to re-calibrate the artificial star with guide star since the guide star moved due to dithering? I saw a Facebook video of the presentation but I am deaf and cannot hear what the speaker said.

I hope with time and experience from SBIG or other companies will come up with a much simpler design of same idea and universal to work with any scopes (Newt, Refractor, SCTs, etc.) to keep the cost down. Yes, I admit that guide scope is easier than OAG and am willing to try if I can get convinced it will work as well as OAG and guaranteed to get round stars for every sub like my OAG does.

Peter

#58 mikeschuster

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Posted 21 October 2013 - 10:48 AM

What about dithering? After each dithering, will it have to re-calibrate the artificial star with guide star since the guide star moved due to dithering?
Peter


I was at the presentation, these topics were not discussed.

As the system flexes, the IR star shifts with respect to the background stars. The IR star may collide and overlap with a background star, which will compromise measurement and differential guiding accuracy. Similarly with dithering.

Also, the positions of the chosen guide star and IR star may be widely separated. This will require a larger guide box size, increasing download times. There may be a need to reposition the IR star, to position it closer to the guide star, but any mechanical adjustability is an additional source of potential flexure. Also, issues like these will make the system harder to use that it otherwise might appear.

An automated setup (ACP, CCDAutopilot, etc) may need to deal with these issues. Positioning the IR star, making sure it does not collide across flexure and dithering, and resetting the intensity of the IR source to match the automatically selected guide star exposure are all issues that may required software development and ASCOM and/or custom interfaces.

Regards,
Mike

#59 vpcirc

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Posted 21 October 2013 - 11:02 AM

If I can make a few points to clarify
1. I posted this to share the new tech with others as not everyone is as fortunate as I to attend AIC.
2. I am not advocating or anyway saying that SBIG has found a solution but am hopeful.
3. My statement about OAG being a pain came directly from Mike Rice who runs NM Skies and has set up systems expertly for 20+ years. I am buying a new planewave 14 (hopefully) and SBIG is working with them to incorporate the new system. When I told Mike that, he said that's great you won't have to deal with the problem of OAG and rotation.
4. I believe that OAG is an absolute necessity in some cases
5. The president of SBIG said this system was most beneficial to SCT owners and that's why they were pursing that system first. I am not an expert nor have I tried to use OAG with an SCT so I have no clue why he feels that way.
6. The second part of the post with AP's new setup for refractors is a far better solution to OAG. AP makes some of the best refractors in the world, and again, if Roland didn't think this was a brilliant idea, it wouldn't be offered. I've used a similar setup for 4 years, but not nearly as secure and stout as they did, and yet I can guide perfectly for 30 min with my inferior system that Roland let me know I had mounted at the wrong point lol.

When I express my opinion, it is from my own experience of learning and asking questions from those much smarter than I and my own failures. I am far from always being right and many times there's more than one way to do things. My only goal is try and help others learning to not repeat my mistakes and make the journey through this learning curve easier. Yes, I seek out the advice of the best and the brightest, had I not, the telescope would be sitting in the closet gathering dust as I would of given up. I'm not bright enough to figure it out on my own.
Anyone that knows me personally will tell you I'd do anything to help another imager, not because I think I'm smarter or better, its just the way most of this community is.

#60 garret

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Posted 21 October 2013 - 11:15 AM

QSI 683wsg with integrated filter wheel and OAG has back focus of 50mm to 53mm depending on T-thread or 2.156" adapter. Wouldn't this camera work?



I want to use 35x24mm ccd arrays...because it give me a large field.
My 5 dmk2 has a coolerbox (-22 Celsius inside) the imaging result are very good only limited by seeing, light-pollution, and poor guiding (I'm working on this: new guider telescope, PEC for mount etc.)


Garret van der Veen

#61 Peter in Reno

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Posted 21 October 2013 - 12:39 PM

6. The second part of the post with AP's new setup for refractors is a far better solution to OAG.


I will try to be as diplomatic as I can. I think once again you chose your words poorly. What do you mean by "better"? "Better" in terms of getting rounder stars than using OAG? IMHO, not necessarily. "Easier" would have been a better choice of word. I can see that placement of guide scope on OTA's tube or focuser rather than on dovetail/tube rings so the guide scope will follow the OTA's flexure and will be better in sync with the main camera. But it is not 100% foolproof because there could still be unwanted hidden flexure anywhere that can happen anytime that will result throwing out some subs but A-P guide scope setup is definitely better than traditional guide scope mounted on top of dovetail/tube rings. OAG may not be 100% foolproof but darn close to 100% since guide camera knows exactly what's happening with the main camera and guide scope does not.

Peter

#62 Peter in Reno

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Posted 21 October 2013 - 12:42 PM

QSI 683wsg with integrated filter wheel and OAG has back focus of 50mm to 53mm depending on T-thread or 2.156" adapter. Wouldn't this camera work?



I want to use 35x24mm ccd arrays...because it give me a large field.
My 5 dmk2 has a coolerbox (-22 Celsius inside) the imaging result are very good only limited by seeing, light-pollution, and poor guiding (I'm working on this: new guider telescope, PEC for mount etc.)

Garret van der Veen


Hi Garret,

Sounds reasonable. I wish you best of luck getting your guiding issues resolved. Let us know if you found a solution.

Peter

#63 Aquatone

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Posted 21 October 2013 - 09:00 PM

6. The second part of the post with AP's new setup for refractors is a far better solution to OAG.


I will try to be as diplomatic as I can. I think once again you chose your words poorly. What do you mean by "better"? "Better" in terms of getting rounder stars than using OAG? IMHO, not necessarily. "Easier" would have been a better choice of word. I can see that placement of guide scope on OTA's tube or focuser rather than on dovetail/tube rings so the guide scope will follow the OTA's flexure and will be better in sync with the main camera. But it is not 100% foolproof because there could still be unwanted hidden flexure anywhere that can happen anytime that will result throwing out some subs but A-P guide scope setup is definitely better than traditional guide scope mounted on top of dovetail/tube rings. OAG may not be 100% foolproof but darn close to 100% since guide camera knows exactly what's happening with the main camera and guide scope does not.

Peter


Using a guidescope mounted on the actual telescope body (NOT rings) is certainly a lot easier than an OAG, especially in more barren areas of the sky. I have been testing the new Astro-Physics guidescope arrangement (using their 60mm finder scope) directly mounted on the backplate of an almost 4,000mm focal length Cassegrain and it works superbly at different pointing angles, thermal, and gravity loads. I have compared guiding results using an SBIG off-axis internal guide chip camera and see little if any difference. (Or at least any variation could just as easily be seeing related) Whereas I would not say that the results are "better" they are no worse. Obviously the mechanical/strutural integrity over the whole chain is critical, but as long as weak points have been identified and an intelligent approach is adopted, there appears no reason in principle why a guidescope solution cannot work at longer focal lengths.

I had a concern that the nylon tightening bolts in the AP Guidescope rings would not be as solid as metal, but at AIC George from AP told me that the nylon tipped metal bolts were harder to procure and I should see no difference. I find myself tightening those things as much as possible, but so far he is right and I have not noticed any difference. Good job AP!

Anyway, just one data point.

Chris

#64 vpcirc

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Posted 21 October 2013 - 10:08 PM

That's very encouraging news. That may very well be the way I go for the planewave 14", the focal length is only around 2500. I told George he took my idea from pics I sent him last year and made it 10x better and correctly mounted!

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#65 elbee

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Posted 22 October 2013 - 01:35 AM

I told George he took my idea from pics I sent him last year and made it 10x better and correctly mounted!


I suspect that was said somewhat in jest :-)

fact is, roland has been advocating direct mounting of a guidescope onto the optical tube for years in the ap yahoo groups. he has repeatedly advised those that were mounting a guidescope on a top plate it was a recipe for trouble.

I started using this setup last year. it is the sbig 100mm focal length e-finder with an STL remote guide head installed on a two generations old A-P finder bracket. I've used it so far with a refractor at 1120mm focal length and it guides extremely well up to 30min exposures.

Posted Image

btw, I did replace the machine screws for metal with nylon tips. not because I was worried about them being strong enough, but because I needed slightly longer ones than what comes with the finder bracket.

#66 freestar8n

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Posted 22 October 2013 - 03:25 AM

I have compared guiding results using an SBIG off-axis internal guide chip camera and see little if any difference.



A key source of flexure in a mirror scope is within the OTA itself - and more rigid mounting of the guidescope won't help with that. In order to assess how small the flexure is, it needs to be expressed in arc-seconds per minute - i.e. as a rate. If you aren't guiding with a common path system like OAG, then there will always be some non-zero flexure rate. That's why this sbig thing has been in the works for so many years. Whether it finally works now I don't know because I have never seen results from that system - but I have sure heard about it for a long time.

So if you find that a small guidescope works well for you that's great - but as a data point it would be good to estimate the actual flexure rate you see - because it will not be zero, and it will prevent getting consistently small and round stars in long exposures and long focal length. 0.1"/minute is a very tiny amount - but in a 10m exposure with 2" stars it would be a problem. With 4" stars it might be tolerable.

Refractors are much less affected by flexure so I can imagine the guidescope mounting plays a bigger role. They also don't create stars that are 2" and below fwhm - so they are much more forgiving in many ways than a mirror scope.

Professional work with large cassegrains is either self-guided or common-path (OAG) guided. They may internally use infra-red light sources for slow active optics alignment of the telescope during imaging - but the guiding itself would be with a real star using the actual optical path at the full focal length.

Frank

#67 vpcirc

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Posted 22 October 2013 - 07:32 AM

Of course my comment was in jest, but I do have a serious question. Before anyone gets their feathers ruffled, I'm not pointing or stating, I'm asking!!! I feel like the term flexure is thrown around loosely at times, so here's the question. How do you know how much is flexure, and how much is the construction quality of the OTA, the PE of the mount, and how much is caused by setup? Would you have to somehow measure each? When I asked Tom Bash about this last year he told me that guiding has changed dramatically in the past 5 years. The old thought was the f-ratio between the guide scope and the OTA couldn't be different than xxx but that doesn't apply anymore. If you're getting great guiding with AP's setup at a 4000 FL, is it because of the stability of the overall system, mirrors that are temp regulated, a solid mount? I am really confused and making the right choice for my new OTA could be a difference of 4-5k in the total cost.

#68 Alex McConahay

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Posted 22 October 2013 - 08:08 AM

>>>>>How do you know how much is flexure, and how much is the construction quality of the OTA, the PE of the mount, and how much is caused by setup? Would you have to somehow measure each?

I am not sure you could ever know the source of all deviations of the locations of the stars. I suspect somebody with lots of equipment may be able to isolate some of the causes, but never all of them.

I have not seen the whole setup that SBIG was touting, although I did see the presentation in Santa Clara. But it seems to me they are adding parts to a system to try to get the flexure out. The more parts, the more chance for a new place to flex, in my opinion. I cannot tell how the LED source for the artificial star is affixed to the camera or the tube, or the focuser, but that seems to be a place for a problem, as well as the location of where and how the retroreflector is.

I think this uncertainty in knowing where the flexure or other error comes from is the strength of OAG. You have the guide sensor and the imaging sensor in exactly the same relationship (although even here, there is room for flexure--but so little).

As for whether OAG is a pain or not--I have to say it can be. It can be hard to find a star sometimes. But, really, with a sensitive enough guider, it is almost always possible to find a guide star--and that is about the only trouble I know about.

Alex

#69 dawziecat

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Posted 22 October 2013 - 10:50 AM

I have used OAG on only two nights so far. But it worked so well, I am determined to use it always now, on all OTAs, even those of ridiculously short FLs.

My experience with external guide 'scopes, both "mini" and "maxi" has been a battle. I will never be sure just what was flexing, but elongated stars on 15 minute 530mm exposures became round as soon as I used the OAG-8300.

I was surprised at how plentiful guide stars were but appreciate such limited experience, and with such a short FL, is no test at all.

I did very quickly run out of back focus however. With the FSQ106EDXIII, the QE reducer, a MMOAG, the shortest adapter Precise Parts can make and an STL with internal FW left me too long in focus by about 1mm. That is AFTER allowing 2.3mm for the filter, CCD window and coverslip. Had I the external, 8 position filter wheel for the STL, it seems I could not use the MMOAG with the QE reducer at the recommended focus at all.

The REAL problem with OAG, as I see it, is not the PITA factor, but the backfocus issue with some gear combinations.

#70 orion69

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Posted 22 October 2013 - 11:16 AM

How do you know how much is flexure, and how much is the construction quality of the OTA, the PE of the mount, and how much is caused by setup?


Easy, install OAG and difference in star quality is flexure. ;)

#71 orion69

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Posted 22 October 2013 - 11:19 AM

The REAL problem with OAG, as I see it, is not the PITA factor, but the backfocus issue with some gear combinations.


Correct.

#72 vpcirc

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Posted 22 October 2013 - 11:40 AM

Now we're getting back to opinions again, for many people OAG is a PITA, but I'm sure you guys have mastered it so it's not for you. Here's my issue. I'm buying a 14" Planewave. To add the combination rotator focuser is an extra $3500. Now if I add a MMOAG it's another $900. Why on God's earth would I do that if I can achieve what Aquatone is achieving great success with AP's new design?

#73 Peter in Reno

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Posted 22 October 2013 - 11:42 AM

That's true. I was somewhat forced to replace my external OAG/FW/CCD camera setup with QSI with integrated FW and OAG to reduce back focus. My new TEC 140 APO with flattener requires 85mm back focus. Previous scope was C-8 EdgeHD which had a whopping 133mm back focus. QSI wsg cameras' back focus is either 50mm (T-Thread) or 53mm (2.156") depending on telescope side adapter.

Peter

#74 Peter in Reno

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Posted 22 October 2013 - 11:45 AM

Using a guidescope mounted on the actual telescope body (NOT rings) is certainly a lot easier than an OAG, especially in more barren areas of the sky. I have been testing the new Astro-Physics guidescope arrangement (using their 60mm finder scope) directly mounted on the backplate of an almost 4,000mm focal length Cassegrain and it works superbly at different pointing angles, thermal, and gravity loads. I have compared guiding results using an SBIG off-axis internal guide chip camera and see little if any difference. (Or at least any variation could just as easily be seeing related) Whereas I would not say that the results are "better" they are no worse. Obviously the mechanical/strutural integrity over the whole chain is critical, but as long as weak points have been identified and an intelligent approach is adopted, there appears no reason in principle why a guidescope solution cannot work at longer focal lengths.

I had a concern that the nylon tightening bolts in the AP Guidescope rings would not be as solid as metal, but at AIC George from AP told me that the nylon tipped metal bolts were harder to procure and I should see no difference. I find myself tightening those things as much as possible, but so far he is right and I have not noticed any difference. Good job AP!

Anyway, just one data point.

Chris


Congrats on getting your guiding to work well with A-P guide scope guiding a 4000mm focal length scope. Can you still achieve round and reasonably small FWHM stars at 30 minute guided exposures (for narrow band imaging)?

Peter

#75 orion69

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Posted 22 October 2013 - 11:51 AM

Now we're getting back to opinions again, for many people OAG is a PITA, but I'm sure you guys have mastered it so it's not for you. Here's my issue. I'm buying a 14" Planewave. To add the combination rotator focuser is an extra $3500. Now if I add a MMOAG it's another $900. Why on God's earth would I do that if I can achieve what Aquatone is achieving great success with AP's new design?


It was a joke.
As I said before in another threads, if it works for you, great.
If not, there is always OAG.






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