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vpcirc
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The end of OAG?
      #6133165 - 10/12/13 02:15 PM Attachment (66 downloads)

I watched the president of SBIG demonstrate a revolution in a new guiding technology last night at AIC. Using the benefit of a wide field guide scope and the generation of an artificial star in the imaging train, the system measures changes in movements between the two to send guiding corrections. By eliminating mirror issues, this seems like very promising new tech to end the pain of OAG and rotators for reflector systems. They are also working on multi star guiding! SBIG has become my new favorite Astro company. It seems this system will be released in the very near future.

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Footbag
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Re: The end of OAG? new [Re: vpcirc]
      #6133173 - 10/12/13 02:20 PM

Quote:

I watched the president of SBIG demonstrate a revolution in a new guiding technology last night at AIC. Using the benefit of a wide field guide scope and the generation of an artificial star in the imaging train, the system measures changes in movements between the two to send guiding corrections. By eliminating mirror issues, this seems like very promising new tech to end the pain of OAG and rotators for reflector systems. They are also working on multi star guiding! SBIG has become my new favorite Astro company. It seems this system will be released in the very near future.




Wow. The artificial star idea sounds very smart. I've always wondered about multi-star guiding as well. Thanks for sharing the info.


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vpcirc
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Re: The end of OAG? new [Re: Footbag]
      #6133176 - 10/12/13 02:21 PM

They're saying it will be announced within the next month

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Tapio
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Re: The end of OAG? new [Re: vpcirc]
      #6133185 - 10/12/13 02:25 PM

Don't quite get it.
Looked at SBIG site and there was only "Sorry, there are no products at this time" in Differential Guiding.
Does this eliminate differential flexure using separate guide scope ?


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vpcirc
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Re: The end of OAG? new [Re: Tapio]
      #6133190 - 10/12/13 02:27 PM

Yes, no flexure

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mattw
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Re: The end of OAG? new [Re: vpcirc]
      #6133226 - 10/12/13 02:52 PM

Very cool, thanks for posting. While I love my OAG for it's nice round stars, if I could forgo the rotator/OAG, and still avoid flexure, I would be sold.

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andysea
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Re: The end of OAG? new [Re: mattw]
      #6133268 - 10/12/13 03:24 PM

That sounds very interesting! I don't quite understand how it works but I can't wait to learn all about it!

How is the artificial star generated?


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orion69
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Re: The end of OAG? new [Re: mattw]
      #6133274 - 10/12/13 03:27 PM

So if I'm understanding this correctly they are measuring difference in position between artificial star and the actual guiding star in guide scope?
In another words they added another device to guiding scope just to accomplish same quality of guiding you would normally get from any OAG?


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Rick J
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Re: The end of OAG? new [Re: orion69]
      #6133353 - 10/12/13 04:05 PM

They've been "coming out" with this for several years now. I remember hearing it was only months away at least two years ago. Maybe this time they mean it. Sounds like there were more technical hurdles than they expected.

There are some things a OAG can't handle, tracking a comet for instance as it is in the field of view. True there is now a guider that can do that but it only works with chips smaller than Mike or I use. While the Paramount will track a NEO making a pass it does so based on its velocity at the start of the image run. With very close ones this is not good enough as the velocity changes too much even in 30 minutes time such that by the end of the run the asteroid is making short trails. This system could eliminate this issue. NEOs are usually bright enough to be seen in a guide scope at closest approach when this becomes an issue for me.

It will be interesting to see how well it lives up to its billing when it finally does come out. I'll be waiting for their reports before considering it however. Often takes a year or so to get complex things like this ready for prime time. No matter how much testing is done it seems users find glitches no tester came across.

Rick


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vpcirc
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Re: The end of OAG? new [Re: orion69]
      #6133355 - 10/12/13 04:06 PM

I'll see if they have a flyer and scan it

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andysea
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Re: The end of OAG? new [Re: vpcirc]
      #6133403 - 10/12/13 04:41 PM

Thanks Mike! Keep us posted.

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vpcirc
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Re: The end of OAG? new [Re: andysea]
      #6133844 - 10/12/13 08:48 PM

Sorry, no documentation, but everyone there said within the next 30 days it will be released. They were talking to Planewave about adapting it to each of their OTA's. It looked operational and I don't think they would of been highlighting it if it wasn't a reality. No commitment was made on multistar guiding that I heard.

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jaddbd
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Re: The end of OAG? new [Re: vpcirc]
      #6133878 - 10/12/13 09:10 PM Attachment (44 downloads)

Is that the "differential guiding" that they have been working on for a while?

Not sure if this is what they are talking about actually becoming a reality.

Here is a blurb:

Differential Guiding: SBIG has a patent pending on a new guiding technique using an artificial guide star. Although artificial stars are used in a variety of techniques on professional telescopes, the SBIG technique is somewhat different and easy to implement on amateur scopes. An artificial star is created near the focal plane of the imaging CCD and an image of this star is retro-reflected into a separate guide scope. By using one real star in the FOV of the guide scope and the artificial star image reflected from the main scope, the difference in separation caused by telescope pointing errors is used to make the corrections to the telescope drive. There is no problem with differential deflection and a single CCD external guider can be used to monitor both the real and artificial guide stars. The artificial star image is not seen by the imaging CCD.

and a diagram.


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jaddbd
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Re: The end of OAG? new [Re: jaddbd]
      #6133883 - 10/12/13 09:12 PM Attachment (41 downloads)

And another...

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vpcirc
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Re: The end of OAG? new [Re: jaddbd]
      #6133933 - 10/12/13 09:54 PM

Yep that's what they said will be ready in 30 days

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Iver
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Re: The end of OAG? new [Re: vpcirc]
      #6134033 - 10/12/13 11:11 PM

Toward the end of this youtube clip from NEAF last year they explain the product.
https://www.youtube.com/watch?v=ti8wvBkF2U8


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pfile
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Re: The end of OAG? new [Re: Iver]
      #6134096 - 10/13/13 12:00 AM

yes unfortunately the same prototype was at AIC last year, so i hope they are really getting it done.

but these guys know what they are doing, so i'm sure we'll see it soon.


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PGW Steve
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Re: The end of OAG? new [Re: pfile]
      #6134179 - 10/13/13 01:22 AM

Sounds like a really neat technique. I can see the importance of not having tube currents in an SCT, I don't know how much the 'boiling' air in the tube will upset the artificial star.
Coming soon, chasing tube seeing and sky seeing. :-P


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Mike Wiles
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Re: The end of OAG? new [Re: PGW Steve]
      #6134223 - 10/13/13 02:10 AM

What benefit does this system offer over an off axis guider? An off axis guider is an awesome way to get rid of differential flexure, reduce weight and get spot on guiding at long focal lengths. With today's more sensitive guiding cameras, the old issue of finding a bright enough guide star for on OAG is all but eliminated as well.

While I applaud SBIG's effort and I'm a big fan of their products.....it seems like a million dollar solution to a 50 cent problem. It's heavier, more expensive and has more points of potential failure.


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vpcirc
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Re: The end of OAG? new [Re: Mike Wiles]
      #6134540 - 10/13/13 09:14 AM Attachment (24 downloads)

Mike for those using a rotator on their system this is a godsend provided it works as promises. They don't have to take flats for every angle that used during the night including flips. They don't have to rotate to find a guide star if they don't need to. It makes things far less complicated. If you're shooting with a refractor, yep, no value to you. In that case AP has come up the perfect solution, but I'm not here to argue what's better if you love OAG then that's wonderful, and why would you care. For those of us who want a different solution hopefully there's options.

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PGW Steve
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Re: The end of OAG? new [Re: vpcirc]
      #6136164 - 10/14/13 12:51 AM

I can see a big advantage in adaptive optics. With the wider field of a guide scope as opposed to an OAG through some 3 meter focal length CDK or RC or something, there should be a much higher probability of a bright star to allow the higher Hz values that make AO able to shoot through the seeing so to speak??
This is just my limited knowledge of AO at the time.


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Warhen
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Re: The end of OAG? new [Re: vpcirc]
      #6145962 - 10/19/13 01:15 AM

Kudos to good friend and former imaging partner George Whitney for this new A-P product!

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garret
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Re: The end of OAG? new [Re: jaddbd]
      #6146283 - 10/19/13 09:38 AM

The retro reflector may cause unwanted reflections or spikes...
The led near imaging camera mean I must drill a hole into the focusser?

Garret


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SL63 AMG
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Re: The end of OAG? new [Re: Mike Wiles]
      #6146645 - 10/19/13 12:46 PM

Quote:

What benefit does this system offer over an off axis guider? An off axis guider is an awesome way to get rid of differential flexure, reduce weight and get spot on guiding at long focal lengths. With today's more sensitive guiding cameras, the old issue of finding a bright enough guide star for on OAG is all but eliminated as well.

While I applaud SBIG's effort and I'm a big fan of their products.....it seems like a million dollar solution to a 50 cent problem. It's heavier, more expensive and has more points of potential failure.




I agree on all these points. In fact, I recently changed the guider on my RCOS from an ST402ME to an STi because I had to move the imaging system closer to the OTA due to the addition of a field flattener. Considering the huge size of the FLI CL1-10 filter wheel, the ST402ME would hit the CL1-10 sitting on top of the MMOAG helical focuser. The STi sits perfectly down into the MMOAG helical focuser.

At first I was worried about having smaller pixels (7.4 micron vs. 9.0 micron), a smaller FOV (648x484 vs 765x510)and less sensitivity, but the Sti, rotated lengthwise to the OAG prism works flawlessly and I never have trouble finding an adequate guide star outside of the FOV of my 16803 chip.

Look at all the guide stars available in my FOV of NGC1491



Besides, why give up a perfectly good rotator which can be used not only for finding a guide star but also for framing an object.

Mike, it looks like you could have used a rotator for your example image.


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SL63 AMG
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Re: The end of OAG? new [Re: vpcirc]
      #6146657 - 10/19/13 12:57 PM

Quote:

Mike for those using a rotator on their system this is a godsend provided it works as promises. They don't have to take flats for every angle that used during the night including flips. They don't have to rotate to find a guide star if they don't need to. It makes things far less complicated. If you're shooting with a refractor, yep, no value to you. In that case AP has come up the perfect solution, but I'm not here to argue what's better if you love OAG then that's wonderful, and why would you care. For those of us who want a different solution hopefully there's options.




Mike,

You make it sound as if we're in agony using our OAG's and rotators.

Nothing could be further from the truth.

When I plan my imaging session I simply open TheSkyX, rotate my FOVI so that my guide chip lands on an appropriate guide star that provides me the best looking composition for the obejct I am imaging and send the position angle to CCDAutoPilot.

As far as flats are concerned, I can tell you from experience that taking flats at every position angle isn't really necessary. All of the dust donuts of concern produced by the imaging system are near the camera. If you look at any of my flats, you'll see that the small tight dark dust donuts are caused from dust on the camera glass cover, the larger fainter ones are caused by dust on the filters. Anything on the secondary or primary mirror is not visible in a flat, BUT, if it were, take sky flats at dusk and dawn at the same PA angle as the image you are capturing is simple. CCDAutoPilot does all the work and produces perfect flats every time.

There is nothing complicated about it.

Besides, guiding at focal length versus guiding at a fraction of focal length is a no brainer.

I'll keep my OAG and I'll bet every owner of a large long focal length reflector will do the same.


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vpcirc
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Re: The end of OAG? new [Re: SL63 AMG]
      #6146806 - 10/19/13 02:35 PM

IF you like OAG that's great Dave, I'm not bashing it, but I can tell you some of the best imagers at AIC I spoke to, would prefer not to deal with rotator other than when they want to use it. Of course, as I witnessed with Adam Block, they all take matching flats on a nightly basis, for illumination reasons because you are correct, the donuts aren't that much of an issue. They must do it on both sides of the meridian keep track if the shot was to the east or to the west. Mike Rice said if this works as advertised it's a godsend. At this point they're only getting ready to release for SCT owners, which SBIG said needed it more than anyone. I don't think I've seen a rotator option for a Celestron Edge, but they worked with Planewave and got all their specs on each OTA and hopefully will be rolling it out before mine is built. I cannot speak from experience, only trust Mr. Rice and others are telling me from their thoughts. I don't think this product is geared towards large RCOS owners, and would likely not be available anyway.

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Peter in Reno
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Re: The end of OAG? new [Re: SL63 AMG]
      #6147157 - 10/19/13 05:43 PM

+1 for OAG.

For the last few years imaging C-8 at 2000mm focal length, not ONCE I had to rotate OAG to find guide stars. No rotator is needed for me. Even after Meridian flipping, guide stars are always available in OAG's guide port. All is needed is a high sensitivity guide camera like Lodestar or ST-i and at least one usable guide star is always available especially in high light pollution area where I live. If you have an excellent mount, then increase guide exposure not only to brighten the guide stars but also to increase SNR.

OAG is getting extremely popular and there are many reports of people struggling to fix guide scope to main scope flexure issues have switched to OAG and swore to never go back to guide scope like myself. Once you get the hang of operating OAG, it's just as easy as guide scope. Another big plus for OAG is saving weight, easier balance and better ergonomics by eliminating guide scope.

I always take flats after each imaging session even if I didn't change camera's orientation. Better safe than sorry. You never know whether dust moved or added on CCD window or filters. It's so easy and quick to take flats. Flat is probably the most critical part of calibration with lights.

I am replacing C-8 with TEC 140 F/7 APO and I will still use OAG. It will be even easier to find guide stars due to shorter focal length or wider FOV.

Peter


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vpcirc
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Re: The end of OAG? new [Re: Peter in Reno]
      #6147222 - 10/19/13 06:25 PM

I'm sure SBIG hasn't done their research and has wasted years and 1000's on a problem that doesn't need to be fixed. Sorry I bothered to share it since it's pointless and OAG is the perfect answer for Sct's. I'll write the president of SBIG and let him know how foolish he's being!

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Peter in Reno
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Re: The end of OAG? new [Re: vpcirc]
      #6147316 - 10/19/13 07:24 PM

You were the one started the argument in your original post:

Quote:

By eliminating mirror issues, this seems like very promising new tech to end the pain of OAG and rotators for reflector systems.




Some of us are simply saying that operating OAG is NOT a P.I.T.A. to operate thanks to today's technology like high sensitivity cameras. Also I never need to use rotators as well.

If you had not mentioned the negatives about OAG, then I would kept it to myself and left this thread alone.

Peter


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vpcirc
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Re: The end of OAG? new [Re: Peter in Reno]
      #6147327 - 10/19/13 07:30 PM

The post was informational and believe it or not for some people it is a problem. It's amazing how some people can't let others look at what's being talked about without immediately saying its wrong. I'm sure the engineers at SBIG know what they're talking about, far more than anyone posting on CN.

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SL63 AMG
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Re: The end of OAG? new [Re: vpcirc]
      #6147356 - 10/19/13 07:47 PM

Quote:

I'm sure SBIG hasn't done their research and has wasted years and 1000's on a problem that doesn't need to be fixed. Sorry I bothered to share it since it's pointless and OAG is the perfect answer for Sct's. I'll write the president of SBIG and let him know how foolish he's being!




Mike,

I find it interesting that you are always "quoting" the best imagers and experts in the industry, but I have never once seen any of these poeple post themselves and back up your claims.

If you want to be an advocate for new products, fine, but at least try using them yourself first before making posts that are anectdotal at their core.

I don't think anyone has issue with you being the first to report a new product, it's just a little annoying when you make claims about a products fitness for merchantibility without having ever even tried it first.

If SBIG thinks this guider is going to replace OAG's in mass quantity, I think they are in for a wakeup call.

I tried guiding my 2857mm RCOS using my ST402ME on both a 250mm FL VarioFinder and a 650mm StellarVue SVRT 90mm Raptor and I can assure you that neither performed anywhere close to using the ST402ME or ST-i with my MMOAG at 2857mm FL.

Their system may work well with short focal length guiding but I don't see how it could become a feasible replacement for long focal length OAG guiding.


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vpcirc
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Re: The end of OAG? new [Re: SL63 AMG]
      #6147367 - 10/19/13 07:58 PM

Dave that's because most of them are in a private google group that's invitation only. They don't waste their time getting involved in silly pointless discussions on here like I do. Also, this system is not proven by any means. I saw the demo for it, I'm not advocating a brand.

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Raginar
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Re: The end of OAG? new [Re: vpcirc]
      #6147402 - 10/19/13 08:27 PM

Sorry everyone is attacking you, Mike. I think it's neat and if it gives us a new tool to work with, that'll be great.

Don't sweat it


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SL63 AMG
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Re: The end of OAG? new [Re: Raginar]
      #6147547 - 10/19/13 10:31 PM

Quote:

Sorry everyone is attacking you, Mike.




I dont get it.

Mike reports a new product.

Mike titles the product with an unlikely conclusion.

Mike then makes anecdotal statements about the likelyhood of the products performance and impact on competitive products though this product has not yet been released and he has never used it.

Mike repeatedly claims he is quoting well known people none of whom have ever publicly back up what he says.

People refute Mikes claims and back it up with facts.

You interpret it as a personal attack on Mike.

Perhaps Mike might consider evaluating his repeated "name dropping" anecdotal statements about things for which he has no personal experience and simply stick to the facts, then there will be no misperception of attacking him personally rather than his statements. Instead, we can simply discuss the merits of the information and products he wishes to share with us.

DISCLAIMER: This is not a personal attack on Mike.


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vpcirc
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Re: The end of OAG? new [Re: SL63 AMG]
      #6147850 - 10/20/13 04:16 AM

Dave there's a reason there's a question mark in the title. I was trying to share an item I saw at AIC that others might be interested in, as not everyone is as lucky as I to attend. I ask the questions of those who are far smarter than I, but they won't get dragged into stupid petty opinions from what one referred to as "armchair engineers" They gave their advice, take or leave it and do what you want.

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garret
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Re: The end of OAG? new [Re: SL63 AMG]
      #6147851 - 10/20/13 04:18 AM

Quote:

Sorry everyone is attacking you, Mike. I think it's neat and if it gives us a new tool to work with, that'll be great.




Not every optical system has enough backspace for a OAG.
I have a newton astrograph, with the canon 5 dmk2; there is zero backfocus left.
The Wyne corrector has only 58mm of backfocus.
You can not even use a SBIG STX 16803 with filterwheel.

I'm waiting for this new guiding system due to guiding troubles, but placing a led near the imager is practically impossible without drilling a hole into the focusser

Garret van der Veen


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freestar8n
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Re: The end of OAG? new [Re: garret]
      #6147868 - 10/20/13 04:38 AM

Quote:

have a newton astrograph, with the canon 5 dmk2; there is zero backfocus left.





Hi-

Then you are definitely in the set of people who would benefit by guiding with a guidescope while avoiding flexure. You have a mirror system prone to flexure, and little backfocus.

In that case there is already a solution in the form of free software called FlexRX. It uses the Shift Guiding feature of MetaGuide to measure and compensate for motion detected in the arriving images. It is all based on free software, and it involves no hardware other than a video camera for guiding.

I am also a strong proponent of OAG and find it has little overhead in the imaging process, but I do aim for the brightest star available for guiding, and that does involve rotation on meridian flip and more flats - for best results anyway. If the OAG is far from the imaging chip, the difference in flats may be negligible.

But for certain systems such as Hyperstar and some Newtonians, OAG isn't practical and alternative solutions have uses.

I heard about this SBIG thing many years ago and expected they would face challenges getting it to work. A key issue is that it involves a moving centroid - which is unusual in autoguiding. For comet tracking MetaGuide also relies on a moving centroid - and I think it is the only software that guides with a moving centroid - and it has been doing so for many years.

Anyway - yes this device has been touted for years, and meanwhile there are already free software solutions for both flexure compensation without OAG, and comet tracking with or without OAG.

Frank


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Raginar
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Re: The end of OAG? new [Re: freestar8n]
      #6148099 - 10/20/13 09:53 AM

Dave, just look at your tone in your writing. Mike obviously isn't quite as versed on all the options as you are. He thought it was neat and shared it. I agree with him, it's neat and i can't wait to see it.

Kind of falls into the ONG area. I dunno if I need to buy one, who am I kidding, I'm a noob who barely can get data let alone make a pretty picture, but it's neat to see something new.

I get it, you think there isn't a problem to solve.


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SL63 AMG
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Re: The end of OAG? new [Re: Raginar]
      #6148266 - 10/20/13 11:40 AM

Quote:

Dave, just look at your tone in your writing. Mike obviously isn't quite as versed on all the options as you are. He thought it was neat and shared it. I agree with him, it's neat and i can't wait to see it.




You have hit the nail on the head.

There's no issue with him finding a product, thinking it's neat and sharing it. For that I am sure everyone is grateful, including myself.

The issue is that he doesn't just let it go at that. Instead he throws out anecdotal comments about the pain of OAG and rotating a camera, which provides a false impression to others who may find themselves in a situation where they need to have an OAG and may want to rotate their imaging camera. Mike does this often and I have decided that I'm not gong to sit back quietly and let it take place.

If that makes me unpopular in CN, so be it, but I know for a fact that I am not the only one that feels this way... I'm likely the only person that doesn't care if I'm unpopular for standing up and saying something about it.

If you think I'm wrong, click on Mike's nickname, then click on "show all user's posts", then see how many times he has been the very first response to someone's question and has provided subjective, rather than objective, responses to someones questions, many for which he has no personal experience.

I don't have issue with anyone wanting to be helpful, but I do have issue with stearing people down the wrong path when real money is involved.

Advice given hear needs to be objective, not subjective, so that people can make informative decisions about purchasing equipment to solve real issues.


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Alph
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Re: The end of OAG? new [Re: vpcirc]
      #6148361 - 10/20/13 12:42 PM

Quote:

Mike Rice said if this works as advertised it's a godsend.



I concur. The device takes us closer to point and shoot astrophotography. You can just slew to an object and start shooting.


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Peter in Reno
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Re: The end of OAG? new [Re: garret]
      #6148366 - 10/20/13 12:47 PM

Quote:

Not every optical system has enough backspace for a OAG.
I have a newton astrograph, with the canon 5 dmk2; there is zero backfocus left.
The Wyne corrector has only 58mm of backfocus.
You can not even use a SBIG STX 16803 with filterwheel.

I'm waiting for this new guiding system due to guiding troubles, but placing a led near the imager is practically impossible without drilling a hole into the focusser

Garret van der Veen




Hi Garret,

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?

Peter


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vpcirc
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Re: The end of OAG? new [Re: garret]
      #6148402 - 10/20/13 01:04 PM

Garret, if I understood SBIG correctly, these have to be engineered to the OTA, so I don't know that they would sell one that had you drilling to mount it. It looks like Frank has a good solution for you. Again, at this point this has yet to be proven in the field by users so I wouldn't bet on this being your solution yet. As Rick stated, they've been working on this for a few years, so it appears to be more complicated than we know. I am not advocating the product only sharing what I saw. I hope it works as advertised.

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mikeschuster
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Re: The end of OAG? new [Re: vpcirc]
      #6148418 - 10/20/13 01:12 PM

A couple of possible issues:

I believe SBIG mentioned using an IR light, which requires a filter on the main camera. If there are other telescopes nearby, it is important that any scattered IR light not affect them.

The retro-reflector mounted at the front of the tube is a source of potential flexure. So flexure remains an issue with this design.

Guide camera exposure time varies due to several factors (guide scope size, guide star magnitude, seeing conditions, etc.). Presumably an IR intensity control will also be necessary.

Thanks,
Mike


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orion69
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Re: The end of OAG? new [Re: Alph]
      #6148493 - 10/20/13 02:02 PM

Quote:

The device takes us closer to point and shoot astrophotography. You can just slew to an object and start shooting.




You can just slew to an object and start shooting only with high end mount without guiding. So, no it does not.

As mentioned before, this device could be usable if there is not enough backfocus for OAG.


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Wmacky
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Re: The end of OAG? new [Re: vpcirc]
      #6148499 - 10/20/13 02:08 PM

Quote:

most of them are in a private google group that's invitation only.




Well aren't they fancy....


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Alph
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Re: The end of OAG? new [Re: orion69]
      #6148513 - 10/20/13 02:26 PM

Quote:

You can just slew to an object and start shooting only with high end mount without guiding. So, no it does not.




It just happens that I own one of those mounts you are alluding to and they don't work that way. They require a lot of setup time and in the end you end up auto-guiding anyway.


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vpcirc
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Re: The end of OAG? new [Re: Wmacky]
      #6148516 - 10/20/13 02:30 PM

I think you misunderstand. They don't get into discussions about processes and procedures, they just share images. That's where they're interest lies, it's has nothing to so with being "special" Dave wanted to know why didn't chime in here. For great technical questions Ron Wodaski runs a great useful group on yahoo ccd-newastro with 4000+ members. His group is private too, but he lets folks in with a request. Most of these guys post their contact info on their web sites and gladly answer questions and help people. They do not however spend their time cruising Astro sites chiming in on every post.

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Hilmi
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Re: The end of OAG? new [Re: vpcirc]
      #6148570 - 10/20/13 03:13 PM

Dave,

In response to your post on page 2 of this discussion.

Those of us with high light pollution and long f ratios do find OAG a pain to use. I have had many targets where I could not find a guide star when I used to image at f10. This is one of the reasons I moved to f8. In light polluted skies even a reasonable guide star is sometimes not very effective.

I agree that a good rotator with an OAG is an idea that appeals to me and I am in fact considering making such a purchase but I believe there is a market for those who find OAG don't work well with their setups.

Different horses for different races. Besides, an experienced company like SBIG will not spend the money researching a product if they did not feel there was a solid business case for it.


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SL63 AMG
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Re: The end of OAG? new [Re: vpcirc]
      #6148672 - 10/20/13 04:30 PM

Quote:

Dave wanted to know why didn't chime in here. [sic erat scriptum]




Please don't put words into my mouth. I never asked why "they" don't chime in here. I am fairly confident I already know the answer to that question.

I merely pointed out that you frequently refer to individuals and groups of individuals to back up your anectdotal comments and those referenced never say the same things as you say.

Of course you have now isolated "them" even further into this elite group of demigods that wouldn't dare mingle with us mere mortals.

I'm sure glad we have you as "their" liason.

What's most interesting about this whole thing is that we have exactly the same situation in Amateur Radio. The elitists, the liasons and the rest of us.

What an awesome society in which we live!


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vpcirc
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Re: The end of OAG? new [Re: SL63 AMG]
      #6148728 - 10/20/13 05:13 PM

I did anything but isolate them Dave. I learn from them because I take the time to contact and ask the questions . Like most imagers they will help anybody at any time. I don't just spout off. Almost every question asked here is one I had myself. I seek the advice from those who have paved the road before me. Don't worry Dave, there's no room to put words in your mouth, there seems to be something in the way.

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Raginar
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Re: The end of OAG? new [Re: SL63 AMG]
      #6148765 - 10/20/13 05:39 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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Peter in Reno
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Re: The end of OAG? new [Re: Raginar]
      #6148875 - 10/20/13 06:36 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


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SL63 AMG
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Re: The end of OAG? new [Re: vpcirc]
      #6148927 - 10/20/13 07:10 PM

Quote:

I don't just spout off.




Quote:

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




Supporting Thread


Quote:

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?


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PGW Steve
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Re: The end of OAG? new [Re: SL63 AMG]
      #6148995 - 10/20/13 07:44 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.


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Peter in Reno
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Re: The end of OAG? new [Re: PGW Steve]
      #6149056 - 10/20/13 08:36 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


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Raginar
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Re: The end of OAG? new [Re: Peter in Reno]
      #6149625 - 10/21/13 10:46 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.


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Peter in Reno
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Re: The end of OAG? new [Re: Raginar]
      #6149679 - 10/21/13 11:26 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


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mikeschuster
super member


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Re: The end of OAG? new [Re: Peter in Reno]
      #6149713 - 10/21/13 11:48 AM

Quote:

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


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vpcirc
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Re: The end of OAG? new [Re: Peter in Reno]
      #6149742 - 10/21/13 12:02 PM

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.


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garret
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Re: The end of OAG? new [Re: Peter in Reno]
      #6149771 - 10/21/13 12:15 PM

Quote:

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


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Peter in Reno
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Re: The end of OAG? new [Re: vpcirc]
      #6149904 - 10/21/13 01:39 PM

Quote:

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


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Peter in Reno
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Re: The end of OAG? new [Re: garret]
      #6149906 - 10/21/13 01:42 PM

Quote:

Quote:

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


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Aquatone
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Re: The end of OAG? new [Re: Peter in Reno]
      #6150692 - 10/21/13 10:00 PM

Quote:

Quote:

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


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vpcirc
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Re: The end of OAG? new [Re: Aquatone]
      #6150815 - 10/21/13 11:08 PM Attachment (9 downloads)

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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elbee
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Re: The end of OAG? new [Re: vpcirc]
      #6151018 - 10/22/13 02:35 AM

Quote:

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.



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.


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freestar8n
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Re: The end of OAG? new [Re: Aquatone]
      #6151092 - 10/22/13 04:25 AM

Quote:

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


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vpcirc
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Re: The end of OAG? new [Re: Aquatone]
      #6151234 - 10/22/13 08:32 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.

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Alex McConahay
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Re: The end of OAG? new [Re: vpcirc]
      #6151274 - 10/22/13 09:08 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


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dawziecat
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Re: The end of OAG? new [Re: Alex McConahay]
      #6151544 - 10/22/13 11:50 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.

Edited by dawziecat (10/22/13 11:51 AM)


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orion69
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Re: The end of OAG? new [Re: vpcirc]
      #6151587 - 10/22/13 12:16 PM

Quote:

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.


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orion69
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Re: The end of OAG? new [Re: dawziecat]
      #6151590 - 10/22/13 12:19 PM

Quote:

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




Correct.


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vpcirc
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Re: The end of OAG? new [Re: orion69]
      #6151626 - 10/22/13 12:40 PM

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?

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Peter in Reno
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Re: The end of OAG? new [Re: orion69]
      #6151631 - 10/22/13 12:42 PM

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


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Peter in Reno
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Re: The end of OAG? new [Re: Aquatone]
      #6151637 - 10/22/13 12:45 PM

Quote:

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


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orion69
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Re: The end of OAG? new [Re: vpcirc]
      #6151647 - 10/22/13 12:51 PM

Quote:

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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WadeH237
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Re: The end of OAG? new [Re: vpcirc]
      #6151687 - 10/22/13 01:15 PM

Quote:

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?




This is not that difficult if you collect guide logs for every session. The guide logs capture the guide commands sent to the mount. But more importantly for this discussion, they also capture the positional error of the guide star centroid from the proper pointing position.

With this data, it is possible to determine with pretty good accuracy how well the guider tracked the guide star. Any tracking errors in the main image that are not represented in the guide error data are the result of flexure.

I think that you can safely rule out periodic error as a source of error when you are guiding. If the rate of error in your PE is enough to exceed what the guider can correct, then you've got bigger problems than flexure.

The biggest practical concern is probably determining the difference between loose parts, shifting mirror (on an SCT), and actual flex of the OTA or parts.

In my experience, if you have an SCT, you will have mirror shift that you will not be able to resolve. I've heard that some larger OTAs may actually have flexure because the OTA and mount actually flex due to weight (I've never imaged through my C14, but have heard that it might have some of this). Assuming stout dovetails and rails with tight connections, the biggest correctable source of flexure for my has been in the focuser, usually on the guide scope, where the drawtube sags a bit. Interestingly, it's this last one that the AP solution specifically addresses.

The good news is that OAG or self-guiding will either handle or avoid flexure from any of these sources. I'm interested in hearing how the SBIG differential guiding solution works. I was really excited about it a few years ago, but finally gave up waiting and went to OAG.

-Wade

PS: For an interesting experiment if you have a guide scope, go through your data to find an all night session on a single target with good guiding. Then, stack the images with no registration. It's interesting to see what flexure looks like when it adds up over the whole night. Note that this assumes that you are not dithering.


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elbee
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Re: The end of OAG? new [Re: vpcirc]
      #6151702 - 10/22/13 01:22 PM

Quote:

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?




you wouldn't.

but for every user making these choices there should be an understanding that what you try may not work or may be harder to implement than you thought. the best answer will always be the one that works for you at the expense level and difficulty level you are willing/able to tolerate. if you find a rigidly mounted guide scope does not work, then you would like to be in a position to "try" something else (=$$$).

it's a difficult hobby and the more options that make it attainable to users with differing goals and budgets, the better. i don't have a permanent setup and i swap cameras between different scopes (all refractors). always used an external guide scope; no OAG, no rotator. but if i ever do get a permanent setup, there's going to be a large reflector in it with OAG and rotator - personally, i would not waste time with anything else. and that would be my advice to you for your upcoming planewave (i have an inherent distrust of mirror support stability :-) but that's just one man's opinion.


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freestar8n
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Re: The end of OAG? new [Re: WadeH237]
      #6151711 - 10/22/13 01:25 PM

Quote:

Then, stack the images with no registration. It's interesting to see what flexure looks like when it adds up over the whole night. Note that this assumes that you are not dithering.




Yes, but you need to make sure it isn't field rotation, which will also show trailing. If the trails are long enough you can tell the rotate around the guidestar and are not due to flexure.

But any steady marching of the stars from one exposure to the next while guiding is definitely not due to periodic error or a guiding problem. It's either field rotation or flexure *somewhere*. People usually blame the guidescope itself - but with a mirror scope it is the mirrors themselves changing slightly.

There is a separate issue with a short guidescope and that is the actual centroid accuracy you can achieve. People talk about short guidescopes being fine for centroids - but it is rarely shown in terms of small fwhm in long exposures. With OAG you get the benefit of greater centroiding accuracy on the pixel scale, along with no flexure.

Many people who have "tried" oag did not go all the way and use a planetarium FOVI to pre-plan the guidestar and dial it in. That is standard practice nowadays and avoids the hunting that people associate with OAG. Some people with high end mounts, such as Peter here, don't bother with that and instead just use longer guide exposures and always find a guidestar.

Frank


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Aquatone
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Re: The end of OAG? new [Re: Peter in Reno]
      #6151750 - 10/22/13 01:49 PM

Quote:

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




You raise a key point that exposure time is a critical variable. I am currently doing 10 minute RGBL subs but with a higher QE KAF-6303E CCD. (As galaxies are my main interest) I have not gone out as far as 30 minutes, partly because I am getting slightly egg shaped stars at that exposure length using *both* SBIG internal guide chip and the AP guide-scope. I am fairly certain this is due to mount alignment and pier issues. I do not have a permanent pier but rather a sturdy 10" ATS tripod, and George at AP suggested that it could be due to something as simple as me using the metal rather than hard rubber pads on the feet, introducing a possible slight slippage on the (hard) ground as the telescope mass distribution changes. I will be changing to hard rubber for more friction. I also have an AP1600GTO with absolute encoders arriving later this week, which will be a significant step in further removing the mount from the equation.

I will try and post some pictures of the current guidescope configuration when I get back from work later.

I know that on/off-axis guide methods are most appropriate at this long focal length, but demonstrating I can guide an almost 4,000mm cassegrain with a guide-scope and that it is possible, has become a kind of perverse (and fun) challenge. At the least it really identifes weak points in the overall pier/mount/telescope assembly.

BTW: I certainly have imaged for 30 to 45 minutes using the new AP guide scope mounted on the focuser of my much shorter 1200mm focal length AP160 refractor with perfectly round stars. That is a very good match and really makes an OAG unnecessary in this less demanding configuration. As has been earlier pointed out, Roland has advocated focuser mounted guide scopes on refractors for some years.

Chris


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SL63 AMG
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Re: The end of OAG? new [Re: Aquatone]
      #6151773 - 10/22/13 02:16 PM

I image at 2857mm FL. I have tried using a 250mm VarioFinder on both a MiniMax and Max-F as well as direct mounting a Stellarvue 650mm FL CF OTA to the top of my RCOS. I have also tried both of these options on my ASA N10 astrograph. I have tried them both on an AP1600GTO CP3 mount and an ASA DDM85X-SL mount.

My experience is that using an MMOAG or QSI camera with a built in OAG are both much easier with which to guide than using guide scope. I believe this is due to at least two issues. I believe guiding at the FL of the main OTA works better for long FL telescopes than guiding at some fraction thereof. Also, it is likely there are issues with differential flexure due to these guide scopes being mounted on the rings of the OTA versus the OTA itself.

In any case, my experience has taught that guiding with an OAG is simple as is finding a guide star, particularly when you have rotator.

Having a rotator has the side benefit of giving one an opportunity to frame an object in an aesthetically pleasing position.

Elbee images with refractors and has great success using short focal length guide scopes mounted directly to his main imaging refractors. This shows that for every system there is a solution that works and no particular solution should be put down versus another without careful examination of the equipment and the circumstances of its deployment.

If the SBIG product solves all or many of these issues for imagers, that's fantastic. Having more options in an expensive hobby is always welcomed.

I'm glad to see the discussion has changed to one of comparison of products under different circumstances rather than that of putting down one method over another.


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Raginar
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Re: The end of OAG? new [Re: Peter in Reno]
      #6153411 - 10/23/13 10:47 AM

Peter I agree. I need to give an OAG more time. Once again I bought the cheaper one and I think I'm learning why that's a bad idea.

I think an ONG would be neat but I worry about putting my camera sideways, my cables are already pretty maxed out.

Sounds like based on the last post there are issues with some of our favorite techniques such as dithering too


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Peter in Reno
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Re: The end of OAG? new [Re: Raginar]
      #6153495 - 10/23/13 11:36 AM

Hi Chris,

ONAG (On Axis Guider) is a great device. It's really like guiding with a guide scope because it has very large FOV for guide camera. The major drawback is it has enormous minimum back focus of 66mm which will never work with my scope/equipment. I ordered it once but cancelled it due to huge back focus.

High quality OAG helps. Also high sensitivity guide camera for OAG is highly recommended but your signature shows you already own a Lodestar and that's good. I used to have Hutech OAG with Helical focuser at guide port. It was a really nice device. Astrodon MMOAG is also very good. Both Hutech and Astrodon OAG's are not exactly cheap. I think SX filter wheel combined with SX OAG would work well but it may not work well with non-SX cameras due to mis-parfocaling between guide and main cameras. SX FW/OAG is designed to work with SX cameras. SX cameras are well built (I owned SXVR-M25C and like it very much).

People who use OAG for the first time usually get confused about parfocaling guide camera with main camera. They sometimes make a mistake parfocaling under the dark sky for the first time. I did that myself. This forum suggested to me to parfocal during the day by aiming for a telephone pole or street sign pole far away. Once daytime parfocaling was done, all it needs is a tiny tweak under the dark sky.

What scope are you trying to use OAG? Is it 12" LX200 as shown in your signature? If you want to image at F/10, then ONAG would work. I am not sure how forgiving Meade/Celestron focal reducer is regarding to back focus (maybe 95mm - 120mm). You don't need to install the camera sideways, you can mount it on top. Also, rotating ONAG is not necessary to find guide stars. I highly recommend ONAG for equipment that allows long back focus. Lodestar is perfect for ONAG since it can see NIR pretty well. ONAG is also pricey. I never own ONAG but there are many satisfied ONAG owners and I have not read one single negative comment except for long back focus (that's me). Do a search for ONAG in this forum (DSLR and CCD).

Peter


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blueman
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Re: The end of OAG? new [Re: Peter in Reno]
      #6153820 - 10/23/13 02:33 PM

The back focus is a big issue many times for OAG. If you are using a focal reducer or field flattener it can be especially problematic. Many of the good OAG systems require a lot of back focus and there may not be enough distance between the flattener/reducer and the CCD chip to allow an OAG between them. Some new ones are thin, but may not work as well as the big ones that have big pick-off prisms. Some are also made with soft materials and are just not good enough for me to support the weight of a camera. I had a brand name THIN OAG that was made of some kind of pot metal or something so soft that the set screws would dig into the material when they were tight enough to hold things. That sucked!

This has been my biggest issue with the OAGs along with the lack of guide stars in areas of the sky outside the Milky Way where there are not so many stars next to a galaxy or whatever. In the Milky Way there are usually stars a plenty and not an issue.

But if you want a specific framing of an object, then many times the OAG will not see a good enough star to guide with at that angle. If you are not too particular about the framing, then there are always stars available.

Also, when you do the meridian flip and you do not have a rotator, then the star you were guiding on is no longer there, that can be a big issue if the OAG does not have a fairly large FOV so that a star will fall on it.

So OAG is good, ONAG is good too if it works for your setup. But there are complications and considerations when you decide to use one or the other.
Blueman


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Corsica
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Re: The end of OAG? new [Re: blueman]
      #6393826 - 02/24/14 08:38 AM

My name is Gaston Baudat, CTO of Innovations Foresight.

I think there are some differences between OAG and ONAG features that should be explained in this thread, since the ONAG technology is relatively new.

With the ONAG you do not need a rotator and therefore you can reuse the flat frames as long as you do not change your imager optical train.

The ONAG allows on axis, as well as off axis guiding, the former is useful to guiding on the target (asteroid, comets, ...). The ONAG works with AO units.
The ONAG uses NIR which exhibits less seeing effects.

One important aspect of using an ONAG (or an OAG for that matter) is the fact that you work with your main scope, which usually has the largest aperture D.
From a star, therefore a guide star, standpoint the key figure of merit is D which defines how much starlight (energy) is gather by the scope. The numerical aperture F is relevant for extended objects, not for stars which remain points (Airy disks) at any magnification.

The energy received from a star increases with the square of D. For instance a 8" scope gathers 6.25x more than a classical 80mm guide scope, which is about 2 magnitudes. A 11" is 3 magnitudes more.
Depending of the star temperature the ONAG may loose from a half to one magnitude (using NIR), but at the end D is making all the difference.

see http://innovationsforesight.com/NIRGuiding.htm for further information.

The ONAG technology offers an unique new possibility, real time auto-focus while auto-guiding. This technique named SharpLock (SL) is available for beta testers.

See http://innovationsforesight.com/SharpLock.htm for further information


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garret
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Re: The end of OAG? new [Re: blueman]
      #6394172 - 02/24/14 12:30 PM

Quote:

The back focus is a big issue many times for OAG




I have a newton telescope, for imaging I use the ASA 3" Wyne corrector, it has a backfocus of only 58mm.
The canon DSLR takes 44mm, the camera adaptor 10mm, left over for a OAG, ONAG...4mm!
Even with a cooled CCD camera with external filterwheel the space for a OAG is only 18 mm.
furthermore the OAG must be large to fit the large 3" wyne corrector (65mm clear aperture).

'I want to have a CCD camera where you select any pixel(s) in the sensor for (AO) guiding'

Garret van der Veen

Edited by garret (02/24/14 12:52 PM)


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Corsica
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Re: The end of OAG? new [Re: garret]
      #6394825 - 02/24/14 07:15 PM

I agree that OAG and ONAG are not for every scope.
Yet SCT, RCT, and many refactors/reflectors have enough back focus, new scope designs usually consider and provide more back focus to allow for more equipment in the optical train, such as AO units.

Newtonian are challenging in term of back focus. Difficult to fit an OAG/ONAG, AO unit, filter wheel, camera, (or DSLR), and maybe a rotator.
My guess is that even with a guide scope and differential guiding the extra back focus required for an AO unit may be just too much.


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vpcirc
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Re: The end of OAG? new [Re: garret]
      #6395230 - 02/24/14 11:24 PM

I'm having great sucess with the new guide scope setup from AP. http://www.astro-physics.com/index.htm?whatsnew/whatsnew
The rigidity of the setup has worked perfectly with my idk at 2160 fl.


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