I am thinking of purchasing an ONAG by innovation foresight for my C11 telescope. It suffers from very noticeable focus shift and i need to refocus every 25 mins. The sharplock feature looks very promising on this matter and the full FOV IR guiding sounds very interesting as well to further optimize guiding. Does anyone have it and use successfully on both IR guiding and focus lock?
IF ONAG opinions
John Hayes is a master with the ONAG, both for focusing and guiding, and swears by it.
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It's a great solution for deep pockets :-)
Tony Gondola:
It's a great solution for deep pockets :-)
Well in my case it s basically the only solution - as i cannot lock the mirrors on my C11 and use an external focuser, the focusing through the primary is tricky and requires frequent autofocus sessions. If i can keep the focusing on point throughout the whole night that should hopefully increase both imaging time and sharpness, so i would say the investment is worth the money. Also deep pockets is relative, a decent quality OAG with a large prism costs around 2-300 eur, the difference is not that substantial if the benefits are there.
Oh, the unit I looked up from innovations forsight was in the $1300 to $1800 range. If there is one for $200 to $300 then yeah, it makes perfect sense.
On a slight tangent, for someone you is comfortable taking optics apart. I wonder how hard it would be to tear down an SCT and lock the mirror, disabling the focusing system but eliminating the mirror flop. Really just an academic problem for me, but I'm curious.
On a slight tangent, for someone you is comfortable taking optics apart. I wonder how hard it would be to tear down an SCT and lock the mirror, disabling the focusing system but eliminating the mirror flop. Really just an academic problem for me, but I'm curious.
Tony Gondola:
Oh, the unit I looked up from innovations forsight was in the $1300 to $1800 range. If there is one for $200 to $300 then yeah, it makes perfect sense.
On a slight tangent, for someone you is comfortable taking optics apart. I wonder how hard it would be to tear down an SCT and lock the mirror, disabling the focusing system but eliminating the mirror flop. Really just an academic problem for me, but I'm curious.
the APSC unit is at 849$, which is no 300$ but *if* the advertised benefits are there, might be worth the difference. End of the day with a remote setup you pay every minute of imaging time so if it truly allows to continually adjust focus throughout the night, with a remote setup it will quickly repay itself.
There are some interesting mods out there to improve the C11 but my scope is in a remote location and would be quite tricky. Also these mods are pretty invasive so i would probably end up messing up something
I have an old Meade 8" SCT kicking around. I'm tempted to tear into it to see how the system works. If nothing else, it will be educational. I fully expect to be surprised at how rudimentary it is.
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If the ONAG is the *only* solution you got the wrong scope out there. If you can afford both that and the siting then I expect a 12" RC would have been my preferred choice. I wouldn't be able to afford either so my interest here is purely academic.
andrea tasselli:
If the ONAG is the *only* solution you got the wrong scope out there. If you can afford both that and the siting then I expect a 12" RC would have been my preferred choice. I wouldn't be able to afford either so my interest here is purely academic.
My pictures would disagree
i love my C11 and it produces images as sharp, if not sharper, than the RC12 i have in the same place, and quite often i struggle to find images as sharp even from people with much more expensive equipment. It's not perfect though, hence my effort to improve it furtherSharpness has nothing to do to suitability for remote operation but rather reliability and repeatability. If you can't keep focus because of mirror flop/shift then I submit that that scope isn't well suited for remote fail-proof operation. But then to each their own…
andrea tasselli:
Sharpness has nothing to do to suitability for remote operation but rather reliability and repeatability. If you can't keep focus because of mirror flop/shift then I submit that that scope isn't well suited for remote fail-proof operation. But then to each their own...
i have been operating this scope remotely for two years and a half now, with much success i would say. Every scope has focus shift throughout the night, this is simply a bit worse than others and requires more frequent refocusing (around 30% more often than my carbon truss RC12). I love the images it produces and before replacing it i will think about it a hundred times, and i wouldnt think twice for any improvement over the current baseline. The ONAG seems like a great improvement throughout, if the benefits are confirmed. That's pretty much all this is about.
The ONAG sounds interesting. I read about it years ago and found it intriguing. If my understanding is correct, especially with SCTs, the mirror movement causes the focus to change. If you used an ONAG, would that negate the need to lock down the mirrors and use a separate focuser(like a 2" esatto or LP)?
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I use one for FF on my Edge 14 and I think it's great; I wouldn't want to play around with an OAG and the tiny outside area that's available..
I've been using the ONAG SC on a refractor for about 10 years and I wouldn't be without it. I think it's brilliant and I'm surprised it isn't more widely used.
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thanks @Roger Gifkins @AstroRBA that's the feedback i was looking for
how do you find the sharplock feature? does it work as advertised? i have read older feedbacks on the CN forum that it was a bit of a hit and miss
how do you find the sharplock feature? does it work as advertised? i have read older feedbacks on the CN forum that it was a bit of a hit and miss
andrea tasselli:
Sharpness has nothing to do to suitability for remote operation but rather reliability and repeatability. If you can't keep focus because of mirror flop/shift then I submit that that scope isn't well suited for remote fail-proof operation. But then to each their own...
Agreed. Dependable and reliable is critical for hardware. There is nothing worse than a flaky piece of equipment (and this applies to all equipment, not just astronomical). One should not have to spend any time at all or buy any add-ons to deal with something that does not work the way it should out of the box.
I have had my share of flaky astro stuff over the past 30 plus years and I have decided I would rather spend the money than have the aggravation.
Just my .02
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Bill McLaughlin:andrea tasselli:
Sharpness has nothing to do to suitability for remote operation but rather reliability and repeatability. If you can't keep focus because of mirror flop/shift then I submit that that scope isn't well suited for remote fail-proof operation. But then to each their own...
Agreed. Dependable and reliable is critical for hardware. There is nothing worse than a flaky piece of equipment (and this applies to all equipment, not just astronomical). One should not have to spend any time at all or buy any add-ons to deal with something that does not work the way it should out of the box.
I have had my share of flaky astro stuff over the past 30 plus years and I have decided I would rather spend the money than have the aggravation.
Just my .02
i have six telescopes operating remotely so i am not disagreeing, i just don't think this applies to the piece of equipment in question
the images i get speak for themselves
Emilio Frangella:
I am thinking of purchasing an ONAG by innovation foresight for my C11 telescope. It suffers from very noticeable focus shift and i need to refocus every 25 mins. The sharplock feature looks very promising on this matter and the full FOV IR guiding sounds very interesting as well to further optimize guiding. Does anyone have it and use successfully on both IR guiding and focus lock?
Emilio,
I’ve been using ONAG on various telescopes for around 6-7 years. You can check out my image page to see what I get out of it. Every one of those images was taken with an ONAG of one sort or another. In my opinion, astigmatic focusing is “the right way” to focus and optical system. (In fact, it is the exact same system used in DVD players that maintain focus on a spinning disk at tens of kilohertz speeds.)
I’ve given a number of presentations at both AIC and at NEAF about long focal length imaging as well as a 4 hour seminar on focusing at NEAF in conjunction with Gaston Baudet where we went into all of the gory details of focusing including ONAG. One thing that I want to clarify is that your C11 has a fairly high thermal sensitivity to focus shift. I don’t happen to have the exact number with me but as I recall, it’s around 1-1.5C. That’s the temperature change required to shift the image out of the critical focus zone. The fact that the secondary mirror magnification is pretty high for the C11 (5x) coupled with the aluminum tube is what makes it so sensitive. The time required between focusing is generally driven by how stable your ambient air temperature is while you image.
The focusing system in the Celestron scopes is generally not the cause of focus drift; however, they do suffer from lateral image shift, which is a translation of the image when focus is changed. That makes it very difficult to do “real-time” focusing while the shutter is open. The fact that ONAG provides both a focus signal along with a guide signal is what makes it so good. If you can solve the image shift problem, you can get excellent full frame guiding along with a very precise auto-focusing system.
The big limitation of ONAG is that it requires a fair amount of “optical distance” and for the Celestron scopes (which have a BWD of 5.75” for the C11 and C14), you won’t have enough physical space to use both ONAG and an external focuser. So, the costs of ONAG is amplified by the need for another focuser as well. The ideal solution for the C11 (or C14) systems is to use the Optec SMFS product. This allows locking the primary mirror in one place and then focusing using the secondary mirror. In my opinion, this is a killer combination. It allows very precise, real time auto-focusing without taking up any of the precious back working distance in the scope. You’ll have to figure out if this approach is workable within your budget but my feeling is that if you can afford it and you are careful to set it up properly, you can get world class results from it.
John
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John Hayes:Emilio Frangella:
I am thinking of purchasing an ONAG by innovation foresight for my C11 telescope. It suffers from very noticeable focus shift and i need to refocus every 25 mins. The sharplock feature looks very promising on this matter and the full FOV IR guiding sounds very interesting as well to further optimize guiding. Does anyone have it and use successfully on both IR guiding and focus lock?
Emilio,
I’ve been using ONAG on various telescopes for around 6-7 years. You can check out my image page to see what I get out of it. Every one of those images was taken with an ONAG of one sort or another. In my opinion, astigmatic focusing is “the right way” to focus and optical system. (In fact, it is the exact same system used in DVD players that maintain focus on a spinning disk at tens of kilohertz speeds.)
I’ve given a number of presentations at both AIC and at NEAF about long focal length imaging as well as a 4 hour seminar on focusing at NEAF in conjunction with Gaston Baudet where we went into all of the gory details of focusing including ONAG. One thing that I want to clarify is that your C11 has a fairly high thermal sensitivity to focus shift. I don’t happen to have the exact number with me but as I recall, it’s around 1-1.5C. That’s the temperature change required to shift the image out of the critical focus zone. The fact that the secondary mirror magnification is pretty high for the C11 (5x) coupled with the aluminum tube is what makes it so sensitive. The time required between focusing is generally driven by how stable your ambient air temperature is while you image.
The focusing system in the Celestron scopes is generally not the cause of focus drift; however, they do suffer from lateral image shift, which is a translation of the image when focus is changed. That makes it very difficult to do “real-time” focusing while the shutter is open. The fact that ONAG provides both a focus signal along with a guide signal is what makes it so good. If you can solve the image shift problem, you can get excellent full frame guiding along with a very precise auto-focusing system.
The big limitation of ONAG is that it requires a fair amount of “optical distance” and for the Celestron scopes (which have a BWD of 5.75” for the C11 and C14), you won’t have enough physical space to use both ONAG and an external focuser. So, the costs of ONAG is amplified by the need for another focuser as well. The ideal solution for the C11 (or C14) systems is to use the Optec SMFS product. This allows locking the primary mirror in one place and then focusing using the secondary mirror. In my opinion, this is a killer combination. It allows very precise, real time auto-focusing without taking up any of the precious back working distance in the scope. You’ll have to figure out if this approach is workable within your budget but my feeling is that if you can afford it and you are careful to set it up properly, you can get world class results from it.
John
John thanks a lot for the answer, it confirms what i was hoping to be true - i will be looking into an ONAG, and a trip to the observatory to set it up.
A couple of clarifications - my C11 is a plain SCT and not an edge, hence there is no way of locking the mirrors, but i have never experienced any lateral image shift/mirror flop using the standard focusing mechanism, at least nothing that i have ever noticed. When focusing the target stays consistently in the middle of the image and i have never noticed any lateral movement in over two years of usage.
Also i am using a starizona 0.7x reducer which has a backfocus of 146mm, that should be more than enough to accomodate the ONAG. I will look into the proper adapters
thanks again
Emilio Frangella:
i have six telescopes operating remotely so i am not disagreeing, i just don't think this applies to the piece of equipment in question
the images i get speak for themselves
Just to clarify. I am not saying that such "flaky" equipment cannot produce good images. I am saying that it does so with much greater fussing about and effort than it really should.
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Emilio Frangella:
John thanks a lot for the answer, it confirms what i was hoping to be true - i will be looking into an ONAG, and a trip to the observatory to set it up.
A couple of clarifications - my C11 is a plain SCT and not an edge, hence there is no way of locking the mirrors, but i have never experienced any lateral image shift/mirror flop using the standard focusing mechanism, at least nothing that i have ever noticed. When focusing the target stays consistently in the middle of the image and i have never noticed any lateral movement in over two years of usage.
Also i am using a starizona 0.7x reducer which has a backfocus of 146mm, that should be more than enough to accomodate the ONAG. I will look into the proper adapters
thanks again
Two things:
1) If you try to focus with the shutter open, you WILL experience image shift and it will be pretty obvious in your images. The Celestron focusing mechanism relies on one tube sliding over another greased tube and no matter how tight the tolerances, it will not slide in a straight enough line to allow focusing with the shutter open. Simply turning the focusing screw is enough to displace the image by way more than you want. Ok, you might get lucky and take a few subs using a short exposure under good conditions where the shift might not be super obvious but you are not going to get good image yield and you will not optimize FWHM values using that method. In my view, there’s no reason to go for the advantages of real time focusing unless you do it right. Simply put: real time focusing will not work well (or at all) with the standard Celestron SCT focusing system.
BTW, this is why Celestron now ships their RASA 14 (and maybe the smaller ones too) with the focusing mechanism that I designed for them. It allows real-time focusing without any problem. Unfortunately, they did not put my design into any of their SCT products—even though I urged them to do so! My former Edge14 system now owned by Brad Rode is the world’s only system that incorporates that focuser and it works incredibly well. The Optec SMFS is the only other internal focuser for the Celestron scopes that works as well!
2) If you are using a reducer, make sure that the ONAG has enough field so that you don’t get excessive vignetting on your sensor. The ONAG-XM has enough field to run a 36 mm x 36 mm sensor at F/10. If you go to F/7, you should make certain that you won’t get more than 50% vignetting in the corners of your sensor. You didn’t say what camera you have but if you are using anything with an IMX455, be careful about the reducer. I virtually never recommend reducers. 95% of the time they cause a LOT more problems than if you simply use a larger chip in the first place.
Good luck with it!
John
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John Hayes:Emilio Frangella:
John thanks a lot for the answer, it confirms what i was hoping to be true - i will be looking into an ONAG, and a trip to the observatory to set it up.
A couple of clarifications - my C11 is a plain SCT and not an edge, hence there is no way of locking the mirrors, but i have never experienced any lateral image shift/mirror flop using the standard focusing mechanism, at least nothing that i have ever noticed. When focusing the target stays consistently in the middle of the image and i have never noticed any lateral movement in over two years of usage.
Also i am using a starizona 0.7x reducer which has a backfocus of 146mm, that should be more than enough to accomodate the ONAG. I will look into the proper adapters
thanks again
Two things:
1) If you try to focus with the shutter open, you WILL experience image shift and it will be pretty obvious in your images. The Celestron focusing mechanism relies on one tube sliding over another greased tube and no matter how tight the tolerances, it will not slide in a straight enough line to allow focusing with the shutter open. Simply turning the focusing screw is enough to displace the image by way more than you want. Ok, you might get lucky and take a few subs using a short exposure under good conditions where the shift might not be super obvious but you are not going to get good image yield and you will not optimize FWHM values using that method. In my view, there’s no reason to go for the advantages of real time focusing unless you do it right. Simply put: real time focusing will not work well (or at all) with the standard Celestron SCT focusing system.
BTW, this is why Celestron now ships their RASA 14 (and maybe the smaller ones too) with the focusing mechanism that I designed for them. It allows real-time focusing without any problem. Unfortunately, they did not put my design into any of their SCT products—even though I urged them to do so! My former Edge14 system now owned by Brad Rode is the world’s only system that incorporates that focuser and it works incredibly well. The Optec SMFS is the only other internal focuser for the Celestron scopes that works as well!
2) If you are using a reducer, make sure that the ONAG has enough field so that you don’t get excessive vignetting on your sensor. The ONAG-XM has enough field to run a 36 mm x 36 mm sensor at F/10. If you go to F/7, you should make certain that you won’t get more than 50% vignetting in the corners of your sensor. You didn’t say what camera you have but if you are using anything with an IMX455, be careful about the reducer. I virtually never recommend reducers. 95% of the time they cause a LOT more problems than if you simply use a larger chip in the first place.
Good luck with it!
John
thanks John, got it - out of curiosity i went and checked during an autofocus routine the amount of shift and it's actually there as you said, even though minimal - that's why i never noticed it.
I wonder if it would be possible to write a nina plugin that signals every time a frame is finished and extend skyward to only perform focus adjustment operations at the end of a frame. There would still be some suboptimal frames i guess if the shift happens intra frame but it would be certainly minimized compared to the current AF approach, plus the time savings. I should probably ask Gaston about that.
Forgot to add -
1) i run the scope with a IMX492 so a fairly small sensor, no risks for vignetting
2) The optec focusing system is not a viable solution unfortunately because my SCT doesn't have a mirror lock
1) i run the scope with a IMX492 so a fairly small sensor, no risks for vignetting
2) The optec focusing system is not a viable solution unfortunately because my SCT doesn't have a mirror lock
Emilio Frangella:
thanks John, got it - out of curiosity i went and checked during an autofocus routine the amount of shift and it's actually there as you said, even though minimal - that's why i never noticed it.
I wonder if it would be possible to write a nina plugin that signals every time a frame is finished and extend skyward to only perform focus adjustment operations at the end of a frame. There would still be some suboptimal frames i guess if the shift happens intra frame but it would be certainly minimized compared to the current AF approach, plus the time savings. I should probably ask Gaston about that.
Skywave has the ability to do between-frame focusing but it’s not easy to set up for every imaging program. That’s certainly one way to handle it if you don’t want to spring for a focuser, but you lose the advantages of real-time focusing.
John
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@Emilio Frangella , NINA offers a option to move the focus point based on a temperature shift, one can apply that after every exposure, my experiences are fairly positive, meaning when I refocus every hour or so, the change in focus is fairly small (i.e. basically a safety net). Also the image shift on a SCT is small, it guiding can cope with it. there is also a NINA plugin on how to estimate the focus shift vs temperature relation based on previous observations. If you use the ZWO EAF, the temperature sensor is not very stable, there is a little script by @Dark Sky Geek . The poor man version of realtime focusing, not a competition in any sense, but better than the usual refocus every hour or so.
CS Matthias
CS Matthias
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