New Celestron OAG is shipping.
Posted 11 July 2013 - 12:18 PM
Posted 11 July 2013 - 04:49 PM
Posted 12 July 2013 - 09:36 AM
Posted 12 July 2013 - 11:10 AM
Posted 12 July 2013 - 12:38 PM
Posted 12 July 2013 - 02:36 PM
Thanks for the advice Rod. It's supposed to be clear the next couple of nights, so I'll have a good amount of time to test it out.
It's a pain in the you know what to get a guide cam focused in an OAG, but you'll get 'er done. Me? I used one for years when I was doing film imaging. I'm too lazy to do so now.
Posted 12 July 2013 - 02:41 PM
This picture is 97 sub frame, and just over an hour total integration: http://www.astrobin....47915/?mod=none
While I think its a great image, it would be nice only to have to take 20-15 subs.
Posted 12 July 2013 - 09:01 PM
That's a good image. I have the same camera, unmodified on a C9.25 EdgeHD. I suggest you use a lower ISO and longer exposure times per sub.
How big is the aperture of the OAG when it is attached to the EdgeHD?
Posted 13 July 2013 - 03:24 AM
Once it is focused you should be able to find random stars to guide on - and you can practice that way just guiding on a star and not trying to image a particular object. That would get practice with calibrating the guider, and allow you to see first results with OAG - which should be pretty good.
Then I recommend calibrating the OAG so you know how far away the center of the guide chip is from the center of the imaging chip - in arc-minutes. This will let you create a field of view indicator (FOVI) for a planetarium program like TheSky - and let you select an optimal guidestar around an object you want. Then you just need to pre-orient the oag angle so that when the object is centered on the main ccd, the guidestar will fall on the guide ccd.
The one trick to setting the angle is that it is 180 degrees from where it "should" be. If the guidestar is on the north side of the object, then - looking at the back of the 'scope (sct or refractor) with north up - you should have the guide port on the 'down' or south side. This is because the image is inverted.
To do all this more precisely I would make an angle readout on the back.
Much of this is described in a write up I did here.
Some people don't worry about pre-planning a guide star, and they just center the object and then use a very long guide exposure until they see stars to guide on. This may work for you and it would take less effort - but it still requires very good focus on the guider side. I prefer to guide on the brightest guidestar available - and I find that pre-planning one and dialing it in is easy and systematic.
Good luck -
Posted 13 July 2013 - 04:26 PM
Frank- Thanks for all the pointers! How do you calculate the distance between the center of the imaging chip and the center of the guide chip?
Posted 13 July 2013 - 05:03 PM
Alfredo- Thanks! Yeah I plan using ISO800 or ISO1600 with 3-4 minute subs once I get the guiding figured out. How big is the aperture? Do you mean the opening, where the camera attaches? If so the opening is the same size as the t-ring adapter which at measured to be 4.2cm.
That is exactly the size I was asking. If it has the same aperture of the T-adapter then it would cause no different vignetting.
Could you post some pictures of your setup?
Posted 13 July 2013 - 05:23 PM
Great! I'm glad I answered your question.
Here is a quick picture during daylight testing. The only one I've taken so far. I'll take a couple more tonight once I get everything setup.
Posted 13 July 2013 - 06:27 PM
It looks very nice! If you can, post one showing the opening.
Seems like a must have accesory. Let us know how the StarShoot Autoguider works with it.
Posted 14 July 2013 - 04:28 AM
The simple way is to orient the guide camera so it is north or south of the imaging camera. Find a bright star and center it on the imaging camera - and note the declination. Then move the scope in dec. until the same star is centered on the guide camera. Make sure you remove any dec. backlash as you do this - and note the change in declination. That is the offset.
If you can plate solve, then just center a known star on the guide chip and then take a few second exposure with the imaging chip. When you plate solve the image it will tell you the exact center of the image, ra/dec, and you can calculate the offset. Again it's best to have the guide camera directly north or south so the only change is in dec.
And note that all this setup stuff and calibration is only needed once per OTA - and after that the OAG usage should be more systematic.
For now the main thing is just to get both things focused accurately - and the moon is good for that since it is big and bright - and at "infinity."
Posted 14 July 2013 - 11:35 AM
I currently own a QHY5 (same as Orion SSAG), but I'm worried it won't be sensitive enough. Are there any recommendations on a replacement? I'd love something like the Loadstar or ST-i, but they may be out of my price range at the moment. Does anyone have experience with the QHY5-II L mono-- it has a very high QE?
Posted 14 July 2013 - 06:59 PM
I just posted a comparison of the QHY5L-ii with Lodestar in the ccd section. Yes, the qhy is very sensitive and works well with OAG - and in my case with MetaGuide.
Posted 14 July 2013 - 09:50 PM
Posted 17 July 2013 - 10:37 AM
In terms of performance I was able to get just ever so slightly out of round stars at 5 min subs and more oblong stars with 10 min subs. I'm using a Orion Sirius EQ as a mount. I will probably need to check my polar alignment. Also, using PHD with such a long F/L guiding is very new to me, so I will need to do some experimentation on the various settings, I'm sure. My PHD "graph" was all over the place-- but perhaps that's normal? I'm used to using a short F/L guiding setup. However, in the end the FWHM for 5 min and 10 min subs was pretty close to that of a 10 sec sub, so I was pretty happy-- all in the range of the seeing conditions at between 3" and 2.5".
Posted 19 July 2013 - 01:12 AM
Thanks for the report and I'm glad the OAG is working. It sounds like you were able to find guidestars. If you saw some out of round in 5m and they were more out of round in 10m, that does sound like field rotation and not a guiding issue but you would need to confirm. OAG should provide smaller stars - so other factors like field rotation will be more visible.
As for the "plot" - this alludes to some of the misconceptions about OAG and motivated design aspects of MetaGuide. If you look at the guide error in terms of pixels, it will change dramatically when you change the optics from a small guidescope to oag. An OAG guidestar error plot will look huge and noisy compared to a very quiet guidescope plot - but what really matters is how it looks in terms of arc-seconds. If the centroid is accurate, the plots should be no different when viewed in terms of arc-seconds - and the tuning should be the same also. In MetaGuide all displays and tunings are based on arc-seconds, which I consider the fundamental unit for autoguiding.
Unfortunately when people see this big and noisy oag plot - they think it is *worse* to guide on because it is "guiding on the seeing" or "chasing the seeing" or something. Instead it is providing a more precise measure of the star centroid, when scaled to arc-seconds - and that's a good thing.
I expect this improved guiding will show in your images once you get the polar alignment and other tunings optimized. Then you just need to focus well and you will be limited by seeing rather than guiding and flexure.
Posted 19 July 2013 - 09:41 AM
I have to say that I really like the Celestron OAG, as big as it is. It's really robust, and I could see hanging a lot of gear off it. The only conditions under which you might run out of backfocus with it (especially with the larger HD's 9.25 to 14) are if you wanted to add a regular focuser, and fix the primary.
BTW, my new QHY5L II arrives tomorrow so I'm hoping to try MetaGuide very soon. AstroFactors shipped my order the very next day!
Posted 25 August 2013 - 09:40 AM
Posted 03 September 2013 - 08:11 PM
Jos to inform I recently bought the OAG from celestron and is amazing! But one horrible problem I found. I own the EdgeHD 8, this error wont happened in the other models of hd. I also bought the reducer for the 8 and the problem is with the back focus. On the 8 with the reducer the back focus is 105mm. The OAG is designed to work on a 133mm back focus that means I can only use it at f/10 so I returned. This wont happened on the other models because the 11hd and 14hd have 146mm of back focus. This is a horrible problem but everyone owning a Edge HD 8 has to know!
Posted 04 September 2013 - 04:49 PM
Posted 16 January 2014 - 12:23 AM
I haven't purchased the new Edge8 FR yet, but when I do, I'm planning to connect it to the scope using this adapter:
I've done the math and the resulting backfocus will be very close to (+-2mm) the 105mm spec.
brought this thread back looking for an update:
Has anyone tried this adapter or resolved this issue of the wrong backfocus distance when using this OAG with a reducer on a C8 Edge.
Also, is there a place to install a 2" LPS filter?