I've been using the ZWO Off-Axis Guider on a 700-mm and a 250-mm telescope and present some pros and cons I've observed as well as an approach for ensuring good focus BEFORE you go outside.
Your suggestion to setup in the daylight was so simple and straightforward. In the daylight, quickly figured out that the backspacing was not going to be short enough with the ZWO OAG when using the helical focuser and the ASI290MM. Had to also remove the provided extension tube that I was using with the guide scope, then removed the helical focuser, went back to the original setup, and got the camera and guide scope all focused together. So simple and straightforward this nugget of wisdom found in this video!
Excellent videos thank you. I just ordered mine and will be using with the ZWO 290 mini. I also have the 1600mm-cool with the 8slot wheel and your previous video was wonderful, I think my train setup time just got reduced a lot. My system is similar I have the ES127ed triplet and I went with the ES 3” Flattener/reducer to get me a 667mm FL. I got the nonrotating focuser for this setup as well and I can’t wait for these to ship!
Thank you for making this video, and the other explaining how to install the ZWO OAG. I’ve been thinking about adding one of these for a while, and just ordered the M68 version for the 2600/6200 camera.
Yeah, I think ZWO has a larger diameter OAG for full frame sensors so be sure and get that one! I’m a convert to OAGs now, but I do want to play with the little WO uniguide scope.
Excellent video James! I have an Orion OAG (almost identical to the ZWO OAG) and tried it on my Celestron EDGE HD 8, but could never get focus. After watching your video, I'm going to go back and try again.
Thanks, David. I hope there was some useful stuff in there and that you get your OAG up and running. I have a C9.25 and for some targets, Stellarium only shows one guide star in the OAG view. Thanks for watching and good luck!
Thanks Ray. Yes, I tried a different cable and tried bypassing the ASI1600 hub. No change. But when I plugged it into a Windows 7 laptop, it worked just like it used to. I'm guessing ZWO took some liberties with the USB standard to improve their throughput and now it isn't compatible with Windows 10 and/or USB3.0. It'd be nice if ZWO would push out a fix. Not holding my breath though.
James Lamb Hi James. I’m having the same issue with the 16 bit mode. I wasn’t using the 1600’s hub but it was a usb 3 port on Windows 10. I’ll try the usb 2 port that my laptop has and see if it changes but not hopeful. I’m busy setting up my Asi1600 with the minifiltereheel and OAG so have found your videos very Helpful. I have the ES102 app too! I’m trying to sort focus indoors but can’t seem to get either camera to focus. Maybe without a reducer/flattened things are not far enough away to reach focus? I’m looking into getting the Hotech sca 2 flattener. I’ve read some good reviews. Clear skies.
Update. I tried the ASI120mm in a usb 2.0 port on my Windows 10 laptop and still no 16 bit mode. I’m concluding that it’s a Windows 10 or ZWO driver issue. Hope ZWO are going to look into this. They seem to have dropped old 120 users from the radar. The ASIAIR and the new ASIAIR pro don’t support it and now more issues. On a different note, I have an Edge8HD with the .7 reducer and was hoping to use the asi oag with it. I’d be working at just over 1400mm focal length. I could use the asi120mm or a Lodestar x2 guide cam. Do you think either is likely to work or am I pushing my luck there? The Celestron oag is so expensive! Thanks again for the very informative and detailed videos.
Hi James, I don't follow your reasoning about needing 16 bit digital resolution due to the pixel resolution of the guide camera. Surely the ADC resolution does not affect the spatial resolution of the camera? Actually the ASI120mm only has a 12 bit ADC, does it not?
Hey, Ian. Yep, the 16 bit (actually 12) vs 8 bit is not a big deal for a guide camera. I suppose there is a marginal benefit to having finer shades of grey might allow the PHD2 algorithm to better identify the centroid of the star. Mostly, I was just ticked that the camera wasn't working in the 16 bit mode like it used to. Certainly not a show stopper. Thanks for watching!
I never could get that Explore Scientific flattener to work as well as I would like. I replaced it with the Hotech Flattener and it's working much better. See the video here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Ror5OXKV8Sg.html Thanks for watching!
In your discussion you say you use your asi174 on your SCT and not the asi120. Are you also using a different OAG on the SCT ie not the Zwo OAG on the SCT? thanks
I use the Celestron OAG on the SCT along with the ASI174 because of the larger prism (OAG) and larger sensor (ASI174). I use the ZWO OAG with the ED102 (700mm) and WO Redcat 51 (250mm). I use the ASI290mini with that OAG.
If one also uses a diffraction mask to focus the imaging camera does the oag prism catch enough peripheral image to also generate a diffraction pattern? Thanks.
Not in my experience. Although, if you could position the bright star in the OAG view, it should work. I've done focusing at 250mm and 700 mm on objects during day --- works great. Lately, I've had to refocus my SCT OAG and just used the image in Sharpcap--works well enough. Perfect focus for the OAG is not critical. Thanks for watching!
James, great video and thanks for all detailed information. Do you have any issues with the oag focus when changing filters ? My broad band and narrow band are not parfocal so I have to choose to have the oag focused to one set of filters or another.
Thanks for watching, Andre! I do see a difference, but it's small as my filters are parafocal. Fortunately, PHD2 is fairly forgiving about out-of-focus stars.
I'm by no means an expert but I would suggest that you always place the filter or filter wheel closest to the imaging camera and certainly after the OAG. That way the filters will not affect the focus of the guider.
Hey Louis, That's absolutely where you wan to put the OAG-you don't want filtered light going to the guide camera. However, the issue is that we generally focus the OAG for the Lum filter. If your other filters are not parafocal, then when you change filters and re-focus for the imaging camera, for the Ha filter, say, your guide camera is now out of focus a little bit because it was in focus with the Lum filter.
HI! I also have an older USB-2 ASI120 camera, and also recently tried to use it with a USB3-only laptop. Initially, it didn't stream at all, whether at 8 or 16bit. I'm using Linux, which is probably even more sensitive than Windows to USB problems. Anyway, it turns out you can Flash the firmware in ZWO ASI USB-2 cameras. astronomy-imaging-camera.com/software-drivers -> FW Update tab. Once I downloaded and installed the tool, and connected to the camera,I updated the firmware to "compatibility". And lo and behold, all issues went away. The camera now works great under both Windows and Linux, using the USB3 ports on the new laptop. Perhaps newer Windows versions and/or USB3 ports on your new laptop also need the camera to be in "compatibility" mode.
Hay James, thanks for the info. ZWO suggested I do that when I brought the issue up on their forum. I downloaded the firmware update program-- but was just too afraid to use it for fear of rendering the whole camera useless. Thanks to your bravery, I'll go ahead and update mine. Thanks for watching!
Hi James I started playing with an OAG and noticed that different filters were not parafocal and that meant that the focus on the OAG would shift when rotating through filters on the imaging camera. Have you had this issue with your setup?
I certainly expect that could/should happen. I have 2nd generation ZWO filters and they are fairly parafocal so I don't notice much of an effect. Fortunately, guide star focus is not nearly as critical as image focus. The centroid algorithm used by PHD2 (and others) should still be able to define an adequate star center to track. In short, you may notice a visual effect but not in the guiding performance. Let me know what your experience is. Thanks for watching, Eric!
@@Aero19612 Yeah, biggest difference for me was between Ha and Lum filters that are different brands. I'll try to focus somewhere in between the two furthest apart and see how that works, Thanks!
Great video James! Did you find overall your guiding total RMS error better with OAG? I bought a ZWO for my ASI 290MM camera and have not switched out the ST80 yet - I wanted to get a baseline first but that seems hard on all by itself.. Also I'm finding my 290mm is not as good as I thought it would be over the StarShoot v1 camera but not sure if I have driver issues or gain issues. I can't seem to find a good gain setting for the 290mm - unity gain works fine on some objects but not others... Anyone know good gain settings for asi290mm?
That's a good question but it's very hard to answer because seeing is such a big variable. Just on principal alone, the OAG should only improve guiding, but may or may not be significant enough to see. The OAG gives you a finer resolution of the guide star so PHD2 should be able to more accurately identify the center of the star. Also, eliminating the weight of the guide scope reduced the mass moment of inertia that your RA and DEC motors have to move. I'm surprised at your observations regarding the ASI290. It works very well for me. I have PHD2 use 50% gain most of the time. It should be more sensitive than the Starshoot if I remember its specs. Thanks for watching, Marty!
@@Aero19612 thanks James! More testing tonight - I'm testing the EAF autofocuser... doing a vide on it... I'm over at @AstronomyEast. What are you using for gain settings for your 290? 50%? What's your connect dialog gain and offset?
Good question. Long answer: 1. Multistar will work with an OAG, but works better for a full-field guidescope because (a) more suitable stars are visible and (b) the light from those widely separated stars pass through very different parts of our atmosphere so the seeing motion of the stars is more random. 2. As focal length goes up and we become much more sensitive to guiding error and want/need to use an OAG. But the OAG only sees a very very small patch of sky and you may only have 1 guide star (especially for galaxy targets) so multistar won't be possible. Bottom line is: If you use an OAG and can see multiple stars, use multistar guiding. It won't hurt, but it may not help much as focal length goes up.
Did you encounter the problem in which the stars viewed in the guide camera all produce a fanned comet tail at focus and out of focus positions? I wonder if the prism isn’t perpendicular to the principal axis. I find no way to adjust that. I guess the guide stars looks like your field edge stars viewed in the observing camera
I believe so. Sometimes, when out of focus, the stars will have an "arrow" like shape. You could describe that as a fanned comet. I tend to think the prism is properly aligned with the body of the OAG; however, the ClickLock that holds everything can permit some tilt and the guide camera itself is held in place with one set screw, which can permit tilt as well. Fortunately, PHD2 isn't too picky about requiring a circular star.
Have you used your OAG enough now (on various targets) to say how well it’s working? That is, how often is finding a suitable guide-star and framing you desired target actually working out?
The ZWO OAG I use for the 700mm and 250mm refractors is a “no worries” solution. I don’t bother thinking ahead about locating a guide star at all. The (Celestron) OAG paired with the 2350mm SCT is a different matter. I’m confident that I can find a guide star, and with careful planning, can set the orientations of imaging camera and OAG before I go outside to ensure that guide star is there (there’s a video for that: “Galaxy Imaging Session Planning and OAG Setup”). That procedure worked ok and gives me confidence I can find an appropriate guide star for a given target for that long focal length OTA. I’m committed to the OAG lifestyle now, haha.
James Lamb Yes it’s my 2032 fl I’m worrying about (still waiting for the new cmos camera). I too plan w/ Stellarium. I forget to buy a protractor when I’m at the store to assist w/ positioning my observing camera’s angle. So it sounds like you haven’t used the your 2350 much yet. Thnx
Using my 2350mm now. Still on first two targets I selected for Galaxy season. Very few good imaging nights in the past 8 weeks. When I have a good night, the focuser binds or the corrector dews over. At least I know the Stellarium planning procedure works. I need a more accurate process for dialing in camera and OAG angles. I bought a digital inclinometer and will probably add degree marks at 3-deg increments on OAG body.
First, make sure you need 55 mm back focus. I think my C9.25 requires something like 110 mm or 115 mm from the back cell. You make need something like this adapter to start off with: agenaastro.com/blue-fireball-sct-female-m48-male-t-t2-female-thread-adapter-t-09.html Then get the additional spacers/extension tubes to get you the rest of the way. Good luck, and thanks for watching!
Yes. I just looked at my spreadsheet where I keep all of the adapters and bits. I started out using a DSLR and Celestron sells an adapter for use with the DSLR. The back focus is 105 mm without the reducer. When I inserted the reduce, I just screwed the cameral/adapter onto the end of the focal reducer (still 105 mm behind the focal reducer). Worked fine. So, I think you need 105 mm from aft-most thread of the SCT flange.
The thread on the Explore Scientific focuser tube is M68x0.75. The thread on the scope side of the OAG is M48. The Explore Scientific field flattener is M42 but I have a M42/M48 thread adapter (from ZWO) that converts it an external M48 thread (same as Redcat 51). I think the WO rotator thread is M63 but I just use the M48.
I do suspect it and don't think I would recommend it to others. I had no trouble dialing in the flat field with the adjustable William Optics Flat6Aiii. It would probably work with the ED102, but I don't want to lose focal length (it's also a focal reducer). Thanks for watching, Ryan!
@@Aero19612 I am looking to upgrade from the red cat to a larger refractor and was looking at the ES 127, but didn’t want to lose any focal length as I really wanted something that would go much deeper than 250 mm so the guys at Starizona, ordered me a Hotech flattener only and said it should either work stock or I can bring it to them and they can reverse engineer it but they’ve had a lot of success with those flatteners and 1-130mm refractors and they’re fairly inexpensive just FYI. Your vids are super helpful to a new guy.
Yes. I have the 2nd generation Explore Scientific field flattener that requires 55mm back focus. I think an earlier generation had a larger back focus. Which one do you have and what back focus are you providing? I'm pretty sure something is wrong in the setup, but just don't know what it is.
I just checked a sub captured with the ES 102mm and the ES FF and the stars are quite good. There is a bit of elongation in 2 corners but nothing I would worry too much about as they will likely end up being cropped at the end. I can email you a jpeg for reference for comparison if you would like. Just let me know.
Mine has “55 mm” written on the side of shoulder. You must be doing something right....and I must be doing something wrong. I’ll give it a good “think” before I use it again. Thanks for checking your setup.
Have you updated PhD2 to 2.6.6? When I did I was getting delays in the guiding with the 120MM. I have since gone back to 2.6.5 which did not give me any problems just a couple of days prior.
Interesting. Yes, I have 2.6.6. But SharpCap, Firecapture, and APT all fail to stream (ZWO's ASIcap works fine of course). When I checked an older Windows 7 laptop, it worked fine with SharpCap.
I'll probably be imaging tomorrow night and I will be able to test 2.6.5 again. If I am not mistaken win10 shoved an update down throat last week. Maybe that's the culprit too... I'll keep an eye on the sharpcap refresh rate when I will polar align tomorrow night.
I am imaging now and using PhD2 on a windoze 10 computer. Phd2 v2.6.5 hasn't skipped a beat since I started 2 hours ago. V2.6.6 was skipping refresh points all the time.
I downloaded PHD2 v2.6.5 and the 120MM worked in that version. The ASCOM settings box is different than in v2.6.6 so I can't confirm if it's in 8-bit or 16-bit mode. I can't stream at in SharpCap or FireCapture. ZWO suggested I update the firmware in the camera. I downloaded the firmware upgrade tool from their website but haven't gathered the nerve to use it yet.
Sorry I know this is an older video now but I'm trying to decide if I should get the traditional guide scope setup for my 8" F/4 scope or if I should get the ZWO OAG. I've got the 120MM Mini and the same EFW and camera as you do, my focal length is pretty close to the 700mm of the scope you have there (800mm ) but my biggest fear is the ability to find guide stars and have the camera in the correct orientation to find guide stars when say doing a mosaic. Would you recommend getting the ZWO OAG of getting a traditional 50 or 60mm guidescope?
I would say the OAG will be fine: (1) I never have an problem finding a guide star with my 700mm scope and (2) I have a couple of videos showing how to use Stellarium to pre-plan an imaging session by setting the orientation of the OAG so a guide star will be in the FoV of the guide cam (I have to do this for my 2220mm scope). Good luck, Wayne!
@@Aero19612 Thanks for the reply and thanks for these videos, they're incredibly informative and have helped me tremendously in improving the imaging I have done.
Great video and review, James. I hope Explorer Scientific can determine why the field is not flat. Here is an interesting blog from Cloudy Night regarding back focus and elongated stars using an Explore Scientific reducer/flattener. I also read on other sites where there were back focus issues with flatteners and reducers with the correct 55mm back focus. I know the back focus is supposed to be 55mm, but I wonder if fine-tuning your back focus using Baader T2 Delrin Spacers would help. www.cloudynights.com/topic/504935-fine-tuning-field-flattener-back-focus/ Baader T2 Delrin Spacer Ring Set: agenaastro.com/baader-t2-delrin-spacer-ring-set.html I'm in the process of setting up a similar camera set as yours on my Astro-Tech 111mm Triplet, 777mm refractor. It took me months to find the correct reducer/flattener for this older refractor. According to Astro-Tech only one model will work. I'm using a ZWO ASI 294 color camera. I just ordered the ZWO OAG, ZWO helical focuser, and ZWO ASI290MM Mini Monochrome guide camera. I'm also installing a Starizona Filter Slider Drawer between the OAG and the camera so I can use a light pollution filter. The optical system comes in at 53.5 mm of back focus but with the Baader spacer rings, I can achieve 55 mm. In addition to the new ZWO guide camera, I also have the same ZWO ASI 120 MM as yours. I haven't used it in years but will let you know if I have the same issue with 16 bit. Thanks again, James, your videos have been extremely helpful. I hope you get the flattener issue corrected. Sincerely, Jim.
Thanks Jim! I took the ED102 out last night and played with the focus per suggestion from Explore Scientific. Haven't had a chance to look at the pictures to see if the stretched stars are still there; however, the guide star image looked stretched. I'll read blog post. Should be able to get more time outside in the next few days. Let me know what you find out with the 120MM. ZWO suggested I reflash the firmware and I downloaded their software--haven't gotten the nerve to try it--afraid I'll lose the camera altogether.
Jim, That Cloudy Nights discussion of flat field back focus is very interesting. I will try to play around with that. Using a different spacer, I can increase the back focus by 1.5mm. I think some thin spacers also came with the ZWO filter wheel. Thanks.
@@Aero19612 James, No problem. As you know, nothing is easy in this hobby. I don't know how many times I have pulled my hair out, trying to get something set up. Fortunately, we have others in the community who have had similar issues. I have the ZWO spacers that came with my ASI294MC. The spacers OD is larger than the extension tube but will be good for testing. Later you can pick up better spacers from Agena Astro Products. agenaastro.com/baader-t2-delrin-spacer-ring-set.html Agena also has spacers for 48mm. In anticipation of problems, I have spacer shims ordered for both my refractor and my 9.25 SCT setup. My 9.25 is another problem child. Several years ago I installed a Moonlite electronic focuser where the 6.3 reducer attaches to the front of the focuser drawtube. I'm working on the back focus for the 9.25 as well. Over the years I have imaged with my Canon T5I, and Celestron Skyris 236c but back focus was always hit and miss experimenting with extension tubes. Now I'm serious and learning. I purchased the Zwo color camera to get started then later will get into monochrome with a filter wheel. I'm a glutton for punishment and need my head examined. I just purchased an older C-11 with a Hyperstar setup. I’ll set it up soon to check it out. Then I need to disassemble the scope for a good cleaning, flock the tube, and maybe have the primary mirror refinished. Just what I need, another project. Now I need to live to 165-years-old to get everything done. Even though at times I complain, rant and rage, I have concluded that researching and fixing issues is just as much fun as looking through the eyepiece. Thanks again, James, for your videos. They have been extremely helpful. Sincerely, Jim
