a few oag questions

[iwols]

tried using my oag with a qhy5 mono ccd tonight(which ive used quite often) but could not get enough steady signal to lock onto with phd2 ,moved the guider in and out,still same,now i know it was half moon ,but the sky was clear,but have never noticed this problem before

so 1..does the moon effect the oag much

     2.. does the oag need a heat strap

    3.. would my asi178 be more sensitive 

thanks 

[alacant]

Hi. It may depend on the focal length of the telescope, the longer the trickier. I was out last night using a zwo clone on our oag at 800mm and it was OK so I don't think the moon upsets it. (**EDIT we were in Leo) Are you sure you are in focus? You need to nail it exactly. Maybe try somewhere with a rich star field over by Orion to make sure you have stars. On the last point about changing cameras and as you haven't had the problem before, I don't think it's the camea's fault; we went through the whole of last year's barren galaxy season and never failed to find a star up to 1200mm imaging at up to 30º ambient.

Not much there I'm afraid but hope it's enough encouragement. Don't give up! The benefits OAGing are amazing.

 

[sloz1664]

When you say you have not had the issue before, is this using an OAG with the QHY5 and did you successfully achieve focus.  I didn't have much look using that camera with an OAG and changed to a Lodestar as it was far too noisy. I would certainly try the ASI 178. You can set the OAG during daylight if you can focus on a distant object, but you will need to reduce the telescope aperture as it will be far too bright to obtain decent images on both the main & OAG cameras. Also, as a starting point you should set your guide camera exposures to around 2 -3 seconds.

Steve

[lukebl]

I would have thought that you should easily find stars with an OAG and the ED80 DS, with the wide field of view. My guess is that the QHY isn't focussed, or the OAG prism isn't positioned correctly.

I use a QHY5 mono / OAG with my 1600mm FL RC8 f/8. Although for some targets I can't find a star at all, there are usually one or two sufficiently bright to guide on, even with the narrow FOV. The QHY5 isn't ideal for my setup (I really need something more sensitive) but I'm sure it's fine for the ED80.

[Star101]

The last couple of nights I have been using my C11 (2800mm fl) with ZWO OAG and Lodestar X2 set at 4s in PHD2. Imaging M108, I had to off center the galaxy so as to get a visible star.

Same again with NGC 3718. Then I slew to NGC 6384 and have a choice of several stars while the DSO is dead center.

It took me a couple of hours to set up my OAG the very first time. As stated above, point to a high density star field. I did try the moon but that was useless. Stars are easier.

Also, the chip of the guidecam and that of the imaging camera should be very close if not same distance backfocus. (check manufacture spec).  In other words, if the imaging cam is 2 inches back from the prism in the OAG, so should the guidcam.  Hope that make sense!

Good luck.

[sloz1664]

56 minutes ago, lukebl said:

I would have thought that you should easily find stars with an OAG and the ED80 DS, with the wide field of view. My guess is that the QHY isn't focussed, or the OAG prism isn't positioned correctly.

I use a QHY5 mono / OAG with my 1600mm FL RC8 f/8. Although for some targets I can't find a star at all, there are usually one or two sufficiently bright to guide on, even with the narrow FOV. The QHY5 isn't ideal for my setup (I really need something more sensitive) but I'm sure it's fine for the ED80.

There is a significant difference between the old QHY5 and the newer QHY5ii. The old QHY5 was a lot noisier

[lukebl]

51 minutes ago, sloz1664 said:

There is a significant difference between the old QHY5 and the newer QHY5ii. The old QHY5 was a lot noisier

Not sure which one the original poster is using. Mine is the QHY5-ii. Still pretty noisy. And you can't use binning with it in PHD, which is a shame.

[sloz1664]

9 minutes ago, lukebl said:

Not sure which one the original poster is using. Mine is the QHY5-ii. Still pretty noisy. And you can't use binning with it in PHD, which is a shame.

Yes, unfortunately you cannot bin with cmos chipped cameras when guiding.

[ollypenrice]

One step at a time.

1) Orientate your OAG prism so that it goes down into the light cone at right angles to the chip and intrudes on the long side of the chip rather than the short because that will allow it to go deeper into the cone without shadowing the chip.

2) Get the prism as deep as possible into the light cone without creating a shadow. You can do this in the daytime by putting a T shirt style diffuser over the objective, as you might do to shoot flats, and lowering the prism till it shows on the images you're taking, than back it up a tad till you no longer see it.

3) Focus the camera. You can get a rough daytime focus by imaging a very distant horizon or object of some kind. Refine this focus on a star.

Personally I wouldn't entertain the idea of using an OAG to guide an ED80. I use a separate guidescope (cheapo ST80) to guide a dual TEC140 rig working at 0.9 arcseconds per pixel. However, you have the OAG and want to get it working so I'd start with the three steps I suggest if you haven't already done so.

Olly

[iwols]

thanks guys im using it with the ts 100 quad ,cheers

[iwols]

well just tried the  asi178 c   in the oag, on the moon for focus just before dusk as it was cloudy later  but had no joy,but on saying that put the qhy5  ii back in and couldnt focus that on the moon either ,will have to wait for a clear night 

[RolandKol]

I am sure ASi178 will be good enough, as my ASimini does it's job in London for my PDS.

If you never had it in focus, try to play during a day time for sure...

Once spacings are in place it is quite easy to adjust focus in the dark, - once close, I was even able to use bahtinov mask.

And yes, push prism as deep as possible as described above, otherwise you will have quite a distorted stars and will guide on "Cucumbers or even Bananas" 

Do no forget to tighten ALL the hex screws and/or bolts once finished...

I had some guiding problems and only after 1 month I found my OAG camera was wobbly a bit as OAG camera holder Hex screw was loose! (even thought to sell the mount!!!)

It caused quite a bad guiding after Meridian flip

The most funny thing, as a reminder to tighten the last Hex Screw,  I even placed the hex key on the magnet close to OAG... Forgot anyway... The hex key and the magnet were not visible in the dark  

Just FYI,

if it will be challenging to find a bright star it in the guidercam, go for Moon, -

and if you use stellarium, - it has OAG FOV option. Moon helped me to place/adjust OAG FOV on Stellarium, - now I can target with it perfectly without platesolving.

[alacant]

Hi. First, position the prism by slowly pushing it into centre FOV takeing a flat frame after each push. Back off a bit when you first see a shadow.

Next focus. Focus any terrestrial object in your main camera. It doesn't have to be distant.. Now focus the OAG using a video app. Lock the OAG focus. Refocus the MAIN camera only when under the stars. That's it.

HTH

[Ouroboros]

On 13 April 2019 at 18:50, ollypenrice said:

Personally I wouldn't entertain the idea of using an OAG to guide an ED80. I use a separate guidescope (cheapo ST80) to guide a dual TEC140 rig working at 0.9 arcseconds per pixel. However, you have the OAG and want to get it working so I'd start with the three steps I suggest if you haven't already done so.

Olly

I am interested to know why. I had thought of adding an OAG to my ED80 set up. But maybe there's a very good reason why I shouldn't. 

[ollypenrice]

1 hour ago, Ouroboros said:

I am interested to know why. I had thought of adding an OAG to my ED80 set up. But maybe there's a very good reason why I shouldn't. 

Well you can certainly do it but the question would be why? An OAG has a feeble light grasp compared with a guide scope but it shares exactly the same imaging light cone as the imaging scope. Which matters most? If you are imaging with a reflector, whose mirror can move slightly because it cannot be rigidly attached to its tube, then guiding on that light cone is essential. If you are imaging at very high resolution then, again, an OAG removes the problem of differential flexure or under sampling. But do you have these problems? If you don't, why solve them and introduce the problems inherent to OAGs. (Look at those little prisms, note that they nibble the crumbs of faint light at the edge of the main scope's light cone, compare this with the solid projection of the sky onto the chip of a guide scope...) It's a choice. I just think it's a good idea to make it an informed choice.

Olly

[Ouroboros]

8 minutes ago, ollypenrice said:

Well you can certainly do it but the question would be why? An OAG has a feeble light grasp compared with a guide scope but it shares exactly the same imaging light cone as the imaging scope. Which matters most? If you are imaging with a reflector, whose mirror can move slightly because it cannot be rigidly attached to its tube, then guiding on that light cone is essential. If you are imaging at very high resolution then, again, an OAG removes the problem of differential flexure or under sampling. But do you have these problems? If you don't, why solve them and introduce the problems inherent to OAGs. (Look at those little prisms, note that they nibble the crumbs of faint light at the edge of the main scope's light cone, compare this with the solid projection of the sky onto the chip of a guide scope...) It's a choice. I just think it's a good idea to make it an informed choice.

Olly

Thanks, Olly.  OK I see you have a point.  I have a Starlight Express Lodestar II with 8um pixels in my SW finder guider scope. When I popped this into my ED80 to see how the longer focal length scope affected guiding I found this improved my guiding RMS error of a little less than +/-1" by  almost a factor of two. (Having changed the various parameters in PHD appropriately of course.)  So, I have wondered whether the 8um pixels of my guide scope are not well suited to my guide scope. An answer perhaps is to try a longer focal length guide scope rather than OAG. On the other hand I could change the camera to one with smaller pixels. But I really rate the Lodestar and am loath to change it.  It's very sensitive and very reliable. And frankly the guiding is just about good enough. I suppose we all wonder if the grass is greener ..... etc etc

[iwols]

hi guys the oag is on my ts100  quad,i used a st80 for guiding with my ed80 worked perfect

[ollypenrice]

12 hours ago, Ouroboros said:

Thanks, Olly.  OK I see you have a point.  I have a Starlight Express Lodestar II with 8um pixels in my SW finder guider scope. When I popped this into my ED80 to see how the longer focal length scope affected guiding I found this improved my guiding RMS error of a little less than +/-1" by  almost a factor of two. (Having changed the various parameters in PHD appropriately of course.)  So, I have wondered whether the 8um pixels of my guide scope are not well suited to my guide scope. An answer perhaps is to try a longer focal length guide scope rather than OAG. On the other hand I could change the camera to one with smaller pixels. But I really rate the Lodestar and am loath to change it.  It's very sensitive and very reliable. And frankly the guiding is just about good enough. I suppose we all wonder if the grass is greener ..... etc etc

I use the same guide camera at 400mm FL to image at 0.9"PP. Perhaps I should try extending the FL of the guidescope but I'm beating 0.5"RMS as it is.

Olly