AndyThilo

Final update, success! Sold the ZWO OAG and my 290MM and bought a Celestron OAG and a 174 mini. I was careful setting up to get my measurements right and not block the 294's sensor and last night used it for the first time. Focusing the 174 was so easy, I focused the main scope on Arcturus, synced my mount and plate solved in NINA. Then in Stellarium, I moved slewed the mount so the OAG would see Arcturus and focused the 174. 

I started imaging M94 and was having trouble with guide stars but soon realised I needed a brighter star to guide on. The 174 shows a huge FOV in PHD2, very impressed and so easy to focus compared to the 290MM. TBH I originally ordered a 290mini but the supplier sent me a MM as the minis were out of stock. 

2 minutes ago, vlaiv said:

I'm for binning

I always prefer better SNR than empty resolution. It is probably worth binning and you should bin your linear subs after calibration and prior to stacking.

Difference on image when show on screen size (fit to screen) is probably going to be rather small. Difference will be most visible when image is shown at 100% zoom level (1:1 zoom - or one screen pixel for one image pixel).

Over sampled images just look blurry at that setting and stars look large. Noise looks different also - there is less of it when binned and it is much more fine grained.

Overall I prefer images that are properly sampled. You can see what sort of sampling you need for your image if you take FWHM of stars in your image (beware - different software will report different FWHM values - I trust AstroImageJ) and divide value with 1.6 - that will give you sampling rate in arcseconds per pixel that you should use.

You can bin afterwards? Not when you take the lights? I generally use WBPP script in Pixinsight.

Thanks for the detailed answers. So is it worth binning in my case? I'm still not sure what binning means with regards to a final image compared to not binning. 

I definitely want to use it at full fl, probably not till next Galaxy season though and definitely not till I’ve got my OAG sorted. 

Hi

One thing I've never understood is binning and what effect it has on the imaging. For my Edge HD 8", 0.7 reducer and ASI294MC Pro, my pixel resolution is 0.67, and the recommended I believe is between 0.67 and 2"/pixel. So I'm right on the edge (pardon the pun ). If I go full 2032mm then i'm at 0.47. Binning to 2x2 results in 1.34 with the 0.7x and 0.94 without. 

In both cases, it would appear that binning 2x2 would be preferable, but what difference am I going to see? How does it effect image resolution, exposure times etc..? It utterly confuses me, please dumb it down for me

Cheers

Andy

4 hours ago, MarkAR said:

That's a cracking image, well done.

4 minutes ago, simmo39 said:

Looking good. nice image

Thanks

Picked up an Edge HD 8" from here with 0.7x reducer. Got out Thu night for a proper first test. Using a 50mm guide scope so kept subs at 60secs.

Specs -

Edge HD 8" with 0.7 reducer and feathertouch focuser

ASI 294MC Pro @ -20

HEQ 5

Orion 50mm Guide scope with ASI 290MM

Took my time to collimate on Arcturus and focused with a bahtinov mask, waiting for my replacement EAF to arrive. 

Only 65 x 60s lights with 30 darks. No flats as again waiting for new panel. I think collimation was still a little off, need to practice more getting that spot on.  Image is 100% uncropped.

M27 Dumbbell Nebula 15-05-20 by Andy Thilo, on Flickr

I wasn't trying to guide on it, just use it to focus the 290MM. 

Well.... Finally got out last night with the OAG. Did a quick polar alignment, slewed to Arcturus, plate solved, focused and tweaked bobs knobs. Synced in Stellarium and used that align Arcturus within the guide scope FOV (theoretically). Slewed to the spot and I saw a star in PHD2! Not far out of focus, but out of focus none the less.

Couldn't get any better focus as I needed to move the camera inwards, but it was already in as far it would go, tried moving the prism down a little as I was only seeing image on 2/3 of the sensor. Tweaked and played, no joy. Star looked horrid and wasn't guidable. Shimmering and moving about. All the little dots are hot pixels as I hadn't done darks in PHD2. 

So I don't know where to go. I think I'll stick with a guide scope. I was getting 2mins no problems with my 50mm, might swap to a 60. The 290MM seems unsuitable for the OAG, too hard to adjust to focus and I'm wasting too much time messing about.

Yeah I could do that, once synced I guess it should be easy to manually slew the mount to position the star in the guide camera. 

Can't tilt the prism in a ZWO OAG though? Anyway tilt is the least of my worries, I just want to see stars

2 hours ago, Merlin66 said:

Andy,

In my experience it’s 100% easier to set up the OAG during the day.

once the imaging camera and the guide camera are both in focus, they will also be in focus for all other objects.

I ‘ve been using the equivalent of an “on axis guider” - a reflective slit plate for spectroscopy for the past ten years - no major issues.

 

Agreed, but it just means I have to take it all out to somewhere. I'm rather lazy and like to do everything from home :D. But in this instant, it would seem I might have to venture out. Now I have it all setup in Stellarium I'll try it again on M27, there's loads of guide star all around it. If I have no success then I'll go out with it during the day. 

10 hours ago, wimvb said:

I assume that you've seen the diagram on the ZWO site about how to connect oag, main camera and guide camera. ZWO generally provide all the spacers you need with their cameras and oag.

You can focus your guide camera this way:

Target a bright star with your main camera and focus with a Bahtinov mask. Leave the mask in place and move the mount so that the same star is in the guide camera fov. Then adjust focus for the guide camera.

Sounds like a plan, I'll try it on the next clear night.

Yeah it’s all set and I’ve measured everything. The only thing that’s an unknown is the guide camera focus. There is about 5mm of movement in the prism post, its nothing. Most people use a mini style nosepiece camera but I need to check the sensor depth difference. I’m sure I’ll figure it out, just hoped someone else had been in this situation.

Or do I just put the nosepiece on my 290MM?

My 290MM (USB3.0 version) screws directly onto the OAG. A Mini can use it's nosepiece to move in and out for focus. Figured the latter would be easier?

Hi

I can't get focus on the OAG as the farthest object I can see is only a few hundred metres away. I did some tests yesterday and left the Edge at the same focus required for stars. I compared the image of both main and guide camera looking at the out of focus tree and think they are similar. Both show out of focus moving leaves so it must be close. 

 I think I'm going to struggle with the 290MM though and would be better with a mini as that allows for easier focus adjustment. I'm not sure how adding the nosepiece to the 290MM would affect focus compared to being hard mounted to the OAG, I'll have to take some measurements. 

On a slightly different note, I stuck my 50mm guide scope on the edge and did a test early this morning. Only managed 5 reasonable frames before clouds rolled in. Guiding was around 0.7 total on my HEQ5 but I think i have either star trails or back focus is out. Stars aren't pin point for sure but not too bad. Again this was only 5 frames of 120secs each.

Hi

First time trying to use an OAG. Last night was only a test night, get the scope focused, find stars etc. Well I succeeded with the 8", eventually got it aligned with Vega and focused up, tweaked collimation to get a central donut with Vega out of focus. Then slewed to M51, plate solved and no issues. NINA got M51 slap bang in the middle (excuse the red light, it was my headtorch). This was just a 10sec exposure :-

Then I load up PHD2 and nothing, just noise. The 290MM is mounted directly to the OAG so minimal focus adjustment via the stalk. So this morning I decide to put my limited AutoCAD knowledge to use and measure and draw it up but I'm not 100% sure my distance in Stellarium is right. I'd assume the prism/ccd distance is the distance from the centre of the image circle to the bottom of the visible image circle on the 290? Image below from CAD :-

I've drawn it for both vertical and horizonal orientation of the 290 sensor. The large centre rectangle is my 294MC Pro sensor, the small purple rectangle the 290MM sensor. The round circle around the 290 sensor is the 5.5mm hole from the OAG prism to the camera.

In Stellarium, my photographed image shows a rotation of 90degs and the stars in the image line up with what Stellarium shows. 

So clearly I've no guide stars in the FOV. So, some questions:

1. Is the 290MM a suitable guide camera and can focus be achieved? Anyone out there use a 290MM (NOT MINI) with the ZWO OAG?

2. Is my process correct? Distance assumptions correct?

3. What gain should I be using on the 290MM? Unity?

4. Is the 290MM sensor best vertical or horizontal in relation to the 294 sensor?

I considered a 174 Mini but it would be a waste as the image circle of the OAG is only 5.5 mm. The 290 covers this almost 100% and I believe sensitive enough for this purpose?

Appreciate in advance any help/advice. 

Thanks

Andy

I had weird colour issues with my flats when using a L-Enhance filter. The LPR filter helped with processing. Also helped increase exposure time which is good for my 294MC Pro.

Is the box metal or plastic? Looks better made than the Gerd one

Lacerta panel sounds like the best option for price then, I'll have a look at Pegasus although I find all their stuff overpriced.

Hi

How are you getting on with the Lacerta panel? I have a Gert 160mm for my ES102 and it works great, but now I need a new one for my Edge HD 8" and the Gerd one is expensive. The Lacerta is much cheaper and they have a dimmer (needed for my 294MC Pro). 

Cheers

Andy

On 02/05/2020 at 13:47, Freddie said:

No need for fancy optics with Ha imaging. Why not an ST102( or ST120) with a 0.5 focal reducer to give you two options on FL. If you don’t get on with the std focuser (it’s not great) then get the SW upgrade for ~£140. All for less than an ED80.

Hmm could do, I’ve already an 0.5 as I got one to use with my ES102. 

I’ve had my EAF for about 5 months, stripping down my ES102 ready to move it to my Edge 8” feathertouch focuser I noticed that the shaft has massive slop and turns and pulls in and out. Will ZWO fix this? Is it user fixable? 
 

It does this powered and unpowered and also while moving to a new position. I don’t remember it doing this when new 😢
 

Yeah I was looking at the ED80, reasonable focuser and not that expensive, definitely on my list