Eta carina with OAG guiding

[Paul Haese]

As some may know I have not been using the OAG on the QSI since I first tried it. I had several issues that just made guiding impossible.

With the completion of Thor's helmet I decided that I would nut this OAG problem out once and for all.

The initial problem was that the stars were like seagulls which made for bad guiding. I have since resolved this problem by getting an adapter made to suit the flattener and give me the correct distance from the flattener to the sensor, which in turn has made the guide stars round and of course flattened the field. One problem licked!

Next I had a focus problem for the OAG. I purchased a spacer from QSI, however I think when I first used it I had it the wrong way around. That made for odd shaped stars in each of the corners. I now have it in the correct orientation and the stars below show that things look better.

Last night I gave the OAG another try. Guiding was certainly better but still not perfect. I have to focus the stars better in the OAG and the primary camera was not well focused. I hurried this a bit. That said though, I can report that I did get better stars than I have previously and with a slight collimation adjustment everything looks a whole lot better.

[Moon]

Paul,
Glad you got it working.:thumbsup: OAG at long focal lengths is a very different 'user experience' but in the end should give better results.

Which guide camera and software are you using?
What process have you settled on for focusing and collimation?
James

[David Fitz-Henr]

That's a nice image Paul - good colour and detail in the nebula! What equipment (scope, etc) were you using ? Sounds like you are having fun with the setup / OAG - anyway, it wouldn't be as satisfying an achievement if it was all easy, would it !!

[wasyoungonce]

Well it's good to see someone do it properly...wrt to my effort.

Paul can you please give me some details on exposures, cameras, scope, F ratio... etc. If you don't mind that is.

This just gives me hints on what I should be trying :D

Your pic is pure eye candy.:thumbsup:

[DavidU]

That's a beauty Paul. Superb work.

[telecasterguru]

Paul,

You give me hope that I may be able to get OAG to work with my rig.

By the way that is a very good image.

Frank

[Paul Haese]

Thanks all, not an image that I reckon is fantastic, but the fact of getting the OAG working is the main thing and will mean I can go to 20 minute subs for my imaging purposes.

Ok now the scope I was using is the RC8". For guiding I was using the Star Shoot Autoguider on the OAG on the QSI583WSG unit.

The software I am using is PHD (not got MaximDL settings sorted yet but that will come).

James for focus I use the Bahtinov mask and for collimation I am using an out of focus star image taken in Maxim. Once collimation is fixed or close I use the mask for focus. I am quite particular normally about this. It takes several minutes to get it just right. Some people can use FWHM but I find that this can be a bit hit and miss. The lower the FWHM the sharper the focus, but the mask really shows what is going on.

David, sorting out flexure with my system has been a real pain. I had it completely sorted when I was using the 40D from Central DS but when I got the QSI things had to be sorted again. Not sure why as the weight was similar, so it has been a challenge to get it right and I still think there is more room for improvement, but this is a huge step in the right direction.

Wasyoungonce, my imaging camera is the QSI583. Exposure duration was 5 minutes subs in LRGB but it really needs 10 minute subs to get this image to shine. For one shot colour, please check out my site for exposure details taken with my 40D. I hope that helps you out.

Frank, getting an OAG working on long focus can be a little bit of a pain. In PHD I have the aggression set to 90%, 500 step calibration, min motion to 0.15, camera gain at 100% and 2.5 second exposures. I tend to think that focus is critical for guiding despite what Craig Stark says where the guide star can be slightly out of focus. My results are always better with a sharply focused guide star. Other may find differing results and I challenge them to show me that I might be wrong.:)

I hope that has answered everyones questions and if you want anymore help please ask and I hope I can answer. The more expert guys on OA guiding are more than welcome to contribute what they know.

Thanks once again.

[wasyoungonce]

Thanks Paul.:thumbsup:

[Bassnut]

Paul, at that FL, are you binning the guide cam?. At over 2m, I bin 3, much shorter exposures, works fine, but sightly out of focus, cause otherwise stars are a bit blocky. At bin 1 or 2, the stars are smoother, but guideing is more unstable due to extra noise with the same exposure times.

I found that slightly out of focus can indeed help, but it depends on the guide image scale. A single block star is rare but fine focused, its when it suddenly becomes 2 pixels it gets nasty, jumps all over the place and defocus is required, albiet at slightly reduced but smoother acuraccy overall. Oddly, a multipixel (shorter FL, or non binned) star can sometimes do with defocus too due to dancing pixels appearing and disappearing on the edges, moving the centriod.

Why does flexure require "sorting" again with the QSI?, doesnt it become irrelivant?.

Why do you need a spacer to adjust focus, cant you slide the guide cam up and down?, or, doesnt the QSI also have a focus adjusting ring?.

[Paul Haese]

Fred PHD does not offer binning on the guide camera but I will use this when guiding in Maxim.

Flexure is a problem when guiding with a guide scope, not when using the QSI. I had trouble getting the settings right with whilst using the QSI's OAG so I wanted to get away from the problems of flexure that I had with the guide scope and that meant using the OAG, which was not working well with the settings I was originally using and given that clear sky is fleeting I went back to what I knew would work more or less. Yes flexure is irrelevant.

I had to get a spacer because the focus ring on the QSI would not go in far enough to gain focus on the RC8. It works fine on other scopes without the spacer but on this scope I needed to have the spacer so that the focus on the OAG was the same as the main sensor.:)

[Paul Haese]

A small repro to bring out more detail and some deconvolution too.

[Bassnut]

More neb there,and I like the way the core pops out, although some may find it somewhat unnatural. Low noise, and tight focussing/guiding though, excellent.

SOOO, PHD doesnt bin guide exposures he. Well here was I thinking its free, everyone uses and loves it, why do I bother with DL. But theres always a catch isnt there :P. No bin guiding is a show stopper for me. Goes to show afterall, you get for what you pay for :whistle:

[Paul Haese]

Yeah I see what you mean about the core. Might need to address that.

Yep Maxim gives you what you paid for and yes there is always a catch to everything that is free.

[telecasterguru]

I understand that PHD does not have binning but doesn't the brain have a gama setting that can replicate this to an extent?

Frank

[gregbradley]

Excellent image Paul. Beautifully tight and round stars.

Greg.

[Paul Haese]

Not seen that in there Frank, perhaps the very latest version, but binning would be better still. I think the gamma/contrast control (perhaps that is what you were thinking of Frank??) in the main interface is just for cosmetic purposes . The setting of this does not affect the camera itself, it's just so you can see the stars. Taking this from Craig Stark's words on the PHD site.

Thanks Greg. Just part of the evolution of my DSO imaging. Might get it right one day.:lol: Might not either. That is the more likely of the two I reckon. At least with Planetary one usually settles on a system of capture and processing and usually sticks with it once you start obtaining great images. Not so with this DSO caper. It seems like a constant evolution. All bizzarly entertaining in a strange way and providing a certain satisfaction when you get more organized. Hmmm

[mithrandir]

You can always ask Craig. If he reckons binning in PHD is worth doing he will get round to it. I donated for PHD, as well as paying for Neb2.

[Paul Haese]

Yeah that is true. Good point

[AlexN]

Gamma settings is more for the user than it is for the software.. Gamma changes the brightness and contrast in order to help you see a star to use for guiding... However if the sensor has not adequately detected the star against the sky background, then there really is nothing that adjusting gamma can do about that.. Binning the guider can make the difference between the guider detecting a useable star, or giving you a blank image at long focal lengths.. Definitely worth while.

Paul - Welcome to the wonderful world of the OAG... Once you get it singing you will wonder how, or more to the point - Why, you ever lived without it... It might take some work to get it all running 100% however if this preliminary image is anything to go by, I dare say you'll have it humming along nicely in no time...

[Geoff45]

I don't think you can bin the Orion Starshoot autoguider with Maxim--at least I can't. I think binning depends on the camera hardware as well as the guiding software.
Geoff

[bmitchell82]

im not 100% sure but there are 2 types of binning, Software and Hardware, almost like Graphics acceleration. the HW version is always alot better.!

[gregbradley]

I find binning the guide camera 1x1 gave better guiding than binning 2x2 or 3x3. If you are using SBIG self guide then yes 2x2 or 3x3 may be needed for those little 237 chips.

If you are getting blocky stars at 3x3 binning or more then a solution is a higher pixel guide camera. The Starfish is 1.3mp and is cheap with subsecond guide exposures available.

I think its way worthwhile to invest a bit extra in the guide camera as it is a vital part of the autoguiding setup.

From your image though it looks like your autoguiding was superb.

Greg.

[Bassnut]

Greg. Guiding binning depends on image scale. bin 1 is best on a wide field guide scope, and bin 2 or 3 with internal or OAG at long FLs. bin 1 is no advantage at long FLs, wasted res, so you bin to get brighter/less noise stars. It can make a diff to the point where bin1 is so dim, its unusable and binning is at a given exposure time..Actually, S/N ratio is what counts more whilst guiding, not resolution so much, which is why the cooled SBIG guide cam is so usefull.Blocky stars arnt too much of a problem if you defocus.

Having said that, for standard external guide with a wide field ST80 for instance, I found the QHY5 small pixels and large FOV perfect for the usual 2 sec exposures (as the starfish would be), there was always a bright enough star in view.

Its with internal/OAG that things got ugly.

[AlexN]

Greg - Do you know what size pixels the starfish has?

My thoughts have always been to try and guide at a similar arcsec:pixel resolution for best results... Or even guiding at higher resolution if possible. I have done tests with 200mm FL guiding 1756mm FL etc and the results can be ok given you really tweak the setup to high hell, however I find best results come from having equal or slightly better guider resolution... My setup is an example of this.. I guide with a QHY5 with 5.2um pixels.. I image with the KAF8300 with 5.4um pixels. I guide using an OAG which means that the guider is getting ever so slightly more resolution than the imager. If I can achieve guiding around 0.3 pixel corrections, my guiding is going to be perfect in the final image. Where as if I were guiding with 0.3 px corrections with the QHY5 in the TMB 80/480, and the KAF8300 in a 12" SCT at 3050mm, the the 0.3px movements in the guider would equate to multiple pixels on the imaging sensor...

The same affect can be assumed when binning a guider in an OAG, or binning the guider in a short FL scope... if your arcsec:pixel ratio starts to undersample horribly, and stars appear as a singular pixel, the guider will not recognize star movement until its moved an entire pixel. Hardly what we want..

[Bassnut]

mmm, well when I was external guiding at 3m with a QHY5 on a ST80, the stars were never 1 pixel and many pixel guide stars allowed sub pixel corrections, worked OK, just.

OAG guiding at 3m with say a 9um imaging cam (at 0.62 A/P) and a QHY5 guiding cam (5.2um, 0.36 A/P), single pixel guide stars means a pixel guide shift is still less than an imaging pixel. And anyway, at that FL, 2 arc sec seeing would see very little image shift even if guiding danced around 2 or 3 pixels (or more), so binning is viable then even if the guide star was a single pixel.

[AlexN]

Agreed Fred, Its when you start using a 50mm finderscope as a guider getting 6 arcsec per pixel that long focal lengths become really difficult to guide. With the ST80 you'd have been looking at 3.3~ arcsec per pixel I would think (something around that figure) and stars would still be spread across a few pixels..