- This topic has 17 replies, 9 voices, and was last updated 6 years, 9 months ago by
.
-
Posts
-
I’be just started using an Alpy 600 with a guide module. The guide camera is a QHY5 II L ( colour).The FOV is very small and it is difficult to find the target star unless it is very bright, eg Betelgeuse. I am using a Celestron 8 Edge HD with a 0.7 x reducer. Do people use their finder scopes to get the star into the FOV of the guide camera? Does anyone else have experience of using this camera to guide an Alpy? Would I be better off using my Alpy on my Equinox Pro 80 ? Do I need a better finder scope or a better guide camera? I was thinking about getting one with a RACI prism and an illuminated reticule eyepiece.
Thanks, John
Hi John,
This is a common problem unless you happen to have a mount capable of very accurate pointing. You can either use your finder scope visually, or more conveniently, attach a small CCD or CMOS camera fitted with a normal camera lens on top of your scope so you can see the wide angle field to which the telescope is pointing on the computer screen. Within this you should be able to see your intended target. By working out where the small field you see in the Alpy guide camera is within the wider field from the piggy-back camera, you can work out how to adjust your mount’s pointing to bring the target into the Alpy guider field.
David
Hi John, as David said this can be a big challenge. My fiber guide head has a field of about 10 arc minutes. Which is too small to reliably plate solve. Although I did manage to make this work with the slightly larger field of a LISA spectrograph.
One relativity cheap solution is to use a flip mirror which works well if you are finding by eye at the scope. Otherwise you would need to add a DIY solution to flip the mirror and another camera.
Another expensive solution is to use a dichroic mirror. I use an Innovations Foresight ONAG and a third CCD in my automated system but light longer than 7500 A is not available to the spectrograph. However, I could find no other solution to automatically finding and centering the target..
Regards Andrew
Hi John,
I’ve also had this problem. I found that not only the mounting, but also the focuser and mirror flop caused problems. I’m not sure whether you have an extra focuser for fine focusing your C8. I used a Crayford focuser on a 14″ Meade for fine focus without moving the mirror. The weight of the spectrograph and 2 cameras caused the focus tube to shift as I slewed, making it nearly impossible to point accurately.
I am using a different setup now (10″ F8 RC) but I found several points that could help you, 2 already mentioned by Andrew and David.
– If you can afford to setup an electronic finder scope then that can be a big help. Otherwise just a good finder so you can easily and accurately point your telescope to bright stars.
– Star hopping from nearby bright stars. Start off with an obvious bright star on which to sync your telescope. Then jump to bright but progressively fainter stars nearer your target, re-syncing your telescope on each star, until you reach your target.
– I used a flip mirror between the spectrograph and telescope so I could use an eyepiece to check where the telescope was pointing. I found this was a big help but not without its difficulties. I could just about get it so the spectrograph and eyepiece were in focus at the same time. A couple of things to bare in mind. First, this moves the spectrograph and cameras further from the back of the telescope, increasing the moment arm on the telescope and mounting. Second, if you use a Crayford or Rack and Pinion focuser for fine focus then this increases the strain on the focuser.
I would expect finding objects to be much easier with your 80mm refractor as the field of view will be larger. As long as the focuser and mounting are up to the job.
Cheers,
Andy
I don’t know about pointing for Spectroscopy specifically, but in general even with a small field of view on the guide camera you could try plate solving. For locating variable stars I use APT’s Goto++ feature which takes an image, plate solves, syncs the mount to the current location and issues repeat goto commands until it is within a specified tolerance of the required location. I don’t see why it would not work with a spectrograph guide camera instead of the main imaging camera. Just connect APT to the guide camera use the Goto++ function the shutdown APT are start guiding as required.
I managed to do a similar thing with The Sky X with Nomad data base (1.1 billion stars), a Lisa spectrograph and my F5.4 300mm Newtonian. I think APT uses the UCA3 which may not have enough star for reliably plate solving the small field available. You can also have problems if a bright star is in the field as with a long enough expose to get enough stars to reliable solve the bright star can swamp the field.
Certainly worth a try.
Regards Andrew
I have a similar setup though the guide camera sensor is a bit bigger (ICX 415AL) I have the C11 on an EQ6 mount on a tripod running EQMod and CdC and the alignment/pointing is pretty poor to be honest. However I use a webcam clamped on the back of the standard guidescope which allows me to see stars to ~mag5. (Ihave a little red LED hanging in front of the finder to illuminate the cross hairs). If I centre the finderscope on one of these near to the target, it easily places them in the guider field where I recentre and sync. I then slew to the target which should be visible (for faint targets or crowded fields I use a DSS image for reference) If not, I sync more nearby bright stars so EQmod can triangulate or occasionally have to star hop in from the bright stars using CdC and the guider image. I also use the same system successfully at f10 with the LHIRES where the guider field is even smaller.
Cheers
Robin
If you are thinking of changing your guide camera, a mono version will be better than colour as it will be that much more sensitive without the Bayer Matrix. Just been scouring the pre-owned pages of Telescope House website and have come across a secondhand Starlight Xpress Lodestar if you are interested,works well with the Alpy.
https://www.telescopehouse.com/offers/preowned/preowned-starlight-xpress-lodestar.html
Regards
Alun
I used a QHY5 II L Colour with PHD2 without much difficulty on a C925+0.63 reducer.
A 1.5 or 2 sec exposure worked well and didn’t over-correct for seeing.
This gave enough stars to easily id the field using Guide9.
However, I soon moved to a Lodestar and would echo the sentiments above. Big improvement in sensitivity.
My pointing accuracy on a CGEM (albeit hyper-tuned) using Guide9, Astroplanner or CdC puts the target in the guider fov, even after a flip. (I should point out I never slew at the highest speed). Although I still use a secondary finder-guider for comfort as David mentioned!
The only downside from the using the Lodestar was a slightly smaller field than the QHY.
Good luck and stick with it. Just practice really!
Regards
T
Would a QHY5 with a finder scope scope be good enough for an electronic finder scope or would I need a wider field of view? Mine is an Altair Astro 60mm with FL about 225 mm. I see some people attach a camera lens to a webcam. Can someone give me more information about this set up and the software used? Thanks, John
A quick calculation using the spec of the QHY5L II camera from their website with a 225mm FL scope indicates a field of view of around one degree. This is probably larger than the field you see in the Alpy guider camera but still quite small if your mount’s pointing is not very accurate. A shorter FL camera lens would give a wider field in proportion to the ratio of their FLs. You could attach a camera lens to the QHY camera with an appropriate adaptor taking account of the distance of the CCD chip behind the front plate of the camera so the lens focuses on the CCD. I don’t know about webcams these days. I imagine the problem would be finding camera driver software compatible with the other software you are using.
Best wishes,
David
My “cheap and cheerful” electronic finder. A Philips webcam mounted afocally on the back of the C11 finderscope, displayed in WXastrocapture and viewed remotely via remote desktop
Cheers
Robin
i took Alun’s advice and bought the secondhand Lodestar. The QHY5 is now attached to the finder and the Lodestar to the guide module on the Alpy.
I lined them up on a radio mast a mile away.
Here’s a write up. All I need is a clear night!
John
This is the electronic / visual finder I use Atik 314 – Skywatcher flip mirror – Borg 45 ed modular which I just finished setting up incase of a camera or computer failure.BUT there appears to be no sideways adjustment (only up and down for the mirror) for getting the object in the centre of the eyepiece crosshairs, which is disappointing but at least the object is in the field of view !
Regards,
Jack
Essex UK
Hi Jack,
I’m not sure of the make of my flip mirror as I bought it a few years ago and it is a generic one without a company logo.
There won’t be any side to side adjustments with flip mirrors, or up and down for that matter. They are designed so the light either goes straight through or is diverted up at a right angle. If you are using this in a finder setup then you would normally mount it within finder rings with screws to hold and adjust the finder scope position.
Flip mirrors aren’t usually used in finders. Instead you use them in the light path of your main scope so you can view with an eyepiece or another camera without have to detach your main equipment. Nothing wrong with using them in a finder, but there may not be any benefit to doing so.
Best wishes,
Andy
- You must be logged in to reply to this topic.