Nexstar 6SE Tracking
Posted 10 April 2013 - 09:53 AM
I am having a little bit of a problem with my tracking when I am grabbing video with my sammy scb2000p.
The video image is stable for a shot period of time then the image stars shift a bit and (sometimes even allot) which causes the image to be blurred out completed especially when using sens up at x512 (10.3sec exposure).
Is there a problem with my backlash settings. Bear in mind I have balanced the tube with the camera mounted on. I also have no idea about backlash at all (none whatsoever )
I know that the tracking wont be perfect on these standard mounts but I am looking at making a wedge at least (not sure if that would even help) but buying an eq mount is out budget for a while now.
If I can get 30 seconds of the video without it moving I would be thrilled.
Thank you all in advance!!!
Posted 10 April 2013 - 10:21 AM
It's possible I, and I'm sure others can help you but there's several aspects to your post to which I would need some clarification.
You are apparently using a Samsung SCB 2000p CCTV video camera but is this imaging through your 6SE's tube at prime focus or is this camera merely attached to the 6SE's tube, (i.e on its outside) ?
Secondly I don't understand what you mean when you refer to " sens up at X512" ? Please could you explain, bearing in mind I'm unfamiliar with your camera.
Thirdly, what, in this instance, are you trying to image ?
Posted 10 April 2013 - 04:42 PM
Can you do a screen capture that shows the problem or post a video clip somewhere?
Backlash could be a problem if there is too much slack in the drive trains. Go ahead and experiment with setting it. The process is very simple. The goal is acceptable lash, zero lash might be impossible. When settings are too high the ota jerks when the motors wind out the slack at the end of a slew.
Also once you have completed the initial alignment, run the calibrate goto item on the menu. You only need to do it when something changes the OTA weight and balance.
Posted 10 April 2013 - 06:58 PM
Posted 11 April 2013 - 01:22 AM
Thank you for the quick reply.
Tel I will post a pic or a link (and here it is http://www.flickr.co...in/photostream/ )of what my setup looks like but the camera is in prime focus on the star diagonal. Sens up is merely the integration on the camera but unlike the MC camera's which i believe work on seconds for integration the scb2000's work with sens up starting at x2 going up to x512 depending on the model. I am trying to image dso's. I seem to have gotten some good video of the tarantula nebula but have much more difficulty when trying to get at least 30 seconds worth of it.
Dave I will give that a try as soon as we get a clear night. Unfortunately I was with my better half last night and couldnt do that.
Any idea on what settings I should use for backlash .. I truly am afraid to touch it seeing that i dont know anything about it.
I dont think that it would be the balance Dan, because I did balance it before mounting it on the scope (with the camera and accessories). I think Dave and Peter gave me instructions on how to do that but again.. I could have done that incorrectly so I will try your idea first and see since its an easier one for me to do with allot less risk of stuffing it up compared to the backlash settings .
Posted 11 April 2013 - 01:41 AM
If you apply the instructions given in the 19th post in this thread, they should provide you with all the necessary information, including anti-backlash setting, you require.
Additionally, if your imaging object still appears to "slip" from your camera's field of view, take a look at the first post on the same thread.
Here's the thread link.
Incidentally, for us to provide numbers for anti-backlash settings won't help you. All of these 'scopes have proved to be individual in this respect and respond accordingly.
Just follow thee instruction for anti-backlash setting within the 19th thread and that should optimise them for your particular 6SE.
Hoping this helps,
Posted 11 April 2013 - 01:53 AM
I have added the link to my camera setup on my previous post. I think the flikr site has a few of the images i've taken so far as well.
Posted 13 April 2013 - 01:15 AM
I was/am in the same boat with you; 6SE with SDC-435 setup, some frustration with the mount's 'random' tracking errors - slightly more annoying is that after slewing to an object, the mount can take up to +20 seconds to stabilize and track nicely, at least for the while. Backlash setting helps with mount settling down to tracking faster, but as for the later 'random' tracking error, I've realized it correlates to how close to the zenith I'm pointed. Putting it in EQ mode (building a wedge) should help, but I've no experience there. The best I've come up with is to operate the setup at a lower focal length and it greatly reduces the apparent tracking 'jitters' (on the plus side, you get better exposure for sure, I found the scope operating at f/6.3 a little to dim for many DSO's) I had mine setup as:
C6 -> 0.63x focal reducer -> diagonal -> 0.5x reducer -> CCTV
Long term solution though, I put the C6 OTA on a GEM mount, and I've not had any issues since with regards to using my SDC-435.
Posted 16 April 2013 - 02:59 AM
All I have now is a 0.5x focal reducer with an extension tube... not too sure what that would bring it to or if I could add on a second reducer to that.
Unfortunately I have not had clear enough skies to be able to test the backlash settings but hopefully this weekend would bring me some clear skies.
When you say it correlates to how close to the zenith I am.. what do you mean?? Is it the further away from it I am the better??
I would really love to see an image of your setup with your focal reducers if you dont mind Peter.
I've got a video on how to make a wedge so as soon as I can.. I will begin with that.
Long term a CGEM is my goal.. but not for the next two years unfortunately
Posted 16 April 2013 - 05:39 AM
If I may, may I advise a word or two of caution with regard to the use of wedges and single arm mounts with spur gears ?
Such an assembly has been known to work, but not without having to overcome substantial difficulties despite the use of a pukka Celestron wedge, (an accessory which is no longer available), but in most cases, including my own, most have failed.
Some of the reasons for this, were identified some years ago now, and related to the somewhat crudeness of the Celestron wedge's design, the fact that tracking STILL relied on the Nexstar mount's spur gear drive, (in contrast to the far superior worm gears contained in most GEMs), and also to the varying weight distribution of the OTA according to where it placed itself in relationship to the mount arm, (i.e. whether it was resting on top of the arm at any one time or hanging beneath it).
Please don't think that I'm trying to put you off the project, for as I said, successful wedge mounting has been achieved, (I believe, if memory serves, our CN friend and colleague "Lord Beowulf" proved it so). I merely wanted to advise you of possible disappointment and of my own personal ineptitude contributing to my failure to make this work !
(I was however, not alone) !
Posted 16 April 2013 - 06:04 AM
Go to the section entitled "Altazimuth Mount" and then to its second paragraph where it mentions the "Zenith Blind Spot" or "Zenith Hole".
Basically though, at or near the Zenith the azimuth axis has a job to keep tracking pace hence the increasing anomalies the nearer one gets !
Posted 22 April 2013 - 09:45 AM
Thank you for the reply. Dont worry, I know that the advise you are giving comes from experience. I am still learning so I listen to everyone and what they say. I think it would be very arrogant of me to not, with the little knowledge I have. I've briefly read about the wedge problem and the reason it was discontinued, so I do heed your warning. I am actually two minded about making it now especially after seeing the images I get with the dslr on a fixed tripod at 15 seconds exposure.
If I could get something close to this with a with improved tracking on my alt az, then I would be thrilled.
Now I need to wait for a clear night to follow the instructions on the link you sent on your previous link. I will read in more detail about the alt az mount once I am home. Just had a squiz through it now only.
Thank you once again.
Posted 22 April 2013 - 02:09 PM
There's no reason why you can't get some good images by, (if this is what you propose), coupling your DSLR to your 6SE, as opposed, (I presume), to what you have been doing to date in imaging directly from your DSLR mounted on a tripod.
If this is indeed what you want to do; you can facilitate this task by firstly ensuring you've optimised your antibacklash settings for both axes and by using the "Precise GoTo" feature where possible when targeting your object.
With regard to the imaging itself, may I suggest you make, or purchase, a Bahtinov mask and use it to achieve best focus with your DSLR on a nearby bright star then slew to your chosen target after invoking the "Precise GoTo".
(I've found that the Bahtinov mask is worth its weight in gold).
You will, (as you know), need to keep the DSLR's exposure time low to eliminate field rotation, (experimentation will give you a good indication of what's feasible and what's not).
Use however of a focal reducer will normally permit slightly longer exposures but do pay heed to the effect the reducer will have on the size of the target: thus choose your targets appropriately,
A download of Rod Wodaski's New Astronomy Calculator will, if you don't yet use it, help in your image and image size selection.
Here's the link.
Hoping this helps you with your imaging a little further,
Posted 23 April 2013 - 01:34 AM
Once again a big thank you. I didn't know that a Bahtinov mask would have an effect on my image. Can this be kept on while imaging DSO's or is it only for stars? I've got the plans to make one so I will get cracking with that now while I have some free time. Got to to a presentation today on basic astrophotography at our society tonight (based on what I've learnt and the equipment I use) which is making me a little nervous. At least this will take my mind off it.
I understand why I would need to keep the exposure times low with this particular mount, but in your experience how long do you think I would be able to go with an object far from the zenith (closer to the horizon maybe)?
With my Samsung SCB2000P I always use a focal reducer. To be honest I have never used the camera without the reducer and dont know what the image would look like with the SCB camera mounted straight on (no reducer). From what I've been told it allows me to gather light from a wider field of view and at a "faster speed" (so to speak).
I've downloaded the ccdcalfull.exe file and will definitely use it.
I think this will definitely help me imaging and most likely be the deciding factor on whether or not I will make a wedge.
Posted 23 April 2013 - 02:37 AM
Good luck with your presentation tonight ! I hope it goes well.
Talking of Bahtinov masks, no, it is ONLY an aid, (and a very good one), to focusing your 'scope.
Placed over the end of your 6SE and with the 'scope pointing at a relatively bright star, it will produce a pattern consisting of a central, somewhat elongated patch of light, (almost like the star itself), from which six diffraction spikes radiate: three from one side of the patch of light and three from the opposite side.
Now, the central spike may not be in position midway between the other two on either side, in which case the 'scope will not be optimally focused on the target star. If this is so, the object of the exercise is then to centralise this spike to produce optimum focus.
Having achieved this, the mask is then removed. The "now in focus" 'scope can now be slewed, (without touching the focus knob), to the object you wish to image.
Now I know nothing about Samsung SCB cameras, but obviously when focusing your 'scope with the mask in place, you do need to be able to see the diffraction pattern. I assume that this is achievable for you ?
In my case, I use a Canon 350D DSLR which is linked to Stark Lab's "Nebulosity" software capture and processing program but I've obviously no idea how you might view the necessary Bahtinov pattern. (Maybe you have a similar program connection or you can view direct at the camera through a viewfinder system) ?
I you do think you may have difficulties in this direction, then please let me know.
As to exposure times at "reasonable " altitudes from the standard Alt./Az. mount, I believe some DSLR users have achieved up to ca. one minute but I personally think not much more than 45 seconds on a wide field basis, (focal reducer in play), and I would probably reckon with somewhere around 30 seconds maximum as a rule of thumb before field rotation becomes apparent.
Finally, by manipulating the figures within Ron Wodaski's New Astro-Calculator with your chosen target alongside on its second screen, this should give ayou a very accurate indication of whether your final picture will "fit the frame" so to speak !
Hoping this helps a little further. Perhaps ask around within your society following your presentation this evening. I'm sure you'll find someone who uses a Bahtinov mask !
Posted 23 April 2013 - 03:25 AM
I should be able to use the Bahtinov mask with the scb200p as it does display the live image on the laptop. Of course when I start with DLSR photography I would need software on my laptop to display the image from the canon as well. I was thinking maxim dl but I am not sure yet.
Unfortunately asking anyone at our society is not an option for me as there is only one other person I know of that does astrophotography there.
The presentation is part of a telescope making course being held there for the public, so not many members will attend anyway.
Achieving almost perfect focus sounds good to me , so Bahtinov here I come.
Thanks for the heads up with the time limitation before field rotation starts to kick in.
Just one more question if you dont mind.. I know this is off topic but how was I able to take 15 second exposures using my 600d on a tripod? I was messing around to try and get star trails but the images were of quite round stars. I used a 55 - 250mm lens using the wide angle end (no zoom at all on the lens, F-5.6 and ISO1600) http://www.flickr.co...in/photostream/
Posted 23 April 2013 - 04:07 AM
Here by the way is a "YouTube" link to indicate the pattern(s) a Bahtinov mask produces when one focuses on a reasonably bright star targeted for the purpose.
As to why your 15 second exposure of the Eta Corina Nebula, (I wish I could see it from England !), showed no sign of star trailing or field rotation, I would say,that I'm not surprised given the vastness of the field of view despite presumably having been imaged from an undriven tripod/mount.
Indeed I think you might have "got away with" an even longer exposure time before these phenomena began to become obvious.
Perhaps, take a look at your image once again under a zoom if you are able to do so. Chances are you WILL see a small drift, (trailing), but one which is virtually invisible in the image scale you have selected either intentionally or merely by accident.
Best explanation I can offer !
Posted 23 April 2013 - 05:08 AM
Definitely the answer I needed. I assure you that this was by accident.
The video explained and showed it quite well. I really need to make this now for all sorts of astrophotography.
You are 100% correct in presuming that this was not motor driven.
Well if you are on fb.. you are more than welcome to add me. I post allot of what I see down here. I am sometimes on NSN if we have clear skies and I am at home.
Again, thank you so very much. I'm printing the template for the Bahtinov Mask and will make one now.
Posted 23 April 2013 - 01:17 PM
Too old to be THAT cool !
Let us all know how you get on with your future imaging.
Posted 23 April 2013 - 01:20 PM
Glad to help Amith, but sorry, definitely no subscriber to FB !
Too old to be THAT cool !
Let us all know how you get on with your future imaging.
Tel - I know the feeling. I am not a fan of Facebook. To be honest, I don't see the appeal of it.
Posted 24 April 2013 - 04:08 AM
You are never too old... never ... I only go on there to post pic and look at others pic.. nice easy way to share the memories. The whole posting comments and stuff is just too much.. even for me.
Just waiting for my T-Ring to arrive now. Just got the T-adapter yesterday. DSO's with my 600D here I come .
I will post a couple of photos here after I sort out the backlash settings.
Posted 24 April 2013 - 09:36 AM
Posted 24 April 2013 - 09:41 AM
Will a camera like the SCB2000P not hit the base of the mount if it is connected directly? I am worried about clearance even when I mount my dslr but I have been assured that when I do eventually do that then no touching or bumping will happen with the base of the mount.
Thank you once again.
Posted 24 April 2013 - 12:04 PM
Posted 25 April 2013 - 01:42 AM
* with the dual focal reducer and diagonal, the overall balance and tracking is not greatly affected. Yes, it's off-center, but it's an alt-az mount and the load vector is pretty much constant (vs. an EQ setup).
* the main issue for me, as mentioned, was waiting for the drive to 'catch up' after a slew, and how the image smears/jiggles every time you press the menu buttons on the camera (an external keypad would solve the problem). Both can also be solved with patience.
* there's also the issue of field rotation creeping in , and the dob/alt-az 'hole' when tracking/goto near the zenith.
* with the camera's low resolution, any amount of optical aberration from the prism (and even collimation, imo) is negligible in the output.
* read the other threads in the video astro forum, with video astronomy imo focal ratio is key to capturing DSO's, especially with the Samsung CCTV that limit you to 8 seconds integration.
* for focusing, just slew to a bright star ~mag2 or brighter, have integration at 6x or lower, and focus until you get nice and tight stars. Again, you're dealing with VGA resolution, it's really easy to get focus. No need for a Bahtinov mask.
* with the 6SE setup, another trick that worked for me was to have an eyepiece that was about parfocal with the camera - ie, I could remove the camera and slip in the eyepiece (with some extension tubes and parfocal rings) - that way I could visually center some objects that might not be exactly in the camera's FOV after a goto.