Advice for guiding setup

[astroexplorer]

Dear friends,

I would like your advice regarding guiding setup, where the guide camera can also be used for planetary imaging.

Based on the advice from the forum, last summer I bought my first telescope, a Skywatcher 200 pds on EQ-6, and currently I use a Nikon D90 for imaging (but next year I intend to buy a dedicated CCD camera).

Having read books and postings I arrived to the following setup: guidescope ST80 with a QHY5L-II or ZWO ASI120MM camera (I have decided that OAG is not for me at this stage). I have 4 questions and I would appreciate your feedback to any of them:

(1)          The telescope – DSLR combination offers a resolution of 1.13 arc.sec/pix and that of the proposed guide setup 1.93 arc.sec/pix. This implies that for each pixel of drift in the guide telescope I have 1.7 pixels drift in my main scope. Is this acceptable, or should I opt for a guidescope with longer focal length (but heavier)?

(2)          The comparison between QHY5L-II and ZWO ASI120MM has been addressed in previous postings, but it is still inconclusive for me (I do not intend to go for the ASI130MM as I will not upscale my laptop any time soon). Any recommendations on the camera? By the way, is the ST-4 port important if I guide with PΗD2?

(3)          I read that for planetary imaging I need resolution for at least 0.25’’/pix which implies that I need a 3X barlow or a powermate. Although I prefer the powermate, this is available at 2.5Χ @ 1¼’’ and 4Χ @ 2’’. What would you choose?

(4)          My previous question takes me to my last one, which is something that I have not figured out for some time now. My optical path for imaging (with my DSLR, my guide camera or a future dedicated CCD) should be 2’’ or I could also reduce it to 1¼’’? To be more clear, if I buy a barlow for planetary imaging what should its diameter be? And the filters? I read that for DSLR the 2’’ is a must to limit vigneting, but if later I use a CCD of say a value of £ 2000 what should I consider now so that I will not have to change my equipment then?

Sorry for the long post and many thanks,

astroexplorer

[toxic]

Dear friends,

I would like your advice regarding guiding setup, where the guide camera can also be used for planetary imaging.

Based on the advice from the forum, last summer I bought my first telescope, a Skywatcher 200 pds on EQ-6, and currently I use a Nikon D90 for imaging (but next year I intend to buy a dedicated CCD camera).

Having read books and postings I arrived to the following setup: guidescope ST80 with a QHY5L-II or ZWO ASI120MM camera (I have decided that OAG is not for me at this stage). I have 4 questions and I would appreciate your feedback to any of them:

(1)          The telescope – DSLR combination offers a resolution of 1.13 arc.sec/pix and that of the proposed guide setup 1.93 arc.sec/pix. This implies that for each pixel of drift in the guide telescope I have 1.7 pixels drift in my main scope. Is this acceptable, or should I opt for a guidescope with longer focal length (but heavier)?

(2)          The comparison between QHY5L-II and ZWO ASI120MM has been addressed in previous postings, but it is still inconclusive for me (I do not intend to go for the ASI130MM as I will not upscale my laptop any time soon). Any recommendations on the camera? By the way, is the ST-4 port important if I guide with PΗD2?

(3)          I read that for planetary imaging I need resolution for at least 0.25’’/pix which implies that I need a 3X barlow or a powermate. Although I prefer the powermate, this is available at 2.5Χ @ 1¼’’ and 4Χ @ 2’’. What would you choose?

(4)          My previous question takes me to my last one, which is something that I have not figured out for some time now. My optical path for imaging (with my DSLR, my guide camera or a future dedicated CCD) should be 2’’ or I could also reduce it to 1¼’’? To be more clear, if I buy a barlow for planetary imaging what should its diameter be? And the filters? I read that for DSLR the 2’’ is a must to limit vigneting, but if later I use a CCD of say a value of £ 2000 what should I consider now so that I will not have to change my equipment then?

Sorry for the long post and many thanks,

astroexplorer

i use the 200pds on the az eq6 gt and i only use a microsoft lifecam 3000 hd as a guidcam connected to the finder as a guidescope and it works well (home made adapter ) and have guided for 25 mins without any problems apart from clouds sorry cant help with ?2 or ?3 i have only had a quick go at planets without a barlow.but you can zoom in with the lifecame and with sharpcap.

[astroexplorer]

Many thanks, I have heard from others as well that this solution works and now I am keen to try it out.

ASTROEXPLORER

[glowingturnip]

1) it seems not, PHD is capable of guiding with sub-pixel accuracy, down to about 0.5 pixel, and if you have too much magnification on the guidescope you end up chasing the seeing etc.  Seems the accepted advice is that you do not need as much magnification on the guide set-up as on the main scope.  So your pixel scales should be fine

2) If you have an ASCOM connection to the scope, and it supports pulseguiding (which I'm sure yours will), then you don't need to use the ST4, but you can try both and see which you prefer.  There seems to be a myth of sorts about ASCOM having slow connections, but this seems to stem from before pulseguiding was commonly supported and the data handshakes between scope and pc could throw off the timings, but pulseguiding has fixed that,  Ascom can also tell PHD information that ST4 can't, such as declination and side-of-pier.

I can't compare both yet, but I have a QHY5Liic which I'm very happy with.  Works a treat, but getting the right codec settings for different software applications can be a pain.  It works fine with PHD, and with the bundled EZPlanetary for planetary capture.  My kids' school are getting a ZWO ASI120 so I'll be able to play around with that and compare soon

3) can't really help - I have a 2" 2x barlow, but Saturn is still quite small with the QHY through that.  (750mm f/l).  I have a cheaper 2x barlow I can bung in the back of the first one and still get focus - image size is ok then, though obviously not a great optics train.  My scope is too short for planetary really.

4) don't really know, but I would imagine you keep your options open, and get everything as 2" for now ?  You can get 1.25" into 2" adaptors (my scope came with one) so the CCD would just go through that when you get it ?

[lensman57]

Dear friends,

I would like your advice regarding guiding setup, where the guide camera can also be used for planetary imaging.

Based on the advice from the forum, last summer I bought my first telescope, a Skywatcher 200 pds on EQ-6, and currently I use a Nikon D90 for imaging (but next year I intend to buy a dedicated CCD camera).

Having read books and postings I arrived to the following setup: guidescope ST80 with a QHY5L-II or ZWO ASI120MM camera (I have decided that OAG is not for me at this stage). I have 4 questions and I would appreciate your feedback to any of them:

(1)          The telescope – DSLR combination offers a resolution of 1.13 arc.sec/pix and that of the proposed guide setup 1.93 arc.sec/pix. This implies that for each pixel of drift in the guide telescope I have 1.7 pixels drift in my main scope. Is this acceptable, or should I opt for a guidescope with longer focal length (but heavier)?

(2)          The comparison between QHY5L-II and ZWO ASI120MM has been addressed in previous postings, but it is still inconclusive for me (I do not intend to go for the ASI130MM as I will not upscale my laptop any time soon). Any recommendations on the camera? By the way, is the ST-4 port important if I guide with PΗD2?

(3)          I read that for planetary imaging I need resolution for at least 0.25’’/pix which implies that I need a 3X barlow or a powermate. Although I prefer the powermate, this is available at 2.5Χ @ 1¼’’ and 4Χ @ 2’’. What would you choose?

(4)          My previous question takes me to my last one, which is something that I have not figured out for some time now. My optical path for imaging (with my DSLR, my guide camera or a future dedicated CCD) should be 2’’ or I could also reduce it to 1¼’’? To be more clear, if I buy a barlow for planetary imaging what should its diameter be? And the filters? I read that for DSLR the 2’’ is a must to limit vigneting, but if later I use a CCD of say a value of £ 2000 what should I consider now so that I will not have to change my equipment then?

Sorry for the long post and many thanks,

astroexplorer

The misconception with the nature of a guide scope/camera is that it has to have a high resolving power, this is not true. In guiding you'd need round-bright but not saturated stars and then the guide software will calculate the position of the centroid with subpixel accuracy. The combination of the ST80 coupled with either of your choices of camera is not only more than adequate but IMHO is overkill and  unless you have exceedingly good seeing the software will be chasing the seeing with the normal exposure loop of 1s.

A.G

[jgs001]

The others seem to have answered questions 1 to 3.  For q4... that, as so much does, depends... on the kit your using. In this specific case it depends on the sensor size. a dSLR with a larger sensor, needs a larger clear optical path to avoid vignetting (an APS-C sensor is about right with a 2" fitting, I think a full frame sensor, will probably need a 3" fitting to avoid vignetting). The QHY5 cameras, have comparatively small sensors, thus, work fine with 1.25" fittings. 

On my 80ED, I use a dSLR with 2" fittings, my barlows etc are all 1.25" and I use these with my QHY5v for moon mosaics, and planets. I've not suffered vignetting with either camera. I could use 2" fittings with the 5v, but that means buying more costly equipment, and in this context, won't actually achieve any benefit.

[astroexplorer]

I really appreciate all the input I have received. Indeed, very useful to help me decide how to proceed.  I think that I will try at first instance a guidescope with the qhy and if I see that I can handle it but need more accuracy I will then move to the ST80. It is also clear to me that to have all options open (especially when I will buy a dedicated CCD) I will try to keep my optical path to 2" to the extent possible. I still have to figure out though the barlow/powermate to use for planetary imaging: 2.5X, 3X or 4X... Many thanks to all for your time and advice.

Astroexplorer