mount for c8 planetary

[iwols]

Hi think its time to give my c8 a tryout after living in its box for the last 12 months but dont want to upset my permanent mount so just wondered if there was a cheap mount i could get that would be ok mainly for photography ,as i believe i dont need to track planets thanks

[vlaiv]

Not sure if I follow - does it need to track the planets, or it does not need to track the planets?

If you want to image planets, well, the least thing you need from your mount is a simple tracking.

Probably the least expensive mount that will carry C8 for planetary AP would be something like this:

https://www.firstlightoptics.com/skywatcher-mounts/skywatcher-eq3-2-deluxe.html

+

https://www.firstlightoptics.com/sky-watcher-mount-accessories/single-axis-dc-motor-drive-for-eq3-2.html

 

[iwols]

just not sure if  i need a tracking mount for planetary 

[vlaiv]

24 minutes ago, iwols said:

just not sure if  i need a tracking mount for planetary 

Depends on how you plan to do planetary.

If you want decent results, then you really should consider doing what is called Lucky imaging approach.

You'll need planetary camera (can use your guide camera if it is CMOS model and supports relatively fast download rates / high fps) and you need to record a video rather than still image. You record video for a few minutes (depends on the planet in question - but most will allow up to 5 minutes due to their rotation). Then comes processing of this video - image is stabilized (so mount does not need to track perfectly - it just needs to hold planet in FOV), best frames are selected, and these frames are stacked in special way (alignment points and all that) - you'll use AutoStakkert!3.0 for this (well, you don't need to use it but it is the best and it is free).

After that you do post processing - color balance and sharpening / deconvolution (wavelets or something else).

FPS needs to be rather high because you want to capture as many subs as you can. You'll also use ROI - region of interest, that is going to be smaller than full resolution of sensor. You'll record something like 640x480px video even if you have camera with large "megapixel" count.

This is for two reasons - first, planets are small and you don't need large sensor to record them, and second - larger the image slower the download rate and slower FPS and you want high FPS in order to record many images (most of them will be discarded because of poor seeing but you want the ones you keep to have enough of them).

Exposure length is order of 5-10ms for most planetary targets.

From all of this you can see that you really need:

1. Mount that is capable of tracking the target for up to 5-10 minutes or so.

2. Mount that is precise enough to keep target in relatively small FOV (you need stepper motor - simple DC motor that has manual speed adjustment is going to be pain to use - I had one of those on my EQ2 and it took constant effort to keep planet in FOV - luckily recording lasted only for few minutes).

Everything else is not really important as long as mount can carry the scope - shake is not important, how long you wait for it to settle is not important for imaging as you adjust focus only once and so on ... Like I mentioned above, I imaged planets on EQ2 type mount with a simple DC motor and produced some nice images with it.

 

Alternative is to try single exposures - but that just does no work good. It's going to be enormous pain to manually align scope - wait for planet to enter FOV and then take exposure. Exposure will need to be longer to get enough signal so that it is not noisy and for that time target will move - creating motion blur and atmosphere will change creating seeing blur. You'll get total mess this way.

[iwols]

so would the manual adjusment mounts be any good 

[jambouk]

You need a tracking mount if you are using an 8” SCT for planetary imaging else you will spend 99.9% of your imaging time trying to get the planet on the sensor of the camera.

[iwols]

would a  Skywatcher EQ3 Pro GOTO Mount & Tripod be ok

[jambouk]

Possibly. I think it would be OK weight wise, but I've no experience of the motors on this mount, and you have a very long focal length and likely a small sensor, and keeping a planet on that sensor is a challenge, even more so if adding in a Barlow or Powermate. So the better the mount and the better the polar alignment, and the better the tracking, the easier your life will be.

James

 

[vlaiv]

Keeping planet centered in FOV is concern, but luckily we can do some sort of calculation to see what will happen in usual circumstances.

EQ3 is know for larger periodic error - let it be 50" P2P for our case (although you could end up with specimen that has closer to 30", but let's take large value to be safe).

You'll be imaging with C8, so 200mm of aperture. For that aperture you want to sample at 0.26"/px as optimum sampling rate. Even if you use color camera and go with twice that (because of Bayer matrix) - that is still 0.13"/px.

You want fast capture and want small ROI - 640x480 for example. When we convert that into arc seconds that is 83.2" x 62.4".

If you align RA axis with X axis of the sensor - you'll have 83.2" of space and mount creates 50" peak to peak RA periodic error. With a bit of luck, you'll be able to keep planet in FOV "indefinitely".

Could be that you have particularly bad sample of the mount and periodic error is larger than this - well do 800 x 600 ROI at expense of somewhat lowering max FPS, and you'll have 104" in X direction - again more then enough to keep planet in FOV.

This is of course at twice optimum sampling rate (or optimum sampling rate for color sensor).

[iwols]

eq5 better then ?

[Cosmic Geoff]

I have done planetary imaging with a C8.

Which mount? If you want to do the job properly, you should use your HEQ5.  If you want a seperate cheap mount, then it's up to you what you go for.  The requirements for planetary imaging are not severe, as it does not matter much should the mound shake a bit during the video run.  So an EQ3-2 will probably work (I assume you have checked the weicht of the C8 OTA against the rating of the EQ3-2 for visual use).  An EQ-5 would, one assumes, be better.

GoTo or RA drive?  Using a mount with RA drive will actually work once you get the planet in frame.  I briefly used an RA-drive EQ-5 with the C8 and it worked okay.  But a GoTo mount gives you a choice of slow motion speeds on each axis.

The SE mount commonly bundled with the C8 is not really up to the job - too much wobble and backlash.  The CPC800 variant on the other hand is a great planetary imaging setup - very solid mount and really smooth and almost backlash-free.

[iwols]

thanks the last time i used my heq5 off my permanent mount it took me ages to get back to normal so dont want to go down  that route😀

[newbie alert]

I'd suggest a minimum heq5, avx or a cem40..

Obviously you have a budget..  you can do planetary with a dob but it's far easier with a tracking mount...more than enough going on with the camera

[vlaiv]

1 hour ago, iwols said:

thanks the last time i used my heq5 off my permanent mount it took me ages to get back to normal so dont want to go down  that route😀

I just realized you have EdgeHD version of C8? That is about 1kg heavier than regular version? Maybe go with EQ5 with tracking motor instead - just to be safe.