Is WO ZS73 too much for a star tracker?

[Coriorda]

Although technically below the payload limit, has anyone got experience of using the WO ZS73 on a star adventurer or Skyguider pro. Is this a stable / reliable combination or is it pushing t(extra key too far with DSLR’s, guide scope etc attached. Thanks 

[Kyle Allen]

Personally, I think it would be too much. I use a ZS61 on my Star Adventurer and it feels like it’s pushing the limits of the mount. With polar alignment in Sharpcap and guiding I can get 2 minute subs with round stars but since my guide error is more than half my imaging scale I lose some effective resolution (so really nothing to gain by going with longer focal length). 

I imagine the ZS73 is quite a lot heavier than the ZS61 because of the extra size and length and because it’s got tube rings, a dovetail and guide scope mounting bar (my ZS61 is the earlier one with a mounting foot instead). Also, focal length is 430mm compared to 360mm. I think a good lens or the Red Cat would be a better option. 

Here’s a picture of my set up. 

 

[Coriorda]

Thank you, it’s really useful to have your insight. I thought in the back of my mind that this might be the case, but always useful to have it confirmed by someone who knows first hand. Thanks for taking time to respond. Your set looks great. Above all I want a simple solution that will give good results so your redcat advice sounds spot on ! 

[Kyle Allen]

No problem. I’m glad it’s helped. The Star Adventurer is a good little mount but I think you’ll get better results by using it within its comfort zone! 🙂

[Coriorda]

Yes helps a lot thank. Probably saved me a few £ and some disappointment caused by poor tracking results 😃

[jimjam11]

Far too heavy, and depending on your camera it will yield approx 1.8"-2.3"/px (@3.8u pixels) which is beyond its tracking accuracy. 

 

 

[Coriorda]

Thank you for your expertise, much appreciated. The camera is a 600d btw. Cheers  

[TerryMcK]

Yes far too heavy once you get gear on it. Mine weighs 4.12 kg with dedicated camera, guidescope/camera and field flattener on board. When I put my DSLR instead on it the mass goes up to 4.3kg.

I think the skyguider has a capacity of 5kg and “should” hold it. Whether it is stable is another matter - some say you should be less than 2/3rds  to 4/5ths of a mounts capacity when imaging. I’m not sure if that figure is applicable to the Skyguider. 
You may be better with the much lighter Redcat.

Edited November 9, 2020 by TerryMcK

[jimjam11]

10 hours ago, Coriorda said:

Thank you for your expertise, much appreciated. The camera is a 600d btw. Cheers  

600d gets you 2.06"/px. Have you considered something like the EF200 F2.8 or Samyang 135 F2? These are super light in comparison and give a much better image scale for a portable tracker. EF200 gets you 4.4"/px and the Samyang gets you 6.5"/px both of which are much easier to handle on a star tracker.

[Coriorda]

I’m sorry but I think you’ve lost me there, are you talking about pixel size or field of view. I’m very new to this game so please excuse my naivety. I would be very interested if you could clarify. Thank you 

[jimjam11]

Apologies. I am talking about sampling and what sampling rates are manageable on a star tracker. In general the star adventurer is fine with sampling of >4"/px at 30s subs without guiding or other faffing. With guiding you might be able to reach 2"/px but then weight becomes a problem.

Basically stick < 200mm of focal length with a star tracker and your camera unless you like hard work and guiding!

[Coriorda]

Thank you that makes perfect sense . Appreciate your response 😃