JMI motofocus on C8

[Knighty2112]

I am considering getting a JMI motofocuser for my C8 SCT at some point later on this year (hopefully for before Mars and Jupiter are at  opposition), primarily to aid in getting a good focus on my C8 SCT when imagining the planets and the Moon with my ASI120MC. However, I have also thought about perhaps instead a dual speed Crayford or similar to give me finer manual control over focusing instead. Not seen too much about the JMI focuser on here, but it seems to get a fair press elsewhere, yet I then see that some user then later on go for another focuser anyway, so would like anyone’s experience with the JMI motofocuser Pro and cons (if any) against going for a different focuser altogether. I will be using my C8 on my 8SE goto mount mostly, but also perhaps on my manual Skytee2 mount also occasionally, so am aware that the extra weight in the Crayford style focusers may add significant weigh on the goto system perhaps and cause issues on the goto mount, whereas there will be no problem with any extra weight to the OTA on the manual Skytee2 mount, so that is one of the reasons why I currently favour the JMI over any other option at the moment. Any thoughts and experience from anyone with any JMI/Crayford focuser combinations on any similar SCT’s welcome!

Cheers!

Gus  

[Merlin66]

I've used various electronic focusers on my SCT's over the years (Meade 8", 10" and 12" and Celestron 9.25 and C11)

I changed to the JMI focuser on the C11, which I now control remotely using the Shoestring FCusb adaptor. Works very well, no issues, no drama.

The mirror flop/slop on the Celestron is much better than the Meade due to attachment mechanism to the mirror.

Always remember to run the mirror focus through the whole travel occasionally to re-spread the grease on the baffle - this will reduce any slop.

I'd recommend the JMI focus motor.

 

 

[Knighty2112]

8 hours ago, Merlin66 said:

I've used various electronic focusers on my SCT's over the years (Meade 8", 10" and 12" and Celestron 9.25 and C11)

I changed to the JMI focuser on the C11, which I now control remotely using the Shoestring FCusb adaptor. Works very well, no issues, no drama.

The mirror flop/slop on the Celestron is much better than the Meade due to attachment mechanism to the mirror.

Always remember to run the mirror focus through the whole travel occasionally to re-spread the grease on the baffle - this will reduce any slop.

I'd recommend the JMI focus motor.

 

 

Thanks for your response. Never thought to do turn the whole focuser shaft to spread the grease out on my C8 focuser shaft. Thanks! I’ll do that at least once a month from now on.  

[At dusk]

I use a crayford focuser with a jmi motofocuser with my c9.25 edge hd when I try to take pictures of the planets. I`d recommend it because being one of the cheapest options, it`s really smooth and it works very well

I replaced the focuser knob for a feather touch that it`s very good for visual work, but the Jmi is  an important improvement for planet imaging. It makes easier to get the right focus and eliminates any vibration.

I always set my c9.25 on a Eq6—r mount so no issues wirh the extra weight. In an alt az mount you must consider that it will add about one kilo to the equipment

The crayford focuser wil increase the focal length of your telescope. I haven`t measured how much but it will probably turn your f/10 systen into a f/12—13. That` s why it`s not recommended for visual work.

Regards

[Knighty2112]

1 minute ago, At dusk said:

I use a crayford focuser with a jmi motofocuser with my c9.25 edge hd when I try to take pictures of the planets. I`d recommend it because being one of the cheapest options, it`s really smooth and it works very well

I replaced the focuser knob for a feather touch that it`s very good for visual work, but the Jmi is  an important improvement for planet imaging. It makes easier to get the right focus and eliminates any vibration.

I always set my c9.25 on a Eq6—r mount so no issues wirh the extra weight. In an alt az mount you must consider that it will add about one kilo to the equipment

The crayford focuser wil increase the focal length of your telescope. I haven`t measured how much but it will probably turn your f/10 systen into a f/12—13. That` s why it`s not recommended for visual work.

Regards

Thanks. Never realised the Crayford would add to the focal length of the scope in such a way. Most likely will go for the JMI as soon as possible. Cheers!   

[Merlin66]

Yes, extending the back focus increases the focal ratio and effective focal length.

I find, with a flip mirror and spectroscope, the C11 runs at f11.