Celestron SE8 Focuser Upgrade advice needed

[Clockwork_Orange]

I haven't been on here for a while, I have a Celestron SE8 the standard focuser as supplied is, shall we say a bit basic, I've seen a couple of the Crayford type dual speed focuser's that attach to the rear of the tube. I have also seen a dual speed micro focuser that replaces the single speed Celestron focuser knob. Now I understand that the Primary mirror actually moves when the focuser is turned with the set up at the moment and with this in mind is the Crayford dual speed a better option, whereby the standard Celestron focuser fitted at present can be used to get it close with fine adjustment then been done using the Crayford dual speed. Just wondered if anyone else had carried out a similar upgrade and could throw a bit more light on which route to take. Bolt on Crayford or dual speed on the Primary mirror. Thanks for looking regards John

[DirkSteele]

Many years ago I imported a Starlight Instruments Feathertouch focuser (before they were available in the UK) (http://www.firstlightoptics.com/starlight-instruments-feathertouch/microfocuser-for-celestron-c11-sct-edge-hd.html ) to replace the standard focuser of my C11. It really has proved to be an excellent addition to my scope, giving the precision needed to bring the image to perfect focus. Of course, you still suffer from the image shift and mirror flop issue as focus is achieved in the same way as normal (i.e. moving the mirror), but as I am a visual only astronomer a little image shift is not a complete disaster. The flop can be a pain if you are imaging a planet on a small chip though. You can reduce the mirror flop issue by ending your focus “uphill,” in other words by finishing focusing with an anti-clockwise movement which moves the mirror up the OTA against gravity reducing the risk the mirror is unbalanced.

As for the rear cell Crayford type focsuers, that would certainly eliminate the problem all together. I have not tried one myself so will leave it to others to comment on the quality.

This is the Feathtouch Micofocuser for the C8. http://www.firstlightoptics.com/starlight-instruments-feathertouch/microfocuser-for-celestron-cpc-800-6se-c8edge-8se.html

Clear skies,

[Peter Drew]

An answer to this topic involves a degree of compromise. I have a 8SE and find the focusing action rather better than the average SCT, for me the relative unsteadiness of the mount when touching the focuser is more of a problem. The optical characteristics of primary movement on a SCT determines that it will always be of a coarse nature as the focus position changes by the square of the amplification of the secondary, in the case of most SCT's this is 25X. An add on independent focuser overcomes this problem but you still have to be careful touching it. A potential improvement would be to have a remote electronic drive to the independent focuser, however I find that they operate rather slowly and you get to the point where you think the object is focused, try just a bit more to be sure and then find you have overshot and have to start over again.

[Clockwork_Orange]

Thank you Matthew and Peter for your replies, I have looked at the FLO microfocuser and it would without doubt be a vast improvement over the stock SE8. I prefer the idea of the bolt on crayford it just seems to make more sense to achieve final focus with this type of unit not moving the primary mirror. thanks for looking guys, I will mull it over for a couple of days might get a reply from someone who has gone down the crayford route

[Pig]

John I have a 6SE and I agree with you about the focuser. I have purchased a Baader steel track Crayford and it works a treat. The only concern I would have with using one on an 8SE is im sure it would crash into your mount should the target object be near the zenith, thus knocking the alignment out and maybe cause some damage. They measure about 130mm fully extended then you have to add on the length of the diagonal. There is a compact version but it is very expensive.£300 plus. The suggestion by Matthew above is probably the best option. The cheapest option is to clip a clothes peg onto the focuser thus effectively extending the diameter of the knob, as crazy as it sounds, it actually works rather well.

[Clockwork_Orange]

The one that I've been looking at is the Williams Optics Digital read out. I think I'm going to get one ordered this week.

Thanks for pointing out the Zenith issue Shaun, I will give the clothes peg a try tonight if it stays clear. I do intend to get a HEQ5 or Celestron VX mount later in the year and just keep the Nexstar mount for in reserve. Just waiting to see some reports from people who have actually purchased a VX before I decide, at the moment I'm more inclined towards the HEQ5.

Regards John

[Pig]

Your most welcome

The William optics has been discontinued I believe - lots of complaints !!!

Apparently it extends outward of its own accord whilst using for long exposure AP

I must stress I have not owned one, its only what I have read.