A couple of questions about SCT telescopes.

[Greymouser]

I am starting this thread here, because both questions are a little basic and I thought they might be useful to others.

The first one is about adding a Crayford style focuser to a C9.25 SCT telescope: Is there going to be any advantage to doing it? Or is it going to make negligible difference? I would rather not waste money on something that will make little difference.

Secondly, I also have a C5, which I love and have as my travel scope. ( Though have not yet used when travelling! ) The thing is that the cover that goes over the end plate is not a very well fitted on and it has a tendency to fall off! The C9.25 one locks in place, but not the C5. So my question is: Is there an after market alternative that will better protect the corrector plate? If not, any suggestions to keeping the damn thing in place, other than tape, which I would rather avoid.

Thank you in anticipation.

 

[JG777]

I once added a Crayford to my SCT, IIRC it means after rough focussing with mirror slop you then use the fine focus that does not move the mirror. Downside is that you make the scope a bit longer and back heavier which may not suit you. I am not sure if it affects focal length or whether you can use a reducer as well, I didn't have it for long because FLO once had this sale on Starlight Fethertouch focusser s which was too good to pass up.

Dunno about the C5, maybe add some felt tape to the inside of the cap to make a better fit?

Edited July 7, 2019 by JG777
Spelling

[johninderby]

I had a FeatherTouch crayford on a C11 and the FeatherTouch Micro Focuser on a C8. The FT crayford  is quite compact and light and didn’t affect the balance of the C11 too much.

Loved the FT micro focuser on the C8. Was a perfect match and made a huge difference to focusing.

For visual would go with the microfocuser but for imaging then the crayford is the way to go.

[Waldemar]

1 hour ago, johninderby said:

For visual would go with the microfocuser but for imaging then the crayford is the way to go.

Having owned a couple of SCT's myself, and used the FT replacement microfocuser as well as the FT Crayford focuser on the visual back, I totally agree. No more mirrorshift because of focussing with the focuser on the visual back. It is a pity though that a mirror lock is not always available...
 

Edited July 7, 2019 by Waldemar

[Greymouser]

12 hours ago, johninderby said:

Loved the FT micro focuser on the C8. Was a perfect match and made a huge difference to focusing.

Quite expensive though and considering two things, I will give that a miss I think, at least for now. There is a crayford focuser out there, on offer with 33% off, ( or so, ) which puts it at £86.10 It is just too tempting, even though it is perhaps offering me some extent of duplication, as I already have an adapter, allowing me to use two inch accessories. It is just so tempting though, even though it is not the best make, it will give me an idea, with little risk, if I should get a more expensive one in the future.  

[paul mc c]

Is there much mirror flop with your 9.25 when focusing? i had a crayford when i had a Meade sct and it was essential especially when imaging planets as there was a lot of mirror flop with this scope,but i sold it when i got a 9.25 as there was almost no mirror flop with this scope,so i now just a clothes peg on the focuser to fine focus and it works a treat.

Edited July 7, 2019 by paul mc c

[Greymouser]

1 hour ago, paul mc c said:

Is there much mirror flop with your 9.25 when focusing?

To be honest, not that I have noticed, that much. I just listen too much to what others say I guess, about the benefits of that fine focus, which I do miss from when I used my Newtonian. Fine focus is just so useful sometimes. It is very difficult to get decent focus on my C9.25 sometimes. For some reason, far easier on my C5...

[JG777]

Two things that help with SCT, every now and again using the focusser are to move the mirror up and down the full extent of travel, maybe half a dozen times as this distributes the grease more evenly, and when you actually focus into an object ensure you are adjusting the mirror to move upwards rather than down where the flop is more pronounced. 

[Owmuchonomy]

I managed to acquire a FT Crayford focuser unit for my 9.25” (in anodised orange). It’s not a necessary upgrade but the focusing experience is vastly improved. Yes, you can use the 0.63 reducer with it and this is where I find it an improvement when taking spectroscopic images particularly. Regarding poorly fitting end caps on scopes then I use the self adhesive felt stuff you can buy for blisters on your feet and put a few pieces on the cap rim to create more of an interference fit.

[kirkster501]

I have a Moonlite focuser on the back of my 14" SCT together with a feathertouch mirror focuser.  I hardly ever touch the mirror focuser any more and it is locked.  As mentioned, I ensure to rack the mirror all the way in and out a few times every few months to keep the grease redistributed.  Having a "proper" focuser transforms the telescope completely.

Be aware that adding a Crayford will effect the focal length quite significantly maybe taking it up to F11 or even F12.  That may not be an issue to you, especially for lunar/plantetary guys.  But it may be for DSO types.

https://agenaastro.com/articles/upgrading-the-focuser-on-your-sct.html

 

 

[Greymouser]

12 hours ago, Owmuchonomy said:

Yes, you can use the 0.63 reducer with it and this is where I find it an improvement when taking spectroscopic images particularly.

I was hoping to still be able to use the reducer, but some people say both cannot be used, together that is. kirkster501 linked an article which says it cannot be doe with most crayford focusers:

Quote

For example, the commonly used 0.63x SCT focal reducer (offered by Meade, Celestron, and others) or the larger 0.7x Celestron EdgeHD reducer will not work optically with an external focuser because it cannot be placed at the required working distance in front of the eyepiece or cameras where it was designed to operate. The external focuser adds too much optical path length in between the focal reducer and eyepiece or camera, and it results in significantly deteriorated optical performance.

So could you, or anyone else for that matter, tell me which is true please? I am confused with this apparent contradiction. 🤔

[paul mc c]

In my experience,the crayford and reducer dont work,i had to use a 2" visual back with the reducer and take the Crayford off.

[Greymouser]

1 hour ago, paul mc c said:

In my experience,the crayford and reducer dont work,i had to use a 2" visual back with the reducer and take the Crayford off.

Now you have confused me even more, I am sure I used the reducer, without the 2" back. I will check tomorrow.

Edit: @paul mc c Ah, I misread your post, now re-reading it I understand what you were saying. Still leaves me a little confused though, because several say it is a no go, i.e. crayford and reducer; but @Owmuchonomy says it can be used. Unless that was with their particular crayford, because kirkster501s' linked article did say some made this possible.
Another thought/question occurs, if adding a crayford alters the focal length, which I can get my head around, just how much does the focal length alter as you add and remove other things from the back of a SCT?

Edited July 8, 2019 by Greymouser

[paul mc c]

5 minutes ago, Greymouser said:

Now you have confused me even more, I am sure I used the reducer, without the 2" back. I will check tomorrow.

Yes you can,but there is to much vignetting as there is to much distance between the reducer and the eyepiece or camera with the Crayford,that was my experiance.

Edited July 8, 2019 by paul mc c

[Greymouser]

Just to tie off this loose end, so to speak: It seems as though it would be better to avoid the cheaper focuser, wait until I can afford the Moonlite, which allows the reducer to be included without a problem. Something to think about. As for the cap on the C5, it seems that I will have to use tape after all which is a little disappointing, but I will live with it.

[fwm891]

Re the C5 cap - use Velcro rather than tape.

[GlenM]

Lenscoat Hoodies from WEX photographic are excellent covers. I use them all the time. I'm sure one would fit your C5.

 

Glen.

 

 

[johninderby]

The XX Large will fit the C5

http://www.lenscoat.com/lenscoat�-hoodie�-large-p-386.html?osCsid=3c40c42c2adc3963d771c4ce772ce010

I use one of the Lenscoat Hoodies on Big Red.

 

Edited July 10, 2019 by johninderby

[Owmuchonomy]

I only use the 0.63 reducer for Spectroscopy.  The visual or larger chip experience will be severely hampered by vignetting as described in previous posts.  The reducer is not really a visual aid.