Focal reducer on SCT6SE

[Look left]

I,m looking to put a 0.63 Celestron Focal Reducer on my Celestron 6 SE to reduce FL to speed up OTA for imaging in EAA.

Do i put Reducer directly onto scope,then fit Crayford to this then ZWO 120 mc onto this.

all assuming I have the right back focus to do this. If so I can use motor focus on the Crayford.

or do I have to put Crayford onto scope,reducer ontomthis then Camera. Or forget Crayford and install reducer directly onto scope fir spare and the camera and use the course original focus knob ?

[callump]

I'm not familiar with the 6 SE, but the Celestron 0.63 FR has a working distance of 105mm - that is the distance from the back glass element of the FR to the front of the sensor. 

I think putting the Crayford after the FR would allow you to change the working distance but not the focus. 

So you would need to put the Crayford onto the scope, then the FR, and then a spacer to get to 105mm. 

I don't know if you would get sufficient back focus though.

/callump

[M40]

I am also unfamiliar with the 6SE having a MAK180 but the two are similar and I have been playing with a focal reducer on that. According to the book of words, to achieve the stated focal reduction, the focal reducer should be installed at the visual back. I would guess that without a Crayford focuser the VB on a 6SE is the same as on the MAK and the FR is fitted into the VB adapter. You then need 105mm between the FR and the EP to get the full focal reduction. I would suggest that if you have a Crayford focuser fitted, the FR should go before the focuser, but that is a just a guess.

On mine, with the FR fitted at the VB, after focusing, bang slap in the middle was a huge great secondary mirror making the thing a waste of time. However, by continuing to play and fitting the FR at different positions, and using different spacing's you can still get focus and the secondary disappears. The best I found was to fit the FR to the EP, what the actual focal reduction was I have no idea but it was still significant.

Hope it helps.

[stash_old]

This might help https://agenaastro.com/articles/guides/focusers/focal-reducers-guide.html#introduction

[Look left]

Thanks very much guys for coming back. Here's the setup and thanks to Callup and M40 for the distance.

Stash _old ,s link shows the Reducer fitted to the FC on the SCT with a spacer between the reducer and the camera. However that means yourbrelying on the OTA focus knob to gain focus. On my Celestron 6SE you cannot get a great focus on it hence going with the Crayford. Now I know what I,m trying to achieve with the distances I,ll experiment.

[Look left]

Does this mean that the 105 mm from the reducer to the camera focal point? Would this also take into account the travel of the Crayford, or go for 105mm ish and then use Crayford just to nail it.!

[Robert Hayes]

Hi. I used the focal reducer spaced to the camera with the sct t adapter. Then slid into the crayford focuser with a 2 inch to sct male adapter. Focus was achieved with the crayford dialed half way out. Then rough focus with the main sct focuser. It allowed the ultra fine  in/out focus with the crayford. That was with a 10 meade and 6.3 reducer. Hope this helps and clear skies 👍🏻👍🏻

[Look left]

Cheers Robert, from camera focal point to reducer lens is that 105mm .is that right.

[Robert Hayes]

Yes. So whole lot moves together. Rough with mirror then fine with crayford. There is no change of length focal reducer 👍🏻👍🏻

[bilbo]

Here's an old pic from a test i did year's ago with a 3.3 reducer, setup is the same for any.  Focuser / reducer / spacers / Camera

 

 

[Look left]

Cheers, this is where I,m at present. I,be read it's 105 mm back focus which is what yours look likes. I,ve got the   Crayford Motorised so I still get that ability to auto focus . It's 110mm so it's out a bit. I,m going to get a thinner 2" fitting with a 42mm thread so can fit Camera directly onto it so will get it around 6 mm closer . Hopefully that is enough. Will keep everyone informed. What's your thoughts on that! 

[bilbo]

The focuser should be first, attached directly to the scope.

The distance between the reducer and the camera needs to be constant.  In your current setup adjusting the crayford will alter the distance between the focal reducer and the camera. This will alter the focal ratio up or down eg could change from 0.63 to 0.6 or 0.66 you would then need to use the scopes focuser to compensate and a vicious circle begins.

Steve

[Look left]

thanks for the advice. Then I would need a 2" tube lens fitting to go into the Crayford with an SCT screw thread so I could then fit a spacer to get the 105 mm focal length and screw camera to it taking into account the focal lens position?

 Would this still work? As the focus isn't great I as its about 5  mm too long, I thought it would still focus but as suggested the f ratio would  maybe 0.6 anyreason whyfocus should be out.

[bilbo]

7 hours ago, Look left said:

thanks for the advice. Then I would need a 2" tube lens fitting to go into the Crayford with an SCT screw thread so I could then fit a spacer to get the 105 mm focal length and screw camera to it taking into account the focal lens position?

 Would this still work? As the focus isn't great I as its about 5  mm too long, I thought it would still focus but as suggested the f ratio would  maybe 0.6 anyreason whyfocus should be out.

Yes thats correct.  As long as there's enough back focus on the C6 to compensate for the addition of the focuser. I have the 8" & 9.25" so can't give you a concrete answer. I don't know why they make the crayfords so big, you only need a few mm travel.

Whereabouts are you, I'm in NE also

cheers

Steve

PS Pic below is an Esatto motorised focuser (67mm length) on a C8 SCT.  but when used on th edge hd it becomes a fine tuner for the focal reducer, (which is your original setup) link to blog

https://www.primalucelab.com/astronomy/blog/esatto-focuser-for-schmidt-cassegrain-and-edgehd-esatto-come-focheggiatore-per-schmidt-cassegrain-e-edgehd/

 

 

 

[noah4x4]

I might be throwing a spanner in the works, but are we talking about an 6" Alt-Az or is it mounted on a GEM? Ignore this post if the latter.

Back focus required is 105mm after the focal reducer. I achieve that by;

OTA > FR > T-Adapter > Baader Varilock > Camera. 

I can just achieve rear end clearance going to the Zenith on my 8" Evolution provided I am using a (short) non-cooled camera. Won't rear end clearance be a problem with a 6SE Alt-Az if you try to add a Crayford Focuser?  There is a little flexibility in the 105mm, but you need to be close. I simply use my regular focusser, albeit motorised. See image.

 

[Look left]

Yeagh Noah your  right the clearance is an issue so I,m putting it onto my CEM 26. !! The scope comes in at just over 4 kgs and mount can manage 5-6 kgs so will give it a try when we get clearer sky's.

A couple of friends at the Astro club are going through the same problem and they've come up with using the flip mirror attachement after the reducer this is acting as the spacer? Haven't tried it yet.

so SCT,Crayford,reducer,flip mirror,maybe some shims,camera.

i,lol let you know if it works.

[noah4x4]

Further to my post above that offers a solution to rear end clearance on Alt- Az, but only for non-cooled cameras,  I have discovered that the 105mm back focus behind the Celestron x6.3 FR is only sacrosanct in Refractors and Reflectors. An SCT achieves focus by moving the mirror and the extent of adjustment is far greater. However, a Crayford Focuser introduces unnecessary challenges with an SCT.

My optical train is now OTA > FR > Celestron 2" dielectric diagonal > Camera. 

The diagonal has a light path of 137mm, far greater than 105mm. But I can achieve perfect focus. Running this through the Wilmsloastro tool it calculates my focal ratio to be 5.3, so my scope is a little faster from extending the light path.. But with either of the 2" solutions I describe, I enjoy perfect focus and suffer no undue aberations with a 4/3" sensor.

 

[Look left]

Sounds good set up.

the reason I need Crayford is I cannot focus correctly by the SCT Focuser I cannot control it and naturally you get camera shake. By having  the DC Hitecast Focuser on the  Crayford I can get Focusing spot on.

[bilbo]

8 hours ago, Look left said:

Sounds good set up.

the reason I need Crayford is I cannot focus correctly by the SCT Focuser I cannot control it and naturally you get camera shake. By having  the DC Hitecast Focuser on the  Crayford I can get Focusing spot on.

 

The way you have it doesn't work so your options are limited,

Dump the crayford and go for the Celestron motorised focuser which works on the main focuser knob and can be controlled from your laptop. No idea how good (or bad) these are.  You would need to dig around and do some homework. but it would also allow you to use a diagonal and gain some extra altitude or clear the mount completely.

Dump the SCT reducer and buy a 2"  Type as in pic. These are reducers only, not correctors.  but being 2" they can be inserted deep inside the crayford so your camera is flush with the back of the focuser.

 

 

Edited March 26, 2021 by bilbo

[Look left]

Hi guys it's been a while. I,ve taken off the Crayford and fitted reducer to back plate and have 110 mm ish.Now it's fine so have Crayford for sale and will fit an EAF Focuser to the focus shaft in the future. Thanks for the assistance.

[Look left]

[bilbo]

37 minutes ago, Look left said:

Hi guys it's been a while. I,ve taken off the Crayford and fitted reducer to back plate and have 110 mm ish.Now it's fine so have Crayford for sale and will fit an EAF Focuser to the focus shaft in the future. Thanks for the assistance.

Good to see you’re in the right direction. Distance does look a little long but I wouldn’t worry about it too much. The reducer can be spaced short/long throughout a wide range so play about to find what gives the best results for your sensor.  

Have fun

Steve

 

 

[Look left]

Cheers Bilbo will have a play around as I,ve got different spacers. That's at the recommended 110 mm back focus.

it definitely gives a wider veiw however as I,m wanting to do EAA with the SCT it's the f 6.3 that I,m after so I,lol try and get it faster as it means shorter image time.

[bilbo]

2 hours ago, Look left said:

That's at the recommended 110 mm back focus.

What camera are you using?

Steve

[ollypenrice]

On 28/04/2021 at 17:49, Look left said:

Cheers Bilbo will have a play around as I,ve got different spacers. That's at the recommended 110 mm back focus.

it definitely gives a wider veiw however as I,m wanting to do EAA with the SCT it's the f 6.3 that I,m after so I,lol try and get it faster as it means shorter image time.

Remember that a focal reducer is not an aperture increaser so it doesn't mean 'shorter image time' without also meaning 'smaller image.' This is not equivalent to opening up the aperture on a camera lens, which really does mean shorter image time.

Olly

Edited May 5, 2021 by ollypenrice
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