View Full Version here: : FLI Atlas focuser + f.r. for C14 edge

09-05-2012, 11:25 PM
hello all.

I'm from the Uk and have read some of the postings on Iceinspace and have found them all informative and very useful so I've joined and have a question.

I have a paramount ME and a C14 Edge still in their boxes about to be installed into a domed observatory. I'm being held up because of a decent focuser to use with the 'scope- yes it's the Edges short back focus problem.

Hence, I'm looking at the FLI PDF or Atlas focuser. Does any body have any experiences (good and bad)they would like to pass on before I spend another small fortune. My prefence is the Atlas, but possibly the PDF might be good enough.

Has anybody yet found a suitable focal reducer that works with the 14 edge or must we still wait for the elusive celestron 0.7 f.r.

Best wishes Eric

09-05-2012, 11:57 PM
Eric, Welcome to IIS

In regards to your first query I think the hoodoo-guru for that brand of focuser would be Mike Sidonio - strongmanmike and I'm sure when he sees this post he'll chime in and others too that are using the kind of gear you're looking at

And in regards to the EdgeHD perhaps you can read this here: http://www.iceinspace.com.au/forum/showthread.php?t=73635

Not too sure if it'll help but hey! information is the strongest currency today:P


10-05-2012, 12:17 AM

thanks for the welcome.

The F.R link was most welcome, I had not seen these postings before. I have seen similar earlier postings by the same guys. Then they were discussing both the CCDT 67 and the Optec lepus F.R.'s. I would like to have a go and follow their efforts as soon as I'm up and running.

Hopefully, Mike might look in and give the benifit of his experiences with the PDF and Atlas.

Cheers Eric

10-05-2012, 08:08 AM
So far as I am aware, the Atlas will not fit on the bare EdgeHD 14 without hitting the focus knob and the mirror lock knobs. Neither will the PDF. It should clear them OK with the Celestron FR in place because the FR comes first.

Nice thing about the Celestron FR is that it does not consume any backfocus, so with it in place, you have the same backfocus distance as you did without it in place.

The Celestron FR for the EdgeHD 14 is certainly not elusive. I have one here. It only took a little over a week to get from order to delivery. Haven't had a chance to try it out yet though.

The Optec TCF-Si fits the scope without bumping into anything, but it consumes 3.5-inches of backfocus plus another 0.1-inch for the rear opening adapter. That doesn't leave much room for anything else.

10-05-2012, 08:16 AM
Hi Erik

As far as the Atlas focuser goes there is no dispute that it is the ultimate in after market digital focusing units if you plan on using anything of any size and weight on any scope system and wish to eliminate the possibilty of flexure - hence why I incorporated it into my fast astrograph from day one: http://www.pbase.com/strongmanmike2002/image/135785837/original

That said as has been suggested there may be issues with fitting it to the back of the Edge HD but if its doable then the Atlas is the best for sure but other robust traditional focusers with robo focus or similar attached should work very well too

Not sure that was all that much help but good luck with your project :thumbsup:

10-05-2012, 08:29 AM

Thanks for the info.

I had realised that the Atlas touches the knobs you mentioned. I constructed a cardboard model to test things out. I would get precise parts over in the USA to make up necesary ZTA to clear this.

Interesting what you say about the Celestron FR for the C14 Edge Had it on order since February, I'll chase this up.

Do they state where the back focus is measured from, would it be the FR lens camera side, if this is so It might be possible to use a different focusing unit. Could you measure the outer diameter of the camera side lens mounting. This might fit into something like the Moonlite 2.5" cls which would gain some mm.

I'm really waiting to see how it performs, I look forward to your results.

Thanks for your reply, much appreciated.


10-05-2012, 08:36 AM

'scope look the part. I also note you seem to have the Orion optics tube cradle which I am thinking of getting for my scope, don't like trusting the expensive telescope to two aluminium screws on the native set up.

thanks for your views on the Atlas. It's a good site this, get a lot of freindly info and experiences.

11-05-2012, 01:11 PM
The Celestron focal reducer screws onto the 3.29-inch rear end opening of the EdgeHD 14. It then presents at the camera end the exact same 3.29-inch threads as the rear end opening of the scope. The new backfocus distance is measured from the camera end of the focal reducer.

Note that you want the optical distance from the back end of the focal reducer to the image plane on the chip to be 146mm. You should therefore engineer it to be so with your Atlas focuser centered via appropriate extensions if needed. When you move your focuser, you'll be changing this distance, so center your Atlas focuser, then rough focus with your mirror focuser knob, then fine focus with the Atlas. That should keep you as close as possible to 146mm.

See the following link (or the attachment):


02-06-2012, 08:03 PM
Frolinmod have you been able to try out you c14 edge focal reducer.
How do you find it performs. I'm expecting mine to arrive shortly, but it will be some time before I can check it out.

03-06-2012, 10:42 AM
No, it's cloudy/foggy (marine layer) almost every night during May and June here. It rolls in at sunset and burns off at sunrise. I'd have to take the whole kit up a local mountain to escape it (and I haven't done that). It may be July before I get any night sky. You'll probably get yours going before I do. I've been doing solar observing in the mean time.

08-07-2012, 08:14 PM
The instruction manual for the Celestron #94240 0.7x Reducer Lens for the EdgeHD 14 indicates that the focal length with this lens in place is 2,488 mm (98). This appears to be a typographical error as that would be F/6.3. Note that F/11 * 0.7 is F/7.7.

Alas, in the real world I'm measuring (via plate solve) closer to F/7.8.

I have the reducer attached to the back of my EdgeHD 14 with my CCD camera set so that the chip is 146mm behind the reducer exactly as the measurement is shown in the manual. The star images are nice and round.

If I move the camera farther back I can get to F/7.7, but then the stars become egg shaped just as the manual warns ("elongated star images toward the edge").

Overall I'm very happy with this reducer.

For me the benefits are:

1. Larger field of view at F/7.8.

2. Preserves the 146mm original backfocus.

3. Makes the device attached immediately after it in the image train clear the mirror lock knobs and the focus knob. Atlas focuser, here I come! Pyxis 2" rotator, here I come!

09-07-2012, 12:37 AM
Thanks for the update, Glad to know it's working.

What camera are you using?

Unfortunetly finances now force me to use a smaller CCD chiped camera, say 20 mm diagonal, so I was thinking of effectively moving the focal reducer in i.e by using native focuser, thereby possibly reducing the focal ratio and reduce effective focal reduction and increase fov

I realise the field edges will get worse, but possibly I could get to a photometrically usable 18mm diameter field.

Does this sound reasonable?

Cheers Eric

09-07-2012, 05:24 AM
I was using a QSI583 with a "ws" cover on it.

09-07-2012, 07:56 AM

No dispute ?

The Clement has been around for many years and is rock solid with very heavy payloads and cantilevered loads and is available in a few different sizes
It uses a flexural hinge mechanism and avoids tilt almost entirely for life as there is no wear, backlash or mechanical clearance required for sliding parts.
The design is used in scientific movement stages.

So it's certainly up there in the range of the "ultimate in after market digital focussing units" too !
If you can get one !


My experiences with 2 different FLI PDF focussers on heavy loads (STL11000, MOAG, RGH, FF) was nothing short of disastrous, they both had huge flexures and the second one broke the flimsy plastic chain that drives the cogs to adjust focus.
The masses were inside the manufacturers specifications.
I also felt the connection method was not satisfactory for heavy loads.

If the Atlas uses anything like the same sort of threaded sliding pin and sleeve design then I expect it would perform similarly after some initial wear because mechanical clearance is an integral/essential part of the design.

I see Bert and Greg both have recently mentioned significant flexure problems in their new systems and have wondered if the Atlas focussers had any measured contribution ?


09-07-2012, 10:08 PM
Hi Rally

The Atlas and PDF are, I am told, very different beasts of completely different engineering in order to address the issues to which you refer. I understand iTelescopes (formerly Global Rent a Scope) will now only use FLI gear for its reliability and stability..?


31-07-2012, 01:58 AM
I now have the correct optical path length in my image train and I'm now getting the expected F/7.7 with the reducer. Note that the diagram I posted earlier in this thread, which was taken from the #94240 instruction sheet, is wrong according to Celestron support. It shows the back focus as being measured from the flange at the base of the reducer output threads. According to Celestron support the back focus is actually measured from the very right most part of the reducer. (Just as it is on the OTA when the reducer is not used.) That's a whopping 5/8" difference that makes all the difference in the world. I'm liking this reducer more and more every day.

13-08-2012, 06:31 PM
Seriously interesting thread considering I am facing the pecise same dilemma. I have been tossing up between a Clement, PDF and Optec.. The Optec eats way to much back Focus to be useful for an imaging system on the Edge 14 but Optec has been hinting at a secondary mirror focuser for the C11 and then C14. I am not waiting for it at this point in time.

For my current money, a lot of it at that, I'm contemplating a PDF but am concerned about clearance with the focus lock knobs. If you have to move the focuser out much, well, whats the point?

I'd like to hear from anyone who uses a Clement. Interesting concept.


14-08-2012, 07:31 AM
You can purchase that Optec secondary mirror focuser right now. I passed on it because I don't have an observatory. I put the aluminum corrector cover on each morning, then cover the whole scope with an Telegizmos 365. Removing the secondary focuser every morning and putting it back on every evening would be too much secondary handling (with accompanying risks) for me.

Will the Clement clear all the EdgeHD knobs?

19-08-2012, 07:27 PM
I think its only the C11 version of the secondary focuser that may be available but I'll check with OPTEC. Its a possibility because I gather it allows the primary to be locked in place.

I think my OTA arrives next week so I'll be able to get an idea of the clearance available for these focusers on a C14. The Clement may also be an option but I recently contacted the manufacturer and he is in the process of a major redesign and wont be in production for at least several months.

19-08-2012, 09:32 PM
Just two weeks ago Jeff at Optec assured me that it would work with my EdgeHD 14. Tina made the same assurances when I talked to her earlier at SCAE in mid July. So either they're just hoping it does, or it really does.

22-08-2012, 02:28 AM
As I may have mentioned above, the #94240 0.7x Reducer documentation has an error in one of the diagrams where they show where the back focus is measured from. I posted a diagram excerpted from that documentation above. Celestron support has confirmed that it's in error.

Here are some corrected diagrams:

02-07-2013, 08:02 PM
Does anyone have experience with locking the main mirror of the EdgeHD 14 in the transport position so that it does not move during a long imaging session and using the Atlas for focusing? I expect that the 146 mm distance from the back plate to the imaging chip would be lowered by the amount that the focal plane moves when the mirror is locked back into the transport position. So, how far is that and would it leave enough room for an adapter between the back plate and the Atlas and provide a flat field across the whole image?

03-07-2013, 02:57 AM
With the mirror in the fully retracted and locked position (the shipping and transport position), I don't think you will achieve focus at 146mm back from the baffle lock nut (or reducer). Focus will be at some other position, beats me where though. And if it's not at 146mm back, then it's supposedly not optimal. I've seen the results of it not being optimal and they are grim (egg shaped stars).

The Atlas obviously won't fit on the baffle lock nut without the reducer in place because the knobs are in the way.

I had Precise Parts make me an EdgeHD 14 to Atlas adapter that allows the Atlas to overlap a full 16mm of the thread on the back of the 0.7X focal reducer, thus giving me 16 additional millimeters of space for "stuff" between the reducer and the camera.

Note that I can get a Pyxis 3-inch rotator to squeeze between the knobs so long as I add a 0.2-inch spacer onto the baffle lock nut between the scope and the Pyxis. The spacer is needed because the opening in the 3-inch Pyxis isn't quite deep enough to allow the baffle lock nut to be swallowed to its full height. Then I can add the Atlas after the Pyxis instead of the other way around.

Precise Parts adapters are expensive, so the cost adds up very quickly when you have several made to cover various possible image train arrangements.

03-07-2013, 05:03 PM
I use a moonlight large format focuser on my 14EDGE has the right sized flange and the correct back focus without the need for adaptors 1 drawtube about half way gives 5.75 works fine with the reducer or without, I focus with the scope first then lock the mirror and if needed I fine tune remotely

05-07-2013, 07:22 AM
I have been advised by the Celestron Technical Support that the 146 mm distance for correct image scale is set in relation to the lens at the rear cell. Therefore, it is not possible to lock the main mirror in the transport position and use an inline focuser to achieve high definition of images to the edge of the field.

06-07-2013, 10:39 AM
I wonder at what distance the focus position is when the primary is backed all the way back against the inside rear of the OTA and then locked in place with the bolts. Probably quite close to the rear baffle lock nut.