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[Chicago Astronomer - Astro Joe]

Upgrading to a 2" Crayford-Style Focuser for the C11 SCT

I have never been a great fan of the SCT type of scope - preferring the ease and robust performance of Newts and the sharpness and contrast of Refractors. I always avoided using the SCTs at the Adler for public events, and was a refractor man for the longest. It's the mirror tilt/image shift that bugged me...

But I do appreciate the light gathering abilities of SCTs 8" and up and when the C11 decided it wanted me... I changed my mind and think they are great. But it's that damned mirror shift that haunts all SCT users - delicate and finicky.

Methods have been devised to keep this to a minimum. From mirror locks, to dual mini 10:1 focusers on the main focus knob and motor focusers. I have a JMI focuser already on the C11 - and it works nicely....but with it's two button action controller...one often passes-by the prime focus and has to come back. The delicate touch is lost with devices like this and although the battery life lasts a very long time, it may run out during a imaging session.

Not cool.

And also, during my testing of the Binoiviewers on the C11 recently, the coarse focusing of the main knob was too crude and sloppy. I needed something more precise, sensitive and hands-on - not using the heavy mirror for the focusing, but the eyepiece instead to find the focal point - like a newt or refractor. SCTs work, but not efficient nor precise.

In comes the SCT Rear Cell Crayford-style type of focusers.

Researching for performance and most importantly - price...I came down to two types. These level of auxiliary focusers are practically all made by the GSO company in China and all the retailer does is stamp their name on and re-sell it. Pockets that are shallow, (like mine), must be content with under $125.00 models and not the very cool type costing $300.00 +


First the Zhumell focuser -

I can get this down to about $103.98 with promo code and rewards. Free Shipping.



The OPT Focuser -

I can get this down to $98.75 with OPT membership reward.

$13.64 shipping = $112.64


Now the differences:

The Zhumell has a ratio of 11:1 while the OPT a nick below of 10:1 -

Dust cap on the OPT, while the Zhumell does not indicate one -

The Zhumell has a tube travel max length of 30mm, while the OPT stops at 25mm -

The OPT has Millimeter focus laser engraved marks on the tube, while the Zhumell has no indication of any -

Both have a 1.25" adapter included -

The Zhumell is a hefty 3lbs while the OPT is 1lb 10.5 oz -

The Opt has anti-reflection baffles, while the Zhumell does not indicate any -

Both have compression rings -

I have thought about this purchase for a few days now and weighed all the differences, pros and cons...and this wasn't an easy one.

I'm going with the OPT.

Because of the lighter weight, tube markings and the much more detailed data sheet and pre-purchase info. And even with the free shipping, the Zhumell seems like a mass produced faceless item, while the OPT offered a Chicago Astronomer/OPT rewards discount of 5%.

Wish I could evaluate both, but for now...It's the Opt.

Full review soon.

[-=CROMAN=-]

The opt looks exactly like the same one I have on my newt. I love mine

[Chicago Astronomer - Astro Joe]

Rich,

You mean your 10" Zhumell Dob?

If so, shouldn't it have the Zhumell focuser on it?

I'm hoping that this new piece of equipment doesn't cut into the light path. I read where such focusers sometimes do - with the rear cell attachment ring blocking, especially with Meade SCTs. There's a wider adapter ring available to allow more photons to enter the focuser and not cheating the user of any FOV theft.

We shall see.

[-=CROMAN=-]

Yeah ... the dob. It looks Exactly like the opt. same markings and everything. 10:1 ratio.

I'm going to have to look into this as the one on my zhumell rocks. With the age of my sct do you think it's compatible with the rear cell?

[patrickm]

Man, this is already on my winter research list for SCT. The little that I have used the Moonlite on my reflector shows just how much I've been missing with the factory course focus on my C9.25. Working with the prime focus for AP was also quite frustrating. I await your report with much eagerness!

[-=CROMAN=-]

did you read this review?

www.cloudynights.com/item.php?item_id=2652

[Chicago Astronomer - Astro Joe]

Rich, yes...I read that before the purchase.

I don't know if the added two pounds is worth it, but I do like the appearance of the Zhumell better.

The reviewer went for it as well and let's see if I fare differently.


Patrick,

The Moonlight focusers are nice, especially the colorful anodized ones. I would get one for the 9.25" without a doubt, but there might be a fit issue at the rear cell threads if not diligent.

C.A. Bill had a William Optics APO Refractor for a while with a Dual speed focuser. I enjoyed the delicate touch it offered for and always desired one. I think it's near a necessity for SCTs - taking into consideration the mirror shift, temperature variances of that big hunk of glass and overcoming the coarse screw thread on the focuser shaft.

[Chicago Astronomer - Astro Joe]

Focuser Arrived -

Waiting for me at my doorstep was a nice box. Just big enough for a focuser. I was hoping it was....

Packed and surrounded by foam, I was excited on receiving this.

It has heft, but not heavy. The focus wheels turn nicely and smoothly with no clicks or dead spots - including the micro focuser knob.

On the bottom are two thumbscrews...

1- Is the tension screw.

Depending on how much drag the user likes, it can be adjusted to nothing, allowing even to be pushed in and out by fingers - or racked down tight where it takes some effort to draw the tube in and out via the focuser knobs.

2 - Is the Lockdown screw.

The drawtube can be locked in any position in the travel. Locked, the focuswheels still turn, but do nothing.

With the two thumb screws totally loosened, the drawtube has play - too much. But it was not meant to be used in this manner, and with the proper tension applied, it's solid and acceptable.

Although the drawtube travels out to 2.50 millimeters, it likes to stop at the 2 Millimeter mark, coming out to the full travel stop only by fiddling with the lockdown thumbscrew- loosening it uncomfortably too much. But...there shoukd be no need to squeeze out this .50 of play.

Hanging on to the right diagonal and eyepieces...

...are nice shiny brass compression rings on both the focuser body and the 1.25" adapter.


And at the rear...

...is rotatable collar that can be locked down with a Thumbscrew located at the top of the focuser. And inside, are threads to accept a focal reducer/field flattener or filters.

A selling point of this particular focuser by the company was the ridged baffling, to help knock off glare. But...I think real flocking here would be superior. Spring time project...

I will be attaching this new piece of hardware on the C11 within the next few days...and perhaps by then, the skies will finally clear.

Just in time for the winter solstice!

[-=CROMAN=-]

That is Exactly the same as the one that came on my Zhumell

[Chicago Astronomer - Astro Joe]

Rich,

Have any issues with your focuser?

How you like it?

[RobbW]

Joe, I'm looking forward to reading your first-light review. This is a piece of equipment I could really use in my arsenal. However, any and all toys will need to wait until funds are flowing again. Till then, I shall live vicariously through others!

[Chicago Astronomer - Astro Joe]

Robb,

I'm thinking about a Chicago Astronomer session this coming Monday, (Dec 26th). Forecast calls for some clear skies this coming week.

There, I'll see how the OPT Focuser performs.

[Chicago Astronomer - Astro Joe]

Finally...Preliminary test of the Crayford Style focuser -

This was the first opportunity I had to test out the new focuser, after days & nights of clouds and sickness to get over with. With a semi-decent clear night and temps comfortable for a January, I set up the C11 outside of the garage for a quick run through...

I had to remove the large adapter ring from the JMI motorized focuser I had on the C11 rear cell and transfer it to the Crayford. Fit with no problems or hitches.

The near full Moon was rather low, so I slewed to Jupiter and found that the focusing was now more satisfactory than with the crude and primitive movement of the huge hunk of mirror glass sliding and tilting back & forth...

But, initially, the main focusing knob needed to be adjusted to focus and the Crayford set "in the middle" of it's drawtube travel. There, the minute focusing adjustments can be made on either side without hitting the end of the run.

Jupiter was very nice this evening, riding high. Now, is this worth it and could I get better views with this new piece of equipment...?

Yes.

Making the rudimentary adjustments on the main focus knob, I brought the Jovian disk into clear view, then transferring the job of final sharpening to the new focuser. Using the larger knob just slightly, I racked it back and forth - passing sharp view point and back again to get the feel of the action. Then when I felt it was at it's best, I went to the 10:1 smaller knob and tweaked it. Not unfamiliar with Crayfords, it still takes a bit of getting used to...trying to get the best view possible. But an 1/8th of a turn here, a 16th there...and it all comes together...

Details like smaller whitish orbs popped out nicely and many minor bandings and dark smudges. The camera does not reproduce what I viewed, but gives a good idea. (I'm having problems with the tracking motors, so it made imaging more difficult.)

I slipped in the binoviwers and was very pleased in the 3-D view of the planet, sharply detailed and hanging there in space... ;D

Before the evening's test session was through, I slewed the scope over to the Moon now, still using the binoviewers, and found focusing a pleasant experience..

Taking some very quick shots, I fought through some heavy atmospheric turbulence, but still managed to bring lunar features into sharp detailed focus.

No longer the frustration of the image sliding out of the FOV when moving the mirror back & forth for crude focus. And I did find it better and easier to focus on the LCD screen on the camera as well. I did not have a change to continue with more sophisticated testings with high magnifications, as it got cold and I'm still fighting this cold, but I was satisfied with this first time out.

I highly recommend a Crayford-style focuser for any scope that will accept one... #Thumbsup#

[magic612]

Very cool - nice review, Joe.

[Skyhound]

Nice write up!!!..During public outreach with a SCT your public will find it very easy to see what is there when they can adjust for their eyesight compared to everyone else's with out moving the object in the field of view. When you are looking for that fine detail by racking in and out of focus slowly it's also a god sent .
I really like your pic's.

[Chicago Astronomer - Astro Joe]

Thx Skyhound...

The crude shoving and pushing of the mirror is for Philistines and old school Orange Celestrons.

In just this brief test, the focusing is much more satisfactory and pleasurable.

More later...

[RobbW]

Joe, I'm very pleased to hear that your new focuser made such a big difference, and that you feel it was coinage well spent. I am going to add a new focuser (possibly this exact same one) to my list of must-have equipment upgrades. Of course, that list comes at the tail end of a VERY long list of baby must-haves as I prepare for the arrival of my next astronomy protege this summer! But we'll see. Maybe I can sneak the focuser in there among all the other expenses!

[Chicago Astronomer - Astro Joe]

Robb,

I'm telling you man, it makes a big difference in observational satisfaction.

Enabling millimeters of just the slightest tweak, brings it all into sharp focus and makes for astrophotography much more easier.

Do it.

I say... slip the purchase price into "Misc" on the list. in between Bassinet and Huggies.

[mojocvh]

Thread resurrection...

Hey everybody

Just found this thread [actually I've been looking for the C-11 teardown threads ??]

I'm kinda getting my Astro mojo back again.

Work still takes up way too much of my life at present but I have been thinking of both a secondary focuser AND binoviewers to increase viewing pleasure and this thread helps solidify those thoughts.

Cheers everybody and clear skies to you all.

Andy B.

[iota]

Nov 3, 2013 4:46:02 GMT -6 mojocvh said:

Thread resurrection...

Hey everybody

Just found this thread [actually I've been looking for the C-11 teardown threads ??]
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The Celestron CPC 1100 thread pattern is 3.290 - 16 TPI for the main ring. I hope this helps and is the info you are requesting...
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...
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I'm kinda getting my Astro mojo back again.

Work still takes up way too much of my life at present but I have been thinking of both a secondary focuser AND binoviewers to increase viewing pleasure and this thread helps solidify those thoughts.

Cheers everybody and clear skies to you all.

Andy B.