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Focuser for Orion StartBlast 4.5

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#1 AstroVPK

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Posted 01 June 2020 - 12:09 AM

Had anyone replaced the focuser on their Orion StarBlast 4.5? I'm looking for recommendations for a new focuser and finder.

#2 Eddgie

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Posted 01 June 2020 - 09:34 AM

Is the focuser broken or are you just looking to "upgrade?"

 

If you are looking to "upgrade," my advice is to not do it because it is jut not cost effective and there are a lot of fitment issues.  It is not like you can just bolt a replacement focuser on.  You have to have the right adapter plate or a 3D printer to print one (or some other solution). You also have to make sure that the focuser tube height and length are correct.   To low a focuser or too short a tube means you might not be able to reach focus and too long a tube means that it can stick down into the light path of the mirror.

 

If the focuser is not working right, try to repair it.   If it can't be repaired, try to get a new one from Orion. 

 

If you are dead set on replacing it,  I would recommend something like the KineOptics HC1.  This uses a three hole mounting and would probably be very easy to mount to your OTA.   Also, for a very fair price, KineOptics will custom print an adapter plate for your scope.  Again, this is a bit problem because no one really makes mounting plates in these small sizes.

 

If you did not want to pay for a custom mounting plate, you could simply use extension tubes to get your eyepieces high enough up to focus. 

 

For scopes this small, I recommend a green laser pointer as a finder.  This one uses a home 3D printed bracket and a "military" size laser, but you can buy brackets and lasers on Amazon or eBay.

 

 

laser bracket close R.jpg

 

 

 

 

 


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#3 AstroVPK

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Posted 01 June 2020 - 01:39 PM

Is the focuser broken or are you just looking to "upgrade?"

If you are looking to "upgrade," my advice is to not do it because it is jut not cost effective and there are a lot of fitment issues. It is not like you can just bolt a replacement focuser on. You have to have the right adapter plate or a 3D printer to print one (or some other solution). You also have to make sure that the focuser tube height and length are correct. To low a focuser or too short a tube means you might not be able to reach focus and too long a tube means that it can stick down into the light path of the mirror.

If the focuser is not working right, try to repair it. If it can't be repaired, try to get a new one from Orion.

If you are dead set on replacing it, I would recommend something like the KineOptics HC1. This uses a three hole mounting and would probably be very easy to mount to your OTA. Also, for a very fair price, KineOptics will custom print an adapter plate for your scope. Again, this is a bit problem because no one really makes mounting plates in these small sizes.

If you did not want to pay for a custom mounting plate, you could simply use extension tubes to get your eyepieces high enough up to focus.

For scopes this small, I recommend a green laser pointer as a finder. This one uses a home 3D printed bracket and a "military" size laser, but you can buy brackets and lasers on Amazon or eBay.


laser bracket close R.jpg


Great suggestions, thank you! The big problem is that the hole pattern and accessory bracket are not standard Orion, otherwise I'd be set. The focuser works fine right now, but it's a low quality focuser - it's sticky, restricted to 1.25" eyepieces, and tends to get a little sticky. The Orion red door is very annoying to align with the main scope - the little thumb wheels just don't allow for precision adjustments in pointing.

#4 Rock22

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Posted 01 June 2020 - 01:40 PM

I agree with Eddgie. I have a StarBlast 4.5” f/4.4 as it my first scope and looked into the options to change the focuser. I wanted to keep this scope for a while to learn stargazing, accommodate my heavier eyepiece (ES 14mm 82-deg), and take some moon shots. The focuser was not robust enough for the weight of my Canon T3, and I saw on CN that many were using refractors for taking pictures with a camera.

There were also really no options for a better focuser that would make upgrading worthwhile. That’s why I ended up just buying an ST80 to try attaching a camera. Worked great.

I still keep the 4.5” reflector for the children and for times when I just want to use it for fun to look around the night sky. The mirror is good, and the tube is light and compact. As for any upgrades, using a RACI finder is the only adjustment that was worthwhile making.

#5 Eddgie

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Posted 01 June 2020 - 02:12 PM

Great suggestions, thank you! The big problem is that the hole pattern and accessory bracket are not standard Orion, otherwise I'd be set. The focuser works fine right now, but it's a low quality focuser - it's sticky, restricted to 1.25" eyepieces, and tends to get a little sticky. The Orion red door is very annoying to align with the main scope - the little thumb wheels just don't allow for precision adjustments in pointing.

Well, as I said, the KineOptics would be a good choice as a replacement.

 

The 2" really is not a good option on this kind of scope. These scope barely illuminate the field of even 1.25" eyepeices. We are talking about fully illuminted circles of just a couple of millimeters and that is only enough for maybe an EAA size sensor, and these can be 1.25"  They would not be at all capable of illumining something like an APS-C size sensor.  The secondary mirrors are just too small.  I don't even think they really fully illuminate even the center of the field but that is just a suspicion. 

 

Here is a KineOptics focuser installed on a 114mm reflector.  Note that it is mounted using three holes and no special adaapter. Very clean and neat install. 

 

 

 

But not something I would do. 

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#6 vdog

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Posted 01 June 2020 - 02:20 PM

I can't seem to find the link where I got the idea, but with my Starblast, what I did was I took the focuser apart and replaced the stock sticky lubricant with good Lithium grease.  I also lined the drawtube with UHMW tape to make the fit more snug.  These were cheap, easy upgrades that improved its functionality.  

 

Replacing the focuser entirely seems a bit overkill for this scope.


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#7 Don H

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Posted 01 June 2020 - 05:01 PM

I adjusted my Starblast focuser when I first got it and it has worked well ever since for me. If you adjust each of the 2 adjustment screws the same amount, it may work better for you. Make small adjustments and dial in a good feel as you go. If you make them too tight, just back each screw off a tiny bit. I also added an o-ring to one knob and screwed a black plastic cap from a Pure Leaf tea bottle over that and it is attached quite firmly. This gave me a knob that was 50% larger and improved fine focus ability. My eyepieces are only around 6-8 ounces, and I would not expect to try anything much heavier. 

 

The red dot finder may just need a simple adjustment too. If you turn the adjustment knobs until they are at the center of their travel, then loosen the mounting screws, you can turn the base until an object in the eyepiece is as close as you can get to the red dot. At that point, tighten the mounting screws and the adjustment screws should make the final centering pretty easy. I actually enjoy the rdf, as it is up at the business end of the tube and requires very little contortion to look through. That is also why I like the reflector eyepiece position, too, and chose this scope as my gng rather than a refractor. I did not appreciate the scope until I got the rings and Versago mount. Now it is set up and ready to go all the time. My low power eyepieces give me about a 3.6 degree fov, so getting the rdf close will get most objects in the eyepiece. Often I just leave my 18mm Radian in for finding stuff, as it gives me 25x and a 2.4 degree fov. Many things really show up well at 25x.

 

I considered trying to install a 2" focuser for a while, but felt the secondary was really designed for 1.25". My fov gain could be over a degree, up to 4.8 degrees, but then a new secondary and 2" wf eyepiece would probably need a coma corrector, which would be more a lot more money. I didn't really want to put all the extra weight on the gng set up, either.

 

 

 

 

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  • 4.5 focuser1.jpg
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#8 Jon Isaacs

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Posted 02 June 2020 - 07:50 PM

My two cents:

 

The 4.5 inch Starblast is F/4. Yes, you can mess around with the plastic focuser but an F/4 scope has a depth of focus of 35 microns, a piece of typing paper is 115 microns thick. It deserves a decent focuser if you want it to really show what it can do.

 

The GSO 1.25 inch Crayford would be my choice. It's a single speed but a good one. I'm can't say for sure it would because I don't know the Starblast Focuser height. But with some washers for spacers to address the base curvature issue, it would be my choice.

 

https://agenaastro.c...ngle-speed.html

 

2 inch focusers on small Newtonians are nice. 

 

Skywatcher 130 with JMI focuser CN.jpg
 
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#9 RLK1

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Posted 02 June 2020 - 08:18 PM

Here's a link for a repair, if needed, on the stock skywatcher 130 focuser which is essentially same as the Orion unit:

http://www.astro-bab...ser Tune-up.htm


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#10 Jon Isaacs

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Posted 02 June 2020 - 09:36 PM

Here's a link for a repair, if needed, on the stock skywatcher 130 focuser which is essentially same as the Orion unit:

http://www.astro-bab...ser Tune-up.htm

I'd say give it a try but don't expect a major improvement.

 

I've reworked a number (>50) of Synta rack and pinion focusers using a similar approach.

 

The metal focusers can actually be quite good, smooth, reasonably light an free from rocking and image shift.

 

I've never been satisfied with the results I've achieved with the plastic focusers, they're better but still make precise focusing a challenge.

 

Jon



#11 Don H

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Posted 03 June 2020 - 07:04 PM

...

The 4.5 inch Starblast is F/4. Yes, you can mess around with the plastic focuser but an F/4 scope has a depth of focus of 35 microns, a piece of typing paper is 115 microns thick. It deserves a decent focuser if you want it to really show what it can do.

 

The GSO 1.25 inch Crayford would be my choice. It's a single speed but a good one. I'm can't say for sure it would because I don't know the Starblast Focuser height. But with some washers for spacers to address the base curvature issue, it would be my choice.

...

The Starblast focuser racked in height is only 2", while the GSO Crayford is listed as 3". Since my eyepieces focus with the drawtube out only around .5 to .75", I would need to rework the ota for the GSO. While your quote on the specification for depth of focus would seem to indicate that precise focusing should be almost impossible with the stock focuser, that has hardly been my real life experience. I can look at a nice cluster, a dim galaxy, or an extended nebula and easily get a sharp image. I generally look for one of the most dim stars in the field, or better yet a dim double. As I gently rack in and out, the dim stars will appear to sharpen and snap to focus, and upon looking at the brighter stars, I see they have become fine points, too. Over the years, I have used many scopes of assorted quality and know the frustration of a poor focuser. Again, I stress that the initial set up and adjustment must be done carefully, and using large eyepieces would probably not work well, if at all. But my TV Plossl, Radian and Delite seem to afford me a very satisfying rich field view. They are all very close to parfocal, so that helps too. Maybe the plastic will not have the long life of a metal focuser, but after a few years, this one still works like new. BTW, it does seem that the pinion and adjustment plates are made of metal.


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#12 Jon Isaacs

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Posted 05 June 2020 - 08:50 AM

Don:

 

Thanks for the focuser height info. That means I need to cross the GSO off the list.

 

I too am a veteran of the era of poor focusers. I would not say it's impossible to reach perfect focus but I would say it's much more difficult. I had this same focuser on a Starblast 6, I did my best tune up but it was never an easy focuser to use.

 

At lower magnifications it was workable but splitting a close double or focusing on a planet at 200x or more, the focuser definitely makes that difficult.One can say that these scopes weren't made for such viewing but in my experience, they are capable of it if one can focus.  

 

Jon




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