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Eyepiece for Orion Starblast 4.5

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#1 kurtenstein

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Posted 13 September 2019 - 07:23 AM

Hi there!

 

I own an Orion Starblast 4.5 and would like to know what would be the most powerful eyepiece I can use with it, say for Moon and planets. I currently use a 4.5 mm Antares (Plossl, I guess) and Soviet 2x Barlow (TEL?). I've watched the Moon with this setup yesterday but found it hard to get a decent focus... wich wasn't the case with my Celestron 8-24 zoom EP. Am I pushing the scope's limits? Bad collimation, perhaps? I use the simple collimation cap provided with the Starblast.

 

Thanks for your help!!!



#2 S.Boerner

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Posted 13 September 2019 - 07:51 AM

Orion says the highest magnification for a StarBlast 4.5 is 228x.  You're pretty close to that with your 4.5mm eyepiece and Barlow at 200x so I'd say that you are pushing the limit.

 

Atmospheric seeing is probably another area of concern. 



#3 kurtenstein

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Posted 13 September 2019 - 08:19 AM

Orion says the highest magnification for a StarBlast 4.5 is 228x.  You're pretty close to that with your 4.5mm eyepiece and Barlow at 200x so I'd say that you are pushing the limit.Is it 

Atmospheric seeing is probably another area of concern. 

Is seeing influenced by magnification power? (Is bad seeing worsened by magnification?)



#4 dcollier

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Posted 13 September 2019 - 08:31 AM

Good rules of thumb for telescopes:

 

1. Max Power=  2 X the aperture in Millimeters.

 

2, Eyepiece Power = Scope Focal Length / Eyepiece Focal Length

 

Barlow: Multiply 2 above by the power of the Barlow. 



#5 Jim Davis

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Posted 13 September 2019 - 08:32 AM

Is seeing influenced by magnification power? (Is bad seeing worsened by magnification?)

Yes. If you magnify as fuzzy image, it gets even fuzzier. Where I live, I rarely go above 200x even with the largest telescopes, due to poor seeing. Every so often we get a period of good seeing, and I have pushed it above 500x, but those are rare.



#6 dcollier

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Posted 13 September 2019 - 08:33 AM

Yes, seeing and transparency will often limit your ability to reach max magnification. 



#7 vdog

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Posted 13 September 2019 - 08:34 AM

Even with good collimation, I never got more than 150x out of my Starblast, which provides a pretty decent view of planets if the conditions are good.


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#8 Binojunky

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Posted 13 September 2019 - 09:18 AM

Orion says the highest magnification for a StarBlast 4.5 is 228x.  You're pretty close to that with your 4.5mm eyepiece and Barlow at 200x so I'd say that you are pushing the limit.

 

Atmospheric seeing is probably another area of concern. 

Thats what Orion states, the optics of a Star Blast can and do vary a bit , they are rich field scopes, I had three over the years and found a difference in what they could handle magnification wise,D.



#9 SeattleScott

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Posted 13 September 2019 - 03:32 PM

The other variable is optical quality. The Starblast is F4, which is quite demanding to make a F4 mirror that can take high magnification well. Not a problem for a $1,500 Vixen R200 but the Starblast isn’t quite made to the same standards. So a theoretical maximum magnification probably isn’t realistic for the Starblast. Hence the sample variation that Binojunky noted.

Also F4 is very demanding on collimation. A collimation cap will come close but it probably isn’t precise enough for maxing out the theoretical magnification with a F4 mirror.

And yes, seeing could have been an issue too.

Scott

#10 MikeTelescope

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Posted 13 September 2019 - 05:17 PM

The f/4 optics of the Starblast are very sensitive to collimation errors.  If you want to push it to 150x or anywhere near there, it must be very well collimated.  You can start with the collimation cap that came with it to get close, but you will likely need to tweak it outside with a star collimation using the actual high-magnification eyepiece.  The focuser has a lot of slop to it, so the collimation can change between using the collimation cap and the real eyepiece (and possibly barlow) that you will use.  

 

I spent a good 10-15 minutes on Polaris getting my Starblast to have the best level of collimation I could, prior to using it for a family star party over the summer.  At 150x (6mm plus 2x shorty Barlow), Jupiter and Saturn were very sharp.  We could see a moon shadow transit of Jupiter.  Cassini division on Saturn was sharp and distinct.  I also let the scope acclimate for about 30 minutes before using it that night. 

 

There is also quite a bit of variation on mirror quality on this scope, I hear.  I have two samples, and they are both good, but reports are that some can be optically mediocre.  



#11 mac57

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Posted 13 September 2019 - 05:17 PM

The problem you have is like mine, not enough focal length to reach high powers.  I see you live near a big city.  Like me, your skies aren't that great.  High mag sounds good, but in practice it may not be.  Mark



#12 izar187

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Posted 14 September 2019 - 07:33 AM

Another vote for collimate carefully, on Polaris if possible.

Plus another vote for 150x, as a better target for general working high power in a short tube 4" newt. 

 

Plus, experiment with focussing critical high power on a nearby star.

Then move over to the planet.

I often find better results doing this, rather than trying to get sharpest focus on the planet itself.

It's an f/4 + planet + high power thing.

With a two speed crayford it might not be an issue.

But it sure can be on a little table top sized newt. 


Edited by izar187, 14 September 2019 - 08:41 AM.

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#13 kurtenstein

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Posted 14 September 2019 - 09:53 AM

Collimation on Polaris: can someone explain how to do that, please???

Thanx for the input!

#14 SeattleScott

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Posted 14 September 2019 - 11:32 AM

Center Polaris in the scope. The reason to use Polaris is it won’t drift out of the view while you collimate. As you rack focus in and out, the donut should be centered and symmetrical on both sides of focus. Of course with the usual slop in these cheap focusers, precise collimation may not be realistic. Ultimately it is an entry level scope designed for low power, wide field views to make finding targets easier. It is not a planetary scope by any stretch of the imagination. Yet it makes sense to try and get as good of planetary views as you can with it. Often people will get another scope for planetary.

Scott

#15 kurtenstein

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Posted 14 September 2019 - 03:00 PM

Thank you, will try that!

#16 MikeTelescope

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Posted 14 September 2019 - 07:28 PM

Collimation on Polaris: can someone explain how to do that, please???

Thanx for the input!

https://garyseronik....pe-collimation/

 

This is an excellent article by Gary Seronik on no-tools collimation, aka star collimation.  Easiest to use Polaris, because it won't drift out of the FOV.  Use an eyepiece or eyepiece+barlow that is about equal to the focal length.  For the Starblast, use something around 4mm.  If you use a barlow for planetary, then have the barlow and the eyepiece in place while doing the star collimation.  

 

Once you get it close, get closer to focus until you have only 2-3 diffraction rings and make any fine tune adjustments there.  

 

Once you get comfortable doing it on Polaris, you can move on to checking it on a bright star near your target of interest.  If your target is at a much different altitude than Polaris, the Starblast focuser slop may change collimation slightly.  



#17 Don H

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Posted 15 September 2019 - 03:49 PM

I have a 4mm TMB Burgess eyepiece that yields 113x and works very nicely with my Starblast. My preference is to use short FL eyepieces rather than add a Barlow. It is a little less taxing on the focuser and avoids a bit of hassle assembling lense combos. As already mentioned, good collimation is required for the best views. At 113x, moon and GRS transits are easily viewed, and some details are present in Jupiter's could belts. I also see a nice sharp Cassini division on Saturn's rings, along with some markings on that planet's disc. I don't try to push it much past the 4mm, since I really prefer the 114mm for rich field, low power views. When you try collimating on Polaris, take note as you finish. It is actually a nice double.

 

So good collimation, let optics cool, only look at planets well above the horizon, actually as close to the meridian as possible, clean your mirrors when they need it, and expect your best views between 100 and 150x or so. Maybe on good nights a bit more, but I might be looking for a different scope if higher powers were routinely desired. I am frequently amazed what my 114 shows me at 25x with and 18mm Radian...


Edited by Don H, 15 September 2019 - 03:50 PM.

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#18 kurtenstein

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Posted 15 September 2019 - 04:13 PM

https://garyseronik....pe-collimation/

This is an excellent article by Gary Seronik on no-tools collimation, aka star collimation. Easiest to use Polaris, because it won't drift out of the FOV. Use an eyepiece or eyepiece+barlow that is about equal to the focal length. For the Starblast, use something around 4mm. If you use a barlow for planetary, then have the barlow and the eyepiece in place while doing the star collimation.

Once you get it close, get closer to focus until you have only 2-3 diffraction rings and make any fine tune adjustments there.

Once you get comfortable doing it on Polaris, you can move on to checking it on a bright star near your target of interest. If your target is at a much different altitude than Polaris, the Starblast focuser slop may change collimation slightly.


Wonderful article indeed!


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