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focal reducing lense for lumicon giant easy guider

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#1 herrindude

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Posted 26 December 2015 - 10:03 AM

I am looking to buy a lumicon giant easy guider and i have found 2, one has no lense and the other does not have one at all. I have searched the world over and cannot find one to buy, and suggestions on where to find one would be greatly appreciated, thanks Jason



#2 herrindude

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Posted 26 December 2015 - 10:05 AM

I meant to say one has a scratched lens and one has none at all, sorry, Jason



#3 DuncanM

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Posted 26 December 2015 - 10:15 AM

Why do you want a GEG?



#4 AndrewXnn

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Posted 26 December 2015 - 10:19 AM

Have you looked at new one from Adorama Cameras? On sale for $220.

 

http://www.adorama.c...CFckYHwodmmICbw

 

I've got no interest in their store, but it popped up with a Google search.



#5 GrandadCast

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Posted 26 December 2015 - 10:31 AM

I have one of those and could not get good guide stars, however I didn't try very hard either. Now, while searching I found a test comparing the Celestron 6.3 reducer and the big easy. I did my own testing and the big easy is much better if you like flatter and smaller stars. So, I removed the guide tube and sealed the hole it left, can be easily put back to OAG and that is what I use as my reducer and flattener. Hope you can locate one.


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#6 DaveJ

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Posted 26 December 2015 - 11:12 AM

Have you looked at new one from Adorama Cameras? On sale for $220.

 

http://www.adorama.c...CFckYHwodmmICbw

 

I've got no interest in their store, but it popped up with a Google search.

That is not a "Giant Easy Guider" but rather a much much smaller version.



#7 GlennLeDrew

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Posted 26 December 2015 - 02:22 PM

I'm reasoanably confident that the Lumicon Easy Guiders used binocular objectives, of 50mm or 80mm diameter, for their reducing elements. You could purchase the lensless version and mount an objective taken from a broken bino. It's been a couple decades or so since I looked at one, and my memory is hazy. It's possible the lens was installed directly, without a dedicated cell/support for the lens; if so, that will simplify things, as long as the lens diameter is compatible. If the lens is a bit too small, a 'cell' of sorts could be made up from a wrapping of space-filling plastic sheet, or something like it.



#8 herrindude

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Posted 26 December 2015 - 07:06 PM

thanks for the comments, the reason i want one is for the different focal lengths that are achievable, f10, f6.5, and f5 and the simple fact that this thing is rock solid. I have seen images and heard testimonials about it having a flatter field and smaller stars. To the guy who thinks that the reducer is a bino lens, if it is a weird size, i am a machinist and can make a cell to hold the objective. Does anyone have any instructions on this geg, I tried to down load some, but only got a bunch of programs on my machine that took 2 hours to get rid off. 



#9 herrindude

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Posted 26 December 2015 - 07:16 PM

How can i find out the specs for the lens, size, focal length, all that stuff?



#10 GrandadCast

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Posted 26 December 2015 - 09:25 PM

I am not sure if this will help but its the best info I was able to find a few years ago.

 

http://www.korner.fr...0/manual01.html



#11 skycamper

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Posted 27 December 2015 - 02:57 AM

Replies to this will be helpful to more than one person!!! That manual posted in the previous comment is the only document I could find.   How to move the reducing lens in the housing would also be useful.  I have the 2" easy guider and im lost!



#12 Martin Lyons

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Posted 27 December 2015 - 04:24 AM

I have an unused, still in original box Lumicon Giant Easyguider.

I will get it out, check all the lens dimensions, focal length etc and also revert regarding what the manual says about different lens positions.

 

I'llbe back shortly...watch this space.

 

Martin


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#13 Martin Lyons

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Posted 27 December 2015 - 05:38 AM

OK, so I've had a good look, taken some photos, scanned the user manual and even measured the diameter and focal length of the lens.

The lens is an 80mm achromat with a focal length of +/-300mm (measured with a steel rule and the sun) and it is in a cell of sorts that can be repositioned either in front of, or behind, the pick-off mirror within the GAG body.

According to the instructions, this provides a varying degree of focal reduction down to f4 when in the most rearward position and used on an f10 SCT.

 

I have attached a few pics and also basic printed info, but the actual instructions are too large for posting here so I'm quite happy to email them privately to anyone who would like a copy seeing as they don't seem to be available anywhere on line.

 

Hope this helps

 

Regards

Martin

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#14 GrandadCast

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Posted 27 December 2015 - 08:29 AM

Martin: "(measured with a steel rule and the sun)"

 

Too early in the morning for learning something. That may come in useful one day.

 

Jess



#15 herrindude

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Posted 27 December 2015 - 09:34 AM

Send me a personal message through the site, i would love to have a copy of those instructions, and I am very grateful for all the help I get here on CL, thanks alot guys, Jason.


Edited by Ken Sturrock, 30 July 2017 - 08:13 PM.
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#16 Martin Lyons

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Posted 27 December 2015 - 10:04 AM

Mail sent



#17 skycamper

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Posted 27 December 2015 - 11:20 AM

Martin, you're a star! I have the two inch version I plan on using on a C11XLT. I'm hoping I won't get a lot of vignetting. Can you send me the file as well?  Thanks so much!!

Abraham


Edited by Ken Sturrock, 30 July 2017 - 08:14 PM.
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#18 GlennLeDrew

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Posted 28 December 2015 - 04:14 AM

Note that the degree of focal reduction scales as the distance of the reducer from the focus. The farther forward (closer to the scope's front end) the reducer is placed, the more focal reduction obtained. The 80mm lens focal length of about 300mm makes it virtually certain it's a bino objective; practically all cemented such lenses have a f.l. near to 300mm. And so the reduction would be 0.5X when the lens-to-focus distance is 1/2 the focal length, or ~150mm.

 

As the focal reduction is made more aggressive, vignetting worsens. The 80mm diameter would mean that its own contributing to vignetting is minimal. To first order, at a reduction of 0.5X it would provide a fully illuminated circle of roughly 40mm. But that would require that the scope delivers a circle of full illumination of ~80mm, which of course is not the case. And so the vignetting will primarily result from the scope, this being the existing illuminated field size reduced in scale as the reduction factor. If the scope's existing circle of full illumination is, say, 30mm, at a reduction of 0.5X it could never be larger than 15mm, no matter how large a reducer employed.

 

As the reduction factor is made more aggressive, aberrations also worsen. An achromat designed for an infinite conjugate is not corrected for this application. At least the ~f/10 beam for an SCT does help; on an f/5 scope such a reducer quickly reveals its inherent 'weaknesses'. Not only does off-axis coma and astigmatism rear their heads, but so too does on-axis spherical aberration. Not to mention field curvature. These issues will be of minimal impact at gentler reductions of about 0.6-0.7X. But for 0.5X, and certainly at 0.4X, the image will likely be noticeably degraded in some respect(s). Of course, this depends on the application and one's own degree of tolerance for defects.


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#19 herrindude

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Posted 28 December 2015 - 09:13 AM

Thank you for your expert advise on this topic. I have done a search and have not yet found this objective, I may be looking at buying a set of bino's and removing the lens to make a cell to hold it. Once again, thanks for the info, Jason.



#20 herrindude

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Posted 07 January 2016 - 07:49 PM

Well the geg is here and so is the rain, maybe in a couple weeks it will clear up to give it a run. The geg looks good and the reducer looks good as well. This thing is built like a tank, I don't think flexure will be a problem. I noticed a c etched on the reducer, I am assuming this is for orientation. I assembled it with the c in line with the guider tube, but I am not sure if this is right. is guiderOn assembly, I noticed that one of the two screws would tighten down on reducer before it seated against the guider tube, i definite flexure issue. I ground down it about 1/32 and it now securely holds guider tube.Anyone using this guider with a c11 and an orion starshoot guider, I am just curious if the long guider tube will focus or will i need the second shorter tube as well. Thanks for the input, Jason.



#21 charles genovese

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Posted 08 January 2016 - 08:31 AM

For the C14 this reducer works great for "snapshots" which is what I like. Snapshots for me means  single image unguided (have my G11 at +-3 arc sec with no PEC correction) with 5 minutes of processing. This is a C14- Lumicon Giant Easy guider- moded Canon XSi image.

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Edited by charles genovese, 08 January 2016 - 08:32 AM.


#22 George N

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Posted 12 January 2016 - 04:02 PM

Could the "reducer lens" be the one from Lumicon's 80mm finder?



#23 GlennLeDrew

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Posted 12 January 2016 - 08:13 PM

If the Lumicon finder has a ~300mm f.l. objective, then it's essentially identical to that in the guider. The Lumicon 80mm 'Super Finder' (or some such moniker) uses a 400 or 500mm f.l., possibly air-spaced objective.


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#24 herrindude

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Posted 15 January 2016 - 07:52 PM

Finally go a cloud free night and I gave the geg a test run. I focused the camera, and when I went to use orion starshoot autoguider, I could not find focus. I tried the extra extension tube , unscrew the lense out of barlows, no dice. So i took a few shots unguided and i love what is possible with this guider. No vignetting and even field illumination across the field. Any body out there have any ideas about how to focus autoguider with geg?



#25 lukedogwalker

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Posted 17 April 2016 - 09:16 AM

Hello all,

 

Mr. Lyons, I would appreciate a copy of the Lumicon GEG instructions.  I had a friend leave his 10" Meade LX200 with me when he moved out of the country.  The box of eyepieces included the GEG.  This will be my first experience with astrophotography.

 

Please send me a personal message through the site.

 

Many thanks,

 

Luis


Edited by Ken Sturrock, 30 July 2017 - 08:14 PM.
Removed personal email address



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