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1.25" Diagonal Recommendations...

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#1 Cotts

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Posted 19 January 2014 - 01:45 PM

...For my AT65EDQ Refractor. (f/6.5, 420mm f.l)

I'm leaning towards an erecting (correct view) 90 degree prism diagonal. The scope's primary use will be astrophotography (no diagonal) but finding and framing would be best done (I assume) with a correct view. I won't be doing much (if any) serious deepsky or high magnification work with the AT65.

I have heard that the correct view prisms put a "line" across the field of view. Is this true of all of them or is there a brand or two which don't have this problem?

thanks,

Dave

#2 Eddgie

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Posted 19 January 2014 - 01:49 PM

It is true that on bright stars, you can get a diffraction spike.

A very high quality Amici prism will in fact greatly minimize this. Baader makes such a prism, but it is very expensive. About the best possible Amici you can buy though because the edge tolerance has been kept very tight (this is what causes the spike is a dull edge on the prism.. The shaper the edge is finished the less noticable the spike, and the Baader is again about the best you can buy).

For daytime, you don't see the spike really unless you look at a sharp glint.

For nightime, only brigheter stars will show a distracting spike, but in the Baader, it takes a very bright star for it to get distracting.

Of course everyone's tolerance is different.

#3 genedalton

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Posted 20 January 2014 - 07:46 PM

I've got two of Scopestuff's RACI's and haven't had any problems, and they are inexpensive. Gene

#4 eyepiecedropper

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Posted 21 January 2014 - 10:55 AM

http://stargazerslou...erecting-prism/

I use the astroshop prism for terrestrial up to 100x and like it.

#5 Eddgie

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Posted 21 January 2014 - 11:06 AM

It did not appear to me that the OP is looking for a finder.

It seemed to me that he was looking for a diagonal.

And since he was the one that experssed the concern about quality, I was simply telling him that if it was important to him not to see s spike when using the diagonal at night, the quality of the diagonal is important.

The Baader people clearly understood that for this application (telecope use) you can't get an excellent result with a cheap Amici prism.

If the OP wants the best result, this will be the way to get it.

Anything else, he is taking a chance that it will get exactly what has been reported, which is spikes on stars and any glint sources in the image.

I have no interest in what the OP buys or does not buy, but it does appear to me that his interest is in a diagonal for his telescope and not a right angle finder scope.

#6 Jon Isaacs

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Posted 21 January 2014 - 12:07 PM

Dave

In my experience the Amici prism diagonals do show a spike but that is not a problem for you. What might be a problem is that generally they have a restricted clear aperture so you may not see the full field of view at low magnifications.

Jon

#7 genedalton

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Posted 22 January 2014 - 03:20 PM

The RACI from Scopestuff is in fact a prism diagonal, no visible spikes with the two I have been using with a binoviewer or a single low or high mag e.p., Gene

#8 Cotts

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Posted 22 January 2014 - 05:05 PM

Thanks, everyone. I'll cogitate for a while.

Stay cool, guys.

Dave

#9 RAKing

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Posted 22 January 2014 - 05:09 PM

Dave,

I use and recommend the Baader Amici T2 prism diagonal. I use it on Luna with my Traveler and also when I want to star hop to DSO with my star charts. I have it set up with a Clicklock holder and it works great with the smaller high-quality eyepieces, such as Panoptics and Naglers.

I have not seen any distracting line across the FOV.

My .02,

Ron

#10 *skyguy*

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Posted 23 January 2014 - 01:29 AM

If you are going to use this diagonal for framing objects prior to imaging ... a very important requirement is to have the diagonal precisely collimated. If the collimation if off, you'll center the object in the scope, replace the diagonal with the camera and the discover the object is now nowhere near the center.






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