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Any users of a 4" f4 FINDER?

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#1 tcmzodiac

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Posted 21 November 2012 - 09:33 AM

Hello all,

Im sprucing up my old 4.25" f4 newt in order to use it on my dob as a finder and general RFT. I built my scope with the ability to balance this load on the UTA without the need for counterweights. The RFT's primary is a very nice older Edmund and the coatings are in great condition.

I know that...being a newt..the RFT will be more "fiddly" than a refractor would be (I have a 60mm f3.6 finder too, as an alternative, not installed at the same time)..requiring collimation which will then offset the aiming with the main scope, but...the EP's of the RFT and the main scope will be in close proximity; Im really looking forward to popping back-and-forth in order to enjoy the two differing views.

Anyone else do this?

#2 Jarad

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Posted 21 November 2012 - 10:29 AM

I have mounted an ST-80 on a newt to use as a finder (80mm f5), which has about the same focal length, but a bit less aperture.

I enjoyed that combo, especially on large objects like Andromeda, Pleiades, etc. If you have a spare nebula filter, you can have some fun looking around the Veil (see the whole thing in the finder, a section in the main scope), or the North American Nebula. I still like setting up both my 14.5" dob and my 101mm refractor nearby, and go back forth on the big objects for a wide view then a "zoomed in" view.

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#3 Jon Isaacs

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Posted 21 November 2012 - 10:51 AM

Hello all,

Im sprucing up my old 4.25" f4 newt in order to use it on my dob as a finder and general RFT. I built my scope with the ability to balance this load on the UTA without the need for counterweights. The RFT's primary is a very nice older Edmund and the coatings are in great condition.

I know that...being a newt..the RFT will be more "fiddly" than a refractor would be (I have a 60mm f3.6 finder too, as an alternative, not installed at the same time)..requiring collimation which will then offset the aiming with the main scope, but...the EP's of the RFT and the main scope will be in close proximity; Im really looking forward to popping back-and-forth in order to enjoy the two differing views.

Anyone else do this?


I have tried a smaller reflector as a finder. I came to the conclusion that refractors are much superior to reflectors as finders. With a small, fast reflector, off-axis illumination is a problem, you can get the widefield views but not the well illuminated widefield views.

Jon

#4 tcmzodiac

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Posted 21 November 2012 - 11:04 AM

Jon, very true but on a cost per inch aperture basis the newt wins. In addition, Im not nearly as picky about the view in the RFT as I am about the view in the main scope.

But you are right, a 4" f4 refractor would be grand!

#5 Jim Romanski

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Posted 21 November 2012 - 11:29 AM

I have that exact setup with a 4.25" F/4 reflector. I believe that mine was built from one of the old Coulter kits. It works very well and because it's such a small mirror and I only use it for low power it doesn't go out of collimation much.

I have a hard time calling it a finder scope though. I think of it as an aux scope. The 4.25" scope itself has a built in flip down finder like a questar. It also has a Rigel red dot finder.

There are some objects like M31 and the Pleiades that look better in a small rich field scope. I love being able to look through the little scope then back over to the main scope a 17.5" reflector. The big scope uses dual focusers for high and low power by pivoting the secondary.

I have some better pics but here's one I had in my email.

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#6 Jim Romanski

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Posted 21 November 2012 - 11:32 AM

Here's another pic.

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#7 tcmzodiac

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Posted 21 November 2012 - 12:31 PM

Thats great! Isnt it nice to have the two focusers so near each other...Im looking forward to that.

#8 Jim Romanski

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Posted 21 November 2012 - 12:43 PM

I can switch between low and high power without having to rebalance.

This scope also has a rotating top to make the viewing positon easier. It's still in a beta testing phase but for the most part it works well.

#9 tcmzodiac

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Posted 21 November 2012 - 01:09 PM

Anything that we can do to improve the ergonomics is really important, IMO. A fidgety observer drops a full magnitude at least! :)

#10 tubehead999

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Posted 21 November 2012 - 02:34 PM

I added a piece of red oak and mounted my Starblast on it [note blue tape holding hex key]....I use a 20MM T2 with it so, the coma is not that invasive. It actually works well as a finder [around 4 degree FOV?] ...I can do minor adjustments by shifting the dovetail and it also freed up a mount with the piggybacking of the Starblast. Since this scope rarely gets used at the house, the less stuff I have to carry to darker skies, the better.

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#11 Jon Isaacs

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Posted 21 November 2012 - 03:12 PM

Jon, very true but on a cost per inch aperture basis the newt wins. In addition, Im not nearly as picky about the view in the RFT as I am about the view in the main scope.

But you are right, a 4" f4 refractor would be grand!


It's not so much the quality of the view but rather the need for a finder to be well illuminated off-axis. And too, fuzzy-fuzzy stars are very useful in picking out small, faint fuzzies...

When all is said and done, I believe an 80mm refractor makes a better finder than a 114 Newtonian. I just fit a 80mm F/5 with a WO 2 inch Crayford from the parts box. With a 31mm Nagler or 35mm Panoptic, its an awesome widefield scope, somewhere around 6 degrees TFoV.

Jon

#12 tcmzodiac

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Posted 21 November 2012 - 03:36 PM

Hi Jon, I have no doubt that you are right. If I owned a decent 80mm f5 Id surely use it as you have! :)

I do have a nostalgic desire to use the 114mm...it's all that is left of my 1970 Edmund Deluxe Space Conquerer (aka "Palamar Junior"). I chopped it down years ago...the tube and mirror cell are all that is left of the original configuration.

One nifty thing tho...you gotta admit that the EP placement will be comfy! :)

#13 tubehead999

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Posted 21 November 2012 - 03:59 PM

Yeah...been there, Jon, but, with this scope, the weight issues were tremendous.....minimal weight for maximum move-ability. I also won the luck of the draw and received a nice specimen from Orion years ago; otherwise I wouldn't have gone to the trouble of mounting a 2 inch focuser and an Antares secondary to it. Actually, it is the only scope I have ever bought from Orion that I have kept for any length of time :).

I really like the Telrad and then popping down to the Starblast, if need be. This scope was fitted for ease of transport and strictly for DSO's in darker skies than the Bortle 11 :grin: I have here at the house. The ST-80 I had on it , plus a decent eyepiece necessitated a tremendous counter-weighting system...just not worth it to me...I am happy with the 4 degrees if I need it ...

But, as we know, each to his own ....

#14 Jim Romanski

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Posted 21 November 2012 - 05:21 PM

When all is said and done, I believe an 80mm refractor makes a better finder than a 114 Newtonian. I just fit a 80mm F/5 with a WO 2 inch Crayford from the parts box. With a 31mm Nagler or 35mm Panoptic, its an awesome widefield scope, somewhere around 6 degrees TFoV.

Jon

I agree with you that a 114mm scope isn't ideal as a finder. However, I also don't think an 80mm Scope is the right choice for a finder either. To me 6 degrees FOV isn't enough for a finder but it's great as a RFT.

I mentioned above that the my little 4.25" scope has a flip down finder like a Questar. The flip down finder allows you to look through the same eyepiece as the main scope. The finder is 30mm using an Amici prism for corrected views. With something like the 24mm Panoptic I get 11-12 degrees FOV. I can star hop around and when I think I'm in the right place flip up the finder and I'm looking through the 4.25" Scope. Then I move my head over and look through the big scope.

BTW - The little 4.25" scope is much lighter than my AT72ED (which would also make a nice Aux scope).

My Late Father-In-Law designed and built the little gizmo. Here's a picture of the mechanism.

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#15 Jon Isaacs

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Posted 22 November 2012 - 04:57 AM

To me 6 degrees FOV isn't enough for a finder but it's great as a RFT.



A 6 degree TFoV is plenty for me, that's more than the typical 8x50. I use a Telrad to get close, a magnifying finder if necessary.

But my point was really that an 80mm F/5 refractor is better as a finder than an 114mm F/4 Newtonian, it offers a potentially wider field of view that is better corrected and more fully illuminated.

Weight is an issue with any finder, particularly with a Dob, but it can be mounted close to the altitude pivot point where it has no effect on the balance.

Jon






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