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Bugsi
super member
Reged: 09/20/07
Posts: 114
Loc: Sunnyvale, CA
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Along similar lines to JimmyK's post asking for eyepiece advice for the 150mm Orion MCT, I'm wondering if anyone has any eyepiece recommendations for the Orion 90mm Mak.
I bought the 90mm Mak for my nephew a couple years ago and started him with the Orion 10mm and 25mm Plossls. My brother and his son find the Plossls to difficult to view because of the very short eye relief.
I use the Baader Hyperion 8-24mm zoom with my Orion 150mm Mak, and I'm wondering if anyone has used that eyepiece with the smaller 90mm Mak, and whether that would be a good or bad pairing with that scope. Simplicity is definitely better for my brother and nephew, as they also have trouble keeping an object in view long enough to stay in view when swapping viewers. I bought them the single axis tracking unit that I'll be installing for them when I visit over the holidays, and I'm trying to decide what eyepieces might be a good match for this scope so they can have a better viewing experience. I'm going to say that eye relief, ease of use, and optical performance are the three targets I'm trying to balance.
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Orion 150mm Mak, Orion 100mm Skyview Pro Refractor, Orion 80mm ShortTube Refractor.
Foothill Observatory, Los Altos, CA
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mwedel
super member
Reged: 12/16/07
Posts: 185
Loc: Claremont, CA
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I have a 90mm Orion Mak and use a 32mm Plossl as my widefield/finder eyepiece. Eye relief is good, I've never had any problems with kidney bean blackouts, and it's easy to swap that eyepiece out for another or back in if I lose my object--which sounds like it might be a concern for your relatives.
Just out of idle curiosity, how long have your brother and nephew been using the scope? I've had mine for almost two years and I've noticed that my ability to find and manually track objects has improved a lot over that span. When I first got the scope I sometimes spent half an hour sweating and cursing to get something into the field of view. Now I can usually get within one or two degrees just dead reckoning, even before I look through the finder. Oh, and speaking of finders, I upgraded mine to a 6x30 RACI, which helped immensely.
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Orion XT6 "Shaft"
Little Maks: Orion Apex 90, Celestron orange tube C90, Synta MC90
Edmund Astroscan "Baby Red"
76mm ongoing ATM experiment
Celestron UpClose 10x50
Celestron SkyMaster 15x70
10 Minute Astronomy
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Bugsi
super member
Reged: 09/20/07
Posts: 114
Loc: Sunnyvale, CA
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We're approaching 2 years on their ownership of the 90mm Mak. I agree that a 32mm Plossl should have satisfactory eye relief. I know their complaints were about the 10mm. I'm curious just how wide a view you get with the 32mm in that scope, as it's still a pretty long focal length scope. -Can you fit M45 in the view? I use the Orion Sirius Plossl 40mm as my widefield on my Orion 150mm, I wonder if it would vignette in the 90mm Mak.
I think the 10mm Plossl is reducing their interest in wanting to continue using the scope, and I think the single axis tracking controller will help. I ABSOLUTELY agree that a 6x30 RACI would be a much better finder than the one that ships with the scope. That's great to hear that it helped a lot on that scope, I'll look at picking one up. Good call!
I might just bring a bunch of my eyepieces with me, try them out in their scope, and order for them whatever I decide works best!
Edited by Bugsi (10/28/09 08:21 PM)
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Wes James
Post Laureate
Reged: 04/12/06
Posts: 3460
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Quote:
I might just bring a bunch of my eyepieces with me, try them out in their scope, and order for them whatever I decide works best!
Ultimately, that's the best way to do it. Individual preferences play such a major part... what someone thinks is best might not work for you- and visa versa. Experimenting with what you have costs nothing but time.
But I know, it's still a question you have to ask!!! I've done it myself! 
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Wes
Atlantic Beach, FL
Some bino’s from Miyauchi 5x32 Binon's up through Garrett 20x110 Signature's,
Some telescopes from a Stellarvue 80mm NHNG up through a couple of 8” reflectors…
And a wonderful 4.25" Delmarva Shiefspiegler!
Some good friends, made here on C/N.
Oh- several cats and a wonderful wife!
Anyone want a cat???? :-O
"When your work speaks for itself- Don't Interrupt" -Gamble Rogers
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scopethis
professor emeritus
Reged: 05/30/08
Posts: 638
Loc: Kingman, Ks
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I don't have the Orion 90mm Mak, mine is the C90 Mak. An EP that I use often in this scope is a Hyperion 8mm. It's kinda large but it has a great FOV and the eye relief is very good.
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slyke
super member
Reged: 02/21/08
Posts: 116
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I would recommend a 13mm Baader Hyperion (or Orion Stratus) to replace the 10mm Plossl. It gives you ~100x magnification with a comfortable eye relief. I used the 13 and 21 mm Hyperions in my StarMax and I thought they were a great combination. I also used a 9 mm eyepiece on the moon and planets but I would say it was the least used.
-Stephen
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bkruschwitz
member
Reged: 04/15/09
Posts: 40
Loc: Waco, TX
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Quote:
I'm curious just how wide a view you get with the 32mm in that scope, as it's still a pretty long focal length scope. -Can you fit M45 in the view?
Bugsi,
I use a formula (that I found somewhere on the Web) for calculating maximum true field of view for a given focal length of telescope: (57.3*27)/1250 = 1.24 degrees. The 1250 is the focal length (in mm.) of the Orion 90mm Mak. The other numbers are based on the field stop of the 1.25" eyepieces. By my calculation, a 32mm plossl, assuming it has a 46mm apparent field of view, gives a 39x magnification (i.e., 1250/32) and 1.18mm field of view (i.e., 46/39), so it will not vignette.
The Hyperion zoom, at the 24mm setting, would give 52x magnification and .96mm FOV.
I think your 40mm plossl has a 44 degree apparent field of view, which would yield 31x magnification and 1.41 degree field of view (and thus would vignette in that scope).
This cool site www.12dstring.me.uk/foveyepiece.php shows the apparent field of view for various scopes and eyepiece combinations on all of the Messier objects.
Best wishes,
Bob
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Orion XT8
Hyperion 8x24 zoom
Bushnell Legend 8x42
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mwedel
super member
Reged: 12/16/07
Posts: 185
Loc: Claremont, CA
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Quote:
I'm curious just how wide a view you get with the 32mm in that scope, as it's still a pretty long focal length scope. -Can you fit M45 in the view?
Not entirely. I can get the 'bowl' part, from Taygeta to Alcyone, but not Pleione and Atlas at the same time.
I just got a orange tube C90 from CNC today. The focal length is 1000mm (f/11, vs f/13.9 for the Orion Mak) and using a 30mm Kellner I can--just barely--get all the bright stars in the Pleiades into the same field.
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Orion XT6 "Shaft"
Little Maks: Orion Apex 90, Celestron orange tube C90, Synta MC90
Edmund Astroscan "Baby Red"
76mm ongoing ATM experiment
Celestron UpClose 10x50
Celestron SkyMaster 15x70
10 Minute Astronomy
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2703
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The formula fails to account for the vignetting caused by the central baffle in a 90mm Mak. This baffle opening is TINY!
My ETX 90 Vignettes with anything over a 20mm eyepiece.
Now you might not easitly detect it, but I do.
And if you want to see the exact point in the field where severe vignetting starts (and this is not hard vignetting, but rather the place were stars start to be cut off), it is simple to do.
Defocus a brignt star in a 32mm eyepiece. Now, start moving it towards the center of the field.
What you will see is that as the fresnel pattern gets about 60% from the center, the edge of the pattern will start to be cut off by a smooth curve (the shadow of the baffle). Continue further and you will see that by 75% of the distance from the center of the field, the Fresnel pattern will be cut in half (the star will be dimmed by half).
Past this, and the star gets to the point that it will almost be completly cut off by the edge of field.
The result of this is that when you look at a target in a field of rich background stars, the stars at the center will be normal brigntess, but the stars closer to the edge will be dimmed. At the extreme edge, most of the stars will simply be too dim to see.
So, you get a wide field, but you get a field that is badly damaged. Star Fields start to look like Globulars where there are stars in the center, but no stars at the edge of the field. You don't see your target "Framed" in the context of where it sits in the Galaxy, but rather you simiply frame it with an unnaturally dark space and a field stop.
I don't personally understand how people can accept this horrendous damage to the field, but if people are willing to see the sky in such an unnatural way, I guess it is really not any of my concern.
Check it though, and it is easy to see that I am correct in the physics of what is happening. Whether it bothers a specific observer though I guess is up to that individual.
Regards.
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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mwedel
super member
Reged: 12/16/07
Posts: 185
Loc: Claremont, CA
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Thanks for the info, I didn't know about that. How much variation is there in baffle dimensions among 90mm Maks? The baffle on my C90 (f/11) is pretty short. Haven't looked at the one on my Apex 90 (f/13.9), but I will. I will also try the test you describe and report back. Maybe not until after Halloween, though!
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Orion XT6 "Shaft"
Little Maks: Orion Apex 90, Celestron orange tube C90, Synta MC90
Edmund Astroscan "Baby Red"
76mm ongoing ATM experiment
Celestron UpClose 10x50
Celestron SkyMaster 15x70
10 Minute Astronomy
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Bugsi
super member
Reged: 09/20/07
Posts: 114
Loc: Sunnyvale, CA
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Eddgie, thanks for that excellent description of how to go about looking for field vignetting. That's exactly the sort of "How to" description that I wish I had more of back when I was starting out with telescopes.
Thanks also to the others with eyepiece advice. I have a much better idea of what eyepieces should perform well with this scope.
-Mark
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Orion 150mm Mak, Orion 100mm Skyview Pro Refractor, Orion 80mm ShortTube Refractor.
Foothill Observatory, Los Altos, CA
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2703
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It isn't just the lenght of the baffle (though that is a part of the equation).
The important dimension is the OPENING of the baffle.
Remove the visual back and look at the opening at the rear of the tube. The inside diameter determines when vignetting will occur. Again, because this cut-off is away from the focal plane of the eyepiece, the vignetting is somewhat "Soft" meaning that the transition from being fully illuminated to the edge of the field appears to drop off steadily, and because of this, you don't see a hard gray edge (except maybe RIGHT at the edge of the field).
Anyway, let me know what you see when you do the experiement.
Regards.
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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mwedel
super member
Reged: 12/16/07
Posts: 185
Loc: Claremont, CA
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I did the experiment just this evening with the Apex 90. With a 20mm EP, no vignetting, no problem. With a 25mm in and a defocused star I could see vignetting of the disk in about the outer 10% or less of the field. With a 32mm EP it started very early, about halfway to the edge of the field.
It's not the end of the world because my most used EPs on this scope are 25mm and shorter, but still, I had no idea that this was going on. Thanks for the pointers!
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Orion XT6 "Shaft"
Little Maks: Orion Apex 90, Celestron orange tube C90, Synta MC90
Edmund Astroscan "Baby Red"
76mm ongoing ATM experiment
Celestron UpClose 10x50
Celestron SkyMaster 15x70
10 Minute Astronomy
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2703
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Nothing like seeing it with your own eyes.
In focus of course the effect is simpy that objects near the field stop are dimmed. Some may still be visible, but really faint stars can totally disappear from the field of view. And that is the part that seems so strange to me.. People will obsess over tiny differences in performance at the center of the field, but ignore the damge done to the VAST MAJORITY of the field when pushing a design far past its limits!
Anyway, enjoy your scope. Don't be afraid to use a 32mm eyepiec, but just recognize that there IS damage to the view that is far worse than you might have previously relaized.
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
Edited by Eddgie (11/03/09 12:57 PM)
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