| cfraser |
| (member) |
| 07/03/09 02:00 PM |
Hyperion Zoom with FL Reducer on 8 SE
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The FL reducer would be the Antares f6.3 one, functionally like the Celestron. My objective is to get lower power as that's what I mostly like. What I'm wondering is how the FL reducer affects my apparent FOV. Can you tell I'm terrible with optics beyond the real obvious?
The 8 SE is otherwise stock optics. Thanks.
| Fogboundturtle |
| (sage) |
| 07/03/09 02:07 PM |
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Re: Hyperion Zoom with FL Reducer on 8 SE
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You get a wider field of view with the Antares F6.3. I tried it last night on the moon and it kinda flattened the field a little.
| cfraser |
| (member) |
| 07/03/09 03:25 PM |
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Re: Hyperion Zoom with FL Reducer on 8 SE
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Do you know what effect it has with the zoom at 24mm? Does it sort of partially compensate for the reduced AFOV at that FL? Does this question even make sense?
| Tel |
| (Post Laureate) |
| 07/03/09 03:39 PM |
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Re: Hyperion Zoom with FL Reducer on 8 SE
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Hi cfraser,
A very warm welcome to CN and to joining us on this our special Celestron Nexstar Forum !
Your 8SE has a focal length of 2030mm. When you use your f/6.3 Reducer this has the effect of reducing that figure to 1279mm. (2030 X 0.63 =1278.9).
Your Hyperion Zoom has a range of focal lengths as follows : -- 24mm, 20mm 16mm 12mm and 8mm, so the magnification each of these focal lengths produce is gained by dividing the focal length of the 8SE by each focal length of this Hyperion Zoom eyepiece.
i.e.
Without your focal reducer:
2030/24 = Mag. X85
2030/20 = Mag. X102
2030/16 = Mag. X127
2030/12 = Mag. X169
2030/8 = Mag. X254
With your 6.3 focal reducer:
1279/24 = Mag. X53
1279/20 = Mag. X64
1279/16 = Mag. X80
1279/12 = Mag. X107
1279/8 = Mag. X160
The True Field of View, (TFOV), is determined by dividing the Apparent Field of View, (TFOV), of any eyepiece by the Magnification it produces with any given telescope. The Apparent Field of View is a property of the eyepiece resulting from its optical construction.
Thus for example, a Ploessl eyepiece has normally a nominal 50 degree AFOV. If then it's, for example, a 25mm, the magnification it produces in your unreduced focal length 8SE will be 2030/25 = X81.
To establish the TFOV therefore, for this 25mm EP when used on on your 8SE : divide its AFOV by the Magnification it produces: ( i.e. 50/81 = 0.62 degree or 37.2 arcminutes [60arcmins. = 1 degree: thus: 60 X 0.62 = 37.2arcmins).
On the other hand, with your focal reducer in place, the same EP would give you a TFOV of 50/(1279/25 = X51)= 0.98 degree or 59 arcmins.
Now to your Hyperion Zoom,. According to specification its AFOV ranges between 50 and 68 degrees. If you work on the basis that the 24mm and the 20mm are 68 degs. AFOV and the 16mm, 12mm and 8 mm are 50 degs. AFOV, then the TFOV for each eyepiece offered by the zoom would be as follows when using your 6.3 reducer :
24mm = AFOV. 68degs./X53 = TFOV. 1.3degs.
20mm = AFOV. 68degs./X64 = TFOV. 1.1degs.
16mm = AFOV. 50degs./X80 = TFOV. 0.63deg.
12mm = AFOV. 50degs./X107= TFOV. 0.47deg.
8mm = AFOV. 50degs./X160 =TFOV. 0.31deg.
You can no doubt now work out the figures in the absence of the focal reducer should you so wish to do so.
These TFOV figures are, as said, based on the assumption that the 24mm and the 20mm EPs in the "Zoom" have an AFOV of 68degs. the other three, 50 degs. This may not be quite the case but it's probably about right.
Hope my maths are right ! !
Best regards,
Tel
| Bob Griffiths |
| (Postmaster) |
| 07/03/09 04:17 PM |
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Re: Hyperion Zoom with FL Reducer on 8 SE
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Gosh Tel....
Just wondering if you ran the batteries in you calculator down doing all that math.... LOL
Even if you did the above is another GREAT post from you....
However I not really that sure at what point a Focal reducer fails to be effective (or offers anything worth the effort) ...I seem to remember reading that one gains nothing if you use one with any possle eyepiece less then 12 mm.
I just do not know...
Bob G.
| cfraser |
| (member) |
| 07/03/09 05:34 PM |
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Re: Hyperion Zoom with FL Reducer on 8 SE
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Thanks guys. I did make a spreadsheet for this, but I assumed the FOV of the zoom was 50 at 20mm and 24mm, and 68 at the shorter FLs. I think that's roughly what it is. By the numbers, it seems as though the AFOV is substantially improved at the longer zoom FLs...to the point it may exceed the capability of the optical back's 1.5" opening even.
I was wondering how it might look in actuality though, if the numbers lie.
It is at the lower powers where I was hoping to get an especially wider view with the reducer, to help compensate for the zoom's narrower FOV there. I know this zoom EP is not supposed to work as well with faster scopes though, but I think the 8 SE at f6.3 is supposed to be borderline OK (??). I guess I'll find out, I ordered the reducer anyway...the gear shop phoned while I was making the post and I thought what the heck. I am pretty sure there are some factors here that I don't know about: I don't actually believe that the reducer will improve my low power AFOV beyond what the zoom itself can do...that's how little I know about real-world optics.
| Tel |
| (Post Laureate) |
| 07/03/09 09:06 PM |
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Re: Hyperion Zoom with FL Reducer on 8 SE
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Hi cfraser,
Peter9 has just pointed out to me quite rightly, that in fact the 50 degrees AFOV on these EPs applies to the longer focal length 24mm and 20mm sections of this Zoom ocular. The shorter focal lengths give the wider AFOVs: i.e. 68.5 degrees.
Thus the following figures should now apply to your 8SE with your 6.3FR in place :
24mm : AFOV 50/ Mag.X53 = TFOV 0.94 deg. or 56 arcmins.
20mm: AFOV 50/ Mag.X64 = TFOV 0.78 deg. or 47 arcmins.
16mm: AFOV 68/ Mag.X80 = TFOV 0.85 deg. or 51 arcmins.
12mm: AFOV 68/ Mag.X107= TFOV 0.64 deg. or 38 arcmins.
8mm: AFOV 68/ Mag.X160= TFOV 0.43 deg. or 26 arcmins.
To give you some kind of comparison, remember that the moon is approximately 0.5 deg. or 30 arcmins in diameter.
Here also is a link which provides some data and reviews relevant to the Hyperion Zoom.
http://www.birdforum.net/showthread.php?t=73147
Hope this helps a little further and apologies for the error in my AFOV assumptions.
Best regards,
Tel
| Tel |
| (Post Laureate) |
| 07/03/09 09:16 PM |
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Re: Hyperion Zoom with FL Reducer on 8 SE
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Quote:
Gosh Tel....
Just wondering if you ran the batteries in you calculator down doing all that math.... LOL
Even if you did the above is another GREAT post from you....
However I not really that sure at what point a Focal reducer fails to be effective (or offers anything worth the effort) ...I seem to remember reading that one gains nothing if you use one with any possle eyepiece less then 12 mm.
I just do not know...
Bob G.
Hi Bob,
Thanks for you kind comment. That took a while and I still got it wrong ! It wasn't a calculator though: the beads fell off my abacus !
Anyway, I've made a fresh calculation relating to the use of the Zoom on an 8SE with a 6.3 FR. Please take a look above if you wish.
For my part now, I'm off to bed. I've been testing some new imaging software outside tonight, ("Nebulosity") and it's now coming up to 2:15am. Needless to say, I'm bushed !
Best regards and good night to all !
Tel
| cfraser |
| (member) |
| 07/03/09 09:26 PM |
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Re: Hyperion Zoom with FL Reducer on 8 SE
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Thanks Tel. I made a mistake in my reducer spreadsheet somewhere...calcs for TFOV came out larger at 20/24mm than the optical back should support...what got me wondering about the real-world results.
It sounds like a few people have done this with the Hyperion zoom (further googling) and it seems to work just fine. I also like that the FLR lens seals the optical back from dust etc., something I never thought of, it's kind of dusty here...
I was really trying to get some decent-quality magnification in the 50X range, without having to largely upgrade the back optics to make fancier EPs really worthwhile at this point. Likely in the future though. I'll report once I get to test it, for closure.
| ibase |
| (Carpal Tunnel) |
| 07/04/09 04:31 AM |
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Re: Hyperion Zoom with FL Reducer on 8 SE
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Sorry for weighing in late but upon coming across this thread, I've done some actual testing with the Baader Hyperion 8-24mm zoom (my favorite EP) and Celestron f/6.3 focal reducer with the C8 and these are my findings:
From my personal observations and estimate with the Hyp zoom, there is a marked reduction of fov from 20mm (where the fov is very much like my Televue 20mm plossl) going to 24mm. On the other end, there is that marked increase in fov from 12mm going to 8mm where the fov opens up real wide to give an immersive porthole wide view which looks more like 70ish than the published 68-deg max. In-between there is just a gradual increase/decrease of fov depending on where you're going.
With the f/6.3 focal reducer installed and using the standard diagonal, the view at the 24mm setting on the Hyp zoom shows an estimated 30 to 40% increase in fov as compared to the FR not installed. Of course there is the usual decrease in magnification when the FR is installed. But by my estimate, if at 20mm the fov is very close to that of a Televue 20mm plossl and if the TV 50-deg published fov were to be assumed to be the actual fov of the Hyp zoom at 20mm, then I would say that at 24mm the actual fov of the Hyp zoom may be less and is maybe around 45-deg only.
In conclusion, with the FR in place, the actual fov of the Hyp zoom at 24mm would roughly be around ~60 deg only, not really much and still cannot be considered as a "wide-field" view in the normal sense of the word. This is the reason also why I opted to get a dedicated Hyperion 21mm - to offset the relatively narrow fov of the zoom at these focal lengths. Hope this helps.
Best,
| Bob Griffiths |
| (Postmaster) |
| 07/04/09 10:01 AM |
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Re: Hyperion Zoom with FL Reducer on 8 SE
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Easy solution, but expensive, is to do what I did and buy a Denkmeier 2" Power switch Diagonal...it has both a 2x Barlow and a Focal reducer built into it... which means you do not need to buy a Barlow and you do not need to buy a focal reducer plus you have upgraded to a very good 2" diagonal ...
Then spend more money (sound familiar) and buy a couple of low power 2" eyepieces...
All of my 26 mm and lower power eyepieces are 2"
and all my under 25 mm higher power eyepieces are 1.25... BUT since I have the Denk each eyepiece gives me 3 different magnifications and 3 different FOV's ..all with the push of a lever BUT with a heck of a lot of refocusing especially if going from the Barlowed Mode of say a 20 mm eyepiece (200x) directly to the Focal reduced mode which yields 67x .. I've learned to do it in steps and go from 200x down to 100x (regular mode) then drop down to 67x...
Actually I personally do 80 percent of my viewing using lower power 26 and above) eyepieces then I do higher power...so the 8-24 zoom would not get a heck of a lot of use... I wish they had a 25-40 zoom eyepiece...
Bob G.
| cfraser |
| (member) |
| 07/04/09 02:02 PM |
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Re: Hyperion Zoom with FL Reducer on 8 SE
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Yes, I know this is a cheap way to try to get what I want, and I know I really need 2" EPs. But I'm just getting started with the 8 SE and want to find out what I *really* want/use before putting much coin into it. I figured the quality of these two pieces was good enough to get a small taste. There is the other issue that I'm nowhere near any even moderately dark sites, so too much FOV can be a hindrance...a balancing act that I'll have to better determine. I don't want any $500 EPs that I only get to use maybe once a year.