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Erik D
Carpal Tunnel
Reged: 04/28/03
Posts: 2551
Loc: Central New Jersey, USA
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Quote:
If you want correct image viewing at 60x and higher with no CA (false color) then an 8" or larger SCT with binoviewer on a Giro II mount is the lowest cost option.
LOWEST cost?
IIRC, My friend's Denk II binoviewer with power X switch was about $1,200, my Giro II DX mount ~$300, 8 inch SCT OTA ~$900, 9.25 inch SCT $1,300, WO 45 deg correct diagonal?
For someone desiring the ease of use & stereo view from a binoscope with RACI for under $750 the above system would be pretty far down my list as a lowest cost solution.
I don't think I'd want to assemble and move a 8in or larger SCT with Giro Mount, counter weight, premium binoviewer etc just for a quick look at 60X. I have used my 4 inF10 SCT for terrestrial viewing many times. I found it pretty awkward if I needed to locate objects quickly. It's nearly impossible without looking in the reverse image finder first.
Never did like seeing the 31% 2ndary mirror obstructions at low power in the daytime either. IMO using a binoviewer behind a bigger 8 inch OTA for terrestrial viewing is not user friendly. I'd recommend anyone thinking of that configuration to test drive first.
2 X Orion 80mm ED?
Erik D
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Joe Ogiba
Post Laureate
Reged: 02/14/02
Posts: 3358
Loc: NJ USA
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Then get a 5" Cat and put it on a tripod with $199 binoviewer for a quick look 60x view with correct image WO diagonal. I don't see the 2ndary mirror obstruction in my 5" Mak or C9.25 with binoviewer in the daytime.
Try pricing a binoscope with a pair of 80 ED's and all the parts needed to turn it into a binoscope.
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Pentax PF-80ED
Meade 102ED APO
Orion EON 72
120ST
Apex 127
C6 XLT
CR150
C9.25
XT10
Zeiss 7x42 FL
Canon 10x42L IS WP
15x50 IS
12x36 IS II
Garrett Optical 28x110 HD-WP Signature Series
Oberwerk BT-80 45
Apogee RA-88-SA
Denk II Power x Switch binoviewer w/13mm Ethos, 20mm Pentax XW's, 20mm Widescan III's.
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BoyntonStu
sage
Reged: 01/22/06
Posts: 263
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2 by 120ST is in the low cost 'binocular' quality optics solution, yet capable of over 100x.
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Joe Ogiba
Post Laureate
Reged: 02/14/02
Posts: 3358
Loc: NJ USA
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The cost of building a 120ST binoscope is alot more than you think. Oberwerk had that setup for $4,795 with mount .
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Pentax PF-80ED
Meade 102ED APO
Orion EON 72
120ST
Apex 127
C6 XLT
CR150
C9.25
XT10
Zeiss 7x42 FL
Canon 10x42L IS WP
15x50 IS
12x36 IS II
Garrett Optical 28x110 HD-WP Signature Series
Oberwerk BT-80 45
Apogee RA-88-SA
Denk II Power x Switch binoviewer w/13mm Ethos, 20mm Pentax XW's, 20mm Widescan III's.
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Erik D
Carpal Tunnel
Reged: 04/28/03
Posts: 2551
Loc: Central New Jersey, USA
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Quote:
Then get a 5" Cat and put it on a tripod with $199 binoviewer for a quick look 60x view with correct image WO diagonal.
I don't see the 2ndary mirror obstruction in my 5" Mak or C9.25 with binoviewer in the daytime.
Hold out a hand at arm length with palm facing away at eye level. You can see almost Everything beyond but the hand is smack in the middle of the field of view.
I don't see the secondary CO in my 4 inch F10 SCT if I use a 25mm /40X EP for day time views. FOV is about 1.25 deg. Switch to a 40mm/25X EP for a modest 2 deg FOV and the CO is visible as a faint black shadow in the center of field. Move my head around and it's like observing objects with a floater in my eye. Project the image on a cardboard and it's a white disk with ~30% dark center. Quite obvious and annoying to ME.
A 5 in 1540mm MCT yield a LOW Power of 38.5X with a 40mm EP. FOV? Close focus?
I don't follow the binoview forum but I am not aware of any $199 binoviewr packaged with a focal reducer.
A 5, 8 or 9.25 inch Cassegrain with binoviewer, wide angle EPs, WO 45deg premium image erecting prism on a Giro II mount and a surveyor tripod is an odd Collection of equipment. It might be of interest to a FEW people interested in exploring "what's possible" for terrestrial viewing. It's Not inexpensive for those who don't have already have all the pieces. It's Not quick to set up or easy to use........But I could be wrong. If so we should be seeing "package deals" from Orion or WO in the near future.
Erik D
PS. Orion lists a 37% focal reducer for SCTs priced at $150. Celestron F6.3 reducer I am not sure if the reducer will have an impact on the CO visible to my eyes in day time viewing.
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Joe Ogiba
Post Laureate
Reged: 02/14/02
Posts: 3358
Loc: NJ USA
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Who said $199 with focal reducer ? You don't need a focal reducer with Cat or SCT and I can't see the CO in my Mak with binoviewer even with a pair of 40mm eyepieces in the daytime.
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Pentax PF-80ED
Meade 102ED APO
Orion EON 72
120ST
Apex 127
C6 XLT
CR150
C9.25
XT10
Zeiss 7x42 FL
Canon 10x42L IS WP
15x50 IS
12x36 IS II
Garrett Optical 28x110 HD-WP Signature Series
Oberwerk BT-80 45
Apogee RA-88-SA
Denk II Power x Switch binoviewer w/13mm Ethos, 20mm Pentax XW's, 20mm Widescan III's.
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Erik D
Carpal Tunnel
Reged: 04/28/03
Posts: 2551
Loc: Central New Jersey, USA
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Quote:
Who said $199 with focal reducer ? You don't need a focal reducer with Cat or SCT....... and I can't see the CO in my Mak with binoviewer even with a pair of 40mm eyepieces in the daytime.
Quite right. No reducer needed with SCT/MCT. I mentioned the focal reduer because on rare occastions someone MAY decidecd to go birding with a 20 lb lb 9.25 in F10 SCT like yours. They might desire slightly LESS power than possible with a pair of 1.5 lb 40mm XW EPs. To me 58X/ 1.19 deg FOV is pretty high magnification for daytime viewing. I don't know if it's practical in the field if 40mm is my low power EP and I don't already have a Denk II binoviewer with X power switch.
Is the $199 WO binoviewer suitable for use with the $495 Pentax 40mm XW? My 40mm EP is a $40 Meade MA. It probably Enchanced the CO in day time viewing.....;-))
Erik D
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12565
Loc: Cumberland, R I , USA42N71.4W
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Erik,
field of view has nothing to do with it. Whether or not you will see the CO is based on exit pupil. And exit pupil has to be pretty darned big to see the CO. I'm not aware of ANY 5" SCT that would allow you to see the CO with a 40mm eyepiece. I've just never heard of it, regardless of the size of the instrument. You would need about an f/6 to f/5 instrument or faster to see the CO with a 40mm eyepiece. In all my years, I can't recall ever reading of anyone who has ever seen the CO in the image for exit pupils smaller than 7mm-8mm.
A 40mm eyepiece in a 8" SCT will generally have a 4mm exit pupil. In my 5" C5 it will have a 3.6mm exit pupil. Even in an 8" SCT with a 0.63 focal reducer, the exit pupil using a 40mm eyepiece would still be 6.3mm!
The lowest power I can get in my C5 is 34x with my 40mm eyepiece. That's a 3.7mm exit pupil. I cannot see the CO.
I've used my 30mm Ultima in my 6" Newt numerous times. It's f/5. that's a 6mm exit pupil. I cannot see the CO.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
Edited by EdZ (06/03/06 05:33 PM)
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Joe Ogiba
Post Laureate
Reged: 02/14/02
Posts: 3358
Loc: NJ USA
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Quote:
Quote:
Who said $199 with focal reducer ? You don't need a focal reducer with Cat or SCT....... and I can't see the CO in my Mak with binoviewer even with a pair of 40mm eyepieces in the daytime.
Quite right. No reducer needed with SCT/MCT. I mentioned the focal reduer because on rare occastions someone MAY decidecd to go birding with a 20 lb lb 9.25 in F10 SCT like yours. They might desire slightly LESS power than possible with a pair of 1.5 lb 40mm XW EPs. To me 58X/ 1.19 deg FOV pretty high magnification for daytime viewing if that's my low power EP and I don't have a Denk II binoviewer with X power switch.
Is the $199 WO binoviewer suitable for use with the $495 Pentax 40mm XW? My 40mm EP is a $40 Meade MA. It probably Enchanced the CO in day time viewing.....;-))
Erik D
You can't use 2" eyepieces in a 1.25" binoviewer and I don't go birding at all. If a bird is in my backyard when I have my C9.25/Denk II setup then I will look at it. If 58x is too high a magnification for daytime viewing for you then use something else that gives you lower power. I enjoy seeing a bird fill my 70-84 deg AFOV with detail better than any photo in a Bird book.
--------------------
Pentax PF-80ED
Meade 102ED APO
Orion EON 72
120ST
Apex 127
C6 XLT
CR150
C9.25
XT10
Zeiss 7x42 FL
Canon 10x42L IS WP
15x50 IS
12x36 IS II
Garrett Optical 28x110 HD-WP Signature Series
Oberwerk BT-80 45
Apogee RA-88-SA
Denk II Power x Switch binoviewer w/13mm Ethos, 20mm Pentax XW's, 20mm Widescan III's.
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Erik D
Carpal Tunnel
Reged: 04/28/03
Posts: 2551
Loc: Central New Jersey, USA
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Ed,
I did not say FOV has anything to do with seeing secondary shadow of SCTs in the day time. I made the point that one must use long focal ratio EPs in F10/F12 SCT/ MCTs to reach lower magnification with reasonable FOV. The longest EP I have is a Meade 40mm and the CO IS visible as a faint shadow in my 102mm F10 SCT at 25X. FOV is probably ~2 deg. Using a 127mm/1540mm Mak or 203mm/F10 SCT and a 40mm XW EP is even tighter. FOV will be 1.81 deg/38.5X for the the Mak and 1.38 deg/50.8X in the 8 in SCT. That's using a premium EP($495) with 70 deg APFOV.
Seeing the CO of MCTs at low power was disscussed in a CD thread a few month back: MCT as a spotting Scope
I guess there is another experienced observer who prefer not to use SCT/MCTs for daytime viewing.
Try projecting the image from a low power EP onto a white index card. It's there as a dark spot in the center. The size appears in proportion to ratio of CO: full aperature. Ie, 4mm exit pupil at 25X: ~1.6mm dark disk.(I did not measure with caliper, just a visual check) The first time I experienced it I was not sure what I was seeing. After I cofirmed what I saw it was easy to spot. This is not an issue for me for astronomy. Perhaps the CO shadow is more noticable in the daytime when my pupils are not fully dilated. The CO disk covers a larger % of the pupil...I hope PCAD can offer a better explanation if he reads this.
Just tried a 32mm TV plossl. Same result.
This thread started with disscussions of whether a pair of 120mm F5 ST OTA is a good basis to built a binoscope. Suggestions were made to use 5, 8, or 9.25 inch Cassergriains with a binoviewer and low power wide angle EPs as low cost sloutions. IMO, neither is. A $200 binoviewer is not the functional equivalent of a $1,200 deluxe unit with power switch+ $200 image erecting prism+ $500X2 EPs.......
My position is we should present pros and cons of each solution. I have a large collection of optical equipment, tripods and gadgets purhcased over the years to suit my fancy. My priority for selecting optics have evolved and the market place too. Some of the "Best Buys" I made just a few years ago are no longer.
Most importantly, the person seekiing advise usually have different requirement, preference and resources than I. The set up I assembled to meet my quirks and twists may be ill suited for another person. Knowing that is important before I make a suggestion. I try to explain what I would or would not recommend and WHY. Whether you or I can see the CO or not is less important. Explaining if the choice using a SCT with a binoviewer is a good alternative to a binoscope for intended application is.
Erik D
PS. Another observer referencing shadow of the SCT secondary at low power: C8 2nd Shadow Next to last paragraph.
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12565
Loc: Cumberland, R I , USA42N71.4W
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Well those were interesting posts. I would note that neither Mike nor Rich, in their posts, mentioned at what point they see CO. They both only mentioned, as does everyone I know, that at low magnifications it becomes visible.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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