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2" diagonal question


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i am waiting for a Megrez 72 APO, 432mm focal length.

i have 1.25" eyepieces and am not about, on my budget, to get any 2" eyepieces at the moment.

i am considering getting a better dielectric diagonal. Question is:-

am i going to get any benefit from buying a 2" dielectric diagonal over the 1.25" dielectric diagonal when using 1.25" eyepieces, i.e. will my eyepiece diameter cause me to lose any potential benefit of buying the 2" diagonal.

thanking you all in anticipation of some assistance.

Mark

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Well personally i got a 2" dialectric diag even tho i got no 2" ep's.

Reason being

1. Quality was much better than my supplied 1.25" diags

2. If i ever upgrade to 2" i now have a diag that fits

Astronomica sell a very nice brand name copy btw.

HTH

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"2 is best I have three 2" eypieces and about (ten or thirteen not sure without counting) 1.25 eyepieces I think you get the best possible views sing the 2" Diagonal I have an Orion And a TeleVue 2" Diagonals whic the TV the is best out of the two I use the Orion one with the Antares 80mm :D

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Mark - if you're buying a reasonable quality diagonal in the first place there's probably little benefit from going to 2". The only possible benefit might be that with diagonals any problems tend to be at the edges of the diagonal mirror.. A 1.25" eyepiece in a 2" diagonal will never use the edges of the mirror thereby using only the better quality central part.

As I've said though, if its a reasonable quality diagonal that shouldn't be a problem.

James

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good point Maccers

if i go for 2" my ideas so far are:-

WO 2" dielectric

Burgess Optical 2" dielectric 1/10 wave error and 1.25" recessed adaptor (cheaper than first)

Astronomica 2" dielectric wave error not specified (cheaper than 2nd by about £5.00

any thoughts

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good point Maccers

if i go for 2" my ideas so far are:-

WO 2" dielectric

Burgess Optical 2" dielectric 1/10 wave error and 1.25" recessed adaptor (cheaper than first)

Astronomica 2" dielectric wave error not specified (cheaper than 2nd by about £5.00

any thoughts

here are the details of my TeleVue 2" as taken from

This 90° 2” mirror-type star diagonal has Everbrite dielectric mirror coatings for 99% reflectivity. In addition to higher reflectivity than a conventional aluminum or silver coated diagonal, the Everbrite coatings also provide higher contrast and resolution during critical planetary, lunar, and binary star observations. The diagonal is designed for refractors with 2” focuser drawtubes, but will also work with Schmidt-Cassegrains by adding optional rear cell adapter #7785C. Optional 1.25” adapter #2715C allows the use of 1.25” eyepieces in the diagonal. A safety stop at the bottom of the 2” eyepiece holder tube prevents 2” eyepieces or 2” Barlows from hitting the surface of the mirror. However, if you use the #2715 1.25” adapter, it is possible that an exceptionally long 1.25” Barlow may project far enough into the diagonal to contact the mirror surface. Any damage caused in this way is not covered by warranty.

The mirror housing and its 2” focuser and eyepiece holder barrels are precision-machined from a single block of solid aluminum, rather than being simply a pair of less-rigid tubes screwed into a flimsy plastic mirror housing or sheet metal stamping, as is the case with lesser diagonals. A solid metal backplate over 4/10ths of an inch thick holds the mirror securely in place to assure permanent collimation of the diagonal’s parts. The 2” barrel that fits into the focuser or visual back is internally antireflection threaded for higher contrast. It is also threaded to accept standard 2” (48mm) filters. A groove cut into the outside of the 2” barrel acts as a safety stop to keep the diagonal from falling should the scope’s visual back or eyepiece holder thumbscrew loosen slightly from cold or use. The 2” eyepiece barrel uses a non-marring soft brass compression ring to hold eyepieces in place, rather than a thumbscrew that contacts the eyepiece barrel directly. The diagonal is finished in a non-reflective matte satin black finish.

This is an absolutely premium 2” star diagonal that will give you all the visual performance your scope is capable of delivering. It's a worthy upgrade for virtually any Schmidt-Cassegrain, Maksutov-Cassegrain, or refractor that uses a 2” star diagonal.

(just for your research you understand :D)

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thanks radioactive, however i cannot stretch to £230 odd for a dielectric. the burgess is 99% reflectivity, 1/10 wave error, brass compression rings on diagonal and 1.25" adapter, plus a safety wedge to prevent fall out.

i don't know what the burgess is made of.

to add to my list i have also seen the GSO at FLO but that is at about my maximum.

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I've got a WO 2" dilectric diagonal and an Antares 1.25" £20 jobbie and TBH if I was being really, really picky I'd say the WO is ever-so-slightly better. I think you'd hard pushed to tell the difference between either of the three you've mentioned in terms of performance. If all three have compression ring fitments, I'd go with the cheapest.

also, know the Megrez is new but am assuming the diagonal i need would be push fit and not SCT thread????????

I'd be amazed if it has a SCT thread! It should be a push fit.

Tony..

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I recently compared a Tele Vue Everbright Dielectric diagonal with a £20 Antares one (both in the 1.25 inch fitting) and found virtually no difference optically between them. I posted my review on SGL:

http://stargazerslounge.com/index.php/topic,19853.0.html

I would go for an ordinary 2 inch diagonal (The Antares push fit's are pretty good) because it gives you the option to use 2 inch EP's and will work perfectly well with 1.25 inchers as well.

There are probably better things to spend money on than very high-end diagonals IMHO.

John

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i am aware and somewhat agree with the views of many who say "don't worry about the diagonal, save your money and spend it on eyepiece instead".

Maccers view re the 2" diagonal (1.25" eyepiece will only use central portion of mirror and therefore no problems if edge defect) seems a plus to buy a 2". i have a 1.25" on my Skymax 127 Mak and wanted a reasonable dielectric for when i get the Megrez 72. i am assuming if i get the 2" i am also not going to be able to use it on the Skymax Mak? i am not at home to measure the hole at the bottom of the Mak tube at the moment.

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mcut,

I believe the William optics 2 Inch Dielectric Coated Diagonal comes with an additional SCT connector as well as the push fit allowing it to be used on both (as advertised on Ian King Imaging website) as well as a 1.25" adapter - a bit expensive though.

I hope this helps

Steve

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I am content with an "ordinary" (cheapish) 2" push fit diagonal on my ST102 - Probably about "comensurate" with the general quality too! But if someone MIGHT want to try out or "upgrade" to 2" eyepieces (at some later time):

Fairly expensive (but I still worth it) for my MAK127 was the Baader T2 modular diagonal. The 35mm mirror one with T2 nose-piece adaptor works well (screws onto!) the MAK127 and provides an increased 35mm optical path, so the MAK can now take 2" eyepieces (with appropriate eyepiece holder) upto field stops of that diameter - e.g. the Baader 31mm 72 Deg Aspheric (Even a Pan 35 / 68 deg?) WITHOUT vignetting! Reasonably effective compression type 2" (or 1.25") eyepiece holders too. Doubtkess also useful (with alternative push-fit nose piece etc.) for an "up-market" small refractor, where (IMO) a full-sized 2" diagonal rather "overload" the back end... aesthetially anyway! :D

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Well personally i got a 2" dielectric diag even tho i got no 2" ep's.

Reason being

1. Quality was much better than my supplied 1.25" diags

2. If i ever upgrade to 2" i now have a diag that fits

Astronomica sell a very nice brand name copy btw.

HTH

Kevin's answer above,is a carbon copy of what I was about to suggest. I have the Astronomica 2" dielectric, and can vouch for it's quality. Very, very good price too. There is always a good chance, down the line, you may get a 2" eyepiece, for a big wide view that 1.25" eyepieces just can't pack into that smaller barrel. The only thing I'd check first, is, what amount of 'in' focus is available on the 72. A 2" diagonal will eat into this a bit, due to the bigger lightpath.

Andy.

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I guess it depends what is the "weakest link" in your scope. A few percent in the diagonal may not effect very much, if the "main" mirror (or whatever) is loosing a lot of light. Aside: I was quite surprised the other day, when shining a bright LED torch through the exit of a MAK127 - To some extent, you can actually see the light source through the deposited secondary mirror on the correction plate! Not easily quantifiable, but intriguing, nonetheless... :D

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