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#51 pete123

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Posted 17 October 2018 - 04:24 AM

Depending on your focal length, the lower power 30-55 still will magnify where you are viewing easily. And the darker the sky, with a low power, will put on quite a show through the eyepiece. Planets you'll want to magnify, certain Messier objects, but like me with my focal length on my major scope, with a low power 82* eyepiece, would fit all of M45 in my eyepiece.

Thanks for that

I believe mine is a 2000mm focal lenth f/10   8 inch tube



#52 pete123

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Posted 17 October 2018 - 04:28 AM

how the hell do i upload pipictures to thithis forum



#53 aeajr

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Posted 17 October 2018 - 04:38 AM

okok i would like to ssay thanks to everyone who offerd advice im pleased i decided to join this forum , ive decided i will go with the celestron x-cel lx eyepieces , and i think i will go for an 18mm and a 2x barlow which i can then use with the 25mm plosll i already have to make a 12.5mm  and then the 18mm to make a 9mm , then i can add some more at a later date , the only thing  thats troubling me now is the ammount of talk on eyepieces that are being discussed from 30mm to 58mm , im finding it hard to imagen what you would actualy see through these as i thought telescopes were for magnification of the sky .

Quite understandable.   Many of us thought that telescopes are all about high magnification, but in reality a telescope is about gathering light.  The more light you gather the more detail you can see and the brighter the image. 

 

But many targets look best under low power.    My 8" telescope can push to 400X if the atmosphere is very clear and calm.  But I spend most of my viewing time under 200X

 

The Pleiades is about 2 degrees wide which means you have to be at a fairly low power in order to get an image that wide.    The Double Cluster looks great at about 40X.    Alberio is a double star that is split at about 20X.    

 

In order to see the entire Andromeda galaxy at a dark site you will need to be able to see over 3 degrees wide.  I believe the North America Nebula is over 4 degrees wide.  In order to see that wide you need to be at pretty low power even with very wide view eyepieces.    Go back and look at the discussion of low power wide view eyepieces.  Any of them offering you a 3 to 4 degree field of view in YOUR scope?  No. 

 

Planets, double stars and globular clusters are examples of targets that often call for higher power, say over 150X.  Many large DSOs are best at lower powers, often under 100X. 

 

I have spent entire evenings of observation at less than 80X because the targets I am viewing look best that way.  Open clusters are a good example.  The widest True FOV eyepiece I have for my 8" scope with 1200 mm FL only offers me 2.2 degrees true FOV at 31X.     

 

That is why many of us have more than one telescope.  Short focal length scopes can offer low power wide views that are optimized to these large, low power targets.   That doesn't mean they can't be used on planets, they can.  But that is not their strength.   I have two scopes that have 400 mm FL and can give me 4 degree FOV at 12.5X for those really big targets or to view star vistas or to explore constellations.   These low power wide views can be wonderful.

 

And there are many targets I prefer in my 10X50 binoculars over my telescope, the Pleiades being one of them.  I can get the entire Pleiades in the 2.2 FOV, but I think they look better at 10-15X in binoculars. 

 

You will learn. 

 

 

 

Your scope is optimized more to high power use.   The widest your scope can go, in stock form, is about 1.3  degree true field of view.  That is not wide enough to see the whole Andromeda Galaxy or the Pleiades, for example.   

 

Fortunately, 1.3 degrees FOV is likely wide enough for about 80%+ of what is up there.   So feel good about your scope and what it can do, but realize that high power is not always the best way to go.  That is why we have been talking so much about low power wide views and that is why I posted that discussion about eyepiece strategy.  Go back and read again.   


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#54 aeajr

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Posted 17 October 2018 - 04:45 AM

how the hell do i upload pipictures to thithis forum

Lower right of the reply window, click more reply options.


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#55 pete123

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Posted 17 October 2018 - 05:08 AM

I CANT BELIVE I DIDNT SEE THAT LOL , SO HERES A PIC OF MY SCOPE

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#56 pete123

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Posted 17 October 2018 - 05:12 AM

i havent actualy used any of it yet still waiting for a clear sky , i was wandering if the no name diagnol flip mirror is actualy anygood , as i cant see any name on it at all and im wandering if its a cheap and nasty.



#57 Jond105

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Posted 17 October 2018 - 05:23 AM

I have a feeling, if all that was bought used, whoever owned it previously must have liked it and is probably good. You got a heck of a score on a used scope with accessories I'd say
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#58 pete123

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Posted 17 October 2018 - 06:12 AM

I have a feeling, if all that was bought used, whoever owned it previously must have liked it and is probably good. You got a heck of a score on a used scope with accessories I'd say

i felt it was a good deal even though its the older version , i managed to get him down to £800 but i had to drive around 70 miles to collect , it was this or the newer cpc i was offerd for the same price with no accessories , and after reviewing they say this is the better model as there was plenty of problems with the newer cpc mount.


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#59 pete123

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Posted 17 October 2018 - 06:37 AM

You asked a simple question about using a barlow.   What follows is about setting an eyepiece strategy for your ongoing purchases.  If this is not of interest, just skip it. 

 

========================================
I am going to outline my eyepiece strategy.  After accumulating over 20 eyepieces I have focused in on this approach.   I have used this for my Orion XT8 8”/203 mm Dob, 1200 mm FL, as the example.  But the same strategy applies to my 80 mm F5 refractor and my 127 mm F15 Mak.    If your FL is different you can redo the calculations for your scope. 

 

STRATEGY SUMMARY

  • One or two low power wide view eyepieces
  • One or two midrange eyepieces
  • Two to four high power eyepieces that include a plan for the top target magnification for that scope
  • Or, Zoom plus Barlow to cover mid range and high power
  • Planning to use a barlow can save you money

Selecting an Eyepiece - Orion telescope
This is a very general discussion of eyepieces and why there are a variety of designs
https://www.youtube....h?v=m7u9Q5hV7yc

 

Useful Formula -

Highest target top magnification =  aperture in mm X 2   So, for my 8" Dob, 203 mm aperture that would be 406X under exceptional good conditions.  For my 80 mm this would be 160X. For my 127 mm this would be 254X.   This is not a limit it is just a target to establish a range of magnifications.  

 

Power or Magnification = Focal Length Scope / Focal Length eyepiece

 

True Field of view  = Apparent Field of View eyepiece (AFOV) / magnification of eyepiece (This is a simplified formula that will provide a very close approximation under most circumstances)

 

Lowest power – often a spec provided by your telescope maker. But it can be whatever you like.   I would recommend something with an exit pupil of no more than 7 mm.  Exit Pupil = Focal length of eyepiece / Focal ratio of scope. If your scope only takes 1.25” eyepieces, your lowest power widest view would be a 32 mm Plossl (50 degree AFOV) to define your lowest power.  If you have a 2” focuser you can likely go lower and wider.

 

Now divide the mag range into three parts.  Using my Orion XT8i as the example, Orion recommends lowest useful as 29X, highest useful as 300X and highest theoretical as 406X.  So I will work out the eyepiece range somewhere between 29X and 300X    For this scope, that beaks down to up to under 100X for low power.    100X to 200X for medium power.  Over 200X as high power.

 

Here is a sample range, for illustration purposes based on a 1200 mm FL.   Remember the formula is:  Power or Magnification = Focal Length Scope / Focal Length eyepiece

 

 

  31X = 38 mm

  60X = 20 mm

 

100X = 12 mm

120X = 10 mm
150X = 8 mm

171X = 7 mm

200X = 6 mm   (can be achieved with a 12 mm and 2X barlow)

 

The above magnifications work almost every night at my site, under my observing conditions.  The magnifications below work when the atmospheric conditions are very good.  See the reference section for information on “seeing”.

 

240X = 5 mm   (can be achieved with 10 mm + 2X barlow)

266X = 4.5 mm
300X = 4 mm   (can be achieved with 8 mm + 2X barlow)
Over 300X – I usually barlow one of my other eyepieces as I can rarely use this much mag

 

You don’t have to have all of these magnifications, but the more you have the better you can match to your target and conditions. Note that the mm gaps get smaller as the power goes up. 

 

Here is how I have addressed this range for my Orion XT8i.  I use many of the same eyepieces in my other two scopes. 

 

Low power

 

38 mm 2” - I have the Agena Astro SWA, same as the Orion Q70 series. I use the 38 mm 70 degree AFOV in my XT8i.  Happy with it but it does show edge distortion in my F5.9 scope.  I consider it acceptable for the price but some would not.  https://agenaastro.c.../agena_swa.html

 

20 mm 2” - I also have the Meade 20 mn 82 degree as my second 2” low power wide view that performs well for me in my F5.9 scope.
https://www.astronom...pieces_c75.aspx

 

 

 

For my Single FL 1.25” eyepieces  I have the Meade and ES 82s.   Like them very much

 

Meade 82 degree
https://www.astronom...pieces_c75.aspx

 

Explore Scientific 68 degree and 82 degree line.  I have two of the 82 degree and really like them.  Many reports compare these favorably with the premium eyepieces.
https://agenaastro.c...scientific.html

 

 

 

TIGHT BUDGET? – Get a zoom and a barlow     An 8-24 mm zoom eyepiece plus a barlow somewhere between 2X and 3X will give most people the full typical mag range of their scope $100.   For your scope, if you get the zoom I would not get a barlow unless you need to push higher than the zoom will go. 

 

 

THE ZOOM EYEPIECE INSTEAD OF SINGLE FOCAL LENGTH EYEPIECES – This is my favorite eyepiece. 

 

The zoom is single eyepiece that effectively replaces a range of eyepieces.  Works like the zoom lens on a camera.   For example an 8 mm to 24 mm zoom would overlap 4 eyepieces above and provide every magnification between them.  If I include a 2X barlow for use with the zoom it will provide every magnification from 50X to 300X without gaps, my primary planning range.

 

The zoom sounds great, but there is a trade-off.  The field of view of the zoom runs from a narrower AFOV at the 24 mm range to a wider FOV at the 8 mm range.  So, like any approach, the zoom is a compromise.  I find that compromise quite acceptable when weighed against the benefits listed below, I prefer the zoom. 

 

I use the Baader Hyperion Zoom.  8-24 mm as my only eyepiece in the midrange and I barlow it to extend it to the high range for the XT8.  But as I have a low power wide view 20 mm eyepiece I tend to use the zoom mostly in the 18 mm to 8 mm range for the midrange.  

 

Lower cost zoom – Celestron 8-24 – This was my first zoom.  Works well at the price and a good way to test your interest in zooms. $66

Higher priced Zoom – Baader Hyperion 8-24 mm – My main eyepiece in my Orion XT8i – $290
https://agenaastro.c...lanetarium.html

 

  • I never expected the zoom eyepiece to become my primary eyepiece, but it has.
  • With a zoom, the eyepiece seems to disappear as you just move in and out at will, no swapping, no thinking about eyepiece changes
  • The Celestron 8-24 zoom is good and comparable to my Plossl eyepieces
  • The Baader Hyperion is great and comparable to my Explore Scientific eyepieces
  • Watching doubles split as I rotate the barrel is wonderful
  • One filter serves over a wide range of magnifications, no screwing and unscrewing to try other eyepieces
  • Moving smoothly between small changes in magnification helps when seeing is not the best
  • I am always working at the optimum magnification for this target.
  • Sharing the view with others is easier, especially in my manual tracking Dob - I hand it over at low mag so it stays in the view longer.  They zoom back in to whatever magnification works best for them.
  • My eyepiece case has been greatly simplified
  • Kids love the zoom

When I observe, 90% of the time, in all of my scopes, I use one or two low power, then the zoom for the midrange.  Then I barlow the zoom for the high range if I need it, and that is all I use.  I have single FL eyepieces in my kit, but they are rarely used.

 

 

REFERENCE RESOURCES

 

Barlow Lens - A barlow is an intermediate optical device that goes between the eyepiece and the objective lens or primary mirror.   It effectively gives each eyepiece two magnifications, one with and one without the barlow. A 2X barlow is used in the example below.  For visual use, barlows ranging from 1.5X to 3X are common.   So, if you have 3 eyepieces properly spaced and add a barlow, you now have 6 magnifications.   You can read more about barlows at this link:  http://www.telescope...rlows/99807.uts

 

 

What is SEEING and why it can be bad.  How it will limit how high you can go.

This is not a problem with your telescope or your eyepiece.

http://www.skyandtel...ing-the-seeing/
http://www.damianpeach.com/seeing1.htm
http://www.damianpea...m/pickering.htm

 

Lower Cost Single FL eyepieces – for your Medium to high power magnifications.

AT Paradigm line 60 degree AFOV.   I don’t have these but I read so many good reports about them, especially in scopes of F5 or higher focal ratios.   The Agena Astro Dual ED are the same eyepieces under a different label.

https://www.astronom...pieces_c52.aspx

https://www.cloudyni...s/?hl=+paradigm

 

Zoom eyepiece review – Includes the Celestron zoom –

This is an older review and the tech specs may not match the current Celestron zoom, but I find the comments nicely reflect the performance of the Celestron zoom I own –

http://www.chuckhawk...m_eyepieces.htm

 

Baader Hyperion Mark IV Zoom review   - The current model  -

https://astronomycon...ox-january-2018

 

A very good discussion, by Al Nagler, about eyepieces and magnification for those who want to go a little deeper.
http://www.televue.c...page.asp?id=102

 

Eyepiece Designs -  This is the one I turn to when I am trying to understand or explain the differences between the various designs.  There are many different designs, Many are named
for their original designer, such as Huyghens, Ramsden, Kellner, Plossl, Konig, Erfle, Branden and Nagler.
http://www.chuckhawk...ece_designs.htm

 

Discussion about Paradigm eyepieces
https://www.cloudyni...s/#entry8229760
https://www.cloudyni...s/?hl=+paradigm

Meade 82 vs. ES 82

https://www.cloudyni...e-82-eyepieces/

so aeajr  do you think id be better off with the zoom to sart with , i have a spare £180 to get a x cel lx and a barlow  or i could get the baader zoom  , but it will be a while before shell let me spend anymore money on telescope gear after this  , so ill have to be happy for a while , obviously im a begginer and not going to be looking at anything too extravigant for a while mainly the moon and planets , and maybe i should get the zoom go from there, tell the truth i was a bit sceptical about the zoom i had looked at it but thought surely a zoom lens cant be any good compared to dedicated fixed lens , but youve changed my mind.


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#60 SloMoe

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Posted 17 October 2018 - 07:04 AM

Morning Pete, you certainly have a lot of replies, but everybody enjoys eyepieces,,,,, 

Your scope will have some wiggle every time you touch the thing, be it for adjusting a zoom or focusing, so a good chair to sit in while the wiggle goes away is nice, set the tripod up low, that will reduce some of the wiggle, 

 

I've read most of them, I picked up that there were some suggestions for 2" eyepieces, my experience with my 8" sct is that there's almost nothing to gain by it and the expense of 2" vs. 1.25" is a no-brainer.

One persons suggest a 6.3 focal reducer, yes to that one, 

 

ES 82° eyepieces are worth the money in your scope, the 8.8mm and 11mm are the two I would start with, and will hook you.

 

Sometimes the gang here get stuck on numbers and values, nothing beats the quality of the view, another great thing about the ES 82° line of eyepieces is that they are parafocal with each other so you can swap out eyepieces and not need but a touch on the focus knob, if you have a wide variety of manufactures eyepieces you'll find yourself working the focus knob more than just enjoying the view. 

 

Here's a link to a gang of astronomers on your side of the pond, might be nice to hook up with them if you already haven't,

 

https://stargazerslounge.com/

 

Here's a link to an online fov & magnification calculator, your scope will only provide about 1.2° tfov so eyepieces that exceed that may have edge of the fov aberrations/distortion that detract from the quality of the view.

.

http://www.csgnetwork.com/telefov.html

 

I noticed in your pictures of your scope that there's a camera and a flip mirror, are you going to be imaging or visual viewing, if your imaging then forget what I said about the ES eyepieces, the flip mirror is ok for centering the star for imaging but for viewing it's marginal.

 

If viewing is your primary use of the scope you'd want a decent diagonal to keep the light path pristine, like a dielectric mirror or prism.


Edited by Mike W., 17 October 2018 - 07:30 AM.

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#61 pete123

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Posted 17 October 2018 - 09:14 AM

Thanks , yes they been very helpfull

#62 aeajr

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Posted 17 October 2018 - 11:59 AM

so aeajr  do you think id be better off with the zoom to sart with , i have a spare £180 to get a x cel lx and a barlow  or i could get the baader zoom  , but it will be a while before shell let me spend anymore money on telescope gear after this  , so ill have to be happy for a while , obviously im a begginer and not going to be looking at anything too extravigant for a while mainly the moon and planets , and maybe i should get the zoom go from there, tell the truth i was a bit sceptical about the zoom i had looked at it but thought surely a zoom lens cant be any good compared to dedicated fixed lens , but youve changed my mind.

Do you have a camera?  I would bet it has a zoom lens.   Would you give up that zoom lens?   Neither would I.

 

When I purchased a 35 mm camera back in the 80s, the first accessory I purchased for it was a zoom lens and that is the one that stayed on the camera all the time. 

 

If you shoot photos with your phone, do you zoom in on the pictures after you take them?  Sure you do.  And some of the new smartphones have optical zooms built in because, well, they are great!

 

The Baader zoom offers many values which I outlined in my earlier post.   The Baader zoom is as good as many of the single FL eyepieces in terms of quality of view, just not as wide as some.  My zoom eyepieces are my primary eyepiece for the midrange and high powers in all of my scopes, and I have 15 other eyepieces to choose from in this range.

 

In my 1900 mm FL Mak, I typically don't use a barlow with the zoom.   In my 1200 mm FL Dob and 400 mm FL refractors I often team the zoom with a barlow.   

 

In my GoTo scopes I don't feel a great need for wide FOV eyepieces as the scope tracks so I don't need the drift time that wide FOV eyepieces offer.  I have wide FOV eyepieces that I can use but I rarely pull them out, preferring to stay with the zoom.     

 

So, yes I would highly recommend the Baader zoom.   It will give you EVERY magnification between 84.7X and 254X.  That will be the full and inclusive practical midrange to high range of your scope on most nights.  That is how I use my scopes.  

 

However, over time you may wish to add a single FL wide eyepiece here and there.  Until then you will have all the magnifications you need in the midrange and high power up to 254X.

 

You are not likely to need a barlow right away and may never need one, depending on your typical "seeing" and transparency conditions.  If you want to get one, I can suggest this one which is fairly inexpensive.  I think is a relabled GSO.   

https://www.firstlig...h-t-thread.html

 

It offers both 1.5X and 2X depending on how you use it.   2X may not be all that useful in your scope because of your long focal length. But 1.5X could be useful on a zoom in your scope.    My zoom is set up with a 1.5X GSO barlow element as standard configuration to get me the best, most useable range in my 1200 mm FL scope.   I don't think you will need it, at least not right away.

 

After the zoom I would focus on the low power wide view options which we have all made such a fuss about.   If you get the zoom then this is where I would focus next.

 

That is what I would do if I had your scope. 


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#63 pete123

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Posted 17 October 2018 - 12:16 PM

That is what ive decided to do , rhank you very much for the help , ive learnt alot in just a few days , and yes i will look in to a low power wide view eyepiece for the future
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#64 Dave Mitsky

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Posted 17 October 2018 - 12:44 PM

I was under the impression that you already had a 2" diagonal, pete123.  If that's not the case and you don't want to go the 2" diagonal and eyepiece route, a focal reducer may be in order to maximize your SCT's TFOV.  As has already been mentioned, it won't be all that large compared to that of a short-focal-length telescope.

 

In light (so to speak) of what you mentioned about a cap on additional spending, a zoom eyepiece may a good choice and the Baader Planetarium Hyperion zoom is a very good one.  However, because of the zoom design the apparent field of view is unfortunately rather small at the 24mm and 20mm settings.  As the effective focal length decreases, the AFOV increases to a maximum of ~68 degrees.

 

Here's an excerpt from the comprehensive review posted at https://astronomycon...binoviewing.66/

Over the course of testing the Baader Hyperion Mark IV Zoom, the eyepiece showed itself to be a capable and potent observing tool. Optically it provided a bright, high contrast, and controlled view that allowed it to keep up with even premium wide-field eyepieces like the Pentax XWs. Although its Abbe Orthoscopic-like AFOV at the longer focal lengths may be too restrictive for some observing situations, its wide field performance at the shorter focal lengths and its flexibility to perform the function of several eyepieces make it a powerful accessory for any telescope.

 

Dave Mitsky



#65 pete123

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Posted 17 October 2018 - 12:53 PM

Ive orderd the Baader zoom , its done , and yes i have a 2'click lock with reducer but my diagnol is 1.25
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#66 aeajr

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Posted 17 October 2018 - 01:12 PM

I have no experience with a 2" adapter on a 1.25" diagonal on an SCT.  Others will have to advise you on that.   The Baader zoom will work fine in a 1.25" diagonal.  No adapter required. 



#67 pete123

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Posted 17 October 2018 - 01:16 PM

I have no experience with a 2" adapter on a 1.25" diagonal on an SCT. Others will have to advise you on that. The Baader zoom will work fine in a 1.25" diagonal. No adapter required.



#68 pete123

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Posted 17 October 2018 - 01:18 PM

The the click lock is in the rear of the scope with a 1.25 reducer the dignal goes in to that which is a 1.25 , so no problem

#69 pete123

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Posted 17 October 2018 - 01:27 PM

 

I have no experience with a 2" adapter on a 1.25" diagonal on an SCT. Others will have to advise you on that. The Baader zoom will work fine in a 1.25" diagonal. No adapter required.

 

If you look at the back of the scope youll see the 2"clicklock with a 1.25 reducer with the 1.25 flip mirror attached

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#70 aeajr

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Posted 17 October 2018 - 03:31 PM

The question/issue that I have read about is not whether you can put a 2" diagonal on the scope but whether the hole in the scope is large enough to benefit from 2" eyepieces.   I don't know anything about your scope so I don't know whether the hole is too small to truly accomodate 2" eyepieces. 



#71 pete123

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Posted 17 October 2018 - 04:31 PM

Morning Pete, you certainly have a lot of replies, but everybody enjoys eyepieces,,,,, 

Your scope will have some wiggle every time you touch the thing, be it for adjusting a zoom or focusing, so a good chair to sit in while the wiggle goes away is nice, set the tripod up low, that will reduce some of the wiggle, 

 

I've read most of them, I picked up that there were some suggestions for 2" eyepieces, my experience with my 8" sct is that there's almost nothing to gain by it and the expense of 2" vs. 1.25" is a no-brainer.

One persons suggest a 6.3 focal reducer, yes to that one, 

 

ES 82° eyepieces are worth the money in your scope, the 8.8mm and 11mm are the two I would start with, and will hook you.

 

Sometimes the gang here get stuck on numbers and values, nothing beats the quality of the view, another great thing about the ES 82° line of eyepieces is that they are parafocal with each other so you can swap out eyepieces and not need but a touch on the focus knob, if you have a wide variety of manufactures eyepieces you'll find yourself working the focus knob more than just enjoying the view. 

 

Here's a link to a gang of astronomers on your side of the pond, might be nice to hook up with them if you already haven't,

 

https://stargazerslounge.com/

 

Here's a link to an online fov & magnification calculator, your scope will only provide about 1.2° tfov so eyepieces that exceed that may have edge of the fov aberrations/distortion that detract from the quality of the view.

.

http://www.csgnetwork.com/telefov.html

 

I noticed in your pictures of your scope that there's a camera and a flip mirror, are you going to be imaging or visual viewing, if your imaging then forget what I said about the ES eyepieces, the flip mirror is ok for centering the star for imaging but for viewing it's marginal.

 

If viewing is your primary use of the scope you'd want a decent diagonal to keep the light path pristine, like a dielectric mirror or prism.

thanks for the info mike , i have signed up for the stargazers lounge but i havent got replies like i have here , and yes primary will be viewing , the photos are from the guy who was selling so it was all rigged up , but i will need a decent diagnal that wont break the bank as the fip mirror is all i have at the moment unless i put the lens straight in to the scope.



#72 pete123

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Posted 17 October 2018 - 04:34 PM

all though i will try the camera at some stage but one step at a time 



#73 pete123

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Posted 17 October 2018 - 04:35 PM

The question/issue that I have read about is not whether you can put a 2" diagonal on the scope but whether the hole in the scope is large enough to benefit from 2" eyepieces.   I don't know anything about your scope so I don't know whether the hole is too small to truly accomodate 2" eyepieces. 

yes my hole is big enough for a 2" eyepice 


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#74 jallbery

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Posted 17 October 2018 - 06:14 PM

yes my hole is big enough for a 2" eyepice 

I think what Ed is referring to is the size of the rear baffle tube.  In the case of a c8, it is about 37mm in diameter.  This is smaller than the field stop of the widest 2" eyepieces.  So in a scope like yours, there will be some vignetting for to the limitations of this baffle tube.  However the focal place is far enough away from the baffle that it is not a hard vignetting, but a rather gentle dimming.   You can detect this dimming if you find a just barely visible star in the center of the field and then pan the scope to move the star to the edge of the field.  However the dimming is--at least the my eyes-- not obvious at all.    



#75 Achernar

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Posted 17 October 2018 - 06:59 PM

The main reason to use Barlows other than in effect doubling or more the number of eyepieces you have is the fact most eyepieces have longer eye-relief in the lower power models than the higher power models. Many simpler eyepieces also have teensy weensy eye lenses to peer into when the focal length is short. In other words you almost have to place your eye in contact with the eye lens to see anything. A high quality Barlow solves both problems and will not detract from the view, poor quality Barlows on the other hand do. That is why I use TeleVue Barlows mainly for imaging, but they also do very well visually as well. However, you would be well served with eyepieces that for your telescope yield low, medium and high magnifications plus the Barlow for the times where extra-high magnifications are advantageous.

 

Taras




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