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Deep sky observing eyepiece advice needed...

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#1 ClusterHunter110

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Posted 09 January 2013 - 07:03 PM

Looking for an eyepiece for deep sky viewing in my 127mak. Right now I'm using a 26mm Plossl, and it's a pretty good preformer. But I want something that gives me a little bit of a larger perspective (or as in less magnification). But I'm on a limited budget of $55 so I can't get a premium eyepiece yet. I'm looking at Orion's Sirius Plossl 32mm as the best one, but when I go to stellarium and use the ocular view, depending on magnification terms, they look almost the same...will there be a difference between a 25mm eyepiece and a 32mm eyepiece? Or are there any other eyepieces good for deep sky viewing? :help: Thanks in advance :whistle:

#2 Jon Isaacs

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Posted 09 January 2013 - 07:21 PM

Looking for an eyepiece for deep sky viewing in my 127mak. Right now I'm using a 26mm Plossl, and it's a pretty good preformer. But I want something that gives me a little bit of a larger perspective (or as in less magnification). But I'm on a limited budget of $55 so I can't get a premium eyepiece yet. I'm looking at Orion's Sirius Plossl 32mm as the best one, but when I go to stellarium and use the ocular view, depending on magnification terms, they look almost the same...will there be a difference between a 25mm eyepiece and a 32mm eyepiece? Or are there any other eyepieces good for deep sky viewing? :help: Thanks in advance :whistle:


Dan:

One of the disadvantages of the ETX-125 is that 1900mm focal length, the field of view is very limited. A good 32mm Plossl will provide you with the maximum field of view, it will be noticeably wider than with the 25mm Plossl but it will still be well under 1 degree.

For wider fields, you have the Meade 60AT-T, if I am remembering correctly, that's a simple 60mm F/6, it should be good for the Pleiades and the like.

GSO 32mm Plossl.

I like the GSO 32mm Plossls, I have two of them but both are older Celestrons, I bought one back in 1996, they might have changed... :)

Jon

#3 newtoskies

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Posted 09 January 2013 - 07:25 PM

I have both those ep's from Orion and there is a bit of a difference when I view with my 6" dob. You can see more with the 32mm. The eye relief is bigger with the 32mm of course. I actually prefer the 25mm and having my eye close to the ep. there is too much stray lp that enters from the flood and street lights where I am.
I manage to get nearly all the M45 stars in fov using the 32mm.
Hope this helps a little. I am sure more experienced members will chime in soon who know more about ep's than I do.

#4 ClusterHunter110

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Posted 09 January 2013 - 07:44 PM

@Jon: I was trying to look for this website but I couldn't remember the name of it. I'm glad you brought it back to my mind! It seems this is a much better deal than Orion's Sirius, both the coating and the price. Also, does Orion have free shipping with their accessories?

@Rob: Well sometimes my ETX isn't fully accurate (and I should've included this to my post), so I have to scan the area to find the object. Another reason why I need a new DSO EP is perhaps easier to scan the object. Maybe even having fun looking through starfields like Cygnus or Saggitarius... :grin:

#5 newtoskies

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Posted 09 January 2013 - 08:12 PM

I love to just explore constellations with the 32 and 25mm. Once I find an object then I add the 2xBarlow for better views. My next ep's are a 20 and 17mm.

#6 molniyabeer

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Posted 09 January 2013 - 08:43 PM

I've seen a 40mm plossl out there that might work, too. I have a 127mm mak and I use a GSO 32mm plossl with it a lot but I'd love to try a bit lower power. Saw a 40mm at the local Good Will store but it was part of a larger kit that they would not let me part out.

My 32mm in the 127 mak will give me maybe 3/4 of a degree true FOV.

#7 ClusterHunter110

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Posted 09 January 2013 - 09:24 PM

I've seen a 40mm plossl out there that might work, too. I have a 127mm mak and I use a GSO 32mm plossl with it a lot but I'd love to try a bit lower power. Saw a 40mm at the local Good Will store but it was part of a larger kit that they would not let me part out.

My 32mm in the 127 mak will give me maybe 3/4 of a degree true FOV.


But the 40mm does have a smaller FOV than the 32mm, which is why I think the 32mm would be a little more fun to use. What kit was at your Good Will store? And how often does astro equipment show up at Good Will stores?

#8 Tony Flanders

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Posted 10 January 2013 - 08:02 AM

Will there be a difference between a 25mm eyepiece and a 32mm eyepiece?


In one word -- yes. It's not like night and day, but it's quite significant. That's what I would get if I owned the same scope.

#9 Jon Isaacs

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Posted 10 January 2013 - 08:29 AM

But the 40mm does have a smaller FOV than the 32mm, which is why I think the 32mm would be a little more fun to use. What kit was at your Good Will store? And how often does astro equipment show up at Good Will stores?



The 40mm will have a smaller AFoV but an identical TFoV. In most situations, situations the larger AFoV is an advantage but in an F/15 scope, there are times when the brighter image (larger exit pupil) is an advantage. It is not a huge advantage but the brightness of a nebula or any extended object is related to the square of the exit pupil.

In the F/15 ETX-125, the exit pupil with the 32mm will be 2.1mm (32mm/15) and with the 40mm it will be 2.7mm, an object will be 56% brighter in the 40mm. This is not a lot but for some objects it can be helpful.

In a faster scope this would not be a concern, trading field of view for image brightness, because faster scopes are capable of providing brighter images. In an F/5, the 32mm would produce a 6.4mm exit pupil which would be 9 times as bright as the ETX-125 though at 1/3 the magnification.

One thing to look into is a focal reducer, it would need to be a full aperture focal reducer and will probably vignette but it can allow for a wider field of view.

I once owned an ETX-125, the GOTO worked well but this very issue of field of view and image brightness did not suit my observing style, I consider maximum field of view of about 0.84 degrees to be a serious limitation for a 5 inch scope. My 25 inch F/5 Dobsonian is capable of a 0.83 degree TFoV...

Just some stuff to think about.

Jon

#10 Jerry-rigged

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Posted 10 January 2013 - 02:04 PM

Dan:

One of the disadvantages of the ETX-125 is that 1900mm focal length, the field of view is very limited. A good 32mm Plossl will provide you with the maximum field of view, it will be noticeably wider than with the 25mm Plossl but it will still be well under 1 degree.

For wider fields, you have the Meade 60AT-T, if I am remembering correctly, that's a simple 60mm F/6, it should be good for the Pleiades and the like.

GSO 32mm Plossl.

I like the GSO 32mm Plossls, I have two of them but both are older Celestrons, I bought one back in 1996, they might have changed... :)

Jon


Back before Christmas, there was a long thread about 32mm eyepieces, and several people spoke well of the GSO 32mm plossl. I bought one right after Christmas, nice price, quick delivery from AgenaAstro, and I really like it. it is not a huge difference between the 32 and the 25/26/28 eyepieces I had been using, but it is noticeably wider, and still has a decent wide AFOV. Those other three are a no-name Chinese 25mm plossl, 26mm Meade 4000 plossl, and a 28mm Edmunds RKE. Oddly, all 3 have almost the exact TFOV - right at 1 deg. However the GSO 32mm is about 1.4 TFOV, and about the same 52-53 AFOV as the 25mm Plossl.

So, long post to say, I agree, get the 32mm GSO. :)

#11 BigC

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Posted 10 January 2013 - 02:44 PM

Here is an inexpensive 40mm ,looks very similar to no-name one I have.

http://www.ebay.com/...-7mm-1-25-4-...

FWIW, my 25/26 are used more than 32/40 except in 2" where 26 and 32 are about equally likely .

#12 John Kuraoka

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Posted 10 January 2013 - 06:25 PM

I think I triggered that thread about the 32mm eyepiece. It's here by the way:
http://www.cloudynig...5582593/page...

After careful consideration, and making a serious attempt to understand the nuances explained by knowledgeable folks, I decided not to buy anything until I'd taken up Jon's offer to let me actually look through each of the eyepieces under consideration in my own scope. I hope to do exactly that next week!






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