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I wear glasses! Plus question about Barlows

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#1 steve-in-kville

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Posted 16 February 2013 - 11:03 AM

I wear glasses, as I am sure many here do. I often use my scope with others, some wear glasses, some do not. I am looking at extended relief EP's but I am quit lost as to where to start. I currently am using the 10mm and 25mm Plossls that came with my scope.

I also would like to add a Barlow but I've heard that it would make my views too dark for my 90mm. So what's the take on that?

#2 howard929

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Posted 16 February 2013 - 11:41 AM

Baader Hyperions all boast a 20mm eye relief. A little pricey but they're reported to be pretty good.

#3 russell23

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Posted 16 February 2013 - 11:43 AM

I wear glasses, as I am sure many here do. I often use my scope with others, some wear glasses, some do not. I am looking at extended relief EP's but I am quit lost as to where to start. I currently am using the 10mm and 25mm Plossls that came with my scope.


There are quite a few options out there that have enough eye relief for use with eyeglasses depending upon how much you want to spend per eyepiece.

Less than $80 per eyepiece options:

Astrotech Paradigms: 60 deg AFOV enough eye relief to see the field stop with glasses on. Very sharp with excellent coatings. No problems with blackouts. FL available: 5mm, 8mm, 12mm, 15mm, 18mm, 25mm. I have the 15mm and find it to be outstanding. Cost $60 each.

Meade HD-60: Plenty of eye relief for wearing eyeglasses. Very good perfomers but not as good as the Paradigms IMO. Come in FL of 4.5mm, 6.5mm, 9mm, 12mm, 18mm, and 25mm. 60 deg AFOV. $79.95 per eyepiece.

Celestron X-cel LX: Celestron's version of the Meade HD-60. $74.95 per eyepiece.

Astrotech Long eye relief eyepieces: 20mm of eye relief which is easily accomodated with eyeglasses. 55 deg AFOV. These are a nice sharp, low cost option.

BST Flat Field eyepieces (available at Agenaastro): The 27mm has a 53 deg AFOV, 19mm has a 65 deg AFOV, and 16mm has a 60 deg AFOV. All 3 eyepieces are very solid performers that have plenty of eye relief for use with eyeglasses. These eyepieces are also available in some FL from Astronomics, Smart Astronomy, and Orion. Cost is ~$75 each unless they are on sale.

I've had at least one eyepiece from all of these lines and my favorite is the 15mm Astrotech Paradigm followed by the BST Flat fields. Given that the Paradigms have the lowest cost of all of they would be my recommendation.

If you are looking to spend over $100 per eyepiece you will open up some wider field options such as the Astrotech AF70's, Celestron Ultima-LX, Baader Hyperions all of which have 17-20mm of eye relief and 68-70 deg AFOV. New these cost ~$120 each. Used maybe ~$90 each.

Expensive eyepiece lines that would have enough eye relief includ the TV Delos and Pentax XW's each with 20mm of eye relief and 72 or 70 deg AFOV. These will cost $330-370 new or $240 to $330 used.

I also would like to add a Barlow but I've heard that it would make my views too dark for my 90mm. So what's the take on that?


It depends upon which eyepiece you barlow and what magnification factor your barlow has. When the exit pupil gets smaller than ~1mm the image starts to get dim - with a 0.5mm exit pupil generally considered the smallest you ever want to go -but I believe some people will push the exit pupil even smaller than that. You can find the exit pupil in several ways. One way is just to divide your scope's aperature by the magnification. Another way is to divide the eyepiece focal length by the telescope focal ratio. So if your 90mm is the f/10 model then your 25mm plossl will give 25mm/10 = 2.5mm exit pupil and your 10mm plossl will give a 1mm exit pupil. I generally find that for deep sky objects I like exit pupils in the 1.5mm to 3mm range the best so in your scope that would be any eyepiece with 15mm to 30mm FL.

So the 15mm Astrotech Paradigm would give you 60x, a 1 deg field of view, and a 1.5mm exit pupil and with the 90mm F/10 achromat you would find that to be an outstanding combination. I have the Skywatcher 90mm f/10 so I know what you're working with.

If you wanted to add a barlow whether or not the view is too dim depends upon which eyepiece you barlow. With a 2x barlow your 25mm plossl will give 72x and a 1.25mm exit pupil. I would look to get a decent quality barlow if you are going to go that route. As with eyepieces the cost jumps up with quality.

Keeping to less than $80 per item I would suggest two barlows for you to consider if you choose to get a barlow. First is the Explore Scientific 2x barlow. It cost $79.95 and is of a design similar to the TV powermates. Another option you might consider is the Baader 2.25x barlow - which costs $69 (Available at Agenaastro). One nice feature with the Baader barlow is that you can unscrew it from the adapter and thread it directly into an eyepiece for a 1.3x magnification - so it gives you more options.

I have the Explore scientific barlow and feel it is excellent. I'm pretty picky about barlows and consider this one a keeper. The Baader barlow I have not used but is getting excellent reviews. You can find lower cost barlows, but generally those lower cost barlows are just average in performance.

Dave

#4 EdZ

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Posted 16 February 2013 - 01:08 PM

Same answer that I gave about 2-3 weeks ago in the refractor forum.

for high powered eyepieces with decent eye relief, try the TMB Planetariess. They are very good eyepieces and I use them with glasses on all the time. Available from Astronomics for $40 each in 4mm thru 9mm.

For medium powers I'd recommend the Astrotech Paradigm, I also use these. the 12mm is my favorite. 12mm, 15mm and 18mm are all good. again see Astronomics. these are $60.

Also by Astrotech and available thru Astronomics, the FlatField 19mm is very good. $80. I use a pair of these for binocular viewing and binoviewer.

These are all long eyerelief eyepieces that are very well corrected. They don't have 20mm of eye relief, but that is really very long. In fact, even TV Radians are more like 17mm. The longer 18mm-19mm focal lengths are a little less corrected than the others. Aslo, these are ALL 58-60° AFOV eyepieces, +/- 20-25% wider than plossls. The 19mmFF is 65°.

You do NOT need to spend a lot of money to get well corrected eyepieces with long eye relief. All of these I mention above are in my case. (Well, except I sold the 15 and 18 paradims due to duplication).

edz

#5 steve-in-kville

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Posted 18 February 2013 - 05:02 PM

EdZ - forgot about that post I started. But thanks again.

To the rest, this info is quite helpful. Thanks.

#6 kansas skies

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Posted 18 February 2013 - 05:19 PM

I wear glasses for astigmatism. This only becomes a problem with lower power eyepieces. At higher magnifications with a smaller exit pupil, my astigmatism is usually not noticeable. One thing I do find is that my glasses reduce my limiting magnitude by as much as a whole magnitude, so I'm careful to not wear them if I can get away with it. That being said, my favorite low power eyepiece is an old Cave 26.6mm Orthostar which has a considerable amount of eye relief that allows me to wear my glasses comfortably.

Bill






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