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Refractor Eyepiece Choices


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Hello all, i find myself having to invest in a couple more eyepieces for my 115mm 805mm focal length frac. The drastic difference in power between eyepieces i had for my mak and this frac is drastic considering 

the huge difference in FL. It looks like i will need a couple of short FL eyepieces for higher powers, somewhere in the 4-6mm range. my question is, is it wiser to buy longer fL eyepieces and just barlow? not sure

if theres an advantage to either choice, either i just buy the short fl eyepieces or, higher fl ones and use a barlow. If it was just a matter of choice, i wouldn't be asking, not sure if there are any reasons why one

would choose one or the other for technical reasons.

Edited by Sunshine
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I hear ya! Ive been thinking about the same thing. I have an Orion 127 Mak and the lowest I usually go on that is 15mm with an occasional 10mm when the nights are good using either my Vixen Zoom or a WO Swan 20mm (barlowed) to get 10mm. I have 10mm and 6.5mm plossls but the eye relief is a little too tight for me. I now have an ED80 and when using it a couple weeks back it liked going down to 8mm with the zoom and even down to 4mm with the barlow in. Felt like I could even push it further. It got me wondering if I should start thinking about a 3.5mm EP for those nights when I want to push the refractor or just keep using the zoom with the barlow at 4mm. A higher power EP would only ever be used in the refractor since that would be too much for the Mak. I bought the refractor for the wide field views and the Mak is there for the high power. So I dont know. I figure I'll figure it out this spring and summer when it warms up and I can spend more time outside with both of my scopes side by side.

Edited by cupton
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Many, including myself, prefer shorter focal length EPs as opposed to barlowing. Some say the less glass in the light path the better, but often short FL EP's have built in Barlow lenses, so that isn't always valid. What I have found though is that eye placement can become fussy when barlowing, but shorter FL EP's often retain the ease of eye placement that longer FL's in the same range have.

One example was my 16mm Nagler combined with Orion short plus barlow. Both had excellent glass in their own rights and the views were good, but maintaining eye placement was tedious due to kidney beaning.

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I go down both routes with my refractors. I have a 21.5mm - 7.2mm zoom eyepiece which I use with a Baader 2.25x barlow to give a 9..55mm - 3.2mm high power zoom which I have found both good optically and very useful for finding the right magnification for particular target / seeing conditions. Coupled with a 30mm wide angle eyepiece the zoom + barlow makes a very good 3 piece set for travel or outreach.

I also have a number of fixed focal length eyepiece down to 3.5mm and the excellent but sadly out of production Nagler 2mm - 4mm zoom.

I've been pleasantly surprised how often I can use 250x - 300x or more magnification with my refractors but having the capacity to fine tune the power to suit the conditions / target is important so small steps in focal lengths makes sense when high power observing.

 

 

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I like barlows for doubling the power of an eyepiece. I often use a 2X barlow with my 17.5mm Morpheus and it delivers great views of DSO's. But, if you're thinking along the lines of a 4 to 6mm eyepiece in its own right, I'd suggest you avoid the cheaper end of the market. For comfort, either the 5mm or 3.5mm Pentax XW will give you superb views. A 4mm Takahashi TOA is reportedly a superb high contrast eyepiece, though I've not yet used one. Often short fl eyepieces can have short eye relief so using a longer fl eyepiece along with a barlow can  help retain longer eye relief  and be more comfortable. Many multi-element high end eyepieces incorporate a barlow into their design without any detremental effects. 

Another option would be to use a binoviewer with barlow and simpler eyepiece designs. This option can produce some outstanding views of lunar and planetary at a fraction of the cost of a high end eyepiece. My own old 5 element plossls selection take some beating as far as high quality views go. Even the binoviewer I use is a cheaper end model, but along with the super plossl's, it gives breathtaking views.

IMG_5329.thumb.jpg.de3eabee57950b5410e65d41edad472d.jpg

Edited by mikeDnight
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With my two refractors - TEC140 and Zenithstar 103 - the best (sharpness, contrast, colour rendition, etc) 4mm eyepiece I’ve used is the Tak TOE 4mm. The Vixen HR 3.4mm might be a bit shorter than you want to go but I think is equally good, perhaps even better. No sig difference in quality that I can see, maybe slight difference in ‘character’. For such short fls, both are quite comfortable to use. You might like to check Bill Paolini’s review of the Vixens.

I also use the 6mm Tak ortho and that too is excellent. Increasingly though, around that fl, I find myself using the 6.5mm Morpheus instead - still sharp, no discernible gap in transmission or any other disadvantage as far as I can see, wider fov (useful if you’re using, say, a manual alt-az) and more comfortable. Sticking to the ones I’ve used, the 6mm Delos would be a great alternative but pricey.  I know others speak v highly of the Pentaxes.

With high quality Barlows or Televue Powermates, I don’t think you lose any quality; and the comfort you gain might make for more effective and enjoyable observing - arguably a better option than struggling with tiny eye lenses and short eye relief. A no-compromise alternative, imv, as long as the quality is there. 

 

 

 

 

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6 hours ago, JTEC said:

With my two refractors - TEC140 and Zenithstar 103 - the best (sharpness, contrast, colour rendition, etc) 4mm eyepiece I’ve used is the Tak TOE 4mm. The Vixen HR 3.4mm might be a bit shorter than you want to go but I think is equally good, perhaps even better. No sig difference in quality that I can see, maybe slight difference in ‘character’. For such short fls, both are quite comfortable to use. You might like to check Bill Paolini’s review of the Vixens.

I also use the 6mm Tak ortho and that too is excellent. Increasingly though, around that fl, I find myself using the 6.5mm Morpheus instead - still sharp, no discernible gap in transmission or any other disadvantage as far as I can see, wider fov (useful if you’re using, say, a manual alt-az) and more comfortable. Sticking to the ones I’ve used, the 6mm Delos would be a great alternative but pricey.  I know others speak v highly of the Pentaxes.

With high quality Barlows or Televue Powermates, I don’t think you lose any quality; and the comfort you gain might make for more effective and enjoyable observing - arguably a better option than struggling with tiny eye lenses and short eye relief. A no-compromise alternative, imv, as long as the quality is there. 

 

 

 

 

Thanks, I'm not so sure about what sort of high powers I can expect out of my refractor, assuming average to good seeing. Having always had large aperture reflectors, I am accustomed to being able to use relatively high powers. Apparently, fracs handle high power well but, for my 115 frac im not sure if I should invest in an eyepiece yielding 200 or more power?. When I say this I mean for lunar and planetary of course, I would love to push as high as possible on lunar but, until I try I wont know the limitations of my refrator. At the moment I have an 18mm APM ultra flat field, a 14mm ES 82 degree, and a 9mm Morpheus, I think ill get one more high power Morpheus and a barlow for starters until I see what the scope can do. Also, lets say I bought the televue 2x barlow, when using it how does it affect the fOV of they eyepiece? does it reduce the FOV? if so by what percentage?.

Edited by Sunshine
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5 hours ago, Sunshine said:

Thanks, I'm not so sure about what sort of high powers I can expect out of my refractor, assuming average to good seeing. Having always had large aperture reflectors, I am accustomed to being able to use relatively high powers. Apparently, fracs handle high power well but, for my 115 frac im not sure if I should invest in an eyepiece yielding 200 or more power?. When I say this I mean for lunar and planetary of course, I would love to push as high as possible on lunar but, until I try I wont know the limitations of my refrator. At the moment I have an 18mm APM ultra flat field, a 14mm ES 82 degree, and a 9mm Morpheus, I think ill get one more high power Morpheus and a barlow for starters until I see what the scope can do. Also, lets say I bought the televue 2x barlow, when using it how does it affect the fOV of they eyepiece? does it reduce the FOV? if so by what percentage?.

It is often the atmosphere or your eyes that are the limiting factor, the scope will likely take it! Last night I used my 3 to 6 Nagler zoom across the range up to and including 3mm which is x300, and this was in my FL102s ie 102mm f8.8. This gives and exit pupil of 0.34mm so my floaters were becoming an issue but the view was still sharp on the Moon when the seeing stabilised. For doubles this would also be useful, and I imagine x150 or so would also work well on Mars.

I'm sure your scope would cope with these magnification too, and as John says, the zoom concept works well to allow you to pinpoint the best magnification for the seeing. If the zoom is decent, like a Nagler then it may be all you need. Otherwise something like a Pentax or Delos at 3.5mm would be very good, or the 3.4mm Vixen HR is amazing.

These days I often binoview with my 4" scopes at high power to avoid the floaters. For me it works particularly well for white light solar and lunar observing. Here I tend to Barlow longer focal length eyepieces as I find it easier to merge the images and is more relaxing.

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Hi,

Stu and John have given some very good points about eyepieces. A good tool for comparing telescopes and eyepieces is this one http://www.stargazing.net/naa/scopemath.htm . Whats good about this tool it explains everything. 

Dave

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It just goes to show how personal preferences vary so much. John, myself, Mike and Stu all using different solutions that wouldn't suit the other. I can't merge bino views for love nor money!

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25 minutes ago, parallaxerr said:

It just goes to show how personal preferences vary so much. John, myself, Mike and Stu all using different solutions that wouldn't suit the other. I can't merge bino views for love nor money!

I've tried bino viewers a number of times but I don't get on that well with them either while other experienced observers are very happy with them.

Eyepieces do seem to be very personal choices don't they ? :smiley:

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44 minutes ago, parallaxerr said:

I can't merge bino views for love nor money!

Tee hee 🤣. It was a long and painful journey for me to get comfortable with them, involving 6 pairs before I finally got ones I enjoyed. Worth it for me for high powers with smallish fracs to avoid the dreaded floaters.

I still prefer a good long focal length for widefield/low power views.

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7 hours ago, Sunshine said:

Thanks, I'm not so sure about what sort of high powers I can expect out of my refractor, assuming average to good seeing. Having always had large aperture reflectors, I am accustomed to being able to use relatively high powers. Apparently, fracs handle high power well but, for my 115 frac im not sure if I should invest in an eyepiece yielding 200 or more power?. When I say this I mean for lunar and planetary of course, I would love to push as high as possible on lunar but, until I try I wont know the limitations of my refrator. At the moment I have an 18mm APM ultra flat field, a 14mm ES 82 degree, and a 9mm Morpheus, I think ill get one more high power Morpheus and a barlow for starters until I see what the scope can do. Also, lets say I bought the televue 2x barlow, when using it how does it affect the fOV of they eyepiece? does it reduce the FOV? if so by what percentage?.

As Stu says, the scope will take it and likely won’t be the limiting factor. My 103 is very comfortable with the 6.5 Morpheus and the 4mm Tak (x180). That’s about as high as it would normally want to go I think, though it was fine with the Vixen 3.4 on the Moon.  As far as I know, using a x2 Barlow will retain the apparent field  of view of the eyepiece while, of course, doubling the mag and reducing commensurately the true fov.  I think your idea of going for a shorter Morpheus next makes perfect sense.  The 6.5 seems excellent to me and great value.

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5 hours ago, JTEC said:

As Stu says, the scope will take it and likely won’t be the limiting factor. My 103 is very comfortable with the 6.5 Morpheus and the 4mm Tak (x180). That’s about as high as it would normally want to go I think, though it was fine with the Vixen 3.4 on the Moon.  As far as I know, using a x2 Barlow will retain the apparent field  of view of the eyepiece while, of course, doubling the mag and reducing commensurately the true fov.  I think your idea of going for a shorter Morpheus next makes perfect sense.  The 6.5 seems excellent to me and great value.

Thanks, considering the eyepieces I have at the moment, I believe a televue 2.5x powermate will be a good choice. it seems as though powermate’s have an advantage over traditional Barlow designs. In the near future I would like an eyepiece in the 3.5 range for lunar as I am sure I can ramp up the power on lunar a fair bit. Always taking into consideration atmospheric conditions of course.

Edited by Sunshine
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Sunshine, I was persuaded to go for the Powermate (2”x2) over the TV Barlow that I had originally planned to buy.  I haven’t regretted it - superb build quality, optically about as good as it gets imv and in use more or less invisible.

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Powermates are superb - as @JTEC says, practically invisible in the optical path apart from the magnification increase. They can create quite a stack when used with a long eyepiece though !

 

bigeps.jpg

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4 minutes ago, John said:

Powermates are superb - as @JTEC says, practically invisible in the optical path apart from the magnification increase. They can create quite a stack when used with a long eyepiece though !

 

bigeps.jpg

Thanks, I see you take every opportunity to show off your “king” the 31mm Nagler, its ok my friend I would do the same haha!

Edited by Sunshine
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7 minutes ago, Sunshine said:

Thanks, I see you take every opportunity to show off your “king” the 31mm Nagler, its ok my friend I would do the same haha!

Its useful to show scale - I don't actually use the Nagler 31 that much :rolleyes2:

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13 minutes ago, John said:

Its useful to show scale - I don't actually use the Nagler 31 that much :rolleyes2:

Feel free to donate it to a loving foster parent anytime, namely ME! :hello2:

Edited by Sunshine
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  • 2 weeks later...

For a 115 f/7 refractor, a 7mm Pentax XW will give you "Resolving Magnification" where finer details can be seen while keeping an elevated level of contrast. This is where focal length of the eyepiece is equal to the focal ratio of the telescope, and you get a 1:1 ratio with aperture:magnification. If and when you decide to get a Powermate or Barlow, you can double the power and get a 2:1 ratio which is said to be the "max useful magnification" of a scope.

I've found the Pentax XW's to be great for all categories of observing; lunar, planetary, & deep sky. They have excellent sharpness, brightness & contrast. Funny thing is, I can a better image when I Powermate a 5mm XW than I do with a 6mm Delos + PM in either of my refractors [SVA130T f/7 and FC-100DF f/7.4]. I'll see how a 7mm XW + Powermate looks compared to a 3.5mm Delos next time out.

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