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8" F5 eyepiece lineup?

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#1 Promentory

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Posted 23 October 2019 - 01:05 AM

Hello all. I have some questions for experienced observers with regards to focal length lineup. I currently have a 31.5 speers waler, nagler 17mm t4, delos 14mm, morpheus 9mm, 2x barlow, and a sky mentor 8-24mm zoom.

 

My first question, I bought a used delos on a classifieds site to test, knowing the focal length was close to my 17mm t4. I really enjoy both eyepieces, and was wondering if it makes sense to sell the t4 and look for a used 22mm t4. That gives me a 1.6x jump to the 14mm delos, and would be a good finder eyepiece for light polluted areas. Is the 22mm as enjoyable as the 17mm? I love the 17mm and am very hesitant to sell it.

 

My second question is in regards to high mag and planetary. I currently have a 4.7mm es 82 deg that I am selling because of eye relief (I observe with glasses). The 9mm morpheus barlowed gives me 4.5mm, which is 222x. My only concern is the increased eye relief with the delos and morpheus. I was thinking of getting a 6.5mm morpheus as well to barlow on those perfect viewing nights. My other thought was the purchase a 2.5x focal extender. That would give me 5.6mm and 3.6mm with my current eyepieces. There is a televue powermate 2.5x close to me used for a great price.

 

I also have plans in the next year to upgrade to a 10 or 12 inch with 1200mm FL if that plays any part. Any advice would be greatly appreciated!



#2 Migwan

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Posted 23 October 2019 - 07:37 AM

I happened on a 17T4 prior to a 22T4.  Love them both and haven't even considered parting with either.  I do use the 22T4 more, but using them on a f10 C11 and f5 ST120, so it might vary for you.  From what I have read, the 22T4 is the most popular.  If I could only have one, I would probably keep the 22T4. 

 

 The 6.5M is a fine and comfortable EP.   On a fast dob, you may still want a shorter fl EP for those really good nights.   

 

In my opinion, high power shorter fl EPs should be spaced closer than low power longer fl EPs.   My most used line up goes 30, 22, 17, 13, 9, 6.5.  Some folk like them even closer together on the high power end.   The idea is to permit the most power that conditions permit.  As you get to higher power, every mm make a bigger difference in power than at lower power.   Most nights I can't use the 6.5.  Some nights I can't use the 9.   If I can't use the 13, I'm probably not out observing, but have had a couple of nights that even that was too far and the 17.5 is it.  

 

Keep in mind that I am using these EPs at near 3000mm fl.  I use the attached f5 ST120 for wide field and as a finder.  Dobs are faster and so shorter fl EPs will likely come into play. 

 

Enjoy.

 

jd


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#3 SeattleScott

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Posted 23 October 2019 - 08:18 AM

The 10/12 would be the same F ratio so just focus on eyepieces for your current scope and they will work the same. 31mm to 17 or 14 isn’t a huge jump for low power. I would be more focused on getting a 6.5 and 4.5 so you aren’t messing with barlow so much.

Scott
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#4 jaraxx

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Posted 23 October 2019 - 09:09 AM

My only contribution is this: The 6.5 Morpheus is as good an eyepiece as the 9mm Morpheus, so if you like the 9 you will like the 6.5.

I can't comment on the 17 vs 22 t4 do to a lack of experience w/ them, but if I really liked the view thru an eyepiece it would be hard for me to part with it. For example: I acquired a 10.5 and 17mm TV Plossl - the older Japanese smoothies - at no cost. I have a set of Morphi that include a 17.5 and the 12.5 and 9. The argument could be easily made that I should get rid of both Plossls - duplicate focal lengths at 17 and the 10.5 is too close between the 12.5 and 9mm. But I like looking thru the Plossls - they aren't "better" than the Morpheus line, and they're narrower in terms of FOV but they are ... different. In terms of color, they seem to be ... deeper? warmer? And then there is the focus thing. With the Morpheus, I move the fine tuning back and forth a bit to settle on the best view. The Plossls really snap - when they come into focus they are in, no use playing with the fine tuning.

So, in spite of the fact that I need (or at least could justify) an eyepiece around 30mm and could sell the two Plossls to get there... I'm not gonna.



#5 SeattleScott

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Posted 23 October 2019 - 12:45 PM

There tend to be a few really big things that benefit from 2-3 degrees. Andromeda from dark skies, Veil nebula, Pleiades, Beehive, Coathanger, etc. This is where your 31mm comes into play, as well as a low power finder eyepiece. Then there is kind of a gap down to Double Clusters at 1.1 degrees, Orion Nebula at 1 degree, etc. The 17T4 provides 1.4 degrees in your current scope. About perfect for medium/low power. It won’t do the huge stuff like Pleiades but it can handle anything in the next tier down. The Delos would work pretty well too, although at 1 degree FOV it might not be quite wide enough for double clusters, and Orion might benefit from a little more framing. The 22T4 doesn’t do anything for your current scope because basically anything that is too big for the 17T4 is also going to be too big for the 22T4. So you would use it on the same targets, just with less magnification.

Where a 22T4 would make sense is with a bigger 10-12” F5. Now it can take on the role of ideal medium low power for that scope, and it would still work fine with your 8” even if the magnification isn’t as optimal. So from a long term perspective, swapping the 17 for a 22 makes sense. It just doesn’t do anything for you now.

Scott
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#6 earlyriser

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Posted 23 October 2019 - 12:59 PM

My 17.3mm Delos (similar to your 17mm Nagler) and 22mm Nagler are my most used eyepieces and I find the step in magnification between them useful. In my case, the step from 17 to 10 is a bit large, so I plan to fill it with something someday. I wish there was a 13mm Delos, but I will probably end up with a 14mm Delos. So I guess what I'm saying is I'd get the 22mm Nagler to fill the gap between the 31.5 Speers Waler and 17mm Nagler, but I would also keep the 14mm Delos.


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#7 Ohmless

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Posted 23 October 2019 - 08:27 PM

IMHO, buy gear for what you have today as tomorrow might not happen.  1000mm focal length is the same as my old 4" f/10 achromat.  My favorite eyepiece for that scope was a 25mm plossl for deep sky.  Back then my planetary eyepiece was a 7mm nagler but that was too small of an exit pupil to give a satisfying view.  Shouldn't be a problem in an f/5 though the eye relief is inadequate for people wearing glasses.

 

I now observe with glasses and found the best benefit in using long focal length eyepieces in a binoviewer with a barlow in front of it.  My current kit(6" f/5 reflector) uses a pair of 25mm HD orthoscopic eyepieces.in a celestron binoviewer using a 2x barlow.  The barlow magnifies more than 2x due to the length of the binoviewer.  The biggest upgrade for my vision was using the binoviewer in a telescope with a shorter focal ratio.  That covered the glasses part along with making floaters less distracting.

 

Hope that give you some ideas.

 

Clear skies!


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#8 SeattleScott

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Posted 24 October 2019 - 12:30 AM

My 17.3mm Delos (similar to your 17mm Nagler) and 22mm Nagler are my most used eyepieces and I find the step in magnification between them useful. In my case, the step from 17 to 10 is a bit large, so I plan to fill it with something someday. I wish there was a 13mm Delos, but I will probably end up with a 14mm Delos. So I guess what I'm saying is I'd get the 22mm Nagler to fill the gap between the 31.5 Speers Waler and 17mm Nagler, but I would also keep the 14mm Delos.

It isn’t really fair to say the 22 and 17 are your most used eyepieces without giving the FL of the scope. I am guessing it is more than the OP’s 1000mm 8” F5.

Scott

#9 SeattleScott

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Posted 24 October 2019 - 12:34 AM

IMHO, buy gear for what you have today as tomorrow might not happen. 1000mm focal length is the same as my old 4" f/10 achromat. My favorite eyepiece for that scope was a 25mm plossl for deep sky. Back then my planetary eyepiece was a 7mm nagler but that was too small of an exit pupil to give a satisfying view. Shouldn't be a problem in an f/5 though the eye relief is inadequate for people wearing glasses.

I now observe with glasses and found the best benefit in using long focal length eyepieces in a binoviewer with a barlow in front of it. My current kit(6" f/5 reflector) uses a pair of 25mm HD orthoscopic eyepieces.in a celestron binoviewer using a 2x barlow. The barlow magnifies more than 2x due to the length of the binoviewer. The biggest upgrade for my vision was using the binoviewer in a telescope with a shorter focal ratio. That covered the glasses part along with making floaters less distracting.

Hope that give you some ideas.

Clear skies!

Very interesting, with my 4” F9.5 I only use a 25mm for large DSO like Double Cluster. Currently I am mostly using a 9mm as my main DSO eyepiece. I regularly use a 7mm Nagler for lunar/planetary and will even pull out a 3.4mm in excellent seeing. Different strokes for different folks!

Scott
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#10 earlyriser

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Posted 24 October 2019 - 07:05 AM

It isn’t really fair to say the 22 and 17 are your most used eyepieces without giving the FL of the scope. I am guessing it is more than the OP’s 1000mm 8” F5.

Scott

10 inch f/5. In my defense, I list the AD10 in my signature.


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#11 Promentory

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Posted 24 October 2019 - 09:06 AM

There tend to be a few really big things that benefit from 2-3 degrees. Andromeda from dark skies, Veil nebula, Pleiades, Beehive, Coathanger, etc. This is where your 31mm comes into play, as well as a low power finder eyepiece. Then there is kind of a gap down to Double Clusters at 1.1 degrees, Orion Nebula at 1 degree, etc. The 17T4 provides 1.4 degrees in your current scope. About perfect for medium/low power. It won’t do the huge stuff like Pleiades but it can handle anything in the next tier down. The Delos would work pretty well too, although at 1 degree FOV it might not be quite wide enough for double clusters, and Orion might benefit from a little more framing. The 22T4 doesn’t do anything for your current scope because basically anything that is too big for the 17T4 is also going to be too big for the 22T4. So you would use it on the same targets, just with less magnification.

Where a 22T4 would make sense is with a bigger 10-12” F5. Now it can take on the role of ideal medium low power for that scope, and it would still work fine with your 8” even if the magnification isn’t as optimal. So from a long term perspective, swapping the 17 for a 22 makes sense. It just doesn’t do anything for you now.

Scott

Thank you for this Scott. I have been navigating eyepieces by FL and exit pupil, this prompted me to do a search and learn how to calculate TFOV. 

 

My eventual plan is to acquire a nagler 31mm t5, which would cover the 2-3 degree slot. The last couple months, the 92 degree series from explore scientific has caught my eye. What do you think of the 17mm at 60x/3.4 EP/1.6 degrees and 12mm at 83x/2.4/1.1 degree in an 8" dob. They are beefy and expensive, but they would last a lifetime. 



#12 SeattleScott

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Posted 24 October 2019 - 12:16 PM

I hear those are excellent. 1.6 degrees is kind of in that dead zone where it would be great for double cluster but not ideal for much else. 1.1 is great for M42, M35 and a few other large clusters.

Of course if you get a bigger scope with more FL that would change a bit. At 1200mm the 17mm would be 1.3 degrees, enough to squeeze in double cluster and still be a good size for Orion, M35, etc. At 1500mm now it can’t quite fit double cluster but it still works for the others. So if you are really set on a 10”-12” in the near future, the 17mm probably makes the most sense as a medium low power. At 1500mm the 12mm really is more of a medium power, so it would still see a lot of use. It would just be medium low with the 8” or medium power with the bigger scope. So either one would work, and you could make a case for getting both.

Scott

Edited by SeattleScott, 24 October 2019 - 12:20 PM.

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#13 Chesterguy1

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Posted 25 October 2019 - 12:38 PM

The OP never mention whether they wear glasses. I have found the Delos to be a really nice choice for the majority of my viewing which is done with eyeglasses. I have the 17.3, 12 and 8. I do have two 82 degree EPs, a 4.7mm ES *2 and a 22 Nagler. The Nagler is my lowest power EP so I could probably use something in the 30 mm range for broader sweeps. However, I don't even use my 22 all that often since all my other EPs are 1.25s. It's not that it is such a big deal to swap out from a larger to smaller collar, but it is one extra step that is required. I prefer taking off my glasses with the 4.7mm.

 

Chesterguy



#14 Starman1

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Posted 03 November 2019 - 05:49 PM

Hello all. I have some questions for experienced observers with regards to focal length lineup. I currently have a 31.5 speers waler, nagler 17mm t4, delos 14mm, morpheus 9mm, 2x barlow, and a sky mentor 8-24mm zoom.

 

My first question, I bought a used delos on a classifieds site to test, knowing the focal length was close to my 17mm t4. I really enjoy both eyepieces, and was wondering if it makes sense to sell the t4 and look for a used 22mm t4. That gives me a 1.6x jump to the 14mm delos, and would be a good finder eyepiece for light polluted areas. Is the 22mm as enjoyable as the 17mm? I love the 17mm and am very hesitant to sell it.

 

My second question is in regards to high mag and planetary. I currently have a 4.7mm es 82 deg that I am selling because of eye relief (I observe with glasses). The 9mm morpheus barlowed gives me 4.5mm, which is 222x. My only concern is the increased eye relief with the delos and morpheus. I was thinking of getting a 6.5mm morpheus as well to barlow on those perfect viewing nights. My other thought was the purchase a 2.5x focal extender. That would give me 5.6mm and 3.6mm with my current eyepieces. There is a televue powermate 2.5x close to me used for a great price.

 

I also have plans in the next year to upgrade to a 10 or 12 inch with 1200mm FL if that plays any part. Any advice would be greatly appreciated!

I'm not sure you need more eyepieces, but my recommendations for an 8" scope are that you pick focal lengths that yield magnification jumps of 50x,

i.e. 50x, 100x, 150x, 200x, and 250x.  You won't be using magnifications about 250x much except, perhaps, on double stars and the Moon.

8" f/5 is a 1016mm focal length, so 250x is a 4mm eyepiece.

The recommendations are for 20mm, 10mm, 6.7-7mm, 5mm, and 4mm.

Plus or minus, of course.  Your perfect eyepiece is likely to be in the 9-11mm range.

For a 10", I'd try multiples of 60x; for a 12", multiples of 70x.

This presumes, of course, you have good seeing conditions.  If you have seeing as bad as I recently saw at a star party, the lowest power eyepiece will become VERY important.  LOL.




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