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Have 24mm Panoptic 68d, need 31mm Baader Aspheric?

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#1 NorthWolf

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Posted 06 July 2014 - 11:41 AM

Question:

I have a 24mm Panoptic and a Celestron Nexstar 6SE Telescope. When I use the 24mm Panoptic I get a FOV or TFOV of 1.03°. Now I bought a 31mm Baader Aspheric thinking the son of a gun would have a 72° AFOV yet it's only 55° which is useless, I'd rather buy a 32mm TV Plossl for half the price.

The Baader Aspheric will give me a FOV or TFOV of 1.22° compared to the Panoptic's 1.03°...

Is it worth keeping or should I go exchange it and add a little bit more money for a 13mm Nagler so that I may have 2 13mm Nagler for binoviewing?

What do you guys think? I don't plan to use 2" eyepieces for the next year or 2. :question:

#2 zsb04

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Posted 06 July 2014 - 11:57 AM

i think you will benefit more from a small refractor. The SCT is not capable of very wide fields. The difference between 1.03 and 1.22 is not terribly large but you will notice it. now if you got a small refractor that 24mm panoptic will produce a 2.5 degree field and that will certainly be a worthwhile increase. I dont have a panoptic 24mm but i do have the explore scientific equivalent. It is pretty cool seeing such a wide field, but i do not think there is anything i would view with an even lower power wider field than the 2.5 degree. For me that is about as low power as i will likely go. I viewed andromeda last night, and it looked its best in the 16mm 82 degree UWAN as opposed to the 24mm 68 degree, but it was a close comparison.

#3 NorthWolf

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Posted 06 July 2014 - 11:59 AM

A refractor purchase is in the works, but 1-2 years away. I want to enjoy the new telescope I just got after a 4 year scope drought!

#4 zsb04

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Posted 06 July 2014 - 12:11 PM

i see, then maybe going to 2" would produce larger field. I don;t know the details of your scope (focal length, f-ratio, etcc..) but i use the televue optics calculator to determine magnification and fov. Although a nice 2" eyepiece can cost more than a small refractor :(

http://www.televue.c...b=#.U7mDCZRdUhY

#5 David Knisely

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Posted 06 July 2014 - 12:49 PM

Question:

I have a 24mm Panoptic and a Celestron Nexstar 6SE Telescope. When I use the 24mm Panoptic I get a FOV or TFOV of 1.03°. Now I bought a 31mm Baader Aspheric thinking the son of a gun would have a 72° AFOV yet it's only 55° which is useless, I'd rather buy a 32mm TV Plossl for half the price.

The Baader Aspheric will give me a FOV or TFOV of 1.22° compared to the Panoptic's 1.03°...

Is it worth keeping or should I go exchange it and add a little bit more money for a 13mm Nagler so that I may have 2 13mm Nagler for binoviewing?

What do you guys think? I don't plan to use 2" eyepieces for the next year or 2. :question:


the 31mm Asperhic does have a 72 degree apparent field of view. Are you using the 2" visual back to get the full field on the 31mm Baader Hyperion Aspheric? The 1.25" adapter on the 31mm will vignette significantly, not allowing the full 72 degree apparent field of the Aspheric to be used unless it is removed and the eyepiece is used in its "native" 2" barrel version. In addition, the opening at the back of the 6SE is so small that it will vignette many 2" eyepieces as well. If you want wider fields than a degree or so, you may have to use a different telescope. Clear skies to you.

#6 csrlice12

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Posted 06 July 2014 - 01:06 PM

Maybe try a focal reducer.

#7 junomike

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Posted 06 July 2014 - 01:20 PM

I don't think anything will best the 24mm Pan for FOV as the baffle opening on the C6 is 27mm which is the same size as the 24mm Pan Field Stop. You may be able to eclipse this by a mm or two but be prepared for Vignetting.
I'd personally stick to the 24mm Pan and maybe ad another SWA eyepiece in the 16mm range.

Mike

#8 SteveG

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Posted 06 July 2014 - 02:12 PM

The 24 Pan or similar is your best choice for wide fields in 1.25".

#9 Scanning4Comets

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Posted 06 July 2014 - 02:27 PM

The 31mm Baader Aspheric is a 72 degree eyepiece, but only worth 1/3rd the price it is selling for. I just sent one back because it was just about as good as my 32mm Orion Q-70 which costs way less.

Not a good eyepiece in a fast scope at all.

This was in my fast reflector, and would work better in a longer FL scope but would maybe vignette in your Celestron Nexstar 6SE.

#10 Jon Isaacs

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Posted 06 July 2014 - 03:11 PM

I don't think anything will best the 24mm Pan for FOV as the baffle opening on the C6 is 27mm which is the same size as the 24mm Pan Field Stop. You may be able to eclipse this by a mm or two but be prepared for Vignetting.
I'd personally stick to the 24mm Pan and maybe ad another SWA eyepiece in the 16mm range.

Mike


I tried some 2 inch eyepieces, even the 31mm Nagler, in a C-5 I had a while back.. Same rear port as the C-6. It was surprising how little vignetting there actually was.. Most scopes, even refractors, do not fully illuminate their maximum field of view but the eye seems quite insensitive to vignetting..

Jon

#11 Starman1

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Posted 06 July 2014 - 04:52 PM

In my experience with a C6, the illumination is down to about 50% at the edge of a 27mm field (the field stop size of a 32 Plossl or 24 widefield).
Going larger than this (which requires a 2" visual back) can be questionable
since, at some point, you WILL notice bad vignetting, but since it varies from person to person, you won't know when or where.
Until you've already spent a lot of money on a visual back and star diagonal to discover that all 2" eyepieces with larger field stops vignette.

A focal reducer won't help illuminate a larger field, either, because the illumination drop off that was at the edge of a 27mm field is now at the edge of a 17mm field.

In fact, though, a focal reducer is a good way to see where you can detect and be bothered by vignetting. It's cheaper than a 2" conversion; it flattens the field of the scope a bit; it reduces coma at the edge of the field; it can easily be removed; and it doesn't increase back focus (significantly reducing clearance) and telescope focal length the way a 2" diagonal will. You can gradually move to 1.25" eyepieces with field stops larger than 17mm until you see vignetting. Whatever the field stop is, it will likely be smaller than the field stop of a 32 Plossl or 24 Widefield. And, whatever than field stop happens to be, you can divide the "power" of the focal reducer into it to get the size of the field stop that could be used in a 2" eyepiece.

For instance, I could see vignetting in any 2" eyepiece with a field stop larger than 30mm when used in a 0.63X focal reducer in my 8" SCT (which has a substantially--52%--wider illuminated field than a 6"). 30/0.63=47.6mm, so I could (and did) successfully use 2" eyepieces with 46mm field stops (the largest in 2") with the 8", just noticing mild vignetting.

And, if you are not bothered by vignetting at all (unlikely, but possible), then a 27mm field stop in the focal reduced C6 yields a 1.64 degrees of field.
Since the C6 isn't really intended to illuminate fields of view much larger than about 1.05-1.1 degrees, you will probably see a lot of vignetting with that big field.

#12 NorthWolf

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Posted 06 July 2014 - 04:53 PM

Question:

I have a 24mm Panoptic and a Celestron Nexstar 6SE Telescope. When I use the 24mm Panoptic I get a FOV or TFOV of 1.03°. Now I bought a 31mm Baader Aspheric thinking the son of a gun would have a 72° AFOV yet it's only 55° which is useless, I'd rather buy a 32mm TV Plossl for half the price.

The Baader Aspheric will give me a FOV or TFOV of 1.22° compared to the Panoptic's 1.03°...

Is it worth keeping or should I go exchange it and add a little bit more money for a 13mm Nagler so that I may have 2 13mm Nagler for binoviewing?

What do you guys think? I don't plan to use 2" eyepieces for the next year or 2. :question:


the 31mm Asperhic does have a 72 degree apparent field of view. Are you using the 2" visual back to get the full field on the 31mm Baader Hyperion Aspheric? The 1.25" adapter on the 31mm will vignette significantly, not allowing the full 72 degree apparent field of the Aspheric to be used unless it is removed and the eyepiece is used in its "native" 2" barrel version. In addition, the opening at the back of the 6SE is so small that it will vignette many 2" eyepieces as well. If you want wider fields than a degree or so, you may have to use a different telescope. Clear skies to you.


David! long time sir, how are ya! How do I fit a 2" eyepiece in the 6SE stock diagonal? If I can do that and notice a significant amount of difference compared to the 24 Pan, I might keep it, otherwise I will get either a 17.3mm Delos or a 2nd 13mm Nagler for binoviewing!

Thanks guys!

#13 NorthWolf

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Posted 06 July 2014 - 10:50 PM

Hi Don,

How come the Field Stop measuerments are not listed on this calculator?

http://www.televue.c...d=212&plain=...

Is the field stop important to know?

#14 Starman1

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Posted 06 July 2014 - 11:07 PM

Yes, field stop measurements ARE important to know, but very few manufacturers list them anywhere.
So I figured out how to calculate them when they're not listed (the unfortunate thing is that many manufacturers do not list the accurate apparent fields of their eyepieces for marketing reasons. It might be hard to sell certain eyepieces if you knew there was variation in apparent field from focal length to focal length in a model line.):
See:
http://www.cloudynig...6616344/page...
and, as for TeleVue, they do list them here:
http://televue.com/e...=214&plain=TRUE
and you can use my spreadsheet or the formula to figure out true field:
TF=(EPFS/TFL) x 57.3
TF=true field
EPFS=eyepiece field stop
TFL=telescope focal length.
If you want to be even more accurate, that 57.3 is really 180/pi

Don

#15 NorthWolf

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Posted 06 July 2014 - 11:28 PM

In my experience with a C6, the illumination is down to about 50% at the edge of a 27mm field (the field stop size of a 32 Plossl or 24 widefield).
Going larger than this (which requires a 2" visual back) can be questionable
since, at some point, you WILL notice bad vignetting, but since it varies from person to person, you won't know when or where.
Until you've already spent a lot of money on a visual back and star diagonal to discover that all 2" eyepieces with larger field stops vignette.

A focal reducer won't help illuminate a larger field, either, because the illumination drop off that was at the edge of a 27mm field is now at the edge of a 17mm field.

In fact, though, a focal reducer is a good way to see where you can detect and be bothered by vignetting. It's cheaper than a 2" conversion; it flattens the field of the scope a bit; it reduces coma at the edge of the field; it can easily be removed; and it doesn't increase back focus (significantly reducing clearance) and telescope focal length the way a 2" diagonal will. You can gradually move to 1.25" eyepieces with field stops larger than 17mm until you see vignetting. Whatever the field stop is, it will likely be smaller than the field stop of a 32 Plossl or 24 Widefield. And, whatever than field stop happens to be, you can divide the "power" of the focal reducer into it to get the size of the field stop that could be used in a 2" eyepiece.

For instance, I could see vignetting in any 2" eyepiece with a field stop larger than 30mm when used in a 0.63X focal reducer in my 8" SCT (which has a substantially--52%--wider illuminated field than a 6"). 30/0.63=47.6mm, so I could (and did) successfully use 2" eyepieces with 46mm field stops (the largest in 2") with the 8", just noticing mild vignetting.

And, if you are not bothered by vignetting at all (unlikely, but possible), then a 27mm field stop in the focal reduced C6 yields a 1.64 degrees of field.
Since the C6 isn't really intended to illuminate fields of view much larger than about 1.05-1.1 degrees, you will probably see a lot of vignetting with that big field.


Also Don, that is very interesting, did not read it before, I need to find out how to calculate field stops, thanks good info. Completely out of subject, but do cameras need or have minimum or maximum field stop requirements when put into ep's or visual backs and diagonals?

#16 NorthWolf

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Posted 06 July 2014 - 11:29 PM

Yes, field stop measurements ARE important to know, but very few manufacturers list them anywhere.
So I figured out how to calculate them when they're not listed (the unfortunate thing is that many manufacturers do not list the accurate apparent fields of their eyepieces for marketing reasons. It might be hard to sell certain eyepieces if you knew there was variation in apparent field from focal length to focal length in a model line.):
See:
http://www.cloudynig...6616344/page...
and, as for TeleVue, they do list them here:
http://televue.com/e...=214&plain=TRUE
and you can use my spreadsheet or the formula to figure out true field:
TF=(EPFS/TFL) x 57.3
TF=true field
EPFS=eyepiece field stop
TFL=telescope focal length.
If you want to be even more accurate, that 57.3 is really 180/pi

Don


Thanks

#17 Starman1

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Posted 06 July 2014 - 11:32 PM

Solve the equation for Field stop:
(TFL X TF)/57.3 = EPFS
You have to do eyepiece timings of a celestial equator star across the field to figure out the REAL true field.
Remember, time in decimal minutes (i.e. 4.1 minutes instead of 4 minutes 6 seconds)/4=true field in degrees.
T/4=TF
From that, you can back into the effective field stop and use that on other scopes too. The advantage of doing a timing is that even distortion in the eyepiece is taken into account.

#18 NorthWolf

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Posted 06 July 2014 - 11:46 PM

Don, I may as well solve the white hole theory, if there is one, while I'm at it, ha! But thanks! Great info on these boards again and again!

#19 NorthWolf

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Posted 06 July 2014 - 11:57 PM

Right now, I need to solve whether I will keep the 31mm Baader Aspheric, which eyepiece to get next and also which 2 eyepieces I would enjoy most on a 22mm wide binoviewer, perhaps in reality it's less than 22mm...

I tried the 6SE for the first time yesterday, in the day as I knew it would be cloudy in the night. I was enjoying the monstrous sunspots that are on display on our star at the moment (With a Baader Solar Film Filter). I managed to get in really close with the 7mm Pentax, an excellent view, but it may be missing that extra final, fine focus touch of a moonlite focuser. But I would not know, I never had one. It may have also been the seeing, which has been terrible lately, probably due to the sun's waves as of late!

I did not see much difference on the 31mm Aspheric and the 24mm Panoptic when I observed the moon that was coming from the south-se. Overall, impressive telescope! I will give the aspheric one more chance in the dark I guess before deciding, maybe it's worth keeping.



#20 NorthWolf

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Posted 07 July 2014 - 12:23 AM

I downloaded the attachment as well thanks for the guide, I need to look into field stops more.

#21 Starman1

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Posted 07 July 2014 - 12:26 AM

Right now, I need to solve whether I will keep the 31mm Baader Aspheric, which eyepiece to get next and also which 2 eyepieces I would enjoy most on a 22mm wide binoviewer, perhaps in reality it's less than 22mm...

I tried the 6SE for the first time yesterday, in the day as I knew it would be cloudy in the night. I was enjoying the monstrous sunspots that are on display on our star at the moment (With a Baader Solar Film Filter). I managed to get in really close with the 7mm Pentax, an excellent view, but it may be missing that extra final, fine focus touch of a moonlite focuser. But I would not know, I never had one. It may have also been the seeing, which has been terrible lately, probably due to the sun's waves as of late!

I did not see much difference on the 31mm Aspheric and the 24mm Panoptic when I observed the moon that was coming from the south-se. Overall, impressive telescope! I will give the aspheric one more chance in the dark I guess before deciding, maybe it's worth keeping.

Remember, the best hours for seeing where the sun is concerned are in the early morning, before the sun has heated up the atmosphere and started it boiling.

#22 NorthWolf

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Posted 07 July 2014 - 12:53 AM

That's good to know I hope there is no clouds around noon next weekend. I cannot see the eastern sky until that time, maybe around 11am.

Might as well look at the sun if every night is going to be mushy. A clear night sky is a bonus now instead of a necessity. :grin:

#23 NorthWolf

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Posted 08 July 2014 - 11:15 PM

So I tried the 31mm on the moon last night and liked the view better than the 24pan. The views and sharpness looked identical, something about the aspheric that made me like it more... the bigger tfov or something.

#24 pbsastro

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Posted 09 July 2014 - 11:53 AM

Remember, the best hours for seeing where the sun is concerned are in the early morning, before the sun has heated up the atmosphere and started it boiling.

Don, your reasoning is correct and it is true 99% of the cases, not my case though. My apartment has one balcony/window facing sunrise and other sunset.
When the sun is high enough on sunrise side, the spot has already been heating for too much time (since sunrise).
When the sun appears on the sunset side, it is very high in the sky and the spot has been on shade all day.
So, my experience is the spot itself (and the nearby air, ground and objects) is more important than the atmosphere. So the best is to use a spot that has been on the shade and has just starting being hit by the sun.

#25 Lew Zealand

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Posted 09 July 2014 - 11:45 PM

In my experience with a C6, the illumination is down to about 50% at the edge of a 27mm field (the field stop size of a 32 Plossl or 24 widefield).


I'd like to emphasize this point. I've experienced all of Don's other points on my 8" SCT but not everyone is familiar with this one.

Pop your widest, lowest power EP in your SCT and defocus a star cluster. M7 (Ptolemy's) is great for this but many others are too, like the Beehive and Pleiades. Note the shape of the defocused stars. Even with an 8" SCT and a 32mm Plossl, you will notice that most of the stars, to rather disturbingly close to the center of the FOV, experience some vignetting. The donut isn't round. There is a very small area in the center of the TFOV in a <9.25" SCT which is unvignetted.

Pop in a 2" refractor diagonal with a 2" visual back adapter and a defocused 40mm 70 EP and the vignetting is just everywhere. Refocus and it looks great, though. The vignetting really isn't particularly noticeable visually and I think I know why - it (fortunately??) starts close to the center and it's gradual. Your (OK, my) eye is fooled by the slow reduction in illumination so a full 2" FOV looks great. And it masks off much of the EOF aberrations in lower quality EPs because those light rays are simply cut off. Starting at f/10 doesn't hurt, either. The 40mm WO SWAN and it's brethren look great!

Pop in an f/6.3 reducer/flattener and a 2" SCT diagonal and the 22mm T4 Nagler still looks fab as does the 28mm Meade 5K SWA. Go any wider than those and you see the vignetting fall away to darkness and the illusion is broken.






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