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Re: New higher power eyepiece for my scope. Suggestions?

Posted: Sun Jul 18, 2021 5:08 pm
by Bigzmey
Not counting stock Kellners you have exit pupils 6.5mm (Swan 26mm), 3.8mm (TV Plossl 15mm) and 1.5mm (BCO 6mm). What missing from the equation are 1mm (4mm FL) and 2mm (8mm FL) exit pupils. 3mm exit pupil is nice to have but not as critical.

IMO having good EP with 2mm exit pupil is a must, because that is where majority of DSOs will look the best. So, if I would be you I would get 8mm EP first and then 2x powermade or barlow which would convert 8mm to 4mm and deliver 1mm exit pupil.

Not all EP lines have 8mm EPs, so 7mm to 9mm should be close enough. Since you already have 6mm covered, I would am for 8-9mm to space it nicely from 6mm.

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Tue Jul 20, 2021 12:41 pm
by 25585
Bigzmey wrote: Fri Jul 16, 2021 9:30 pm I believe everyone should have a good quality barlow or focal extender (powemate) in their EP case. It is such a useful tool. Saying that one still need to have a good EP to barlow. Barlowing 15mm Plossl or 6mm BCO will get you nice high power views but the eye relief and FOV will still be tight.

I had quite a few barlows over the years. My favorites are Baader Q barlow and Televue 2x and 3x. At the end I sold TV barlows and have two Baader Q barlows now, not because I did not like the views, but because TV barlows were colliding with prisms in my diagonals due to the length.

For the EPs you will see 'for' and 'against' opinions for ES 82, Delos, Morpheus and Naglers, but Delites seems to be universally loved. In my personal experience I have tried and moved away from ES 82, Morpheus and Delos, but Delites are keepers. :D
Barlows are good. Though I don't like TV eyepieces apart from Delites (lots of issues), their accessories like Powermates are good. I use 4x Powermate with long FL eyepieces to go short.

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 10:07 am
by turboscrew
Bigzmey wrote: Sun Jul 18, 2021 5:08 pm Not counting stock Kellners you have exit pupils 6.5mm (Swan 26mm), 3.8mm (TV Plossl 15mm) and 1.5mm (BCO 6mm). What missing from the equation are 1mm (4mm FL) and 2mm (8mm FL) exit pupils. 3mm exit pupil is nice to have but not as critical.

IMO having good EP with 2mm exit pupil is a must, because that is where majority of DSOs will look the best. So, if I would be you I would get 8mm EP first and then 2x powermade or barlow which would convert 8mm to 4mm and deliver 1mm exit pupil.

Not all EP lines have 8mm EPs, so 7mm to 9mm should be close enough. Since you already have 6mm covered, I would am for 8-9mm to space it nicely from 6mm.
My mistake was going with the 3x Barlow, which is not very good. Also, I've heard from other Finnish astronomers, that 300x (4 mm) can be used quite rarely. The typical max, due to the atmosphere, is about 250x.
That's why I was thinking of getting the 5 mm DeLite (240x) first.

On the other hand, I basically have good 15 mm and good 6 mm. This might be the time to rethink my eyepiece set.
The 26 mm is a bit too much, but it's usable for polar alignment. It's TFOV radius is 80.8" bigger that the distance of polaris from the north pole. 26mm, 68° would be better (2.8" difference), but no one seems to make those.
polar_align.png

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 4:27 pm
by Don Pensack
There are quite a few 26mm 70° eyepieces and one 27mm 68° (Panoptic), but I see the field stop diameters are all over the place.
If you are using the TF = AF/M formula, be aware it overstates the true field by anywhere from 5 to 15%.
For figuring true field of view, it's better to use the formula
TF = (field stop / telescope focal length) x 57.296

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 5:00 pm
by notFritzArgelander
Don Pensack wrote: Wed Jul 21, 2021 4:27 pm There are quite a few 26mm 70° eyepieces and one 27mm 68° (Panoptic), but I see the field stop diameters are all over the place.
If you are using the TF = AF/M formula, be aware it overstates the true field by anywhere from 5 to 15%.
For figuring true field of view, it's better to use the formula
TF = (field stop / telescope focal length) x 57.296
Just for clarity the 57.something is just for converting the natural measure of angle, the radian, into the Sumerian measure of angle, the degree. ;)

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 6:21 pm
by Bigzmey
turboscrew wrote: Wed Jul 21, 2021 10:07 am
Bigzmey wrote: Sun Jul 18, 2021 5:08 pm Not counting stock Kellners you have exit pupils 6.5mm (Swan 26mm), 3.8mm (TV Plossl 15mm) and 1.5mm (BCO 6mm). What missing from the equation are 1mm (4mm FL) and 2mm (8mm FL) exit pupils. 3mm exit pupil is nice to have but not as critical.

IMO having good EP with 2mm exit pupil is a must, because that is where majority of DSOs will look the best. So, if I would be you I would get 8mm EP first and then 2x powermade or barlow which would convert 8mm to 4mm and deliver 1mm exit pupil.

Not all EP lines have 8mm EPs, so 7mm to 9mm should be close enough. Since you already have 6mm covered, I would am for 8-9mm to space it nicely from 6mm.
My mistake was going with the 3x Barlow, which is not very good. Also, I've heard from other Finnish astronomers, that 300x (4 mm) can be used quite rarely. The typical max, due to the atmosphere, is about 250x.
That's why I was thinking of getting the 5 mm DeLite (240x) first.

On the other hand, I basically have good 15 mm and good 6 mm. This might be the time to rethink my eyepiece set.
The 26 mm is a bit too much, but it's usable for polar alignment. It's TFOV radius is 80.8" bigger that the distance of polaris from the north pole. 26mm, 68° would be better (2.8" difference), but no one seems to make those.

Image
Yes, you do have two good quality EPs which also happened to provide useful exit pupils in your scope: ~4mm and 1.5mm. You next move should be to fill 2mm and 1mm exit pupil positions. One way to go about this for now is to get 2x barlow/powermate and barlow your 15mm to 7.5mm which will get you close to 2mm exit pupil and on the nights of super good seeing you can barlow 6mm to 3mm. This should take care of your EP needs for now and will give you extra time to think about wide field EPs.

Many of us have low glass count EP set consisting of good quality Plossls and Orthos for challenging targets and wide field EP set for comfortable observing with long eye relief and wide TFV.

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 6:42 pm
by turboscrew
Bigzmey wrote: Wed Jul 21, 2021 6:21 pm
turboscrew wrote: Wed Jul 21, 2021 10:07 am
Bigzmey wrote: Sun Jul 18, 2021 5:08 pm Not counting stock Kellners you have exit pupils 6.5mm (Swan 26mm), 3.8mm (TV Plossl 15mm) and 1.5mm (BCO 6mm). What missing from the equation are 1mm (4mm FL) and 2mm (8mm FL) exit pupils. 3mm exit pupil is nice to have but not as critical.

IMO having good EP with 2mm exit pupil is a must, because that is where majority of DSOs will look the best. So, if I would be you I would get 8mm EP first and then 2x powermade or barlow which would convert 8mm to 4mm and deliver 1mm exit pupil.

Not all EP lines have 8mm EPs, so 7mm to 9mm should be close enough. Since you already have 6mm covered, I would am for 8-9mm to space it nicely from 6mm.
My mistake was going with the 3x Barlow, which is not very good. Also, I've heard from other Finnish astronomers, that 300x (4 mm) can be used quite rarely. The typical max, due to the atmosphere, is about 250x.
That's why I was thinking of getting the 5 mm DeLite (240x) first.

On the other hand, I basically have good 15 mm and good 6 mm. This might be the time to rethink my eyepiece set.
The 26 mm is a bit too much, but it's usable for polar alignment. It's TFOV radius is 80.8" bigger that the distance of polaris from the north pole. 26mm, 68° would be better (2.8" difference), but no one seems to make those.

Image
Yes, you do have two good quality EPs which also happened to provide useful exit pupils in your scope: ~4mm and 1.5mm. You next move should be to fill 2mm and 1mm exit pupil positions. One way to go about this for now is to get 2x barlow/powermate and barlow your 15mm to 7.5mm which will get you close to 2mm exit pupil and on the nights of super good seeing you can barlow 6mm to 3mm. This should take care of your EP needs for now and will give you extra time to think about wide field EPs.

Many of us have low glass count EP set consisting of good quality Plossls and Orthos for challenging targets and wide field EP set for comfortable observing with long eye relief and wide TFV.
I haven't found a 2x powermate. The 2.5x seems to mess up the plans. Also, I've wondered what kinds of alternatives do I have with this scope. I know TVs are good, so are BCOs. I guess some of the ES eyepieces are fine too, but which?
And how about Pentax eyepieces? Would they be good for my tube? It's just that I have hard time to find right focal lengths. Like, I haven't found 8 mm or 12 mm BCOs.

It looks like, instead of nice series, I need to go somewhat ad hoc.
At the moment, I think ~250x is what I'd need, when it gets dark again.
At the moment I have, basically, 48x, 80x and 200x. and a questionable 120x.
The 15 mm with 2.5x powermate becomes equal to the 6 mm, and the 6 mm becomes (mostly unusable) 2.4 mm (500x).
And the 26 mm is 2", so it wouldn't fit into the 2.5x powermate. There is a 2" 2x powermate, but it costs more than 400 eur.

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 7:08 pm
by SpyderwerX
You may also look into the Explore Scientific 2x focal extender. Same beast as the Powermate, but a bit less pricey. I did't want to go with a 2" 2X Powermate due to size, weight and expense, so I opted to try one of the 1.25" ES units, and have been very pleased.

I despise barlows, so the 4 element "extender/powermate" is the only route I would consider. :)

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 7:17 pm
by Bigzmey
Yes, BCOs only come in 3 focal lengths: 6, 10 and 18mm (and 32mm Plossl). However, if you get Baader Q-barlow which provides 2.25x and 1.3x factors and BCO 18mm you can convert 6mm BCO to 4.6mm and 18mm BCO to 8mm and 13.8mm.

The BCOs set has a great value (I have two of those :)). It will work great and cover your EP needs in any type of scope, since it gives you 12 focal lengths. In terms of optical quality (light transmission, sharpness, contrast and light scatter control) these EPs match or beat performance of any premium EPs I have tried. At the price of one premium EP ~209 EUR.

https://www.teleskop-express.de/shop/pr ... w-len.html

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 7:22 pm
by Bigzmey
SpyderwerX wrote: Wed Jul 21, 2021 7:08 pm You may also look into the Explore Scientific 2x focal extender. Same beast as the Powermate, but a bit less pricey. I did't want to go with a 2" 2X Powermate due to size, weight and expense, so I opted to try one of the 1.25" ES units, and have been very pleased.

I despise barlows, so the 4 element "extender/powermate" is the only route I would consider. :)
I see why extenders/powermate could be attractive, but prefer good quality barlows myself. Not sure what is so bad about barlows. I can't detect any image degradation and in fact they clean up the views of some EPs.

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 7:27 pm
by notFritzArgelander
Bigzmey wrote: Wed Jul 21, 2021 7:22 pm
SpyderwerX wrote: Wed Jul 21, 2021 7:08 pm You may also look into the Explore Scientific 2x focal extender. Same beast as the Powermate, but a bit less pricey. I did't want to go with a 2" 2X Powermate due to size, weight and expense, so I opted to try one of the 1.25" ES units, and have been very pleased.

I despise barlows, so the 4 element "extender/powermate" is the only route I would consider. :)
I see why extenders/powermate could be attractive, but prefer good quality barlows myself. Not sure what is so bad about barlows. I can't detect any image degradation and in fact they clean up the views of some EPs.
The barlow changes the position of the exit pupil while the extender/powermate doesn't. It bothers some. The BCO barlow is quite nice and is highly recommendable optically if you don't mind finding the exit pupil anew.

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 7:58 pm
by notFritzArgelander
notFritzArgelander wrote: Wed Jul 21, 2021 7:27 pm
Bigzmey wrote: Wed Jul 21, 2021 7:22 pm
SpyderwerX wrote: Wed Jul 21, 2021 7:08 pm You may also look into the Explore Scientific 2x focal extender. Same beast as the Powermate, but a bit less pricey. I did't want to go with a 2" 2X Powermate due to size, weight and expense, so I opted to try one of the 1.25" ES units, and have been very pleased.

I despise barlows, so the 4 element "extender/powermate" is the only route I would consider. :)
I see why extenders/powermate could be attractive, but prefer good quality barlows myself. Not sure what is so bad about barlows. I can't detect any image degradation and in fact they clean up the views of some EPs.
The barlow changes the position of the exit pupil while the extender/powermate doesn't. It bothers some. The BCO barlow is quite nice and is highly recommendable optically if you don't mind finding the exit pupil anew.
OH! I found that when I had my f4 Newtonian that the 24mm and 19mm Panoptics combined with the 2x and 4x power mates provided excellent coverage from exit pupils of 6mm down to 1.2mm. It was my standard travel kit as the powermates were almost as good as a Ploessl or Abbe. They were on a par with the 1.25" BCO 2.25x barlow.

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 8:08 pm
by SpyderwerX
notFritzArgelander wrote: Wed Jul 21, 2021 7:27 pm
Bigzmey wrote: Wed Jul 21, 2021 7:22 pm
SpyderwerX wrote: Wed Jul 21, 2021 7:08 pm You may also look into the Explore Scientific 2x focal extender. Same beast as the Powermate, but a bit less pricey. I did't want to go with a 2" 2X Powermate due to size, weight and expense, so I opted to try one of the 1.25" ES units, and have been very pleased.

I despise barlows, so the 4 element "extender/powermate" is the only route I would consider. :)
I see why extenders/powermate could be attractive, but prefer good quality barlows myself. Not sure what is so bad about barlows. I can't detect any image degradation and in fact they clean up the views of some EPs.
The barlow changes the position of the exit pupil while the extender/powermate doesn't. It bothers some. The BCO barlow is quite nice and is highly recommendable optically if you don't mind finding the exit pupil anew.
To add to the reasoning notFritz pointed out, it technically comes down to working with a diverging (angled) light path from a barlow, versus a parallel light path of the extender. Granted, most times this is not noticeable with a quality barlow, but can still pose a factor for possible aberrations.

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 9:00 pm
by Big_Eight
While a quality barlow is a great addition I would also say you can't go wrong with that ES 4.7mm 82° eyepiece. I have a few ES eyepieces and love them.

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 9:08 pm
by turboscrew
At this point I ordered 5 mm DeLite.
I have to look at things later, but I think 5 mm at this moment is what I need the most.

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 9:12 pm
by Bigzmey
turboscrew wrote: Wed Jul 21, 2021 9:08 pm At this point I ordered 5 mm DeLite.
I have to look at things later, but I think 5 mm at this moment is what I need the most.
Congrats, this is a quality EP. I am sure you will put it into a good use.

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 9:14 pm
by SpyderwerX
turboscrew wrote: Wed Jul 21, 2021 9:08 pm At this point I ordered 5 mm DeLite.
I have to look at things later, but I think 5 mm at this moment is what I need the most.
I think you will be quite happy with the Delite. I don't currently own any, but have had the opportunity to view through them a few times, and they are indeed wonderful.

Be very careful however, there are eight more EPs in that series that just beckon to be had also. :lol:

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 10:57 pm
by turboscrew
SpyderwerX wrote: Wed Jul 21, 2021 9:14 pm
turboscrew wrote: Wed Jul 21, 2021 9:08 pm At this point I ordered 5 mm DeLite.
I have to look at things later, but I think 5 mm at this moment is what I need the most.
I think you will be quite happy with the Delite. I don't currently own any, but have had the opportunity to view through them a few times, and they are indeed wonderful.

Be very careful however, there are eight more EPs in that series that just beckon to be had also. :lol:
I know, but my surname is Aaltonen, not Bezos.

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Wed Jul 21, 2021 10:58 pm
by SpyderwerX
turboscrew wrote: Wed Jul 21, 2021 10:57 pm
SpyderwerX wrote: Wed Jul 21, 2021 9:14 pm
turboscrew wrote: Wed Jul 21, 2021 9:08 pm At this point I ordered 5 mm DeLite.
I have to look at things later, but I think 5 mm at this moment is what I need the most.
I think you will be quite happy with the Delite. I don't currently own any, but have had the opportunity to view through them a few times, and they are indeed wonderful.

Be very careful however, there are eight more EPs in that series that just beckon to be had also. :lol:
I know, but my surname is Aaltonen, not Bezos.

:lol: :lol:

Re: New higher power eyepiece for my scope. Suggestions?

Posted: Thu Jul 22, 2021 3:25 pm
by turboscrew
Does this look like a good plan?

Code: Select all

focal length    magnification   exit pupil
26              46              6.50
15              80              3.75
12              100             3.00
8               150             2.00
6               200             1.50
5               240             1.25
4               300             1.00
Maybe 20 mm too (60x, 5 mm exit pupil)?