IMO having good
Not all
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 longBigzmey 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.
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.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.
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.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
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 yourturboscrew wrote: ↑Wed Jul 21, 2021 10:07 amMy 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.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.
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.
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 theBigzmey wrote: ↑Wed Jul 21, 2021 6:21 pmYes, 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 yourturboscrew wrote: ↑Wed Jul 21, 2021 10:07 amMy 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.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.
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.
EP needs for now and will give you extra time to think about wide field EPs.
Many of us have low glass countEP set consisting of good quality Plossls and Orthos for challenging targets and wide fieldEP set for comfortable observing with long eye relief and wide TFV.
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.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.
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.Bigzmey wrote: ↑Wed Jul 21, 2021 7:22 pmI 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.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.
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.notFritzArgelander wrote: ↑Wed Jul 21, 2021 7:27 pmThe 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.Bigzmey wrote: ↑Wed Jul 21, 2021 7:22 pmI 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.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.
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.notFritzArgelander wrote: ↑Wed Jul 21, 2021 7:27 pmThe 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.Bigzmey wrote: ↑Wed Jul 21, 2021 7:22 pmI 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.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.
Congrats, this is a qualityturboscrew 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.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 know, but my surname is Aaltonen, not Bezos.SpyderwerX wrote: ↑Wed Jul 21, 2021 9:14 pmI 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.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.
Be very careful however, there are eight more EPs in that series that just beckon to be had also.
turboscrew wrote: ↑Wed Jul 21, 2021 10:57 pmI know, but my surname is Aaltonen, not Bezos.SpyderwerX wrote: ↑Wed Jul 21, 2021 9:14 pmI 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.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.
Be very careful however, there are eight more EPs in that series that just beckon to be had also.
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
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