Searching DSO's

[ObscuredbyClouds]

What is the better EP for searching DSO's? Im unsure weather to get a 25mm or 32mm EP and was looking at the SW 32mm Super Plossl to use in an f/5 scope.

Anyone used this method, or have done?

[kenmyers]

hello, It is helpfull to zoom out as far as you can for a lovely widefield,to see most dso's.

a 32mm will give you a wider fov but also the 25 mm will be good.

[michael.h.f.wilkinson]

It depends. My 22mm Nagler has a wider FOV true than a 32mm Plossl. A 24mm Hyperion and a 32mm Plossl are about the same in terms of true FOV. If you are limited to 1.25" EPs, a 24mm Hyperion would generally be preferable to a 32mm Plossl, because the former gets you a smaller exit pupil (4.8 vs 6.4mm exit pupil), and therefore a darker background. This makes DSOs just a bit easier to spot, in my opinion. I generally use my 31mm Nagler in my F/10 scope, and occasionally the 40mm Paragon for just a touch wider FOV, and these really help in the search for faint fuzzies (3.1 and 4mm exit pupil)

[DazC]

For DSO hunting and just scanning the sky, i use a 32mm GSO. It really is a good quality ep for it's price (£40).

It is by far the most used ep in my set.

D.C

[Charon]

I too use my 31mm Nagler.

[ObscuredbyClouds]

Thanks for the replies and confusing me a bit more now lol

[michael.h.f.wilkinson]

Thanks for the replies and confusing me a bit more now lol

Let me try to make a few points clearer. Two things help in DSO hunting: large field of view and a reasonable exit pupil. The large field of view is obvious: you get to see more of the sky, so you are more likely to have your target in the FOV. Given eyepieces of the same design (e.g. Plossl), the 25 will show less than the 32, and there is no real contest between them in terms of FOV. However, if my magnification is very low, the exit pupil (width of the beam of light coming out of the EP) becomes large. In an F/5 scope the exit pupil is the focal length of the EP divided by 5 (so 5.0 for the 25 and 6.4 for the 32mm). If the exit pupil becomes larger than the pupil of your eye, the excess will not enter the eye, and is wasted. At age 50, the average observer has a maximally dilated pupil of about 6.2mm, but there are large differences between individuals (so 5.0 and 6.4 are still quite reasonable).

Using say a 50mm EP in an F/5 scope means an exit pupil of 10mm which is only useful for certain nocturnal lemurs . Losing light means DSOs are harder to see. Besides, the sky background looks lighter at those magnifications, whch also leads to less contrast, making DSOs harder to spot. This effect occurs at lower exit pupils, between 4 and 6 in my experience. This is why switching to a shorter EP but with a wider apparent field of view (like the Naglers) is beneficial. You keep the exit pupil down, while still retaining the wide true field of view. A 24mm Panoptic or Hyperion will show the same stretch of sky as the 32mm Plossl, but at a higher magnification (and spread out over a wider angle before your eyes (68 deg in stead of 52).

[paul schofield]

It would be the 32 for me from your choices, I think seeing more sky will make DSO hunting easier on most objects. The 25 is no slouch though. Does your scope have a 1 1/4 and a 2in focuser ? Thats another thread I suppose.

[ObscuredbyClouds]

It would be the 32 for me from your choices, I think seeing more sky will make DSO hunting easier on most objects. The 25 is no slouch though. Does your scope have a 1 1/4 and a 2in focuser ? Thats another thread I suppose.

Yes my scope is a 200p f/5 so has both 1.25 and 2 inch

[ObscuredbyClouds]

Let me try to make a few points clearer. Two things help in DSO hunting: large field of view and a reasonable exit pupil. The large field of view is obvious: you get to see more of the sky, so you are more likely to have your target in the FOV. Given eyepieces of the same design (e.g. Plossl), the 25 will show less than the 32, and there is no real contest between them in terms of FOV. However, if my magnification is very low, the exit pupil (width of the beam of light coming out of the EP) becomes large. In an F/5 scope the exit pupil is the focal length of the EP divided by 5 (so 5.0 for the 25 and 6.4 for the 32mm). If the exit pupil becomes larger than the pupil of your eye, the excess will not enter the eye, and is wasted. At age 50, the average observer has a maximally dilated pupil of about 6.2mm, but there are large differences between individuals (so 5.0 and 6.4 are still quite reasonable).

Using say a 50mm EP in an F/5 scope means an exit pupil of 10mm which is only useful for certain nocturnal lemurs . Losing light means DSOs are harder to see. Besides, the sky background looks lighter at those magnifications, whch also leads to less contrast, making DSOs harder to spot. This effect occurs at lower exit pupils, between 4 and 6 in my experience. This is why switching to a shorter EP but with a wider apparent field of view (like the Naglers) is beneficial. You keep the exit pupil down, while still retaining the wide true field of view. A 24mm Panoptic or Hyperion will show the same stretch of sky as the 32mm Plossl, but at a higher magnification (and spread out over a wider angle before your eyes (68 deg in stead of 52).

Thanks for that explanation, i now have a better understanding regarding exit pupil, couldntget my head around it before. Definatley something to think about now regarding my decision of eyepiece