Exit Pupil

[adamw]

I have recently bought a vixen SLV 5mm EP to use in my 152 f7.9 frac. I was having a mess around with an exit pupil calculator on the internet and it worked out the exit pupil would be .63mm it also said the image may be dimmed. Does anyone know if this will be a problem or if the Ep is not suitable for my scope? Hopefully I am worrying about nothing but I have not had chance to try it yet.

Adam

[Stu]

I frequently use exit pupils down to 0.5mm or a little below on my fracs. It does lead to a dimmer image but is ok for lunar or planetary use, or doubles too. A bigger potential problem is that floaters show up in your eye much more with small exit pupils. Depends if you have any awkward ones I guess.

Finally, in this case magnification is as important as exit pupil. At x240, you will be pushing the limits of the seeing unless it is particularly clear, but will be good on steady nights

[Roy Challen]

Agree with Stu, but would add that a small exit pupil would be more of a problem with deep sky observations- faint objects and low contrast need larger exit pupils.

[michael.h.f.wilkinson]

I frequently go down to 0.7, and sometimes push it to 0.5. Works fine on brighter objects. I have the SLV 5mm and it is a cracking little EP. Holds its own against the big boys like Pentax XWs (except in terms of field of view).

[John]

I frequently use 5mm, 4mm and 3.5mm and even 3mm eyepieces with my 102mm F/6.5 and 120mm F/7.5 refractors and they work very well on the Moon, Planets and double stars. As has been said above, not really so good for extended deep sky objects but I usually view those at lower magnifications anyway.

[michael.h.f.wilkinson]

But high magnification can be very good for some planetary nebulae. I have viewed the Eskimo Nebula and a few others with the XW10 and even XW7 in my C8 (exit pupils 1.0 and 0.7 respectively)

[adamw]

Ok thanks for that everyone. At 240x I cannot see me being able to use it on anything other than doubles and the moon anyway. Maybe Jupiter on a really good night. I also have the SLV 6mm.

[John]

Ok thanks for that everyone. At 240x I cannot see me being able to use it on anything other than doubles and the moon anyway. Maybe Jupiter on a really good night. I also have the SLV 6mm.

Saturn and Mars respond well to high power. Better than Jupiter does. Mercury as well, if you can get your scope on it at some time when it's favourably placed.

[Stu]

Saturn and Mars respond well to high power. Better than Jupiter does. Mercury as well, if you can get your scope on it at some time when it's favourably placed.

That's very true, Mars can need that sort of power to pull out any detail, provided the seeing is good

[Moonshane]

I like small exit pupils. They create wonderful images of stars with tight disks and airy rings.