What kind of scope would I use a 3.5mm eyepiece in?

[jonathan]

I have been told that the best magnification I can expect from my 8SE is with a 10mm eyepiece, which I have, so I was just wondering which scopes would allow the use of a 3.5mm eyepiece, and what I would expect to see with it.

[Pete Presland]

i would guess on a good night, with good seeing conditions you could use a bit more power.

a 10mm gives you approx 200x maybe 8mm approx 250x if you want to use your 3.5mm you need a scope with a shorter focal length

[E621Keith]

3.5 mm can be used for observing planets with fast Newtonian or small apo. 3.5 mm is far too powerful for SCT.

I use a 2.5mm with my 80/480 apo for planets. A 5mm only give me 96x, while the 2.5mm give me 192x, so a 3.5mm could come in handy to fill the gap between the two.

[John]

I have a 3.5mm Nagler eyepiece and use frequently with my 102mm F/6.5 and 120mm F/7.5 ED refractors where it gives 189x and 257x respectively. It's showed excellent views of Mars and Saturn with the 120mm - Mars especially needs high powers (plus a decent scope ans seeing conditions of course) I feel. The eyepiece is also excellent for tight binary stars and lunar observations.

[jonathan]

Interesting... so would I be able to effectively use a 3.5mm (or smaller?) in a Skywatcher Equinox 80mm Apo Pro? Does quality really count in this scope, and what would be recommended for visual use at the highest practical magnification (assuming I'm standing out in the middle of nowhere)?

[John]

The usual advice is that the max practical magnification is around twice the aperture in mm so for an 80mm thats 160x. Under good conditions and on certain object types you may be able to exceed that with an Equinox 80 - possibly as high as 200x, maybe ?

You would need a 2.4mm eyepiece to get 200x but it might not be used that often.

[Saleratus]

I've just recently been doing a lot of testing with a 3.5 vs a 2.5 mm EP in a good quality 80mm F/6 refractor. I think the 3.5 is great, but it's probably as low as I will want to go when using this instrument. I don't really see more with the 2.5; it's just bigger, and as you get into those high mags, eyepieces become less comfortable to use and you can be bothered with floaters. But 3.5 is really effective and fun.

[newman]

Anything with a short focal lenght and plenty of aperture, really.

[Stu]

I have a 2.5t6 nagler and a 3 to 6 nagler zoom.

Most of the time, I use the zoom at between 5 and 4mm for high power in both my 66mm 388mm f/l and 106mm 690 mm f/l fracs. These give x77 to x97 and x138 to x172 respectively which is ideal in many conditions.

If the seeing is really stunning then I occasionally use the zoom down to 3 mm or the 2.5 t6 in the 106mm which takes me up to x276. This is right at the limit of what it will take but I used it on mars a couple of times earlier in the year with very good results.

As often said though, mags in the x150 to x200 range are used far more often.

Stu

[Moonshane]

the best scope for highest powers in the best conditions is the one with biggest aperture / best optics. resolution is a factor affected by aperture. unfortunately, we rarely get the conditions described above so we compromise. my best views of Mars have been with my 16" f4 dob masked down to 170mm (effectively f11) at about 300x with my 3-6mm Nagler zoom set at 6mm. take the mask off and the detail is still there but seeing conditions affect more aperture more adversely so it's more intermittent.

[Polar Bear]

I have been told that the best magnification I can expect from my 8SE is with a 10mm eyepiece, which I have, so I was just wondering which scopes would allow the use of a 3.5mm eyepiece, and what I would expect to see with it.

A 3.5mm would suit a scope like my 150mm F5 C6-N newt. This would give 214X mag, well within the scopes capabilities. Would be good for Moon observing and the larger planets.

Paul

[michael.h.f.wilkinson]

I use a Pentax XF 8.5mm quite frequently in my C8, and combine the 12mm T4 with 2x Telextender to get 6mm, and once or twice did the same with the 10mm Radian to get a 5mm (only on Mars and the moon). I really want to have a 7mm in between. I used to have one, but sold it when I got my (previous) Radian 8mm.

Regarding the question: scopes faster than F/7 could handle the 3.5mm (half the F-ratio gives ep focal lenght in mm for the maximal theoretical magnification). A 2.5 is OK in scopes faster than F/5 (but it might see little use)

[Pete Presland]

i have used my 3.5mm Hyperion it gives a ridiculous mag of around 770x but the view err... is not great

[E621Keith]

I've just recently been doing a lot of testing with a 3.5 vs a 2.5 mm EP in a good quality 80mm F/6 refractor. I think the 3.5 is great, but it's probably as low as I will want to go when using this instrument. I don't really see more with the 2.5; it's just bigger, and as you get into those high mags, eyepieces become less comfortable to use and you can be bothered with floaters. But 3.5 is really effective and fun.

Interesting, I found the opposite when I tested my XO 2.5 vs Radian 3 on Jupiter and Saturn. The XO consistently delivered sharper images with better detail and contrast.

Having said all that, the view from the 80mm wasn't as good as my C925+LVW13, so don't go and buy a 80mm APO for planet if you have a C8 already. The 2.5mm is only useful on my Lomo 80/480, none of my other scopes can handle it. A 3.5mm will be more useful eyepiece for most 80mm.

[Naemeth]

I think the best answer to your question is to use a 3.5mm EP in a scope where the focal length is short enough to give you around 200x - 250x magnification, providing the optics can support this, so larger apertures would be better as they give better resolution.

With these calculations, you are looking between 700mm and 875mm focal length .

Of course, you can have a scope with a shorter focal length, but in this case the 3.5mm EP would not be the limit of the scope (such is the case with my Skywatcher 130P Heritage), for that maximum I have to use a 2.5mm EP.

[LukeSkywatcher]

I often use an 8mm EP with my 8SE, mainly for planets and the Moon. I have also used a 6mm with the same scope for the same objects. I have not tried my 4mm Omni EP yet with the scope so cant comment.