Will a TV 3.7 EP cut it on a 130mm refractor

[axle01]

I have a United Optics 130 mm Refractor Triplet 925 mm focal length and F7 and I put a Explore Scientific 6.7 EP 82* on it last night which is about X 138 and the view of Saturn was great but I have a TeleVue 3.7 Ethos 100* on the way which will be 250 X, will this be to much or will I get even better views of Saturn.

Alan

[michael.h.f.wilkinson]

Try it! That is the best way to find out. 250x is a bit much perhaps, but tastes differ. Saturn is rather low in the sky this year, so conditions are not optimal. However, under really good conditions, 250x for a 130mm triplet it is not way over the top. I would not advice you to buy such an EP (5mm might be a better option), but as you already have it, just give it a go, I would say. Looking forward to hearing the result

[axle01]

Try it! That is the best way to find out. 250x is a bit much perhaps, but tastes differ. Saturn is rather low in the sky this year, so conditions are not optimal. However, under really good conditions, 250x for a 130mm triplet it is not way over the top. I would not advice you to buy such an EP (5mm might be a better option), but as you already have it, just give it a go, I would say. Looking forward to hearing the result

Thanks for your reply, the EP was $150 off new price and I'm told it is in as new condition so I snapped it up, sould be here next week.

If I see a good 5 mm at the right price I will look into it.

Alan

[John]

I use 257x with my ED120 refractor on Saturn, the Moon and binary stars and get some great views. I use a Pentax XW 3.5mm for this. The Ethos SX 3.7mm will deliver fantastic views with your scope if the seeing conditions are good.

It's good to have a slightly lower power to fall back on for when seeing conditions are not so great and I have a 5mm XW (180x) or I can use a Powermate on my 8mm Ethos for 225x. It's good to have some high power options

[DirkSteele]

The OP, according to his profile is actually based in Australia, so Saturn will be better placed for him than us poor Northern dwellers. I have often taken (when sky conditions allow) my TMB 115 triplet Apo to 250x and had great results. I imagine you will have some great views.

[axle01]

I am happy with the 6.7 but I will keep my eye out for a good 5mm.

Can't wait for the Ethos to turn up.

Sorry Matthew I was just a lucky to be born an Aussie.

Alan

[michael.h.f.wilkinson]

Hadn't seen the downunder bit. Saturn should be ideally placed for you. I have on occasion taken my C8 to 290x on Saturn, and it is great. On Mars I have even used 406x on a night of outstanding seeing. Hope the Ethos arrives quickly

[Stargazer_00]

Certainly a 3.7mm Ethos is more likely to have been designed for your type of scope than any other, i would say.

[umadog]

Give it a shot but expect the image to be on the dim side, since you will have an exit pupil of 3.2/7=0.46mm If your optics are good then you should be able to use this power, although it might be more suitable for double stars than for planets: http://www.cloudynig...php?item_id=547 Personally, I find when planets are dimmed that much that they lose detail, so I like exit pupils >=1mm. It's a personal thing, though. Also, floaters (should you have them) become more of a problem at smaller exit pupils. At the high power end you probably want the eyepieces more closely spaced. e.g. a 5 mm eyepiece would be useful too. That would give you an option between 130x and 250x.

[Stargazer_00]

3.7/7 = 0.52. not much difference but critically over the 0.5mm that's quoted as lowest practical exit pupil. personally I think you'll see floaters particularily on bright objects like the moon and planets. I find anything less than 0.7 shows floaters as intrusive but floaters are very much related to the individual in both physical terms and how much they actually distract your perception of the view.

[umadog]

Oops, yes. Got the exit pupil calculation wrong!

[LukeSkywatcher]

250X for a 130mm scope here in Europe is doable under ideal conditions. Maybe in Oz it would be more realistic due to local conditions.

[John]

3.7/7 = 0.52. not much difference but critically over the 0.5mm that's quoted as lowest practical exit pupil...

Rules are fun to break

My Pentax XW 3.5mm gives .4666 with my ED120 and I do see one or two floaters when viewing the moon with it. Not enough be be distracting (for me) though and not at all an issue on objects that occupy a lot less angular size such as Saturn and Jupiter.

The lunar surface at 246x and a 110 degree apparent FoV with a good apochromat refractor is going to be a stunning sight and I envy the OP the opportunity to see it

And under Australian skies too !

[axle01]

Thanks everyone for your replies, I have just had conformation the eyepiece has left the US and should have it late next week.

Alan