Decent planetary EP for 80mm f/6 APO

silversheltie · #1 12-03-2016, 12:13 AM

Hi all, I am looking for some help choosing a decent EP for planetary work with a f/6 LOMO 80/480 apo refractor. Right now I have the 5 and 21mm Baader Hyperions.

The planetary EP I am currently using is a 2.5mm skywatcher UWA (A TMB planetary clone). It rattles and has some smudges which can been seen when it is used. It's a long story...

It gives okay views on the planets but it looks like that 2.5mm is pushing the limit for the scope. I am looking for a 3mm EP instead which would still give a x160 magnification.

I have done some research and have found a few possible choices: A replacement Skywatcher 2.5mm, an Orion edge-on 3mm or the Long Perng planetary 3mm. The Long Perng seems much cheaper and possibly the same as the edge on. I have also thought of a Radian or an actual TMB Planetary II but they don't seem to be very easy to find in Melbourne. Does anyone have any opinions on these eyepieces, or maybe something else? Thanks for your help.

SkyWatch (Dean) · #2 12-03-2016, 11:11 AM

I have used the LP 3mm. I think you are correct in that it is the same as the Orion Edge-on, but lots cheaper!
It is a nice eyepiece, and sharp to the edge even in an f5 scope. Great eye-relief. It does show a bit of reflection from bright objects just out of the field, like the moon and Jupiter, and it doesn't offer quite as bright an image as the TV 3-6 zoom operating at 3mm- but it is hard to pick much difference. (A slight difference in colour too.)
However, for the price I don't think you can go wrong - and it doesn't rattle!

All the best,

Dean

silversheltie · #3 12-03-2016, 08:51 PM

Ended up ordering a vixen SLV 2.5mm from a recommendation on SGL. looks to be better quality and don't mind the smaller FOV!

MortonH · #4 12-03-2016, 09:48 PM

Conventional wisdom is that the maximum useful magnification is twice the aperture in mm. Once you go beyond that the images get dim and you start to suffer from diffraction effects.

The 2.5mm will give you 192x. Might be ok on the Moon and double stars but I suspect the planets will appear too dim to be satisfying. Let us know how you go.

silversheltie · #5 12-03-2016, 10:20 PM

Thanks for your input, will definitely do. I have a 2.5mm already as said in the OP and it is suprisingly good, with decent detail and brightness, but it could be better. Can't wait to see how the SVL does, it should arrive on Thursday. I am aware that a small aperture refractor is not the best choice for planetary viewing

Renato1 (Renato) · #6 13-03-2016, 03:29 AM

Your new eyepiece delivers 192X, which equates to 61X per inch of aperture.
APO refractors are meant to be able to give decent results at somewhere between 50 to 100X per inch depending on their quality, so there is a good probability that your eyepiece will be fine with good atmospheric conditions.
Regards,
Renato

silversheltie · #7 13-03-2016, 06:58 PM

thanks for your input Renato. Will see how it does.

Renato1 (Renato) · #8 13-03-2016, 10:14 PM

Quote:

Originally Posted by silversheltie

thanks for your input Renato. Will see how it does.

Just don't be unduly concerned if you initially get mushy images - it can just be due to the atmosphere - if the stars are flickering, you won't get a sharp image.

When I used to live in suburbia surrounded by houses, I'd often get mushy images some nights when I took my 80mm ED refractor to 160X or more - though I could see the cause of the mushiness by defocusing the image (sometimes it was the atmosphere, sometimes the neighbours' heaters). But on some nights I would get nice sharp images.

Unfortunately, now that I've moved out of sububia proper to a place surrounded by one acre blocks, but next to a gully and near the bay, I get mushy images most nights. Sharp images are a rarity here.

So pay attention to your surroundings - is the atmosphere flickering? Are you looking over your own house, or a neighbour's house which has been hot all day but is now cooling down? Or which now has heating going?
Regards,
Renato

silversheltie · #9 13-03-2016, 11:42 PM

I'm excited to see how it does! I just hope it doesn't turn out to be a bad decision but LOMO refractors are supposedly very good so it should be able to take advantage of the high magnification. Will wait for a day with steady seeing, its usually hit and miss in Melbourne.

silversheltie · #10 17-03-2016, 03:12 PM

Unfortunately theres been a delay - the shop didnt actually have it in stock so it is now being ordered from japan,it will take at least a week longer.