is 8mm ep as low as i can go?

[LukeSkywatcher]

Howevere there are two limiting factors. The first is the aperture of the scope. A scopes maximum magnification is 2x for every mm of aperture. So for a 5" scope with an aperture of 130mm you get a theoretical maximum of x260 magnification. Bear in mind image quality drops off as you go towards maximum.

Well that answers MY question. Your answer fits my scope specs perfectly. My scope is quite comfortable with about 200x for lunar observing. Over that and it struggles. I guess "seeing" is also a big factor (something i sometimes forget). Last night i pushed it to 216x (which is ok observing the moon for me) but it started to throw a hissy fit when pointed at Mars (86x was the best i could use). Think i'll stick to 9-10mm (no barlow) for planets. It is about the best i have experienced.

[lostinspace]

i know what you mean paul, i spent some time watching saturn both with barlowx2 + 10mm together but found sharper more pleasing views (allthough slightly smaller) with just the 10mm on its own i`m wondering if it was the quality of the barlow lens not being very good. does cooling the scope do anything else other than reduce heat distortion? had three great days viewing ON THE TROT woo hoo happy viewing peeps

john

[John]

As the scope cools the warm air currents in the tube gradually disperse (more quickly if you leave the tube uncapped of course) and the mirrors cool down to something close to outside temperature. As both these things happen the quality of the images gradually improve but I've always suspected that warm air currents in the tube have a greater adverse effect on image quality than the temperature of the mirror glass.

Tube currents can be quite persistant and tend to cling to the walls of the tube - if you de-focuss a star to a disk you can see the currents and plumes of air moving around quite clearly.

Some scopes have fans fitted at the mirror end of the scope (and elsewhere on occasions) to speed up the cool down process - I guess you could fit one to your scope although a 6" should be cooled in 30-50 minutes.

The barlows supplied with scopes can be really poor quality - I've even come across some that are not achromatic which are pretty disastrous for image quality. I'm not suprised that the 10mm on it's own produces sharper images.

[LukeSkywatcher]

i know what you mean paul, i spent some time watching saturn both with barlowx2 + 10mm together but found sharper more pleasing views (allthough slightly smaller) with just the 10mm on its own i`m wondering if it was the quality of the barlow lens not being very good. does cooling the scope do anything else other than reduce heat distortion? had three great days viewing ON THE TROT woo hoo happy viewing peeps

john

I have up til RECENTLY only observed Saturn (or any planet) with a 90mm refractor. Mars has always been a non-starter while others have been great. Cooling the scope down is/was not an issue (3.5" refractor). I found Saturn an absolute WOW experience with just a 9-10mm EP (no barlow). Jupiter also the same.The Barlow i have is a cheap 2X celestron (EP kit one). I NEVER had luck with it when using my 90mm scope. It works pretty well with my new 130mm scope though ( i am using it with a 6mm EP for observing the moon). I have not yet observed Saturn etc with the new scope. In MY experience................planets look best with just 9-10mm EP (no barlow). Barlows only add an extra layer of glass to the equation.

I got my best view ever of Mars a couple of nights ago using the 130mm scope and a 15mm EP. I saw colour (instead of just white) and i detected a hint of polar cap also.

As both these things happen the quality of the images gradually improve but I've always suspected that warm air currents in the tube have a greater adverse effect on image quality than the temperature of the mirror glass.

Totally agree.

[johnkirkpatrick]

i just looked at mars with my scope (see sig) with my 2x barlow and 10mm wasnt up to much. it was as if the bottom area of mars had been smudged. like drawing a disc then rubbing your finger on the edge of it. i was viewing it at x130. the fact that even the slightest touch of my scope makes the most terrible shakes

and very hard to get a good focus

[LukeSkywatcher]

i just looked at mars with my scope (see sig) with my 2x barlow and 10mm wasnt up to much.

Bit too much magnification there. Drop the 2X and have another look. Wont be much better (depending on "seeing") but should help a little.

I am not washing my hands of Mars yet but it wont be my main focus again for a while. I'm really looking forward to later on this month when Saturn rises at a reasonable hour. I'm really looking forward to my first light of Saturn with my new 130P scope. It was/is mind blowing with my 90EQ.