4mm EP - Useful magnification question?

[Catweazel]

Hi again folks,

I have been looking at getting a 4mm EP for planetary viewing. I have 3 scopes, a Megrez72 APO frac, an Evostar 120 frac and a 200P f5 reflector. I am guessing that the 4mm EP would be too powerful for the first two in most circumstances, and OK on the 200P. Does that seem right?

Magnifications would be:

Megrez - 108x

Evostar - 240x

200P - 250x

Any advice much appreciated. Thanks. CW

[John]

The Megrez should be OK for 120x or a bit more so that's OK. With the other two scopes the 4mm could be used on nights of really good seeing on the moon, binary stars, Saturn and Mars but be prepared to back off a bit if the image is not clear.

[ronin]

Any particular 4mm ?

If a plossl then suspect not great on any, if a planetary then agree with John. Megrez should be OK but the other 2 I would doubt if the image quality would be worthwhile.

[Moonshane]

I use my 6-3mm Nagler reasonably regularly at 4mm on the moon and double stars in my scopes. and this creates 400x and 460x, albeit with comfy eye relief at 10mm.

[Catweazel]

Thanks John, I got that completely the wrong way around then

@ronin, I was thinking of getting yet another TMB Planetary; may not be worth bothering just for the Megrez though, as I generally use that for AP, and get a fairly decent view of Jupiter & Moon through my 5mm on visual.

Thanks again guys!

[RikM]

I have had a couple of nights with my 250PX using a 10mm with a 2.5x barlow, giving the equivalent of a 4mm. When the sky will take it, it's very nice to have available.

[Ags]

I would go for it and get one - 250x should be doable on some nights and some targets with the 200P.

[Catweazel]

I struggle to split double stars with the Megrez, as it has a Dawes Limit of 1.611 arc/seconds. I wonder if it would improve the doubles with the Evostar though?

[Ags]

In my experience doubles can take silly magnification, and 240/250x is far from silly - it's an ambitious magnification, but not outrageous :-)

[Naemeth]

Personally, I'd go for the 4mm, and probably get a 6mm too so you can squeeze out all the magnification possible from the conditions.

[rwilkey]

Hi CW, from my viewing preferences point of view, I would not consider a 4mm (250x) even with the 200P. It would not get much use with me. I think the 200P is more suited to lower magnifications and wider rich fields.

[earth titan]

Have to say I've never really found any use for anything smaller than 6mm in a reflector or SC. My smallest usable is generally 8mm in UK skies.

Typed by me on my fone, using fumms... Excuse eny speling errurs.

[michael.h.f.wilkinson]

People are sometimes timid with magnification. I use my 7mm quite a bit in the C8 (290x) and the 10mm and 8.5mm (203x and 239x) are used very frequently indeed. On Mars I even go up to 338x (12m plus 2x TeleXtender) or even 406x (10mm XW in TeleXtender). A 10" scope should be able to handle 250x with a lot more ease.

Remember that it is not just in nights of perfect seeing that these come in handy, but even on ordinary nights there are (brief) moments of near perfect seeing. Stay at the scope and try to catch them! Great fun when it pays off.

[alan potts]

I don't go above x250 very much as I tend to like a clear image. Shane must have some super stable air near to him, I know he has a 16 inch but i would have thought 400 plus was pushing it a bit. I only tried this magnification in my 12 inch when i was looking for the center star in the ring nebular, and I saw it.

Maybe big scopes handle it that much better, but I would not have thought a 12 inch was small.

Alan.

[Moonshane]

I tend to use the higher mags near the Zenith as this is where the air is indeed more stable with less atmosphere to look through and less influence from chimneys etc. It's most usable on double stars where I can often use more) and the moon. usually Jupiter is best between 150-200x but for fun I sometimes rack the power up to 460x (4mm) or even 613x (3mm) but the view is quite mushy as you'd expect.

[michael.h.f.wilkinson]

There is simply less air to look through at zenith. On December 7, I could do 203x on Jupiter early on, and managed 239x near zenith.

[freeflyjay]

I just got a meade 4000 zoom the other day, 8-24mm (nice bit of kit) and tried it with a x2 barlow at 8mm on jupiter a couple of nights ago through my 250 dob gives 300x mag, stunning and clear as a bell grs and banding really clear, last night went out with newly aquired 3x barlow which can go upto 450x, but could only just manage around 250x-300 before quality started to suffer, so guess it`s alot to do with conditions, but for brief times jupiter would take 450x but only for very short periods and to be honest a bit too much nudging at that mag with a dob.

[perrin6]

I thought the 200p was F6 ie 1200mm fl and the evostar 120 1000mm Focal length.

I regularly use 300X + even in my 222mm newtonian for the same reason stated by Michael above ie. that even in moderate seeing the air will steady momentarily so aiding the splitting of v. close double stars. I use v. high magnifications on the moon & mars as their high surface brightness tend to smear detail at moderate powers - perhaps due to my 47 year old eyes ?

[RikM]

There are two versions of SkyWatcher 200P. The Explorer 200P f/5 FL = 1000mm and the Skyliner 200P f/6 FL = 1200 mm. the Evostar 120 is indeed FL = 1000mm