6mm struggles

[iamjulian]

Hello, quick question. I have a 6mm EP that costs about £30 new. With my scope it gives 250x magnification, and apart from the moon, the views are always too dark and too hard to focus - globs, galaxies, planets. So is it the quality of the EP or the magnification?

My better quality 13mm gives far better planetary views than the 6mm. But should I look at getting a better 6mm, or would something more like 8mm or 10mm be a wiser move? Any opinions? Thank you.

[Merlin66]

Probably the seeing conditions are limiting your Magnification - I don't think it's the eyepiece....a 8-10mm sounds like a reasonable option.

[tbird]

I get good views of Jupiter with 8mm in my 12", depending on conditions.

[michael.h.f.wilkinson]

I can get 250x out of my 8" (using the 8mm EP) quite frequently on planets and the moon (but not on fuzzies, that requires lower mag!), but the seeing has to be good. A 12" should be able to handle that as well. In case of a fast Newtonian, collimation needs to be spot on as well. The speed of the Newtonian can also make focusing more difficult. Note that I also have 200x at my disposal, with a 10mm EP, and that is used more often. I am going to get a 12mm as well. In planetary observing, i find that matching the magnification to seeing is essential for the best views.

[Earl]

The more you push the optics the better the conditions need to be.

[rwilkey]

You need really good seeing conditions to get 250x, I have never managed it myself even though I have the capacity in ep's, my 8mm Hyperian has given me the best planetary views (125x) on Saturn last year.

[spaceboy]

As the others have said the more magnification you use the better the seeing has to to get a decent image. Also the more magnification you use the darker the image will appear as the exit pupil will be smaller. It's very rare I use x250 magnification and find x166 - x200 to be the most I can use on the average to good nights.

[catburglar]

The original post indicated that the views were too dark as well as hard to focus.

I'm assuming your scope is around F5- with a 6mm eyepiece that should give an exit pupil of around 1.2mm- this shouldn't result in an image that's too dark, but it will be darker than a longer focal length eyepiece. I have a small refractor and find that for many objects a 1mm exit pupil gives the best view because the sky background is nice and dark, but the objects still obvious.

The difficulty focussing could be seeing related, but could also be due to the narrow focal zone of an F5 scope. Do you have a dual speed focusser?

[brantuk]

A fast scope of f5 will be less forgiving of poorer quality eyepieces. What make is your 6mm eyepiece? I use a 5m Radian in my 12" dob and the view is allways clear and crisp and never dark. But I rarely get to use it with UK seeing the way it is.

You might benefit from a TMB or BST which I understand are good for the price. But I would try a few loaners at your local astro soc or obs group first, to find out what you feel would be best for you and your equipment:)

[iamjulian]

Great advice everyone, thank you. I am at f/4.9 and I don't have the dual speed focuser. I don't think that's really the issue though, more likely the quality of the seeing as you all suggest. The EP is a skywatcher "ultra wide". It was really nice in the old 6" at f/5, but then it was only at 125x magnification. Sounds as though something like an 8 or 9mm would be a better bet. Thanks.

[lukebl]

I would also add that I wouldn't attempt that sort of magnification on galaxies, as you suggest in your original post. They are simply to large (generally) and diffuse, and a much lower magnification is more suitable. Say, with a 25mm EP.

[iamjulian]

Fair point.

Another question, if you barlow an EP, does it reduce the eye relief? I am wondering whether a 1.5x barlow, which would give me about 170x would be a good move. But the eye relief is already tiny on the 13mm EP. Hmm.

[James]

I'll second what everyone is saying about the seeing - I usually stop at around the 180x mark as not that many nights allow much more magnification (a short focal length eyepiece is always on hand for those really good nights...).

Barlowing should increase your eye relief a little I think...

James

[newman]

Another question, if you barlow an EP, does it reduce the eye relief?

A barlow will actually do the opposite, it will increase eye relief. If that's a problem, Powermates don't do that, it's one of the main differences between a powermate and a barlow. Of course, like all things TV, it also comes with a hefty price compared to most barlows

[swamp thing]

Hi

Whilst I do agree that on Planets 250x is often more than enough to exploit the seeing. On DSO,s specially globs, your big 12" scope should easily be able to use a 6mm eyepiece, without the subject becoming to dark.

I use a 12mm + 2x Barlow very frequently in both my scopes without the object becoming too dark or difficult to focus.

In fact often the use of really high power helps to darken the sky background and bring out more detail.

It sounds to me as if yours has problems.

Barlows increase eye relief as James stated

Regards Steve

[faulksy]

i managed 270x and 290x last night on jupiter but had wait for those moments of calm.

[MjrTom]

i managed 270x and 290x last night on jupiter but had wait for those moments of calm.

That's impressive!

The most I could muster from Jupiter was about 100x, or 30x aperture. On the rare occasions can I push it to 50x aperture.

[faulksy]

That's impressive!

The most I could muster from Jupiter was about 100x, or 30x aperture. On the rare occasions can I push it to 50x aperture.

i would say so at 160x there was no deviation in contrst or clarity at all and around 290x you could see the cloud bands around the poles then you would get your good seeing spell and it was proper clear.a bit pale though which i think might have something to do with the glare of the moon:D

[Charon]

My best views of Jupiter so far have been with my 36mm Aspheric (56x), conditions have been poor over here.

[ronin]

If f/4.9 and if the eyepiece is a plossl then you are probably beyond the comfort zone of a plossl. You may need to consider a flat field eyepiece that are designed for the image curvature cause by fast scopes.

I would go get an 8mm Explorer, TMB or Flat Field eyepiece and reduce to around the 180x mark. At f/4.9 I would consider a flat field eyepiece as it could be the field curvature that is the root cause.

Also check the collimation, it will need to kept accurate all the time.

[JimFR]

Hello, quick question. I have a 6mm EP that costs about £30 new. With my scope it gives 250x magnification, and apart from the moon, the views are always too dark and too hard to focus - globs, galaxies, planets. So is it the quality of the EP or the magnification?

My better quality 13mm gives far better planetary views than the 6mm. But should I look at getting a better 6mm, or would something more like 8mm or 10mm be a wiser move? Any opinions? Thank you.

y'can't go far wrong with a decent barlow - you get decent eye relief, and a magnification boost. the downside is that your light is going through more surfaces. have you got a 2x ? might be worth getting a 3x barlow, or a 4/5x powermate.

[iamjulian]

Thanks Ronin, am leaning towards a TMB 9mm which would give 166x. I'm not really a planetary observer but it would be nice to get a nice view for when other people want to look at the planets through the scope.

Jim, thanks, but the more I read about barlows, the less I want one. A 5x Powermate would make the 13mm 600x

[Adz]

An 8mm Plossl I use 90% of the time and when the seeing allows its the 6mm BGO to grab 250x

[Mr Spock]

I never cease to be amazed at how low people's magnifications are. At x181 (13mm) a lot of detail on Jupiter is too small to see. On 50% of nights x261 (9mm) is of most use - on the other 50% I usually pack up, I don't see any point in looking at a fuzzy blob. On better nights x294 (8mm) is still really crisp. I don't go above that on Jupiter due to lack of contrast in fine detail.

On the very few excellent nights (rarities), x336 (7mm) on Saturn and x392(6mm) on the moon/Mars are my top limits. Even the 6mm is still bright though on planets.

For deep sky I keep to x181 (13mm) max on globulars and x107 (22mm) max on galaxies.

[James]

I never cease to be amazed at how low people's magnifications are.

The magnifications I use are largely determined by the seeing... on those very rare nights (2-3 in the last 3 years) where seeing has been amazing I've happily gone up to 400x (I've had to make sure the collimation is spot on mind...)

James