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M45 - eyepiece to see the whole thing?


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Hi Guys

I was happily ferreting around the further reaches of the cosmos last night using my longest eyepiece (24mm maxVision 68deg on 250 f4.8 dob) when I headed for the comfort of M45. The view was lovely but frustratingly incomplete.

Obviously, this will not do. So a short look on the ES website uncovered a MV 34mm 68deg. My question is 3 part|:

1/ would this show me the whole of M45?

2/ if Yes - what other targets would benefit most from this eyepiece over the 24mm 68deg.

3/ is this the best option for this scope / price / target?

Paul

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I have the 250px Flextube Dob and the Televue 31T5 fits it in beautifully. It is something I go to every session.

It's not cheap but I haven't regretted it for a second. The sharpness and contrast make it a superb sight.

Other objects with the eyepiece I enjoy are M31, M32 and M110 in the same field of view, also the Beehive cluster although if memory serves me right I can't get that all in quite.

Because it is f4.8 it performs best with top quality eyepieces. My advice would be to buy the best, one eyepiece at a time. I have to admit i'm a Televue fan.

Simon

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I have the 250px Flextube Dob and the Televue 31T5 fits it in beautifully. It is something I go to every session.

It's not cheap but I haven't regretted it for a second. The sharpness and contrast make it a superb sight.

Other objects with the eyepiece I enjoy are M31, M32 and M110 in the same field of view, also the Beehive cluster although if memory serves me right I can't get that all in quite.

Because it is f4.8 it performs best with top quality eyepieces. My advice would be to buy the best, one eyepiece at a time. I have to admit i'm a Televue fan.

Simon

TV Nagler 31mm is such an amazing eyepiece. I always borrow one from a friend whenever we meet up. Absolutely superb in my 8" F4.5.  But that said, my ES 82 30mm does an almost as good job for considerably less money. You really have to pay for that extra 5%.

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Thanks Guys.

I'll get saving! I'm sure that some green will sidle into my collection at some stage.

Wonder how long I'll be able to fight it......

Paul

You might as well give in now. I bought a Revelation set when I first started and whilst there's nothing wrong with it, with my gained experience i would advise a beginner to buy one quality eyepiece as you go. If you can buy some Televues 2nd hand they will retain most of their value. It all depends of course whether you have the funds available to do this.

Simon

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I use the 28mm ES 68° eyepiece as my lowest power with a Skyliner 250PX and that fits the whole of M45 in:

med_gallery_5915_414_5679.jpg

I used to use a 30mm Vixen LV, which was a superb eyepiece but the larger exit pupil meant that the background sky was very bright and I didn't get the contrast I wanted. Dropping to 28mm (or a 27mm Panoptic as an alternative) just gives it that extra pop for me. I guess it depends how dark your skies are. If my sky was darker I think I would have gone for 30mm ES 82°, which is also very good in the 250PX.

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Why not buy a 6" newt f5. that would give you a field of 2.2 degrees which is more than adequate for M45 and cost about £50-100 used. a new wider field scope is often cheaper than a wider field eyepiece.

the view of the pleiades through my (£25) 114mm f4.4 newt and tv 25mm plossl (£60) (field of 2.5 degrees) is much nicer then my 16" dob and 26mm Nagler (field of 1.2 degrees) but it is also nice in my 12" dob and 26mm Nagler (1.8 degrees).

just encouraging a different line of thought by the way.

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Why not buy a 6" newt f5. that would give you a field of 2.2 degrees which is more than adequate for M45 and cost about £50-100 used. a new wider field scope is often cheaper than a wider field eyepiece.

the view of the pleiades through my (£25) 114mm f4.4 newt and tv 25mm plossl (£60) (field of 2.5 degrees) is much nicer then my 16" dob and 26mm Nagler (field of 1.2 degrees) but it is also nice in my 12" dob and 26mm Nagler (1.8 degrees).

just encouraging a different line of thought by the way.

Great suggestion - sometimes some lateral thinking is needed  :smiley:

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TV Nagler 31mm is such an amazing eyepiece. I always borrow one from a friend whenever we meet up. Absolutely superb in my 8" F4.5. But that said, my ES 82 30mm does an almost as good job for considerably less money. You really have to pay for that extra 5%.

Hmmm, I'm toying with those two to replace my Aero ED 30. I have a 7mm Nagler and tbh I find the eye relief a little tight. How does the eye relief compare between the Nagler 31 and the ES 30? Also what are their weights???

Sorry to gatecrash the thread Paul :-S

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Good suggestion Shane. I think M45 looks much better when seen in a larger fov which allows it to be framed with dark sky. It just puts it in context and allows you to see the shape of it. As said, somewhere above 2 degrees is enough for this, the 31t5 would just about do it in the 250, but a shorter focal length scope would be another way around it.

Stu

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Looks like M45 is 110 arc min so say 2 degrees, your present set up gives 1.36 degrees.

You need about 50% more so either similar type EP at around 36mm or the 24mm at ~100 degree.

ES82 at the 30mm 2" fitting would do it.

So would the TV 55mm plossl

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My favourite view which encapsulates M45, is through a pair of 15x70 binoculars.

Aye, that said, M45 is the perfect binocular object. I always find that as the telescope view is back to front it just doesn't look like the M45 you recognise with the MK1 Eyeball.

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Binoculars! I've got some of those! Didn't even occurs to me. I guess that it is a case for "best tool for the job" - Exam question answered.

Obviously I will give in and get a longer eyepiece for the other big objects which aren't so bright.......

I think that M45 really benefits from having a decent amount of surrounding starfield to contrast with the spectacular M45 stars.

Paul

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Hi, at f4.8 your going to have to consider the issue of exit pupil and under normal suburban skies id go nothing over 5mm and even in dark skies im not sure id go much further depending on your age. So with this in mind I think youd start losing light at 24mm eyepieces and above so the 34mm you mention would be way too big and have the affect of stopping down your aperture.

the way around this is to go for the wider field 82 and 100 deree eyepieces to open up the field more but keep the same magnification , they are moremexpensive but worth it and with cheaper 82 degree eyepieces liken the wo uwan and es ones youll get a good view without paying tv money although im not sure if they make a 24mm so you have have to go for a 22mm.

hope this helps

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Why not buy a 6" newt f5. that would give you a field of 2.2 degrees which is more than adequate for M45 and cost about £50-100 used. a new wider field scope is often cheaper than a wider field eyepiece.

the view of the pleiades through my (£25) 114mm f4.4 newt and tv 25mm plossl (£60) (field of 2.5 degrees) is much nicer then my 16" dob and 26mm Nagler (field of 1.2 degrees) but it is also nice in my 12" dob and 26mm Nagler (1.8 degrees).

just encouraging a different line of thought by the way.

Great line of thought, you know! I absolutely adore my TV EP's, but when you consider that for each of them you could buy a pretty darn good scope, it sure does put things into perspective!

(This being said, my EP's aren't going ANYWHERE!) :)

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Hi, at f4.8 your going to have to consider the issue of exit pupil and under normal suburban skies id go nothing over 5mm and even in dark skies im not sure id go much further depending on your age. So with this in mind I think youd start losing light at 24mm eyepieces and above so the 34mm you mention would be way too big and have the affect of stopping down your aperture.

Good point. Not previously considered. Basic basic question here:

. Does this mean that my dark adjusted 40 year old mk1 eye would only pick up a beam of light 5mm in diameter at any one time? Therefore I would only get a portion of the potential view and would need to move my head around to explore the wider view bit by bit (rather defeating the object!!)?

Is there a simple calculation for exit pupils (and eye relief)?

Paul

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Age is one consideration as your dark adapted pupil size reduces as you get older but also light pollution in suburban areas means you never reach total adaption anyway. Im a similar age to you and always take 5mm as my limit so try to keep my exit pupils below that.

If you google "exit pupil" youll find some better explanations than I can give but basically if you divide the eyepiece focal length by the scope f ratio you end up with the exit pupil size ie a 30mm eyepiece in an f4 scope gives a 7.5mm exit pupil, the same eyepiece in an f6 scope gives a 5mm exit pupil.

cheers

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Thanks

Have been experimenting with my 24mm MV 68deg and recon that it is about on the limit of useful exit size for me.

Skies here in rural west Berkshire are reasonably dark. Can see M31 with the naked eye tonight if you know where to look.

Paul

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