Meade 40mm Series 5000 Super Wide Angle Eyepiece .

[Dave Wall]

Has anyone used the meade 40mm Series 5000 Super Wide Angle 2" Eyepiece . Ace camera's have them on sale for £149.99 seems a good deal.

[E621Keith]

Not sure about the 40mm SWA, but the 40mm SW Aero ED is cheaper (£135).

What scope do you have? If you have a fast scope newt, a 40mm may black out due to the over size exit pupil.

[Dave Wall]

Hi Keith i have a skywatcher 200 mate

[John]

Is that the F/5 equatorially mounted one or the F/6 dobsonian ?.

40mm is probably a bit on the long side for either really.

[Dave Wall]

F/5 equatorially mounted one John.

[alan potts]

Dave,

I have one and it is a very good eyepiece as long as you use it in a scope no slower than F7 I used it for a long time in my LX200 as a wide field, I then bought a 41mm Panoptic.

Alan.

[alan potts]

Sorry I was talking and pressed the wrong button. For your scope you really need something no longer than 35mm, the 40mm will have an exist pupil that is too big. This means that the light that your scope is collecting has been made into a cone that is larger than the pupil of your eye can open to, so light is being wasted. For young people this cone size is generally no larger than 7.0mm in size but for old gits like me 5.0- 5.5mm is nearer the mark. You find this out by dividing the F/L of the scope into the F/L of the eyepiece.

Alan.

[John]

F/5 equatorially mounted one John.

I'd stick to around 30mm as a maximum eye piece focal length then, for the reasons that Alan gives above.

[alan potts]

I am good at mistakes today and even John did not pick up on it, I was meanintg to say the Focal Ratio of the scope, I.E, If a scope is F6 and an eyepiece is 30mm the exit pupil will be 5mm.

Sorry for that,

Alan.

[rory]

so a 35mm e/p with a telescope focal ratio of f/6 would be around 5.8mm exit pupil ?

i.e- 35 / 6 = 5.83 ? that correct .

[alan potts]

Rory,

I hope so that is the way I have always done it but today is National make mistakes day. I think I got out of bed the wrong side, everything i touch has gone wrong.

Alan.

[Mr Moff]

Rory,

I hope so that is the way I have always done it but today is National make mistakes day. I think I got out of bed the wrong side, everything i touch has gone wrong.

Alan.

I'm having one of those days as well. Made a coffee earlier and put the sugar in the fridge.

A nice clear night in the garden should help.

To the op an eyepiece worth looking at in that price range is the Hyperion Aspheric 31mm. Or a televue 32mm plossl.

[deepspacehunter]

 I have a 12" Dob... f,5 and I have a MEADE 40mm SWA 5000 SERIES.....  ... and a 35mm PANOPTIC.... I have heard talk of ... too big of an exit pupil... lost light... and other problems... I am 57 years old and I TOTALLY LOVE the views that the BIG MEADE EP gives me in my DOB.... SUPERB FIELDS.... pinpoint stars throughout... The MEADE 40mm SWA is MY FAVORITE EP....

Mark

[Charic]

Dave.......You're pupils are variable in size during observation.  Deciding on your lowest powered eyepiece has certain  limits, and the limits are based on your own eyes! You need to estimate/measure your pupil size?

Now take your telescopes focal ratio and multiply this by the approximate size of your pupil, so take @ 6.3mm for your age? and f/5 and  you  end up with an EP of about 31.5mm.

I have an f/6 telescope and with a pupil size of 5.6mm ( this is my own working estimate ) I get an eyepiece of 33.6mm, well within limits, my 32mm Panaview works well for me.

Having too big an  exit pupil only allows the final image to be at its brightest, but your eye simply reduces this larger exit pupil to a size it can accommodate, effectively your eye is reducing the aperture of the telescope, as it cannot capture all 100% of the  bigger exit pupil.

In this case you would get the same image quality by simply using a smaller telescope?

[John]

I agree with Charic on this. Here is a useful Sky & Telescope article on exit pupils which is worth a read:

http://www.skyandtelescope.com/astronomy-equipment/a-pupil-primer/

The general views with these long focal length eyepieces in fast scopes can be nice but when you compare the views of deep sky objects, especially extended ones, with an eyepiece that generates an exit pupil that allows the full aperture of the scope to be deployed, you do notice that they show more contrast and brightness with the latter.

[russ.will]

I wouldn't worry too much about exit pupil - It's an overstated issue stated as law, when it's merely a rule of thumb. Yes, you may be loosing a little light, thus making your scope's effective aperture smaller, but you aren't loosing any angular resolution and you are still illuminating your eye with as much light as it can possibly accept. Have a look at this S&T article by Al Nagler.

The secondary shadow can be more of an issue, but I found my MV 34mm SWA (a de-badged 5000 Series) worked very nicely in a F4.9 Dob. Balancing was fun though!

Playing it safe, the Maxvision 28mm SWA is a very nice, well corrected EP in an F5 Newt, although again, they're quite heavy. It's certainly a much nicer EP than a SW Panaview and with the current ridiculous Euro/£ exchange rate, that would land for about £90.

Russell

[alan potts]

I fully understand all the exit pupil do's and don't, I like you Russell do not pay too much attention to them though it is of course nice to know what is needed to get the best from any given scope on a specific target. I tend to use really wide low mag views just for pleasure and my rule of thumb is, if you can do it then why not. You do have to go a fair bit over the 7mm in my M/N 190mm to see the seconary, I can use the 41mm Panoptic, just. The 55mm TV Plossl gave interesting results when I had it and was a bridge too far.

Alan.

[Charic]

I wouldn't worry too much about exit pupil - It's an overstated issue stated as law, when it's merely a rule of thumb. Yes, you may be loosing a little light, thus making your scope's effective aperture smaller, but you aren't loosing any angular resolution and you are still illuminating your eye with as much light as it can possibly accept. Have a look at this S&T article by Al Nagler.

The secondary shadow can be more of an issue, but I found my MV 34mm SWA (a de-badged 5000 Series) worked very nicely in a F4.9 Dob. Balancing was fun though!

Playing it safe, the Maxvision 28mm SWA is a very nice, well corrected EP in an F5 Newt, although again, they're quite heavy. It's certainly a much nicer EP than a SW Panaview and with the current ridiculous Euro/£ exchange rate, that would land for about £90.

Russell

Russell. Why do you say  overstated?

By trying to  match the exit pupil of the eyepiece  to your own pupil can only be of  benefit to  the optical light path into your eye. Exceeding this rule of thumb, as you put it, can only vignette the image or reduce the aperture, depending which way you exceed?

[russ.will]

Russell. Why do you say  overstated?

I say overstated, because it's frequently quoted as a hard and fast rule, when it's not. It's guidance.

Lets run with 7mm exit pupil for the sake of argument and plenty of people do, despite having no idea if they can even achieve 6, never mind 7mm. Does a 6.8mm exit pupil look noticably better and a 7.2mm look catastrophically worse? No it does not. If it worked like that, then there should be glut of 31mm Naglers on the market (or F5 scopes) from astronomers passing the age of 50.

I think Unc Al explains it quite nicely in the link I provided. he suggests a 7-8mm exit pupil as a maximum for reflectors, but read it and see what you think. I certainly suffered no blackouts in my F4.9 Dob and to be honest, was only just starting to see it with the 40mm when testing the theory. I'm 43 for the record.

The thing is, I personally don't think the EPs are the problem - It's this bizarre leaning the market has toward sub F5 scopes for visual purposes. Why aren't there more F6 scopes, especially in the sub 12" class? It would be easier on EP choice and quality (TV conspiracy?) and certainly save my aging back the grovelling around, bent double on subjects below 45deg declination! <insert decrepit emoticon> 

Russell

[John]

The difference that I have seen, and quite often, is that the contrast in extended deep sky objects is greater when the exit pupil is less than 6mm. Thats a personal thing I guess partly to do with my age and also the moderate light pollution that I have where I observe. Under darker skies its less apparent. so guideline is what it should be and no more than that.

[Charic]

I understand your take a little better......and I've read that article so many times in the past, and still I see new bits of info!

The 7-8mm is based on the theoretical maxim, but as he says, everyone is different. And no, a .5 here and there wont make a massive change to the exit pupil, but the theory I believe still remains true, based on trying to match the exit to pupil, for the best transfer of light into the eye, at least thats how I percieve it. At least its a starting point, so as not to venture to far from the extremes?

I still like and have often quoted the A.N line, about framing your subjects.