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32mm Televue Plossl problems


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Hey all,

Finally after some good weather I have had the opportunity to use my newly bought Televue 32mm Plossl.

Both in my 60mm refractor and 200mm reflector (now sold) I experienced lots of viewing problems :rolleyes: What I am finding is that is is nearly impossible to get my head and eye still and in the right place to view a circular field of view.

What I am finding is that massive black portions appear to block off my view whenever I deviate slightly in position. Is this a common problem?

I made my purchase based upon their great reputation and I am well aware of the quality of product and the pinpoint view I can get. But this situation is ruining it for me! My dad hasn't a clue what I am talking about and says it is the best thing he has ever looked through, so I am presuming this is an exit pupil thing?

Thanks :D

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Sometimes I experience this with some eyepieces, I was looking at Saturn through a friend's 6" refractor with a TS Planetary 8mm last night and I experienced the same trouble, there were times when the planet disappeared and would reappear when I moved slightly. It is a case of getting the eye into the correct position, some eyepieces allow you to get close, others not so.

It has nothing to do with the eyepiece or the scope being faulty, just a matter of position.

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Hi Adam, some Televue ep's are a bit tricky when it comes to eye position although I have never used the 32mm plossl, you have had the familiar kidney bean effect where it blacks out the view in large portions. I sit whilst observing which really helps and move my eye carefully into the ep, it can take a bit of time to get used to it, when I have shown friends and family some objects with the scope they too have noticed this effect. You are correct in assuming it is related to exit puple size.

here's a link on it

Telescope Reviews: Kidney Bean/Blackout Effect qqestion

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Hi Adam

It's a combination of a large exit pupil, and the increased eye relief of a relatively long focal length eyepiece. If your Newtonian is a fast one, it's quite possible that the exit pupil using the 32mm is greater in diameter than your own dilated eye pupil. And because the eye relief is so much greater than, say, a 12mm eyepiece, you have to hold your head further off while having to keep steady and square on.

There's nothing wrong with your TV eyepiece - it's just a different viewing experience. If you can't get on with it (I own but don't often use 50mm, 30mm & 26mm eyepieces for much this reason) try a shorter, but wider field eyepiece. I love the 19mm Panoptic - a similar true field to a 26mm Plossl, but greater magnification, and darker background.

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Very helpful thanks all, it puts my mind at rest.

Neil is there a way of me know what length of shorter eyepiece would be suitable?

I have been thinking about a panoptic for a long time. Perhaps the 27mm?

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What you want to do is avoid an exit pupil of more than about 5mm, maybe 6 if you have young eyes that will open wide! More than 7 is a total waste of time. To calculate the exit pupil divide the aperture by the magnification. (Magnification is focal length of scope divided by FL of EP.) This should inform your choice of EP.

Being seated makes finding the right eye relief much easier.

Olly

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Thanks for the help Olly, nightfisher perhaps they have different eye reliefs?

I always thought the more eye relief the better hmm...

With my 200p dob and 32mm plossl. It would be 1200 divided by 32 equals 37.5 magnification. 200 divided by 37.5 equals 5.3mm eye relief?

Now from what Olly mentioned I am guessing that is too high?

Something strange is that I am 22 years old and my dad is 55, yet I am the one with the problem?

Edited by Adz
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Hi Adam

As Olly says, avoid excessively large exit pupils. In terms of the arithmetic, the newtonian is 1200mm focal length, 200mm aperture. 1200 divided by 200 is 6, so your f/ ratio is 6. Olly suggests a maximum exit pupil of 5mm, 5mm times 6 gives a longest eyepiece length of 30mm. At the other end of the scale any exit pupil much below 0.75mm is starting to become hard work, so your shortest eyepiece should be no shorter than 0.75mm times 6 ie. 4.5mm.

Lots of manufacturers state the eye relief of a given eyepiece. The comfort factor of 20mm eye relief is the same, irrespective of whether in a long f.l. widefield eyepiece, or a long eye relief (sometimes branded LER) planetary one. Find an eyepiece you feel comfortable using, and use its eye relief as a guide when choosing others.

The 27mm Panoptic is rather close to the 32mm Plossl in focal length. It may present the same problems as the Plossl. I also think sky backgrounds would tend to be rather light. Unless you're lucky enough to be where Olly is.

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Thanks Neil very helpful.

I see others on this forum rave about the 32mm Panaview from Skywatcher. Surely the math we have done doesn't rule that out completely?

I shall have another venture out the the eyepiece tonight and report back.

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Surely the math we have done doesn't rule that out completely?

It doesn't rule it out, but the sums suggest "proceed with caution". If you have an exit pupil issue with the TV32mm Plossl, you may also have one with any other 32mm eyepiece. Also check what the eye relief is on the Panaview. Some of the wide angle eyepieces I have tried have short (too short) eye relief.

Best,

Neil

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Well I just had a great session trying out everything on the moon.

For me the most easiest position of eye etc. viewing seems to happen when my eye is closer to the glass than when it is further away (even if it is less comfortable being right next to the glass)

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You have got the rubber eye cup in the "up" position havn't you ?. When they are supplied, eyepieces some times have the eye cups folded down and I once met someone who did not realise that, unless you wear glasses, they are meant to be used in the "up" position - he could not get on at all well with any of his eyepieces until he found that out !. The TV 32mm Plossl has a particularly large eye cup I seem to recall.

Edited by John
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Yeah I am using it with the eyecup up thanks John. Oddly enough though, when using my binoculars, using the rubber eyecups down seems to be more comfortable for me!

I am willing to give this EP some patience

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