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Alan White

Televue 32mm Plossl - Dissapointed

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I bought a new 32mm TV Plossl from Simon at Widescreen Centre a week or so ago; last week of the London Store, I paid £143.
Anyway, finally a short first light tonight and I am dissapointed, had set my heart on it being great :sad2:

Such long eye relief it kidney beans on my 6" 150p Newtonian, I stuck in my 25mm Meade 4000 and although the clarity was better in the TV, I found it very easy to use.
Big shame as my Mrs bought it for my 50th birthday, so doubly sad.

Is this just too much for my scope, the EP or me.
Your thoughts and advice please.

Edited by Alan White
Cannot type!

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 I bought one second hand and assumed I was one of the few who did not like it as the comments online were pretty good...... I used it twice and sold it on.  A significant outer portion of the field of view showed useless kidney beans implying the field stop may as well have been bought in like the 40mm. 

8mm through to 25mm are all brilliant performers.  

 

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I had one a while back, but stopped using it -  just too much eye relief -  your scope is not the problem. Ok you can buy  an extender for it but why should you have too.  After all, as good as the views are it's still just a 32 plossl.  Perhaps you could exchange it, tell them it was unsuitable.

Happy birthday anyway :smiley:

andrew

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Alan, I found the same with the TV 40mm Possl. Eye relief is just too much to get comfortable. I passed it on. If you can exchange it, I can recommend the 24mm Panoptic, I know it's about another £100 or so, but that's a magnificent eyepiece and the most  used with my refractor. 

Good luck,

Chris

Edited by Cjg
Typos
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The eyeguard extension transforms this eyepiece.  that said it's frustrating that such an extension is not built in

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I agree with the views above. The TV 32PL is excellent WITH the eye guard extension but that pushes the price up even further :dontknow:

It's one design where TV should have recessed the eye lens a bit to ensure that the rubber eyecup was long enough to correspond with the eye relief.

 

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32 mm Plössls have a long eye relief and may take some time to get used to, especially when the exit pupil is close in size to the user's pupil. 

Kidney beaning, however, should not happen with TeleVue or any other Plössls as they tend to have well behaved exit pupils. (Kidney beaning comes from spherical aberration of the exit pupil. Until the first generation Naglers this was a rare phenomenon.) Could it be blackouts that you're seeing?

I have a 32mm GSO Plössl. Had some blackouts at first, but got used to the eyepiece, and the blackouts disappeared. I think you too may get used to your 32mm Plössl.

Here is how blackouts occur.

Blackout.gif

With long eye relief, steady eye placement becomes difficult. The movements of the eye cause blackouts in which the image disappears from one side to the other. When the image is partially illuminated, it is as if a curtain is drawn over one side of the image

Here is how kidney beans occur

kidney bean.gif

With kidney beaning a kidney shaped shadow forms between the centre and the edge of the field, while both centre and edge remain fully illuminated. Kidney beans arise from even subtle eye movements, especially with larger exit pupils. When the eye movements get larger, blackouts will also occur.

Below, a kidney bean occurs as one of the red rays can not enter the eye, yet the more extreme off-centre green ray still can. (The brain inverts what's on the retina, hence the shadow appears below the centre.)

kidney bean demo.png

 

Fortunately, spherical aberration of the exit pupil is, to a large extent, a thing of the past.

 

 

 

Edited by Ruud
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Thank you folks for your input.
I think the extension may be needed, but as you have said, makes it an expensive Plossl.

As Rudd has shown, it may be black out rather than Kindey Beaning as I stated (you live and learn), thank you for that information Rudd.

It was something that I was much looking forward to using, perhaps too much so and the bar was raised too high. 
The other TV 20mm I have is stunning so had set the bar height.
Time or extension will tell.

 

Edited by Alan White
typos as always
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Could be that the world has moved on a bit from the Plossl design? Sure, the transmition is splended. But, there are limitations.

ie. Egg shaped sun in the outer 1/3 inthe 25mm TV.

But the main question must be around black outs linked to head positioning. 

 Why didn't TV sort this out.?

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1 hour ago, Alan White said:

Time or extension will tell.

That's the stuff! Pick yourself up and get back on it. All part of the fun and learning what works for you.

I struggled with eye placement, too, but now use an eye extender. It helps a lot.

Your Mrs bought you an eyepiece. What a lovely thing to do. Don't be disappointed.

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Like Floater says!

On pondering my reply earlier. Maybe we are asking a lot from an eyepiece that, whilst not cheap, is splended value for money. One thing is certain. That with your eye in the right place, the stars don't come any crisper and contrast is about the best that you can get!

It will be worth persevering. 

Paul

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As many others have said, an eye guard of right height may mitigate your issue.

There's simple, inexpensive way to make your own eye guard(starman1's post and the link to a picture there), see if it helps:

http://www.cloudynights.com/topic/405040-meade-uwa-24mm-2-dialectric-diagonal-159/?p=5212801

2 hours ago, Ruud said:

Kidney beaning, however, should not happen with TeleVue or any other Plössls as they tend to have well behaved exit pupils.

I beg to differ:smiley: If there's one brand plossl which has kidney bean effect, it's most likely to be Televue.

2 hours ago, Paul73 said:

Could be that the world has moved on a bit from the Plossl design? Sure, the transmition is splended. But, there are limitations.

ie. Egg shaped sun in the outer 1/3 inthe 25mm TV.

But the main question must be around black outs linked to head positioning. 

 Why didn't TV sort this out.?

Exactly, here's the link to Televue's plossl patent

https://www.google.com/patents/US4482217

Here's quote of relevant paragraphs:

" BACKGROUND OF THE INVENTION

As is well known in the art, a Plossl type eyepiece is a relatively wide field eyepiece comprising two achromatic doublets in which the crown elements usually face each other. Such eyepieces are capable of good performance, i.e., acceptable degrees of aberrations, to about a 50° field. Generally, in order to minimize aberrations at the exit pupil and distortion, all air glass surfaces of the eyepiece are made convex. However, thre have been Plossl type eyepieces used commercially in astronomical instruments in which the external flint surfaces are plano.

"

GENERAL DESCRIPTION OF THE INVENTION

For astronomical viewing, pupil aberrations and geometric distortions are not as important as the correction of coma and astigmatism which control image sharpness at the edge of the field.

The red marked sentences mean that TV plossl with its concave eye lens has more aberrations at the exit pupil than other plossls, and the kidney bean effect will show more easilty in day time than night sky.

Our eyes are all different, some may cope the kidney bean better, others don't.

 

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I'll have to make sure I avoid this EP. 

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Have to agree with the comments above.  While there's no doubting the optical quality of the TV Plossl - With the price of this EP now adding in the required eye guard extension makes this a seriously expensive Plossl!   What EPs do you have already?

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47 minutes ago, Davesellars said:

Have to agree with the comments above.  While there's no doubting the optical quality of the TV Plossl - With the price of this EP now adding in the required eye guard extension makes this a seriously expensive Plossl!   What EPs do you have already?

Dave I have the following do collection to date. Some good some reasonable and some are so so.

32mm TV Plossl

25mm Meade 4000 Plossl. Reasonable to good.

20mm TV Plossl.   Love it to bits.

15mm Meade 4000 Plossl Japan Made. Good but not as good as 20mm TV.

9.5mm Meade 3000 Japan Made. Love it to bits.

6.7mm Meade 4000 Plossl. So so. 

 

I measure the EP set against the 20mm TV and 9.5 Meade as the benchmark.

I am a working bloke, normal financial pulls so the price band I am in is where I will stay for some time. The 32mm to me was a lot of money to be honest.

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Personally I'd question the need for a 32mm EP for your 150p (which is f/5?) to be honest unless your skies are really dark LP you're not going to have enough contrast for DSOs with a rather massive exit pupil - so unless you're using it with a narrow-band filter on large nebulae I would stick with your 25mm as the longest focal length EP in your arsenal.

You've got some nice quality EPs.  Which focal length do you use the most and what is your prime observing interest?  i.,e lunar/planetary or DSOs or both?

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I've always been very happy with my 32mm, very wide field for a 50° EP and it's a useful finder. It is the ONLY eyepiece I have which gets used on every session. True there is too much eye relief and I pick up a fair amount of coma towards the edge, but it's never bothered me and the latter is my scope's fault anyway. I bought mine 2 years ago though when the price was a lot lower than it is now. Considering the jump I'm not sure I'd buy it today when there's superb wide angles you can pick up for less.

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1 hour ago, Davesellars said:

Personally I'd question the need for a 32mm EP for your 150p (which is f/5?) to be honest unless your skies are really dark LP you're not going to have enough contrast for DSOs with a rather massive exit pupil - so unless you're using it with a narrow-band filter on large nebulae I would stick with your 25mm as the longest focal length EP in your arsenal.

You've got some nice quality EPs.  Which focal length do you use the most and what is your prime observing interest?  i.,e lunar/planetary or DSOs or both?

Dave

I think you may be right, perhaps I am wanting something I cannot have from my location and scope.
I have light polution but also very local overlighting fromtwo sets of insecurity lights and they are not open to any negotiation from the two neighbors concerned.

I love lunar observation and planets when I can see them, try DSO but to be honest I hoped the 32mm would help, your right about the lack of contrast.
EP most used is the 20mm and 9.5mm, barlow the 9.5 down with my TAL x2 barlow. The 25mm is used as a step from the finder scope to scope view.
I am on an alt az AZ4 mount so sky hop badly still.

Sounding a bit mad here but I came from a cheapy old 80mm reractor to the 150p reflector and although brighter I think the scope is also partly my challenge as well as in it collect too much light and pollution so is not such a contrasty view, does that make any sense?

Thanks for the thoughts.


 

 

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Spike 95609 How do you deal with the eyerelief on your 32mm TV?

I see you have Vixen SLV at shorter FL, is the twist out eyepiece the solution to eyeplacement on these?

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13 hours ago, Cjg said:

Alan, I found the same with the TV 40mm Possl. Eye relief is just too much to get comfortable. I passed it on. If you can exchange it, I can recommend the 24mm Panoptic, I know it's about another £100 or so, but that's a magnificent eyepiece and the most  used with my refractor. 

Good luck,

Chris

I agree with Chris. £143 for a plossl, whatever the brand name, is ridiculous in my view. Go for an Explore Scientific 24mm 68 degree, available from several UK retailers for around £100. Argon purged (dust proof), waterproof, TV level build and much bigger field of view. Very nearly as good as the Panoptic 24mm but c£150 cheaper..No contest!


Dave

Edited by F15Rules
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Dave (F15rules) and Ben (Ben the Sane) you are both saying this about the ES and Ben said the same before I bought the TV.
I should perhaps have listened. 
 

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This is an interesting thread…

I have a TVP 32mm which, after I bought the 24mm 68deg ExSci became very redundant, particularly when observing from home, with the light pollution and air glow… the main issue I had was lack of contrast, not eye placement although reflections were very annoying.

However I did invest in an eye guard extender which has made the EP a lot more workable and user friendly, however I still, from home, use the 24mm or above because it keeps (and this is all in my head so is probably wrong) the exit pupil down..

My thoughts were if its bright and the Ep exit pupil is large and my eyes aren’t dilating enough then my eye isn’t getting the full benifit of the EP at work. (again I have no understanding of the techy side... just what the gremlins in my mind tell me!)

If I’m out and about in darker sky, then the TVP 32mm with an extender is a very useable bit of kit in my 200P Newt.  The extender certainly helps with placement and comfort in respect to eye relief..

It maybe interesting to see how the EP performs in your scope under darker sky’s, it could be a case of just the wrong location and too much LP for you to see it’s potential?

Just a thought..

Ta

Fozzie

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