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6mm and 6.7mm eyepieces

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#1 ac4142

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Posted 27 September 2020 - 09:56 AM

Hello, I have an Apertura 8 inch reflector (ad8) and I want to buy the highest magnification for it which I've been told is 6mm. Would there be much of a difference in magnification between the 2 eyepieces? example, I have a 9mm and a 10mm and both show saturn and jupiter at about the same size. Thanks!



#2 Barlowbill

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Posted 27 September 2020 - 10:01 AM

I doubt you would notice the difference.  I have an 8" Orion Dob and I use a 5mm a lot and occasionally a 3.2mm.  



#3 ac4142

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Posted 27 September 2020 - 10:15 AM

thanks viking!



#4 izar187

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Posted 27 September 2020 - 10:23 AM

It is going to depend on the eyepiece.

6mm what vs 6.7mm what?

 

A  6mm vt ortho is more comfortable to look thru, than  6mm plossl. IME

My old 6.7 Meade UWA was a whole different thing then either.

I personally like more eye relief down near these somewhat shorter focal lengths.

Longer eye relief also stays cleaner for me, longer.



#5 AstroVPK

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Posted 27 September 2020 - 10:23 AM

Hello, I have an Apertura 8 inch reflector (ad8) and I want to buy the highest magnification for it which I've been told is 6mm. Would there be much of a difference in magnification between the 2 eyepieces? example, I have a 9mm and a 10mm and both show saturn and jupiter at about the same size. Thanks!


Where did you hear that a 6mm eyepiece would give you the highest magnification for your scope? A 6mm eyepiece produces 200X on your scope. 200X is where Jupiter, Mars, and Saturn begin to show enough detail to warrant repeated observation. However, by no means are you limited to 200X. I regularly use up to 350X and even have on occasion used 480X (one exceptional night a month ago - Saturn looked like a picture from a book!).

Edited by AstroVPK, 27 September 2020 - 10:24 AM.


#6 dan_h

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Posted 27 September 2020 - 10:27 AM

You will see similar differences with the 6 vs 6.7 as you do with the 9 vs 10mm.  It can be difficult to see a 10% change in image size.  If you can't see some detail with the 6.7mm, it would be very unlikely that you would see it if you switched to a 6mm.  If you have a 2x Barlow, you can experiment for yourself using it with your 9mm and 10mm eyepieces.  It will provide a little more magnification than the 6mm but similar viewing conditions. 

 

Keep in mind the highest usable magnification is not a hard line. Nothing is going to break or get damaged if you exceed it. The views may not be so nice but that's about it.

 

Most of the time the highest usable power is dependent on the seeing. As you increase the magnification, you begin to see the effects of the atmosphere and this is what will make the image less pleasing.  Blurring details and wavy images are the result of turbulence, not poor optics.  High magnification may also make the flaws in your eye easier to see and can interfere with observing target detail. 

 

As others have stated, 6mm may not be the real limit for you and your circumstance.  

 

dan


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#7 ac4142

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Posted 27 September 2020 - 11:03 AM

Thanks for the help fellas. A tech told me at Highpoint that my 8 inch reflector could only handle 200x so a 6mm he said is about the highest i can go. i tried a 10mm 70 degree view with a 2x barlow (5mm) and got a rather fuzzy image of jupiter on a clear night as jupiter peaked in the sky. I got a crystal clear view of jupiter with a 15mm plus barlow (7.5mm) so i think the barlow works ok. I'll either get the orion 6mm 66 degree view or the explore scientific 6.7mm 82 degree field of view. what do you think? Thanks!



#8 e7FvPDZR

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Posted 27 September 2020 - 11:31 AM

I have an 8" f/6 dobsonian. What I decided on for maximum magnification was to get 7mm and 5mm eyepieces, which bracket the 6mm "ideal" maximum magnification.

 

I wanted Televue eyepieces, for a number of reasons, quality being one of the most important. The Delos line would be my preference, but at about $350 a piece, they are a little too expensive, and they are a little too heavy. The weight of the 6mm Delos is 16 ounces. So, I decided on the Televue Delite line. About a hundred bucks less per eyepiece, and around 7.5 ounces for the 5mm and 7mm focal length eyepieces.

 

I am very pleased with how this worked out. The 7mm (174x with a 1.2mm exit pupil in my scope) works great for Planets. The view of the planets is quite good unless the seeing conditions are poor. If the seeing conditions are great, the 5mm (244x with a 0.8mm exit pupil in my scope) works well. A few nights ago the conditions were spectacular, the view of the great red spot on Jupiter was amazing and Saturns rings were razor sharp. But, most of the time, the 5mm eyepiece just magnifies the turbulent view. But, at the "point of average seeing", the 7mm provides great maximum magnification views. Of course, it is a matter of personal preference, but I find the aperature in millimeters to be a good point of maximum magnification. (Which works out to a 6mm eyepiece in an 8" f/6 telescope.)

 

What's kind of funny, is that a single 6mm Delos would have cost me less that the two Delite eyepieces. But, I am pleased with how it worked out. I have a little more versatility when it comes to maximum magnification.


Edited by e7FvPDZR, 27 September 2020 - 11:32 AM.


#9 25585

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Posted 27 September 2020 - 11:33 AM

Baader Morpheus 6.5mm 76° waytogo.gif


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#10 RLK1

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Posted 27 September 2020 - 11:38 AM

ES 6.7 82AFOV. (Maxvision variant cheaper with same optics).



#11 ac4142

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Posted 27 September 2020 - 11:40 AM

thanks a lot fellas for the input. i'll either get the bbaeder or the es. wide view is great. i had a 4mm plossl and got rid of it because saturn was fuzzy. i can get it back and try it on saturn on a super clear night. 



#12 e7FvPDZR

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Posted 27 September 2020 - 11:41 AM

The difference between 6mm, a 9mm, and 10mm eyepieces in a 8" f/5.9 Apertura reflector is:

 

focal length     magnification     exit pupil
6                       200                     1.0
9                       133                     1.5
10                     120                     1.7



#13 ac4142

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Posted 27 September 2020 - 11:48 AM

sputnik what does exit pupil mean?



#14 BDS316

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Posted 27 September 2020 - 12:57 PM

I have owned a 6.7mm ES 82 for a while and enjoyed it in my XT8. Recently I was gifted a 6mm Circle T Ortho. Next time I do some planetary observing I'll compare them directly.

#15 ac4142

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Posted 27 September 2020 - 01:06 PM

thanks merc!



#16 CeleNoptic

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Posted 27 September 2020 - 05:38 PM

Thanks for the help fellas. A tech told me at Highpoint that my 8 inch reflector could only handle 200x so a 6mm he said is about the highest i can go. i tried a 10mm 70 degree view with a 2x barlow (5mm) and got a rather fuzzy image of jupiter on a clear night as jupiter peaked in the sky. I got a crystal clear view of jupiter with a 15mm plus barlow (7.5mm) so i think the barlow works ok. I'll either get the orion 6mm 66 degree view or the explore scientific 6.7mm 82 degree field of view. what do you think? Thanks!

 

High Point tech  probably said that knowing where you live. For planetary seeing is king all other stuff is secondary. PA is under the Jetstream so the seeing probably is mostly average or below. Being your southern neighbor in central MD I used to reach max of 200x on my 8" Dob on most nights and not that rare even less than that for planets.  But on very rare nights anything like 240x to 300x especially on Mars worked pretty well.

 

As for eyepieces, all depends on your preferences and budget. 7mm Celestrone XL-LX (it's actually 6.5mm), 6.7mm ES82 or better 6.5mm Baader Morpheus will be fine. Buy used from CN Classifieds or Astromart and you'll save a lot of money. Wouldn't recommend the 6mm Expanse for planets. I have one of rebrands (9mm Agena EWA) from that series and it has less than optimal light scatter control, sharpness and shows strong spherical aberration causing blackouts. But for DSOs the 9 and 6mm would be OK.

 

Also, please note that Jupiter and Saturn are quite low in the sky these years. For optimal views you need them at least at 30* above horizon or up that will happen next year and they go higher in 2022. But Mars is good now.


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#17 ac4142

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Posted 27 September 2020 - 11:43 PM

thanks apollo, you're right, he did ask me where i lived. i appreciate your input very much.



#18 chrysalis

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Posted 28 September 2020 - 03:40 AM

sputnik what does exit pupil mean?

Exit pupil is the size of the exiting light cone coming from the eyepiece. It is simply aperture (mm) divided by magnification.

 

Sky conditions affect maximum useful magnification.

 

On superb nights you could reach 50x/inch or more. On crummy nights, even going beyond 12-20X can be problematic.

 

I have both the 6 mm Orion and the 6.7 ES eyepieces. Both work nicely, but I prefer a wider field.

 

It appears your FL is 1200 mm (f/6). Magnification is calculated as objective FL/eyepiece FL. So 6 mm yields 200X, while 6.7 mm yields 179X.



#19 noisejammer

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Posted 28 September 2020 - 04:59 AM

I concur with Vlad's guess that your tech was expecting that you'll be seeing limited - I was about 250 miles north of you (Toronto) and my scope could very seldom do better that 200x.

 

As for a choice of eyepiece, it really depends on your budget. I would certainly be chasing down something with eye relief that is longer than an Abbe (orthoscopic) or Plossl design - unfortunately this costs a fair bit extra.

 

Some options that haven't been mentioned -

 

Takahashi 5LE and 7.5 LE - good quality eyepieces with 52* fields of view and great eye relief. $245 ea

(I have pairs of these for planetary binoviewing)

 

Televue 5 mm and 7 mm Nagler Type 6 - 82*. These are great although they're $330 ea.

(I have pairs of these too.)

 

Explore Scientific 6.5mm / 82* $249

(no personal experience)



#20 ac4142

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Posted 28 September 2020 - 08:01 AM

thanks chrysalis and noisejammer for great information!


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#21 OIC

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Posted 28 September 2020 - 08:09 AM

Don't believe everything you are told. I use my 4.7mm all the time on my 8". Under some circumstances it is too much, but it's one of my most used eyepieces.

Have fun with this wonderful hobby.


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#22 SeattleScott

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Posted 28 September 2020 - 09:07 AM

Meade 5.5mm UWA is another consideration.

When I got my first scope, an 8” reflector, what made the most difference in planetary views wasn’t upgrading from a Plossl to a Delos or anything like that. The major improvement came from purchasing a laser collimator.

Scott
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#23 csrlice12

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Posted 28 September 2020 - 09:45 AM

I checked in with Eyepieces Anonymous and they suggest buying them all and letting your eyes sort them out....they also asked to remain anonymous....



#24 e7FvPDZR

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Posted 28 September 2020 - 11:23 AM



sputnik what does exit pupil mean?

 

Exit pupil is the diameter of the light beam coming from the eyepiece of your telescope at the focal point. The human eye has a maximum pupil diameter of about 7mm for younger folks, maybe around 5mm for older folks. For a given telescope, the useful exit pupil range is about 1mm for maximum power to 7mm for maximum brightness. Older people 1mm to 5mm.

 

Depending upon the aperture of the telescope and the seeing condition, some people like to sometimes use a higher magnification that provides a 0.5mm exit pupil. But, the view becomes dimmer and defects in your eye may interfere with the view in older people.




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