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Too much eye relief on a 40mm Plossl

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#1 Mbinoc

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Posted 12 June 2019 - 07:33 PM

About 2 weeks ago I ordered some inexpensive Plossl eye peices, (a 40mm, 25mm, 10mm), and just recieved the last of them today. The 10mm and the 25mm are both comfortable to use, but the 40mm requires me to hold my eye a greater distance from the cup (about 1/2") making it more diffulcult to center the image. Is this normal?

 

To combat the issue, I cut a small piece of pvc to use as a spacer. The pvc spacer pushes right into the existing cup, and makes it much easier for me to look at it from a apropriate distance. For storage the spacer fits right over the base of the eyepeice, and still fits within the supplied case.

 

IMG_6124.JPG

 

IMG_6126.JPG

 

Once I find the most comfortable size for the spacer, I think I may make it a more permanent modification by painting the pvc black,and do something like this and then glue the the rubber cup to the end of the pvc.

 

IMG_6129.JPG

 

Maybe the extra space needed is just something you get used to with time. But I'm coming from the factory eyepeices that get supplied with scopes, and am used to holding my eye closer to the cup.


Edited by Mbinoc, 12 June 2019 - 07:57 PM.

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#2 ngc7319_20

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Posted 12 June 2019 - 07:48 PM

Yup thats normal with 40mm Plossls.  Another option is to get one with a sliding / adjustable eyecup:

https://agenaastro.c...n-eyepiece.html


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#3 msl615

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Posted 12 June 2019 - 09:13 PM

Yes, and the Televue solution for their 40mm plossl is an eyecup extender and/or a DIOPTRX to move your eye away to the correct distance.  Without some type of spacer, as you have created, using the eyepiece has challenges for eye relief.

 

Mike


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#4 Mitrovarr

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Posted 12 June 2019 - 09:52 PM

I always prefer 32mm plossls myself. The 32mm is already as wide a field as 1.25" can accommodate; the 40mm plossl doesn't actually show any more true field. Well, not unless you get a rare 2" one.


Edited by Mitrovarr, 12 June 2019 - 09:52 PM.

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#5 25585

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Posted 13 June 2019 - 06:20 AM

No such thing as too much eye relief for me as I wear glasses! Noting 40mm as possible purchase... cat24.gif  


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#6 Sarkikos

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Posted 13 June 2019 - 08:44 AM

Yup thats normal with 40mm Plossls.  Another option is to get one with a sliding / adjustable eyecup:

https://agenaastro.c...n-eyepiece.html

Neat!  I would get it for visual.  How good can the optics be, though, at $79?  I'd like to be pleasantly surprised.

 

Mike


Edited by Sarkikos, 13 June 2019 - 08:51 AM.

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#7 Sarkikos

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Posted 13 June 2019 - 08:46 AM

I always prefer 32mm plossls myself. The 32mm is already as wide a field as 1.25" can accommodate; the 40mm plossl doesn't actually show any more true field. Well, not unless you get a rare 2" one.

The 40mm will have a wider exit pupil than the 32mm.   This will produce a brighter image and field, which may or may not be an advantage.

 

Mike


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#8 Mbinoc

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Posted 13 June 2019 - 10:01 AM

Thanks for all the replies, I m going to go ahead and eventually permantly attach a spacer. After futher research I probably should have purchased a 32mm plossl instead, as what I was really looking for in its purchase was a wide field of view.


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#9 nicoledoula

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Posted 13 June 2019 - 12:24 PM

Too much eye relief? Or is one not able to hold one's head in the right place in a stable manner? 32mm plossl's have their own eye placement problems as you will find. 25mm and 20mm plossl's are easy to use. Lots of people add eyeguard extensions. Good idea.



#10 ngc7319_20

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Posted 13 June 2019 - 12:45 PM

Neat!  I would get it for visual.  How good can the optics be, though, at $79?  I'd like to be pleasantly surprised.

 

Mike

Tough crowd.  OK, how about $59?  Romer still has them on sale.  Thats where I got my pair.

https://romer-optics...oject-lens-1-25

 

Quality-wise they are fine.  No issues.  Fully multi-coated.  Coatings pretty similar to TV 40mm PL.  Heres a pic comparing the coatings.  Maybe the coatings very slightly darker in the TeleVue.

 

IMG_2301 40mm coatings a.jpg


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#11 ngc7319_20

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Posted 13 June 2019 - 12:57 PM

If you want, you can also take off the sliding eye cup thing, and have a very long eye relief 40mm -- if you are wearing glasses or something.  I liked this flexibility.

 

IMG_2311 40mm 2ax.jpg


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#12 Mbinoc

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Posted 13 June 2019 - 04:02 PM

Too much eye relief? Or is one not able to hold one's head in the right place in a stable manner? 32mm plossl's have their own eye placement problems as you will find. 25mm and 20mm plossl's are easy to use. Lots of people add eyeguard extensions. Good idea.

I don't typically use motorised scopes, I just have one, and Its not the one I typically take out, (A Meade ETX-60). So where I found it diffulcult is when I'm manually adjusting the scope, If I move just alittle out of range of this 40mm eyepeice it will black out. It is hard for me to turn the motion controls, and keep head / eyepeice alignment at the same time. It seems if I even touch the scope, it shakes for a few seconds making things even more diffulcult.

 

One of these days I think I will get a nicer scope that will make things much easier, but have not done so yet. I'm still in the beginning stages of this hobby, and am currently experimenting with lower cost items.

 

My belief is if I start at this level first, I will have a better understanding going forward in how to wisely spend money on the things I really need. So far my total investment in this hobby is still right around $200, and it has been well worth it.

 

When beginning a new hobby some people like to start with higher qaulity products right from the start, and I can also understand that view point. I like to start low with a minimal expense, and slowly upgrade. Then when I do make a jump, it lets me appreciate the moves upward, and gives me a beter perspective of where I started from. I enjoy the upgrade / flip process.

 

Every hobby I have ever taken up has started the same way. (Stereo, Vintage Cars, Bikes, Flyfishing, and now Telescopes). In each hobby I start low, and once I become more knowledgeable they pay for themselves. I then eventually reach a level where I am content with what I wanted to accoumplish.

 

Within this hobby, I still do not know how far I'm willing to take it. I'm just having fun trying to figure all this stuff out.

 

________________________________________________________________________________

 

Cloudy nights has its own community where everyone here speaks the same language, for a beginner much of the terms used are equilvelent to a foreign language. It took me a while to understand most of the terminology used. I still have to research some of the things I read to figure out what was really said.


Edited by Mbinoc, 13 June 2019 - 05:24 PM.

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#13 Sarkikos

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Posted Yesterday, 07:57 AM

Tough crowd.  OK, how about $59?  Romer still has them on sale.  Thats where I got my pair.

https://romer-optics...oject-lens-1-25

 

Quality-wise they are fine.  No issues.  Fully multi-coated.  Coatings pretty similar to TV 40mm PL.  Heres a pic comparing the coatings.  Maybe the coatings very slightly darker in the TeleVue.

 

attachicon.gif IMG_2301 40mm coatings a.jpg

Looks like the same GSO eyepiece for $20 less.  I never heard of Romer.  I might give them a try.

 

Mike



#14 Sarkikos

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Posted Yesterday, 08:07 AM

I just now ordered the 40mm GSO eyepiece from Romer.  They do charge for shipping, which I think Agena does not.  But still less at $67 shipped.

 

Mike


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