10 replies to this topic

[Mbinoc]

In the last week I have taken out three different scopes and have found that a eyepeice that works best in one scope can be less than ideal in another.

 

The difference in performance is amazing, and the scope makes much more of a difference than I thought it ever could.

 

This may be common knowledge, but the first hand experiance was a eye opener for me.

 

I feel this can make eye peice recomendations very diffulcult, unless you have the same scope as the person asking for suggestions.

 

It also helps explain the many different opinions we sometimes see on the same eye-peices. (Sometimes someone may say its excellent, and others will counter that they were not impressed). Some of the reviews seen here may not be exclusively due to qaulity control, but also do to the different equipment we all use.

 

I have recently  found even the filters can behave diferently in different scopes, and this makes sense due to the different characteristics that are inherent in there light gathering capabilities. A filter that may enhance the vision in one scope, can degrade the same image in another.

 

A eye peice that is well balanced and offers great contrast and detail in one scope, can also look washed out in another.

Edited by Mbinoc, 08 December 2019 - 12:29 AM.

[SeattleScott]

The F ratio in particular makes a difference. That is why we generally ask that people give the scope or F ratio of a scope whenever they discuss how they feel about the performance of an eyepiece. For example, Joe thinks highly of budget eyepieces. Well Joe has one scope, and it is F8.3, so budget eyepieces work great for him. I have scopes from F4-F12 so I try to get eyepieces that perform well at F4, rather than have a premium set and a budget set for my slow scopes. In general, when people talk about eyepieces that perform well in fast scopes, they are typically referring to F4-F5. Slow scopes are more like F8 and up, say F15. F6-7 is kind of in the middle where quality is important but not as critical as with fast scopes.

Now the part about being contrasty with one scope and washed out in another, that has to do with exit pupil. Which also has to do with F ratio. The exit pupil is the focal length of the eyepiece divided by the F ratio of the telescope. So my 24mm ES eyepiece delivers a 6mm exit pupil in my F4 scope, and a 2mm exit pupil in my F12 scope (not quite technically correct but good enough for now). The 6mm exit pupil is orders of magnitude brighter, giving a brighter background sky and more of a washed out appearance. The 2mm exit pupil is much dimmer and more aesthetically pleasing. It can be tricky because large exit pupil is typically how to maximize the FOV. Generally I am willing to tolerate a brighter background sky if it allows me to frame the Pleiades in the FOV of the scope. But aesthetically I prefer a 4-5mm exit pupil.

Scott

Edited by SeattleScott, 08 December 2019 - 12:38 AM.

[scngc7317]

In my case I have two types of eyepieces

My good stuff for me and club members

Then there are my Good sub 100 dollar eyepieces

These are for club outreach at schools and public star parties

the last thing you want on your Nagler is bubble gum, ice cream or a runny nose 

 

[sg6]

The f number is often the one given as the "steepness" of the light cone has a fair significance. The problem in this area is that "fast" scope is more difficult to compensate for, the other factor is that manufacturers and ourselves seem to be heading for fast scopes.

 

The other that I read was that the focal plane of a refractor curves one way, whereas the focal plane of a reflector curves the other and we use the same eyepieces on both. Focal planes are not flat, unless we intervene.

 

So ultimately different eyepieces will produce different results.

 

Does raise the question of are all eyepieces designed for a flat field and hope the extremes are acceptable or do some get designed for a refractor field more or less then for a reflector field?

 

Filters should do nothing, they, I would say, will have a greater effect on the eye and the brain then the actual scope optics. To my thinking they sort of remove stuff and often the less stuff (wavelengths) floating around the system the easier/better. If you had just 1 color then no CA sort of thing.

 

Also people seem to like one brand or another, and almost immaterial of the actual performance they will go with or suggest what they have "adopted". If suggesting items I tend to specify the accepted good ones amd list by the cost. People can then make up their mind.

[SloMoe]

When I first got back into the hobby a few years ago, I had an 8" SCT, Celest Nexstar 8i, a basic scope by today's standards but all the same a very nice set of optics and slow, f 10, so looking for advise I took a road trip up to the only brick & mortar store of telescopes in the area.

 

Man what a great staff, very helpful and didn't try to empty my wallet they answered my questions, so I started out with ES 82's, 8.8, 11, & 14.

They were fantastic as far as I was concerned, then came this site, and a 10" f 4.7 Dob, hooked past the barb.

 

The edge of the view wasn't as sharp, so I got an HRCC, learned how to use it, then came the 100's, when you got real estate, use it, right.

 

Lunt/APM's, then ES, now Ethos, but the first few views using the HRCC and ethos weren't what I had hoped for.

 

Now I have a Paracor II, the views are what I was expecting, so in designing eyepieces and other light control lenses I've learned it's best to stick to one brand, Al designed both to work together.

 

Now I've experimented with a few Short Fast refractors and discovered Naglers work better in them than ES do, better edge correction for fast scopes.

 

I've also had a few different brands of eyepieces that were less expensive, more affordable to most beginners, 

I've learned that long eye relief unless the eyepiece has a nice twist up cup are not very good starter eyepiece's,

It takes knowing that there are black out area's so the twist up eye cup can be set for proper distance.

 

So now to the filters, I've learned, and studied, read & read & read, topics, reviews and yes, your eye will see something a bit different than mine same filter same scope.

Also there's a huge difference in quality control of mass produced less expensive filters, 

 

Most older, retired eyeballs have cataracts, fact of getting old, things break down, the more floaters you see when viewing the greater the odd's that you have a cataract starting, cataracts disperse detail, the brighter the target the greater the glare and wash out, the less a filter will do you much good.

 

99% of the time I recommend the OP's of the beginners forum to watch youtube video's and reviews before purchasing anything, keep reading and asking questions before you buy anything.

 

Now owning 3 Short tubes, a ST 90, ST 70 and a WO Petzval 66, the SCT & Dob and full circle back to a Mak.

When in doubt, buy a Nagler

 

I've owned more than thirty different filters, I use 5.

 

So what was the question again?

 

Right, not a question but a what have you learned, I've learned I could be driving a Porsche if I'd hadn't got back into this hobby.

[SloMoe]

And I'll add this, 99% of the time a beginner is asking what or which? 

I want to suggest he purchase a Cat 5 cable and just stream Hubble to his wide screen and be done with it.

[Achernar]

The type of telescope and its focal ratio determine what kind(s) of eyepieces work best with any given telescope. After that the build quality and what your budget can bear have the final say. Before recommending eyepieces, these factors have to be taken into account first. That said, I have noticed how some eyepieces work well, or at least adequately in some telescopes, but in others they perform very poorly. The same was true of nebula filters, namely the larger the telescope, the more objects they benefit.

 

Taras

Edited by Achernar, 08 December 2019 - 10:49 AM.

[Jon Isaacs]

In the last week I have taken out three different scopes and have found that a eyepeice that works best in one scope can be less than ideal in another.

 

The difference in performance is amazing, and the scope makes much more of a difference than I thought it ever could.

 

This may be common knowledge, but the first hand experiance was a eye opener for me.

 

I feel this can make eye peice recomendations very diffulcult, unless you have the same scope as the person asking for suggestions.

 

It also helps explain the many different opinions we sometimes see on the same eye-peices. (Sometimes someone may say its excellent, and others will counter that they were not impressed). Some of the reviews seen here may not be exclusively due to qaulity control, but also do to the different equipment we all use.

 

I have recently  found even the filters can behave diferently in different scopes, and this makes sense due to the different characteristics that are inherent in there light gathering capabilities. A filter that may enhance the vision in one scope, can degrade the same image in another.

 

A eye peice that is well balanced and offers great contrast and detail in one scope, can also look washed out in another.

 

There is a lot to know about eyepieces and telescopes.  But I would really like to know the specific eyepiece and telescope comparisons you have made.  

 

The reason for this is that the most important thing about an eyepiece is the focal length.  The focal length of the eyepiece and focal ratio of the telescope determine the exit pupil which in turn determines the image brightness.  This has very little to do with the quality of the eyepiece.

 

Consider two telescopes, both have 200mm apertures, one is F/5, the other is F/10.  The focal lengths are 1000mm and 2000mm.  If we use the same 25mm eyepiece in both scopes, the exit pupil will be 25mm/5 = 5mm at F/5, the exit pupil will be 25mm/10 = 2.5 mm in the F/10. The area of the exit pupil determines the image brightness so the F/5 scope will be 4 times as bright, the sky will seem 4 times as bright and more washed out.  That has nothing to do with the quality of the eyepiece itself.  

 

That same eyepiece will provide 1000mm/25mm = 40x in the F/5 scope and 2000mm/25mm = 80x in the F/10 scope. The views will be very different in the two scopes, not because of the quality of the scope or the eyepiece but because the exit pupil and magnifications are very different.  

 

In general, when one compares eyepieces, the focal lengths should be the same or very close and the same scope should be used.  This puts both eyepieces on equal footing.  If one is comparing them in different telescopes, identical exit pupils are a reasonable way to make the comparison.  This requires nearly identical eyepieces that only differ in the focal length.  

 

So without knowing the specifics of your comparisons, it's difficult to really help explain what you are seeing. The washed out look is almost certainly due to a large exit pupil that results from a faster scope.

 

Learning how to match the exit pupil/magnification to the object, the sky, the conditions, this fundamental to choosing the right eyepiece for the situation.

 

Filters also behave differently, again because of the image brightness/exit pupil.  Deep Sky filters like the UHC, O-llll and H-Beta dim the background sky by 1-2 magnitudes so that faint objects are more easily seen.  A larger exit pupil is useful because the object itself is brighter. 

 

(The exit pupil is the diameter of the beam of light projected by the eyepiece. the bigger the diameter, the brighter the image.  You can see the exit pupil if you look at the eyepiece in the telescope from a distance.)

 

Jon

[Mbinoc]

There is a lot to know about eyepieces and telescopes.  But I would really like to know the specific eyepiece and telescope comparisons you have made.  

 

The reason for this is that the most important thing about an eyepiece is the focal length.  The focal length of the eyepiece and focal ratio of the telescope determine the exit pupil which in turn determines the image brightness.  This has very little to do with the quality of the eyepiece.

 

Consider two telescopes, both have 200mm apertures, one is F/5, the other is F/10.  The focal lengths are 1000mm and 2000mm.  If we use the same 25mm eyepiece in both scopes, the exit pupil will be 25mm/5 = 5mm at F/5, the exit pupil will be 25mm/10 = 2.5 mm in the F/10. The area of the exit pupil determines the image brightness so the F/5 scope will be 4 times as bright, the sky will seem 4 times as bright and more washed out.  That has nothing to do with the quality of the eyepiece itself.  

 

That same eyepiece will provide 1000mm/25mm = 40x in the F/5 scope and 2000mm/25mm = 80x in the F/10 scope. The views will be very different in the two scopes, not because of the quality of the scope or the eyepiece but because the exit pupil and magnifications are very different.  

 

In general, when one compares eyepieces, the focal lengths should be the same or very close and the same scope should be used.  This puts both eyepieces on equal footing.  If one is comparing them in different telescopes, identical exit pupils are a reasonable way to make the comparison.  This requires nearly identical eyepieces that only differ in the focal length.  

 

So without knowing the specifics of your comparisons, it's difficult to really help explain what you are seeing. The washed out look is almost certainly due to a large exit pupil that results from a faster scope.

 

Learning how to match the exit pupil/magnification to the object, the sky, the conditions, this fundamental to choosing the right eyepiece for the situation.

 

Filters also behave differently, again because of the image brightness/exit pupil.  Deep Sky filters like the UHC, O-llll and H-Beta dim the background sky by 1-2 magnitudes so that faint objects are more easily seen.  A larger exit pupil is useful because the object itself is brighter. 

 

(The exit pupil is the diameter of the beam of light projected by the eyepiece. the bigger the diameter, the brighter the image.  You can see the exit pupil if you look at the eyepiece in the telescope from a distance.)

 

Jon

I still have a bit to learn.

 

I was just comparing a Celestron 6" Dob, to a Celestron 90mm refractor, and also a 60mm Jason Japan made scope. In my comparisons I was not considering focal ratios, but just the effect each eyepeice had in the individual scopes.

 

Considering the filter used "Polarising filter", I thought it may have helped in a larger apature, but harmed the same view in the smaller scope.

 

Another thing I did not consider, is I was viewing across several nights. The atmosphere was probably a bit different.

 

.

Edited by Mbinoc, 10 December 2019 - 06:21 PM.

[25585]

I agree with Don Pensack that all eyepieces could be F4 capable, edge to edge.

 

There are some, but the cost in money, comfort and other factors may make some unsuitable for an individual. The advice on CN is star parties or others willing to let you try. Or a seller with a reasonable return/refund policy.   

[dan_h]

In the last week I have taken out three different scopes and have found that a eyepeice that works best in one scope can be less than ideal in another.

 

The difference in performance is amazing, and the scope makes much more of a difference than I thought it ever could.

 

This may be common knowledge, but the first hand experiance was a eye opener for me.

 

 

"It is not usually made clear, that these elements, objective and eyepiece, are by no means comparable in importance. The astronomer's hopes are almost wholly tied to the size and quality of the objectve. The objective of even the smallest telescope, because of its larger dimensions, the severe optical requirements it must meet, and the difficulty of its construction, completely overshadows the eyepiece."

- "How to Make a Telescope," by Jean Texereau, Page 1, Paragraph 2. "