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your favorite EP for planetary observation (f/10)?

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#26 azure1961p

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Posted 17 March 2013 - 09:01 AM

I'm looking at purchasing a high power EP for a CGEM 925 HD. Do you have any favorites you would recommend? TIA

Rick


Rick if its highpower you want 10mm isnt going to get you there. Id go no less than 7mm, or 6mm for that matter. The 10mm is a nice working mag ocular for a variety of planetary an d lunar but it simply isnt highpower for that scope. 10mm by contrast is a nice medium power as is 13mm. A 5 or 4mm orthoscopic is the high end of highpower for your set up that could prove to be rather conditional for
planetary use. It has its place but its a narrow niche.

Pete

#27 Rick M.

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Posted 17 March 2013 - 09:38 AM

Pete, I'm thinking I could get a 10 mm. and use a Barlow for those very rare times that atmospheric conditions permit. Does that sound reasonable?

Rick

#28 Sarkikos

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Posted 17 March 2013 - 09:58 AM

Markus,

XO 5.1. That puts an f/10 scope at about 0.5mm exit pupil, the highest I usually go for planet observation. IMO, the XO's are the best eyepieces for viewing planets, unless maybe you want to pay two or three times higher for a ZAO.

Mike


CGEM 925 HD = 92.5" FL = 2349.5mm FL

That would give him 460x....far too much power.


That is a broad generalization. Far too much power for what object, under what conditions, for what instrument and for what observer?

460x would be about 50x per inch and a 0.5mm exit pupil. As I said, that is the highest I'll usually go for planet observation. But I've often gone that high for Mars and Saturn, though I usually stay closer to 300x for Jupiter.

Unless the observer lives permanently under the jet stream, 50x per inch is certainly doable for bright planets if the instrument has decent optics. In fact, I recently pushed my C6 SCT to 294x - about 49x per inch - when viewing Jupiter under good seeing, with good results. Luckily, I have a C6 with excellent optics. I'm pretty sure a 925 HD could do as well as a C6.

Mike

#29 droid

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Posted 17 March 2013 - 11:46 AM

Hmmmm interesting question.....and your liable to get dozens of answers, lol.
And theres a good reason for that , we see differantly....at 56 my eyes aint what they used to be....some one say in theyre 20s or even early 30s with normal vision, may see very differantly.

My two favorite eps for high power views, only in my f/10 4inch refractor , are the 10mm Rini planetary, puchased from Sarkikos, it has a narrower fov, and took a bit of use to learn to get my eye at the sweet spot and keep it there. And my new to me Nagler type 2 with a 2x ED barlow.for a 6mm view.
which gives me roughly 170x with the nagler barlow combo ,still under the 50x per inch. and 102x with the 10mm.way under the 50x per inch limit.
Forced to choose one, Id choose the nagler / barlow combo for obvious reasons.

But thats just my observing. And Ive never looked through dozens if not hundreds of very good eps....so your results ..will...vary.

#30 Rick Woods

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Posted 17 March 2013 - 12:55 PM

Re. the original question: When conditions allow its use, the Brandon 6mm is the finest planetary eyepiece I've ever used.

#31 Eddgie

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Posted 17 March 2013 - 01:40 PM

In theory, there is no limit to magnification.

For example, look at some of the best images taken with large reflectors. These scopes are often working with the equivilent of a 2mm to 4mm eyepeice.

But if you attempted to use this much power visually, it would produce a horrible image.

The telscope presents all of the detail it is capable of rendering with the magnification reaches about 1.1x per millimeter of aperture. This is when the smallest detail that the scope is capable of resolving is provided with sufficient angular magnification to be resolved at the focal plane.

Past this, you can go bigger and bigger, but no new detail is ever presented.

Ah, but what happens is that the illumination falls. The eye likes illumination. For a given contrast of a given detail, the brighter you make that part of the image, the easier it is for the eye to see it.

For the average observer, the illumination starts to fall once the exit pupil gets smaller than abou .8mm. Larger details with more contrats get bigger and easier to see maybe, but the smallest, lowest contrast detail starts to fall below the observer's contrast sensitivity threshold.

The right power for every obesrver will vary with the target and conditions of course, and I would never tell people that there is no value to pushing higher because image scale in itself can be pleasing.

But once you go past about 1.1x to 1.3x per millimeter of aperture, you make the image bigger, but often at the risk of loosing some of the more enrichig detail.

In my own scopes, I find a 1mm exit pupil to give me about the most detail I can extract from a planet. Past this, I can make it bigger, but usually no new detail is presented. And past about .7mm, and I can see that the most challanging detail is fading.

But this is me. We are all different.

The main reason I resist the message that 50X per inch is the right planetary detail is because over the years, I have heard so many people question if their telescopes were defective. They would read these reports about 50x per inch, but when they used their scopes, they were not seeing any new detail.

They thought their scopes must be defective because the message seemd to be that the more power you use, the more detail you would see.

And it doesn't work that way for most of us.

Factor in seeing, and 300x is the practical limit for most of us on most of the time anyway, but someone should not be surprised at all if they find that going to 50x per inch doesn't result in additional detail.

#32 johnnyha

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Posted 17 March 2013 - 01:48 PM

In my own scopes, I find a 1mm exit pupil to give me about the most detail I can extract from a planet. Past this, I can make it bigger, but usually no new detail is presented. And past about .7mm, and I can see that the most challanging detail is fading.

+1. I have confirmed this since getting my Leica Zoom, it is readily apparent that the planet dims below 1mm to a point where there is a loss of resolution - it starts getting "grainy" looking. On a good night I can go a little less but at .5mm it is much, much dimmer than 1mm and the difference is not 2X it is 4X+ dimmer.

#33 Sarkikos

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Posted 17 March 2013 - 03:47 PM

Eddgie,

In theory, there is no limit to magnification.


Yes. Actually this has been my first response to observers who question why I don't push the power more for some objects. Of course, you can increase the magnification to whatever your telescope, eyepiece and Barlow will produce. But the resulting image may look like a wooly smudge and may show you less detail than you could have seen at a much lower magnification.

And as a matter of fact, I have often been the champion of less is more when it comes to magnification for observing planets.

For example, look at some of the best images taken with large reflectors. These scopes are often working with the equivilent of a 2mm to 4mm eyepeice.

But if you attempted to use this much power visually, it would produce a horrible image.


I don't even want to compare photography with visual, except maybe to find out how much I'm able to see without all the fancy AP equipment and computer processing.

The telscope presents all of the detail it is capable of rendering with the magnification reaches about 1.1x per millimeter of aperture. This is when the smallest detail that the scope is capable of resolving is provided with sufficient angular magnification to be resolved at the focal plane. Past this, you can go bigger and bigger, but no new detail is ever presented.


1.1x per mm of aperture would be about 28x per inch, or about 280x in my 10" Dob. I'm not sure if we should take this as a hard and fast rule. In fact, I'm sure it isn't. There are too many factors involved.

For instance, the adaptation level of the eye should be taken into account. If the eye can be kept closer to photopic, more detail can be seen in the image of a planet at a more moderate level of magnification. If the eye is looking at fainter objects and is well dark-adapted, then more magnification will be needed to begin to see structure in the object. I've seen both of these effects for myself many times.

Also, even among bright planets, I've seen a difference in "best" magnification. As a general rule, Saturn and Mars do better at higher magnifications than Jupiter. Many observers have seen this. The reasons are probably both the different types of contrast for these objects and also the different image scales of the objects themselves. Personally, I think Mars does well at higher than 28x per inch, sometimes much higher, particularly when its apparent diameter is less than about 7 arcsec.

The main reason I resist the message that 50X per inch is the right planetary detail is because over the years, I have heard so many people question if their telescopes were defective. They would read these reports about 50x per inch, but when they used their scopes, they were not seeing any new detail.


I would never make the blanket statement that 50x per inch is the "right" magnification for planet detail. Just as I would never have said that 50x per inch is "too much magnification." Experience should tell us that the interaction among equipment, observer, object and atmosphere is much more complicated than that. Rules of thumb are not laws of nature.

They thought their scopes must be defective because the message seemd to be that the more power you use, the more detail you would see.


This, of course, is a newbie attitude. Reality is more nuanced. Unfortunately, I've seen this attitude too often in more experienced observers who should know better.

Factor in seeing, and 300x is the practical limit for most of us on most of the time anyway, but someone should not be surprised at all if they find that going to 50x per inch doesn't result in additional detail.


Of course. On the other hand, this doesn't mean than an experienced observer cannot appreciate what a good instrument can do under the right conditions when observing some objects.

Mike

#34 azure1961p

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Posted 17 March 2013 - 04:54 PM

Pete, I'm thinking I could get a 10 mm. and use a Barlow for those very rare times that atmospheric conditions permit. Does that sound reasonable?

Rick


Sounds very reasonable . A 2x televue barlow would be a great thing. To that end dont rule out a 3x barlow farther down the road for superhighpower doublestar or planetary nebula study. Itd be too much on the planets but fine on the targets mentioned . Itd be specialty barlow while the 2x would be more of a working tool with the 10mm. On a small mars, saturn or neptune in 7/10 seeing the 2x would be a fine thing.

Stay in touch and post your finds. That IS a great scope you have.


Pete

#35 Rick M.

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Posted 17 March 2013 - 05:28 PM

Thanks, Pete!

Rick

#36 CollinofAlabama

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Posted 17 March 2013 - 06:08 PM

Rick,

Don't own a very long focal ratio instrument, but I'd have to say the 12mm Brandon does a great job, particularly in combination with my old school, long tube Made in Japan 2x Orion Barlow (I'm sure a TV 2x would do at least as well). I also like the TeleVue Nagler T6 series. In my case, the 7mm works wonders if the Brandon/Barlow is too much power. For you, I'd think the 9 or 11mm models work work more consistently for you, since a 7mm would likely be too much power most nights in your scope.

Good luck

#37 mdowns

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Posted 17 March 2013 - 06:41 PM

Rick,
In my c11 my fav is a 12mm brandon,8mm brandon on steady nights and a bco 10mm coming in at third.

#38 Lane

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Posted 18 March 2013 - 04:01 AM

For DSO high power viewing in the 9.25 I generally use a 10mm Pentax XW. If seeing will not support it then I drop to the a 12mm Nagler or 13mm Ethos. If seeing is really good then I will use a 9mm Nagler.

I prefer Orthos for planetary viewing, but I don't generally use Orthos with my SCTs unless I attach my crawford focuser to the back. I find the narrow field of view causes problems due the mirror shift when focusing. For that reason the 10mm Pentax XW is normally what I will use on planets.

#39 Sarkikos

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Posted 18 March 2013 - 05:52 AM

The XW's are great wide-field eyepieces for planets. Well, they are wide-field compared to orthos - 70 degrees vs 44 degrees.

Mike

#40 Rick M.

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Posted 18 March 2013 - 07:31 AM

Hmmm...I will have to look into Pentax XW. How does the 10mm. Delos compare? I see a thread on Delos vs. Pentax XW but the 10mm. eyepieces are not compared.

Rick

#41 Sarkikos

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Posted 18 March 2013 - 07:41 AM

I've never looked through a Delos, but judging from the reports I've read, it seems a toss up, at least for planet observation. So that would make me gravitate toward the XW's, which are less expensive whether bought new or used.

For deep sky, there may be an advantage to the Delos. Some observers say the Delos have a bit better light transmission than the XW. But if the Delos do not actually have better light transmission - or somehow allow dimmer objects to be perceived than through the XW's - I see no advantage for the Delos over the XW's.

Mike

#42 andydj5xp

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Posted 18 March 2013 - 08:16 AM

For deep sky, there may be an advantage to the Delos. Some observers say the Delos have a bit better light transmission than the XW.



The intensity perception of the human eye is a logarithmical one. Light throughput differences of say 3% (98% to 95%) would correspond to just 0.26dB in logarithmical measures. I have a hard time to imagine that anybody would be even close to discriminating such minute intensity differences.

I'm aware that some fellow CNers report to be able to do so. But the noticed differences will almost certainly not been caused by intensity differences but something else. There are lots of possible sources for perceived differences between eyepieces.

Andreas

#43 Sarkikos

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Posted 18 March 2013 - 09:30 AM

Andreas,

I am skeptical but have an open mind to reports from first-hand experience in the field. On the other hand, I allow theory and studies to inform my experience, not determine it.

The received data from perception studies might be based on conditions, objects and subjects that are not strictly transferable to amateur astronomy. When attempting to discern faint, LSB objects near the LM of an instrument, I think it might be possible for small differences in light transmission to have a more crucial effect.

I'm aware that some fellow CNers report to be able to do so. But the noticed differences will almost certainly not been caused by intensity differences but something else. There are lots of possible sources for perceived differences between eyepieces.


The variation in perception of faint objects through different eyepieces might not be due to an appreciable difference in light transmission that is measureable through instrumentation. The effect might be due to other attributes of the eyepieces. But still, a perceived variation is there and will make a difference in the discernment of faint objects through the eyepiece.

Maybe we should be using a different term than "light transmission" to make the Optics Police happy. Maybe something like "Perceived Limiting Magnitude" would be better?

:grin:
Mike

#44 Sorny

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Posted 18 March 2013 - 01:03 PM

15mm or 20mm in my binoviewer, with the power switch either disengaged, or using barlow or reducer depending on seeing. I do most of my viewing with the 20mm pair, not just planetary.

If I'm going mono, then it is either my 8mm or 13mm or 17mm depending on seeing conditions. I've got a C11, so what works for me won't be quite the same as a C9.25...

#45 Rich V.

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Posted 18 March 2013 - 01:34 PM

With my C9.25 I find my XW 10 is most useful for planetary. On rare nights of great seeing the XW 7 comes into play.

Seeing would have to be crazy good to be able to use an eyepiece that's less than 7mm in a C9.25 so barlowing a 10mm probably wouldn't be very useful for you on most nights...

I used Plossls before I got into Pentax EPs and they were fine for planetary viewing with a driven scope so you don't have to break the bank if you don't want to. ;)

Rich

#46 Lane

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Posted 18 March 2013 - 01:46 PM

The view in the 6mm Delos does look more curved to me than the view in the 5mm or the 7mm Pentax XW. However the stars are still sharp all the way across. So I suppose it is not really a problem but it does look different for some reason. The same thing might apply to the 10mm eyepieces.

For light transmission, I have compared my 6mm Ortho to my 6mm Delos and compared my 7mm Ortho to my 7mm Pentax XW just to see if I could find a faint star in one that I could not find in the other, but I was not able to find one. I was also comparing other eyepieces at the same time, two of them being the TMB Planetary 6mm and 7mm, and I was able to see a very faint star in my Delos/Pentax eyepieces that I could find in the TMB eyepieces. So it is definitely possible to have light transmission differences that can be detected.

#47 Sarkikos

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Posted 18 March 2013 - 04:05 PM

This agrees with my experience. When I had TMB Planetaries, the image always seemed darker compared to other eyepieces of the same focal length.

Mike

#48 Phil Cowell

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Posted 18 March 2013 - 05:55 PM

12mm and with good seeing 8mm Brandon's. Good color rendition razor sharp on planets. Give them a try in your scope the view speaks for itself. Better than descriptions can.

#49 johnnyha

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Posted 18 March 2013 - 05:56 PM

I had a TMB Planetary and the view actually WAS coffee-colored. :grin:

#50 Sarkikos

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Posted 18 March 2013 - 06:00 PM

They make TV Plossls look like cafe au lait!

Mike






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