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Pentax 2" SMC XW40-R for a dob?

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#1 rushhourjohn

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Posted 21 January 2021 - 05:05 AM

Is it a good eyepiece for an 8in dob (f/5.9)?

Anyone have any experience with it in that scope?

Trying to maximize tfov here.

Or is the 41 pan just way better?

#2 ubernator

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Posted 21 January 2021 - 05:22 AM

The panoptic is better on the edges, the XW is a little better in the center, but the difference is subtle since TV puts out top quality. 

 

The XW is slightly wider by about .5mm of field stop if I recall, but the 41 pan is pretty much perfect to the edge other than the coma in your scope (the astigmatism the panoptic is corrected for is a bigger offender than coma at f6).



#3 rushhourjohn

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Posted 21 January 2021 - 05:28 AM

The panoptic is better on the edges, the XW is a little better in the center, but the difference is subtle since TV puts out top quality. 

 

The XW is slightly wider by about .5mm of field stop if I recall, but the 41 pan is pretty much perfect to the edge other than the coma in your scope (the astigmatism the panoptic is corrected for is a bigger offender than coma at f6).

 

If you had an 8in dob , which would you pick?

 

Also, what do you mean about astigmatism? Are you saying the pan has it? What does astigmatism look like?

 

Thanks,

 

John



#4 junomike

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Posted 21 January 2021 - 07:28 AM

I found the Field Stop of the 41Pan fuzzy (no one else on CN reports this).

The 40mm XW was ok but I didn't like the eye placement.

Out of the two the XW is cheapest so that would be my pick.


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#5 Sarkikos

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Posted 21 January 2021 - 07:44 AM

One advantage to the 41 Pan is that it can take a Dioptrx.

 

Mike



#6 Muffin Research

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Posted 21 January 2021 - 08:04 AM

I found the Field Stop of the 41Pan fuzzy (no one else on CN reports this).

The 40mm XW was ok but I didn't like the eye placement.

Out of the two the XW is cheapest so that would be my pick.

Huh? The XW is super comfortable, but then I saw the Paragon 40 in your sig and that was to me also a super comfortable non straining, non blackening or beaning eyepiece.



#7 adamckiewicz

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Posted 21 January 2021 - 08:06 AM

Just read that the xw could too, but I don’t really know if that is exact.


In fact partially :

https://astromart.co...x-xw40-and-xw30

I would prefer the panoptic if dioptrix is necessary.

I prefer not use dioptrix because I practice with other persons and the long eye relief allows me to keep my glasses.

#8 areyoukiddingme

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Posted 21 January 2021 - 09:30 AM

While it's true that the 40/41 will max out true field, you may find that it's pushing things a bit.

 

At F6, I usually find that a 30/31mm gets more use than my 40 XW.

 

But if your dilate pupil is large, and you spend a good amount of time in really quite dark places, then the 40/41 may get more use.



#9 SeattleScott

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Posted 21 January 2021 - 10:22 AM

Spot on. I have used a 42mm on a F6 Dob for Pleiades. It worked ok but background sky was bright in urban skies.

Of the two I would go XW because performance is similar, the XW is lighter and cheaper.

Scott
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#10 Echolight

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Posted 21 January 2021 - 06:04 PM

I picked the XW because I figured it was the best thing going under 2 pounds. 25 ounces fit what I was trying to achieve in a set of eyepieces.

And it was on sale. And because I have an f/10 SCT and a f/8 refractor.

 

But in an f6 dob, I think a 30-ish mm eyepiece might be my preference most of the time. A 5mm exit pupil is plenty for me, and sometimes more than I want.



#11 BillP

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Posted 21 January 2021 - 09:46 PM

Is it a good eyepiece for an 8in dob (f/5.9)?

Anyone have any experience with it in that scope?

Trying to maximize tfov here.

Or is the 41 pan just way better?

Not in an 8" f/5.9, but I use the 40XW in my 10" f/4.7.  Without Paracorr the off-axis has, yes you guessed it, coma from the main mirror.  With Paracorr sharp to the edge.  Exit pupil is of course large (as Scott notes), but when one needs TFOV it give it nicely and those big star clusters look grand.


Edited by BillP, 21 January 2021 - 09:47 PM.

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#12 ABOAS

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Posted 21 January 2021 - 09:50 PM

I use the 40XW in my refractors only. It does not perform well in any of my reflectors. The 35 Panoptic would be another option. Great eyepiece.
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#13 Miranda2525

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Posted 21 January 2021 - 10:01 PM

The panoptic is better on the edges, the XW is a little better in the center, but the difference is subtle since TV puts out top quality. 

 

The XW is slightly wider by about .5mm of field stop if I recall, but the 41 pan is pretty much perfect to the edge other than the coma in your scope (the astigmatism the panoptic is corrected for is a bigger offender than coma at f6).

I beg to differ. I prefer the 40mm XW at F/6. I found the 41mm Panoptic has fuzzy edges. There is some apparent vignetting.

 

I prefer the 35mm Panoptic or 31mm Nagler over any of the above.


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#14 rushhourjohn

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Posted 22 January 2021 - 01:14 AM

Well thankyou for everyone who has responded, I ordered the Pentax and am excited to try it out. I hope it does well.
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#15 ubernator

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Posted 22 January 2021 - 06:27 AM

I beg to differ. I prefer the 40mm XW at F/6. I found the 41mm Panoptic has fuzzy edges. There is some apparent vignetting.

 

I prefer the 35mm Panoptic or 31mm Nagler over any of the above.

Admittedly I based my comparison on the 40SWaA copy of the 41 pan.  I do remember hearing about the fuzzy field stop on the 41. But people still bought them, but not as many as the 31 nagler.

 

But at the same time, fuzzy field stop and well corrected star images are not the same. The panoptic is more aggressively designed to correct astigmatism at the edge than a 40XW. But it wasn't night and day, the Pentax is not uncorrected like a 40 SWAN, tv wide field or 4000swa. 

 

But my final comparison between the panoptic copy and the 40xw was in my c11 ....



#16 Miranda2525

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Posted 23 January 2021 - 02:41 AM

Admittedly I based my comparison on the 40SWaA copy of the 41 pan.  I do remember hearing about the fuzzy field stop on the 41. But people still bought them, but not as many as the 31 nagler.

 

But at the same time, fuzzy field stop and well corrected star images are not the same. The panoptic is more aggressively designed to correct astigmatism at the edge than a 40XW. But it wasn't night and day, the Pentax is not uncorrected like a 40 SWAN, tv wide field or 4000swa. 

 

But my final comparison between the panoptic copy and the 40xw was in my c11 ....

True about fuzzy field stop not having any bearing on correction. I don't mind if it is minor, but when it is very noticeable, it can be somewhat annoying. And yes, Televue does have outstanding quality, but I am not a big fan of the Type 4 Naglers. Mainly the 12mm and the 17mm. The 22mm is very well liked in longer focal lengths telescopes or shorter focal length telescopes when used with a coma corrector.



#17 rushhourjohn

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Posted 23 January 2021 - 02:49 AM

Im losing it...

 

I ended up cancelling the pentax order before it shipped, 

 

Now im leaning towards the nag 31....


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#18 junomike

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Posted 23 January 2021 - 08:46 AM

Im losing it...

 

I ended up cancelling the pentax order before it shipped, 

 

Now im leaning towards the nag 31....

Good decision IMO.


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#19 Sarkikos

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Posted 23 January 2021 - 01:32 PM

I prefer a sharp field stop.  But it has no bearing on the optical performance of the eyepiece.   AFAIK, it just means the field stop was not positioned exactly at the focal plane of the eyepiece. 

 

I have heard that the perceived sharpness of the field stop can vary depending on the optical performance of the observer's eye.  I usually wear my eyeglasses when viewing through eyepieces, so that factor usually wouldn't affect me.

 

Mike


Edited by Sarkikos, 23 January 2021 - 01:33 PM.


#20 Sarkikos

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Posted 23 January 2021 - 01:38 PM

Im losing it...

 

I ended up cancelling the pentax order before it shipped, 

 

Now im leaning towards the nag 31....

Yes, I would get the 31 Nagler.  Then, at a later date, if you want a decent 30mm that is lighter and smaller than the 31 Nagler, I'd consider the 30 XW or the 30 UFF APM.  But in the long run, I don't think it should be an either / or decision.

 

The same equation holds true for the 41 Pan and the 40 XW.

 

I wonder if there'll be a 40 UFF APM?  thinking1.gif

 

Mike


Edited by Sarkikos, 23 January 2021 - 01:42 PM.


#21 25585

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Posted 24 January 2021 - 08:39 AM

One advantage to the 41 Pan is that it can take a Dioptrx.

 

Mike

So can the XW.


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