Blue penguin (eg Skywatcher Infinity 76) - eyepiece set afov??

[furrysocks2]

Hi,

I recently acquired a blue penguin for £20, complete with the three EPs - 15x, 30x erecting and 50x (at a scope FL of 300mm, this means EPs 20mm, 10mm and 6mm, I think).

I notice a huge difference in AFOV, particularly in that the 15x is "nice and wide", and the 30x is a disappointment by comparison. That the scope typically only comes with the 30x is perhaps a shame for owners, imo.

 

Regardless, the housing has split slightly and no longer supports the primary in place - it rattles a bit. I'm considering remounting and using this as a finder for my 12" - 76P f/4. Given the rebuild, I don't necessarily need to retain these EPs, but I may not rebuild, or I may acquire another scope/mirrors.

 

Does anyone have a reference to the actual specifications of the EPs in the set, or an estimation? In particular AFOV?

[furrysocks2]

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20 mm eyepiece giving 15x mag and a field of about 3.25 degrees

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The apparent field of view is surprisingly large, I guess it to reach about 55°

 

An answer there, perhaps. Should have searched harder.

[furrysocks2]

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It came with an erecting eyepiece of 10mm f.l., giving with the 76/300 parabolic primary a magnification of 30x and a TFOV of 1,26 degrees (AFOV narrow at 40°). I ordered an additional 20mm eyepiece for 15x and a TFOV of about 3°.

 

And again. The 30x does appear to be narrower in afov than the 15x.

 

Wonder if I could push it up to 25mm 68 degree... I guess it depends on geometry of the light cone, secondary, 1.25" focuser, etc. At 12x and a true field of view of ~5.6 degrees, that might make it comparable to a 9x50 finder with twice the light. But even the supplied 15x would be twice the TFOV of my longest 2" EP.

 

[Stu]

I have one of these in the loft somewhere, I could dig it out and try with a 24mm Panoptic (68 degree afov) if that would help you decide?

[furrysocks2]

45 minutes ago, Stu said:

I have one of these in the loft somewhere, I could dig it out and try with a 24mm Panoptic (68 degree afov) if that would help you decide?

That would make for quite a finder!

I'd possibly say not to go to the trouble on my account, unless you think you'd enjoy a view through it one night. Already having the 15x (20mm) at 50 degrees for 3.3 degrees or so is a decent start. I believe the pins can be removed from the focuser to permit standard EPs, or perhaps focuser might change if I remount the mirrors some other-how.

From there, I suppose it's just a matter of seeking a larger fov where vignetting permits, and that perhaps only for star hopping.

 

I have another 76/350 at f/4.6 (rather than 76/300 at f/4) that I trialled as a finder on my old dob, which works out at something like -15% TFOV in comparison. I could always try mounting that first rather than destroying the penguin.

I was also considering whether I could attach a camera to it, perhaps with focal reducer. Would have to employ the seconary at that diameter of primary due to obstruction... perhaps just better off with a 70mm binocular objective.

 

I'm going off my own topic.

[Nyctimene]

On 4.12.2017 at 10:49, furrysocks2 said:

Wonder if I could push it up to 25mm 68 degree... I guess it depends on geometry of the light cone, secondary, 1.25" focuser, etc.

Just found this:

"I have found that it will indeed take standard 1.25" eyepieces. All you have to do is take a sharp knife and snip off the two little pegs that the normal eyepiece uses to focus. A 1.25" eyepiece will then slot in nicely and move smoothly thanks to two small pieces of felt inside the tube. This means that normal eyepieces will focus in the Infinity 76. With a SW 25mm plossl you can hold the thing pretty steady and find things with relative ease". (Post by Blackheart from Sept. 15, 2010).

So, it seems to be worth a try with a 25/68°, considering the price and the loose primary.

Hth.

Stephan

[furrysocks2]

28 minutes ago, Nyctimene said:

Just found this:

"I have found that it will indeed take standard 1.25" eyepieces. All you have to do is take a sharp knife and snip off the two little pegs that the normal eyepiece uses to focus. A 1.25" eyepiece will then slot in nicely and move smoothly thanks to two small pieces of felt inside the tube. This means that normal eyepieces will focus in the Infinity 76. With a SW 25mm plossl you can hold the thing pretty steady and find things with relative ease". (Post by Blackheart from Sept. 15, 2010).

So, it seems to be worth a try with a 25/68°, considering the price and the loose primary.

Hth.

Stephan

Cheers! I have a vague memory of reading either that or another suggesting pins could be removed but didn't know about the felt. I'd like to look through it from a dark site, just for fun. As a finder, 25mm would definitely be good.

[furrysocks2]

Incidentally, opticalvision said:

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The x15 and x50 eyepieces are no longer available. The telescope is still available but only with the x30 erecting eyepiece. We do not have the data you need on file since it must be  ten years since we supplied those eyepieces

 

[Nyctimene]

You can still buy the 20 mmf eyepiece, giving 15x mag, from astroshop for 9,90€ (looked this up today). Again, no specific data  (eyepiece type, AFOV) available.

Stu has tried a 7 mm Nagler with the Penguin, and the results were "quite good":

"Now I think about it, I tried a 7mm Nagler in mine and the results were quite good. No need for anything like that, a simple but decent quality Plossl is worth a go."

[furrysocks2]

Shame to break it just for a finder...

But they're cheap enough, and I have all three eps.