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A beginner and his Nexstar 127...


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I've recently joined the mak club and have been researching about maximising my field of view (although I didn't buy it for widefield :icon_scratch: )

I would be careful buying an eyepiece based on the maximum field of view from the eyepiece or a 1.25" eyepiece as the limit on a maksutov will be the internal baffle that you can see poking out of the primary when you look in the objective.

Looking on the celestron website it says the 127 slt has a max field of view of 44ft at 1000 yards or 0.83 degrees. So buying an eyepiece which exceeds this will give you vignetting.

If those figures are correct then the field stop of the baffle is only 22mm and the biggest field stop in 1.25" eyepieces is 27mm so an eyepiece with a field stop above 22mm won't increase your true filed of view.

You can calculate the true filed of view (tfov) from the apparent field of view (afov) by dividing the afov by the magnification the eyepiece gives.

For 25mm plossl with afov of 50 tfov=50/60=0.8333 (this would be your limit in the mak)

for 60 degree eyepieces like bst or x-cel the limit would be around 21mm eyepiece

for 70 degree eyepiece the limit would be around 18mm eyepiece.

The way I understand it anymore than these limits won't increase you true field of view anymore due to the limit of the baffle in your mak. I'm still a noob at all this though so if I've got it wrong I'm sure someone can correct me :clouds2: !

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Thanks Jim. I've been reading over your info for the past couple of days Jim, and I still can't quite get my head around it!

The most I can gather is the higher the FoV, the lower the limit of the eyepiece is going to be. Which is what seems to be the lesson. I'm just stumped when it comes to the understanding :)

Would upgrading the diagonal to 2" make any improvement on this?

P.s. I was also looking at a getting a focuser as the mount is incredibly shaky when turning the focusing knob by hand. As far as I can see there's specific focusers for each scope. I can't seem to find one specific to the 127 though.

A search seems to just bring up home mods (which I'd have no chance of achieving!).

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Thanks Jim. I've been reading over your info for the past couple of days Jim, and I still can't quite get my head around it!

The most I can gather is the higher the FoV, the lower the limit of the eyepiece is going to be. Which is what seems to be the lesson. I'm just stumped when it comes to the understanding :)

Would upgrading the diagonal to 2" make any improvement on this?

P.s. I was also looking at a getting a focuser as the mount is incredibly shaky when turning the focusing knob by hand. As far as I can see there's specific focusers for each scope. I can't seem to find one specific to the 127 though.

A search seems to just bring up home mods (which I'd have no chance of achieving!).

Hey,

I warned you I was a noob at all this.... :headbang:

On reflection I checked out some other figures for other Celestron scopes as the 0.83 degrees seemed to conveniently close to the 25mm Plossl and I suspect that Celestron seem to quote figures for the supplied 25mm eyepiece. However I would still be careful with Maks and SCT as the baffle in them is still smaller than the max field stop size for 1.25" eyepieces. You just don't want to get a 72 degree 32mm eyepiece for the mak

The best way to understand it is by comparing 2 eyepieces; a 50 degree AFOV eyepiece of 32mm focal length will show the same area of sky that a 60 degree eyepiece of 24mm focal length shows in the same scope. The 24mm will just be more magnified.

As for fitting a 2" diagonal, the limit will still be in the baffle in the Mak which may not be 22mm as I previously stated as I don't trust the Celestron figures but I've seen posts saying it's around an inch. As you only get 2 inch eyepieces in long focal lengths then the field stop of these eyepieces will be larger than the baffle and you'll get vignetting. From what I've read though as the baffle is away from the focal plane of the eyepiece it's like a soft vignetting which may not be immediately apparent but you would see it more in illumination of the field of view if you looked through a scope without the effect.

The only reason I would fit a 2" diagonal to a 127 mak would be if I had some large 1.25" eyepieces that would benefit from a more substantial mechanical connection to the scope.

You can fit another focusser to the mak but I think you need to get a 'mak to sct' adaptor then get a focusser for an sct (schmidt-cassegrain)

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If you're a noob, what does that make me!? (please don't answer that :headbang:)

Thanks though Jim. 'Tis a great help! It seems I shouldn't be worrying about the FoV so much considering the restrictions the 127 Mak is throwing at me. Looks like the PanaView is out the windows and the GSO Plossl may be a money saver and the better option!

I currently only have the one EP (excluding the stock 9 and 25mm EP's), which is a Baader Hyperion 10mm. The 25mm doesn't seem too bad at all, but the 9mm didn't really give a good image as others have said. But with having the Hyperion, I was curious to see what benefit I would gain from a 2" diagonal, seen as I had the EP :)

Thanks for the answer on focusers too. It would be nice to have a new focuser as the vibration makes it incredibly hard to focus, I can only imagine how difficult this will be at higher magnifications. Maybe I'll have to settle for some vibration pads for now :)

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I use a GSO 32mm plossl for my SW 127 Mak and it's very nice. Very bright, sharp views, and about as wide a feild of view as you can get from the scope - just a little over 1 degree. very usefull for viewing Messier objects.

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Thanks tjr. That's exactly the reason I was after a wider FoV. Seen as I don't know the skies, a wider FoV is bound to help.

Now to solve my vibration problems! It probably doesn't help that I've been looking out my window thus far and the scope is setup on hard wood :headbang:

I think I have the problem of just wanting the new shiny objects that are more expensive. I did the exact same with my PC... one day I'll learn :)

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This is a hobby that rewards patience. Your scope will show you lots, but at some point you may want to upgrade it compliment it with something different. Best to take your time in discovering that though.

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