Wide fov ep for 127 slt

[John]

Looking at the 2" issue there is a great review about a 100 degree 9mm BST eyepiece with both 1.25" and 2" fittings sold by Sky's the Limit. How is that possible? They say it is the same as the one marketed by TMB and Zhumell in the US. It certainly comes from a respected stable.

It's actually a 1.25" eyepiece but they give you the option to use a 2" fitting because the eyepiece is heavy. The Tele Vue Ethos range below 17mm have a similar "hybrid" barrel.

[Nibor]

A very interesting thread!! I have a Mak 127 and I am interested in a wider FOV eyepiece to improve its DSO capabilities. Currently I am using an Antares focal 0.5 reducer to get a marginal improvement in FOV.

It seems to work quite well but I suppose because light has to pass through another piece of glass then brightness is compromised.

I have used the following website to get a better understanding of eyepiece matters:-

Field of View Calculator | Sky at Night Magazine

It is very intuitive but make sure you choose the "visual" option!!

As I understand it the 0.5 focal reducer would reduce the Mak's focal 1500mm length to 750mm which you can then feed into the scope's data. You can then see what difference the FR makes.

Any thoughts / experiences on FR's for Maks from experienced users for visual use?

[Ags]

I have a focal reducer which i bought for photography but I cannot reach focus with it in my ST80. Next clear night I will try the reducer visually in the mak. I am not expecting much - the field of view is constrained by the baffling of the scope so the reducer cannot squeeze much more FOV out of the system, surely?

[John]

.....the field of view is constrained by the baffling of the scope so the reducer cannot squeeze much more FOV out of the system, surely?

Yes, that's my understanding too. One degree of true field is about the most you are going to get from an 5" F/11.8 mak. Fortunately many deep sky objects will fit into that

[Dunkster]

Ahhh so all is not lost/wasted then?

This has been really educational for me - thanks to every contribution!

[Dunkster]

At this point I'm torn between the original choice, TV 32mm plossl, the Baader Hyperion 24mm and the 25mm BST Explorer - different ends of the price spectrum for sure, will mull over until at least pay day!

[Nibor]

At this point I'm torn between the original choice, TV 32mm plossl, the Baader Hyperion 24mm and the 25mm BST Explorer - different ends of the price spectrum for sure, will mull over until at least pay day!

Please let us know which one you choose and how you get on!!

[Lobotomik]

Yes, that's my understanding too. One degree of true field is about the most you are going to get from an 5" F/11.8 mak. Fortunately many deep sky objects will fit into that

Tech specs in Celestron's web page quote a 0.85 degree FOV. This matches quite well with the view one would get from the included 25mm Plossl. This leaves me wondering if that is the maximum FOV achievable with this scope,meaning that a longer , or a different 25mm eyepiece with a wider apparent FOV would vignette? Or is this the FOV achieved with the scoPe "as delivered", meaning there would be hope in trying to opening a wider view with longer, better eyepieces or focal reducers?

Anybody here has any evidence that the true FOV of this device is any bigger than 0.85 degrees? Any experience with a 35mm Plossl? Or with a wide AFOV 25mm eyepiece? I would really like to know, because this scope is in my short list, but I am afraid it could be a total failure with DSOs.

[Karen]

Budget 32mm plossls work very well in the 5" Mak because of its long focal length (1500mm) and achieve its maximum true fov .

[John]

Eyepieces are limited in the width of the field of view they can deliver by the internal diameter of their barrels. In the 1.25" size the maximum apparent fields of view go something like:

At 18mm - 82 degrees

At 24mm - 70 degrees

At 32mm - 52 degrees

At 40mm - 43 degrees

If you do the maths on the amount of true field the above eyepieces can show in a particular scope, the result is not far off same. The magnification it's delivered at varies though.

In a 127mm F/11.8 maksutov-cassegrain all the above eyepieces will show around 1 degree of sky + or - 10%.

The 25mm plossl would have an apparent field of view of 52 degrees which equates to .86 of a degree true field of view. So the Celestron web page is pretty much correct.

None of this means that these scopes are not good for deep sky objects though - most of them will fit into a 1 degree field of view as I've already said.

[Dunkster]

I still haven't pulled the trigger

So far I've really been enjoying the Moon, Jupiter and even Uranus! I did invest in a 15mm BST explorer which I really enjoy looking through. The LP is pretty bad here, but I have snuck up on a few DSOs with the stock 25mm and the BST. I need a good dark site for more I think.

Then a 6SE practically fell in my lap this week, but it's the same FL as my 127, so the hunt continues... Although it came with a 25mm Celestron E-lux, I haven't had a chance to see if that's any better than the 25mm that came with my Mak.

[John]

The E-Lux is a decent enough plossl - similar to the Skywatcher and other Taiwanese ones. It may be exactly the same as the one you have with a slightly different paint job !.

[Dunkster]

LOL

It's bigger, heavier, with a wider...erm... eye piece

[John]

LOL

It's bigger, heavier, with a wider...erm... eye piece

That sounds good then

Is your other 25mm the one that came with the scope ?.

[Dunkster]

Yes - the 127 came with a 25mm and 9mm. Neither have any markings besides "Celestron 9mm" and "Celestron 25mm"

As soon as the clouds part ways, I'll try them both out

[michael.h.f.wilkinson]

Looking at the 2" issue there is a great review about a 100 degree 9mm BST eyepiece with both 1.25" and 2" fittings sold by Sky's the Limit. How is that possible? They say it is the same as the one marketed by TMB and Zhumell in the US. It certainly comes from a respected stable.

The key issue is the field-stop diameter (which is determined by the AFoV and the focal length of the EP). This field stop determines how much of the image plane of the scope is seen through EP. If the field stop is less than about 28mm you can fit it into a 31.7mm (1.25") barrel. Anything up to about 48mm fits into a 2" barrel.

You can always fit a 1.25" EP with a 2" barrel without compromise. Some EPs like the 12mm Nagler come with such a dual-barrel configuration. The reverse does not work so well: if the field stop is bigger than 28mm the 31.7mm (out diameter!) barrel will start to block light noticeably.

[chiltonstar]

For field of view and "viewing comfort", I've found that a Celestron Omni 40mm works rather well with my Mak 127 - the FoV is probably no wider than say using a better 25mm EP, but it works well for me.

Chris

[michael.h.f.wilkinson]

The advantage of a 24mm Hyperion vs a 32 or 40 mm Plossl with the same true FoV, is that the higher magnification makes the background darker, which can be handy in bringing out detail in faint objects.

[Ags]

...And a darker sky background LOOKS nicer too :-)

[rwilkey]

I have asked if anyone has used the BST 100 degree on this forum but could find no one who actually has one. I remain dubious, and will stick to my 65, 68 and 82 degree ep's that I already have.

[Dunkster]

Eeek! 200 notes

[rwilkey]

That's what I thought, I'd rather save up for a TV, but out of my range anyway.

[Dunkster]

Yes, it's definitely getting into that price range. The 60 degree is great value (in my limited experience!) at only 41.

I see you have Hyperions (Hyperii?) in your sig, rwilkey - I'd be interest in your opinions on those, relative to the BST maybe. My scopes are F10+, at least for now

[michael.h.f.wilkinson]

Hyperions have a good rep. I have used Hyperions in the 16" F/8 RC of our university, and they are very good.

[rwilkey]

Hi, the Baader Hyperions are top quality comfortable viewing ep's, a comparison with the BST Explorers is difficult because viewing with a BST Explorer is a different experience, esp. on the planets and the Moon, where the BST excels. At the end of the day I would choose the Hyperian as it gives a wider viewing experience, and the build quality is an absolute premium. The build quality of the BST's is also fantastic for the price. It's a hard call I am afraid, but if you are on a budget, you will certainly not be dissappointed with a BST Explorer.