Wide fov ep for 127 slt

[Dunkster]

Sorry for another 127 Mak thread

Could anyone recommend a decent 1.25" ep with a wide fov, I'm guessing 32mm FL is best for my scope (sig).

For example...

Televue 32mm plossl

Meade 4000 32mm

GSO super plossl

Preferably one where I can add a filter (that is where it goes, right?!)

Considering the cost of my mak, I don't want to go too crazy... Televue would be a bit of a stretch, but I'd probably be using it a lot.

Thanks!

Dunkster

[John]

Focal lengths longer than 32mm don't show any more sky because of the 1.25" barrel restriction so thats the optimum low power focal length eyepiece in that fitting. In a slow scope like a Mak I reckon any of the 3 brands you list would perform pretty well.

The filter can either be screwed into the end of the 1.25" eyepiece barrel or, for more convenience, you can screw it onto the end of your diagonal barrel. Than you can change eyepieces without having to switch the filter as well.

[Dunkster]

Thanks John, I would have amused myself for hours trying to fit the filter on

Would the Televue be overkill, or more to the point, overspent, with my scope?

[John]

Would the Televue be overkill, or more to the point, overspent, with my scope?

My personal view is that you will never regret buying quality

I'd be looking for a used one although they get snapped up pretty quickly - you can save £30-£40 over the new price then.

Another point is re-sale - if you buy wisely, you will have no problem re-selling a used Tele Vue for practically what you paid for it, if you decide to move onto something else. The fact that the brand sells so quickly on the 2nd hand market speaks for itself

[Dunkster]

OK thanks, John, sounds like I just need to convince my wallet to open up now

[DoctorD]

Hi

I'm please with the performance of the 32mm GSO plossl with my 102 MAK.

PAIL

[Dunkster]

Thanks PAIL, good to know. I need to go shopping and make a choice

[M4lcs67]

Interesting reading your post. I have the same scope as you and am in the market for a couple of new eyepieces. Had contemplated Celestron X-cel's. Had not considered Televue, but maybe I should take a closer look before making a final desicion.

Was outside with my scope last night and ended up using my stock 25 mm ep the most during the session.

[Dunkster]

Yeah, I've been using my 25mm a lot this week, the 9mm not so much

However, I have no frame of reference (yet!) as to what is good v bad

Only one way to find out...

[Ender Of Days]

Ive been using my 32mm sp (meade) and can see its going to be a regular for the scope,

Ive a 40mm which is also a nice one,but it is a wider f.o.v isnt it ?

although a narrower "aparent" f.o.v ??

JJ..

[ronin]

The TV plossl is good and in your scope would give a field of view of 1.1 deg.

As a less expensive, and different, alternative consider the BST Explorers. They do a 25mm with a 60 degree view giving 1 degree in your scope. Small decrease but not a lot.

Best I know the only retailer is Alan at Sky's the Limit.

[Dunkster]

OK chaps, now I'm confused ... is there a good "dummies" guide for deciphering fov and afov to discern between eyepieces?

[John]

This guide is good:

http://stargazerslounge.com/beginners-help-advice/80772-eyepieces-very-least-you-need.html

The terms are confusing although in your scope things are simpler because a decent 32mm plossl (like the ones you originally listed) will give you the widest field of view that you can get with your scope plus it will work well with it.

[Dunkster]

Thanks John! Read and understood I think

So what's the relationship between fov and focal length? If the TV (32mm FL, 50deg view) gives a 1.1 degree view, but a 25mm BST at 60deg gives 1.0 degree?

From what I've so far (tried to) understood, the fov of the eyepiece determines how wide it looks in the eyepiece, but how does that relate to the aperture of the scope?

[Moonshane]

I have just bought a TV 32mm Plossl and it's a really nice eyepiece. I have other TV eyepieces but this one will get most use in my 90mm f5.5 frac and my 6" f11 dob. the latter is quite similar to your Mak.

if I could have afforded one, a 24mm Panoptic would have been my choice but the 32mm Plossl gives the same field but less power. the exit pupil is manageable in my two scopes mentioned so I am really happy with it. as John says you can get a good used 32mm TV Plossl for about £65.

the advantage is this will work well in other faster scopes down to f4 if you ever decide to buy a different or additional set-up.

[John]

Thanks John! Read and understood I think

So what's the relationship between fov and focal length? If the TV (32mm FL, 50deg view) gives a 1.1 degree view, but a 25mm BST at 60deg gives 1.0 degree?

From what I've so far (tried to) understood, the fov of the eyepiece determines how wide it looks in the eyepiece, but how does that relate to the aperture of the scope?

Eyepieces, as you know, have fields of view of 40, 50, 60, 70 degrees and so on. These are what is known as the apparent field of view (AFoV). What we really want to know of course is how much sky we will see when we use them in a scope - this is known as the true field of view (TFoV). To find the TFoV that a given eyepiece / scope combination gives you divide the AFoV of the eyepiece by the magnification that the eyepiece is giving you in the scope.

Example 1: 32mm plosssl with a 52 degree AFoV in a 1000mm focal length scope: 52 (AFoV) divided by 31.25x (mag) equals 1.664 which is the TFoV in degrees - how much sky you can see.

Example 2: 13mm Ethos with a 100 degree AFoV in the same scope: 100 (AFoV) divided by 76.92x = 1.300 degrees TFoV.

You will notice that I don't mention aperture above - it's not a factor.

Hope that helps

[Dunkster]

OK, thanks! I think I've got it.

So what we really want is larger TFoV

Is there a reason why some of the more pricey eyepieces - panoptic, nagler, etc - only come in the 2" barrel size with longer eyepiece FL?

Is it just a case of assumption that the buyer of an expensive eyepiece will have a suitable scope? Or is there a maximum limit for a given barrel size?

[Dunkster]

I guess what I'm trying to say is that so long as the TFoV isn't overly compromised (shrank), then a shorter focal length ep with wider AFoV is OK, maybe even desirable?

[Ags]

I had the same dilemma with a similar scope and in the end bought a 24mm hyperion which gives the same TFoV as a 32mm plossl.

[John]

...Or is there a maximum limit for a given barrel size?

Yep - that's it.

If you want ultra wide fields of view in focal lengths longer than 17mm or so then you need a 2" barrel to enable this.

[Dunkster]

OK thanks - try and find balance in the force, I will

[Dunkster]

Ignoring the cost of the eyepiece being 1/3 the cost of the scope (), can my scope fully utilise the 24mm Hyperion?

[Ags]

The 24mm hyperion shows the same sky as the 32mm plossl, so if your scope shows an unvignetted view for the 32mm then it would do the same for the 24mm. I am pretty sure the EP would work well in your scope.

[Dunkster]

OK cool - thanks! Roll on pay day

[Domino]

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.