Anyone have any experience with Hyperion zoom EP & Coma corrector?

[Gasmac]

I bought my zoom for my F4.7 Dob over 6 months ago and loved it.... Then I bought an ES maxvision Ep and realised that the zoom wasn't coping with the speed of the scope as well as I had hoped. 

I have been tinkering with idea of adding a MPC III coma corrector to improve the situation and bring it up to a more manageable speed when using the zoom +/- barlow.

Has anyone got any experience of this pairing? Will it not work at all as the zoom is not parfocal completely negating any benefit from its ease of use with swapping rings?

Or should I bite the bullet and go down the ES route instead?

Any help would be appreciated

[Tinker1947]

I have never used my Baader MPC III while viewing but they are required when used with a Newt for imagining, quality of the EP's will help a lot @ F4.7

[Gasmac]

In that case i may just keep my zoom until i get a second slower scope and buy a few ES EPs instead, as i'm not upto the Pentax/ Televue market at the moment.

Shame I had high hopes for the zoom.

Sent from my iPhone using Tapatalk

[Tinker1947]

The zoom will work in the right type of scope (what ever that is) you don't need Pentax / Televue but i can't recommend anything.......

[Don Pensack]

I bought my zoom for my F4.7 Dob over 6 months ago and loved it.... Then I bought an ES maxvision Ep and realised that the zoom wasn't coping with the speed of the scope as well as I had hoped. 

I have been tinkering with idea of adding a MPC III coma corrector to improve the situation and bring it up to a more manageable speed when using the zoom +/- barlow.

Has anyone got any experience of this pairing? Will it not work at all as the zoom is not parfocal completely negating any benefit from its ease of use with swapping rings?

Or should I bite the bullet and go down the ES route instead?

Any help would be appreciated

Commercial coma correctors available:

To review coma correctors currently available in 2":

magnification factor 1.00 Baader MPCC Mk III. This requires either experimentation or precise measurement to get the spacing with the eyepiece correct.

it will need a different spacing with nearly every eyepiece, so it will be helpful to have a lot of different thicknesses of spacers available.

One note: when perfectly adjusted for each eyepiece, all eyepieces should be parfocal, which makes a practical method for finding the right spacers

for each eyepiece. Optimize one, focus the scope, lock the focuser, and adjust spacer lengths on all the other eyepieces until they're in focus at the same

focuser position. It probably won't be possible, but if you come close, and just leave the necessary spacers on the eyepieces, transferring the MPCC from

eyepiece to eyepiece is no harder than moving a filter.

magnification factor 1.06 Explore Scientific HRCC. This has a tunable top (finely helical) with a large range. It requires a lot more in-focus than the Paracorr,

but should correct coma well. You use it by optimizing one eyepiece to perfect edge correction, then insert every other eyepiece and focus using the top of the HRCC.

Record all the positions used (there's a scale), and pre-dial that position before the next time that eyepiece is inserted. In this way, you'll achieve

optimum correction for every eyepiece and parfocalize your collection.

magnification factor 1.10 GSO/Astrotech CC. This one may require some fiddling with spacers in the CC and barrel extenders and parfocalizing rings on the eyepieces.

You adjust one perfectly and all the others will focus at the same point once the correct spacers are installed on the eyepieces.

You'll only have to do this fiddling once. So it will help to have a set of parfocalizing rings, adapters, and a few barrel extenders handy.

magnification factor 1.15 TeleVue Paracorr II. If you have TeleVue eyepieces, you can find the right settings of the tunable top on the TV website. If you have even one

TeleVue eyepiece, you dial the top to the optimum setting for that one and focus all your other eyepieces with the tunable top to find their optimum settings. Then you pre-dial that position for the eyepiece before you insert it. All your eyepieces end up parfocal after that.General instructions for setting any coma corrector when you don't know the eyepiece settings:

This applies to the GSO coma corrector, the Explore Scientific HRCC coma corrector, and the TeleVue Paracorr coma corrector. The Baader MPCC Mk.III coma corrector screws onto the eyepiece, so you mess around with spacers of different thicknesses instead, but the idea is the same: optimize one eyepiece and all the others follow from that one.

1) Insert longest focal length eyepiece into coma corrector (GSO) or coma corrector with adjustable top all the way down (TeleVue, ES). Focus scope. Examine stars at edge of field. Still show a trace of coma?

2) Pull eyepiece 1/8" out of coma corrector (GSO) or turn up the adjustable top one tick (TeleVue and ES) and clamp down. Refocus scope. Examine stars at edge of field. Better but not fully corrected?

Then repeat, pulling eyepiece 1/8" farther out of coma corrector or by turning the adjustable top up one more tick. Repeat until star images at edge look perfect. If you feel this results in having the eyepiece unsafely pulled out of the CC (GSO), then add a barrel extender to the eyepiece (or add a spacer in the middle of the CC (GSO)). Either way should work to safely support the eyepiece. Some eyepieces with 1.25" and 2" barrels, if used as 2" in the Paracorr or ES coma corrector will also need barrel extenders (examples: 6mm and 8mm Ethos)

3) Now that you have optimized one eyepiece, all the rest of your eyepieces will follow. Do not touch the focuser after optimizing eyepiece 1. Insert eyepiece 2 and pull it out of the CC until it is in focus (or turn the adjustable top up until the eyepiece focuses). That will be the perfect position for that eyepiece. It will help to add a parfocalizing ring to the eyepiece so the next time you insert the eyepiece it returns to exactly the same point (GSO) or record the setting where the eyepiece reaches focus (TeleVue, ES). In this manner, you can set all your eyepieces to their correct positions for best coma correction.

4) After you're done, all your eyepieces will be parfocal (+/- a millimeter or so) and they will all use the CC with the focuser at approximately the same point.

Q1. So what happens if eyepiece 2, when inserted all the way into the CC (GSO) or the top turned all the way down (TeleVue, ES), still hasn't reached focus?.

Then start out with that eyepiece in the CC first and go back to step one. It will be the eyepiece you use to determine the setting of the CC relative to the telescope's focal point.

Whichever of your eyepieces focuses the farthest in will be the eyepiece you use for the "control". If you already know that, start with that eyepiece. If you don't already know that, it's commonly the longest focal length (but there are many exceptions).

Q2. So what happens if coma gets worse as you pull that first eyepiece out of the coma corrector, i.e. its position of best correction would be farther in, closer to the CC?

Well, barring having a custom top machined for the CC, that eyepiece will not be fully corrected by the CC. But note: You will not use that eyepiece to set the initial position of the CC--you'll use another eyepiece. This is not too far-fetched. It applies to the Nagler 31, and Ethos 17 and 21 when used in the original Paracorr, for example.

Q3. Hope can I optimize that eyepiece that needed to get closer to the CC lens?

If it's a 1.25" eyepiece, no problem. There are 2" to 1.25" adapters available that lower the eyepiece 1/8" below the shoulder of the CC (TeleVue AIT) or up to 1/2" below the shoulder of the 2" CC (Astrosystems, Scopestuff, etc.). If it's a 2", just accept that though correction won't be absolutely perfect, 95% of the coma will be eliminated, and that's enough for most people.

Q4. What factors make coma more apparent?

--wider apparent fields at any magnification.

--darker skies, where the outer edge of the star image becomes more visible.

--shorter f/ratios, where coma is worse.

--field curvature in the eyepiece, where defocus makes the comatic star larger.

--experience with eyepiece aberrations, which helps in identifying coma

--experience with another scope without coma

--eyepieces with other edge aberrations that add to coma to make ugly star images

--short telescope focal length (more field curvature in scope)