Advice required ref CCs and WA eps

[Ally8446]

Hi folks

Even though I had a fabulous session last Friday (see Observing Reports) I'm now certain I need a coma corrector. No way can I stretch to (or justify) a Paracorr T2. From what I can see my choices are SW, Baader MPCC or (if I can find one) Paracorr T1. I predominantly view on axis so the view doesn't really have to be 100% coma free just considerably better than it is. Any advice greatly appreciated.

Secondly I'm in need of a lower FL WA ep than my ES24 68°. Problem is I'm nearly 50 so exit pupil may be an issue. An ES30 82° has an exit pupil of 6.5mm, might that be a little too large ? 

I'm open to any suggestions with regards the CC and suitable ep. Budget could be better but I could probably push to £300 for both (2nd hand of course). 

Thanks for your patience.

Al

[John]

I can't advise on the CC because I don't use one (my 12 inch dob is F/5.3). On the eyepiece, I have to say that I don't use my 31mm Nagler (exit pupil 5.85mm) half as much as I do the 21mm Ethos with my 12 inch dob because the background sky darkness of at the higher power plus the more efficient exit pupil make the 21mm a much more effective deep sky observing tool. I'm 59 this year so a little older than yourself.

I wonder if the ES 24mm 82 might be a better bet with your scope than the 30mm ?.

Other options to give you more true field while maintaining an effective exit pupil might include the Myriad 20mm / 100 degree, the APM/Lunt 20mm / 100 or even the 28mm Nirvana / UWAN perhaps ?

 

 

[Louis D]

3 hours ago, Ally8446 said:

From what I can see my choices are SW, Baader MPCC or (if I can find one) Paracorr T1.

I'm not sure why you left out the GSO/Revelation CC.  I use an OPT labelled GSO CC.  I just had to add a 25mm M48 spacer tube between the optics section and the eyepiece holder to work with the majority of my eyepieces that focus at the shoulder.  Eyepieces that focus within 1/4" (6mm) of the shoulder are still very well corrected for coma.

It has a 1.1x magnification factor despite what the TH page says.  It only requires 10mm to 15mm or so of in-focus for use with eyepieces.  It also allows my Dob to reach focus with a DSLR.

There's also the much more expensive Explore Scientific CC that requires 32mm of in-focus.

[Ally8446]

On 02/04/2019 at 14:35, John said:

I can't advise on the CC because I don't use one (my 12 inch dob is F/5.3). On the eyepiece, I have to say that I don't use my 31mm Nagler (exit pupil 5.85mm) half as much as I do the 21mm Ethos with my 12 inch dob because the background sky darkness of at the higher power plus the more efficient exit pupil make the 21mm a much more effective deep sky observing tool. I'm 59 this year so a little older than yourself.

I wonder if the ES 24mm 82 might be a better bet with your scope than the 30mm ?.

Other options to give you more true field while maintaining an effective exit pupil might include the Myriad 20mm / 100 degree, the APM/Lunt 20mm / 100 or even the 28mm Nirvana / UWAN perhaps ?

 

 

Food for thought indeed John. Tbh I've been thinking about the ES24 82° but wondered if I were to go to 28 or 30mm would the extra 1.5mm exit pupil really be a problem ? I have 20/20 vision and don't wear glasses. 

[Ally8446]

On 02/04/2019 at 17:11, Louis D said:

I'm not sure why you left out the GSO/Revelation CC.  I use an OPT labelled GSO CC.  I just had to add a 25mm M48 spacer tube between the optics section and the eyepiece holder to work with the majority of my eyepieces that focus at the shoulder.  Eyepieces that focus within 1/4" (6mm) of the shoulder are still very well corrected for coma.

It has a 1.1x magnification factor despite what the TH page says.  It only requires 10mm to 15mm or so of in-focus for use with eyepieces.  It also allows my Dob to reach focus with a DSLR.

There's also the much more expensive Explore Scientific CC that requires 32mm of in-focus.

I never even gave the GSO one a thought Louis. Thanks for the suggestion. The view just needs tidying for my needs. 

Al

[John]

33 minutes ago, Ally8446 said:

Food for thought indeed John. Tbh I've been thinking about the ES24 82° but wondered if I were to go to 28 or 30mm would the extra 1.5mm exit pupil really be a problem ? I have 20/20 vision and don't wear glasses. 

I don't wear glasses and my vision is OK. I find the larger exit pupil leads to dimmer DSO's under my moderately light polluted skies which is why the 21mm Ethos gets the nod over the 31mm Nagler most of the time when I'm using my 12 inch F/5.3 dob. If your skies are nice and dark then this might not be an issue.

 

[Louis D]

1 hour ago, Ally8446 said:

I never even gave the GSO one a thought Louis. Thanks for the suggestion. The view just needs tidying for my needs. 

Al

Then you'll probably like it.  It gets you 95% of the way to Paracorr level correction for a fraction of the price and effort.  It also nicely flattens the field.

I don't know about the UK, but they come up used here in the states every month or so for $75 to $90, so keep a look out for them on the classifieds.

[Paul73]

If you are going the Coma Corrector route, you may as well go wide with the eyepiece. I found the exit pupil from 28mm and 30mm a bit too much for me and settled on a 24mm 82° Which is just right. This is used with an old Type 1a Parracor which cleans things up really well (it doesn’t have enough intravel for a lot of the 100° Eyepieces).

Paul

[rwilkey]

On 02/04/2019 at 14:16, Ally8446 said:

Problem is I'm nearly 50 so exit pupil may be an issue. An ES30 82° has an exit pupil of 6.5mm, might that be a little too large ? 

Hi there, I can't help you on the CC, but on the exit pupil of 6.5mm this should not be a problem for you.  The expansive view of this ep will 'wow' you, as it did me!