WTB a 4 inch or larger refractor

tungkian · Post by **tungkian** » Wed Oct 03, 2007 11:06 am

hihi,

i'm currently using a nexstar 6SE. but would like to upgrade to a 4 inch and above refractor. why? cause although the images in the 6SE are brighter, i feel like they are smudgy compared to my long sold vixen 80mm refractor. and it sorts of "disturbs" me..haha..

however, i do not want to use an equatorial mount as i observe from my balcony (cant find alignment for GEM), so i hope to mount the refractor on the 6SE mount. i checked out the weight of the 8SE and the 8inch SCT OTA tube is 5.7kg. this means that the refractor tube can be up to 5+ kg i guess..

another factor is the ability to point to zenith. i'll be hard with the long refractors, so i guess a 'fast' one will be better.

i'm looking at the astrotech 102ED, william optics megrez 110, stellarvue 102ED. as i'm a newbie when it comes to this sort of stuff, pls pls gimme your suggestions and comments..and of course any other possible equipment that i can consider..

don't wish to spend too much on the OTA so my budget is around SGD2000. thanks in advance for all the help that i hope i'll get!!!!!

Post by **weixing** » Wed Oct 03, 2007 11:47 am

Hi,
IMHO, it'll be very hard to find one >= 4" APO that can use on NexStar SE mount safely. Clearing the mount base will be difficult (you still need to install diagonal) even you don't look at zenith unless you off balance the scope by a lot (SCT are back heavy... so got more space between the diagonal and mount base when balance, but Refractor are usually front heavy or equally heavy).... but the NexStar SE mount is not a "powerful" mount and may not perform properly if you do that.

Have a nice day.

kayheem · Post by **kayheem** » Wed Oct 03, 2007 11:51 am

The images through the 6" look smudgy?

Have you collimated the scope properly at high power? You have to do this using a star test.

Kay Heem

tungkian · Post by **tungkian** » Wed Oct 03, 2007 11:53 am

kayheem wrote:The images through the 6" look smudgy?

Have you collimated the scope properly at high power? You have to do this using a star test.

Kay Heem

yeap its calibrated. but somehow it does not have the sharpness..i just can't put myfinger on it but somehow it looks different..

Post by **weixing** » Wed Oct 03, 2007 12:02 pm

Hi,

however, i do not want to use an equatorial mount as i observe from my balcony (cant find alignment for GEM)

By the way, alignment a GEM on balcony can be done (there are few members that observe/imaging at their balcony using GEM)... It'll be easier if you do visual only as you don't need very accurate alignment... compass alignment will do.

Have a nice day.

ariefm71 · Post by **ariefm71** » Wed Oct 03, 2007 12:07 pm

Smudgy as in less resolution? the only cure is to increase the aperture. Upgrade to 8SE and retain the mount.

You might want to compare the performance of a good 8" SCT compared to a 4" refractor before making the decision.

If die die must have a portable refractor, wait for the new Orion 102 f/7 FPL-53 doublet (no, this is not a typo) which will be released later this year. Optically it should be better than the SV or AT or WO which is using FK-51.

kayheem · Post by **kayheem** » Wed Oct 03, 2007 12:30 pm

tungkian wrote: yeap its calibrated. but somehow it does not have the sharpness..i just can't put myfinger on it but somehow it looks different..

I don't mean to sound negative, but did you do and/or check the collimation yourself? SCTs are very sensitive to collimation problems. But once you get it, you will be rewarded. Do not try to collimate using a laser...it does not work. Anyway, 'calibration' is not equal to 'collimation'

If you don't know how to check, give a yell, and the SCT old-birds can help you out e.g. VinSnr

Kay Heem

tungkian · Post by **tungkian** » Wed Oct 03, 2007 12:46 pm

hmm..i collimate by using a 200+ x eyepiece on a bright star. so i'll turn the little screws at the front until the rings look round and nicely spacely out..that should be ok right? hmm..

any ideas where i can look through a good 4 inch refractor?? would like to make a comparison first before buying...

weixing: can you tell me how to go about aligning a GEM mount without stars? is it just set the altitude to 1 degree, then turn it to face north..lidat?

kayheem · Post by **kayheem** » Wed Oct 03, 2007 12:56 pm

tungkian wrote:hmm..i collimate by using a 200+ x eyepiece on a bright star. so i'll turn the little screws at the front until the rings look round and nicely spacely out..that should be ok right? hmm..

Something like that, but you should bump up the power as high as possible. I collimated my C5 last time at 375X. When you turn the collimation screws, the rings should be nicely spaced out *at focus*, not de-focussed.

If the rings are not round i.e. pinched, it means you have tightened too much.

Post by **weixing** » Wed Oct 03, 2007 2:43 pm

Hi,

any ideas where i can look through a good 4 inch refractor?? would like to make a comparison first before buying...

You can try Astro Scientific Center.

weixing: can you tell me how to go about aligning a GEM mount without stars? is it just set the altitude to 1 degree, then turn it to face north..lidat?

Correct... Set altitude to 1 degree and using a compass to point at North... that's accurate enough for visual use.

Have a nice day.