Is 2deg tfov really necessary?

[ariefm71]

hi vin, the 40mm XL can't be used with FR in place (severe vignetting), 32mm is max. Therefore might go with 32mm MK80, 30mm Pentax XW, or Pan 27 (personally tested by Al Nagler with his C8/FR combination).
Would love to have 31 or 26mm Nagler, still out of my wallet's fov though :-)
cheers,

[VinSnr]

hi vin, the 40mm XL can't be used with FR in place (severe vignetting), 32mm is max. Therefore might go with 32mm MK80, 30mm Pentax XW, or Pan 27 (personally tested by Al Nagler with his C8/FR combination).
Would love to have 31 or 26mm Nagler, still out of my wallet's fov though :-)
cheers,

oh ic.....

Ever thought of using the 30mm 1RPD 80 degree eyepiece? it's 2 inch and I bet it's very close if not better than the MK80. And it cost only US95.

I have this eyepiece, and though it's cheap, it's a wonderful performer. I have use it on M7, using my FR and 8" SCT in the past. The view was amazing. Sharp pinpoint stars till maybe the last 5 degrees or so. It is one eyepiece I will never sell. I have a set of Pentax XL which I will never sell too, so if I put this cheapo eyepiece in the same league as the XLs, you should know how much I appreciate this eyepiece.

You may want to try this first and see if you like it before plunging in with all those bucks on a MK80 or a Nagler

[Airconvent]

mmm... obviously a large FOV is useless visually for the Andromeda Galaxy I thought all we can see is the core anyway. The rest of the stuff you need to take an longer exposure shot to bring it out?

rich

[weixing]

Hi,

mmm... obviously a large FOV is useless visually for the Andromeda Galaxy I thought all we can see is the core anyway. The rest of the stuff you need to take an longer exposure shot to bring it out?

You can actually see a oval shape object with a bright central core. I had seen it in Mersing and even in Singapore at good clear night. But I still can't see any of the spiral arm structure even using the 10" teleport in Mersing...

Have a nice day.

[Airconvent]

Hi,

mmm... obviously a large FOV is useless visually for the Andromeda Galaxy I thought all we can see is the core anyway. The rest of the stuff you need to take an longer exposure shot to bring it out?

You can actually see a oval shape object with a bright central core. I had seen it in Mersing and even in Singapore at good clear night. But I still can't see any of the spiral arm structure even using the 10" teleport in Mersing...

Have a nice day.

yes...what we see of the core and bits outside the core is only about the same size as the moon. I think the actual real size is much bigger...

rich

[weixing]

Hi,
The last time I saw it (I think at merina south), it actually a lot bigger than that. I remember seeing the bright core with a fade oval shape patch that spread nearly across the FoV which is around 2 degree. Anyway, I think we should able to see 60% to 70% of the M31 in Singapore during very clear night.

By the way, in Mersing, I can see the oval patch spread fully across the FoV if you put the bright core at the centre, but you still need to shift the scope to see the two end of M31.

Have a nice day.

[MooEy]

something that i don't really get, u mention the mk80 is us$250 used. how can that be consider affordable while a televue is out of reach? a new 27 pano is only us$330, the 35 pano is us$365, i think they are definately more worth considering than the mk80.

i have not much idea if the 32mm mk80 would work, but if it does, then the 35 pano should work too. also, do try out the 1rpd as suggested by vin snr. it's much cheaper than any of the other options.

~MooEy~

[elton]

Weixing, I thought we saw dark lanes clearly in M31? But spiral structure was not apparent. If I remember correctly, it stretched all across the 40mm XL (2 deg TFOV) plus a bit more.

Astro mathematicians, pls correct me if I'm wrong .... Besides using TFOV=AFOV/Mag, the other factor limiting TFOV is the eyepiece barrel : TFOV (limit) = 46/2000 X 57.3 for a 2000mm C8 with a 2" eyepiece gives about 1.3 deg. This means you need a barrel larger than 2" to get a larger unvignetted FOV.

Arief, if you use a 40mm XL without FR, you will get exactly 1.3 deg without vignetting. The 1RPD will give 1.2 deg without FR but at a higher magnification, also a good choice. I'm curious if anyone has hit 2 deg TFOV in a C8 though.

[MooEy]

hmm..shouldn't a 2" eyepiece have a 50.8mm barrel, thus the equation should be 50.8/2000 x 180/3.14159 = 1.455

also, since a 6.3 reducer is being used, the focal length is now roughly 1300 instead of 2032. therefore the equation would have become 50.8/1300 x 180/3.14159 = 2.24

but then, the main issue here isn't the formulas. but rather whether the scope is able to produce an unvignetted view. if we take the unvignetted barrel size to be roughly 40mm at 1300mm, then the equation would work out to be 40/1300 x 180/3.14159 = 1.76

the 27mm panoptic gives a tfov of roughly 1.42, the 35mm panoptic gives roughly 1.83 when used with reducer. if my above equation is somewhere there, then the 35mm pano will vignet slightly, thus al nagler only said that the 27mm pano would not vignet. it seems that he already noes the 35mm pano would vignet.

the main reason why i'm impress by his determination is that the cost of all the wierd stuff to assist him in reaching the 2 degrees tfov would cost more than the price difference between the c8 and r200ss.

~MooEy~

[ariefm71]

The main reason I will stick with C8 is its airline carry-on portability (yes, i've carried on the ota to airplane's cabin on my two overseas trips, mount and tripod were checked-in). No other 8" scopes can do that (well, except UTI that will cost you ten times of a C8 ). Off course, the final solution is to get a 4" short tube premium apo, but that will happen only sometime in the distant future.
Mo, pano is still within the reach, its the low power naglers that i was referring to.

cheers,