Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

My Widest Telescopic TFOV Ever

NV
  • Please log in to reply
31 replies to this topic

#26 Vondragonnoggin

Vondragonnoggin

    Cosmos

  • *****
  • Posts: 7737
  • Joined: 21 Feb 2010
  • Loc: Southern CA, USA

Posted 12 March 2019 - 05:16 PM

I’m going to give it a go with the series 4000 56mm first. I’ll use my Baader adapter and try it with my mak and see what I can get for afocal use reduction. If it works there, then might try with AT72ED

 

Agena had them on sale for $69.95 which is more my experimental price range than the $243 for the TV. 

 

Thanks for answering my questions.



#27 Vondragonnoggin

Vondragonnoggin

    Cosmos

  • *****
  • Posts: 7737
  • Joined: 21 Feb 2010
  • Loc: Southern CA, USA

Posted 14 March 2019 - 03:45 PM

My Meade 4000 56mm plossl arrived today. I should be able to start some experiments with it soon. Nice eyepiece. Not too heavy, but way more weighty than the GSO 30mm Superview projection eyepieceI have in 2”. Eyecup should work nicely with afocal use to keep stray light out. A sturdy eyepiece.



#28 Vondragonnoggin

Vondragonnoggin

    Cosmos

  • *****
  • Posts: 7737
  • Joined: 21 Feb 2010
  • Loc: Southern CA, USA

Posted 15 March 2019 - 12:38 AM

Ok, so I was too lazy to take out my mak 150 early and let it cool down and too lazy to take out my T-Rex.

 

I did take out my AT72ED on Manfrotto tripod. It suits my lazy ways too. First attempt with 56mm plossl, 2” 3nm filter on the end of the plossl, Baader digiscoping adapter, NVD Micro in adapter. This came to Focus with my focuser drawtube racked out about 3 1/4 inches. Could see the focal reduction at work. Nice bright image of M42. Could make out ic434, HH lump, and flame. 

 

Next I put the Antares .5x focal reducer on the end of the plossl and the 3nm screwed into the focal reducer. Had to rack in the drawtube a good inch but all came to focus easy. Detail on HH was better. Image smaller for sure. It would not come to Focus with focal reducer on the end of the diagonal. Not enough back focus but worked very well with FR on end of eyepiece barrel. I don’t know the TFOV and didn’t measure it. The three belt stars of Orion fit in the center of the view with a lot of room to spare on each side. Rough guess would be easily over 5 degrees. I’ll try to get a better guesstimate later. I can compare to my 8x42 (have to look this one up again but over 7°) and 10x50 (6.1° TFOV) bino views and get a better idea. I did see some vignetting but edges actually looked pretty good and some of the apparent vignetting might have been from the eyecup opening being a tad smaller than the envis lens. The moon was up nearly 3/4 and positioned above and to the right of Orion. I am in Bortle 7 skies. Not bad for moon and LP to see as much detail as I did. The 3nm helps in those conditions.

 

Next experiment though will be on the mak 150 for sure. Very interested to see what reduction I can get with the combination here. That scope is 14lbs compared to 25lbs of my 6” F/5.9 and lately would rather use smaller and lighter scopes. If I can reduce it enough to give me some good narrowband summer nebula views that aren’t too noisy I’ll be very happy. At F/12 the Ha starts to get very noisy and my Micro has no adjustable gain. I only have adjustable gain in my 25mm tube devices. I think I can effectively reduce my F/12 mak to somewhere near F/3.8 using both .5x reducer and the Micro afocally over the 56mm plossl. cool.gif

 

All in all it was a success for reduction and focusing confirmation. Will add more as I find out more. A few minor kinks to work out like maybe plugging the envis lens all the way inside the eyecup opening to keep from vignetting or possibly removing the eyecup and make my own small shroud to block stray light and keep from vignetting. The Baader adapter is light weight and has many adjustments to easily position the NVD where you want above the eyepiece. Has an adjustment that allows tilting the NVD directly off the eyepiece in click stop increments too for easy compare of regular eyepiece view to afocal NVD view.


Edited by Vondragonnoggin, 15 March 2019 - 02:09 AM.

  • chemisted likes this

#29 chemisted

chemisted

    Vostok 1

  • -----
  • topic starter
  • Posts: 180
  • Joined: 24 Feb 2012

Posted 15 March 2019 - 07:43 AM

Nice report!  I have recently used the GSO .75X reducer with my TV-140.  In this case, I am just dropping it into the 2" diagonal followed by the 55mm Plossl with H-alpha filter screwed to the eyepiece and Micro screwed onto the Plossl.  This doesn't give me a full .75X reduction but it gets me to f/2.0 and a very nice 3.6 degree FOV.  The Horsehead, Flame and sigma Orionis field is just stunning.


  • Vondragonnoggin and Gavster like this

#30 Vondragonnoggin

Vondragonnoggin

    Cosmos

  • *****
  • Posts: 7737
  • Joined: 21 Feb 2010
  • Loc: Southern CA, USA

Posted 15 March 2019 - 07:58 AM

While I didn’t have enough back focus for the reducer before the diagonal, I did still have quite a bit of drawtube out with reducer on the eyepiece. I think I might be able to reduce further if I put a 25mm extension between the reducer and eyepiece. It will make the stack taller, but that’s not really a problem for me. I believe I have enough back focus left to use the extension. Will try this next time out.



#31 Gavster

Gavster

    Messenger

  • -----
  • Posts: 420
  • Joined: 07 Mar 2014

Posted 15 March 2019 - 10:08 AM

Nice report!  I have recently used the GSO .75X reducer with my TV-140.  In this case, I am just dropping it into the 2" diagonal followed by the 55mm Plossl with H-alpha filter screwed to the eyepiece and Micro screwed onto the Plossl.  This doesn't give me a full .75X reduction but it gets me to f/2.0 and a very nice 3.6 degree FOV.  The Horsehead, Flame and sigma Orionis field is just stunning.

How much reduction do you think you get with this setup? I guess one of the advantages of this reducer is that you don’t have to worry so much about getting an exactly correct distance from the reducer to the eyepiece - is that right?



#32 chemisted

chemisted

    Vostok 1

  • -----
  • topic starter
  • Posts: 180
  • Joined: 24 Feb 2012

Posted 15 March 2019 - 04:44 PM

My best estimate is that I am achieving 0.82X for the reducer.  As far as I know all reducers can be used at shorter distances than the one required for the specified reduction.  For example, my 27TVPH needs 175mm spacing between the optics to achieve 0.75X reduction but I use it with a shorter spacing when doing afocal with the RC-10 since that is dictated by the backfocus of the telescope.  In this case I achieve ~0.8X reduction and a very nice flattening of the curvature that is inherent in the RC design.  On the other hand, the TV-140 is a flat field instrument to begin with and using the reducer did introduce some distortion at the very edge of the field but I didn't mind as the FOV is enormous and the targets of interest were sharp.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics







Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics