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

Short report on using Dob with TV 67mm Plossl + Afocal NV

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

#1 slavicek

slavicek

    Ranger 4

  • *****
  • topic starter
  • Posts: 373
  • Joined: 01 Aug 2017
  • Loc: Massachusetts

Posted 28 August 2020 - 07:19 PM

I am not a fan of Afocal NV set up hence it took me a while before I’ve got myself the 55mm TV Plossl to  67mm Fl converter lens. And I was not expecting much more then what I already can see with my prime focus set up. BUT! I must confess, this think is really awesome! Those so called “bright nebulas” just fit right into the FOV and they are bright indeed! My 22” f3.3 scope with the 67mm set up and 5nm Ha filter gets me FOV of 1.45 degrees. Almost perfect for most nebulas!
So last week (around New Moon) I’ve looked at these nebulas: Eagle, Omega, Lagoon, Trifid, Crescent, Pelican, Rho Ophiuchi, IC1470 “Comet”, Eastern Vail was “awesome”, I paned around Western Vail and I paned around N.American. I've also looked at some Sh2 nebulas. I am going to have to start taking pictures, it’s just so nice with lot of details! So, if you have a fast Dob then go for it and try it out! I definitely recommend this set up.

The only problem with this set up is that it looks like a chimney!

First comes the 2” Extender (needed to get this contraption into focus), then comes the TV 55mm Plossl with the 67mm converter lens and the Ha filter, then it’s the 25mm Tamron C lens and then it’s the MOD3. It’s definitely sticking out of the telescope, so one has to be careful not to bang into it. Again, I am not fan of the Afocal NV but in this case, it’s worth it. However, I am not sure I’d use this for astronomy outreach.

So what’s next? I will try to find some Barnard dark nebulas with this set up. And of course, hopefully one day I will finish converting my 200mm f1.8 Cannon lens for use with NV. I still have some “technical” issues with it and NO time to work on it. And based on what the 67mm Afocal NV set up can do for me, who knows if I ever finish the Canon project at all. smile.gif

 

Afocal-separate-small.JPG

 


  • Jeff Morgan, alanjgreen, Tyson M and 3 others like this

#2 Jeff Morgan

Jeff Morgan

    Voyager 1

  • *****
  • Posts: 12,342
  • Joined: 28 Sep 2003
  • Loc: Prescott, AZ

Posted 29 August 2020 - 12:21 AM

I was watching 200mm lenses on fleaBay just about the time 67 conversion lens came out. After the success of that lens, it occurred to me that a telescope might be better:

 

The 67 Plossl gives an approximate effect of a 0.4x reducer.

 

200mm / 0.40 = 500mm.

 

Refractors of 500mm focal length are quite easy to find. A 80mm f/6 apo is close. With that reduction f/6 becomes f/2.4.

 

And refractors are more astro-friendly than large telephotos.

 

The only issue I have so far is field curvature. Working on that one. I'll probably restrict SLR lenses to true hand-held applications - 135mm or less.

 

YMMV of course.


  • GeezerGazer and AllStarez like this

#3 alanjgreen

alanjgreen

    Mariner 2

  • -----
  • Posts: 269
  • Joined: 31 Aug 2013
  • Loc: Cumbria, UK

Posted 29 August 2020 - 03:00 AM

Nice report. The focal ratio speed up from the 67mm setup really does increase brightness substantially and as you found delivers great results.

 

You will get the same boost for galaxies too.

 

Alan



#4 a__l

a__l

    Vanguard

  • -----
  • Posts: 2,189
  • Joined: 24 Nov 2007

Posted 29 August 2020 - 03:03 AM

Telescope f/3.3. There is no paracorr-2 in this locomotive. But the most interesting thing about this thread is that uses a 25mm Tamron C lens for afocal. In my memory, this is the first thing that has been applied besides Envis (or its Katod clone - or vice versa in terms of cloning).

This is probably a happy coincidence of the enlarged exit pupil location TV55 + 67mm converter and the smaller entrance pupil location 25mm Tamron. This leaves me a chance to try again with the Fujinon-CF25HA-1. For the Nagler 31, this is definitely not a chance.



#5 a__l

a__l

    Vanguard

  • -----
  • Posts: 2,189
  • Joined: 24 Nov 2007

Posted 29 August 2020 - 03:07 AM

You will get the same boost for galaxies too.

 

I don’t think so. For the vast majority of galaxies, the scale is very small. Prime focus to help. Barlow can be added.

 

Possibly galaxy clusters. But I still have not been able to do the experiment on my 24" f/3.3 due to the small field in the equipment I have.


Edited by a__l, 29 August 2020 - 03:39 AM.


#6 AllStarez

AllStarez

    Explorer 1

  • -----
  • Posts: 60
  • Joined: 29 Sep 2019

Posted 29 August 2020 - 06:22 AM

I was watching 200mm lenses on fleaBay just about the time 67 conversion lens came out. After the success of that lens, it occurred to me that a telescope might be better:

 

The 67 Plossl gives an approximate effect of a 0.4x reducer.

 

200mm / 0.40 = 500mm.

 

Refractors of 500mm focal length are quite easy to find. A 80mm f/6 apo is close. With that reduction f/6 becomes f/2.4.

 

And refractors are more astro-friendly than large telephotos.

 

The only issue I have so far is field curvature. Working on that one. I'll probably restrict SLR lenses to true hand-held applications - 135mm or less.

 

YMMV of course.

Fully agree, i stopped looking for big lens considering my TV 76 would provide exactly f/2.4 with 67mm Plossl.

i keep a few camera lenses for hand held views and pleasures, plus a finder forits astro firiendly conception



#7 alanjgreen

alanjgreen

    Mariner 2

  • -----
  • Posts: 269
  • Joined: 31 Aug 2013
  • Loc: Cumbria, UK

Posted 29 August 2020 - 07:14 AM

I don’t think so. For the vast majority of galaxies, the scale is very small. Prime focus to help. Barlow can be added.

 

Possibly galaxy clusters. But I still have not been able to do the experiment on my 24" f/3.3 due to the small field in the equipment I have.

Thanks for giving me the benefit of your non-NV experience.

 

I have over 2 years experience using NV with galaxies and I am correct, the increased brightness arising from focal acceleration with the 67mm WILL benefit my quest to see arms in the brightest 200 galaxies.

 

Your assertion of using prime focus won’t actually help. For views of spiral arms you need an accelerated focal ratio so long focal length eyepieces are actually best...

 

For increased scale you need to get a long focal length scope such as big dob or SCT.

 

Once you actually purchase NV then you may be able to speak from experience too...

 

https://www.cloudyni...d-night-vision/


Edited by alanjgreen, 29 August 2020 - 07:35 AM.

  • Joko likes this

#8 cnoct

cnoct

    Viking 1

  • *****
  • Posts: 967
  • Joined: 02 Sep 2010
  • Loc: Hawai'i

Posted 29 August 2020 - 07:47 AM

a_i is well experienced with NV, has their own NV kit and does quite bit more adapting than most NV astro user on here.  



#9 a__l

a__l

    Vanguard

  • -----
  • Posts: 2,189
  • Joined: 24 Nov 2007

Posted 29 August 2020 - 08:43 AM

Once you actually purchase NV then you may be able to speak from experience too...

 

https://www.cloudyni...d-night-vision/

I bought an NV in the spring.
Moreover, I made all the adapters for it myself.
Moreover, I was able to made an adapter and use paracorr-1 in NV  prime focus.
Moreover, the sky allowed me to observe galaxies in it (in a dark enough sky).

Moreover, I made all my dobs myself (excluding optics) smile.gif
And I've been observe at galaxies in them for over 10 years.

What I don't have is a large field when viewed in NV (for my dobs). For example such TV55 + 67. I observe for afocal only through Nagler 31 (I also made the adapter myself). The field is slightly different from prime focus and the picture did not impress me.

According to your link, I do not see a comparison when observing galaxies in afocal using TV55 and using NV without many glass (prime focus).

 

Needless to say, I only observe galaxies in dark skies. Regardless of whether it is NV or ethos-delos.
Therefore, I expect a similar comparison in terms of observation conditions.

I believe that the garden and the galaxies are incompatible concepts. An exception if your garden is  within 20-30 kilometers of other gardens and lanterns.


Edited by a__l, 29 August 2020 - 09:18 AM.

  • cnoct likes this

#10 hoof

hoof

    Surveyor 1

  • *****
  • Posts: 1,784
  • Joined: 07 Apr 2005
  • Loc: Monroe, WA

Posted 29 August 2020 - 04:39 PM

My 6" F/4 astrograph with my TV 67mm Plossl setup is 233mm equivalent, at an effective F ratio of F/1.6 or so.  Throw in my 0x85x reducer, and I'm at 200mm equivalent and F/1.3 to F/1.4, albeit it vignettes a bit, so I only get an AFoV of around 33-36 degrees.

 

Not sure I'll find a camera lens that's 200mm and F/1.3 ;)

 

So I definitely agree that past a certain point, a telescope is better!



#11 slavicek

slavicek

    Ranger 4

  • *****
  • topic starter
  • Posts: 373
  • Joined: 01 Aug 2017
  • Loc: Massachusetts

Posted 29 August 2020 - 07:18 PM

Telescope f/3.3. There is no paracorr-2 in this locomotive. But the most interesting thing about this thread is that uses a 25mm Tamron C lens for afocal. In my memory, this is the first thing that has been applied besides Envis (or its Katod clone - or vice versa in terms of cloning).

This is probably a happy coincidence of the enlarged exit pupil location TV55 + 67mm converter and the smaller entrance pupil location 25mm Tamron. This leaves me a chance to try again with the Fujinon-CF25HA-1. For the Nagler 31, this is definitely not a chance.

The happy coincidence is that the (sky side) thread on the 25mm f/1.8 Tamron C-lens fits

a) 1.25" filters (for 1x observing) and

b) it also fits the TNVC adapter (for use with 67mm eyepiece). I do get some vigneting and field curvature with this set up but who cares, for nebulas it's just awesome!



#12 slavicek

slavicek

    Ranger 4

  • *****
  • topic starter
  • Posts: 373
  • Joined: 01 Aug 2017
  • Loc: Massachusetts

Posted 29 August 2020 - 07:41 PM

I bought an NV in the spring.
Moreover, I made all the adapters for it myself.
Moreover, I was able to made an adapter and use paracorr-1 in NV  prime focus.
Moreover, the sky allowed me to observe galaxies in it (in a dark enough sky).

Moreover, I made all my dobs myself (excluding optics) smile.gif
And I've been observe at galaxies in them for over 10 years.

What I don't have is a large field when viewed in NV (for my dobs). For example such TV55 + 67. I observe for afocal only through Nagler 31 (I also made the adapter myself). The field is slightly different from prime focus and the picture did not impress me.

According to your link, I do not see a comparison when observing galaxies in afocal using TV55 and using NV without many glass (prime focus).

 

Needless to say, I only observe galaxies in dark skies. Regardless of whether it is NV or ethos-delos.
Therefore, I expect a similar comparison in terms of observation conditions.

I believe that the garden and the galaxies are incompatible concepts. An exception if your garden is  within 20-30 kilometers of other gardens and lanterns.

It may all depend on where you do observe the galaxies from.

With my portable 22" f/3.3 DOB I do observe from dark side (and near New Moon). Most of the time I do get better views of galaxies using Ethos rather then NV, but not always.

When I observe with our clubhouse 25" f/3 DOB, which is located in suburbs, then the NV (with long pass filter) makes the galaxies brighter.

 

I will definitely try the 67mm + NV set up on galaxies, just to see how it goes

And I am curious, why do you use 31 mm Nagler with NV?



#13 a__l

a__l

    Vanguard

  • -----
  • Posts: 2,189
  • Joined: 24 Nov 2007

Posted 30 August 2020 - 01:51 AM

And I am curious, why do you use 31 mm Nagler with NV?

I don't see any advantages over prime focus. A little more field. At the start, I planned to use something like Fujinon CF16 or CF12.5, but they are not compatible for afocal use with the N31.

Now I decided to buy a TV55+67. This is the maximum possible field for a 2" format.
Maybe I will replace Katod with Fujinon-CF25HA-1 for afocal. I have both of these lenses and I like the image in the second one better.



#14 GOLGO13

GOLGO13

    Fly Me to the Moon

  • *****
  • Posts: 5,313
  • Joined: 05 Nov 2005
  • Loc: West Virginia

Posted 30 August 2020 - 08:02 AM

I'll have to get one of these eventually. Currently I am all 1.25 inch with filters and eyepieces when doing afocal. That saved me a lot of money and before the 67 adapter I saw no need to change. I do combine a .7 adapter and my 40mm plossl with afocal to get pretty good reduction. But I don't see myself buying this for a few years at this point. Maybe if I find some sales.

#15 GrahamDFyffe

GrahamDFyffe

    Mariner 2

  • -----
  • Posts: 253
  • Joined: 07 Apr 2016
  • Loc: Central Arizona

Posted 31 August 2020 - 11:57 AM

The happy coincidence is that the (sky side) thread on the 25mm f/1.8 Tamron C-lens fits

a) 1.25" filters (for 1x observing) and

b) it also fits the TNVC adapter (for use with 67mm eyepiece). I do get some vigneting and field curvature with this set up but who cares, for nebulas it's just awesome!

Which Tamron 25mm has a 1.25 filter thread? I would consider getting one



#16 slavicek

slavicek

    Ranger 4

  • *****
  • topic starter
  • Posts: 373
  • Joined: 01 Aug 2017
  • Loc: Massachusetts

Posted 01 September 2020 - 08:16 PM

Which Tamron 25mm has a 1.25 filter thread? I would consider getting one

It's a Tamron 2/3" 25mm f/1.4 c-mount manual iris lens. It goes for around $160. It has  front 30.5-0.5mm threads which "just" fit the 1.25" filters.



#17 GrahamDFyffe

GrahamDFyffe

    Mariner 2

  • -----
  • Posts: 253
  • Joined: 07 Apr 2016
  • Loc: Central Arizona

Posted 02 September 2020 - 09:49 AM

It's a Tamron 2/3" 25mm f/1.4 c-mount manual iris lens. It goes for around $160. It has  front 30.5-0.5mm threads which "just" fit the 1.25" filters.

I see that there is also a 16mm version of that lens with the same filter thread. That should be able to do the full FOV of the 55mm Plossl or close to the full FOV of a Panoptic using the TNVC adapter.



#18 a__l

a__l

    Vanguard

  • -----
  • Posts: 2,189
  • Joined: 24 Nov 2007

Posted 02 September 2020 - 05:34 PM

http://www.televue.c...id=36&Tab=_work

You need to know the monocular entrance pupil location for this lens.



#19 GrahamDFyffe

GrahamDFyffe

    Mariner 2

  • -----
  • Posts: 253
  • Joined: 07 Apr 2016
  • Loc: Central Arizona

Posted 02 September 2020 - 06:08 PM

http://www.televue.c...id=36&Tab=_work

You need to know the monocular entrance pupil location for this lens.

how on earth do I find that? I've never seen any discussion on "entrance" pupils



#20 a__l

a__l

    Vanguard

  • -----
  • Posts: 2,189
  • Joined: 24 Nov 2007

Posted 02 September 2020 - 06:45 PM

There may be a complete specification for this lens on the internet. I dont know. The fastest option is to check it out by personal experiment.


  • slavicek likes this


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





Also tagged with one or more of these keywords: NV



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics