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

Does 1-degree make a star hopping difference?

  • Please log in to reply
21 replies to this topic

#1 Chris K

Chris K

    Messenger

  • *****
  • topic starter
  • Posts: 423
  • Joined: 20 Sep 2017
  • Loc: Long Island, Earth

Posted 12 April 2021 - 04:53 PM

When star hopping, is there a tipping point for when a finderscope’s wider TFOV makes enough of a difference for the hopper to justify the larger?

5 vs 6 degrees?
6 vs 7?
5 vs 7?

(Magnified, not zero power of course)

Asking for a friend. ;)

#2 Jim1804

Jim1804

    Viking 1

  • -----
  • Posts: 521
  • Joined: 26 May 2011
  • Loc: Raleigh-Durham NC, USA

Posted 12 April 2021 - 06:23 PM

As someone who most often star hops at the eyepiece, I would think that 5 degrees would be plenty. That’s all of Orion’s Belt, plus some. Star hopping is very effective at the 1 degree eyepiece FOV.
  • Asbytec, Chris K and Star Geezer like this

#3 harbinjer

harbinjer

    Viking 1

  • *****
  • Posts: 691
  • Joined: 17 Dec 2008
  • Loc: Southeastern Minnesota

Posted 14 April 2021 - 11:51 PM

I have to agree with Jim1804: 5° is plenty.  I wouldn't like less than 4° though. As long as the finder is helping and not hurting, it' fine. I almost always have binoculars with my scope, so 7-8° is possible with them.


  • Chris K likes this

#4 Star Geezer

Star Geezer

    Mariner 2

  • -----
  • Posts: 270
  • Joined: 22 Apr 2018
  • Loc: Lat. N 40º 56' Long. W 87º 8'

Posted 15 April 2021 - 12:26 AM

I agree with Jim1804. 1 degree seems to be a sweet spot for me as well. Not too narrow, not too wide. Just right.


Edited by Star Geezer, 15 April 2021 - 12:27 AM.

  • Chris K likes this

#5 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 92,658
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 15 April 2021 - 05:43 AM

For me, somewhere around 6.5 degrees is about ideal.

 

The two main factors are the magnification and the field of view.  A reasonably sharp 6.5 degree field at 10x in a 50 mm RACI is what I am currently using.  With the cross hairs accurately centered and aligned to the vertical-horizontal axes of the scope, it lets me use stars any where in the field to accurately point the scope at relatively high magnifications. In the main scope, my finder eyepiece is often either the 13mm Ethos (216x) or the 10mm Ethos (282x).  I am using Sky Safari 6 Pro for my charts to they are aligned to the current location and time with cross hairs that match the finder. 

 

Most finders do not offer such generous fields and most finder eyepieces with cross hairs are not very sharp across the field of view.  A few years ago, I decided it was time to take it to the next level, I took a 24mm TeleVue wide field and added cross hairs.  In the 50mm F/4 finder, it provides a 6.8 degree field at 8.3x and it's sharp compared to most finders but I wanted more magnification with a similar field of view so I found a used Explore Scientific 20mm 68 degree eyepiece and added cross hairs.  That was pretty tricky because I had to remove the sealing ring.

 

It's really quite a nice view.  There is field curvature from the 50mm F/4 objective but I focus about 1/4-1/3 from the center so it's pretty decent across the entire field.  

 

I have 70mm and 80mm finders, they go deeper but there are plenty of stars in a 50mm at 10x and their fields of view are closer to 4 degrees than 5 degrees, I find the 6.5 degrees at 10x to be my favorite.  An ST-80 with a 2 inch eyepiece could provide 6 degrees but it would be very heavy and require an expensive 2 inch RACI diagonal.  My big scope has a balance ratio of 5.5:1 so I would need to add at least 20 pounds of counterweights.  

 

Jon


  • bumm and Chris K like this

#6 Tony Flanders

Tony Flanders

    Hubble

  • *****
  • Posts: 19,681
  • Joined: 18 May 2006
  • Loc: Cambridge, MA, USA

Posted 15 April 2021 - 06:08 AM

As someone who most often star hops at the eyepiece, I would think that 5 degrees would be plenty. That’s all of Orion’s Belt, plus some. Star hopping is very effective at the 1 degree eyepiece FOV.

Heaven knows I've done star-hopping through an eyepiece yielding a 1-degree field of view often enough. But I would not call it "very effective." First of all, it pretty much requires using some kind of electronic device; no paper atlas shows enough stars in a 1-degree field of view to star-hop reliably in the star-poor parts of the sky. And second, it just takes a lot of time to work your way across the sky one degree at a time.

 

For covering significant distances, I'd say that a finderscope with a 5-degree true field of view is at least 10 times faster than star-hopping through an eyepiece yielding a 1-degree field of view on your main scope. But obviously, if you're looking for a faint object, it won't be directly visible through the finderscope but might well be visible through the main eyepiece at 50X or higher.

 

Mind you, all of this varies a lot depending on sky quality. It's vastly easier to star-hop under dark skies than from a typical suburb, or on a moonlit night.

 

I've never done the experiment, but my guess is that once a finderscope's field of view reaches 5 degrees, I would get relatively little benefit from using a wider field of view.


  • Asbytec and Chris K like this

#7 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 92,658
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 15 April 2021 - 06:47 AM

I've never done the experiment, but my guess is that once a finderscope's field of view reaches 5 degrees, I would get relatively little benefit from using a wider field of view.

 

 

I have done this experiment in a number of ways.  The 9x50 Orion finder has a 5.0 degree field, the GSO 8x50 has a 5.6 degree field, various combinations of 50mm finders with interchangeable eyepieces go all the way to 7.0 degrees, all measured.  

 

I think about it very much like binoculars, I much prefer 10x50s with a 6.5 degree field to 10x50s with a 5.0 degree field, there is just more room to work with.  The viewing area is about 70% greater with the 6.5 degree field.  

 

Jon


  • bumm and Chris K like this

#8 Jim1804

Jim1804

    Viking 1

  • -----
  • Posts: 521
  • Joined: 26 May 2011
  • Loc: Raleigh-Durham NC, USA

Posted 15 April 2021 - 07:10 PM

Heaven knows I've done star-hopping through an eyepiece yielding a 1-degree field of view often enough. But I would not call it "very effective." First of all, it pretty much requires using some kind of electronic device; no paper atlas shows enough stars in a 1-degree field of view to star-hop reliably in the star-poor parts of the sky. And second, it just takes a lot of time to work your way across the sky one degree at a time.

For covering significant distances, I'd say that a finderscope with a 5-degree true field of view is at least 10 times faster than star-hopping through an eyepiece yielding a 1-degree field of view on your main scope. But obviously, if you're looking for a faint object, it won't be directly visible through the finderscope but might well be visible through the main eyepiece at 50X or higher.

Mind you, all of this varies a lot depending on sky quality. It's vastly easier to star-hop under dark skies than from a typical suburb, or on a moonlit night.

I've never done the experiment, but my guess is that once a finderscope's field of view reaches 5 degrees, I would get relatively little benefit from using a wider field of view.

Well, you don’t star hop your way from Sirius to Polaris at the eyepiece. That would be extremely inefficient. I get it close using a Quickfinder - ie a nearby bright star - and then hop from there. It’s not always quick - depends on how far you need to go, but you can almost always get to within 5-6 degrees with the Quickfinder. It’s true that I use SkySafari to do this - which is very effective indeed. My point was that any more than about 5-6 degrees probably isn’t a great return on investment, considering that a lot of us starhop quite successfully at 1 deg. Of course, everyone is different.

Edited by Jim1804, 15 April 2021 - 07:11 PM.

  • Chris K likes this

#9 Chris K

Chris K

    Messenger

  • *****
  • topic starter
  • Posts: 423
  • Joined: 20 Sep 2017
  • Loc: Long Island, Earth

Posted 15 April 2021 - 07:26 PM

I've recently started using SkySafari and now it's a billion times easier for me than with my Jumbo PSA.

 

I have been using a 31mm nagler in a 72mm scope and except for having to change out a 2.5lb eyepiece after I find the target/area it's worked out for me with the 5.5ish TFOV.

 

I've experimented with a 1º FOV and agree, not ideal and time consuming. However quite satisfying for someone who was really struggling with hopping using a newtonian and a RACI.

 

With all this info, I have a Russell Optics 56mm on order which will give me about a 6º TFOV. Less than half the weight so less worry about balance and less handling of an expensive EP.

 

I hope it's not too wide and too bright.

 

Thanks for all the advice.


  • Jim1804 likes this

#10 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 92,658
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 15 April 2021 - 07:30 PM

Well, you don’t star hop your way from Sirius to Polaris at the eyepiece. That would be extremely inefficient. I get it close using a Quickfinder - ie a nearby bright star - and then hop from there. It’s not always quick - depends on how far you need to go, but you can almost always get to within 5-6 degrees with the Quickfinder. It’s true that I use SkySafari to do this - which is very effective indeed. My point was that any more than about 5-6 degrees probably isn’t a great return on investment, considering that a lot of us starhop quite successfully at 1 deg. Of course, everyone is different.

 

I can star hop with a 1 degree field of view and a Telrad/red dot but I am much more efficient, much more effective with a Telrad and quality RACI finder with a 6.5 degree field.

 

In my mind, I am not thinking about return on investment, I am thinking about the most effective tools. A 10x50 finder with a reasonably sharp 6.5 degree field of view combined with a Telrad is a better tool than a 10x50 finder with a 5.0 degree field of view.  People spend thousands of dollars on GOTO mounts, spending several hundred dollars on the most effective finders seems like a trivial cost by comparison.  

 

For me, one of the advantages of a good RACI finder is that it lets me point the scope much more accurately than a Telrad so I can often put the object near the center of field at 200-300x.  

 

Part of this is that I am star hopping with relatively large telescopes which is more challenging than with smaller scopes.. 

 

Jon


  • Dave Mitsky, Jim1804 and Chris K like this

#11 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 92,658
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 15 April 2021 - 07:36 PM

With all this info, I have a Russell Optics 56mm on order which will give me about a 6º TFOV. Less than half the weight so less worry about balance and less handling of an expensive EP.

 

 

I think you will find the field of view is not much wider if any and the usable field will be significantly less than the 31mm Nagler.  And with the lower magnification, 7.5x versus 13.5x, it will not be very effective. 

 

For cheap and light, I would go with the $65 34mm 72 degree Svbony from Telescope-warehouse.  It has a 40mm field stop compared to the 31mm Naglers 42mm. 

 

For light, I would go with the 30mm APM UFF, not quite as wide a field as the 31mm Nagler but similar in quality of view and only about 55% of the weight.

 

Jon


  • Chris K likes this

#12 Jim1804

Jim1804

    Viking 1

  • -----
  • Posts: 521
  • Joined: 26 May 2011
  • Loc: Raleigh-Durham NC, USA

Posted 15 April 2021 - 07:38 PM

I've recently started using SkySafari and now it's a billion times easier for me than with my Jumbo PSA.

 

I have been using a 31mm nagler in a 72mm scope and except for having to change out a 2.5lb eyepiece after I find the target/area it's worked out for me with the 5.5ish TFOV.

 

I've experimented with a 1º FOV and agree, not ideal and time consuming. However quite satisfying for someone who was really struggling with hopping using a newtonian and a RACI.

 

With all this info, I have a Russell Optics 56mm on order which will give me about a 6º TFOV. Less than half the weight so less worry about balance and less handling of an expensive EP.

 

I hope it's not too wide and too bright.

 

Thanks for all the advice.

In the interests of full disclosure, I did just get a RACI for use on my dob (just over 5 degrees), but haven't had a chance to use it yet. I think the combo of the Quickfinder and the RACI will be a lot faster, no doubt. 

 

You'll have to let us know how you like your finder!


  • Jon Isaacs likes this

#13 Chris K

Chris K

    Messenger

  • *****
  • topic starter
  • Posts: 423
  • Joined: 20 Sep 2017
  • Loc: Long Island, Earth

Posted 15 April 2021 - 07:45 PM

I think you will find the field of view is not much wider if any and the usable field will be significantly less than the 31mm Nagler.  And with the lower magnification, 7.5x versus 13.5x, it will not be very effective. 

 

For cheap and light, I would go with the $65 34mm 72 degree Svbony from Telescope-warehouse.  It has a 40mm field stop compared to the 31mm Naglers 42mm. 

 

For light, I would go with the 30mm APM UFF, not quite as wide a field as the 31mm Nagler but similar in quality of view and only about 55% of the weight.

 

Jon

Oh well, it's already paid for and on the way. When you say less usable field are you referring to insufficient sharpness around the perimeter of the field?


  • Jon Isaacs likes this

#14 Jim1804

Jim1804

    Viking 1

  • -----
  • Posts: 521
  • Joined: 26 May 2011
  • Loc: Raleigh-Durham NC, USA

Posted 15 April 2021 - 07:55 PM

I think you will find the field of view is not much wider if any and the usable field will be significantly less than the 31mm Nagler.  And with the lower magnification, 7.5x versus 13.5x, it will not be very effective. 

 

For cheap and light, I would go with the $65 34mm 72 degree Svbony from Telescope-warehouse.  It has a 40mm field stop compared to the 31mm Naglers 42mm. 

 

For light, I would go with the 30mm APM UFF, not quite as wide a field as the 31mm Nagler but similar in quality of view and only about 55% of the weight.

 

Jon

Chris K - easy solution - just send me the Nagler! Problem solved!


  • Jon Isaacs and Chris K like this

#15 Chris K

Chris K

    Messenger

  • *****
  • topic starter
  • Posts: 423
  • Joined: 20 Sep 2017
  • Loc: Long Island, Earth

Posted 15 April 2021 - 08:03 PM

Chris K - easy solution - just send me the Nagler! Problem solved!

Oh i still have another scope to for it's lot in life! Love that EP which is way I want to take it out of harms way.



#16 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 92,658
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 15 April 2021 - 10:34 PM

Oh well, it's already paid for and on the way. When you say less usable field are you referring to insufficient sharpness around the perimeter of the field?

 

That and the lower magnification. 

 

Your scope is a 72mm F/5.8.  A 56 mm Plossl provides a 9.6mm exit pupil at 7.5x.  If you pupil dilates to 7mm, the effective aperture of this scope will be

 

72mm x 7mm/9.6mm = 52mm.  So what you have is a 7.5 x 52mm finder with a 6 degree TFoV.  The field may be reasonably sharp because with the reduced aperture, you will be operating at about F/8.

 

The 31mm Nalger provides you with a 14x 72mm finder with a 5.7 degree TFoV.  

 

Jon


  • Chris K likes this

#17 spkerer

spkerer

    Vostok 1

  • -----
  • Posts: 109
  • Joined: 22 Jul 2020
  • Loc: Virginia, USA

Posted 16 April 2021 - 08:56 AM

I've never used a finderscope - neither with my 10" dob nor my 120mm refractor.

 

For me, a Telrad does the job amazingly.  With its concentric rings and either a scaled printout of the rings on acetate for a printed atlas or "show Telrad rings" on SkySafari - I can get much closer than 1 degree of accuracy on the target.

 

That's what I use for any "long" jumps if I'm star hopping.  For close hops, I'll use my 21mm eyepiece - which yields a bit of 2 degree FoV for my setup.



#18 rowdy388

rowdy388

    Skylab

  • *****
  • Posts: 4,310
  • Joined: 09 Apr 2013
  • Loc: Saratoga County, NY

Posted 16 April 2021 - 11:37 AM

I've never used a finderscope - neither with my 10" dob nor my 120mm refractor.

 

For me, a Telrad does the job amazingly.  With its concentric rings and either a scaled printout of the rings on acetate for a printed atlas or "show Telrad rings" on SkySafari - I can get much closer than 1 degree of accuracy on the target.

 

 

My 12.5" NMT came only with a Telrad as a finder scope. The Telrad can be all you need if your skies are reasonably dark. My problem is I love a capable

refractor finder that doubles as an alternative low power, lower exit pupil view of my target area. My 80mm refractors were too heavy to piggyback on the 

New Moon. Jon Isaacs shared his under two pound 70mm frankenfinder build on a thread here a couple years ago and I've been using that with great success.

I still use a Telrad (on a 4" riser) with the 70mm finder and with that combination I prefer to sacrifice field of view for higher power. The finder view is sharper with

a smaller exit pupil and narrower field plus Messier class objects shine in the finder. My favorite finder eyepiece (9 Morpheus) yields 35X, a 2mm exit pupil, and a

field of view of 2.2 degrees. That 2.2 degrees is all I need to star hop, which I can almost always do faster than a goto mount. In fact, it almost seems like cheating

using the Telrad and 70mm finder.

 

Edit: Last week there was a stretch of great weather and on a whim I thought I'd see how many galaxies I could find by memory in Leo in under 10 minutes.

Answer: 43. Most not visible in the finder of course but the finder got me there. It helped that many of the galaxies were in clumps.


Edited by rowdy388, 16 April 2021 - 07:34 PM.

  • Jon Isaacs, Chris K and Voyager 3 like this

#19 Chris K

Chris K

    Messenger

  • *****
  • topic starter
  • Posts: 423
  • Joined: 20 Sep 2017
  • Loc: Long Island, Earth

Posted 16 April 2021 - 09:58 PM

I think you will find the field of view is not much wider if any and the usable field will be significantly less than the 31mm Nagler.  And with the lower magnification, 7.5x versus 13.5x, it will not be very effective. 

 

For cheap and light, I would go with the $65 34mm 72 degree Svbony from Telescope-warehouse.  It has a 40mm field stop compared to the 31mm Naglers 42mm. 

 

For light, I would go with the 30mm APM UFF, not quite as wide a field as the 31mm Nagler but similar in quality of view and only about 55% of the weight.

 

Jon

Not sure how i missed the 34mm in my search - plus TFOV and price were equal criteria for me. Picked one up last night, thank you. It'll be interesting to compare to the RO 56mm, but the Svbony seems optimal and the weight is similar to the RO.


Edited by Chris K, 16 April 2021 - 09:59 PM.


#20 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 92,658
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 16 April 2021 - 10:24 PM

Not sure how i missed the 34mm in my search - plus TFOV and price were equal criteria for me. Picked one up last night, thank you. It'll be interesting to compare to the RO 56mm, but the Svbony seems optimal and the weight is similar to the RO.

 

Chris:

 

I bought the 34 mm Svbony several months ago.  It's not a 35 mm Panoptic in terms of sharpness across the field of view. But it's as good as a 2 inch wide field gets for under $100 and ought to make a decent finder eyepiece for you.

 

I calculate 5.5 degrees at 12x..

 

Jon



#21 BillP

BillP

    ISS

  • *****
  • Vendors
  • Posts: 21,587
  • Joined: 26 Nov 2006
  • Loc: Spotsylvania, VA

Posted 16 April 2021 - 10:26 PM

Lots of things are "good enough", but my favorite setup is to have either a Telrad or RDF and a small finder scope both mounted.  I have a Telrad with right angle accessory and 8x50 RACI finder on my 10" Dob and it is a breeze to star hop and get zeroed in on anything.


Edited by BillP, 16 April 2021 - 10:26 PM.


#22 Chris K

Chris K

    Messenger

  • *****
  • topic starter
  • Posts: 423
  • Joined: 20 Sep 2017
  • Loc: Long Island, Earth

Posted 16 May 2021 - 10:34 PM

Chris:

 

I bought the 34 mm Svbony several months ago.  It's not a 35 mm Panoptic in terms of sharpness across the field of view. But it's as good as a 2 inch wide field gets for under $100 and ought to make a decent finder eyepiece for you.

 

I calculate 5.5 degrees at 12x..

 

Jon

Jon, I've had the 34mm out a few times now and it's exactly as you described. Works well as a finder EP for me but sort of ends there. The stars smear at the perimeter pretty badly but again, I just need their location not their majesty. I struggle a bit with getting it in and out of the diagonal. I have a twist-lock diagonal and it feels like the EP barrel is not perfectly round. Not having similar trouble with others.

 

Anyway, I wanted to say thank you!


Edited by Chris K, 16 May 2021 - 10:34 PM.



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