What is the maximum TFOV you would like for DSOs

[GavStar]

In the past I’ve beem happy with a maximum tfov of around 2 degrees. However recently with my NV I’ve hankered for larger fov.

At the moment with my smallest scope I can get around 5 degrees however for scanning larger nebula and star fields I’m wondering if this is still too small. Eg barnards loop doesn’t fit. I do have the option of just the NV on its own giving 40 degrees but that’s a big jump. 

It looks like I may be able to use a right angled 50mm or 60mm finderscope to get around 7.5 degrees and am wondering whether this would be a worthwhile jump from 5 degrees. Because of the use of Ha or band pass filters and low magnification, optical quality of the finderscope is not that critical.

Just wondered what members views are on the maximum tfov that you would like to have?

Heres a couple of SkySafari pictures showing some options, 5 degrees against 6.8 and 7.7 degrees.

[Demonperformer]

I suppose a big question would be how many objects are you going to be interested in that are >5 degrees, but <7.5 degrees - only you can answer that one. But in the grand scheme of things, it seems to me that the cost of a RA finder is probably fairly small (especially as I am spending your money). To potentially get a 50% increase in the fov, I would say that it is probably worth a punt.

[GavStar]

7 minutes ago, Demonperformer said:

I suppose a big question would be how many objects are you going to be interested in that are >5 degrees, but <7.5 degrees - only you can answer that one. But in the grand scheme of things, it seems to me that the cost of a RA finder is probably fairly small (especially as I am spending your money). To potentially get a 50% increase in the fov, I would say that it is probably worth a punt.

Thanks, that’s in line with my current thinking. I don’t think I would need the extra fov that often but it would potentially be an interesting option to attach to a bigger scope to give an easy switch from say a 2 degree fov to 7.5 degree fov on the same area of sky. Also as you say, the finders aren’t that much - not sure if the 50mm or 60mm would be better though.

[Macavity]

I suppose it depends on how you define a DSO...

Not a *classical* imager, but I got away with about 20 arc minutes
with my "Video Astronomy" 8" f/4 "light bucket" + "half inch" chip? 

But reminded that a majority of Messier / Caldwell objects do *FIT*!
There are *other* objects, which require different setups / ideas...

[Peter Drew]

I would try the NV unit on its own in the first instance. Your cost would just be your time. 

[GavStar]

1 hour ago, Peter Drew said:

I would try the NV unit on its own in the first instance. Your cost would just be your time. 

Yes I have done (sorry I realise I didn’t make this clear) but at a 40 degree tfov and 1x mag objects are a generally a bit small. Really the question is whether going from 5 degrees to 7.5 degrees is worthwhile on some objects.

[Peter Drew]

I think it probably would considering the relatively small outlay. For my previous post, I had in mind objects like Barnard's Loop.  

[Macavity]

Admitting fault above, but what's an "NV"? Hadn't realised, until quite
late in the game, that a DSLR + Photo lenses took over, where Astro
Scopes leave off... Notably re. larger fields of view (Barnard's Loop). 

[Peter Drew]

Night Vision. 

[alanjgreen]

32 minutes ago, Macavity said:

Admitting fault above, but what's an "NV"? Hadn't realised, until quite
late in the game, that a DSLR + Photo lenses took over, where Astro
Scopes leave off... Notably re. larger fields of view (Barnard's Loop). 

Attaching military "Night Vision" to the eyepiece.

http://www.loptics.com/articles/nightvision/nightvision.html

 

[GavStar]

5 minutes ago, alanjgreen said:

Attaching military "Night Vision" to the eyepiece.

http://www.loptics.com/articles/nightvision/nightvision.html

 

Although I don’t think I’d put that setup into a 50mm finderscope!! ?

[alanjgreen]

4 hours ago, GavStar said:

In the past I’ve beem happy with a maximum tfov of around 2 degrees. However recently with my NV I’ve hankered for larger fov.

At the moment with my smallest scope I can get around 5 degrees however for scanning larger nebula and star fields I’m wondering if this is still too small. Eg barnards loop doesn’t fit. I do have the option of just the NV on its own giving 40 degrees but that’s a big jump. 

It looks like I may be able to use a right angled 50mm or 60mm finderscope to get around 7.5 degrees and am wondering whether this would be a worthwhile jump from 5 degrees. Because of the use of Ha or band pass filters and low magnification, optical quality of the finderscope is not that critical.

Just wondered what members views are on the maximum tfov that you would like to have?

Heres a couple of SkySafari pictures showing some options, 5 degrees against 6.8 and 7.7 degrees.

Gav,

Doesn't scope SPEED become a problem if you go wider. I could put a 0.5x reducer on my Borg but the focal length becomes too short to get any magnification. Its just as easy to use the 55mm Plossl and skip the reducer.

If we get too slow then the nebulas won't show up (isnt that right)

Alan

 

What about a Borg f5 guide scope

https://www.firstlightoptics.com/borg-astrograph-telescopes/borg-50mm-achromatic-f5-guide-scope-set-helical-focuser-for-t-threaded-cameras.html

If youre feeling flush, the Borg 55mm is f3.6

https://www.firstlightoptics.com/borg-astrograph-telescopes/borg-55fl-f3-6-astrograph-with-feather-touch-focuser-set.html

At least with Borg's you can buy the tube in 50mm (and also 25mm) sections to get the exact length you need to find focus.

https://www.firstlightoptics.com/borg-collective-other/borg-80-dia-25mm-tube-white.html

 

 

[GavStar]

6 minutes ago, alanjgreen said:

Gav,

Doesn't scope SPEED become a problem if you go wider. I could put a 0.5x reducer on the Borg but the focal length becomes too short to get any magnification. What is the f ratio of finder scopes?

If we get too slow then the nebulas won't show up (is that right)

Alan

Alan,

I’m not looking for magnification here, only getting as wide a tfov as I can for the huge objects like barnards loop.

So with an f4 finderscope and 40mm plossl this would give a nice fast f2.7 system to pick up the large nebulae. Magnification would be quite low at 5x or so. Your Borg with the 55mm plossl should give some nice widefield views.

[GavStar]

13 minutes ago, alanjgreen said:

 

If youre feeling flush, the Borg 55mm is f3.6

https://www.firstlightoptics.com/borg-astrograph-telescopes/borg-55fl-f3-6-astrograph-with-feather-touch-focuser-set.html

At least with Borg's you can buy the tube in 50mm sections to get the exact length you need to find focus.

 

I did see this scope Alan but the price for a 55mm scope did make me wince!!! (But it would do the job ?)

[alanjgreen]

6 minutes ago, GavStar said:

Your Borg with the 55mm plossl should give some nice widefield views.

Another reason to skip the reducer. I need a 2" diagonal to use the 55mm plossl.

The Borg reducer will fit to my T2 Baader diagonal but would vignette on the 2" diagonal I believe.

[GavStar]

4 minutes ago, alanjgreen said:

Another reason to skip the reducer. I need a 2" diagonal to use the 55mm plossl.

The Borg reducer will fit to my T2 Baader diagonal but would vignette on the 2" diagonal I believe.

Yes I’ve tried reducers on several scopes including my 72mm frac and with the 55mm plossl and reducer it did vignette badly - the image circle is just too small.

However, using a 55mm plossl plus 0.75 astro physics photo visual reducer on my tec160 works really well and gives me a really fast 2.6 f ratio for those faint nebulae. The Ap reducer works well with my c11 and 55mm plossl as well.

[GavStar]

That 55mm Borg with a 55mm plossl would give an 11 degree fov - wow! I wonder if it would vignette heavily though...

[Stu]

I’m sure @PeterW would be able to give guidance on this one Gavin. Do you need it mounted for viewing and attaching or is there a simpler way of attaching a lens which gives you say x3 over normal to allow direct monocular viewing?

[alanjgreen]

8 minutes ago, GavStar said:

That 55mm Borg with a 55mm plossl would give an 11 degree fov - wow! I wonder if it would vignette heavily though...

Im no expert but I guess it depends on the reducer (part 7880)

http://www.sciencecenter.net/hutech/prices/borgparts/html/7880.htm

http://www.sciencecenter.net/hutech/borg/techdocs/7880.pdf

The 71mm is native f5.6 with no reducer. So a 2" diagonal and 55mm Plossl should go in there.

https://www.firstlightoptics.com/borg-astrograph-telescopes/borg-71fl-f56-series-80-with-feather-touch-focuser-ota-set.html

(cheaper too)

 

[GavStar]

3 minutes ago, Stu said:

I’m sure @PeterW would be able to give guidance on this one Gavin. Do you need it mounted for viewing and attaching or is there a simpler way of attaching a lens which gives you say x3 over normal to allow direct monocular viewing?

Yes hopefully Peter will add comments in due course. I know many NVers go for the pirate telescope viewing approach ? nice and quick - binocular like. But I was also thinking about mounting to enable wide field phone pics.

[alanjgreen]

Heres the link to all the Borg "sets"

http://www.sciencecenter.net/hutech/products/BorgPackage/0.htm

if you got the 55mm WITHOUT the 0,8x reducer (saving $500) then it becomes a 250mm f4.5 scope

You would need an extra 50mm of tube to make up the extra focal length. But it should now work with a 2" diagonal and 55mm plossl.

http://www.sciencecenter.net/hutech/prices/borgparts/html/7051.htm

Once you have a Borg parts list then I am sure FLO can get a quote. The "sets" are just fixed sets of parts, you dont have to stick rigidly to them.

Full parts list

http://www.sciencecenter.net/hutech/prices/borgparts/index.htm

HTH.

[pete_l]

49 minutes ago, GavStar said:

I’m not looking for magnification here, only getting as wide a tfov as I can for the huge objects like barnards loop.

Just use a DSLR + lens for large objects. Or failing that a mono CCD + lens adapter + lens if you want to record narrow band.

[Stu]

10 minutes ago, pete_l said:

Just use a DSLR + lens for large objects. Or failing that a mono CCD + lens adapter + lens if you want to record narrow band.

That won’t work with NV I don’t think, unless you can use perhaps a c mount adaptor between lens and NV?

[PeterW]

My slightly reduced  80mm f4 pirate style frames the north America or heart nicely, but I back off to 3x for the monster nebulae. I have a 50mm f3.2 “guide scope” (50mm Finder with no eyepiece), 1.25” slide to focus... not tried it much yet. You might want to get advice about the Borg to make sure it’ll work and the bits you need. At least at this aperture you can just tape the filter on the front.

With the cloaks changing it’s pretty much closer season for nebulae now...

Peter

[Stu]

2 minutes ago, PeterW said:

With the cloaks changing it’s pretty much closer season for nebulae now...

Yes, I’ve changed from my thick cloak to my waterproof cloak  

@GavStar I do think that perhaps going in search of another expensive scope, perhaps the simpler approach of the x3 might be just as effective if not moreso on those huge nebulae like Barnard’s loop. Worth a go first?