Finder scopes

[Ken82]

 

Please correct me if im wrong but surely the celestron finderscope should be 5° true field of view not apparent field of view ?

https://www.firstlightoptics.com/finders/celestron-illuminated-right-angle-correct-image-finderscope.html

Im looking to get a slightly larger finderscope  for my dob (60mm) to pick out fainter stars and just working out true field of view etc.

Im thinking to get the APM 60mm finderscope (228 focal length) with 24mm apm reticule eyepiece. So magnification 228/24 =9.5x       
 

Apparent field of view 55/9.5 = 5.7° true field of view.

 

So if im correct the apm would have brighter stars but also have a wider true field of view ? 

Cheers Ken 

[Pixies]

It looks similar to my Altair Astro 60mm RACI finder.

https://www.altairastro.com/altair-10x60mm-raci-finder-scope-90-deg-erect-image-prism-variable-illuminator-eyepiece-2504-p.asp

I've never tried to work it out, but the TFOV appears to be the same as the outer ring of the Telrad - which is 6 degrees.

You can, of course, use whatever EP you want to! You could put in a 32mm plossl and perhaps get an even wider view? I don't know, whether the diagonal or any baffles might stop that down. I'll check for you. Give me 15 mins!

 

[Pixies]

OK. Here is the view with the reticle EP (which I reckon is around 6 deg TFOV):

and with a 30mm Vixen NPL plossl:

[Ken82]

25 minutes ago, Pixies said:

It looks similar to my Altair Astro 60mm RACI finder.

https://www.altairastro.com/altair-10x60mm-raci-finder-scope-90-deg-erect-image-prism-variable-illuminator-eyepiece-2504-p.asp

I've never tried to work it out, but the TFOV appears to be the same as the outer ring of the Telrad - which is 6 degrees.

You can, of course, use whatever EP you want to! You could put in a 32mm plossl and perhaps get an even wider view? I don't know, whether the diagonal or any baffles might stop that down. I'll check for you. Give me 15 mins!

 

Yea it looks exactly the same as the APM one. Not in stock unfortunately, may be waiting a long time as things stand with astro gear.   

[Pixies]

Just now, Ken82 said:

Yea it looks exactly the same as the APM one. Not in stock unfortunately, may be waiting a long time as things stand with astro gear.   

I put a wanted ad in AB&S for this model and had 2 offers in a few hours. Worth a shot if you don't mind used?

[Ken82]

8 minutes ago, Pixies said:

I put a wanted ad in AB&S for this model and had 2 offers in a few hours. Worth a shot if you don't mind used?

Sounds like a plan, thanks

 

[Ken82]

How about the 60mm primalucelab finderscope (it’s in stock) how to get that into a finder bracket though ??

https://www.firstlightoptics.com/guide-cameras/primaluce-lab-60mm-compact-guide-finder-scope.html

[Second Time Around]

I've got and can recommend the 10x60 Antares RACI Versascope from Rother Valley Optics that takes standard 1 1/4 inch eyepieces.  It comes supplied with a 23mm/50 degree crosshair eyepiece, so a 5.0 degree field with an exit pupil of 6.0mm. 

I've fitted mine with a 20mm SWA 70 degree cross hair eyepiece. This gives 11.35x and a 6.16 degree field with an exit pupil of 5.3mm. 

I got the replacement eyepiece from Agena in the States, but I've seen similar ones over here, with and without illumination.  It not only has a wider field of view, but also the reticle itself can be focused if you have a moderate amount of short or long sight and you're not wearing glasses.  It also accepts a Dioptrx to correct astigmatism, although you need an O-ring or elastic band.

The Versascope has a lockable helical focusser at the objective end with a very large amount of adjustment - about 25mm.  So no focusing problems.  There's also a locking collar at the eyepiece end so that you can rotate the RACI diagonal.  If you remove this collar you have access to a standard T2 thread for guiding, camera or accessories.  Back focus is approx 93mm.  Versatile it certainly is!  It also has a long built-in dewcap.

Cost is only £145 including rings plus a Synta base!  Go to https://www.rothervalleyoptics.co.uk/antares-versascope-10-x-60-guiding-x-hair-finderscope.html

 

 

[mikeDnight]

It looks nice!  How are the stars across the field of view?  I bought a 60mm finder for my Equinox 120 some years ago but only the centre of the field was useable, so I sent it back. It's put me off ever since.

[Paul73]

You won’t regret going large on your finder scope. I have a Celestron 70mm travel scope strapped to the side of my Dob. Teamed with a Telrad to get roughly in the right spot, it works a treat!

Paul

[Louis D]

On 14/03/2021 at 17:03, Pixies said:

I've never tried to work it out, but the TFOV appears to be the same as the outer ring of the Telrad - which is 6 degrees.

Telrad outer circle is 4 degrees.

[Second Time Around]

2 hours ago, mikeDnight said:

It looks nice!  How are the stars across the field of view?  I bought a 60mm finder for my Equinox 120 some years ago but only the centre of the field was useable, so I sent it back. It's put me off ever since.

Like all short focus achromats there's field curvature.  So it's not the sort of scope you'd use for high power. 

However, with a finder I'm not so concerned about off-axis images as the aim is to literally find stars so that they can be seen in the main scope. 

As a finder the Versascope is excellent, with more light grasp than a 50mm.