F30070M as a cheap finder scope?

[furrysocks2]

Currently have a red dot on my 12" dob. Hoping to get a telrad at some point, but also considering a finder. Dozens of online sellers supply the above for £25+

• 70mm aperture and 300mm focal length (f/4.3).
• 0.965" focuser and diagonal
• 20mm and 6mm eyepieces
• mini tripod

The 20mm would give 15x and assuming a tight afov, probably around 3 or less of tfov.

Could this be of any use? Assuming focuser slop could be shimmed, and perhaps using a 0.956" to 1.25" adapter, an extension, could I expect a reasonable result as a straight through finder with my Vixen NPL 30mm at 10x and 5 deg tfov? A 10x70 finder?

I tried a few searches but didn't find any mention of these, perhaps I missed.

[Cosmic Geoff]

10X70 would give a 7mm exit pupil, probably wasting light unless you have young eyes.

[furrysocks2]

13 minutes ago, Cosmic Geoff said:

10X70 would give a 7mm exit pupil, probably wasting light unless you have young eyes.

That did cross my mind.

Another ready alternative might be an old 25mm plossl, giving 12x, 5.8mm exit pupil, 52 degree afov (?), 4.3 degree tfov.

 

I guess the other question is whether the 0.965" focuser would permit this.

[Ricochet]

I wouldn't bother with this idea. For a finderscope I think that 5° really is the magic number and the 24.5mm focuser will restrict your field of view to about 4°. In addition if the scope costs £25 you've only got another £20 to play with to buy an eyepiece and adaptors before it becomes more expensive than a standard Synta 9x50 finder and we haven't even started thinking about how you will align the two scopes. 

[furrysocks2]

18 minutes ago, Ricochet said:

I wouldn't bother with this idea. For a finderscope I think that 5° really is the magic number and the 24.5mm focuser will restrict your field of view to about 4°. In addition if the scope costs £25 you've only got another £20 to play with to buy an eyepiece and adaptors before it becomes more expensive than a standard Synta 9x50 finder and we haven't even started thinking about how you will align the two scopes. 

I hear you.

£22 for the scope, £6 for a 1.25" adapter and reuse existing eyepiece... but for the reduced tfov and a whole lot of grief fettling focuser slop and mounting.