Finderscope or low power eyepiece?

[-chris-]

Hi all,

I have a cheap 6 or maybe 7x30 finderscope on my telescope, the problem is its been sitting in my shed for quite a while and now its all dusty, the lenses have misted over and looks in general bad shape.

What would the best option to go for, either a new finderscope or something like a 32mm eyepiece.

I'm eyeing up a skymax 127 that comes with a red dot finder but no space for a finderscope. It seems the 32mm would be an ideal choice, however, would the eyepiece be as good as a finderscope reading star charts? With the skymax being more of a narrower angle view would I benefit more with a wider angle finderscope by adding a double shoe for fitting both red dot finder and finderscope?

I'm a little confused?

Thanks.

[Stu]

15 minutes ago, -chris- said:

Hi all,

I have a cheap 6 or maybe 7x30 finderscope on my telescope, the problem is its been sitting in my shed for quite a while and now its all dusty, the lenses have misted over and looks in general bad shape.

What would the best option to go for, either a new finderscope or something like a 32mm eyepiece.

I'm eyeing up a skymax 127 that comes with a red dot finder but no space for a finderscope. It seems the 32mm would be an ideal choice, however, would the eyepiece be as good as a finderscope reading star charts? With the skymax being more of a narrower angle view would I benefit more with a wider angle finderscope by adding a double shoe for fitting both red dot finder and finderscope?

I'm a little confused?

Thanks.

A 32mm will still only give around 1.1 degrees of sky, so finding things with that will be challenging. For comparison a 6x30 gives about 7.5 degrees and a 9x50 about 5.6 degrees so you can see these really do have value. I do think it worth finding a way to add a finder, either replacing or alongside the RDF. In RDF of some sort in conjunction with an optical finder often works well.

[-chris-]

Thanks @Stu thats cleared that decision up easily.

Which size would be the best to have? As I understand it now the smaller one would give a wider view but the bigger one would give a more magnified view.

Are there star charts on the Internet designed for finderscopes? I usually use stellarium and zoom in or out to match what I see in the eyepiece.

Thanks.

 

 

[John]

I use 6x30 right angle, corrected image finders with my smaller refractors, 9x50 with my larger ones and my 12 inch dobsonian. I also use an illuminated reticule Rigel Quikfinder to complement the optical finder on the dobsonian.

You can cut or make templates from acetate sheets or wire rings to represent the size of the finder field on a hard copy star atlas. The PC and mobile based planetarium type software has finder reticules that you can switch on which are useful.

 

[-chris-]

Thanks @John

How would I go about making the right size circles?

Are there any links that would point me in the right direction?

Many thanks.

[John]

The star chart will have a scale on it somewhere. Work out the diameter of the circles needed to represent the view that your finder gives using the figures that @Stu has given above and cut them out of acetate sheet or use soft wire (eg: garden wire) to make circles the correct diameter - this will vary depending on the star atlas that you choose to use.

There was a thread on the forum recently on doing this - I'll see if I can find it when I have more time.

 

 

[John]

Here you go. See the post from @cloudsweeper a few posts down the thread:

 

[Zermelo]

You can create acetate rings to overlay onto your printed atlas as described above, or here's an alternative I use.

I downloaded Michael Vlasov's Sky Atlas  and I'm selectively printing off and laminating the pages I need as I go.  I use dry wipe markers to temporarily highlight objects in the evening's observing plan, which might just be an arrow if it's an obvious target, but could be a simulated finder or telrad circle, drawn by putting the marker into one of those old fashioned compasses with a "claw" grip. I worked out that (on my printer at any rate) my 7 degree finderscope corresponds to a 6.1cm diameter circle, and then a standard telrad set would require 4 degrees at 3.5cm, 2 degrees at 1.75cm and 0.5 degree at 0.44cm, though the last would be quite fiddly to draw with compasses, as would any circle corresponding to any eyepiece except those with the widest TFOV.

[-chris-]

Thank you again @John

I've dug out my Cambridge star atlas, I can't see a key referencing the degrees, but a daft question, is the declaration used as the key, is it the same measurement?

[-chris-]

Thanks @Zermelo I shall have a look at Michael vlasovs sky atlas now.

[bomberbaz]

Some other ideas from myself, mr nibble and fozzybear in this thread . 

[Stu]

9 hours ago, -chris- said:

I usually use stellarium and zoom in or out to match what I see in the eyepiece.

You can add the ocular Plug-in to Stellarium and get it to show circles the correct size for your finder or any eyepiece combination. I’m not a big user of Stellarium, but do the same thing in SkySafari in my phone, very handy. You can setup your scopes and eyepieces and then simulate the field of view for any combination.

For instance, the first image here has Telrad circles overlaid on it, the second one has a 6x30 finder, 9x50 finder, and the smallest on is a 24mm eyepiece in my 4” refractor just as an example. You can also invert, reverse, or turn the image upside down to match the view through your finder or scope which is very handy.

[-chris-]

Thanks @bomberbaz and @Stu I shall look into doing both of these, one as a hard copy and one digital copy, best of both worlds!