Diagonal finder

[JJDOBBER79 (Jas)]

Hi all,
Quick question. I have a finder scope similar to the one pictured. I would prefer a right angle finder and it occurred to me that they are the same thing with a diagonal on them. It looks like a 0.96. Can I get a diagonal that has 0.96 at one end and 1.25 at the other so I could use a comfortable plossl. Or is it cheaper and easier to buy a right angle finder?

[GraemeT (Graeme)]

G'day JJ. I had the same problem. It was just as convenient to buy a right angled finder from Andrews.
I've since upgraded to a Stellar-Vue with an illuminated reticule which is better still.

[JJDOBBER79 (Jas)]

G'day Graeme, yeah I thought a bit more about it and figured if I used a regular eyepiece, how would I focus it?

[astro744]

Note there are two types of right angle finders. One is simply RA (Right Angle) and the other RACI (Right Angle Corrected Image).

The RA one will reverse the image left right as does a star diagonal in a refractor or SCT, neither of which then match a star chart or unaided view.

An RACI or straight through finder does not reverse the image left right. In a straight through the image is upside down but it still matches a star chart. Being upside down is not normally a problem as often you look from the side and can twist your head or spin your star chart to match.

If you are using a Newtonian reflector get a straight through or RACI finder. If low to the ground an RACI makes it easier otherwise a straight through if on a larger EQ mount higher off the ground.

Stellarvue make 1.25" finders in straight or RACI configuration and you can either use their 23mm cross hair eyepiece which can be illuminated or supply your own standard eyepiece. See http://www.stellarvue.com/finderscopes.html

I personally prefer a non-illuminated non cross hair eyepiece and even Stellarvue recommend a highly corrected eyepiece given the f3.75 focal ratio of their finders. The use of a highly corrected eyepiece has only one disadvantage and that is cost but the main advantage is sharper stars to the edge of field and when you are looking for faint fuzzies, sharp stars to the edge also means a galaxy is likely to be seen at the edge than be invisible due to distortion from a poor eyepiece.

I use a Meade 20mm Plossl in my Stellarvue F80M finder but occasionally use a 16mm T5 Nagler for simply spectacular views. The latter gives me almost 19x and over 4 deg. field which nicely matches the outer ring of a Telrad.

[AstralTraveller (David)]

I've always used straight-through finders and just cannot get used to right angle jobs, mind you mine are not corrected but that isn't the problem. With a straight-through you can look at the sky with both eyes, one naked eye and the other at the finder. After a bit of practice you will merge the images and perceive the cross hairs in the finder projected onto the sky at zero power. That gets you close to the object (often very close) and then you close one eye and use the finder alone. You can't get that convenience with a right-angle finder. Then there is the whole image flip issue to deal with.

I used to do that with my old 10" f/8 on a eq mount where the finder was a long way off the ground. I was also much younger then and could bend and twist into strange positions (not all of them in parked cars ). Now with shorter scopes on dobs mounts and being older and less flexible that isn't viable for me. I'm just pointing out the possibility because many people aren't aware of the technique and so may not know to even try it.

[The Mekon (John Briggs)]

Originally Posted by JJDOBBER79

Hi all,
Quick question. I have a finder scope similar to the one pictured. I would prefer a right angle finder and it occurred to me that they are the same thing with a diagonal on them. It looks like a 0.96. Can I get a diagonal that has 0.96 at one end and 1.25 at the other so I could use a comfortable plossl. Or is it cheaper and easier to buy a right angle finder?

If you are looking to convert this finder to a right angle, it may not come to focus as the light path will be too long.
I agree somewhat with astrotraveller, it is sometimes easier to use a straight through as you can better "point" it to the area of sky you want.
I have found the best finder is with a 45 degree amci prism. I have one, and it is better than my stellarvue RACI finder or a straight through type.
Trouble is you cannot buy it, I put it together from vixen parts many years ago.

[JJDOBBER79 (Jas)]

Thanks Guys, you sure know your stuff. Maybe it is not such an issue with my 12" as it was with a 6" given that I am almost upright when looking in the finder. To be honest, I cant believe they sell 6" dobs with a straight through finder, I'm 6' 2"and it was seriously hard work the higher the object was. I think I will just stick with it. Thanks again