what should I be able to see with a 100mm Refractor

[casemonster]

..Just wondered about this. I have been observing Jupiter and moons and can just about make out faint bands on Jupiter. I have some naff lenses, an H20 and a K12.5. oddly enough the k12.5 gives a more magnified view. I thought a 20 mm would increase magnification??? It doesn't appear to.

Pretty dissapointed with Andromeda as very faint so I am not expecting anything deep space as it seems too slow. What lenses would suit a slow old 60's refractor to make things more worthwhile?

[John]

The higher the number in mm on the eyepiece, the lower the magnification. What scope do you have ?. I'm asking because we need to know if it will take 1.25" eyepieces.

A refractor with a 100mm objective lens can show some nice detail on Jupiter under good conditions, with decent eyepieces. The Andromeda galaxy won't appear as more than an oval smudge though.

Edited February 24, 2012 by John

[casemonster]

Hi John,

OK not sure what make it is. Have al ook at my first thread "newbie and refractor advice needed." (or something like that) posted last Friday.

A ha the lower the number the greater the magnification,. I use an adaptor ring which fits lenses in the focus tube.

[casemonster]

Here is a picture. No names on it at all!!

[Luke]

The amount of magnification is the focal length of the telescope divided by the focal length of the eyepiece.

For example, my 100mm refractor has a focal length of 900mm.

A 10mm eyepiece would give 900/10 = 90x magnification.

A 20mm eyepiece would give 900/20 = 45x magnification.

So as John says, the higher the eyepiece number, the lower the magnification.

In our 100mm we love looking at the planets, splitting some double stars, looking at the moon, some of the brighter DSOs like the Orion Nebula - especially the trapezium stars - and some of the brighter clusters like the Beehive and Double Cluster.

[John]

That looks like a nice old English refractor

It's hard to tell from the photo - will the focuser tube take 1.25" eyepieces or is it restricted to the .965" types ?.

Also you would find a 90 degree diagonal makes viewing easier. You can get one that converts a .965" scope into a 1.25" one which is very useful as you cannot get .965" eyepieces easily any more.

[casemonster]

Thanks John & Luke,

I will need to measure the diameter tomorrow and post it up for further advice. BTW I paid £35 for the lot!!!

Speak tomorrow,

Cheers,

Chris

[MjrTom]

With 100mm from a dark site you can see most the messier objects, loads of double stars even with quite small separations not to mention lunar, planetary and solar astronomy (with the correct filtration)

There was a famous astronomer (modern day) who only used a 4" telescope for all his viewing but because he trained his eye to detect detail under dark skies he was able to excel. (having brain freeze, can't remember his name....)

Edited February 24, 2012 by MjrTom

[swamp thing]

With 100mm from a dark site you can see most the messier objects, loads of double stars even with quite small separations not to mention lunar, planetary and solar astronomy (with the correct filtration)

There was a famous astronomer (modern day) who only used a 4" telescope for all his viewing but because he trained his eye to detect detail under dark skies he was able to excel. (having brain freeze, can't remember his name....)

Stephen James O'Meara?

He can see an astonishing amount with his 4" TV frac. Mind you he's observing from a pretty good site.

Just shows the value of getting to dark skies.

Regards Steve

[glowjet]

To give you some degree of perspective, Charles Messier did most of his work, when he created his lists of objects to avoid, with only a refractor of some 3/4" bigger objective than yours, and the quality of Glass would not be in the same ballpark, but he would have had nice dark skies. If your interest lies with Planets, double stars etc, then a good Orthoscopic ep would serve you well, something in the Circle T or better, the Badder Orthoscopic MC range, these often appear on the s/h market and you should see a major difference compared to the H ( Huygen ) and K ( Kellner ) eps you have, or for general work or some good quality Plossls in various powers

[MjrTom]

Thanks Steve been bugging me trying to remember.

[casemonster]

Hi John

Just measured the diameters and it will take both but with an adaptor for the 0.965" but the 1.25" needs no adaptor. So going for a Plossl What size would you suggest to get a bit more magnification?

[LukeSkywatcher]

Hi casemonster. I remember this scope from last week. Glad to see you got it working. What was the issue with it?

BTW.................what is the focal length of this scope (how long is it from tip to tip?).

1500mm???????

I have a 90mm refractor with 1000mm focal length (F11). For planets i find a 8-9mm EP brilliant.

Edited February 24, 2012 by LukeSkywatcher

[spaceboy]

It must be me but it looks thin for a 4" scope ???

[LukeSkywatcher]

It must be me but it looks thin for a 4" scope ???

Yeah it is is 100mm aperture (is that 4"?), the F/L looks to be over 1000mm.

[casemonster]

Hi Luke(?)

It was quite simple really, Have a look at the previous picture and now look at this one. There was a inner tube which had been pushed in for transit, when I picked it up at the boot fair. I was trying to remove the ineer ring to bodge a 9" extension tube when the ring twisted out with a brass extension tube attached!!

Ok, do I measure the focal length from the ojective lens to the point of focus and add on a bit for the diagonal?

[Richard_B]

On 24/02/2012 at 00:51, MjrTom said:

With 100mm from a dark site you can see most the messier objects, loads of double stars even with quite small separations not to mention lunar, planetary and solar astronomy (with the correct filtration)

There was a famous astronomer (modern day) who only used a 4" telescope for all his viewing but because he trained his eye to detect detail under dark skies he was able to excel. (having brain freeze, can't remember his name....)

Didn't Messier do most of his work with a 4" refractor?

[scotty38]

On 22/04/2021 at 12:14, Richard_B said:

Didn't Messier do most of his work with a 4" refractor?

And he was probably still around when this thread was started 🤣

[Voyager 3]

Good one Scott ! 😂

[Richard_B]

On 26/04/2021 at 20:15, scotty38 said:

And he was probably still around when this thread was started 🤣

🤣 realised after I posted how old it was 🤣