50mm Finder vs 50mm "Toy" Telescope

[samtheeagle]

So getting my DSI to focus when using my 50mm finder and an extension tube is a real pain, so I've been looking at ways to get a 1.25" focuser hooked into the mix. I found one possible solution, but it'll be a bit of a bodge... So I thought of a different tack, how about getting an el cheapo 50mm telescope, like a kids introductory one? That's the same size aperture, and will already have a rack and pinion focuser built in to it. There's this one at Argos: Buy National Geographic Compact 50mm/180x Junior Telescope. at Argos.co.uk

So the question is, will the "toy" telescope be significantly worse optically than a 50mm Antares finder? I would guess probably not, I can't see a finder having great quality glass in it.

Cheap and cheerful, small and lightweight is what I'm after...

[Psychobilly]

Probably work ok just a bit bigger and longer FL than the Finder scope..

Peter...

[dark knight]

You could always take the rack and pinion focuser off the toy scope and fix it to your existing finder scope maybe...

[samtheeagle]

You could always take the rack and pinion focuser off the toy scope and fix it to your existing finder scope maybe...

Yarr, that is of course that fall back option

[Psychobilly]

have you worked out why you cant get the finder scope option to focus...

Do you need to move the Camera further out or further in to get focus?

Peter...

[rwg]

Aren't a lot of the really cheap telescopes stopped down inside the tube somewhere to reduce the effective aperture and mask the deficiencies of the optics. It's certainly a trick Tasco used to pull with both their scopes and finders...

Robin

[samtheeagle]

have you worked out why you cant get the finder scope option to focus...

Do you need to move the Camera further out or further in to get focus?

Peter...

I can get it to focus, but it's very fiddly and annoying. I have to manually adjust the DSI position in the extension tube, and the sweet spot is pretty small. And then for extra fun, when I tighten the retaining screw it tends to shift a bit and messes the focus up again I just think that a "proper" focuser, even a cheap one, will make life a lot easier.

I've tried a parfocal ring, but sods law being what it is means that the point at which I want to secure it in place is just where there's a step machined into the DSI nosepeice, so it never holds in place. Sigh.

So I'm exploring other options...

[acey]

Longer focal length will give smaller field of view, and it will be a bigger scope, possibly leading to balance problems. May also have stopped-down aperture, giving fainter images. Still probably useable as a finder but I don't see why it would be worth the hassle.

[Psychobilly]

Any chance of some pics of the setup...so I can how much room you have to play with..

I use cheap t-mount telephoto lenses bought of ebay for guiding with the DSI's...

Peter...

[samtheeagle]

I can certainly supply some pics this evening Peter What sort of "room" are you wondering about? Also, the "room" I have is potentially not important, as I'm happy to change things around a bit for ease of use.

So how does one go about attaching a telephoto lense to the DSI? Are the threads on the front where the nosepiece goes a standard size? Would this screw straight onto the front? http://cgi.ebay.co.uk/-200-mm-F4.5-TELE--PHOTO-LENS-M42--T-MOUNT-LENS_W0QQitemZ260568331415QQcmdZViewItem?rvr_id=&rvr_id=&cguid=4d7c2bba11d0a0e202c2e462ffd131aa

Ta.

[Psychobilly]

Yes . .. the thread behind the nose piece is a standard t thread so you need a suitable spacer to get the CCD somewhere close to 60-65 mm behind the lens thread. That way you will get stars to focus using the lenses buit in helical focusser but not always corresponding to the infinity mark on the focus scale...

Peter...

[adamsp123]

I simply use a "push in stop" in other words I found a position where pushing in the cam and extender I could get good focus using the finder front adjustment and then found something of the right width to use a stop when pushing in the cam assembly into the finder, in my case it was a tie wrap.

Pete

[samtheeagle]

Oooooo interesting So yet another possible avenue to explore... How do you attach the guide scope in your setup Peter?

[adamsp123]

Pic of my original version here http://stargazerslounge.com/diy-astronomer/84726-diy-finder-guider.html

Looking at the exploded pic 2nd one I put a tie wrap around the cam on the second level of flange so when I pushed in the cam and adaptor into the finder it would stop the cam/adaptor going in too far by hitting the edge of the finder tube.

Someone at work made me a plastic, purpose built, adaptor including spacer but honestly the first bodge worked just as well.

I use a standard finder bracket, got rid of the spring and rubber band then drilled and tapped extra holes to give 2x3 way screw fixing to hold the scope in place and is adjustable in direction.

[samtheeagle]

And of course, now that I know the thread is standard I can get another 1.25" nosepiece and permanently fix it into the custom sized extension tube already crafted... I just didn't want to do anything destructive the nosepiece that came with the DSI.

[Psychobilly]

Glad it look like your going to get it sorted... Cheers Pete

[samtheeagle]

Yarrrr, but there are so many options! To be honest, in my very limited experience the finder guider has done me proud, so I see no real reason to change it, but I would like to make the whole process easier for myself... So knowing that I can get another DSI nosepiece gives me the option of fixing it firmly in place once I've spent gawd knows how long finding focus with the manual tweaking method

I'd really like to get the guide scope mounted on the top of the main too, and then I can have another finder in place, for you know, finding things.

[greenkat]

Hi Sam

As I have 2 S/W scopes, I have 2 finders, so, I use a S/W finder as a guide scope with my DSI1 using same idea as someone elses thread on here.

Took out the eyepiece end, hacksawed a bit off, sanded down the outer of a 2"-1.5" adapter until it fitted snugly.

DSI attatches with normal nosepiece and bring to focus with the front lens of the finder.

So, once ive alligned my scope with "normal" finder, I just remove it from the shoe and put on the guide finder, no extra weight

Greenkat

[adamsp123]

Hi Sam

As I have 2 S/W scopes, I have 2 finders, so, I use a S/W finder as a guide scope with my DSI1 using same idea as someone elses thread on here.

Took out the eyepiece end, hacksawed a bit off, sanded down the outer of a 2"-1.5" adapter until it fitted snugly.

DSI attatches with normal nosepiece and bring to focus with the front lens of the finder.

So, once ive alligned my scope with "normal" finder, I just remove it from the shoe and put on the guide finder, no extra weight

Greenkat

Using a Punch and Judy voice - "thats the way to do it"