Right Angle finder mod

[DaveL59]

Been thinking about adding a right-angle viewer to the TAL 6x finder for a little while and purchased a couple of camera angle finder adaptors with this and the polar scope in mind.

Looking at the TAL finder I just happen to have a bit of acrylic tube that is a snug fit over the focus ring. Funnily enough this was incorrectly sent when I ordered a couple 100mm lengths to make up the extension piece that was missing from the TAL-M scope I recently overhauled, so a handy mis-ship for me 🙂 

Now the plate on the end also just fits in the end of the tube too, tight but will need better securing with the weight of the angle finder and a clumsy observer jamming his eye against it in darkness

The other side of the plate that's meant to clip over the camera finder will need mods to fit the end of the TAL finder (beauty ring removed)

I think this could well work. The TAL focuser isn't tight so the whole thing will rotate with the weight of the angle finder I expect. Plan is to cut a length of the acrylic tube to extend past the focuser so I can tap a hole to run a nylon clamping screw which hopefully will lock the focuser well enough to make this work. Also add another lock screw to hold securely to the focuser ring.

Note that the angle finder won't make this RACI, image will still be inverted tho looks to be correct L-R.

 

[DaveL59]

A word of caution to anyone else thinking of trying this. The Pentax one I purchased can rotate and has stiffness so it will hold position and clicks at 90-degree angles. I noticed today that the other one doesn't and just flops. Unscrewing the knurled ring that the camera eyepiece plate fits onto I can see why. It IS supposed to do the same as the pentax one but is missing the detent ball/bush:

Arrowed the detents in the ring and the hole for the missing pin. The brass you can see at the bottom of the hole is sprung so will see if I've anything suitable to replace the missing part.

So beware of any little ping-fsck-its if you do happen to unscrew this ring 😉 

[markse68]

I did buy an angle finder a while back with exactly the same intention but I gave up as the image was too small. I think i bought the wrong one- should have gone for something more modern. The one I have has a tiny aperture much smaller than yours by the looks. Interested in how this works out for you Dave.

Mark

[DaveL59]

that does look like a small lens on your one Mark. These I have do lose some FoV but not much from a quick play when I got them. Image is nice and bright so am hoping under stars they'll perform well enough. Might as well have a play and see if I can rig something while the nights are so clouded out huh. It's times like this tho where you start to think "3D printer would be handy" but not sure I have the space for one of those and curious kitties may wreak havoc there too.

[DaveL59]

So working on this idea, I've cut a length of the acrylic tube so the occular is close to the end of the tube

Marked up the set screws in the focuser and also for the focus lock screws and drilled for a 4mm tap. Only tapped the ones on one side for the moment, will see if I need to tap the matching holes at 120 degree offsets once I test fit, already drilled them ready. I'm using regular HSS taps so went slow and careful so as not to just shred the acrylic, seems to have worked.

Seems to lock just fine with a single thumbscrew so no need to tap the other holes tho they'll be handy to tap out if these threads get shredded in use 🙂
Next up, trim the metal clips so the bracket clears the occular.

Still a nice tight fit into the tube end. Will have to consider how best to secure it rather than rely on a tight push fit, wouldn't want the angle finder to drop out in use after all. Am thinking to drill and tap for small setscrews into the bracket edges which would give a 3-point securing system and threadlock them into place.

Now refit the bracket onto the angle finder and black the surface facing the occular. Will sort a means to screen stray light entering via the clear tube later on.

So here we have the components ready to assemble.

The finder assembly fitted up and almost ready to go.

Holds well with the focus lock screw when cranking the angle finder to another position which is good news. Hopefully it'll perform well under the stars too.

Oh, thought I'd test-fit for a photo opp on the TAL-1 and guess what? The focuser ring on that older scope is wider than the tube bore, drat! Same for the finder on the TAL100RS 😞 So I can't just make this transferrable as I'd intended unless I open the bore of the tube up a little, oh well, a job for later on then... 

Edited September 28, 2020 by DaveL59

[markse68]

1 hour ago, DaveL59 said:

The focuser ring on that older scope is wider than the tube bore, drat! Same for the finder on the TAL100RS

That’s odd. I’ll have to measure mine. Looking good though Dave 👍

[markse68]

Sure enough I have 2 at 30mm and 3 at 31mm! (don’t ask...) How odd and what a pain! I wonder if they use different oculars? 

[DaveL59]

3 minutes ago, markse68 said:

That’s odd. I’ll have to measure mine. Looking good though Dave 👍

thanks Mark. yeah I was a bit confused by that too, esp since the 100RS finder looks identical, the older one on the 1 I can believe but such is life. I'll probably sand out the inner bore so it'll slip onto all 3 and see if I then need to add further clamp screws. At least once the bore is sanded a couple coats of black sharpie pen will dull off any stray light 🙂 

Daylight testing the view is good, doesn't seem to lose much FoV which is a bonus. Of course is all clouds here at the mo so a night sky test isn't likely.

[DaveL59]

6 minutes ago, markse68 said:

Sure enough I have 2 at 30mm and 3 at 31mm! (don’t ask...) How odd and what a pain! I wonder if they use different oculars? 

haha I've 2 at 31 and a bit (31.6 on the 100RS) and the one I built against is a shade over 30mm. I guess they changed the machining for the focus ring as the older one looks slightly different to the other two. Still I've made a start at least after having these bits sat around for a couple months 😉

Might make a second one for the larger focuser and have them both able to be used at the same time, tho I had vaguely planned to use the second angle finder for the polar scope but might park that idea for now. Will need to sort something for the missing detent but I think a re-worked bit of brass screw from a plug may do the job there.

[DaveL59]

so I gave rig this a quick test as the moon has appeared from behind cloud now and a few patches where stars are visible, tho only the brighter ones with the devil's floodlight in the sky. Seems to work with a decent FoV, moon centered in the cross-hairs with around 3 moon diameters to the field edge. I did note some reflections aimed at the moon however, probably between the occular and the adapter lenses? Might open these angle finders up and see if there's any stray light control I can add internally.

Aiming at UM I could make out a couple of the stars, hand holding the finder so not an ideal test and of course cloud then hid most, but they were there and nice pinpricks in the finder.

[DaveL59]

ok so I decided I'd open the bore of the acrylic tube up so it'll fit the other TAL finders, bound to happen huh. After a while of running a sanding wheel on the dremel-a-like on the inside I got it to fit the one on the TAL-1 🙂 Needed even more tho for the one that came with the 100RS, so in fact mine are 3 different dimensions on the finder ring.

Still, onward and.. all that.

While playing with leccy machines I also drilled for 2mm screws into the bracket for the angle finder and I just happen to have some brass 2mm pan head screws that are the exact length I need, from the bits I bought for the vintage scope.

and the tube after grinding (well, sanding) the inner bore test fitted on the TAL-1 finder

Black matt paint pen on the bracket and sharpie on the inside if the acrylic tube

Once all dried off I'll reassemble and hopefully the acrylic tube will hold up after removing around 1mm from the wall thickness. Oh I decided to also tap out the other M4 holes in case they're needed later.

[DaveL59]

and here it is, assembled and fitted on the TAL-1, not too shabby I think 🙂

Of course, having done all that boring out of the acrylic tube it dawned on me... the 100RS finder at 31.6mm is just under the old russian 32mm eyepiece diameter. I already have some acrylic tube of that bore from when I made the 32mm extension piece for the TAL-M. Got lulled into them looking alike so thinking they're all the same build, DOH!!! Oh well, tis done now but if the acrylic doesn't hold up having thinned the walls by a shade over 1mm I can always re-do with a piece of the other tube 🙂 

[DaveL59]

tonight I notice Jupiter vaguely showing, lots of cloud which doesn't help but thought I'd at least give the finder mod and the zoom EP a quick try.

Had to reverse the finder bracket for a more comfortable fit but it worked well and much easier to switch from EP to finder and back. I think I'll be rebuilding the acrylic adaptor with the 32mm ID tube so that I've more depth for the screws to hold, didn't like the sound of acrylic straining plus to remove it needs the screws undone most of the way. They of course easily drop out as there's only a shade under 2mm of tube holding the screws at that point.

Overall tho it seems a reasonably good mod and the pentax angle finder is nice and sharp giving good views without losing much FoV.

The SV171 zoom performed fairly well, nice and sharp at the low power end with Jupiter showing well but no detail at all, tho I put that down to very poor seeing. Zooming in I did need to tweak focus but the view became more fuzzy. Not a good test really given the cloud and then Jupiter all but vanished so most likely the clouds that made the zoomed view poor. Will have to test again on a better night when I can then swap to other fixed EPs to see how things compare.

I think I am going to have to re-tap the finder securing screw as it wasn't good before with the metal original thumbscrew loose in the threads. This nylon one felt a little more secure but can't take any securing pressure. And sort the rusty screw holding the focuser in place too, hadn't noticed that before this pic.
 

[DaveL59]

investigated the securing screw issue on the TAL100RS finder foot, unfortunately not viable to re-tap to 5mm as the hole is too close to the edge. So the solution I adopted was to run a drill through the existing hole and drill out the opposite side using the original hole to help guide the bit. Then a simple re-tap from the other side with a 4mm HSS tap and we're in business.

The bevelled inner edge of course guided the drill downward into the plate base but that's fine. A touch of black paint pen and it'll look passable 😉

So, on with the finder and yes, it's holding nice and secure as it should be

Of course I'll continue with using nylon thumbscrews here so the ally doesn't end up chewing out the thread again as it had done with the original screw in previous ownership, it was always loose since I purchased this scope so is about time I put it right 🙂 

[DaveL59]

decided to have a closer look at the other angle finder and open it up to see what the rattle is. Vainly hoping it might be the missing detent pin of course but no such luck.

So here it is, a pretty simple affair really, an angled mirror that the objective projects onto and ahead of the eyepiece end a pair of lenses that handle the image flip. 

The rattle is coming from the lens cell pictured which uses a crimp at 120 degree separation around the edge to secure the lenses in place. Not something I think I'll be attempting to try to open up, may just melt a drop of wax at the edges to try get the lenses to stay put a bit better (worked fine on the Wetzlar Jagd's so could be worth a go).

Still need to sort something for the missing detent pin, looks to be m2.5 diameter and approx 3.5mm long, so a ball bearing of m2.5 and a small packing piece might work if I can lay my hands on a single ball bearing from somewhere.